PDA

View Full Version : Universal expansion - could someone help me to understand?

Occam
2010-Feb-15, 11:05 PM
I tossed up putting this in the ATM section but I'm not really proposing anything here - just trying to get something clear in my mind. Hopefully, someone can explain why my concept doesn't fit the facts. Here goes...

The Universe is expanding as a result of the Big Bang.
The more distant an object, the faster we perceive it moving away from us.
Various models have been proposed to explain this - dark energy, a cosmological constant etc.

What I can't get my head around is why things like dark energy are needed to explain apparent acceleration. Now, I know the Big Bang wasn't actually an explosion as such but as an exercise imagine it to be one. So, at the moment of the Big Bang, expansion starts at a phenomenal rate, creating space as it goes. Continuing the explosion analogy, as the proto-universe continues to expand, it's initial energy starts to taper off and, as 'new material' moves outward from the source it is doing so at a steadily decreasing rate. If that were the case, no matter where you end up in the resulting universe, every object would appear to be moving away from you, even if they were essentially moving in the same direction as you.

So, what I'm asking is this - if what we observe could simply be explained by relative velocities, why do we need a (so far) unobserved phenomenon as 'dark energy'?

I've tried everything I can to get the answer to this and failed miserably. Can someone please try and help me understand this in terms that don't rely on higher maths?

edit - just another thought. When we look at a single distant object, is it seen to recede at an increasing rate? If so, I've just realised what my misconception is.

Kwalish Kid
2010-Feb-16, 01:59 AM
The Universe is expanding as a result of the Big Bang.
There may have been no "Big Bang". The Big Bang theory really only says that the universe is expanding and has been for a certain amount of time.

The more distant an object, the faster we perceive it moving away from us.

Various models have been proposed to explain this - dark energy, a cosmological constant etc.
In a standard expanding universe, the farther away from us an object is, the faster is appears to be receding. The cosmological constant (and dark energy) have been added to the mix because there is an additional acceleration on expansion.

So, what I'm asking is this - if what we observe could simply be explained by relative velocities, why do we need a (so far) unobserved phenomenon as 'dark energy'?
Because everything cannot be simply explained by relative velocities. There is an additional acceleration (on nearby things relative to more distant things) that leads specifically to the addition of a cosmological constant.

Occam
2010-Feb-16, 02:20 AM
Thanks,
after posting that, I realised I wasn't thinking about it correctly (hence the edit). The picture in my mind was of distant objects speeding away, the greater the distance the greater the velocity. Of course, that isn't acceleration - D'Oh!

See, this is why I maintain desktop PCs and not the LHC.:o

Gomar
2010-Feb-16, 04:25 AM
"So, at the moment of the Big Bang, expansion starts at a phenomenal rate, creating space as it goes."

Does this imply there was no space before the big bang? ok, so what was there? a solid wall?
If I am in a room that measures 50'x25' and I blow up a balloon, its expansion does not create space. But it does create space inside the expanding balloon. Thus, when the balloon fills the room it can expand no more. Now either the walls of the room collapse, or the balloon pops, or the air is let out of it and the balloon goes back to its original state.
So, either the universe continues to expand, and whatever is beyond it is being pushed further away with no end;
or it simply explodes upon reaching the edge of space;
or it collapses back into its original pre-big bang size upon reaching the end of space.

01101001
2010-Feb-16, 04:33 AM
"So, at the moment of the Big Bang, expansion starts at a phenomenal rate, creating space as it goes."

Does this imply there was no space before the big bang? ok, so what was there? a solid wall?

The Big Bang Theory does not address what came before.

Ned Wright Cosmology FAQ: What came before the Big Bang? (http://www.astro.ucla.edu/~wright/cosmology_faq.html#BBB)

The standard Big Bang model is singular at the time of the Big Bang, t = 0. This means that one cannot even define time, since spacetime is singular. In some models like the chaotic or perpetual inflation favored by Linde, the Big Bang is just one of many inflating bubbles in a spacetime foam. But there is no possibility of getting information from outside our own one bubble. Thus I conclude that: "Whereof one cannot speak, thereof one must be silent."

astromark
2010-Feb-16, 06:26 PM
As the contributers above have also expressed a sameness in the want to better understand the Universe. It would appear that the answer is just not available.
We do not know why or how the great expansion known as the Big Bang happened.
We do know it did happen as the remnants of it are still to be found. From careful study of CMB much has been learned. That the known universe is accelerating away from us could start a paranormia...:)I have understood that we are not at the center of the universe. From our perspective...It would seem that is a problem.

cosmocrazy
2010-Feb-16, 08:36 PM
"So, at the moment of the Big Bang, expansion starts at a phenomenal rate, creating space as it goes."

