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Moonhead
2009-Jan-13, 02:44 PM
An often-used model for universe's centerless expanding, is a rubber ball or balloon with dots painted on it, representing galaxies (or clusters of galaxies). When the ball grows larger, the distances between the dots grow.

It would seem to me that on a real inflating ball, dots painted on it would grow proportionally - to have it represent the expansion of the universe more accurate, the dots should be remaining their original size, while the ball grows.

Now, a growing ball with dots remaining the same size equals a ball remaining the same size with shrinking dots on it: if you only look at the size of the ball and the size of the dots, there is no way to distinguish between the two.

So I was wondering to what extent the expansion of the universe could also be regarding as a 'shrinking in' on the local levels (galaxies, clusters).

Would looking at the universe's expansion this way - let's coin this 'the shrinking dot' model -
1. be in harmony with the observed redshift?
2. imply that the fundamental forces shrink accordingly? (because we don't experience any change on our local level, so if matter is shrinking, the forces holding it all together should be shrinking proportionally to maintain their relative strenghths)

This 'shrinking dot model' would be similar to saying the earth is the unmoving center of the solar system, with the sun circling it, and the other planets circling the sun. Or saying that, when Chuck Norris walks, he remains where is, while the earth moves under his feet (apparently moving the entire universe with it). Not really untrue, but unnecessary elaborate.

Nevertheless, I am curious if this 'shrinking dot' model is a valid (be it not necessarily the most useful) way to look at it. If so, I think it would be easier for me to visualize what happened on the grand scale. (And if not, the kind person who answers me would explain why not, and this would further my understanding. So, asking this question is a win-win situation for me :) )

gzhpcu
2009-Jan-13, 02:56 PM
So I was wondering to what extent the expansion of the universe could also be regarding as a 'shrinking in' on the local levels (galaxies, clusters).

Would looking at the universe's expansion this way - let's coin this 'the shrinking dot' model -
1. be in harmony with the observed redshift?


If galaxies and clusters shrink, light leaving one galaxy and traveling to another galaxy would not be red-shifted because, there is no actual expansion of the universe.

The "dots" on the balloon would quickly disappear from view if their shrinkage is proportional to the corresponding expansion of space. They can not shrink indefinitely. The Planck length is the lower limit.

Moonhead
2009-Jan-13, 03:27 PM
If galaxies and clusters shrink, light leaving one galaxy and traveling to another galaxy would not be red-shifted because, there is no actual expansion of the universe.

The "dots" on the balloon would quickly disappear from view if their shrinkage is proportional to the corresponding expansion of space. They can not shrink indefinitely. The Planck length is the lower limit.

Thanks! So, in order to maintain the 'dots are shrinking', one would need to have all parameters, including the speed of light and Planck length to shrink proportionally?(Which, of course, would be unpractically absurd)

Gigabyte
2009-Jan-13, 03:59 PM
What an interesting thought.

Moonhead
2009-Jan-13, 05:36 PM
What an interesting thought.

:lol: I love sarcasm.

I admit it's bordering stupidity. I'm glad I asked though, to get it out of my head.

gzhpcu
2009-Jan-13, 05:49 PM
Thanks! So, in order to maintain the 'dots are shrinking', one would need to have all parameters, including the speed of light and Planck length to shrink proportionally?(Which, of course, would be unpractically absurd)
Except that I do not see how red-shifting occurs...

Moonhead
2009-Jan-13, 06:05 PM
Except that I do not see how red-shifting occurs...

I suppose that the above described model would require that the speed of light diminishes over time... But I'm not even sure about that, because I have a hard time visualizing it.

Btw I'd like to stress that I am not proposing anything weird going on, or that "scientists got it all wrong" or so. My question was meant as: how would such a 'model' have to deal with observations? Your first reply already made it clear that it wouldn't make things easier at all (indeed it would turn out to be just as useful as the aforementioned 'Steady Chuck Norris Universe').

astromark
2009-Jan-13, 06:32 PM
Moonhead; Its not un-reasonable to challenge the standard model of the expanding universe ,and the balloon. The problem here is with your perception is not supported by observation. The galaxies are not shrinking. The universe is continuing to accelerate as it expands. Tested and observed by direct observation and mathematics. Done and dusted. Confirmed. So change the question and try to see the facts as others have. How can we / you, better understand what and why it is happening. Ignore the balloon. I see a 3D model expanding ever faster. We are in it. Like a gas cloud released into a vacuum. Were gravity has lost the war. Dark energy is the unknown mystery that is pulling the universe to bits. What is it. Now theres a good question.

Moonhead
2009-Jan-13, 07:38 PM
Moonhead; Its not un-reasonable to challenge the standard model of the expanding universe ,and the balloon. The problem here is with your perception is not supported by observation. The galaxies are not shrinking. The universe is continuing to accelerate as it expands. Tested and observed by direct observation and mathematics. Done and dusted. Confirmed. So change the question and try to see the facts as others have.

Thanks for the answer. But I wasn't challenging anything. I was just curious how a model, in this case the inflating balloon-with-dots, could be apllied in another way, and still confirm all tested, done and dusted observations. It was soon pointed out that this other way wouldn't contribute to any insight.

My question was more along the lines of "what would I gain if I turn a globe inside out and stick my head in through the South Pole". One of the obvious observations that would need to be dealt with in this model, is that the map would be mirrored; so the model would need to correct that. It would be much less easy to work around the improper curvature. It would sacrfice the Antarctic region. The model wouldn't contribute.


Dark energy is the unknown mystery that is pulling the universe to bits. What is it. Now theres a good question.

:lol: For the forum, for science or for mankind?

Gigabyte
2009-Jan-13, 08:08 PM
I wasn't being sarcastic.

Argos
2009-Jan-13, 08:15 PM
Yeah, shrinking objects would be equivalent to an expanding universe. I personally find it 'unnatural', so I stick with the expansion.

There are several threads in which this hypothesis is brought up, and if the memory serves me, Ken G has some ideas about it.

Moonhead
2009-Jan-13, 09:30 PM
I wasn't being sarcastic. In that case, and provided you weren't trying to be "ironic" or "cynic" (qualifications arguably less fitting to a scornful interpretation of your phrase), I should say 'thank you'. Thank you :)



Yeah, shrinking objects would be equivalent to an expanding universe. I personally find it 'unnatural', so I stick with the expansion.

Considering it, I was actually wondering whether it would be less unnatural than expansion.

My thoughts could be summed like this: What is expanding? The totality, the wholeness of it all, the universe. How could that be? The totality remains the totality. It would seem to me that it might be kinda anthropocentric to suppose the universe is expanding while 'the local stuff' (which might be a pseudo-humble euphemism for 'we' :) ) remains the same size. As long as there are no objective references of scale, it would be more proper to say that the universe, the wholeness of it all, the totality remains the same size, while we, including our measures and perception of measurement, shrink. As far as my limited understanding and imagination reaches, the planck limit, the speed of light and the relation between the fundamental forces might be such objective references of scale. So a 'shrinking dot' model, as far as I can imagine, would require to have those constants to shrink proportionally (or maybe otherwise explain them within the model, like they're changing so slowly that we having noticed. Which would not be too hard to stomach, provided we haven't been around that long).

This is much more a matter of conceptualization than of 'what is really happening'. But the same is true for the 'steady Chuck Norris universe'.



There are several threads in which this hypothesis is brought up, and if the memory serves me, Ken G has some ideas about it.

What keywords should I use to find them?

I'm curious whether such a 'shrinkage' model would require a proportional shrinking of all sorts of established constants (like the speed of light, the fundamental forces), or how it would otherwise deal with the fact that we perceive an expanding universe.

Argos
2009-Jan-13, 10:04 PM
What keywords should I use to find them?

Use 'shrinking', 'expanding'. See this post for example

http://www.bautforum.com/against-mainstream/37796-where-objectivity-7.html#post702969


I'm curious whether such a 'shrinkage' model would require a proportional shrinking of all sorts of established constants

Well, shrinkage would require all objects to shrink at the same rate. Thatīs considerably more problematic than having only one universe with one given rate of expansion.

Remember that the concept of inflation has been introduced to address this homogeneity problem [plus the flatness and isotropy]. An expansion fits more naturally in this scenario. It would be a legacy from the ancient inflation.

slang
2009-Jan-13, 10:19 PM
It would seem to me that on a real inflating ball, dots painted on it would grow proportionally - to have it represent the expansion of the universe more accurate, the dots should be remaining their original size, while the ball grows.

I've heard the analogy described as a balloon with coins glued to spots on the surface. The balloon inflates, distances increase, the coins stay the same size, thus avoiding the "dots should grow with balloon" flaw.

publius
2009-Jan-13, 10:26 PM
Actually, there's no physical way to distinguish between expanding space and shrinking local systems (if the math is done correctly, of course :) ). Since there is no physical way to distinguish them, they are actually physically equivalent!

This is just another matter of coordinates, actually. Sitting here, we hold a ruler, which we declare is fixed. The proper distance between distant galaxies (which is coordinate thing itself which doesn't mean what you think it means, but we won't make too much of fuss) using that fixed ruler is increasing with time. Now, just consider that expanding distance to be your fixed unit of distance, and now you local ruler is simply shrinking.

There are many ways to coordinatize a given space-time. The physical invariants are not affected, and thus GR's covariant formulation doesn't care either. The coordinates are not important.

Now, our little human minds like to think of things in a certain way. And that way just doesn't have any meaning in GR's covariant formulation. But we still fret over them, cause because we still hold on to that absolute type of thinking.

There's all sorts of things we could imagine happening in some absolute, God's eye view sense. For example, God could decide to take a vacation and simply put the universe "in stasis" for umpteem trillion years. Everything just freezes until he gets back and starts it up again. We'd never know the difference. It wouldn't be physically detectable, so it doesn't matter.

-Richard

Moonhead
2009-Jan-13, 10:38 PM
Actually, there's no physical way to distinguish between expanding space and shrinking local systems (if the math is done correctly, of course :) ). Since there is no physical way to distinguish them, they are actually physically equivalent!

This is just another matter of coordinates, actually.

This was my initial thought (but much better phrased, of course). But then I started worrying about the observed redshift and the fundamental forces... From your reply I take it that there would be no problems ("if the math is done correctly, of course :) "), and that the whole idea is simply a coordinate matter.

Thanks!

Moonhead
2009-Jan-13, 10:46 PM
Use 'shrinking', 'expanding'. See this post for example

http://www.bautforum.com/against-mainstream/37796-where-objectivity-7.html#post702969



Thanks!



Well, shrinkage would require all objects to shrink at the same rate. Thatīs considerably more problematic than having only one universe with one given rate of expansion.

Seems to makes sense, but then Publius answered it's all a coordinate thing... :confused: [EDIT: He also made it clear that it doesn't matter, as it is not observable, so maybe I shouldn't bother about it.]


Remember that the concept of inflation has been introduced to address this homogeneity problem [plus the flatness and isotropy]. An expansion fits more naturally in this scenario. It would be a legacy from the ancient inflation.

I would think that, if the observed expansion could be explained as 'shrinkage', so would inflation. If indeed it is mere a coordinate matter than neither one would be a better explanation...

I'll read up on the urls you supplied!

publius
2009-Jan-13, 11:00 PM
Seems to makes sense, but then Publius answered it's all a coordinate thing... :confused: [EDIT: He also made it clear that it doesn't matter, as it is not observable, so maybe I shouldn't bother about it.]

..............

I would think that, if the observed expansion could be explained as 'shrinkage', so would inflation. If indeed it is mere a coordinate matter than neither one would be a better explanation...



It's all a matter of how you think about things. Local systems stay the same size and "space expands". Or space stays the same and local systems shrink. It may be easier to imagine that one thing, space expands, than everything, local rulers included (and therefore your definition of things that depend on local distance, like units of force, etc, etc) is shrinking. But they are physically equivalent in terms of what you can physically measure.

So if you can't distinguish them with any tool available in this universe, what's the difference other than what seems the most sastifying to your mind? :)

-Richard

Moonhead
2009-Jan-13, 11:56 PM
So if you can't distinguish them with any tool available in this universe, what's the difference other than what seems the most sastifying to your mind? :)


Indeed, satisfying the mind might be what it comes down to... The 'shrinking dot' model makes it more acceptable for me to apprehend what's happening. Even though it's merely coordinates.

Argos
2009-Jan-14, 01:22 PM
I would think that, if the observed expansion could be explained as 'shrinkage', so would inflation. If indeed it is mere a coordinate matter than neither one would be a better explanation...


So we start with a big, infinite sapce, and get objects to shrink within it, after an exponential shrinkage in the beginnings...

Of course it doesnīt matter geometrically [and I have conceded that], but then not all mathematical results are useful to describe the physical reality. Physically something is happening, either an expansion or shrinkage. We have a neat way to explain the homogeneity of the expansion, but I think it is diffcult to explain the homogeneity of the shrinkage of individual objects [of course, Iīd appreciate some explaining, if someone bothers].

gzhpcu
2009-Jan-14, 02:48 PM
Maybe I am slow, but will someone explain how redshifting occurs in this scenario?

Moonhead
2009-Jan-14, 06:51 PM
Maybe I am slow, but will someone explain how redshifting occurs in this scenario?

An attempt: the shrinkage of local systems would increase the distance between emitter and receiver. The farther a star is from its observer, the more obvious the effect will be for that observer.

Again this is not different from an expanding universe.

gzhpcu
2009-Jan-14, 06:57 PM
An attempt: the shrinkage of local systems would increase the distance between emitter and receiver. The farther a star is from its observer, the more obvious the effect will be for that observer.

Again this is not different from an expanding universe.

OK, I forgot that the yardstick shrinks, resulting in an increase in distance...

Moonhead
2009-Jan-14, 07:03 PM
not all mathematical results are useful to describe the physical reality.

I agree.


Physically something is happening, either an expansion or shrinkage. We have a neat way to explain the homogeneity of the expansion, but I think it is diffcult to explain the homogeneity of the shrinkage of individual objects

Why do you think this would be more difficult for the 'shrinking model'? Please note that this is NOT a rhetorical question; actually I think that the reason I do not see the difficulty, is that my knowledge of the homogeneity problem is fairly limited. Please share your thoughts.

