Why the universe is expanding faster and faster

[enricfemi]

it seems the big bang can't explain it

 

[Wallace]

Your thorough explanation of modern cosmology is astounding Have a quick read of these forums, or indeed anything written about modern cosmology then come back when you actually have a question or and interesting problem to pose in a little more detail.

 

[pervect]

We do have possible explanations for why the universe's expansion is accelerating - try a google search for "dark energy" or "cosmological constant".

The area remains one of active research - currently, an accelerating expansion appears to be the "best fit" to observation. This acceleration is not a problem to explain theoretically via a "dark energy" mechanism, but since this is the only observation that supports the existence of dark energy (AFAIK, anyway), some caution is advised. Ideally we'd like to have multiple experimental confirmations.

 

[enricfemi]

i really know little about this problem and i am searching about dark energy.

thank you for your guide,my dear pervect.

 

[keinve]

i could rant for hours on end about this. but i'll put it into a couple lines.

the matter in the universe in not dense enough to at least slow down the universe temporarily. hence, it simply follows the laws of physics, and gets bigger. there's nothing stopping it.

 

[enricfemi]

thank you,keinve.it's really more conciser,but seems havn't explained the acceleration.

 

[George Jones]

thank you,keinve.it's really more conciser,but seems havn't explained the acceleration.

Maybe on cosmological scales gravity is repulsive. Maybe the vacuum has energy. Maybe some other field causes the acceleration.

More detail.

 

[pixel01]

As I have read several articles recently about dark matter. Instead of attracting, the dark matter repels. And darkmatter occupy about 85% of all matter, so it accelarate the expanding of the universe.

 

[enricfemi]

thanks Regards and pixel01.

 

[cristo]

As I have read several articles recently about dark matter. Instead of attracting, the dark matter repels. And darkmatter occupy about 85% of all matter, so it accelarate the expanding of the universe.

Sorry, but what articles where these? I think you're confused and thinking of dark energy.

 

[pixel01]

Those articles are on space.com about a month or so ago. Even scientists are confused dark matter and dark energy, the two things are linked and influence each other. Anyway, I think the explanation is quite good for the acceleration of the universe expansion.

 

[trueuniverse]

i could rant for hours on end about this. but i'll put it into a couple lines.

the matter in the universe in not dense enough to at least slow down the universe temporarily. hence, it simply follows the laws of physics, and gets bigger. there's nothing stopping it.

keinve: I'm not a cosmologist, but does that mean that as the universe becomes less dense the force of gravity decreases causing acceleration of the expansion from the original point of highest density to increase?

 

[n4nova]

as far as i know... this expansion of the universe is the result of the big bang explosion.at the beginning , the the explosion occurred & the universe started to xpand from the zero state(ie.infinitely large density n infinitely small volume).till now the universe is xpanding & now the xpansion rate is growing higher and higher...coz..the repulsion force between the elements (ie. stars, planets..etc..) is growing higher. and i should mention here that this repulsion force between them is directly proportional to the distances between them.and now if u r asking the question..."mention the time till when the the universe... will expand..".then i will answer u..."as the universe is xpanding...the density is decreasing...n goinh almost near to 1..when it will reach 1 ,the universe will collapse to a point with an infinite density & after that moment another big bang will occur and a new universe will be created. this process is eternal."...


and at last of all...i want to tell u that... these all theories (given by different scientists) may be proved wrong in futute...coz...no one can say that...this or that theory is completely right,,,, they may change in future.

 

[EL]

This thread seems to be full of confusion.

i could rant for hours on end about this. but i'll put it into a couple lines.

the matter in the universe in not dense enough to at least slow down the universe temporarily. hence, it simply follows the laws of physics, and gets bigger. there's nothing stopping it.

A low matter density does not imply an acceleration, but only that the expansion speed decreases more slowly with time.

As I have read several articles recently about dark matter. Instead of attracting, the dark matter repels. And darkmatter occupy about 85% of all matter, so it accelarate the expanding of the universe.