Does this imply there was no space before the big bang? ok, so what was there? a solid wall?
If I am in a room that measures 50'x25' and I blow up a balloon, its expansion does not create space. But it does create space inside the expanding balloon. Thus, when the balloon fills the room it can expand no more. Now either the walls of the room collapse, or the balloon pops, or the air is let out of it and the balloon goes back to its original state.
So, either the universe continues to expand, and whatever is beyond it is being pushed further away with no end;
or it simply explodes upon reaching the edge of space;
or it collapses back into its original pre-big bang size upon reaching the end of space.

Its difficult to get your head round we know. The current mainstream model suggests that there was a BB, or more correctly termed a very rapid expansion of space. Now what was prior to or outside this universe is not known and may never be known. It is believed that space and time came into existence at the point of the BB how and why we don't know either but its hard for us to imagine. The way I deal with it is to try and imagine nothing, in that I mean if there is no space there is no time and thus they go hand in hand expanding together. If nothing lay outside of this then there would be no boundary in any form and no anything to expand into. When you use the balloon analogy the balloon itself is already within a space time universe so it is bound to that no matter what.

Gomar
2010-Feb-19, 04:41 AM
Ok, so what caused the Big Bang? How much time passed before the BB occurred? Was there emptiness for a million years and then all of a sudden... boom, and here we are?!
Let's suppose all matter was the size of a pin's head had existed in a space/time prior to the BB for 125Billion years. Fine, but where did it come from? Something cannot just come out from nothing. There must've been a cause and effect.

01101001
2010-Feb-19, 05:43 AM
Fine, but where did it come from? Something cannot just come out from nothing. There must've been a cause and effect.

Van Rijn
2010-Feb-19, 05:50 AM
Ok, so what caused the Big Bang?

NorthernBoy
2010-Feb-19, 10:56 AM
"So, at the moment of the Big Bang, expansion starts at a phenomenal rate, creating space as it goes."

Does this imply there was no space before the big bang? ok, so what was there? a solid wall?
If I am in a room that measures 50'x25' and I blow up a balloon, its expansion does not create space. But it does create space inside the expanding balloon. Thus, when the balloon fills the room it can expand no more.

Your analogy is not a good one for the universe, as we have no reason to believe that there is anything "outside" being pushed. We don't think that the universe is embedded in a "room" as in your example.

It is a problem because you have taken an analogy which is good to explain why the galaxies are moving apart, but then assumed that other pieces of it (a 3d object in our 3d world) apply too.

Something cannot just come out from nothing.

Why do you say this? Again, it sounds as though you are looking around you at your everyday world of apples, baseballs, sandwiches, buildings and so on and assuming that properties of objects on this scale define the properties of objects on others, and that you can therefore invent this rule.

We see something coming from nothing all of the time if we are willing to look closely enough. The hardest vacuum of interstellar space actually is a foaming sea of creation and annihilation if we look at it on a small scale, so we know that far from it being impossible to make something come from nothing, it is happening everywhere, all the time.

Energy can be magicked from nowhere for a short time, particles can pop into existence, all sorts of weird stuff is going on, and so it's hardly a stretch to think that a universe can pop out from its own vacuum function.

If you are not happy with the idea of rules existing without a universe, consider the rules of logic, or of geometry. We are happy to say that these would still be true even if the universe was no longer here to observe them, and so may it be with the physical laws that let all we see around us just begin.

To be honest, if you think that the idea of the universe having a beginning is unsatisfactory, just consider the alternative, that something has been here for infinitely long. It's hard to even know what that phrase could mean.

blueshift
2010-Feb-20, 04:57 AM
Ok, so what caused the Big Bang? How much time passed before the BB occurred? Was there emptiness for a million years and then all of a sudden... boom, and here we are?!There was no "emptiness" because one would need a container that had volume and volume did not exist.

