Thursday, November 16, 2006

Hubble Finds Evidence for Dark Energy in the Young Universe

NASA's Hubble Finds Evidence for Dark Energy in the Young Universe
Scientists using NASA's Hubble Space Telescope have discovered that dark energy is not a new constituent of space, but rather has been present for most of the universe's history. Dark energy is a mysterious repulsive force that causes the universe to expand at an increasing rate.

Investigators used Hubble to find that dark energy was already boosting the expansion rate of the universe as long as nine billion years ago. This picture of dark energy is consistent with Albert Einstein's prediction of nearly a century ago that a repulsive form of gravity emanates from empty space.

So, that's the big cosmology news for today. It's very closely releated to what's discussed in the Beyond Einstein article of a couple of days ago.

Actually, in a way, it's kind of boring, since the findings are pretty much what "conventional wisdom" (of the last 6 or 7 years) has expected. No apple carts have been upset as a result of this. But further confirmataion of accepted theories is in its own way very important too.

The take-away is that NASA now has even better justification for the JDEM kind of mission to obtain better supernovae data in order to put tighter limits on the w parameter in the "equation of state" for dark energy.

I've written a lot about this stuff before in much more detail here, but perhaps I'll revisit that to highlight the most important ideas as they relate to the present news.

There are some presentation materials here from today's NASA press conference.

Tags: , cosmology

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6 Comments:

Blogger L. Riofrio said...

Evidence for DE still looks shaky. However, there is the discovery that firefly luminosity is constant.

11/20/2006 02:39:00 PM  
Blogger Charles Daney said...

Evidence for DE still looks shaky.

I don't see where it's so shaky. This graph shows a decent fit with acceleration following deceleration at z=1.5. Just as predicted for Λ≠0 and w=-1.

Charles

11/21/2006 01:09:00 AM  
Blogger L. Riofrio said...

The only evidence of cosmic acceleration is redshifts. This graph charts redshifts logarithmically. The thick black prediction line matches the data precisely, without any artificial "dark energy" parameter.

11/22/2006 06:25:00 PM  
Blogger Charles Daney said...

Louise,

Your link doesn't work, but I think you meant this one.

That only goes as far as z=1, unlike the new Hubble results that have 13 examples with z>1.

My question for you is this: Does your theory fit a curve like what Riess et al give with their data, using -1.2 < w < -.8 (p. 63 of their arXiv paper, astro-ph/0611572).

If your theory fits such a curve, it would make the same predictions as FRW with dark energy. In that case, I have to ask whether there's any data that could distinguish between your theory and dark energy.

In particular, does your theory predict the deceleration that the Hubble data shows at z>1?

Charles

11/23/2006 01:13:00 AM  
Blogger L. Riofrio said...

Charles, thanks for finding that. (I left out "-")

The new data has not been added to the graph yet, but quick calculation shows that new supernovae also fit Theory's prediction. At z>1 Theory predicts a decelerating curve.

Corroborating data may come from comparing Earth's geological record with the "faint young sun." There are additional indicators from the LLRE and discovery of massive primordial Black Holes. More work still needed.

11/23/2006 11:16:00 AM  
Blogger Charles Daney said...

Louise,

What does your theory predict as the amount of time since the big bang? If c has been decreasing, this should be less than the prediction of FRW with Λ=0, shouldn't it?

Charles

11/25/2006 10:58:00 AM  

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