Dark matter must be attractive in order to explain what it is suppost to explain (dynamics on galactic, cluster, and large scale structure scales.)
The connection between dark matter and dark energy is just something some scientists are hoping for, and is in any way much more complicated then what seems to be the case from the post by pixel01. At the moment I havn't heard of any promising attempts of explaining the cosmic acceleration with the help of a dark matter model.

as far as i know... this expansion of the universe is the result of the big bang explosion.at the beginning , the the explosion occurred & the universe started to xpand from the zero state(ie.infinitely large density n infinitely small volume).till now the universe is xpanding & now the xpansion rate is growing higher and higher...coz..the repulsion force between the elements (ie. stars, planets..etc..) is growing higher. and i should mention here that this repulsion force between them is directly proportional to the distances between them.and now if u r asking the question..."mention the time till when the the universe... will expand..".then i will answer u..."as the universe is xpanding...the density is decreasing...n goinh almost near to 1..when it will reach 1 ,the universe will collapse to a point with an infinite density & after that moment another big bang will occur and a new universe will be created. this process is eternal."...


and at last of all...i want to tell u that... these all theories (given by different scientists) may be proved wrong in futute...coz...no one can say that...this or that theory is completely right,,,, they may change in future.

I think you need to be more clear on what you are trying to say. All I see is a lot of words and incoherent claims (which even one bye one not seem to be correct).

 

[Garth]

enricfemi, an empty universe will expand at a constant rate - the Mine model.

Add matter evenly throughout the universe and the mutual attraction between the particles will affect the curvature of space and the expansion rate and slow it down, the universe will decelerate in its expansion.

Add positive pressure into the universe (a hot gas or radiation field such as the CMB) and counter-intuitively under GR gravitational theory the universe's deceleration will increase.

Add an exotic form of pressure which has a negative pressure (tension) and this effect is reversed, the universe's deceleration would decrease. If the negative pressure were high enough the universe would eventually accelerate in its expansion. For acceleration to happen the total pressure would have to be less than minus one third (in geometric units) of the total density. p < - \frac{1}{3}\rho c^2.

A cosmological constant, \Lambda, acts like a negative pressure with p < - \rho c^2.

Distant SNe Ia are fainter than previously expected, which, if they are standard candles, is interpreted as them being further away than expected because the universe's expansion has accelerated.

Therefore it seems this mysterious negative pressure dominates the universe and it has been given the title Dark Energy.

I hope this helps.

Garth

 

[Chris Hillman]

Dark Energy versus Dark Matter

Hi, pixel101; ditto Cristo: I think you have confused dark energy and dark matter.

Those articles are on space.com about a month or so ago. Even scientists are confused dark matter and dark energy, the two things are linked and influence each other.

Depending on what you mean by "influence each other", this could be wrong.

space.com sometimes has some decent articles, but it also has some very bad ones. As always when surfing the web, be careful to distinguish between authoritative and nonauthoritative sources of information, factor in the PR machinery used by universities to promote their image (often at the expense of truth or at least of balance), and so on.

 

[notknowing]

The cosmological constant, \Lambda, acts like a negative pressure with p < - \rho c^2.

Distant SNe Ia are fainter than previously expected, which, if they are standard candles, is interpreted as them being further away than expected because the universe's expansion has accelerated.

Therefore it seems this mysterious negative pressure dominates the universe and it has been given the title Dark Energy.

I hope this helps.

Garth

I would like to make a remark about making predictions about the consequence of a cosmological constant on the evolution of the universe, as based on the Einstein field equations. If \Lambda is related to quantum fluctuations (as is often assumed), how can we then rely on predictions using the Einstein field equations when we don't have a satisfactory theory for quantum gravity ? Why should the field equations give the correct answer for an entity for which it was never conceived ?

Rudi Van Nieuwenhove

 

[Garth]

I would like to make a remark about making predictions about the consequence of a cosmological constant on the evolution of the universe, as based on the Einstein field equations. If \Lambda is related to quantum fluctuations (as is often assumed), how can we then rely on predictions using the Einstein field equations when we don't have a satisfactory theory for quantum gravity ? Why should the field equations give the correct answer for an entity for which it was never conceived ?