Let's suppose all matter was the size of a pin's head had existed in a space/time prior to the BB for 125Billion years.It didn't exist an any "place". "Places did not exist. The BB could not have started at any location in the universe. If it did then, just as with any explosion or as with the spokes of a bicycyle, it would have spread out and stars and galaxies would be getting less dense and less dense the further one observes in our largest aperture telescopes. That does not happen. The density of galaxies does not change in any direction we point our telescopes.
Fine, but where did it come from? Something cannot just come out from nothing. There must've been a cause and effect.Cause and effect breaks down in the quantum world. One needs to know both the position and velocity of an object to predict the object's future and that cannot be done at the quantum level. Knowing the velocity destroys one's ability to measure its position. Knowing the position destroys one's ability to measure its velocity.

astromark
2010-Feb-20, 07:00 AM
I keep seeing this question... Where, what, how ?
and the answers are;:)not expecting a mass agreement...:eh:

Where = everywhere. ( and that includes right here.)
What = everything. ( and that includes you and all the empty space as well.)
How = Energy became matter. ( I have no idea.)
and of course when... When = 13.7 billion years ago

Cougar
2010-Feb-20, 04:33 PM
The density of galaxies does not change in any direction we point our telescopes.

Except back in time, perhaps. At much higher redshifts, wouldn't one expect galaxies to be generally closer together? Then there's the overall star formation rate, which peaked about 5 billion years ago1. The known evolution of structure in the Universe apparently obviates homogeneity with respect to time. Of course, there's no reason to think that the fundamental laws of physics would be any different throughout the evolution of the Universe.

___________________________
1 Alan Heavens at the University of Edinburgh observed 90,000 distant galaxies and concluded that 5 billion years ago the overall star-formation rate began steadily decreasing to the rate we see today. - Jeff Kanipe, author of Chasing Hubble's Shadows, The Search for Galaxies at the Edge of Time (2006)

Cheap Astronomy
2010-Feb-21, 04:53 AM

From Hubble's work, we used to think the universe was expanding linearly (because distant things were moving away faster). However, more recent data from distant type 1a supernovae suggests the expansion rate is accelerating.

Before Hubble, Einstein showed that cosmic models of the universe could be derived from general relativity - but his equations indicated that the universe would change over time, so he plonked in the cosmological constant to keep his model in 'steady state', which was the prevailing view of the universe at that time.

Your explosion theory implies there should be a leftover area of greater energy/mass density from which everything is being (or has been) expelled from... at a steadily decreasing rate. Any interesting idea but you need some observational data to back it up.

As far as what drives the expansion of the universe - good question :-)

Ken G
2010-Feb-21, 10:22 AM
edit - just another thought. When we look at a single distant object, is it seen to recede at an increasing rate? If so, I've just realised what my misconception is.I think you still have a question here, because this is not the answer. We actually cannot see a particular object accelerating away from us, we'd have to look at it and then check back in on that same object millions of years later. We don't have that luxury! So instead, we have to infer acceleration by looking at objects at different distances, and looking at their redshifts. It's quite a bit more subtle where the "acceleration" comes from.

Since we are not using the same object to infer the acceleration, we need to make an assumption about how the different objects are related. The key assumption is called the "cosmological principle", which essentially means that all objects in the universe undergo the same history of expansion from each other, but the redshift we see from the closer objects is only sensitive to the more recent expansion, while the redshift we see from more distant ones is sensitive to a longer period of expansion. It's the same expansion, we are just seeing slices of the expansion lasting different time intervals.

Using that assumption, we expect a particular relation between distance and redshift for any given rule for the dynamics of the universe as a whole (by "dynamics" I mean the way the scale factor of the universe is changing with time). If the scale factor is increasing linearly with time, we call it "constant expansion" and expect the redshift to be proportional to distance. But if the more distant objects are not as redshifted as we expect, then we conclude the early periods of the expansion were not as fast as the more recent expansion was, so the objects whose redshifts are affected by the early expansion (the distant objects) are less redshifted than we would otherwise expect. That means the expansion has been accelerating.

If you are not used to thinking in terms of "scale factor of the universe", there is a very straightforward analogy. Imagine a rubber chess board, with little ants walking around on it in all directions. The ants always move over the board at the speed of an ant (the speed of light in the analogy). However, the rubber board is itself being stretched, and the "scale factor" is the size of the squares on the board, relative to what they are "now" at any given moment in the process. Then if there is a pair of ants that start walking toward you at some point early in the expansion, the distance between those ants will be stretched, prior to their arrival at you, by the same amount that the scale factor is stretched during their journey (that's the redshift). Hence the distance between ants, relative to their distance initially when they set out, is a record of the total amount of stretching the board underwent during their journey, so ants that come from a long way away and have a big distance between them will record the full history of the expansion, while ants that started their journey much more recently will be closer together and record only the recent expansion.

