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Aaron
2008-May-11, 12:31 PM
Heard a questions on astronomy cast that got me thinking.
-is the universe spinning? A: in relation to what?

for the question: "is the universe expanding?" shouldn't the only logical/ observable/provable answer also be "in relation to what?" we're comfortable saying the universe is expanding (though that is only in relation to us; after all, the residents of the universe)... Isn't it just as possible that all within the universe are simply shrinking within the singularity?

The shrinking contents of a singularity, after a space-time "grid" is formed within, might also lead to an easier understanding of the "expansion" of space without a center since people won't be imagining a "big-bang" throwing things out from a point.

If there "is" (with our time being a construct of the universe all tenses may be equally applicable) existence outside the singularity and our universe's "expansion" of space-time isn't overtaking any real-estate, it stands to reason that the singularity (if observed from outside) hasn't expanded at all, but instead has formed a space-time, hence our universe within itself.

If there is not existence outside the singularity, the universe expanding or singularity contents shrinking (within its contained but "expanding" space-time grid) are equally as likely but undefinable.

For now, I'm forced to assume that the universe isn't expanding, but instead, we are shrinking. eek!, says my ego.

This is very unsettling for me, please help
Aaron

dcl
2008-May-11, 05:11 PM
If the Universe were shrinking, we'd see distances between pairs of objects decreasing on average. Instead, we see them increasing on average, so the only conclusion that makes sense is that the Universe iss expanding. The answer to the question "in relation to what" would be "most arbitrarily selected pairs of objects".

Aaron
2008-May-11, 08:59 PM
I'm saying just the opposite. The universe isn't shrinking, everything within it is. As shrinking residents of the universe, there appears to be much more space for us and between objects, but that's because we're getting smaller. along with every wave/particle acting in relation to the shrinking threads of the space-time fabric.

Imagine the universe is a closet... fill it with people... say we're packed in like sardines and have developed 1 unit of measurement, the "body width" or BW. the closet is 4'x4' (4 BWx4 BW) so we have a total of 16 people in the closet. the people each measure 1x1 within the closet universe. Shrink the people's width by 50% every minute. after 1 minute, they are 6"x6", 3"x3" after 2 minutes, 1.5"x1.5" after 3 and 3/4"x3/4" after 4... from outside the closet universe, if there is an outside, there has been no change(unless one looks inside the "closet dimension"). The closet is still 4'x4' but for those inside, it appears that the closet/ universe is expanding. Friends that were just 1 BW from each other are around 16 BW's away after 4 minutes and will be 32 BW's away in 5... While those that started farther from me are moving at a much faster velocity in relation to me at any given time... those that started at 2 BWs away are 32 BWs from me after 4 minutes and will be 64 BWs away in just a minute. That's twice as fast simply because they are farther away. The same is true for everyone within the closet with everyone else in every direction... I must confess though that before I shrank too much and lost contact, I locked eyes with this girl names Andromeda, so we're planning on meeting soon. Other than that, I'll eventually get too small (with the relative distance too great) to be able to contact anyone in this universe. Plus, I know that the speed of light is constant at approx. 1 million BW/sec since the threads in the fabric of space in this closet is shrinking right along with me, I soon won't even be able to see anyone else... If light had a constant of 50 BW per second, it's easy to see how contact is lost as relative to us, some vary far away objects seem to be moving faster than the speed of light, but in reality, we're simply shrinking (or the universe is expanding... I just don't know what room should be forced to give up floor space for our closet. Do we really think our closet is that special that it deserves to expand? More likely that we're just shrinking).

Edit: Even with light moving at a constant of about 1 million feet/sec. (or more correctly 1 million BWs per second in our closet universe), it wouldn't take too many minutes for the residents of the closet to be too "far" from each other to pass information or for light to travel the distance between any two people in the closet, but the cosmic radiation of their body heat would still be present from the earlier minutes when they were larger.

The "big-bang" gave people a picture of everything running away from a point into outerspace like an explosion. When the "expanding universe" is discussed, most people think of things within the universe like galaxies as opposed to the actual fabric of space-time that is expanding. "Expanding into what/where/when?" Seems like a more accurate mental image would be had if it were taught that the universe is constant in size (still a singularity?) but we, and everything within the universe is shrinking.