Rudi Van Nieuwenhove

The Cosmological Constant (\Lambda) is a possible component of Einstein's field equation. It serves the function of an integration constant in that its presence does not violate the conservation properties of the Einsteinian tensor with respect to covariant differentiation. It need have no counterpart in quantum physics, it is simply part of how gravity on its own might behave.

\Lambda represents a repulsive force that becomes significant only at large ranges, whereas the normal Newtonian force becomes increasingly significant at shorter ranges. If weak enough \Lambda would be undetectable in the solar system yet dominant at cosmological ranges.

Cosmic acceleration may be evidence of \Lambda having a non-null value.

The zero point energy field, detected only as the weakest of forces, the Casimir force, is something different; although it should behave gravitationally identically to \Lambda and is often confused with it.

Theoretically ZPE is of huge energy density and if it affected gravitational fields it would totally dominate over all else, being OOM 10¹²⁰ times larger than \Lambda.

As you indicate the resolution of this enigma awaits a full quantum gravity theory.

Garth

 

[notknowing]

What about quintessence ?

The Cosmological Constant (\Lambda) is a possible component of Einstein's field equation. It serves the function of an integration constant in that its presence does not violate the conservation properties of the Einsteinian tensor with respect to covariant differentiation. It need have no counterpart in quantum physics, it is simply part of how gravity on its own might behave.

\Lambda represents a repulsive force that becomes significant only at large ranges, whereas the normal Newtonian force becomes increasingly significant at shorter ranges. If weak enough \Lambda would be undetectable in the solar system yet dominant at cosmological ranges.

Cosmic acceleration may be evidence of \Lambda having a non-null value.

The zero point energy field, detected only as the weakest of forces, the Casimir force, is something different; although it should behave gravitationally identically to \Lambda and is often confused with it.

Theoretically ZPE is of huge energy density and if it affected gravitational fields it would totally dominate over all else, being OOM 10¹²⁰ times larger than \Lambda.

As you indicate the resolution of this enigma awaits a full quantum gravity theory.

Garth

I've been reading about quintessence which has the property that it has a spatial and temporal dependence. As you explained before, the cosmological constant is a possible component of Einstein's field equation but it is really a constant, independent of space and time. What I don't understand however is how this can be reconciled with quintessence. Why is there suddenly a new component which is not a real constant and yet compatible with Einstein's field equation? How does this mathematically makes sence?

 

[Garth]

A good question!

One problem with \Lambda is that its energy density is roughly equal to that of matter in the present epoch. Why should this be so as \Lambda is a constant, as you say, and matter-energy density has decreased by a huge factor ~~10⁸⁰ since the Inflation era?

If we look at the Einstein Field Equation:

G_{\mu \nu} = 8\pi G T_{\mu \nu}

\Lambda enters in on the LHS of the equation as part of the G_{\mu \nu} description of the nature of space-time curvature, whereas quintessence, ZPE, etc. etc. would enter in on the RHS of the equation, if they exist.

The differences between these various speculative possibilities is their equation of state, that is, how their energy relates to their pressure.

Cosmic acceleration demands that overall p < -\frac{1}{3} \rho
and if DE is given the equation of state p = - 1\rho, then that fits the data pretty well.

If you move \Lambda across to the RHS of the equation then it also has this equation of state, which also happens to be the equation of state of the false vacuum, ZPE.

Hence either \Lambda or false vacuum is the leading candidate, but that suggestion then has to explain why its density is so small.

As an alternative you can make up whatever equation of state you want for a hypothetical 'quintessence' to make it fit the data, but until you have identified it in the laboratory its just 'pixie dust' IMHO!

Garth

 

[aman malik]

has ether has to do something with dark matter or dark energy??

 

[EL]

has ether has to do something with dark matter or dark energy??

Probably not with dark matter. Depending on what you mean by "aether" it could have something to do with dark energy. Please define what you mean by aether first.