If you also have some way to tell how far the ants came (perhaps by how tired they are when they arrive), you could use ants from a range of different distances and note the arrival distance between them, to figure out the full history of the stretching of the board, and whether or not whoever is stretching it is doing so at a constant pace, or an accelerating pace. With actual light, we have a variety of ways to infer how far away the light was emitted, most notably the brightness and duration of type Ia supernovae, and we infer acceleration that way.

DrRocket
2010-Feb-21, 03:14 PM
I tossed up putting this in the ATM section but I'm not really proposing anything here - just trying to get something clear in my mind. Hopefully, someone can explain why my concept doesn't fit the facts. Here goes...

The Universe is expanding as a result of the Big Bang.
The more distant an object, the faster we perceive it moving away from us.
Various models have been proposed to explain this - dark energy, a cosmological constant etc.

What I can't get my head around is why things like dark energy are needed to explain apparent acceleration. ....

edit - just another thought. When we look at a single distant object, is it seen to recede at an increasing rate? If so, I've just realised what my misconception is.

Perhaps KenG's response has answered your initial question, based on the edit. But perhaps not, though what he said is correct.

Your first two bullets are correct, and they summarize the state of knowledge prior to about 1998. The expansion of the universe was a known at that time, and Einstein has retracted his cosmological constant, which was proposed as a means of allowing a static solution to the equations of general relativity. The big bang was, and is, widely accepted. The major open question at the tiime was whether or not there was sufficient mass/energy in the universe to cause it to be closed, and eventually contract under the influence of gravity. Basically was there enough gravity to stop things from flying apart and to again coaelesce to a small blob.

Then it was found as a result of observations, particularly of standard candles known as type 1A supernovae, that the expansion of the universe was not slowing down, but rather was accelerating. Gravity was not causing the initial expansion rate to decrease, which was quite a surprise. That was the impetus that resulted in the hypothesis of "dark energy" or a positive cosmological constant, which is the same thing. Dark energy is not really a definite cause, or a solution, but rather a name for a solution that is still not known or understood.

The reason that it is needed is that an accelerating expansion requires a phenomena that counters the effects of gravitation, and we more or less understand gravitation. We don't know what that phenomena actually is. A few things have been proposed, in particular the effects of the quantum vacuum. However, those proposals result in effects that are many, many orders of magnitude different from what is actually observed (like 120 orders of magnitude different, which is gargantuan).

So, nobody knows what is causing the accelerated expansion, but the data shows that something is. Lacking understanding, it has been given a name -- dark energy.

blueshift
2010-Feb-21, 03:43 PM
Except back in time, perhaps. At much higher redshifts, wouldn't one expect galaxies to be generally closer together? Then there's the overall star formation rate, which peaked about 5 billion years ago1. The known evolution of structure in the Universe apparently obviates homogeneity with respect to time. Of course, there's no reason to think that the fundamental laws of physics would be any different throughout the evolution of the Universe.

___________________________
1 Alan Heavens at the University of Edinburgh observed 90,000 distant galaxies and concluded that 5 billion years ago the overall star-formation rate began steadily decreasing to the rate we see today. - Jeff Kanipe, author of Chasing Hubble's Shadows, The Search for Galaxies at the Edge of Time (2006)
I agree Cougar. In fact, I think that if we went far enough back into time, and our measuring equipment allows us to do that, then we will be looking at the universe that was both much hotter and denser and no matter which way we point our equipment in the sky we should be looking at the same objects. There should even be some anomalies that accompany it with some of the light (exremely stretched out by now so likely it will be gravitational waves that we will measure) emitted by a given object will reach us before those waves emitted later by the same object since we were all closer together at the earlier time. Streaks will likely appear that we could mistaken as lensing arcs but will merely just emitted by the same object.

forrest noble
2010-Feb-21, 11:58 PM
Occam,

So, what I'm asking is this - if what we observe could simply be explained by relative velocities, why do we need a (so far) unobserved phenomenon as 'dark energy'?