EDIT: Do you mean, that it would be weird that all the shrinking systems would apparently be shrinking at the same rate?




[of course, Iīd appreciate some explaining, if someone bothers].

So would I!

Argos
2009-Jan-14, 07:07 PM
I personally find it easier to believe in God [and maybe Santa Claus] than to believe that things are shrinking. There are plenty of expansive phenomena in the universe, so itīs not hard to extend the reasoning to an original 'mother of all expansions'. On the other hand, thereīs nothing within the universe that can lead us into concluding that objects shrink. Itīs just absurd, and mathematical interpretations in this sense should be disregarded.

Moonhead
2009-Jan-14, 07:41 PM
I personally find it easier to believe in God [and maybe Santa Claus] than to believe that things are shrinking.

Concerning your sig, that's a bold statement!

[EDIT: I suddenly remember that movie, The Incredible Shrinking Man. At the end, it is suggested the poor guy will be getting so small that he will disappear from our universe. But, explains the narrator, it doesn't matter because God still loves him and everybody else. Or something along that line.]

The described model wouldn't be suggesting that "things are shrinking". It would suggest that matter as a whole, on a large scale, is shrinking. Moreover, like Publius said, is just a coordinate thing, and, if the math would be set up properly, would be indistinguishable from the expanding space model. It wouldn't reveil some hidden properties of the universe. It might open some new perspectives, thinking it over but those would be more on the philosophical level.

Anyway, it doesn't require believing.


There are plenty of expansive phenomena in the universe, so itīs not hard to extend the reasoning to an original 'mother of all expansions'. On the other hand, thereīs nothing within the universe that can lead us into concluding that objects shrink.

If we would be made of shrinking matter, it would indeed be unnoticeable for us. Unless, maybe, in a very indirect way, like space appearing to expand on the grand scale.



Itīs just absurd, and mathematical interpretations in this sense should be disregarded.

:lol: I bet you plagiarized that phrase from an early 19th century science fiction novel.

Now I'm on a less serious note anyway: have you ever washed woolen clothes at too high a temperature?

Argos
2009-Jan-14, 07:59 PM
:lol: I bet you plagiarized that phrase from an early 19th century science fiction novel.

Not really. :). Frequently, mathematical results that donīt comply with reality are discarded, e.g. tachyons, which have precise mathematical meaning and still have no real existance.

Geometry [the coordinate thing] allows for the shrinking paradigm. But why should we adopt it so readily? Whatīs the initial size of the universe in the shrinking paradigm? How do distant individual objects display a so neatly tuned rate of shrinking? What would be the analog of Cosmic Inflation in the Shrinking paradigm?



Now I'm on a less serious note anyway: have you ever washed woolen clothes at too high a temperature?

If I could shrink along with it your point would be proven. :)

Gigabyte
2009-Jan-14, 08:16 PM
I've noticed that sometimes people shrink as they get older.



























Except for their ears and their nose.

Jeff Root
2009-Jan-14, 08:34 PM
I pretty much agree with Argos. The huge, enormous, insuperable problem
with the notion of everything in the Universe shrinking is that everything
just happens to be shrinking at the same rate. On smaller scales in nature,
we see variations in the rates at which things happen. Faster here, slower
there. Way, way too much of a coincidence that everything is shrinking in
perfect synch with everything else.

-- Jeff, in Minneapolis

Moonhead
2009-Jan-14, 09:21 PM
Not really. :). Frequently, mathematical results that donīt comply with reality are discarded, e.g. tachyons, which have precise mathematical meaning and still have no real existance.

Geometry [the coordinate thing] allows for the shrinking paradigm. But why should we adopt it so readily? Whatīs the initial size of the universe in the shrinking paradigm?

What about calling it "1"? Or, exactly the same as in the expanding model?


How do distant individual objects display a so neatly tuned rate of shrinking? What would be the analog of Cosmic Inflation in the Shrinking paradigm?


In all reasonability (ouch, that's an ugly dutchism but there comes no proper english term coming to my mind) you are right. There is nothing gained or clearified by 'the shrinking paradigm'(*. To the contrary, as is demonstrated by you and other posters.

It's a nice thought experiment though.

*(Btw nice term! if I would write a crackpot-science softcover bestseller about it and use that term, would that count as plagiarizing?).





If I could shrink along with it your point would be proven. :)

That might just be worth trying. If you would shrink, then you would weight the same as a duck, and therefor made of wood... Therefor a witch!

publius
2009-Jan-14, 09:26 PM
:lol: Okay, then why is it so easy to believe that space is uniformly expanding -- every part of space is expanding at the samer rate. Why is that any easier to accept than every ruler in space shrinks at the same rate? It's all in your mind.


And that's what the lesson of GR is. There's a lot less to reality than you think there is. The two notions, expanding space vs shrinking stuff in space are physically equivalent. No way to tell the difference. And so we shouldn't think of them as two different things that we can't tell the difference between, but as the same thing. If two things are physically indistinguishable, then they're the same thing. The only difference is in your mind, not in reality. :)

There all sorts of ways to coordinatize the space-time manifold that is our Universe. Space and time are arbitary "foliations" of space-time. Things like expanding vs shrinking live in those coordinatizations, they don't live in the invariant properties of the manifold.

It's no different that two observers in relative motion arguing over who is really moving. A dust speck is hurtling towards earth at 0.5c I find it easier to believe that the dust speck is moving that fast rather than the massive earth. Can you imagine how much kinetic energy the earth would have at
0.5c? I just can't believe that. :)


-Richard

Argos
2009-Jan-14, 09:32 PM
What about calling it "1"? Or, exactly the same as in the expanding model?

Now youīre cheating. :naughty:

It illustrates the problem with that notion, though. And yes, itīs a nice thought experiment. :)

Moonhead
2009-Jan-14, 09:32 PM
I pretty much agree with Argos. The huge, enormous, insuperable problem
with the notion of everything in the Universe shrinking is that everything
just happens to be shrinking at the same rate. On smaller scales in nature,
we see variations in the rates at which things happen. Faster here, slower
there. Way, way too much of a coincidence that everything is shrinking in
perfect synch with everything else.

-- Jeff, in Minneapolis

Again, I'm talking about a model, not trying to pin down what is actually happening. (Although I too tend that forget that, at times.)

If the shrinking model and the expanding model would be indistinguishable from each other, the explanation for the 'perfect synch shrink' would be the same as is is now (and then it might indeed be as unpractical as saying 'the earth is fixed in space and sun turns around it, while the other planets turn around the sun').

Like I just said to Argos: as is demonstrated by you and other posters, there is nothing gained or clearified by the shrinking model.

Moonhead
2009-Jan-14, 09:39 PM
There's a lot less to reality than you think there is. [...] If two things are physically indistinguishable, then they're the same thing. The only difference is in your mind, not in reality. :)

Great post! Thanks, Richard.

(I've only quoted the best of the best of it to save space.)

Argos
2009-Jan-14, 10:05 PM
It's no different that two observers in relative motion arguing over who is really moving. A dust speck is hurtling towards earth at 0.5c I find it easier to believe that the dust speck is moving that fast rather than the massive earth. Can you imagine how much kinetic energy the earth would have at
0.5c? I just can't believe that. :)

Richard, Iīm starting to suspect that your presence in a building can cause experiments to fail :)

Seriously, speaking in terms of universal evolution [what the universe once was and what it is now], thereīs a reality that must be faced, no matter how identically it can be treated mathematically with the employment of any of the views.

If the Inflation hypothesis had to be appended to GR to give us a faithful representation of reality, it seems, from an empirical point of view, that the evolution of the universe should present very different aspects depending on whether space is expanding or matter is shrinking.

Iīm aware of your proficiency in this field, so please donīt take my questioning as a challenge to your position. Iīm just a dumbhead, insistent fellow.

publius
2009-Jan-14, 11:03 PM
Seriously, speaking in terms of universal evolution [what the universe once was and what it is now], thereīs a reality that must be faced, no matter how identically it can be treated mathematically with the employment of any of the views.

That's my position exactly. However the reality that must be faced is there is less to reality that you think! Whether space is exanding or stuff is shrinking (and there are other valid coordinates whether neither is happening, too -- see static deSitter for example) all lives in that realm of arbitrary mathematical choice.




If the Inflation hypothesis had to be appended to GR to give us a faithful representation of reality, it seems, from an empirical point of view, that the evolution of the universe should present very different aspects depending on whether space is expanding or matter is shrinking.

What is inflation? It is a rapid, accelerating expansion. That can be modelled in GR just fine, through a large Cosmological Constant. But wait, that means it has to vary with time, so it's not a constant. So you adopt the view, by moving a term to the RHS of the EFE, that it is caused by some sort of stuff in space-time, called dark energy. You can more easily accept that some sort of stuff can change with time. But it could be some sort of time-variable aspect of the geometry itself and stay on the LHS.

So, whatever -- there's this stuff that causes space to expand (well accelerate in addition to the inertia of the co-moving matter). Why not say that stuff, in different mathematical form, causes other stuff to shrink. And that rate of shrinkage varies. Inflation was a period of very rapid shrinkage.

In terms of the invariants, what is there is a component of space-time curvature. During inflation, that curvature component was very high, then tapered off. When you coordinatize things, you get into resolving that curvature as expanding space, or shrinking rulers, or whatever. It doesn't matter and isn't any part of invariant reality.




Iīm aware of your proficiency in this field, so please donīt take my questioning as a challenge to your position. Iīm just a dumbhead, insistent fellow.

Oh pish. I'm about as proficient as I fear my avatar and his buddies are in, well, whatever they think they're doing! :lol:

-Richard

Gigabyte
2009-Jan-15, 01:41 AM
... It's no different that two observers in relative motion arguing over who is really moving. A dust speck is hurtling towards earth at 0.5c I find it easier to believe that the dust speck is moving that fast rather than the massive earth. Can you imagine how much kinetic energy the earth would have at
0.5c? I just can't believe that. :)




There is another interesting thought. I'm not kidding.

WayneFrancis
2009-Jan-15, 03:13 AM
:lol: Okay, then why is it so easy to believe that space is uniformly expanding -- every part of space is expanding at the samer rate. Why is that any easier to accept than every ruler in space shrinks at the same rate? It's all in your mind.


And that's what the lesson of GR is. There's a lot less to reality than you think there is. The two notions, expanding space vs shrinking stuff in space are physically equivalent. No way to tell the difference. And so we shouldn't think of them as two different things that we can't tell the difference between, but as the same thing. If two things are physically indistinguishable, then they're the same thing. The only difference is in your mind, not in reality. :)

There all sorts of ways to coordinatize the space-time manifold that is our Universe. Space and time are arbitary "foliations" of space-time. Things like expanding vs shrinking live in those coordinatizations, they don't live in the invariant properties of the manifold.

It's no different that two observers in relative motion arguing over who is really moving. A dust speck is hurtling towards earth at 0.5c I find it easier to believe that the dust speck is moving that fast rather than the massive earth. Can you imagine how much kinetic energy the earth would have at
0.5c? I just can't believe that. :)


-Richard

No they are not the same thing.

You either have to say that space is expanding at a relatively uniform rate across the universe.

Or

You say that all matter is shrinking at a relatively uniform rate across all the universe and all fundamental forces are changing at the the same rate including the planck length. But light isn't included in this because if it was we wouldn't see the redshift and oh the electromagnetic force is inversely changing with the shrinkage so that it still emits the correct frequency of photons from quantum level events.

Personally I would like to say that all the fundamental constants in the universe are actually constant and that 1 thing is changing, the size of the universe, instead of say that all the constants are in some grand coordinated flux besides the frequency of photons from distant object.

I mean do you look at a dog poo in the ground 1 day then look at the same pile the next and notice that it is bigger and say "****, the earth and everything on it is shrinking, but that poo hasn't changed size!" or would you say "Hey I think some dog pooed in the same place again"

We can either have 1 thing be variable or everything is not only variable but also orchestrated in such a way that it just looks like everything is really constant besides that original variable.


For those that like the thought experiments if everything was coordinated you would have to say that a photons frequency is not subject to the change after they are emitted to account for the cosmic red shift but some how the speed of the photon is effected after it leaves the source. Now you have to explain why one attribute of a photon is effected while another isn't.

Cougar
2009-Jan-15, 03:12 PM
And that's what the lesson of GR is. There's a lot less to reality than you think there is. The two notions, expanding space vs shrinking stuff in space are physically equivalent. No way to tell the difference.

That is, within the structure of GR. But this idea doesn't seem to address the standard model of particle physics at all. It rather thumbs its nose at the standard model by such neglect. I've got to line up behind Argos and Wayne Francis on this one.

The two scenarios may be equivalent in terms of the Einstein field equations, but when Hubble's redshift observations are thrown into the mix, the "shrinking stuff in space" model seems to have problems to me, regardless of whether my ruler is shrinking. I'll have to develop this more when I have a little time....

max8166
2009-Jan-15, 05:32 PM
I Feel the main problem with a shrinking local Universe and an expanding Universe is the beginning. It is thought that the Universe started with a singularity, I am unable to conceive of a shrinkage within a singularity!
Admittedly I have problems with dark energy expanding as well but not quite so many :)

astromark
2009-Jan-15, 05:45 PM
We have knowledge tested and confirmed. The universe is expanding at a accelerating pace. Observation of the farthest reaches of the visible universe.
I have not been aware of any observed shrinkage. Could you share from where this idea has come from. If as I suspect, you are just attempting to know some thing no-one else does... this is not the place for that discussion.

Jeff Root
2009-Jan-15, 07:26 PM
Mark,

Richard is saying that if we had a big set of architectural scale drawings
of the entire Universe (or at least the part of it that is expanding -- or
at least the part of it that we can see), showing the Universe at two
different points in time, there would be no way to tell if the galaxies in
the later drawings had moved apart from each other or if they had all
stayed in the same places but shrank in size.