 

[aman malik]

actually it was belived or rather it is believed that the universe is filled of a material known as ether. a spaceship moving in a ether would see a light ray traveling from behind moving at a faster pace.
for further reading read stephen hawkings universe in a nut shell page 3-5
the spelling is ether not aether

 

[jquark]

i refer ether to be an anesthetic and solvent, and aether as a medium for light waves. my preference.

 

[Chronos]

The case for 'aether' was refuted by the michelson-morley experiment. See
http://galileoandeinstein.physics.virginia.edu/lectures/michelson.html

 

[keepitmoving]

hypothetical thought about the dark energy - if the extra dimensions do exist and were compactified during the early high density gravitation of the early universe, could the extra dimensions be decompactifiying into our visible dimensions in the relatively low density gravity universe of today, and that is the extra space that is occurring between galaxies (dark energy)?

 

[keepitmoving]

hypothetical thought - if the extra dimensions are found and they were compactified in the early high density universe and are now decompactifiying into the visible dimensions of our relatively low density universe, could that be the source of the extra space that is occurring (dark energy)?

 

[Hal King]

Actually, whether the universe expansion is accelerating or decelerating -- now or in the past -- is completely model dependent.

The current popular model has been modified to incorporate 'dark energy' -- something made up to make the model better fit the data because it couldn't account for the departure -- i.e. EITHER the data compared to the model made it look like acceleration OR the model didn't work. So the normal cosmology solution was applied. Make up something 'dark' that can't be seen to account for it.

Same process was used for exotic dark matter. The models weren't working so some matter was added to fix it.

hippy dippy cosmologist says: ITS DAAARK ...

 

[Wallace]

Yeah, those cosmologists are idiots. Imagine changing the theory in light of new evidence! That Galileo bloke has a lot to answer for...

 

[Naty1]

Post 27 and 28 above reflect some possibilities and uncertantities in the big bang model.

A recent related thread, https://www.physicsforums.com/showthread.php?t=318568
might be of interest to the original poster, and also my post #7 there which refers to another model, a cyclic model (instead of a one time big bang model) which has incorporated many findings of the last 20 years and eliminates the required fine tuning in the big bang model.

Current expansion and dark energy required further fine tuning of the big bang model...another way to say it is that the original big bang expansion hypothesis has no explanation for the current dark energy...so it had to be "glued on"...doesn't make it wrong, but suggests there are fine points, perhaps major ones, we have not yet understood.

Let's face it, cosmological models (and our understanding) are in their infancy: Not so long ago, about the 1920's?? maybe, it was believed our puny galaxy WAS the universe! ...then we "discover" black holes, which Einstein thought impossible, then dark matter and dark energy, the latter two accounting for perhaps 96% or so of all matter and energy!; next maybe we'll find supermassive black holes by the billions have gobbled up another 5% 10% 50%?? or whatever of original matter and energy...
and just recently Hawking decides information is not really lost forever in black holes when multiverses are considered..."consensus science" on big issues has never been initially right; no reason to expect it would suddenly change now.

 

[Hal King]

All normal for human nature. And cosmologists have to recognize that they are human too.

Its good that people -- as individuals or groups -- support and work on their models of choice.
But one must always remember that 'consensus' is NOT the goal -- the science is.

If full consensus were ever reach, scientific investigation would come to a halt.

It's not going to ever happen -- for there will NEVER be a 'theory of everything'. (see Godel)

I guess my problem is the 'labels' people put on the problems in a model. Such as 'dark matter' or 'dark energy'. Such labels carry mental baggage implying that they are a known commodity of existence. In fact, in both cases they are used to describe collections of problems that have been lumped together. Sometimes the only reason for their groupage is that the problems were enountered in a similar timeframe.

This results in any solution not only having to address one problem -- but many others that may be completely unrelated -- even the 'unrelation' has to be 'proved'.

This system of thinking is slowing progress and diverting efforts.

 

[Wallace]

All normal for human nature. And cosmologists have to recognize that they are human too.

What are you referring to??

But one must always remember that 'consensus' is NOT the goal -- the science is.
If full consensus were ever reach, scientific investigation would come to a halt.

I love this debating tactic (politicians and advertisers use it all the time). State something that everyone agrees on/does in order to (falsely) imply that some other group does. E.g.