Way past my bedtime.
Aaron

a-l-e-x
2008-May-11, 11:57 PM
Ive this argument before... and also, theorized was the changing value of constants, such as the speed of light and the alpha fine structure constant. If everything changes... how would we be aware of any change at all?

dcl
2008-May-13, 10:32 PM
There is a philosophical principle call Occam's Razor that says of two possibilities, the simpler one is the more likely to be the correct one. With all that we know of physics, it is much more reasonable to suppose that space is expanding and carrying its contents with it than that everything in a fixed space is shrinking. There is no plausible basis for a supposition that matter is shrinking, whereas the Big Bang theory offers a plausible basis for the Universe to have started from an extremely hot concentration of energy that was converted into extremely energetic particles of mass via Einstein's E = mc^2 as it cooled.

damian1727
2008-May-14, 07:56 AM
also if matter was shrinking are the force ratios keeping in step?

and if matter was shrinking the distance between gravitationally locked objects would appear to increase which it does not

funny idea tho

:):):):):)

damian1727
2008-May-14, 07:57 AM
it is well cool now innit lol :)

Aaron
2008-May-14, 06:25 PM
also if matter was shrinking are the force ratios keeping in step?

and if matter was shrinking the distance between gravitationally locked objects would appear to increase which it does not

funny idea tho

:):):):):)

Force ratios work just the same as with inflation... which is why light from super-distant objects can never reach us since the apparent expansion of space between us is accelerating at a rate faster than the speed of light. The objects themselves aren't running away from eachother, they're just shrinking so the relative distance between them is expanding at faster than the rate of the speed of light. From those super distant object's perspective, we're actually moving at faster than the speed of light, just not in relation to space... we're simply shrinking causing the apparent distance to grow faster than the rate that light travels. Inflation works the same, but is difficult to conceptualize without focusing on the objects accelerating away from each other, once we focus on the objects moving away from each other, the picture breaks down and we start breaking laws.

I'd be willing to bet that in a 100 +trillion years when we shrink along with the fabric of space at such an accelerated rate to the point where light can no longer travel between two objects in orbit, gravitational effects can't reach either... just the same as with inflation in 100+ trillion years. That effect is already present. The rate of (apparent) expansion of space is simply still slower than the rate of acceleration caused by gravitational forces between some objects or systems. Throughout the universe, gravitationally locked systems have been prevented, are and will be being "unlocked" as the rate of (apparent) expansion of space will be greater than the rate of acceleration caused by gravitational attraction between two objects. Isn't one of the predictions of inflation that space will be expanding at such an accelerated rate that even nuclear forces won't be able to stay locked and all will "rip apart" since the expansion rate of space will be faster than the attractive rate of those forces? If light eventually won't be able to reach, neither will the effects of gravity. -same as "inflation", but very different from the big-bang style singularity firecracker that focuses on objects accelerating from one another (bad) as opposed to the (apparent) accelerated expansion of space between objects (good).

With the "shrinking people in a closet" analogy, all those differentiations between inflation and big-bang jump out and can be conceptualized easily: what will eventually happen to light/ gravity between objects (loss of ability to transmit that information), how there is no center, the uniformity of the cosmic background radiation, as well as the eventual failure of even nuclear bonds... the 50% "shrinking" (or 50% rate of expansion per minute) was super high speed turning 100's of trillions of years into a matter of hours... slow down that rate to something proportional with the actual universe's and "gravitationally locked" objects will have plenty of time to dance as they currently do in the universe.

If we draw the universe and it's contents on a 4x4 grid every 1 billion years, we'll need a finer and finer pen to compensate for the expansion of space. That's how inflation and shrinkage are identical. Just a different perspective. One says the graph paper expands, the other says we draw smaller within. One says the universe expands, the other says all within are shrinking. Both require the same "dark" energy.


Aaron

speedfreek
2008-May-14, 07:56 PM
Force ratios work just the same as with inflation... which is why light from super-distant objects can never reach us since the apparent expansion of space between us is accelerating at a rate faster than the speed of light. The objects themselves aren't running away from eachother, they're just shrinking so the relative distance between them is expanding at faster than the rate of the speed of light. From those super distant object's perspective, we're actually moving at faster than the speed of light, just not in relation to space... we're simply shrinking causing the apparent distance to grow faster than the rate that light travels

So how would one explain a galaxy with a redshift of z=7, which, using the mainstream "expanding space" model, was 3.5 billion light years away (angular diameter distance) when it emitted the light we are now seeing 12.9 billion years later. That galaxy is now estimated to be nearly 29 billion light years away, due to the expansion of the universe during that 12.9 billion years that the light was travelling for.