Argos, Cougar, Wayne, and I are saying that even if the plans look
identical, the building techniques are so radically different that one
(pushing the galaxies apart) gets bid on and constructed, while the
other (shrinking galaxies without shrinking the spaces between them)
is too much of a hassle for any contractor to bother with.

-- Jeff, in Minneapolis

publius
2009-Jan-15, 07:59 PM
Mark,

Richard is saying that if we had a big set of architectural scale drawings
of the entire Universe (or at least the part of it that is expanding -- or
at least the part of it that we can see), showing the Universe at two
different points in time, there would be no way to tell if the galaxies in
the later drawings had moved apart from each other or if they had all
stayed in the same places but shrank in size.

Argos, Cougar, Wayne, and I are saying that even if the plans look
identical, the building techniques are so radically different that one
(pushing the galaxies apart) gets bid on and constructed, while the
other (shrinking galaxies without shrinking the spaces between them)
is too much of a hassle for any contractor to bother with.

-- Jeff, in Minneapolis

:clap: By George, I think you've got it. Adjust the scale to keep the map of the universe fitting on your monitor. The scale doesn't matter, it's the relative relations of stuff in the drawing. If the contractor is going to shrink with the galaxies, then he's fine.

This is just a trivial mathematical exercise in coordinate transforms. Let x be our current fixed ruler. The number of x's between galaxies is increasing with time according to same scale factor a(t). Now, define a new unit of length, l according to

l = a(t) *x.

The l is increasing with time. It's an expanding ruler. Now, transform all you equations of physics, Standard Model included, into l rather x. In terms of l, everything is shrinking.

You say, well, that's because your silly ruler, l, is expanding with time. I say, no silly, my ruler is fixed, but it is in fact your ruler, x, that is silly and shrinking with time, x = l/a(t). Why do you want to use such a silly shrinking ruler?

But you reply, no idiot, my ruler is fixed and it is in fact your stupid ruler that is expanding with time. We're not silly shrinking, because my physical constants are constant with time using my ruler.

Well, I say, what's so great about that? These dimesionful constant things are just silly things you've chosen because you insist on using arbitrary units, and not the natural relative scale of the universe. I say the distant between galaxies is one huge humdinger of a unit. It should be the thing that is constant, since in my philosophy that is so important. So the fact that appears to be increasing with time indicates that your silly rulers and constants and stuff are varying with time.


What I'm trying to get you all to see is that both sides of that argument are equally silly. It doesn't matter. It's the invariants, the stuff that lives in the observable relative relations between everything that are coordinate independent, which are the only thing that matters.


-Richard

speedfreek
2009-Jan-15, 10:22 PM
What I'm trying to get you all to see is that both sides of that argument are equally silly. It doesn't matter. It's the invariants, the stuff that lives in the observable relative relations between everything that are coordinate independent, which are the only thing that matters.


-Richard

But it seems to be human nature to want to choose between those silly sides, to see which is less silly than the other. Is silliness relative? Is there a preferred position of silliness?

If we happen to choose the speed of light as an invariant, is that just as silly? Isn't there a third possible silly option, where the neither the universe is expanding nor the matter within it is shrinking, but the speed of light is variable? No, that's just tired-light extra-silliness, we think we have ruled that one out due to having to find new mechanisms for time-dilation in supernovae, distant galaxy formation and angular size and the like. Those high redshift galaxies were close to us (or all galaxies were larger!*) when they emitted their light, we have no mechanism to describe how they might actually have been really large and really far away (or larger but at the same distance?!*) back then. ;)

I wonder why the shrinking matter within the universe theory seems less palatable than the expanding universe theory if both are equivalent? Notions of Occam's razor perhaps?

*(in a universe where everything is shrinking)

Jeff Root
2009-Jan-15, 11:23 PM
I wonder why the shrinking matter within the universe theory seems less
palatable than the expanding universe theory if both are equivalent?
One requires only a single event, the pushing apart of matter at the
Universe's beginning. The other requires uncountable separate but
identical shrinkings of everything in the Universe except the spaces
between widely-separated galaxies, precisely co-ordinated throughout
all that matter, from the beginning onward.

-- Jeff, in Minneapolis

Gigabyte
2009-Jan-15, 11:37 PM
One requires only a single event, the pushing apart of matter at the
Universe's beginning. ...

I'm no expert on the BB theory, but I am sure that isn't correct. It is supposed to be space-time that expands, not matter.

speedfreek
2009-Jan-16, 12:19 AM
One requires only a single event, the pushing apart of matter at the
Universe's beginning. The other requires uncountable separate but
identical shrinkings of everything in the Universe except the spaces
between widely-separated galaxies, precisely co-ordinated throughout
all that matter, from the beginning onward.

-- Jeff, in Minneapolis

I thought that the accelerating expansion precluded the idea that a single event was wholly responsible? This idea was fine when the expansion of universe was simply decelerating, but with the acceleration of that expansion we need another mechanism too. Some even think that dark energy is the left-overs from the field that caused inflation, and might have been responsible for the initial expansion before inflation (one field going through two phase transitions). But of course I get your overall point anyway, it still seems the simpler of the two options.

But can we theorise an invisible energy that could be equally valid in explaining a universe where everything shrinks? If we can, are both theories still physically equivalent?

Jeff Root
2009-Jan-16, 12:44 AM
One requires only a single event, the pushing apart of matter at the
Universe's beginning. ...
I'm no expert on the BB theory, but I am sure that isn't correct.
It is supposed to be space-time that expands, not matter.
What does that mean?




What is observed is that widely-separated clusters of galaxies
are moving away from each other. The farther apart they are,
the faster they are moving away from each other.

(Okay, that isn't true, either. What is observed is redshift which
varies with distance. But the interpretation of galaxy motion is
straightforward.)

-- Jeff, in Minneapolis

Jeff Root
2009-Jan-16, 12:50 AM
One requires only a single event, the pushing apart of matter at the
Universe's beginning. The other requires uncountable separate but
identical shrinkings of everything in the Universe except the spaces
between widely-separated galaxies, precisely co-ordinated throughout
all that matter, from the beginning onward.
I thought that the accelerating expansion precluded the idea that a
single event was wholly responsible?
I'm just ignoring the acceleration for this particular comparison.
Pretend this is 1997.

-- Jeff, in Minneapolis

WayneFrancis
2009-Jan-16, 01:13 AM
I'm no expert on the BB theory, but I am sure that isn't correct. It is supposed to be space-time that expands, not matter.

Correct but the idea still holds in general. It is only 1 factor that is changing. Instead of many factors having to coordinate in huge production to get the same results.

(not directed at Robinson)
For example explain to me why a photon's speed would be be effected by the shrinkage but the frequency wouldn't. Why does one aspect of a zero rest mass particle stick with the "ruler", the speed, but another one, the frequency, doesn't?

There are many problems with the "Shrinking Model". I've just choose one to point out. In an expanding model there is not this problem. C isn't getting faster with space expanding. Space is expanding and photon's speed and frequency isn't tightly coupled with it. Sure it is effected but not tightly bound. In the shrinking model we have C's speed tightly bound to the rate of shrinkage.

I don't need to go into any of the more complex issues at this time. Much like if Einstein was wrong it would only have taken 1 scientist to prove him wrong. It only take one fatal flaw with a hypothesis to disprove it. Trying to say that the expanding universe and shrinking universe are identical and can to been distinguished is FALSE.

astromark
2009-Jan-16, 10:14 AM
I have envisaged this idea and reworked my thinking to encompass a shrinking state of matter while the space between remains constant... and can not find information to support this idea. I can imagine how it might look the same as the reality. I can and have found information backed by direct observation of a expansion still eccelarating... This subject has become a ATM idea and is unsuported by science.

Argos
2009-Jan-16, 01:45 PM
I'm just ignoring the acceleration for this particular comparison.
Pretend this is 1997.

You can keep it if you want. In fact, the accelerating expansion comes in handy to this discussion because thereīs a mechanism that accounts for it: Dark energy. Now, we need to find something that causes matter to shrink in synch across the entire universe if we want to adopt the shrinkage view. Or maybe Dark Energy is that something. :)


I have envisaged this idea and reworked my thinking to encompass a shrinking state of matter while the space between remains constant... and can not find information to support this idea. I can imagine how it might look the same as the reality. I can and have found information backed by direct observation of a expansion still eccelarating... This subject has become a ATM idea and is unsuported by science.

In fact, this thread (http://www.physicsforums.com/archive/index.php/t-227812.html) on Physics Forums discussing this very same subject has been closed by the mods for being considered immaterial. Speaking in pedagogical terms, nothing is gained or clarified by the shrinking paradigm [as Moonhead points out], as thereīs a tradition to refer to the universal evolution as an expansion. It introduces an unnecessary noise.

Ken G
2009-Jan-17, 07:32 PM
I agree with publius-- if two models are purely 100% indistinguishable by any physical experiment, so make all the same predictions, then they are exactly the same model (until such a time as they can be distinguished). In the absence of any demonstrable distinction, the only difference between them could be termed pedagogical-- i.e., differences in how you explain or picture the model. Indeed, physics is positively rife with pedagogical differences in its models. The best way to handle them is to know them all, and select whichever pedagogy serves the need at hand. You never know which way of picturing something will stimulate the next useful idea.

In regard to "shrinking dots", that pedagogy is particularly useful in answering the common questions: "what is the universe expanding into?" and "where is the center of the expansion?" Framed as a shrinking, it becomes more obvious why these could actually be nonsensical questions.

Nereid
2009-Jan-17, 10:01 PM
I agree with publius-- if two models are purely 100% indistinguishable by any physical experiment, so make all the same predictions, then they are exactly the same model (until such a time as they can be distinguished).

[...]
(bold added)

Anyone think there's a good chance that some models in which physical experiments* could break the 'philosophical degeneracy' (or perhaps the 'pedagogical degeneracy') will come on the scene in the next decade or three?

* if only in principle; observations included within 'experiments' too

Moonhead
2009-Jan-18, 11:39 PM
In regard to "shrinking dots", that pedagogy is particularly useful in answering the common questions: "what is the universe expanding into?" and "where is the center of the expansion?" Framed as a shrinking, it becomes more obvious why these could actually be nonsensical questions.

Good point! So, I was too early to conclude that nothing is gained or clarified by the 'shrinking dots' model. (Yet when I would explain what's happening to someone, I would start with the 'expanding space' model.)

I must say that model-wise, (and, as far as my knowledge and ability of visualisation reach) I agree with Publius and Ken G. But the way I understand what they are saying, they do not contradict any observations; neither do they claim an origin of either shrinking matter or expanding space. So, it's a bit surprising some people disagree...

Those who disagree, are arguing that expanding space need just one thing (being expanding space :) ) while shrinking matter would need several things to shrink in an unbelievably perfect synch shrink.

I would be willing to agree to that, but when I think about it, I realize I do not know enough. The following might be interpreted as 'nagging', but it isn't meant as such. It's not my defense of some outrageous idea, rather an attempt to enquire why several (intelligent) people are positively sure it couldn't be that way (as opposed to: we can't tell the difference between 'expanding space' and 'shrinking dots'). It's not meant as a disqualification of their ideas.

1) At first, I thought the observed redshift might be a problem in the 'shrinking dot' model. I now think that it isn't, because the units of measurement of the beholder would shrink, so the distance between an emitter and a receiver of light would grow in the same way it does when assuming space is expanding. I'm surprised Cougar disagrees, and I hope he clarifies.

2) Furthermore: what things (particles, forces, patterns, entities) whatever could be hardly imagined to shrink in perfect shrink? I mean, at what level does the unlikeliness / unbelievability come in? Is it, that e.g. the neutrons in the Local Cluster would have to shrink at the same rate as the neutrons in the Virgo Cluster? Or is it, that all particles and the fundamental forces would have to shrink at the exact same rate? Is it both?

_____

A totally different (yet on-topic considering the thread title) question about expansion I'm occasionally bothering with, is: Are there any thoughts / ideas / hypotheses / theories on the necessity of (accelerating) Universal Expansion? I mean, I know there is/are (a) scientific explanation(s) for it, but are there also (main stream) scientists considering the observed expansion as either an unavoidable by-product of our universe, or a necessary condition for it? Or is it thought off as 'just happening to be that way'?

Jeff Root
2009-Jan-19, 12:54 AM
A totally different (yet on-topic considering the thread title) question
about expansion I'm occasionally bothering with, is: Are there any
thoughts / ideas / hypotheses / theories on the necessity of
(accelerating) Universal Expansion? I mean, I know there is/are (a)
scientific explanation(s) for it, but are there also (main stream)
scientists considering the observed expansion as either an
unavoidable by-product of our universe, or a necessary condition
for it? Or is it thought off as 'just happening to be that way'?
Funny you should sugget that. My ATM hypothesis should have
predicted the acceleration of the expansion before it was observed,
but I wasn't smart enough to realize it, so I missed the boat. I have
probably said enough about that hypothesis here over the years for
a persistent Googler to figure out its main ideas. (They are very
simple and obvious.) But at the moment I'll just be all mysterious
about them and keep them semi-proprietary. Until I have developed
them a bit more or experiments in extreme low-energy physics have
disproved them-- whichever comes first.

In any case, nomatter what the cause of the acceleration, the
acceleration will be seen as unavoidable/necessary once that cause
is known. Everything that isn't prohibited by the laws of physics is
required by the laws of physics. At least, that's the way it seems...

-- Jeff, in Minneapolis

Nereid
2009-Jan-19, 02:42 AM
Funny you should sugget that. My ATM hypothesis should have
predicted the acceleration of the expansion before it was observed,
but I wasn't smart enough to realize it, so I missed the boat. I have
probably said enough about that hypothesis here over the years for
a persistent Googler to figure out its main ideas. (They are very
simple and obvious.) But at the moment I'll just be all mysterious
about them and keep them semi-proprietary. Until I have developed
them a bit more or experiments in extreme low-energy physics have
disproved them-- whichever comes first.