"We on our side of politics support freedom and democracy"
"Our clothes are Lead free"
etc etc

The statements above are in the same vein.

I guess my problem is the 'labels' people put on the problems in a model. Such as 'dark matter' or 'dark energy'. Such labels carry mental baggage implying that they are a known commodity of existence. In fact, in both cases they are used to describe collections of problems that have been lumped together. Sometimes the only reason for their groupage is that the problems were enountered in a similar timeframe.

Dark energy and dark matter are different and probably unrelated things. You need to be much more specific in your rantings if you want to make sense. For instance, detail where and why they were introduced. What were they problems that were being addressed by their introduction?

This results in any solution not only having to address one problem -- but many others that may be completely unrelated -- even the 'unrelation' has to be 'proved'.

Again, you need to be specific. It is not at all clear what you are talking about here?

This system of thinking is slowing progress and diverting efforts.

Really? Because progress in cosmology has never happened more rapidly than in the last decade.

What is your alternative? I don't mean what is your alternative theory, but an alternative system for doing cosmology? At present there is a lively and intelligent debate within cosmology about all kinds of interesting ideas. It is a very exciting time to be doing cosmology, precisely because things are changing so fast. The idea that there is a rusted on sets of ideas that are being held irrationally due to the resistance to change is just fanciful.

 

[Hal King]

Afraid it's not.

And I wasn't saying dark matter and dark energy were the same -- if fact just the opposite. Even going so far as saying that the problems people are using dark energy to solve may not be the same in all cases ... LIKEWISE for dark matter.

In fact, I believe your response 'proves' my point.

 

[mark2929]

Dark matter is not understood and like God is used as a fixit for whas unknown What we do know is the universe is expanding faster and the likliest cause is new matter is entering so
1) The big bang is ongoing and creating new matter well time hasnt stopped so it must be.
2) Matter is coming through from another dimension maybe that's what dark matter is? The result of another dimensions black hole coming out this side?
3) We are being pulled towards an outer edge and as we get nearer so its gravity pulls us faster.
4) The equipment for measuring time is faulty or something missed.

 

[Hal King]

Dark matter is not understood and like God is used as a fixit for whas unknown What we do know is the universe is expanding faster and the likliest cause is new matter is entering so
1) The big bang is ongoing and creating new matter well time hasnt stopped so it must be.
2) Matter is coming through from another dimension maybe that's what dark matter is? The result of another dimensions black hole coming out this side?
3) We are being pulled towards an outer edge and as we get nearer so its gravity pulls us faster.
4) The equipment for measuring time is faulty or something missed.

Well, first I do NOT agree that the universe is expanding 'faster'. That is supposition based on a known faulty model (Milne Empty Model is being used as the reference).

1) Not sure that the amount of any new matter 'created' is significant.
2) 'Dark' matter is just normal baryonic matter we can't see. Our estimates for the mass of galaxies
are far too high due to our faulty understanding of 'how gravity works'. Simple calculations
show that when matter starts to 'clump' into a galaxy the amount of matter within one or two
times the currently seen diameter and velocities is much smaller than what is being quoted
for the current mass. Conclusion should be that our model of gravity is wrong -- NOT to invent
more 'dark matter' (that must have come into existence after the galaxy was formed?)
3) As I said our current model of gravity is wrong.
4) I'd rather believe a faulty gravity model than such a problem with time.

 

[Chronos]

Wallace raised a point that has been largely ignored by ATM proponents. The correct theory of the origins and evolution of the universe must wrap its arms around ALL of the good observational evidence. Cherry picking exceptions to promote alternative views is insufficient. The LCDM model did not fall out of the sky. It was methodically crafted from thousands upon thousands of good, independent measurements and observations. Candidate replacement models must undergo the same rigorous process.

 

[Hal King]

Wallace raised a point that has been largely ignored by ATM proponents. The correct theory of the origins and evolution of the universe must wrap its arms around ALL of the good observational evidence. Cherry picking exceptions to promote alternative views is insufficient. The LCDM model did not fall out of the sky. It was methodically crafted from thousands upon thousands of good, independent measurements and observations. Candidate replacement models must undergo the same rigorous process.