Occam, the dark energy proposal is not simple -- such as "Occam's" Razor should be:

The current hypothesis concerning variations in the expansion of space, called dark energy, includes many variables. Inflation theory proposes that the universe first vastly accelerated in expansion. Next according to the dark energy hypothesis the universe continuously decelerated its expansion until about 6 billion years ago; then it started accelerating again with no discernible period of constant expansion.

http://nedwww.ipac.caltech.edu/level5/March08/Linder/Linder2.html

Quote:
".....these recent discoveries offer further evidence that the universe turned from decelerating expansion to accelerating 6 billion years ago"

http://www.cnn.com/2004/TECH/space/05/18/dark.energy/index.html

If expansion, Inflation, acceleration, deceleration are all valid (as the above links and related dark energy hypothesis propose), it would seem (to some) that inflation must have slowed down to a very small number or stopped, then started up again 6 billion years ago.

Some mainstream dark energy models seem to put all of these possible characteristics embolden above, under the single category of dark energy that accordingly would be the cause of the hypothetical expansion of space in the first place along with its vacillating changes over time. Other dark energy models propose an on-again off-again approach where gravity takes over when dark energy is inactive.

http://en.wikipedia.org/wiki/Dark_energy
http://www.pha.jhu.edu/~mspecian/astrophysics/Supernova%20Discoveries%20at%20High%20Redshift%20P rovide%20Evidence%20of%20a%20Decelerating,%20Then% 20Accelerating%20Universe%20-%20A%20Summary.pdf
http://nasascience.nasa.gov/astrophysics/what-is-dark-energy

Even though this dark energy hypothesis may not seem probable/ reasonable to some as yourself, it is the favored mainstream idea at this time. It's something like the dark matter hypothesis that must be unevenly applied for the hypothesis to work based upon observations.

astromark
2010-Feb-22, 05:00 AM
'Occam' ; I think you see the mainstream view as a bit of a leap of faith. This so called Big bang. That was proceeded by absolutely nothing I can know about. As Space time did not exist prior to that BB. We do not know and can but speculate as to what might have been the state that allowed such a BB to happen. The excepted theroum that I find difficult to except is that All of the Universe was born in a plankt length where all of what is now was triggered into existence from pure energy... and the problem I have is that I can not understand from where that came.. as there was no before. Then if you advocate the multi universe is a reality then we as occupants of this vessel have no perception of any other... Pie in the sky. As has been said. Make up your own version. cos we do not know.
I obviously do not. I can live with that.

DrRocket
2010-Feb-22, 05:52 AM
'Occam' ; I think you see the mainstream view as a bit of a leap of faith. This so called Big bang. That was proceeded by absolutely nothing I can know about. As Space time did not exist prior to that BB. We do not know and can but speculate as to what might have been the state that allowed such a BB to happen. The excepted theroum that I find difficult to except is that All of the Universe was born in a plankt length where all of what is now was triggered into existence from pure energy... and the problem I have is that I can not understand from where that came.. as there was no before. Then if you advocate the multi universe is a reality then we as occupants of this vessel have no perception of any other... Pie in the sky. As has been said. Make up your own version. cos we do not know.
I obviously do not. I can live with that.

The Big Bang is not a leap of faith.

If you take the empirical observation that the universe is expanding, plus the observation that there is a certain minimal amount of mass in the universe, then apply general relativity you reach an inevitable logical conclusion that the universe began in an extremely compact form in the distant past.

That is theorem that proved with the combined efforts of Hawking and Penrose.

The theorem actually predicts a singularity. The singularity may be simply the result of a breakdown in the applicability of known physical principles. We know that general relativity and quantum theory are mutually incompatible. We know that quantum effects would be important if the universe were extremely compact. So, we know that our knowledge is not complete. We have essentially no idea what was going on in the first fraction of a second after the Big Bang. Any proposals regarding that time are speculation. But the confidence in the origin of the universe in a compact form -- the Big Bang is quite good.

I have no idea where you come up with a theorem regarding origin in a Planck length. The best estimate that I have seen is a few centimeters -- see Hawking and Ellis, The large-scale structure of spacetime.

astromark
2010-Feb-22, 09:46 AM
yes... 'I think'. I said, I think. and yes it is. For as no matter how many Mr Hawking and others. We can not other than speculate. That is all they are doing. The difference being that 'they' are equipped better than I... Its still asking us to except what others have concluded. I find it 'as a leap of faith' is required. Thats not your problem, its mine.
I am exceptive of the understanding of the singularity. We might use different words and ways.. We are in agreement.