In any case, nomatter what the cause of the acceleration, the
acceleration will be seen as unavoidable/necessary once that cause
is known. Everything that isn't prohibited by the laws of physics is
required by the laws of physics. At least, that's the way it seems...

-- Jeff, in Minneapolis
But the key point, that publius and Ken G stressed, is whether there's any way - even in principle - to distinguish between any given pair of models.

If not, then the models are equivalent, in terms of their predictive and explanatory power, wrt that part of the universe which is within their domains and within reach of our observations and experiments.

"Everything that isn't prohibited by the laws of physics is required by the laws of physics." - a.k.a. the ergodic principle, sorta (actually I learned it as "compulsory" rather than "required", but six of one, half a dozen of the other ...).

Ken G
2009-Jan-19, 03:24 AM
Anyone think there's a good chance that some models in which physical experiments* could break the 'philosophical degeneracy' (or perhaps the 'pedagogical degeneracy') will come on the scene in the next decade or three?Indeed, I have a hard time seeing how they could ever be distinguished.

astromark
2009-Jan-19, 03:28 AM
The facts as I understand them... The universe is expanding at a accelerating rate.
If I were to wonder across this board and this forum as a newbie just hunting for intelagance... Then wow! I was wrong, its shrinking and thats why we are getting further away from everything. THAT IDEA IS VERY WRONG. So why is it being discussed as if it were fact. Its not.
This universe, ( the only one we know of. ) Has rules. This is one of them.
Now if per chance I am in the wilderness on this and am found to be completely wrong. Meaning that the universe is not expanding at all but that the matter in it is shrinking so much as to increase the gaps between things, thus giving to the idea of massive expansion... I feel ashamed and humiliated. How could I be so wrong for so long...? :) Please avail of me the information that has changed the fact that I thought I new... and if you can not do that then please have the decency to tell me. a getting very confused, mark.

Ken G
2009-Jan-19, 03:28 AM
1) At first, I thought the observed redshift might be a problem in the 'shrinking dot' model. I now think that it isn't, because the units of measurement of the beholder would shrink, so the distance between an emitter and a receiver of light would grow in the same way it does when assuming space is expanding. Right, there's no problem at all with cosmological redshift.


2) Furthermore: what things (particles, forces, patterns, entities) whatever could be hardly imagined to shrink in perfect shrink? I mean, at what level does the unlikeliness / unbelievability come in? Is it, that e.g. the neutrons in the Local Cluster would have to shrink at the same rate as the neutrons in the Virgo Cluster? Or is it, that all particles and the fundamental forces would have to shrink at the exact same rate? Is it both?A number of things would have to change, they would respond to a change in the global gravitational potential. Why that was changing is not explained, but neither does "expanding space" explain why.

Or is it thought off as 'just happening to be that way'?
Ultimately, all scientific theories would seem to come down to that statement-- it should not bother us. All we should be bothered by is a sense that we have failed to achieve a level of simplification and unification that might be possible. Of course, with simplification, we pay a price.

Ken G
2009-Jan-19, 03:33 AM
This universe, ( the only one we know of. ) Has rules. This is one of them. But one of the "rules" is that all ideas that lead to the same experimental predictions are the same idea, insofar as science is concerned. They may seem very different-- this is not at all uncommon in physics. (For example, google "Newton's laws", and look up "Hamilton's principle". I wager they will look nothing like each other-- yet they are viewed as equivalent formulations expressly because they generate the same equations of motion. As does "shrinking dots", it can be made to give the same equations, and the same predictions as expanding space-- as long as the result is the Einstein field equations. The pictures we use to explain the physics is not the physics, it is the pedagogy.)

publius
2009-Jan-19, 04:32 AM
....THAT IDEA IS VERY WRONG. So why is it being discussed as if it were fact.
....

This universe, ( the only one we know of. ) Has rules. This is one of them.

.....
a getting very confused, mark.



Mark,

Take a deep breath and relax. Nothing has changed. I must admit I find it pretty amusing how such a simple coordinate change has upset a number of posters here. "No, no!", you all say, and I'm having fun.

There is zero physics in coordinates, and all we've done is just change coordinates. It's like that famous picture which can be either a white vase against a black background, or two black faces against a white background depending on how you look at it. That's all coordinates are. That's pedagogy.

Look at this way. The ratio of the size of the earth, the solar system, whatever local reference you wish to the distance between galaxies is certainly decreasing. That's the fact. Now, whether the numerator is fixed and the demoninator increasing, or the demoninator fixed and numerator increasing is a matter of coordinates. Heck, both could be changing in however way you like so long as the ratio is preserved.

You're thinking of "expanding" or "shrinking" in absolute terms. Something is absolutely expanding or something is absolutely shrinking. There are no such absolutes.

"Space" is merely a coordinate dependent construct anyway. So you shouldn't be suprised that questions of whether "space" is expanding, or "stuff in space" is shrinking (or other coordinates where neither is happening) are likewise coordinate dependent.

Yes, the universe has rules. But those rules are coordinate independent.


-Richard

publius
2009-Jan-19, 04:44 AM
And BTW, what's all this opposition to stuff shrinking anyway? If I accelerate off towards say Andromeda at 0.9999c, everything in the entire universe shrinks in one direction. Andromeda and the Milky Way I leave behind get very wide and thin looking. When I write the equations of physics in those coordinates, it predicts everything will shrink in that direction. No physics changed, just the coordinates.


-Richard

Argos
2009-Jan-19, 02:01 PM
neither do they claim an origin of either shrinking matter or expanding space

But they should. Give me a picture of the origin, the initial state, of a unverse in which matter is destined to shrink and Iīll be happy.

Also, concepts like the Holographic Principle have problems with the shrinkage of matter idea, since it requires a physically expanding universal horizon.


So, it's a bit surprising some people disagree...

Publius talks of the equivalence of both views, and I agree, as far as mesurements are concerned.

Matter and energy are equivalent. Should they be treated equally then? Dealing with 1kg of lead is different than dealing with the energy contained in 1 kg of lead.

Those who disagree with the shrinking view are not alone, since the standard jargon to treat the evolution of the universe is that of an expansion. This is a thought expriment that does nothing more than hinder the pedagogy of the whole thing [as if talking about the evolution of the universe as an expansion wasnīt complicated enough for the non-initiated].

Moonhead
2009-Jan-19, 02:12 PM
A number of things would have to change, they would respond to a change in the global gravitational potential.

Might we then say that, in the 'shrinking dot' model, there is just 1 thing changing: the global gravitational potential? Or am I now simplifying too much?

Are there any (main stream) scientists wondering if the supermassive black holes in the center of galaxies might be warping space-time in such a way that it causes the apparent accelerating expansion? (This reminds me of an article I read somewhere last year on a Dutch astronomy blog, suggesting that time dilation could be a / the cause for the apparent expansion, but I had no time then to trace the origin and solidness of that suggestion. If I remember right, it was suggested that time would be 'running faster' in the voids, as compared to the 'filled' parts of space, explaining the acceleration of the expansion (but not necessarily the expansion itself, I would guess)).


Ultimately, all scientific theories would seem to come down to that statement-- it should not bother us. All we should be bothered by is a sense that we have failed to achieve a level of simplification and unification that might be possible. Of course, with simplification, we pay a price.

I will have to read that more times to fully apprehend it :)

Moonhead
2009-Jan-19, 02:41 PM
This is a thought expriment that does nothing more than hinder the pedagogy of the whole thing [as if talking about the evolution of the universe as an expansion wasnīt complicated enough for the non-initiated].

You and others have made several statements like this, as if even talking about it is harmful. That surprises me... Especially when Publius made it clear it's all just a matter of coordinates and Ken G. mentioned at least one pedagogical advantage of the 'shrinking model' .

The concept of an expanding universe is not under siege. :) But by claiming that another way of looking at it, is harmful or even ATM, you act like an orthodox religious person who is shocked when someone asks "if God created everything, where did God himself come from?" and might be achieving the opposite of what you want... I assume your intentions are good: you want to keep the teaching of science / this forum free of noise and of unfounded speculation, right? But if a certain common pedagogical model is presented as the only proper way to describe reality, and alternatives are declared to be 'hindering', than it makes me scratch my head...

Besides, how is a visitor to this forum supposed to know to what degree his question would be 'hindering pedagogy for the non-initiated'? :confused:

Argos
2009-Jan-19, 02:47 PM
Dogmatic me? No, no. See my sig. :)


I assume your intentions are good: you want to keep the teaching of science / this forum free of noise and of unfounded speculation, right?

Right. Actually Iīm worried about the teaching of science.


Besides, how is a visitor to this forum supposed to know to what degree his question would be 'hindering pedagogy for the non-initiated'? :confused:

My previous answer renders this question moot.

I insist in the question about the initial conditions/initial size of the universe. The question is pertinent [Alan Guth has invested a lot of effort in it, eh?].

Nereid
2009-Jan-19, 02:50 PM
But they should. Give me a picture of the origin, the initial state, of a unverse in which matter is destined to shrink and Iīll be happy.

Also, concepts like the Holographic Principle have problems with the shrinkage matter idea, since it requires a physically expanding universal horizon.



Publius talks of the equivalence of both views, and I agree, as far as mesurements are concerned.

Matter and energy are equivalent. Should they be treated equally then? Dealing with 1kg of lead is different than dealing with the energy contained in 1 kg of lead.

Those who disagree with shrinking view are not alone, since the standard jargon to treat the evolution of the universe is that of an expansion. This is a thought expriment that does nothing more than hinder the pedagogy of the whole thing [as if talking about the evolution of the universe as an expansion wasnīt complicated enough for the non-initiated].(bold added)

That's a very good point!

Let's look again at what's been said about coordinates, shrinking, expanding, etc ...

Is there any experiment, even one that could be done only in principle, that could show the distinction between "1kg of lead" and "the energy contained in 1 kg of lead"? If so, then in some way (domain of applicability) physics needs to address this; the distinction is not pedagogical.

But if no experiment could distinguish between the two - even in principle - then they are equivalent, from the POV of physics theory.

Not only has the equivalence between two (or more) models been discussed, in terms of pedagogy, but also presented has been a very clear means of deciding whether such equivalence is only pedagogical!

In the Land of Physics, Experiment Rules, OK?

WayneFrancis
2009-Jan-21, 05:13 AM
I have no problem with different ideas. What I point out is that it is more then just a coordinate change.

Forget the facts that only certain properties of quantum mechanics seem to change with the coordinate system of a shrinking matter model.

The point is if everything is shrinking then almost all the constants in the universe would have to be changing. Sure this might be happening but if it is happening in the way that is trying to be explained then what have you achieved? Nothing, you say the constants are all tightly bound, which I don't have a problem with, and they are constantly in flux but remain absolutely relative to each other.

Why complicate a model and make all constants are really variable but in a manner that would be undetectable? But in the real world you have to make most but not all constants variable.

One of my friends tries to argue for the "shrinking dot" model to get away from a "beginning" of the universe. I haven't got him to see that even with his "shrinking dot" model that if you reversed time you still come to a point where matter would be HUGE and really close together.

Ken G
2009-Jan-21, 09:12 AM
Might we then say that, in the 'shrinking dot' model, there is just 1 thing changing: the global gravitational potential? There are two things changing in both the shrinking and the expanding pictures. One is measurable, the other is a part of the theory we use to describe the measurable. The first is the "scale parameter" of the universe, which is a ratio of large distances between galaxies to the standard of distance (the latter being a small distance governed by matter), and the second is the gravitational potential. In both pictures, both these things are changing in exactly the same way, and that's why they are indistinguishable as physical theories. As you already see, you can get the scale parameter to change by altering either the numerator or the denominator, or any combination thereof, in that ratio.


Are there any (main stream) scientists wondering if the supermassive black holes in the center of galaxies might be warping space-time in such a way that it causes the apparent accelerating expansion?It doesn't seem like a productive avenue to take-- Einstein's theory of gravity still works fine, and does not predict that kind of effect. But somebody is probably wondering about it-- when the seeds are picked over, most of the birds fly away, but there's always one or two still sifting though, looking for some that were overlooked.

(This reminds me of an article I read somewhere last year on a Dutch astronomy blog, suggesting that time dilation could be a / the cause for the apparent expansion, but I had no time then to trace the origin and solidness of that suggestion. If I remember right, it was suggested that time would be 'running faster' in the voids, as compared to the 'filled' parts of space, explaining the acceleration of the expansion (but not necessarily the expansion itself, I would guess)).Standard time dilation is included in all cosmological models, so no one could be getting the jump on anyone else simply by including it unless they had some different idea of how it would work-- and Einstein's approach works quite well (if you don't mind dark matter and energy).

Ken G
2009-Jan-21, 09:22 AM
But they should. Give me a picture of the origin, the initial state, of a unverse in which matter is destined to shrink and Iīll be happy. That's a lot to ask for. Can you give a picture of the initial state of the universe that is destined to expand? You may be using the "explosion" picture, but if so, you are simply beguiling yourself-- that picture is badly inaccurate and does not work. The truth is, we have no idea why the universe expands, other than that it satisfies the Einstein field equations to do so, but the same could be said about matter shrinking. People, it is not the job of physics to give us pictures of why things are the way they are, that's just what we do for our own recreation, or to help us understand how to apply some theory-- i.e., pedagogy.

Those who disagree with the shrinking view are not alone, since the standard jargon to treat the evolution of the universe is that of an expansion. So because we have a "standard jargon", we should view with suspicion and disapproval all equivalent alternatives? This is how we should teach physics, that it is a form of dogma?



This is a thought expriment that does nothing more than hinder the pedagogy of the whole thing [as if talking about the evolution of the universe as an expansion wasnīt complicated enough for the non-initiated].As I mentioned above, the "non-initiated" invariably ask what the universe is expanding into, and where is the center. Those are both perfectly natural questions if one adopts the expanding picture-- so there is nothing wrong with the questions, the problem is the pedagogy. To put those questions off with answers that basically say "the pedagogy is fine, it is your question that is nonsensical" miss the point-- the questions expose a flaw in the pedagogy. Now, the pedagogy has other good points, so I don't recommend using shrinking matter as the first picture we should describe. But using both pictures is a good way to explain just what a pedagogy is, and why all pedagogies are mixed bags. That's a lesson that could be even more valuable than a dogmatic attachment to describing the history of the universe in some particular coordinates.

