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Dark Energy

  
 
Quantum
12:33 / 14.07.06
Until the mid-1990s most cosmologists believed that gravity, created by ordinary matter and invisible dark matter, sculpted the Universe. Then, exploding stars in deep space hinted that a cosmic force was driving the Universe apart. Astronomers dubbed this force dark energy.

So it's only since 2003 dark energy has been 'unassailable', it's cutting edge stuff. The 2005 Lambda Cold Dark Matter model is the simplest known model that is in general agreement with observed phenomena but "ΛCDM says nothing about the fundamental physical origin of dark matter, dark energy and the nearly scale-invariant spectrum of primordial curvature perturbations: in that sense, it is merely a useful parameterization of ignorance."

The universe is not only expanding but the expansion is accelerating. So what is this 'Dark Energy'?

What is Dark Energy? As yet, no scientist can give the answer to this fundamental question. We do not know what the nature of dark energy is, and unveiling this mystery will most probably reveal new physics and even might shake modern particle physics to its very foundations.

Interesting article, quite short but has excellent pictures and technical detail. The wikipedia Dark Energy page is good of course and what really fascinates me is the two theories of what dark energy is- the cosmological constant and quintessence (more on those in a later post though). One upshot of which one is right is the Big Rip hypothesis, the possibility that the univeverse will eventually tear itself apart.
The actual math and physics equations are beyond my meagre understanding (too many Greek letters and logarithmic functions) but the theory is pretty accessable, and has changed cosmology.
Whaddaya reckon? Will Dark Energy kill us all? What is it?

(One thing I love about this subject is the language used, I mean, the only other place you'd be discussing "phantom energy, a more extreme form of quintessence" is the Temple or a roleplaying forum.)
 
 
Henningjohnathan
15:02 / 14.07.06
I asked a WMAP scientist about this and here is the response (not as detailed as I'd like):

John,

The universe of 4-dimensional spacetime doesn't have an edge or a center.
It's geometry is described by the equations of General Relativity. A
'dark energy' term appears in the equations and was called by Einstein the
Cosmological Constant. He originally proposed that it was just strong
enough to balance gravity on the largest scales, producing a static
universe. When Hubble showed the universe was far from static most
cosmologists assumed the term was negligibly small, but observations of
accelerating expansion can be explained by a very small, but non-negligible
value.

I had thought that "dark energy" was "something" like regular energy or matter, and that made it sound like a new version of the "Aether" that was dispelled prior to relativity. Now it sounds like it is more a component of "space-time" or "empty space" and, as pointed out above, general relativity describes it.

It is strange to think that the universe is "repelling" itself.
 
 
grant
17:57 / 14.07.06
I'm reading the articles, and I'm wondering -- does ordinary energy affect space itself? I know gravity (in some models) does.

Oh, and I'm quite fond of the following phraseology:

Moreover, ΛCDM says nothing about the fundamental physical origin of dark matter, dark energy and the nearly scale-invariant spectrum of primordial curvature perturbations: in that sense, it is merely a useful parameterization of ignorance.
 
 
Henningjohnathan
18:07 / 14.07.06
Yes, that last bit makes me think that this must be some quality inherent to space-time (like the warping of gravity) that we don't understand rather than "stuff" in the sense of matter or energy.
 
  
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