Cougar
2010-Feb-22, 02:22 PM
For as no matter how many Mr Hawking and others. We can not other than speculate.

Well, "speculate" is like an educated guess when you have no evidence. How the expansion initially got started is speculative. The general outline of the big bang theory, however, has considerable evidence supporting it, so it is not just speculation.

NorthernBoy
2010-Feb-22, 02:52 PM
yes... 'I think'. I said, I think. and yes it is. For as no matter how many Mr Hawking and others. We can not other than speculate. That is all they are doing.

Why do you feel the need to be so insulting to the man, first of all to deny him his hard-won proper title, and secondly to claim that he does no more than to speculate?

Do you honestly believe that scientists just speculate?

cosmocrazy
2010-Feb-22, 08:44 PM
Why do you feel the need to be so insulting to the man, first of all to deny him his hard-won proper title, and secondly to claim that he does no more than to speculate?

Do you honestly believe that scientists just speculate?

I don't think Astro was intending to insult Mr Hawking, speaking on his behalf, I should imagine that he has the up most respect for such a great scientist. The point he was trying to make is that although the current evidence strongly suggests that the universe started from a BB how and why such a event occurred is still very much a mystery and requires much speculation to try and understand it. :)

forrest noble
2010-Feb-22, 11:55 PM
cosmocrazy,

I don't think Astro was intending to insult Mr Hawking, speaking on his behalf....

I concur.

One of astromark's points, I think, was that a lot of cosmology such as dark matter, dark energy, the beginnings of the universe, etc., many consider to be still up for grabs, hypothetical.

One of NorthernBoy's points was he should be addressed as DR. Hawking since the Mr. was used, which I think was a small oversight. Much of what Dr. Hawking has proposed is considered theoretical since it can be supported by both observation and his derived equations. Some of it is referred by some as hypothetical when there is seemingly no observational support such his proposal of multi-verses. Hawking radiation to my knowledge also has not been observed directly or indirectly. A few of his speculative ideas, which have not been published, were also discussed in his books.

What I believe astromark intended by his statements was that many of these matters, as far as competing proposals are concerned, is a matter of speculation for those evaluating them. Of course astromark will probably speak for himself.

Kwalish Kid
2010-Feb-23, 12:08 AM
If expansion, Inflation, acceleration, deceleration are all valid (as the above links and related dark energy hypothesis propose), it would seem that inflation must have slowed down to a very small number or stopped, then started up again 6 billion years ago.
No, that's not what the science related to those ideas says. The theories of special inflation are independent of the theories of and evidence for dark energy. As far as we can tell, and there are efforts to try to determine this, dark energy has been constant at least since any inflationary period ended (over 13 billion years ago). Acceleration began about 6 billion years ago, but this was the result of the competing influence of mass (which retards acceleration) and dark energy (which advances acceleration).

astromark
2010-Feb-23, 09:59 AM
Seemingly...I have insulted one of the most envied minds... That was never my intention. I will add that 'A doctorate holder' Doctor is replaced by Mr. So when I said Mr Hawking. That is what I wanted to say. but 4 U. I agree with everything the eminent Doctor Hawking has ever said. but confess to not understanding all of it. I am indeed fortunate to have sat in and herd Prof., Robert Kirchner from the Harvard University. He came to NZ on a lecture tour. The Wellington presentation was most in lightning...:)and might be on U tube. This explaining the expansion was made to sound easy. A great explanation of methods of data gathering was presented and explained.
As you come away from such an informative talk it's easy to sound flippant about what we know. I understand all the man hours and all the testing. Us mortals still have a place and questions to ask. Thank you for the support:eh:I am not challenging the mainstream view. Just by way of excepting what we are told is as a act of faith. Mr Kirchner's left no doubt as to the facts attained. As he said.
" We found it hard to except the acceleration rate found. We had to have faith in the data gathered and in the conclusions attained. It was In our face and yet...?"
So.. yes Its not the BB i question or the facts attained sense. Just wanting and wishing for a better understanding of what it actually was. A proper understanding of what Dark Energy is. Is still a question begging for an answer...

forrest noble
2010-Feb-23, 04:34 PM
Kwalish Kid,

No, that's not what the science related to those ideas says. The theories of special inflation are independent of the theories of and evidence for dark energy. As far as we can tell, and there are efforts to try to determine this, dark energy has been constant at least since any inflationary period ended (over 13 billion years ago). Acceleration began about 6 billion years ago, but this was the result of the competing influence of mass (which retards acceleration) and dark energy (which advances acceleration).