Ken G
2009-Jan-21, 09:24 AM
And BTW, what's all this opposition to stuff shrinking anyway? If I accelerate off towards say Andromeda at 0.9999c, everything in the entire universe shrinks in one direction. Yes, exactly. I always marvel at how we are expected to teach students about "length contraction" when we do special relativity, and the next week we come to general relativity and we tell them that "space itself is expanding", without batting an eye. If a student inquires about that seeming inconsistency, we are supposed to, what, smile knowingly and say that if they knew as much as we do they would not ask such foolish questions?

Argos
2009-Jan-21, 01:54 PM
That's a lot to ask for. Can you give a picture of the initial state of the universe that is destined to expand?

The Inflation Hypothesis is an attempt at explaining the very early universe, no?

As a positivist, Iīm feel a certain unease to see pure mathematical models, which are approximations, substituting the empirical reality. We can have a host of entities that are topologically equivalent to a sphere. However, in the real world, a sphere is a sphere, isnīt it?

DrRocket
2009-Jan-21, 04:11 PM
Might we then say that, in the 'shrinking dot' model, there is just 1 thing changing: the global gravitational potential? Or am I now simplifying too much?

I think that in the shrinking or expanding dot analogy a key point has been glossed over a bit.

In the balloon analogy the dots are a pedagogical representation of a point. The analogy is intended to illustrate that if a manifold is expanding (an effect of a time dependency of the metric) then one can have a situation in which all points appear to move radially away from one another, and the rate of recession is proportional to the distance separating them. Points, unlike dots, have no size, and do not expand as the manifold expands.

A solution of the Einstein field equations with no matter, de Sitter space, exhibits this sort of simple expansion. When you throw local concentrations of matter into the mix then the expansion is not so uniform and matter inhibits local expansion through gravity, keeping "dots" of matter from expanding noticeably.

In the contracting case, in the absence of matter, the situation should be just the reverse. In the presence of matter, however the contraction and gravitation should reinforce one another and dots should contract.

As publius noted one must be careful with a choice of coordinates, and the above discussion is relative to a normal earth bound observer for which the cosmic background radiation is isotropic.

Aristarchusinexile
2009-Jan-21, 04:22 PM
Moonhead; Its not un-reasonable to challenge the standard model of the expanding universe ,and the balloon. The problem here is with your perception is not supported by observation. The galaxies are not shrinking. The universe is continuing to accelerate as it expands. Tested and observed by direct observation and mathematics. Done and dusted. Confirmed. So change the question and try to see the facts as others have. How can we / you, better understand what and why it is happening. Ignore the balloon. I see a 3D model expanding ever faster. We are in it. Like a gas cloud released into a vacuum. Were gravity has lost the war. Dark energy is the unknown mystery that is pulling the universe to bits. What is it. Now theres a good question.


Astro .. if the entire universe is expanding, the galaxies must be expanding also. Are there measurements to confirm the expansion of galaxies?

Argos
2009-Jan-21, 04:24 PM
Sheesh... It is getting worse.:rolleyes:

Aristarchusinexile
2009-Jan-21, 04:37 PM
I'm new here and don't know if I'm even posting in the right place. But here it is.

I am offering an alternative, possible explanation of the Red Shift measurements, those measurements currently accepted my many observers as due to Big Bang, that theory which I have never been able to accept. Feel free to bear with me if you like.

Due to voids like the Bootes Void I have read that the universe is supposed to look like swiss cheese or foam rubber .. with vast numbers of voids throughout the known universe.

Let us suppose in a casual way that the voids may be expanding from an energy within .. the voids may then of course either have to expand to eventually include and engulf galaxies close to the voids' borders, or the expansive power might cause an expansion of space, moving the space the galaxies are in as well, the galaxies remaining outside the voids' borders. As the voids seem roughly spherical, with no galaxy intrusions, it seems the possible expansion of the voids may be causing space to expand, as the voids borders seem to define the borders of space containing galaxies, instead of space containing galacies defining the borders of neighbouring space.

What do the voids contain?
Theorized Dark Matter and Dark Energy seem to be actually dense compared to a vacuum. Let us suppose on vast scales the theorized Dark Matter and Dark Energy form a kind of rubbery material, like sponge rubber, a media known as space .. with the galaxies floating within what is commonly thought of as DM/(DE?) halos.
Let us suppose the expansion of the voids moves space .. causing movement of galaxies, groups and supergroups.
Let us imagine two voids are in our direct line of sight.
Let us examine the space between the voids.

The voids' expansion, which squeezes space containing the galaxies, would cause the galaxies on the void's border closest us to be squeezed slightly 'towards' us compared to the squeezing of the space on the far side of the border of the void closest us, those galaxies being moved further away from us approximately at the rate the void is expanding. These small fluctuations in the overall redshift of galaxies may be measurable .. with the accumulation of countless voids' expansion creating the increasing redshift of galaxies as their distance from us increase.

Galaxies being squeezed together could account for grouping, and groups being squeezed toether could account for supergrouping.

What might start all of this in the beginning? Vast numbers of quantum fluctuations over vast space creating vast numbers of stars (according to Pascual Jordan this is entirely possible) .. instead of an explosion, the beginning being a vast, slow twinkling. I think entirely possible the same quantum fluctuations could create the voids themselves .. since every particle is said to have an anti-particle, perhaps quantum fluctuations can have anti-fluctuations, which instead of creating matter and energy including DM and DE, create anti-DM anti-DE which inflate the voids .. anti DM?DE not mixing with DM/DE in the same way oil and water do not mix.

Swift
2009-Jan-21, 04:44 PM
Aristarchusinexile,
I posted this in the Introduction thread when you commented about your alternative ideas, but I guess you have not seen it yet. I suggest you post your alternative ideas in the ATM section of the forum, where they can be debated. This section is for the more straight forward, mainstream answers to astronomy questions.

Aristarchusinexile
2009-Jan-21, 04:54 PM
You and others have made several statements like this, as if even talking about it is harmful. That surprises me... Especially when Publius made it clear it's all just a matter of coordinates and Ken G. mentioned at least one pedagogical advantage of the 'shrinking model' .

The concept of an expanding universe is not under siege. :) But by claiming that another way of looking at it, is harmful or even ATM, you act like an orthodox religious person who is shocked when someone asks "if God created everything, where did God himself come from?" and might be achieving the opposite of what you want... I assume your intentions are good: you want to keep the teaching of science / this forum free of noise and of unfounded speculation, right? But if a certain common pedagogical model is presented as the only proper way to describe reality, and alternatives are declared to be 'hindering', than it makes me scratch my head...

Besides, how is a visitor to this forum supposed to know to what degree his question would be 'hindering pedagogy for the non-initiated'? :confused:


I'm surprised to find free speech in question here, as I was referred here by a concensus moderator (APOD) because some of my views are non-consensus. However, perhaps I should not be surprised, because in reading histories of science I find that almost every major new discovery-discoverer or even suggestion of newness was quickly dumped in the trash heap by the concensus, by the establishment, by those who could not understand the new discovery. Many paths were taken to discredit the 'new', but the reason remains the same .. to keep the topmost person on 'the glorious pyramid of attainment' topmost. Pyramids are difficult to shake. What is clear is that those who resist change the most are forgotten by history except for their inability to accept change, while the 'new' are elevated to the top of the pyramid (where, unfortunately, sometimes even they resist change). This is truly sad, and counterproductive, hindering science in a truly tragic way.

Argos
2009-Jan-21, 05:20 PM
I'm surprised to find free speech in question here, as I was referred here by a concensus moderator (APOD) because some of my views are non-consensus.

Dear Aristarchus. IMO, this whole shrinking matter talk should be in the ATM section. The various adherents to the standard expanding space discourse have raised many objections to this view that havenīt been adreesed by the "absolute relativists". Maybe we could have a chance there.

Ken G
2009-Jan-21, 06:21 PM
The Inflation Hypothesis is an attempt at explaining the very early universe, no?Certainly, but you need expansion (or shrinking) before you can get inflation (that's what triggers the inflation). It is not an explanation of the expansion, it is a consequence of it, and ends up altering its properties (but would also for the shrinking picture).


As a positivist, Iīm feel a certain unease to see pure mathematical models, which are approximations, substituting the empirical reality. We can have a host of entities that are topologically equivalent to a sphere. However, in the real world, a sphere is a sphere, isnīt it?That is a pretty deep question, that I'm not sure I can answer. I would tend to say that whether or not something is equivalent to a sphere depends on the context. You are imagining contexts where there is a real difference between a sphere and something else, whereas in a purely topological context, there may not be any difference at all. The mathematical notions are our servants for understanding reality-- but when no observations can distinguish two pictures, then even an empiricist (especially an empiricist) must admit that no difference can be established.

Ken G
2009-Jan-21, 06:32 PM
IMO, this whole shrinking matter talk should be in the ATM section.Actually, that is a demonstrably false suggestion-- shrinking matter is simply not ATM. Let me give you an example of why. Let's imagine a universe of just our solar system, and one light in the sky that looks like a stellar spectrum, but it is redshifted. We can see nothing else in the universe, let's say. Now let's say that the mainstream astronomers formed the view that the star's light was redshifted because that star was moving away from us. Now, someone else comes along and says "actually, we can just as well imagine that star is stationary are we are moving away from it, the two pictures make all the same predictions so there's no physical difference there". What should be done with that suggestion? Should it be considered to be ATM, and harmful to the dogma of the receding star picture that all young astronomers are taught? The principle of relativity tells us quite clearly what should be done with that suggestion-- it should be elevated to the level of a crucial observation about the nature of reality, that there is no difference between a receding star and a star that we are moving away from. The combination of the two pedagogies is where the truth lies, not in one or the other. To label it ATM completely misses that important point.


The various adherents to the standard expanding space discourse have raised many objections to this view that havenīt been adreesed by the "absolute relativists".On the contrary, no objections have been raised that are not purely a matter of personal taste-- the two models are identical in every demonstrable way that could in principle be distinguished. The ATM idea is thus that there is a difference between them, and it would be easy to shoot down that ATM idea, at least in regard to current observations.

DrRocket
2009-Jan-21, 07:53 PM
Astro .. if the entire universe is expanding, the galaxies must be expanding also. Are there measurements to confirm the expansion of galaxies?

It is not true that expansion of the universe implies expansion of galaxies. The forces that cause large-scale expansion of the universe (the space-time manifold) can and appear to in fact be in equilibrium with the gravitational forces that hold galaxies together, at least in the present universe. Similarly you are a tiny (very tiny) bit taller than you would be without the expansive forces, but the expansive stress is counterbalanced by the gravitational and electromagnetic forces that hold you together.

Argos
2009-Jan-21, 08:40 PM
Actually, that is a demonstrably false suggestion-- shrinking matter is simply not ATM. Let me give you an example of why. Let's imagine a universe of just our solar system, and one light in the sky that looks like a stellar spectrum, but it is redshifted. We can see nothing else in the universe, let's say. Now let's say that the mainstream astronomers formed the view that the star's light was redshifted because that star was moving away from us. Now, someone else comes along and says "actually, we can just as well imagine that star is stationary are we are moving away from it, the two pictures make all the same predictions so there's no physical difference there". What should be done with that suggestion? Should it be considered to be ATM, and harmful to the dogma of the receding star picture that all young astronomers are taught? The principle of relativity tells us quite clearly what should be done with that suggestion-- it should be elevated to the level of a crucial observation about the nature of reality, that there is no difference between a receding star and a star that we are moving away from. The combination of the two pedagogies is where the truth lies, not in one or the other. To label it ATM completely misses that important point.

Good defense, Ken. I appreciate that. Iīm gathering myself up and collecting arguments for another round of attack [if I can].

publius
2009-Jan-21, 09:29 PM
Matter and energy are equivalent. Should they be treated equally then? Dealing with 1kg of lead is different than dealing with the energy contained in 1 kg of lead.



Let's look at the statement a little closer. What do you mean by "the energy contained in 1kg of lead"? What you imagine is the 1kg of mass-energy has *changed form*. It is no longer sitting there contained in atoms of lead in whatever lattice structure they like to arrange themselves in that gives us the macroscopic notion of a chunk of lead. Those lead atoms have become photons, or whatever your notion of "pure energy" is. :)

In either case, the chunk of lead or its equivalent in photons are exactly
1kg of mass-energy, the same sense as 1kg of water is the same as 1kg of that same lead. Mass-energy is one property. What distinguishes lead from water and both from the photons we can imagine converting them to is something apart from the mass-energy.

If I drop a pound of feathers on you, the results will probably be different than if I dropped a pound of lead.

-Richard

publius
2009-Jan-21, 09:39 PM
As a positivist, Iīm feel a certain unease to see pure mathematical models, which are approximations, substituting the empirical reality. We can have a host of entities that are topologically equivalent to a sphere. However, in the real world, a sphere is a sphere, isnīt it?


What do you mean by "empirical reality"? Do you mean what can be measured? Or do you really mean some pedagogy about those measurements?

There is much less to "empirical reality" that we all like to think, and that's the point here.

If you live in a world where the tools available to you cannot distinguish between a sphere and whatever "homeomorphisms" of it that might exist, then they are all equivalent.

We can take a flat sheet of paper and roll into a cylinder without any distortion. That piece of plane and the cylinder and thus homeomorphic (I apologize if I'm screwing up the terminology). If all we can do it measure the areas of things vs the lengths of the sides, we will find no difference. That is, if our measurments are confined to the information contained in Ricci curvature, then both are equivalent.

However, if our measurement ability can access the notion of "straight" relative to the tangent space, we can detect the full Riemann curvature and know the flat sheet has been rolled around.


