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michel123456, on 23 May 2012 - 05:12 PM, said:

Hmmm. Interesting. Recent observations say the expansion of space is accelerating. No one knows what is causing the expansion to speed up -- its been given the name dark energy. If we assume this mysterious dark energy stays the same over time (a big assumption since we don't know what it is) and we assume the universe will exist for an infinite amount of time, then I guess this says the expansion of the univere will reach an infinite rate.

Have I missed something here? Comments?

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wucko, on 9 May 2012 - 11:17 PM, said:

There is no need to reconcile. Special relativity says nothing (no information) can travel faster than the speed of light through space. General relativity says there is no limit to how fast space itself can expand.

space noob, on 15 May 2012 - 10:56 PM, said:

Dark flow? Your words sent me on a google search. I found an article on testing with supernovas that seems to say this dark flow theory isn't right.

http://arstechnica.c...k-flow-mystery/

So I think dark matter and dark energy are still the favored theories of current mainstream physics.

Comments?

Ya, the "laws" of physics are time-symmetric -- they do not show a direction of time. But the 2nd law of thermodynamics is a different kind of law. It is a deduction based on probability. This is because the odds of a number of constituents being highly ordered gets dramatically lower as the number gets larger.

For example, if you have three cards -- Ace, two, three -and you shuffle them, the odds of drawing them in order are one in six. (3! = 3x2x1) But if you have four cards -- Ace, two, three, four, the odds of drawing them in order grows to 24 (4! = 4x3x2x1). With 10 cards, its 3,628,800. The odds very quickly become astronomical.

So the increase in entropy or disorder we see as a indicating an arrow of time is just a probability-based argument, due to the very large number of constituents in the macro world. It is not a physical "law" in the same sense as other physical laws.

I don't think there is anything new in these arguments.So I think the "possible solution" to the "paradox" is interesting but nothing new.

timo, on 14 May 2012 - 08:55 PM, said:

Ya but no one knows what is causing the acceleration of the expansion of the universe. The most popular theory is the vacuum of space itself is somehow producing this outward push. And physicists model this mysterious "dark energy" by adding a cosmological constant to the right side of Einstein's field equations of general relativity.

Or maybe its Einstein's general relativity itself which is wrong at cosmic distances? Maybe there is some fifth force or other idea which accounts for the acceleration of the expansion.

I've heard these arguments for a number of years now. The link I gave is the first actual test I have come across which examines this question. And the test results tend to support general relativity. They point to this vacuum energy as the cause. I think this is a very big deal. And not at all boring.