The apparent angular diameter of an object shows how large it looked when the light was emitted. If you see a moving object, you see it as it was when the light came from it, not as it is when you receive the light (by which time it might be closer, or further away). In that context, are we assuming here that photons also shrink in size whilst they are travelling through space? Is the speed of light constant too? Would that mean the speed of light was constant relative to the size of a shrinking photon and therefore not constant at all?

Aaron
2008-May-14, 08:05 PM
There is a philosophical principle call Occam's Razor that says of two possibilities, the simpler one is the more likely to be the correct one. With all that we know of physics, it is much more reasonable to suppose that space is expanding and carrying its contents with it than that everything in a fixed space is shrinking. There is no plausible basis for a supposition that matter is shrinking, whereas the Big Bang theory offers a plausible basis for the Universe to have started from an extremely hot concentration of energy that was converted into extremely energetic particles of mass via Einstein's E = mc^2 as it cooled.

Big-Bang... if one imagines object in the universe running away because of an "explosion" there's no way to account for accelerated rate of expansion, uniform cosmic background radiation; and who knows what else. The problem is "big-bang" focuses on things within the universe as opposed to the fabric/construct of space itself.

From my understanding, Inflation solves this by focusing on space as opposed to the objects within. The big x factor then seems to be what is the energy causing the accelerated rate of expansion. "dark" energy. We know nothing about it so we call it dark, I think. If there is an "energy" causing a universal expansion, that sounds pretty complex... I've never heard even a speculative explanation as to how "dark" energy can interact with space to make it expand


I'm a total layman so bear with me for a moment... but if it's simple enough for me to have a mental image

Perhaps energy reacts with the fabric of spacetime causing that fabric to vibrate or resonate with effect of quarks and things phasing or spinning in and out of our observable existence... all that quantum quirkiness. Maybe that smallest/ most basic of energy's interaction with the fabric of space-time is energy causing a resonation or vibration on the space-time fabric resulting in wave/particles... Perhaps this happens on threads in the fabric of space-time that are the "alpha-fine" in size. If this exchange of energy and particle/wave causes a split or potential split in a "thread" of the fabric of space-time causing 2 smaller threads in the fabric where there once was one, this would cause everything in proportion to "shrink". Energy then continues to react with space-time's fabric, but the fabric of space "resonates" at a lower "amplitude" and "frequency" causing all particles/waves to be smaller and move slower relative to the overall size of the universe since those "Alpha-fine" threads of the fabric of space-time are now smaller relative to the universe.

edit: meant fabric of space-time resonates at lower amplitude/higher frequency, resulting in a proportionally smaller quantum interaction with space-time fabric for all wave/ particles.

We don't have the special right to say that the universe is expanding and we're spatially constant any more than we have the right to claim to be the center of the universe compared to another, or that our time is "true" time. The "non-special" law would probably trump the "simplicity" law, but since there is no difference in complexity it's not even necessary-
only the speculation as to what is constant has changed: the size of the universe, or the size of it's contents... Occam's Razor doesn't apply or might even favor a constant size when the 4th dimensional ("dark") energy interaction with the shape and fabric of space is considered.

If there is anything simpler that can explain how "dark" energy might cause the universe's expansion to accelerate, and how the big bang can result in objects moving faster than the speed of light relative to one another, and the uniform cosmic background radiation, I'm more than willing to go where pointed to find the info... I'm just trying to get a more accurate view in my head and simply don't have any emotional connection to the big bang... Inflation/ shrinkage are identical but assume different constants. The shrinking might give people a more accurate picture simply because it won't be confused with ideas from the big-bang that are no longer in line with what we can now observe.

Aaron
2008-May-14, 08:33 PM
So how would one explain a galaxy with a redshift of z=7, which, using the mainstream "expanding space" model, was 3.5 billion light years away (angular diameter distance) when it emitted the light we are now seeing 12.9 billion years later. That galaxy is now estimated to be nearly 29 billion light years away, due to the expansion of the universe during that 12.9 billion years that the light was travelling for.

The apparent angular diameter of an object shows how large it looked when the light was emitted. If you see a moving object, you see it as it was when the light came from it, not as it is when you receive the light (by which time it might be closer, or further away). In that context, are we assuming here that photons also shrink in size whilst they are travelling through space? Is the speed of light constant too? Would that mean the speed of light was constant relative to the size of a shrinking photon and therefore not constant at all?