-Richard

Moonhead
2009-Jan-21, 10:50 PM
There are two things changing in both the shrinking and the expanding pictures. One is measurable, the other is a part of the theory we use to describe the measurable. The first is the "scale parameter" of the universe, which is a ratio of large distances between galaxies to the standard of distance (the latter being a small distance governed by matter), and the second is the gravitational potential. In both pictures, both these things are changing in exactly the same way, and that's why they are indistinguishable as physical theories. As you already see, you can get the scale parameter to change by altering either the numerator or the denominator, or any combination thereof, in that ratio.

Thanks for clarifying that, and also for the other parts of your reply.

Thinking about the evolution, another matter bothers me (not directly connected to the shrinking/expanding issue, but on-topic, considering the thread title). The observable universe can be regarded as a sphere around us; the farther you look, the more you look back in time. So, if we look at objects at, say, 11 billion ly away (this number might not be the most suitable for my question; please substitute if more appropriate), do they appear larger than they actually are / were? My reasoning: as space is expanding, there was less empty space 11 billion years ago than there is now, so the non-empty parts take up a larger portion of the panorama than they would if we would see them how they are now... Or am I now doing things double? Maybe it's just bad reasoning trying to separate observed objects from their distance in space and time...

speedfreek
2009-Jan-22, 12:10 AM
So, if we look at objects at, say, 11 billion ly away (this number might not be the most suitable for my question; please substitute if more appropriate), do they appear larger than they actually are / were? My reasoning: as space is expanding, there was less empty space 11 billion years ago than there is now, so the non-empty parts take up a larger portion of the panorama than they would if we would see them how they are now... Or am I now doing things double? Maybe it's just bad reasoning trying to separate observed objects from their distance in space and time...

You are entirely correct in your thinking, have a look at the link below:

The Distance Scale of the Universe (http://www.atlasoftheuniverse.com/redshift.html)

You are referring to the angular-diameter distance, how far away the galaxy was when it emitted the light we are now seeing. Due to the very fast rate of expansion of the universe early on, we are seeing galaxies whose light has been travelling for 12.9 billion years but those galaxies were only 3.5 billion light-years away when they emitted that light.

The relationship between light-travel time and angular-diameter distance is unusual. For close galaxies whose light hasn't been travelling too long we see the expected picture - the higher the redshift, the larger the angular-diameter distance (galaxies look further away). But over a certain redshift, which represents the distance where a galaxy was apparently receding at c when it emitted that light, the angular-diameter distance decreases (they look closer).

Things look smaller and smaller the more distant they are (in light-travel time), but over a certain distance they get larger and larger again!

Moonhead
2009-Jan-22, 08:54 AM
Thanks for your reply, Speedfreek! Haven't had the time yet to take more than a superficial look at The Distance Scale of the Universe but I will read it later.


Things look smaller and smaller the more distant they are (in light-travel time), but over a certain distance they get larger and larger again!

Yes that's what I wondered... So there must be a certain distance at which these two phenomenons cancel each other out. Is there anything special to this distance? Does it have a name?

EDIT: I did read the article, and it's very informative! Something to bookmark (done), and regularly look at to get it into my head.

The 'special distance' I asked for, seems to be at 5.8 Gly. At that point the Angular Diameter Distance curve goes down again. I still have to 'conceptualize' the whole picture into my head though.

Argos
2009-Jan-22, 12:59 PM
What do you mean by "empirical reality"?

The pain I feel when I stumble on a stone.

All I can say is that this feels like a Pythagorean, idealistic, discussion. There is a reality that the [various] principles of relativity are supposed to address. But they donīt create reality. They are subjected to it.

I try to find references to the shrinking matter view to substantiate my arguments, but it is a desert out there [I do find a thread on the issue (see link somewhere above) on the Physics Forum - closed for being deemed a speculative question]. I looks like itīs only a BAUT meme.

Other members have raised objections too. As Wayne says, the Standard Model seems to behave well in an expanding space universe, but have problems the other way round. The Holographic Principle also seems to require a growing universal horizon.

Ken G
2009-Jan-22, 04:36 PM
You are entirely correct in your thinking, have a look at the link below:

The Distance Scale of the Universe (http://www.atlasoftheuniverse.com/redshift.html)That's a very nice link.

Ken G
2009-Jan-22, 04:51 PM
There is a reality that the [various] principles of relativity are supposed to address. But they donīt create reality. They are subjected to it.That is a point that I think we can all agree on-- basic scientific realism is in fact the core of the argument that publius and I are putting forward. It still hurts just as much when you stub your toe in a universe where matter is shrinking as in a universe where space is expanding. The pedagogy never alters the experience, that's what we mean by two very different sounding pedagogies corresponding to the same "empirical reality".


I try to find references to the shrinking matter view to substantiate my arguments, but it is a desert out there [I do find a thread on the issue (see link somewhere above) on the Physics Forum - closed for being deemed a speculative question]. I looks like itīs only a BAUT meme.Yes, I brought it up when I first came onto BAUT, and I think there were a few past threads on it as well, but it's not widely discussed. I think the reason for that is that some people view it as too obvious to be worth discussing (the equivalence seems tautological to them), while others are erroneously using a faulty version of the picture (a version that would actually make different predictions, like having the fundamental constants changing with time, or some such error). Personally, I find it very illuminating to recognize that our minds tend to imagine that "scale" is an absolute concept dealing with actual quantities, but in fact it is only a relative notion dealing with ratios of quantities that are themselves perfectly arbitrary. What's real is the ratio, that's what "hurts when you stub your toe."


Other members have raised objections too. As Wayne says, the Standard Model seems to behave well in an expanding space universe, but have problems the other way round.I don't recall that objection, but it is erroneous, the two pedagogies make no different predictions that could lead to any "problems" unique to either. One way to see the equivalence is to imagine a chess board made of rubber that is expanding. Two players are playing out a game on this board. Now I will create an equivalent description of that very same game by simply watching the game from a larger and larger distance, such that the board takes up the same angular size in my perception. In my version of that game, the pieces are shrinking and the board is staying the same size. Regardless of other things going on in the room that could distinguish these pictures, there is nothing happening on or to the board itself that could distinguish them-- it's the exact same chess game either way. Only in the case of the universe, there is nothing outside the board, it's all just the chess game.

The Holographic Principle also seems to require a growing universal horizon.Thank you for referring to the Holographic Principle, because I had not heard of this interesting idea. But it doesn't have anything to do with the equivalence of shrinking matter and expanding space, both of those pedagogies admit the identically same holographic principle.

DrRocket
2009-Jan-22, 10:13 PM
What do you mean by "empirical reality"? Do you mean what can be measured? Or do you really mean some pedagogy about those measurements?

There is much less to "empirical reality" that we all like to think, and that's the point here.

If you live in a world where the tools available to you cannot distinguish between a sphere and whatever "homeomorphisms" of it that might exist, then they are all equivalent.

We can take a flat sheet of paper and roll into a cylinder without any distortion. That piece of plane and the cylinder and thus homeomorphic (I apologize if I'm screwing up the terminology). If all we can do it measure the areas of things vs the lengths of the sides, we will find no difference. That is, if our measurments are confined to the information contained in Ricci curvature, then both are equivalent.

However, if our measurement ability can access the notion of "straight" relative to the tangent space, we can detect the full Riemann curvature and know the flat sheet has been rolled around.


-Richard

A nit. The cylinder and the plane segment are not homeomorphic. In fact they have different homotopy type. The fundamental group of the cylinder is the integers and the fundamental group of the plane segment is trivial (i.e. {1}).

publius
2009-Jan-22, 11:12 PM
A nit. The cylinder and the plane segment are not homeomorphic. In fact they have different homotopy type. The fundamental group of the cylinder is the integers and the fundamental group of the plane segment is trivial (i.e. {1}).

I was afraid I was getting that screwed up. So learn me some stuff, here. What do we call the relation between a plane segment and a cylinder? We can roll that plane into a cylinder without distorting areas on it, and, again, if I've got it right, the cylinder has zero Ricci curvature (but has full Riemann curvature). So what do we call this where two entities have the same Ricci curvature?


-Richard

DrRocket
2009-Jan-23, 12:25 AM
I was afraid I was getting that screwed up. So learn me some stuff, here. What do we call the relation between a plane segment and a cylinder? We can roll that plane into a cylinder without distorting areas on it, and, again, if I've got it right, the cylinder has zero Ricci curvature (but has full Riemann curvature). So what do we call this where two entities have the same Ricci curvature?


-Richard

I don't know the answer to the question in the generality that you have sated it. Also a general disclaimer, I am not an expert in Riemannian geometry. But I think I can provide some insight into your question.

There is a theorem that states that manifold is locally isometric (or locally conformally equivalent) to flat Euclidean space if and only if it is Ricci flat (has Ricci curvature zero). I am glad that you asked. It forced me to do research and learn some things.

You can see that with the cylinder and plane. Locally the cylinder is isometric to the plane. If you imagine a grid on the cylinder being wet ink lines and then rolling it across the plane you get a grid on the plane with no distortion preserving distances (hence angles) for nearby points. But it does not preserve distances globally -- here think of wrapping the plane segment around the cylinder and note that points that are near the edges and far away become close together at the "seam".

So, I would call spaces like the cylinder and the plane that are both Ricci flat, locally isometric. But they are not isometric.

In topology spaces are equivalent (isomorphic) if they are homeomorphic.
In differential topology equivalence is up to diffeomorphism. In Riemanian geometry (or semi-Riemanian geometry) equivalence is up to isometry. These are increasingly fine distinctions. Diffeomorphism implies homeomorphism and isometry implies diffeomorphism but the converses do not hold in general.

The subject of when lesser levels of isomorphism imply higher levels is complex. Only recently has it been established that the Poincare conjecture is true and objects with the homotopy type of a sphere are homeomorphic to a sphere. They are also (I think) diffeomorphic in dimensions 1,2,3 but not necessarily in dimensions 4 or higher.

A very good reference for geometric questions related to what you might run into in relativity is Barret O'Neill's Semi-Riemannian Geometry with Applications to Relativity. I do not claim to have read and understood everthing or even most things in the book. But I can recommend it.

publius
2009-Jan-23, 01:27 AM
DrRocket,

Thanks so much. The details of these "morphisms" vs isometries and all that good stuff are beyond me and get me all discombobulated. And that's a good point about the seam of cylinder -- I see there will be all sorts of complications about that.

Really, with a cylinder, where is the seam anyway? It is closed in one direction and we could define the seam to be anywhere. So what if we define the plane segment so that it just wraps around, that is, when we get to the edge, we just jump back around to the other side? Then global distances would be the same for both.

But I guess if we do that, we don't technically have a plane segment anymore, do me? :lol: We've got something that wraps around via some crazy jump discontinuity at the edges.

Yes, that's a good point about the seam. Local vs global considerations, indeed.

-Richard

Ken G
2009-Jan-23, 03:56 AM
So what if we define the plane segment so that it just wraps around, that is, when we get to the edge, we just jump back around to the other side? I think you have a cylinder if you do that! At least, if you are not allowed to leave the plane for any reason. And if you play the same game with the other two edges, you get a doughnut. Yum.

DrRocket
2009-Jan-23, 04:42 AM
I think you have a cylinder if you do that! At least, if you are not allowed to leave the plane for any reason. And if you play the same game with the other two edges, you get a doughnut. Yum.

That is exactly correct. What you are describing is the formation of a manifold by use of what is called the quotient topology.

If you take a rectangle and identify opposite sides, straight across then you get a cylinder.

If, as you suggest you also identify the ends, straight across then you get a torus (a doughnut).

If you identify the ends, but do it so that opposite corners are identified you get the Klein bottle, a non-orientable surface that cannot be embedded in three-space.

And if you take the cylinder and identity opposite sides so that opposite corners are identified you get a Mobius band, a non-orientable surface.

To be careful here the rectangle is closed on the sides that are being identified and open on the sides that are left alone.

Q: What is a topologist ? A: Someone who can't tell the difference between a doughnut and a coffee cup.

grav
2009-Jan-23, 05:06 AM
I think you have a cylinder if you do that! At least, if you are not allowed to leave the plane for any reason. And if you play the same game with the other two edges, you get a doughnut. Yum.If you guys are talking about walking the same distance around to the other edge as across the sheet of paper, a doughnut shape would require a lesser distance to walk around the center of the doughnut than around the outer edge, so a different distance along the length of the paper across its width producing oval shaped ends. Although still not the same as the distance across a sheet of paper unless it is circular, I'm thinking a sphere might be the closest thing to walking the same distance in any direction. In other words, a doughnut hole. :)

publius
2009-Jan-23, 05:26 AM
I was thinking about doing it just by defintion. We leave the plane truly flat and just define it so you if walk off the edge you magically appear on the other side. But I reckon such "magic" is no longer Riemannian geometry! That is, that is "impossible" by the rules of "nice geometry".

And thanks for mentioning the Klein Bottle. As you note, that's a 2D surface that cannot be embedded in 3-space, but requires 4D. We need 2 higher dimensions in order to close that sucker back in on itself in the required manner without intersecting. That's an example I'll try to remember to use of a 2D surface that requires more than one higher dimension to embed.

If you allow it to intersect itself, you can made a 3D version. Wiki has an article with pictures:

http://en.wikipedia.org/wiki/Klein_bottle

Note the non-orientable ("Mobius strip" like properties). If you walk around on the "outside" around the loop, you are then on the "inside" of the bottle. Keep going another circuit and you are back "outside". Thus there is only one side so to speak. And your normal will point in the opposite direction if you go around one, then return if you go around twice.

Just as you can imagine preventing a curve in the plane from intersecting by lifting one piece over the other via a 3rd dimension, so you can lift the one of the pieces of the Klein bottle "over" the other end via the 4th dimension and close it in the required manner.

-Richard

DrRocket
2009-Jan-23, 05:56 AM
And thanks for mentioning the Klein Bottle. As you note, that's a 2D surface that cannot be embedded in 3-space, but requires 4D. We need 2 higher dimensions in order to close that sucker back in on itself in the required manner without intersecting. That's an example I'll try to remember to use of a 2D surface that requires more than one higher dimension to embed.

