Dark Energy, and why the Universe may change again

Reply Mon 3 Mar, 2003 11:13 am
Assuming our standard models are even close to right, then just as the dimensions folded and the quarks condensed to form baryonic matter so many eons ago, then so may the Universe reach another stage in which matter can no longer exist.


The vast majority of our Universe is composed of a dark energy which we cannot identify. And that energy is accelerating the expansion of the Universe.


The Universe seems to pass through stages. I wonder what, if anything, lived before the stage we exist in. I wonder what will evolve after our stage ends and new Universal rules take over.
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cicerone imposter
Reply Mon 3 Mar, 2003 11:26 am
rosb, These are subjects way beyond my level of comprehension, but I shall bookmark to listen and learn. c.i.
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Reply Wed 5 Mar, 2003 11:31 am
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Reply Wed 5 Mar, 2003 12:43 pm
For decades the problem seemed to be a symmetry or cancellation
mechanism of some sort that would make the cosmological constant precisely zero. The
single greatest failure of our most promising theories (such as string theories) is that they
do not satisfy this requirement. Now that a dark energy has apparently been found, the
problem is even harder: not just to explain why the dark energy is so tiny compared with
what would have been expected theoretically, but also to explain why it happens to be
of the same order of magnitude (roughly twice) as the energy in matter at the present
moment in the history of the universe.

Hmmm, I wasn't able to post on this after I'd quoted... must have been some sort of "dark matter" problem. That quote was from the first of the many, many citations. What an amazing website that is. When I used to share a computer, those photographs came in the email everyday. They are just astounding.

So Rosm.... do you understand this and can explain more? Are you a physicist?
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Reply Thu 6 Mar, 2003 12:42 pm

"Observations of distant supernova have suggested for a few years that dark energy dominates the universe, and our finding provides independent evidence that the universe is dominated by this type of energy we do not understand."

The researchers came to this conclusion as they were refining their calculations for the age of globular clusters, which are groups of about 100,000 or more stars found in the outskirts of the Milky Way, our galaxy. Because this age (about 12 billion years old) is inconsistent with the expansion age for a flat universe (only about 9 billion years old), Krauss and Chaboyer came to the conclusion that the universe is expanding more quickly now than it did in the past.

The only explanation, according to Chaboyer and Krauss, for an accelerating universe is that the energy content of a vacuum is non-zero with a negative pressure, in other words, dark energy. This negative pressure of the vacuum grows in importance as the universe expands and causes the expansion to accelerate.

When I first heard that the universe was expanding at an accelerated rate, it gave me the oddest feeling. How can humans have any stability when the universe itself is "shifting sands"?
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