Exactly the same as inflation... (apparent) expansion is still at an accelerated rate... only the speculation as to what is constant has changed: the size of the universe, or the size of it's contents...

Speed of light is constant in relation to the fabric of space-time, and therefore constant when observed/ measured by anyone and everything within the universe whose wave/particle make-up is based on the same fabric of space with its ever-decreasing "alpha-fine" size of quantum interaction.

Speed of light is never constant in relation to the size of the universe. It's constant in relation to us and the fabric of space. The math stays the same. It would only change if viewed from outside the universe.

speedfreek
2008-May-14, 10:57 PM
But the question is, have photons shrunk by the same amount as the rest of the contents of the universe?

If a collection of photons were emitted towards us from a galaxy long ago, those photons would move through space parallel to each other (this is how we see coherent images of distant objects) and the angular diameter of the source object, the amount of sky it takes up, would show us how large it was when it emitted the light we are now seeing.

We assume that galaxies were the same size then as they are now, in order to work out the original distance away using their angular diameter. We see that redshift z=7 galaxy, with a size in the sky that, assuming galaxies were the same size then as they are now, puts it at around 3.5 billion light years away, 12.9 billion years ago.

But the redshift factor of z=7 is assumed, using expansion theory, to represent a time when the universe was smaller by a factor of 1+z. So the universe was supposed to be 8 times smaller then, than it is now.

If that is not the case, and instead that galaxy was 8 times larger than it is now, how far away was it? 29 billion light years?

How old is your universe where there is no expansion, no increase in distance between objects, where everything stays in the same place and simply shrinks?

Aaron
2008-May-15, 06:01 AM
But the question is, have photons shrunk by the same amount as the rest of the contents of the universe? -yup, along with everything else in the universe
If a collection of photons were emitted towards us from a galaxy long ago, those photons would move through space parallel to each other (this is how we see coherent images of distant objects) and the angular diameter of the source object, the amount of sky it takes up, would show us how large it was when it emitted the light we are now seeing.

We assume that galaxies were the same size then as they are now, in order to work out the original distance away using their angular diameter. We see that redshift z=7 galaxy, with a size in the sky that, assuming galaxies were the same size then as they are now, puts it at around 3.5 billion light years away, 12.9 billion years ago.

But the redshift factor of z=7 is assumed, using expansion theory, to represent a time when the universe was smaller by a factor of 1+z. So the universe was supposed to be 8 times smaller then, than it is now.

If that is not the case, and instead that galaxy was 8 times larger than it is now, how far away was it? 29 billion light years? -Everything within the universe was 8 times larger then (including photons) so the relative distance was 8 times as small

How old is your universe where there is no expansion, no increase in distance between objects (there is an increase in apperant/ realtive distance), where everything stays in the same place (there is motion following all laws of motion as we currently unserstand 'em, but things aren't, being magically accelerated anywhere) and simply shrinks? 13.7 billion years old +/- 200 million (from our perspective in Space-time) from what I hear.
Responses are bold within the quote.
most questions were answered in previous posts. Being a layman, I might not be using the correct language set to define everything properly.

damian1727
2008-May-15, 04:03 PM
jesh louise life is complicated enuff without confusing it further and disapearing up your own black hole!!

;)

Aaron
2008-May-15, 04:57 PM
listened to EP 81 again and did some pondering. With the constant (apperant) expansion rate, attractivly bonded systems wouldn't break apart as I thought before.

With the constant expansion of space "pulling" these items apart as space expands between 'em they are moving toward each other due to gravity, thus negating the rip-effects of the accelerating expansion of space in relation to distance since they won't be farther apart.

With my shrinking analogy, assuming a shrinking rate of 1BW/minute/2 BW, only non-locked systems would eventually lose the ability to exchange information). The only way for systems to be torn apart (either gravitational or nuclear) there would have to be a constantly increasing rate of acceleration, ie: 1BW/minute/2BW/minute or whatever timeframe.

In line with the inflation model where at 20 km/sec/megaparsec attractively force-locked objects would not be ripped apart since even as space between them expands, through their path of orbits that expansion and their attraction remains constant so they're kind of spiraling in as space expands. For the "big rip" to happen, that accelerated expansion rate would have to be increasing and be something like 20km/sec/megaparsec/year or whatever timeframe.

speedfreek
2008-May-15, 07:21 PM
What about gravity then? Gravity is what is theorised to have been slowing down the rate of expansion until around 6 billion years ago, when objects were far enough apart that the rate started to accelerate due to something we call dark energy.