If you allow it to intersect itself, you can made a 3D version. Wiki has an article with pictures:

http://en.wikipedia.org/wiki/Klein_bottle

-Richard

There is a general theorem due to Whitney that an n-manifold can be embedded in a space of dimension 2n or less. In the case of the Klein bottle, a 2-manifold, you need to go all the way to dimension 4.
http://en.wikipedia.org/wiki/Whitney_embedding_theorem

So any manifold can be realized as an embedded manifold. But one does not need an embedding to develop Riemannian geometry, and this is an important perspective for general relativity. The universe need not be imbedded in anything, which seems to be a difficult concept for some.

Ken G
2009-Jan-23, 06:02 AM
Q: What is a topologist ? A: Someone who can't tell the difference between a doughnut and a coffee cup.Or may I suggest this variant, if the mods allow. Topologist: someone who can't tell their arse from a hole in the wall.

publius
2009-Jan-23, 06:18 AM
There is a general theorem due to Whitney that an n-manifold can be embedded in a space of dimension 2n or less. In the case of the Klein bottle, a 2-manifold, you need to go all the way to dimension 4.
http://en.wikipedia.org/wiki/Whitney_embedding_theorem




OK, then answer me this. Consider a helix, a coil of wire. That is a 1D curve that seems to me to require 3D Euclidean space. And I can imagine doing something similiar with a curve in 4D that seems to require all 4. So what's going on there?


-Richard

publius
2009-Jan-23, 06:19 AM
Or may I suggest this variant, if the mods allow. Topologist: someone who can't tell their arse from a hole in the wall.

:lol: :lol:

-Richard

Ken G
2009-Jan-23, 06:20 AM
I was thinking about doing it just by defintion. We leave the plane truly flat and just define it so you if walk off the edge you magically appear on the other side. Right, but if you are constrained to move only on the plane, that magical definition really is the same as the cylinder. In other words, to ant mathematicians, they might think a cylinder is just your magical flat plane! Then some smart-alecky ant will come along and say that an alternate pedagogy is that there is really a third dimension, and the reason the plane edges connect is that they wrap around through that dimension, but that would still seem indistinguishable from magic to ants. Then again, I guess pretty much everything is indistinguishable from magic to ants.


But I reckon such "magic" is no longer Riemannian geometry! That is, that is "impossible" by the rules of "nice geometry". True for 3D, as you and DrRocket have pointed out. But we must beware of backward logic-- we use 3D geometry because it works, not because the world is "really 3D". If a 4D geometry works somewhere, then that becomes the "nice" geometry, like if we find some theory that says particles are oscillations on Klein bottles, who knows.

DrRocket
2009-Jan-23, 07:27 AM
OK, then answer me this. Consider a helix, a coil of wire. That is a 1D curve that seems to me to require 3D Euclidean space. And I can imagine doing something similiar with a curve in 4D that seems to require all 4. So what's going on there?


-Richard

The helix is no different from a topological or manifold perspective than a straight line. A straight line is easily embedded in 2-space. Since isometry only requires preserving arc lengths you can make this an isometry as well.

The case for manifolds of dimension >1 is more difficult. The Whitney theorem is for smooth manifolds, and diffeomorphisms, not Riemannian manifolds. For Riemannian manifolds and isometric embeddings the situation is a bit more difficult. They are still embeddable in a Euclidean space, but the dimension required can be higher. There you need the Nash embedding theorem.

http://en.wikipedia.org/wiki/Nash_embedding_theorem

DrRocket
2009-Jan-23, 07:34 AM
Or may I suggest this variant, if the mods allow. Topologist: someone who can't tell their arse from a hole in the wall.

I'd be careful there. I know some awfully smart topologists. Remember Ed Witten has no Nobel Prize, but he does have a fields medal for work in the classification of smooth 4-manifolds, a topic in differential topology.

And guys like Pierre Deligne have taken some interest in quantum field theory and strings. If there is anybody on the planet who is clearly smarter than Deligne I can't think who it might be (Grothendieck basically left mathematics after serving as Deligne's thesis advisor because he thought Deligne was too good to compete with, and Grothendieck was a giant).

Argos
2009-Jan-23, 01:58 PM
I hope you guys have enjoyed my "litany against shrinking matter'. :)

Of course when faced with solid arguments I must abandon preconceived notions and rethink my stance.

This thread have been very informative and has received many intelligent interventions from all the participants.

The Principle of Equivalence is not subject to questioning, but since it allows me, I will, in honor of Edwin Hubble and the memories of my teenager amazement at discovering the most fundamental things about the universe [and the sheer size of that abyss out there], stick to the expansion discourse.

speedfreek
2009-Jan-23, 03:20 PM
So there must be a certain distance at which these two phenomenons cancel each other out. Is there anything special to this distance? Does it have a name?

EDIT: I did read the article, and it's very informative! Something to bookmark (done), and regularly look at to get it into my head.

The 'special distance' I asked for, seems to be at 5.8 Gly. At that point the Angular Diameter Distance curve goes down again. I still have to 'conceptualize' the whole picture into my head though.

That "special distance" is the Hubble distance, the distance to the edge of our Hubble sphere. It is the distance where the expansion of the universe causes objects to apparently recede at c. Light is currently arriving here that was emitted at the edge of (or passed into) our Hubble sphere 9.1 billion years ago, when it was 5.8 billion lightyears away.

All the light we detect that was emitted less than 9 billion years ago came from regions of space inside our Hubble sphere (as it was at that time) and that light was travelling through regions that were receding from here at less than the speed of light when it was emitted.

All the light we detect that was emitted more than 9.1 billion years ago came from regions of space beyond our Hubble sphere, where the recession speed of the objects emitting that light was faster than c. The expansion of the universe was still decelerating back then, which eventually allowed that light to pass into our Hubble sphere and make its way towards us.

So, in effect, all the light we see today that was emitted in the first 4.6 billion years of the history of the universe was itself receding from us due to the fast expansion and it was only when that light passed the objects on the edge of our Hubble sphere that it could actually make progress towards us alongside the light from objects at that "edge". This is why objects over that distance look larger, their light was emitted when they were closer than that, but the expansion "dragged" their light away until the rate of expansion had slowed enough for all the light we see to be moving through space that was receding sub-luminally.

Ken G
2009-Jan-23, 07:07 PM
I'd be careful there. I know some awfully smart topologists. The joke is entirely for sport, I'd say it is well recognized that advanced mathematics is one of the very most intellectually challenging human pursuits there is.

Ken G
2009-Jan-23, 07:14 PM
I hope you guys have enjoyed my "litany against shrinking matter'. Indeed, it stimulated an interesting discussion, and thank you for your graceful abandonment of its more dogmatic elements!

The Principle of Equivalence is not subject to questioning, but since it allows me, I will, in honor of Edwin Hubble and the memories of my teenager amazement at discovering the most fundamental things about the universe [and the sheer size of that abyss out there], stick to the expansion discourse.The beauty of successful pedagogies is that one is free to indulge one's own preferences.

heldervelez
2009-Jan-25, 05:38 PM
Mr. MoonHead : congratulations on your OP. It is rather refreshing.

In another forum I've posted something equivalent to your reasoning, and I quote myself from there:
"Just because we are measuring an increase on the ratio space/matter, we can not say 'ad hoc' that it is an expansion. Other scenarios are possible."

It seems that you can think on an alternative scenario.
I've post also there two conceptual experiments that can shed some light on this way (and they kept undiscussed there).
"world ‘o’ and world ‘O’" (http://www.physicsforums.com/showthread.php?t=279200)
and another one "particle creation and annihilation and the remaining fields problem" (http://www.physicsforums.com/showthread.php?t=271606)
may be after you consult those experiments we can advance with some 'why' and go deeper in the conclusions.

heldervelez
2009-Jan-25, 07:26 PM
Lets explore this situation to make clear what this
"world ‘o’ and world ‘O’" (http://www.physicsforums.com/showthread.php?t=279200) could signify.
I will remember here a book of our childhood :
Gulliver and the Liliputians (it happened that Gulliver went to the world of Liliput where liliputians are much smaller than Gulliver)
Lets assume that Gulliver has the same number of atoms, molecules and living cells as the liliputians.
And what the story forget to tell us is that Gulliver had in his pocket a white lamp.
When he left the world of liliputians he offered that lamp to the king of the liliputs and after that it remained in the royal museum with this label "Red lamp kindly offered by the legendary Gulliver".
The liliputians went on with an evolved technical civilization, and many years later one of museum curators analysed the lamp with a spectrometer and he found an amazing fact: The Red Lamp has the same spectrum as his White lamp, but redshifted.
How is it possible ? Simple explanation : on the magic world of our childhood anything is possible. But it makes me think that there must be some kind of enlightment on this story.

heldervelez
2009-Jan-25, 09:32 PM
...

Considering it, I was actually wondering whether it would be less unnatural than expansion.

... As long as there are no objective references of scale, it would be more proper to say that the universe, the wholeness of it all, the totality remains the same size, while we, including our measures and perception of measurement, shrink. As far as my limited understanding and imagination reaches, the planck limit, the speed of light and the relation between the fundamental forces might be such objective references of scale. So a 'shrinking dot' model, as far as I can imagine, would require to have those constants to shrink proportionally (or maybe otherwise explain them within the model, like they're changing so slowly that we having noticed. Which would not be too hard to stomach, provided we haven't been around that long).
...

I'm curious whether such a 'shrinkage' model would require a proportional shrinking of all sorts of established constants (like the speed of light, the fundamental forces), or how it would otherwise deal with the fact that we perceive an expanding universe.

...
It is so unnatural to expect a space expantion (I call it a free lunch) as natural to think that matter has to give something in order to set fields in space at c speed, and this is not a free lunch.
...
As you say "As long as there are no objective references of scale"
...
If we try to change the fundamental constants all along it will be unphysicall. Why ? because c, G and others are properties of the space itself. It is the way that space keeps telling us that it exists and phenomena had to obey his laws. Phenomena propagate in space at the pace it permits. Constants are like 'impedance' or 'resistance' to change.

But the quantities Mass, Length, Time are intrinsecally bounded to matter and if we mess with one quantity we will mess with the others. We pick an atom from our local world and make a measuring rod, a physical one, and define those quantities as standard and make measures by comparison with that selected atom.
Yes, also Time is bounded to matter size, because space 'c' constant says so to the electrons on the atomic cloud. If atoms were bigger in past then our local atoms (now) will have a speeder clocks compared to past.
Velocities are invariants ( L/T vary in accordance).

A complete physical and math model of this scenario can be found here (http://arxiv.org/PS_cache/astro-ph/pdf/0208/0208365v1.pdf).

Both scenarios of 'expanding universe' or this one of 'shrinking matter' appear to be equivalent. I know that they are not equal in the consequences, and it is on those consequences that we can make a clear distinction on what is the better approach.

Ken G
2009-Jan-26, 08:50 PM
Both scenarios of 'expanding universe' or this one of 'shrinking matter' appear to be equivalent. I know that they are not equal in the consequences, and it is on those consequences that we can make a clear distinction on what is the better approach.I don't see anything in what you are saying that establishes any difference in consequences, it sounds like just the same indistinguishable pedagogical choice this thread has been about.

heldervelez
2009-Jan-26, 09:04 PM
I don't see anything in what you are saying that establishes any difference in consequences, it sounds like just the same indistinguishable pedagogical choice this thread has been about.

First one, and I can mention a handful:

Get rid of Dark Energy.

It appears to be inquestionable.

Moonhead
2009-Jan-26, 09:15 PM
@ Heldervelez: I've read your posts and the ones you linked to with interest, but I must admit it's a bit over my limited understanding!

I was about to suggest you cut your ideas into separate questions, and ask them one by one in this forum (and I for one would sure have read those threads), but I noticed you're already engaged in a discussion with someone who has a little more bagage than I do.

speedfreek
2009-Jan-26, 10:12 PM
First one, and I can mention a handful:

Get rid of Dark Energy.

It appears to be inquestionable.

Surely something analogous to dark energy would also be required for the "matter is shrinking" model, in order to explain the acceleration of the shrink rate.

heldervelez
2009-Jan-26, 10:47 PM
@ Heldervelez: I've read your posts and the ones you linked to with interest, but I must admit it's a bit over my limited understanding!

I was about to suggest you cut your ideas into separate questions, and ask them one by one in this forum (and I for one would sure have read those threads), but I noticed you're already engaged in a discussion with someone who has a little more bagage than I do.

I will try to cope with you Mr. Moonhead.
Again my congratulations for your opening post. I dont know why you figure out those ideas of looking in the 'reverse way'. You have more imagination that most of us (including me, because I did not get it by myself, I have been told of that perspective). I hope you will understand what I will describe.

heldervelez
2009-Jan-26, 11:35 PM
Surely something analogous to dark energy would also be required for the "matter is shrinking" model, in order to explain the acceleration of the shrink rate.


In the link "particle creation and annihilation and the remaining fields problem" (http://www.physicsforums.com/showthread.php?t=271606)
I tried to equate a problem that actual theory does not address.

The compound Matter+Field (think of atom+gravitational field) has to be in balance.
Why ? because it is not possible to have a spreading field (ever and ever, forever spreading in space (at 'c' speed) since the moment of creation, without beeing responsible, and accountable for that phenomenon of - lets say in this way - affect more and more space.
If something changes outside the particle (the quantity of field in space, or space itself) then ssomething has to change in the 'inside' of the particle.

The particle spread itself in space loosing slowly its mass/energy in favour of space.

If it not in this way I call it a 'free lunch'.

We can continue the discussion of the 'shrinking model' (Evanescent Theory as the author named it) even if we do not know if it is, or it is not, this proposed phenomenon the responsable for the happening.

As we can devise, and discuss, a probable cause for the 'shrinking' we are ahead of the 'standard model', hands down.

We are not obliged to offer a mechanism the same way as 'standard model' do known what 'Dark Energy' is.

Lets discuss later, your obvious statement that it is an accelerated shrinking.
First we must understand if it is possible, or not, that a 'shrinking' model address available data as observed.

Another interesting question that the Evanescent Theory (I do preffer this way) brings is that we have no need to figure out why on Earth space is 'fueling itself' in order to expand or multiplicate. Again I call it a 'free lunch'.

