Does Dark Energy Exist?

[Bikewer]

Scientific American's cover article this month posits an idea that may bypass the perplexing notion of dark energy:

http://www.sciam.com/article.cfm?id=does-dark-energy-exist

Dark energy being hypothesized as an explanation for the acceleration of the universe's expansion, as a result of the observation that distant supernovae are further red-shifted than they should be...

As I understand this idea (and I'm no cosmologist...) the idea is that this extra red-shift might be the result of an unevenly expanding universe, wherein observations from an area of relative "void" into a denser area might appear to be the result of acceleration.

Instead of the "expanding baloon" model, think of a balloon with a number of weak areas that bulge out more...
No real evidence, according to the article, but some experiments are being planned .

 

[arthwollipot]

I've seen an analysis that suggests that dark energy may be an artefact of the fact that we are observing from within a galaxy - ie, a large concentration of mass, and therefore gravity, and therefore our flow of time is out of sync with the flow of time in the intergalactic voids where there is a lot less matter and a lot less time dilation.

ETA: Wow. I'm sure I could have said that better, but it's late and I have to be up early in the morning...

 

[aggle-rithm]

Is it at all possible that gravity is like the "electro-weak" force, which attracts protons to each other when they are really, really close together, but repels them when there is any distance between them? If there was an analogue with gravity, then the attraction between two massive bodies might turn into a repulsion if they are far enough away.

Not too likely, I guess, since the attraction between two particles caused by the weak nuclear force doesn't act much like the attraction caused by gravity.

Never mind. Return to your previous discussion.

ETA: You know, I really need to start thinking these things through before I post.

 

[sol invictus]

Such things are possible. However, they require that the earth is at the center of a nearly perfectly spherically symmetric void.

One can understand the reason pretty simply. We know from observation that the universe is very close to perfectly isotropic (i.e. it looks the same in all directions). There are two possible reasons for that:

1) the universe is isotropic viewed from any point, so there's nothing special about us, or our location, or

2) we are literally at the center of the universe. If we were anywhere else, we'd see something very anisotropic, but since we're at the center of a spherically symmetric universe, things look isotropic.

Starting from 2) one might be able to explain dark energy by a void (although I suspect even then there will be problems from large scale structure). But you can take your pick which of those two options you think is more reasonable.

 

[aggle-rithm]

Starting from 2) one might be able to explain dark energy by a void (although I suspect even then there will be problems from large scale structure). But you can take your pick which of those two options you think is more reasonable.

What about the recursive turtles theory? That's pretty reasonable.

I mean, we KNOW there are turtles, we DON'T know there is dark energy.

 

[roger]

I'm currently reading Warped Passages by Lisa Randall. There she advances the idea that dark matter could just be matter that is in the extra dimensions, since gravity can work across these dimensions. Is this still an accepted hypothesis? I'm not exactly a fan of string theory, but then I'm not exactly educated in it to a level where any reasonable person would lend any weight to my opinion.

 

[Cuddles]

As Sol says, the problem with ideas like this is that they require abandoning the Cosmological Principle. Once you leave that behind and say that the Earth is actually in a special position, you can come up with all kinds of ideas that could fit obvservations from Earth but have no way of being tested properly since we can't actually travel anywhere else.

I'm currently reading Warped Passages by Lisa Randall. There she advances the idea that dark matter could just be matter that is in the extra dimensions, since gravity can work across these dimensions. Is this still an accepted hypothesis? I'm not exactly a fan of string theory, but then I'm not exactly educated in it to a level where any reasonable person would lend any weight to my opinion.

Well, to start with dark matter and dark energy are completely separate things that are connected only by the presence of the word "dark", so that really belongs in a different thread. That said, the big problem with claims like that is that there's exactly no evidence for them. We don't know that there are any more dimensions, we have absolutely no idea if parallel universes could exist if there are (and many theories that propose that sort of thing explicitly say that it is impossible to ever find out), and we have no idea if gravity would actually behave any differently than the other forces if those things turn out to be true.