In a static universe with shrinking matter, is gravity still somehow responsible for slowing the rate of shrinkage and if so, how? With an expanding universe, gravity defines how objects move relative to each other and at the same time can slow the rate of expansion between all objects. Surely gravity cannot be responsible for the slowing rate of shrinkage, so don't we need to introduce another new force? We still need the analogue of dark energy too, to explain the acceleration of the rate of shrinkage when it was initially decelerating.

Aaron
2008-May-16, 02:10 AM
So far, I figure, Gravity affects the motion of matter and has no bearing on the expansion of space, only it's internal structure; or how the grid is drawn on the donut or astroid screen.

Throuh history, it seems that each time theorists adding magic speed ups and slow downs to theories, a more acurate picture comes along and the voodoo-math is no longer necessary.

IE.. the voodoo math necessary to comply with big-bang theories in regards to accelerated expansion and cosmic background radiation... hence, inflation. It only seems that people mix the two up or try to make a magic leap from one to the other. I think my view is the same as inflation. The only difference is that I redraw the universe on the same sheet of grid paper in my head (so everything gets smaller). I envy everyone who can visualize an expanding grid and not apply force/inertia to the objects as they move apart due to the expansion of space. However, with inflation, this is what causes most people's picture of inflation to break down.

speedfreek
2008-May-16, 05:41 PM
The redshift-distance relationship does not contain fudges, or magic slow downs. It shows the rate of expansion was not constant, but started fast and was slowing down for a long time. I'm not talking about any hypothetical inflation, I'm talking about what we have actually observed to have happened since.

At the large scales we use the redshift of light to derive how much the size of the universe has scaled up since that light was emitted. When we plot this relationship we see that the rate of expansion was slowing down for the first 7 billion years of the history of the universe.

If you want to replace the expansion of the universe with the contraction of matter in a static universe, you have to find a mechanism to explain the changing rate of contraction. Gravity slows expansion so we have that mechanism already in an expanding universe.

Aaron
2008-May-17, 08:04 AM
On 10x10 grid, draw the universe as you imaging it at 1 minute.
On another piece, , draw the universe at 2 minutes.
On 10x10 grid, draw the universe at 1 hour.
On another piece, draw the universe at 24 hrs.
On 10x10 grid, draw the universe at at 1 year.
On another piece, draw the universe at 10 years.
On another piece, at 100 years
On another piece, draw the universe at 1 million years... etc...

For your picture to remain accurate, you'll need a finer and finer pen for each drawing... This is the equivalent of the threads of space-time taking up less volume since they keep splitting, thus, creating a relative expansion of space that directly correlates to distance and is unaffected by gravity so doesn't need a push by dark energy shortly after to change the decreasing rate of expansion to an increasing rate of expansion.

If inflation is easier to imagine for you, keep visualizing it that way, then the expansion of the universe is simply the uniform addition of threads in the fabric of space-time all the same size. Much simnpler having 'em split since dark energy will no longer be necessary but all observable effects (that I heard it to be responsible for)will already be accounted for. This will still be independent of gravity, since at least with a donut-shaped universe, all gravity of all wave/particles are pulling all the others in all directions and as space expands between 'em the attractive forces between some objects "pull" them together at a rate faster than than space is expanding between the objects. Since the distance isn't increasing between the objects (because of their movement toward eachother) as space expands, the objects form groups and clusters within space's expansion. and the space between the objects expands since their attractive forces aren't accelerating them toward each other faster than the rate of expansion between them.

The trap with inflation is in our minds as we imagine objects having inertia and by force (of dark energy) breaking free of gravitational interaction with other objects as they move away from each other with the expansion of space. "Big-Bang on the Brain syndrome"