As we can figure out that space can be 'stable' (not expanding neither shrinking) we get rid in this moment of this two ideas:
Space Expantion and Dark Energy.

We will get rid of much more 'artifacts' as we will see.

We will get rid of the actual "Dark Era of Cosmology" ( I think I coined this expression, eheh, google that).

Ken G
2009-Jan-27, 05:25 AM
Surely something analogous to dark energy would also be required for the "matter is shrinking" model, in order to explain the acceleration of the shrink rate.Right. It would be interesting to see how the different pedagogy might alter our picture for what dark energy is. The usual picture is that it induces antigravity via having a negative pressure, and the reason it has a negative pressure is that you get more (dark) energy when the volume increases, rather than less energy the way adiabatic expansion works when the pressure is positive. But if the volume is not increasing, then we would need to be dealing with a different concept of antigravity-- one that does not cause matter to move apart, but rather that causes it to shrink. The curvature of the spacetime is induced by the changing standard of distance, which in turn is caused by dark energy, which in turn is interpretable as a negative pressure because its energy increases relative to the standards, even though it does not "actually" change at all. I'd say it's a rather generalized meaning of pressure, but then, one is already using the concept quite fast and loose in the standard dark energy picture.

publius
2009-Jan-27, 06:00 AM
Right. It would be interesting to see how the different pedagogy might alter our picture for what dark energy is.

That is a good question, but unfortunately I'm too lazy to try to figure out what it looks like. :)

I'll just say this. In terms of the invariants, "dark energy" produces a certain type of space-time curvature, which will not be changed by whatever coordinates we use. We haven't changed the space-time, just our mental picture of what's going on in it, of course.

You mentioned negative pressure and the bears some elaboration. If we move the cosmological constant term to the RHS of the EFE and interpret it as some sort of stress-energy source term, then we've got (a type of) "dark energy".

This stress-energy tensor is just -Lambda*g, the metric. Using a postive time-like convention, there's a negative sign on the right-hand side anyway, so pulling that out, T_00 is postive, but the diagonal is negative. That diagonal is the pressure (and we assume a near-Minkowski metric with all ones down the diagonal. We really don't need it in the general case, but it makes it easier to see how it works).

The Newtonian limit of lambda looks like negative mass, but that's due to the contribution of the negative pressure. In GR, div g, where g is the Newtonian 'g' field (well, something you can define mathematically that behaves like it, even though the Newtonian field doesn't really have any meaning in the strong field) is actually 4pi*G(trace of stress energy tensor), and that trace is just rho + 3p/c^2 where p is the pressure. Normally, p is so small it doesn't make much difference.

However, in the cosmological constant/"dark energy" version, it is huge and negative, and the trace is 1 - 3 = -2*lambda, which gives us our negative mass looking contribution in the Newtonian limit. But it's important to appreciate that in the full GR version, dark energy is not negative energy density, it's just large negative pressure.

So, "all we have to do" is just look at what that dark-energy stress-energy tensor looks like in our shrinking-matter coordinates. But that does not change the invariants. Of course, if you just leave it on the LHS, then it's just geometry anway -- empty space-time just happens to be deSitter and not Minkowski.


-Richard

heldervelez
2009-Jan-27, 12:26 PM
Mr Publius:
In this thread I will not comment on GR but to those there are more in dept with GR:
I quote from this papper "Cosmological Principle and Relativity - Part I" (http://arxiv.org/PS_cache/astro-ph/pdf/0208/0208365v1.pdf)

"This generalization of Relativity Principle embodies Cosmological Principle"

Can you devise that GR can be also subject to a generalization? look there.
Deserving a lot of considerations that had to be left to other moment I will only mention that GR as Einstein wrote it has nothing to do with an Expansion Universe. GR was written thinking on an infinite in time universe (in those times it was unthinkable that matter can have a finite age). The equations of GR have a so called "Cosmological Constant" to deal with the gravitation looping back in the geodesic from the antipodal point of the universe to our local point. Is has to be a residual and it becames the "Cosmological Constant". Beeing so the history, it seems that Dark Matter was implanted on GR and can configure a misuse.
GR precedes the Space Expansion notion. So GR does not need Space Expansion.

If you study the above papper may be you, and someone else, can find that the generalization embodied by the Cosmological Principle provides a complete framework that justifies the shift of paradigm that the OP proposes.

In the papper "A relativistic time variation of matter/space fits both local and cosmic data" (http://arxiv.org/PS_cache/astro-ph/pdf/0208/0208365v1.pdf) there is no stress on GR and both models are compared side by side as one seems the dual of the other.
With this post I wish to slow down further considerations on GR for the time beeing.

heldervelez
2009-Jan-27, 01:38 PM
...
I was about to suggest you cut your ideas into separate questions, and ask them one by one in this forum ...

Beeing Time T, Mass M, Length L, Charge Q physical quantities that are attributes of matter or derived from matter scale.
Beeing c, G, and epsilon constants imposed by the space, and assuming that space 'is stable'.

The most basic physical laws, rock solid, that relates matter with the fundamental forces are expressed with the dimensional equations:

c = L / T
G * M = L * c^2
sqrt( G / epsilon) * Q = L * c^2

Einstein in GR let us know that those equations had to be invariant if they are true physical laws.

We have a bunch of variables and only three equations.

The physical way is not to mess with space properties, and devise how those equations became invariants.

Bigger atoms in the past means more Mass, more Length and more Time if compared with actual tiny atoms. This is the proposal.

That papper (http://arxiv.org/PS_cache/astro-ph/pdf/0208/0208365v1.pdf)made the study and concluded that the only way, maintaining the physical sense, is vary accordingly M,L,T as a funtion of some rate of change (alfa) -- damned keyboard.

alfa(t) = L/c = z + 1 ; the usual z as we know it, derived from observations.
This alfa(t) his the only parameter needed within this formulation.

This model makes no more assumptions and invoking Occam's Razor (http://en.wikipedia.org/wiki/Occam%27s_razor) reasoning :) we can proceed because the Expanding Universe ...

the above laws can be rewritten as (time is implicit) :

L = c * alfa
T = alfa
M * G = alfa * c^3
Q * sqrt(G / epsilon) = alfa * c^3

M,L,T can vary according to those relations and physical laws are kept invariant.

Now I will invoke one philosophical principle that I do not know the name but in my head is like that: If things can present themselves in a multiple way of beeing, it is abusive to choose only one of them as we do now.

Resuming : we have to accept the more general form of physical laws as they also contain the version as we see them now.

Cougar
2009-Jan-27, 02:28 PM
Right, there's no problem at all with cosmological redshift [wrt the shrinking model].

Why do more distant objects seem to be shrinking more rapidly than less distant ones, judging by the measurements of their redshifts?

Ken G
2009-Jan-27, 03:03 PM
Of course, if you just leave it on the LHS, then it's just geometry anway -- empty space-time just happens to be deSitter and not Minkowski. Yes, that's an interesting point, there's a bit of a pedogogy choice right there in terms of what you put on the right and what you leave on the left! If we think of dark energy as some kind of active agent that alters what we would otherwise have thought of as "empty space", then we put it on the right and call it a form of stress-energy. If we think of it as "just the way the geometry of empty space is", we leave it on the left and there's no "negative pressure" or energy or anything. So I guess the question is, in the "shrinking" pedagogy, which treatment of dark energy would seem to make the most sense? I think if one takes the geometrical view of dark energy, there's not much to say about shrinking matter or expanding space, as they are the same geometry. If one thinks of dark energy as an active agent in an otherwise "intuitive" empty space, one must allow that it is somehow causing the matter to shrink. Take yer pick.

Ken G
2009-Jan-27, 03:07 PM
If you study the above papper may be you, and someone else, can find that the generalization embodied by the Cosmological Principle provides a complete framework that justifies the shift of paradigm that the OP proposes.An important correction here: the OP does not propose a shift in paradigm, it proposes an alternate pedagogy to view the exact same paradigm. This is not mincing words, the distinctions here are central to the whole thread.

Argos
2009-Jan-27, 03:12 PM
If one thinks of dark energy as an active agent in an otherwise "intuitive" empty space, one must allow that it is somehow causing the matter to shrink. Take yer pick.

But thatīs the whole problem with this discussion. Various members pointed out the need for a mechanism for the shrinking in the beginning of the thread.

Ken G
2009-Jan-27, 03:14 PM
Why do more distant objects seem to be shrinking more rapidly than less distant ones, judging by the measurements of their redshifts?The answer to that question, and all questions, is found simply by translating the answer to the exact same question in the current expanding space picture. In the shrinking picture, cosmological redshifts are "caused" by the history of the shrinking of the material that constitutes the apparatus that is registering those redshifts-- nothing at all happens to the light itself, and anything that happens to the object that did the emitting is irrelevant after the light has been emitted. Prior to the light emission, that object was shrinking too, so the more recently the light was emitted, the smaller the wavelength of the emission (emitted wavelength will scale with the atoms in the object), and the less the measured redshift. This dependence on history after the emission has the exact same flavor as the expanding space picture, where redshifts are "caused" by the history of the expansion of the space through which the light has passed, and again nothing the object does after the emission matters. However, in the latter picture nothing ever happens directly to the object, and in the former picture, nothing ever happens directly to the space or to the light. By one way of counting, I'd score that 2 to 1 in favor of shrinking matter!

Ken G
2009-Jan-27, 03:19 PM
But thatīs the whole problem with this discussion. Various members pointed out the need for a mechanism for the shrinking in the beginning of the thread.But that objection was not addressed because it is wholly groundless as a criticism of a physical theory. What is the "mechanism" by which stress-energy creates curvature of spacetime? Or even, how can "space expand", what is the mechanism there? Physics is not grounded in mechanisms, it is grounded in unifying ideas, and the idea that matter can shrink in response to an evolving gravitational environment is just such a unifying idea. And it is equivalent to the unifying idea that space can expand under similar conditions (why don't people demand a mechanism for that?).

Put differently, while it is true that physics does invoke mechanisms as we picture our mathematical schemes for making predictions, every mechanism that can be described relies on some other mechanism that cannot. It is mechanisms all the way down, and physics never gets "to the bottom". We kid ourselves if we do not recognize that at some point we have to settle for "I guess that's just the way nature is". That doesn't mean we should ever stop digging beneath every rock, it just means we should always expect to find... more rocks.

Ken G
2009-Jan-27, 03:41 PM
Resuming : we have to accept the more general form of physical laws as they also contain the version as we see them now.Right-- if L, T, M, and Q all scale with the cosmological scale parameter (your alpha [sic]), then nothing needs to happen to space and we'll still see just what we do see, given the same alpha(t) that is now used in the expanding space picture. It is alpha(t) itself that is the "paradigm" here, whether one uses an expanding space picture or a shrinking matter picture. An interesting side issue here is that one does not need to rescale M and Q in the shrinking matter picture, if one simply allows that the fundamental constants change with time to keep the physics invariant with the same M and Q. But since M and Q are purely conventional constructs (only ratios of these concepts matter physically), I favor also scaling them with alpha to keep the fundamental constants the same. That allows us to imagine that the values of the constants are part of the "form" of the physics that we are trying to leave invariant.

heldervelez
2009-Jan-27, 04:35 PM
The two views that we are analysing here are like Ptolemy and Galileo views. Apparently they describe numericaly the same reality but one addresses better the world than the other.

Can we remember that BB appeared after we 'realize' that Space is Expanding as Hubble had discovered ?

It galaxies were now receding ones from the others than logically they had to be in the same point of the space in some past moment.

Then the Inflation enters in scene (clearly a law violation) because it was the only way to express : phenomena had to occurs so fast that the only way is with this patch.

With this nouvelle formulation (like a mirror image) there is no need for BB neither Inflation.

The CMB can be as it appears to be: "mostly homogeneous" in all directions as a remnant of the moment matter was "created", or whatever generalized event that had ocurred.

And now a sacrilege sentence:
Now we can say that BigBang can suffer a BigBang and we can live.

After this, everyone will try to spank me.

Ken G
2009-Jan-27, 04:49 PM
The two views that we are analysing here are like Ptolemy and Galileo views. No, that is exactly what we are not analyzing here. Ptolemy and Galileo's (or better, Kepler's) models made quantitatively different predictions, and Ptolemy's proved wrong when better data was available. That is the only reason it was dropped-- not because anyone didn't like its pedagogy. Venus really went through gibbous phases, that was never an issue of preference.

Now we can say that BigBang can suffer a BigBang and we can live.Well, we can choose not to call it the "Big Bang", certainly that is a well-known misnomer. But the model is the same under another name, we still cannot "live" without alpha(t).

heldervelez
2009-Jan-27, 04:54 PM
Can we stop looking for Dark Matter? Indeed we can.

Dark Matter was another artifact derived mainly because velocities are invariant.
In this scenario L and T vary at the same pace and velocities maintain the original value as gravitation dictates at the moment of the imprint.


Black Holes? theoretically they can exist.
But the most recent news: "A giant BH was found there and there and there ..." are originated because this way of thinking were out of scene.

( I'm only the postmen not the author of that rather astonishing idea of Evanescent Matter )

Now it becames clear that we can get rid off the actual "Cosmological Dark Era". (coined by me, eheh)

heldervelez
2009-Jan-27, 05:17 PM
...Ptolemy and Galileo's (or better, Kepler's) models ...That is the only reason it was dropped-- not because anyone didn't like its pedagogy. ....

I do preffer to say Galileo as it was the first Relativist in history (The boat experiment).

Before Galileu everyone see and accept that the Sun and the whole Universe are capable of make a complete revolution around the Earth in 24 hours.

sidenote:
please accept my apologies because I make a lot of errors when I try to write in English.

To the laymen (*) around us I will say that a book online (http://outrafisica.blogs.sapo.pt)that has been written along the last year.
( It must be read from the beginning as a usual novel)
The bad side is that it is in Portugueese language, but there is a link to google translator in each page.

(*) I am also one of them because I am only an amateur (=lover) in science.