So was the Ptolemy solution.

Science isn't about explaining yesterday's answers -- but solving today's problems.
Any new model will still have to address to the old problems too.

 

[goksen]

enricfemi,

A cosmological constant, \Lambda, acts like a negative pressure with p < - \rho c^2.


Garth

In a review on dark energy, it says the continuity equation implies p_\Lambda = - \rho_\Lambda using the Friedmann equations with a cosmological constant. I think it is related to fluid dynamics but don't know much about it. Can you explain how?

 

[Bodicea]

i really know little about this problem and i am searching about dark energy.

But enricfemi, if you can't understand the basics of the expansion then how do you expect to understand the impact of dark energy...never mind dark matter. If I were you I would familiarise myself with the mechanics of the fundamentals first, then move up a notch at a time. If you don't understand the basics then you don't stand a chance when it comes to the new stuff (not being sarcastic just trying to save you a lot of brain drain and grief)

 

[Cryptonic]

I'm not a mathematician and know nothing about hyper-dimensional geometry etc... but I wonder sometimes, IF our universe is truly one with a positive curvature (a "wraparound" universe, or a 4D hypersphere), could our perception of an accelerating 3D expansion actually be a contraction/implosion in 4D? Or no go?

 

[Sourabh N]

On average, our universe is very close to flat.. not with a positive curvature

http://en.wikipedia.org/wiki/Universe"

 

[Slave2myPC]

The universe is expanding and excelerating due to two actions. 1.) The Big Bang caused the first expansion, at which time there was no gravity, as the singularity moved outwards at a rate of speed greater than the speed of light. Dark energy pushed the matter outwards at this incredible speed. 2.) At the moment of the Big Bang, the fabric of space was warped like ripples on a pond when a stone is thrown into it. These great ripples, moving outwards from the singularity, are what the universe is riding on as it expands (much like a surfer on a wave). Dark energy has no speed limit. It overcomes gravity and light speed to the point of controling the fabric of space to expand all matter within it.

 

[Slave2myPC]

Theory Two...Our universe came out of a super massive black hole that reached its own critical mass, or passed its gatherings of matter from one dimension to another. If our universe is estimated to be 13.7 billions years old, it might be that the black hole that our universe came out of had been gobbling up matter for at least that long before reaching critical mass and then disgorging its content in the Big Bang. Excerlerated expansion can be explained by the fact that beyond the edge of our universe, there is no fabric of space. An immense vacuum may exist out beyond the farthest reaches of our universe. The vacuum beyond the edge could be so great that it pulls on and overcomes any force that gravity might have on the matter within our universe. Therefore causing excerlation.

 

[Spekel]

Just a thought.

The universe was created from nothing, just like a black hole. When the big bang happened, time began. Time does not exist in a black hole and it slows down the closer you get, there for as time/space moves futher away it speeds up.

 

[AtrusReNavah]

A low matter density does not imply an acceleration, but only that the expansion speed decreases more slowly with time.

But if there was another factor, say vacuum energy, would it not imply this? If you were to pretend space were expanding into a vacuum, it need not decelerate. Thus as you overcome the forces of gravity, I would expect to begin to see an acceleration. Am I wrong in this thinking?

 

[Naty1]

Some good reading here:

http://arxiv.org/PS_cache/arxiv/pdf/1002/1002.3966v2.pdf

Why all these prejudices against a constant?
Eugenio Bianchi, Carlo Rovelli
Centre de Physique Theorique de Luminy, Case 907, F-13288 Marseille, EU
(Dated: July 15, 2011)

"The expansion of the observed universe appears to be accelerating. A simple explanation of this phenomenon is provided by the non-vanishing of the cosmological constant in the Einstein equations.
Arguments are commonly presented to the effect that this simple explanation is not viable or not sufficient, and therefore we are facing the great mystery" of the nature of a dark energy". We argue that these arguments are unconvincing, or ill-founded...
In gravitational physics there is nothing mysterious in the cosmological constant. At least nothing more mysterious than the Maxwell equations, the Yang-Mills equations, the Dirac equation, or the Standard Model equations. These equations contain constants whose values we are not able to compute from first principles. The cosmological constant is in no sense more of a "mystery" than any other among the numerous constants in our fundamental theories."