It seems like the asteroids videogame is an excellent model of the universe... if the number of lines of resolution on the TV screen would continually increase, all within it would shrink relative to the constant TV screen sized universe. But it wouldn't shrink towards a "center point" since there is no centerpoint as the bottom wraps straight into the top (mmm.. donuts)... Gravity has no effect on the increasing lines of resolution (expansion of space) and objects' gravitational interaction with space wouldn't instantly bend space into the formation of a black hole since as we can see from the cosmic background radiation being near uniform, that early mass, gravitationally, would be warping the fabric of space (the lines of resolution) all directions at the same time resulting in everything in space attracting everything else in all directions "simultaniously" thus basically negating it's effects. As the number of "lines of resolution" increases, the relative distance between objects would also increase as they appear smaller on the screen (as each line of resolution is now smaller) thus allowing systems to form as the gravitational effects of objects are reduced in relation to the increased relative distance between the objects. Furthermore, since (as evident from observing background radiation) mass exists with all its quantum quirkiness and is not perfectly uniform through space, objects begin to accelerate toward on another (in all directions on the donut at the same time) forming systems and clusters. If mass was perfectly uniformly distributed throughout the universe, all attractive force would always be equal in all directions and no systems would ever have resolved themselves... ty quantum quirkiness.

Inflation needs dark energy to continually add more lines of resolution in space uniformly accross the astroids screen thus continually increase the size of the screen/universe. However, if the lines of resolution were instead splitting occasionally (perhaps due to the quantum activity of wave/particles spinning, phasing, vibrating, resonating in existence on these individual lines/threads), wouldn't the effects of dark energy already be accounted for?

It seems like dark energy is only necessary to allow us to hold on to a constant (ie. the alpha-fine-structure-constant, or the width of the threads of fabric of spacetime or width of each line of resolution in our astroids screen universe). Reminds me of Einstein's cosmological constant where a little "dark energy" was used to allow for a static-state universe.

Aaron
2008-May-17, 09:39 AM
Gravity slows expansion so we have that mechanism already in an expanding universe.

We only need to compensate for gravity with an expanding universe if thinking in 3d having a "Big-Bang firecracker" center. If the universe is flat and finite (bottom of a cube connected to top, left to right, and front to back) or donut shaped, or basically like an "astroids" screen, then gravitational effects even at the very early stages would negate themselves as everything is "pulled" in all directions, or space is actually curved in all directions simultaniously. Even with the inflation theory, dark energy doesn't need a delayed reaction... Once thinking in 4d gravity can be viewed as independant from expansion of space and is irrelevent for space's expansion. space expands uniformly from within, like increasing "lines of resolution" within the universe. Logically this seems to hold right back to the singularity where the universe was 1x1x1(x1...) where perhaps all quarks and whatever quantum widgets there are were perhaps spinning, resonating, phasing in turn until that singularity was worn out causing it to split, thus increasing the lines of resolution in the
universe to 2x2x2(x2...).

This may lead to the theoretical possibility of a new space-time universe being created within a singularity of a black hole when there in enough matter/ energy that joins that point of singularity perhaps "overloading" that "point" of space causing a split and formation of a new universe within, though from our perspective it still the size of the black hole's singularity, a quark or whatever the smallest quantum thing doing its spin/phase/vibration thing

It seems dark energy "suddenly getting involved" at some point to stop gravity from slowing expansion is only necessary if thinking in the 3d and requiring the objects to have inertia as the relative distance between them expands.

If all the lines of resolution remain a constant"width", dark energy is needed to create more lines uniformly throughout the universe, but if these threads of the space-time fabric split, total energy throughout the universe can remain constant with an observable accelerating expansion related to distance within the universe.

speedfreek
2008-May-17, 04:01 PM
We only need to compensate for gravity with an expanding universe if thinking in 3d having a "Big-Bang firecracker" center. If the universe is flat and finite (bottom of a cube connected to top, left to right, and front to back) or donut shaped, or basically like an "astroids" screen, then gravitational effects even at the very early stages would negate themselves as everything is "pulled" in all directions, or space is actually curved in all directions simultaniously <SNIP>

Not at all. The flat and finite example you give is a 3-Torus and gravity would still have the same effect - as distances increase the gravity-density decreases. Gravity slows the expansion, but the amount it can slow it by reduces as time goes on. In the end (depending on the amount of matter in the universe) you either have continual deceleration, deceleration to a constant rate of expansion, or deceleration to a halt and then contraction.

But if there was a repulsive force lurking in the background all along (dark energy), it would only manifest itself once the gravity-density was low enough. It doesn't miraculously appear, rather it has always been there but its effects were negligible until a certain epoch.

whatdoctor
2015-Aug-11, 10:49 PM
If we were shrinking, rotation would start to set in as objects began to orbit their common centre of gravity. Even if there were some original rotation to the mass of the Universe, conservation of momentum would have reduced that to near zero by now - due to the expansion.