In the Question and Answer section when contradicting a statement which provides links to support what has been said it is advisable to also provide links for your own statements so that a reader can evaluate all links and statements without having to do research concerning the possibilities of alternative hypothesis.

Along the lines of your statement in the same posting #19 above I also said (supported by link) "Some mainstream dark energy models seem to put all of these possible characteristics embolden above, under the single category of dark energy that accordingly would be the cause of the hypothetical expansion of space in the first place (Inflation theory) along with its vacillating changes over time." This hypothesis would also include beginning inflation along with the continued expansion of space. Of course there are a number of related hypothesis concerning Inflation and dark energy that do not necessarily agree with each other.

Kwalish Kid
2010-Feb-23, 05:25 PM
In the Question and Answer section...
One reading this exchange can certainly note that I quoted the part of the post that I objected to: your inference about the science. If your links worked, they would back up my claims.

astromark
2010-Feb-23, 06:38 PM
Tested and observed as true is that the expansion has overcome the gravity of the mass. Five to eight billion years ago the acceleration rate was slower. Direct observation of Nova events and understanding the distant objects are seen as they were. Not as they are. The science is understood, tested and confirmed.
I never provide links. I expect those interested will search and find. Looking up Prof., Robert Kirshner from the Harvard University is a good starting point.
That a trivial 4% of the mass of the Universe is observable.
Its as if gravity holds secrets we do not yet see.

gzhpcu
2010-Feb-23, 06:48 PM
So, nobody knows what is causing the accelerated expansion, but the data shows that something is. Lacking understanding, it has been given a name -- dark energy.
The New York university physicist Giorgi Dvali thinks that maybe it is just gravity leaking away from our universe. He bases this on the M-theory model of the gravition being a closed loop string, so that it is not tied to our universe-brane like all other particles, which are open-ended strings with their end points tied to our universe-brane. Reat that LHC physicists hope to detect gravitons and then see if they disappear, which would confirm all this...

forrest noble
2010-Feb-23, 10:58 PM
Kwalish Kid,

One reading this exchange can certainly note that I quoted the part of the post that I objected to: your inference about the science. If your links worked, they would back up my claims.

Especially when contradicting a posting based upon references one should provide their own link/ references to corroborate their own statements so that a reader can judge the validity of the statement or contradiction without having to do separate research. Because one objects doesn't mean their interpretation is valid, or that it is the only existing interpretation.

All links in posting #19 are presently operational after correction. Show me where they back up your claim concerning Inflation theory or provide another link for your statements. Even if your statements of Inflation are valid does not mean my statement was invalid so that I should be contradicted.

My quote posting #19 which you objected to.

If expansion, Inflation, acceleration, deceleration are all valid (as the above links and related dark energy hypothesis propose), it would seem (to some) that inflation must have slowed down to a very small number or stopped, then started up again 6 billion years ago.

So that there would seemingly be no objection I added "to some" in the original quotation, posting #19, since it apparently doesn't seem that way to you, and may not to others with your opinion.
It doesn't seem that way to me either since I ascribe to an altogether different model to explain observations asserting expansion, Inflation, dark energy, and dark matter, as you probably know.

Occam
2010-Feb-24, 02:03 AM
I'd like to thank everyone for the excellent responses to my questions. They've gone a long way to increasing my understanding of universal expansion. Just to clarify something for Astromark - I don't see the Big Bang as "a leap of faith". I fully accept it, just as I accept universal expansion/acceleration. My questions were really about me trying to get my head around the acceleration concept, more than anything.

Thanks again to all that responded.

Kwalish Kid
2010-Feb-24, 04:32 AM
So that there would seemingly be no objection I added "to some" in the original quotation, posting #19, since it apparently doesn't seem that way to you, and may not to others with your opinion.
Yes, by adding "to some" you turn a false statement in to a true one. There are always some people who believe a false statement, even when it is a non sequitor.