 

[Siavosh]

I have a theory about the increased acceleration of the expansion of the universe.
Isn't it possible that there is a minimum-potential-energy-state that the universe is expanding into, but that this minimum-potential-energy-state is limited? This would then mean that this so called minimum-potential-energy-state is a state where the universe has expanded more than the current state (due to the measured acceleration of expansion). Then it would also mean that when expanding past that minimum-potential-energy-state(we are not there yet), the expandiing acceleration would decrease. An assumption then will have to be that the big bang was not really a big bang but more like a compression (followed by a decompression) where one of the maximum-potential-energy-states were reached (maximum compression), where after the decompression(expansion) was followed. Then this would mean that there is a another maximum-potential-energy-state where the expansion is at max (a state which is also limited).
The assumptions that are made are then that the universe is finite and that it is frequently(with a very, very low frequency) expanding and compressing towards maximum-potential-energy-states, which in between a minimum-potential-energy-state exists. This also leads to that the expansion-/compression-acceleration is increasing on the way to the minimum-potential-energy-state which is a more expanded state than the current state. These are some thoughts that I have. Some of the assumptions I made might be proven wrong already. Tell me if this is the case and also feel free to give some thoughts.

 

[goodguy40]

I think it is because there's less stuff to hold everything together! In the deep open space things will move faster less drag less energy and so on! Could also be the slingshot effect from leaving the mass of stuff in our universe!

 

[marcus]

I agree with Naty, that article is a real eye-opener, and it is written in simple direct straightforward style.

Some good reading here:

http://arxiv.org/PS_cache/arxiv/pdf/1002/1002.3966v2.pdf

Why all these prejudices against a constant?
Eugenio Bianchi, Carlo Rovelli
Centre de Physique Theorique de Luminy, Case 907, F-13288 Marseille, EU
(Dated: July 15, 2011)

"The expansion of the observed universe appears to be accelerating. A simple explanation of this phenomenon is provided by the non-vanishing of the cosmological constant in the Einstein equations.
Arguments are commonly presented to the effect that this simple explanation is not viable or not sufficient, and therefore we are facing the great mystery" of the nature of a dark energy". We argue that these arguments are unconvincing, or ill-founded...
In gravitational physics there is nothing mysterious in the cosmological constant. At least nothing more mysterious than the Maxwell equations, the Yang-Mills equations, the Dirac equation, or the Standard Model equations. These equations contain constants whose values we are not able to compute from first principles. The cosmological constant is in no sense more of a "mystery" than any other among the numerous constants in our fundamental theories."

The acceleration is real, but "dark energy" may well be a phony/misleading concept not needed to explain what we observe.
The regular Einstein equation of GR, with its two natural constants (Newton's G and the cosmological curvature constant) seems adequate to explain the acceleration data, and evidence continues to mount that this interpretation of the data is, in fact, correct.

 

[RUTA]

The acceleration is real, but "dark energy" may well be a phony/misleading concept not needed to explain what we observe.
The regular Einstein equation of GR, with its two natural constants (Newton's G and the cosmological curvature constant) seems adequate to explain the acceleration data, and evidence continues to mount that this interpretation of the data is, in fact, correct.

I've been looking into this and generated fits for the Union2 Compilation data using LambdaCDM, Einstein-de Sitter, and some other cosmology models. The data is distance modulus vs redshift. If the data is accurate (still a bit of hedging among observationalists, but it's looking good), then the explanation of that data using currently understood physics is the universe is expanding at an accelerated rate. There were some attempts using conventional physics to explain the data without accelerated expansion, but those loopholes are probably closed or closing fast (otherwise the 2011 Nobel would not have been given for discovering the accelerated expansion of the universe). It looks like new physics will be required to explain the data without accelerated expansion. Thus, in the context of conventional physics, marcus's statement holds.