Ken G
2015-Aug-28, 04:16 AM
This is an old thread that is being revived, but there is no observable way to distinguish between a universe which has dynamically expanding space, and a universe that has dynamically shrinking bound systems, because all observations of universal dynamics will always be a comparison between the behavior of unbound systems, regarded as "embedded in space", and bound systems, regarded as "held together by internal forces." We simply choose a language to talk about the comparisons between these types of systems, like choosing English or French to talk about them. The standard choice of language is that space is expanding, but there are no observational tests of that choice of language, it's just a matter of convention.

Now, sometimes it is asked if shrinking matter would change the laws of physics. We don't want the laws of physics to change, they seem to work fine throughout the history of the universe. Thus, the shrinking must simply be accomplished without changing the laws of physics, if that is the language we want to use instead. So for example, the speed of light must not change-- when rulers shrink, what we mean by a second must be less than what it meant in earlier eras. This accounts for the cosmic redshifting perfectly well, we simply say that the speed of light is constant, but the wavelengths appear longer because the rulers shrink, and the frequency appears smaller because a second today is not what it used to be. If you wonder about conservation of angular momentum for the Earth orbiting the Sun, we certainly need to conserve the angular momentum, but we do-- remember that nothing at all is observed in the Earth-Sun system, there is no change in perception of any distances or any times. The "shrinking" only appears when you compare to distant galaxies, there's no difference to what we think we mean by a meter, or a second, or an astronomical unit, or a year. So there's no effect on our reckoning of the angular momentum of the Earth-Sun system, or any bound system.

You can actually see all this right from the metric character of GR itself. All GR needs is a metric and its dynamics, and all a metric tells you is how many times a clock (a bound system) will tick as it follows a given path through spacetime between two causally connected events, or how many stationary rulers are needed to connect two events that are not causally connected. That's all a metric deals with, so you can see the whole structure of GR is completely agnostic about the comparison between what the rulers and clocks are doing, and what "space is doing."

mkline55
2015-Aug-28, 12:33 PM
I find the shrinking concept attractive (no pun intended), but in order to work, there would have had to be a starting point. How would someone describe the first few seconds of existence in that model? What would have kept all the matter and energy from collapsing into itself? If one were to claim that it could not collapse because it had no center and extended forever, then what could have ensured that all like particles at infinite distances had the same properties simultaneously so that their current properties also matched?

Ken G
2015-Aug-28, 01:09 PM
I find the shrinking concept attractive (no pun intended), but in order to work, there would have had to be a starting point. How would someone describe the first few seconds of existence in that model? It's not a model, it's a different language for talking about the same model-- the Big Bang model. As such, all answers are the same as for the Big Bang model, it would be like answering in French instead of English. The answer is, there is a dynamical equation, and an initial condition-- it's the Big Bang model.

If one were to claim that it could not collapse because it had no center and extended forever, then what could have ensured that all like particles at infinite distances had the same properties simultaneously so that their current properties also matched?There isn't a clear answer to that in the Big Bang either, but it is thought that perhaps there was a vast inflation that imposed both flatness and the cosmological principle. In the language of shrinking, inflation becomes a spectacular collapse of bound matter into itself, caused by the same rather nebulous ideas we currently have (vacuum phase change, etc.). But rather than wonder which language is "more correct", the important thing is to realize that neither language is actually saying anything demonstrably different. It's not just that they both work, it's that they are saying the same thing. Relativity is a great place for discovering that you can hear the exact same thing being said, yet have it sound completely different!

Empyre
2015-Aug-30, 02:09 AM
So, using that other "language", the the singularity that the universe started with becomes infinitely large particles and an infinitely long second? And runaway inflation becomes a runaway collapse? I think I'll stick to the more familiar language.

Ken G
2015-Aug-31, 04:48 AM
So, using that other "language", the the singularity that the universe started with becomes infinitely large particles and an infinitely long second?Exactly, though most wouldn't extrapolate all the way back to a singularity, only to a place where physics as we know it breaks down. However, you can see certain advantages to this "other language"-- for one thing, if the second is infinitely long, you certainly don't have to worry about a "beginning", do you? You also don't have to worry about "what is the universe expanding into", because no one asks what a particle is contracting into.
I think I'll stick to the more familiar language.Most people do, that's why you see it everywhere. Indeed, that's the sole reason you see it everywhere-- no observations adjudicate between them, and the fact that general relativity is a metric theory shows it is completely ambivalent about the distinction.