Anti-Matter Concerns

[Gatekeeper]

This has been a most informative, if somewhat over my head, kind of thread.

[KrazyHorse]

Originally posted by Seeker
"Future measurements of supernovae, gravitational lensing and
clusters of galaxies from a Large Synoptic Survey Telescope, LSST, and the Joint Dark Energy Mission,
JDEM, will reveal definitively whether dark energy behaves like Einstein’s cosmological constant or
like some new substance that changes with time as the universe evolves."

Now I'm going to piss you off by quoiting a popular magazine...to me these experiments seem to indicate doubt that the universe will be fundamentally the same forever, especially if 'dark energy' changes (drastically) over time, say reversing

a) My thesis advisor is co-chair of the JDEM science definition team (the guys that wrote up the initial reccommendations for what to look for in the mission proposals)

b) Right now the best explanation for dark energy is that it's vacuum energy, i.e. it doesn't change over time. There's no evidence of it changing over time. Nevertheless, we're going to see if we can find any evidence of it changing over time because our best answer is just a guess

c) It is, of course, theoretically possible to construct a model of dark energy which would do some ridiculous stuff. But whacko theories are whacko theories until they have some evidence

Like I said, I freely admit that we don't know everything. There are an infinite number of ways all of our theories could fail that we haven't seen yet. But until I see evidence of them failing, I tend to accept them and their conclusions, with a mental reservation that nothing is certain.

[Seeker]

Well I suppose I will end this by saying I guess I'm just much more cautious than you are.

[KrazyHorse]

I don't understand.

I'm saying that you're right. Things could be weirder than we think. I've always accepted that.

My only problem was with the logic you were presenting for why things could be weirder than we think. The failure of current physical theories in the early Universe is not, so far as I can see, related to failures which might crop up in the late universe.

[Ben Kenobi]

That seems naive to me...on the time scale I'm talking about I'm assuming the evapouration of all black holes and the decay of all normal particles. To recreate the conditions of the early universe all space/time would have to be reduced to an unknowably small point, not merely some matter stuck in some gravity well.

So thinking a bit further ahead, eh?

You are right that eventually the black holes themselves will decay, but that's a quite different state then the early stages of the universe which are thought to be very energy dense. The situation you describe is quite the opposite, energy very diffuse and spread out throughout the universe.

[Seeker]

"The situation you describe is quite the opposite, energy very diffuse and spread out throughout the universe."

my whole point is wondering does this particular situation last forever, like so many seem to assume it does, or is there a possibility of some random event or process similar to the event or process which created the universe in order to cause a new collapse/expansion phase.

All these possible processes are speculative, I've already mentioned dark energy 'reversal', but other candidates include a so-called "false vacuum". There may be a possiblity involving something called a 'scalar field' which seems similar to a false vacuum but I don't understand it and it may be a product of fringe science.

This is called the 'Oscillating Universe' (google search, see also Big bang/Big Crunch) theory by some, it makes sense to me as a theory of causation for the universe, connecting the end to the beginning. And, to sum up everything, if the oscillating universe theory is correct then it seems like an exception to entropy.

[Ben Kenobi]

Oscillating theory is a real waste of time in my opinion. There seem to be two much more plausible models that would be superior options.

An open universe that just expands, or a closed universe where the expansion slows, halts and then everything rushes together.

The problem with the oscillating theory is that it has to show why the expansion of the universe should slow, and how we go from having everything inside one supermassive black hole to some form of expansion again.

My question is why do we need an oscillating universe? Why are the two other options listed unsatisfactory? I think I know the reason behind it, and it's because none of the cosmologists who back the oscillating universe like the conclusion that the Universe has a definitive beginning.

[Seeker]

"An open universe that just expands"

since that is where the evidence seems to point, that is what I believe.

HOWEVER, I also believe that an 'open' universe does not preclude one of the previously mentioned random processes from occuring....

..nor does it prevent such a random fluctuation from occuring at any time! It's just cosmically unlikely, which is why I talk about infinite periods of time.

Re: my possible motives: lol, don't try to squeeze Odin into that gap...an oscillating universe doesn't answer any religious question about why is there an oscillating universe in the first place, or a anything like that, it's purely speculation but it is also purely physical speculation, not metaphysics.

I don't like connecting metaphysics with physics.

[Seeker]

http://www.world-science.net/othernews/060514_bouncefrm.htm

The findings appear in the current issue of the research journal Physical Review Letters.

same thing from a less poppy source to ameliorate the foes of such mags as 'Discovery' and 'Scientific American'...

[Flip McWho]

This has been a most informative, if somewhat over my head, kind of thread.

Yeah very interesting.

[Vince278]

Lets not forget to take other dimensions into account. We can decrease entropy here if the deficit is made up in one or more of the hidden dimensions believed to exist. (My Multidimensional Law of Conservation )