Why the universe is expanding faster and faster

[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.