Inspired by the “By the time Earth is doomed, would there be any life sustaining planets left?” thread by CrazyChop.
According to a Discovery Channel special on the universe, two leading hypothesizes about the fate of the universe is either:
a) the universe expands, expands, and expands for billions of years and then snaps back on itself and the universe will shrink and shrink, to a size around the pre-big bang size, obviously killing all life
or
b) the universe will continue expanding for countless billions of years until everything becomes so far apart that atoms separate and expand away from each other, then quarks separate and expand away from each other, obviously killing all life.
My question is that if either of these two hypothesizes are correct, is life in this universe inevitably doomed? Are there other hypothesizes that this Discovery Channel show did not mention that are less tragic for all of life?
As expansion proceeds it probably won’t be able to overcome the gravity of close objects, let alone the nuclear forces. This means that while distant galaxy clusters may recede out of our light cone, the Local Group will probably hang together.
There’s some theorizing that as the stars use up their hydrogen and go out, life may be able to endure on the thin trickle of Hawking radiation that escapes from black holes. It would exist at just a few fractions of a degree above absolute zero and would think and move very, very slowly, but it would still be capable of reproduction and cognition.
The physicists of that far future age will probably be firmly convinced that life was impossible during the highly energetic early moments of the universe when huge balls of fusing hydrogen dominated space … .
Something I don’t get about this line of reasoning: If the separation of atoms is all it takes to destroy life, does that mean that life is nothing more than a particular arrangement of atoms? If that’s the case, how could life be *destroyed *any more than a rock could (as opposed to merely rearranged)?
…or is that getting too philosophical for this thread?
Because atoms themselves are not alive. Once the arrangement of atoms that allows life is destroyed then the life itself is destroyed, even though the atoms remain. The arrangement is the life, so to speak.
I must say that once I learned my personal life was inevitably doomed, I lost a great deal of interest in the larger question for all life. I suppose there is a sense that the general notion of life in general is somehow more significant than the life of a particular individual. I’m not quite sure why. Why is the existence of life a more important consideration than say, the formation of a new galaxy, or a rainbow, or whatever? Is it because of the way those announcers pronounce sentences like “**life **is renewed again” in those documentaries?
Until we figure out a different timeline for the universe, life is doomed. But worrying about it reminds of the woman in a physicist’s lecture who suddenly exclaimed, “Oh! Did you say five billion years til the sun burns out and the earth dies? Thank goodness! I thought you said five million.”
A possible ‘way out’-scenario is what Tipler calls the Omega Point: in a certain Big Crunch scenario, as the universe approaches collapse, its computational capacity rises exponentially faster than the time runs out; a computer taking advantage of this capacity could thus, in theory, complete infinitely many operations, and consciousnesses downloaded into this computer would thus live forever, though the existence of the computer itself would be finite with the universe. Tipler also argues that this infinite capacity implies that every possible simulation will happen, including a simulation of you, which would mean a ‘resurrection’ of sorts at the end of time.
It seems to me that if there is some process which got us all this free energy in the first place, then perhaps that same process can be used by our hypothetical descendants down the road.
The classic discussion of the issue was in a set of 1978 lectures “Time Without End: Physics and Biology in an Open Universe” by Freeman Dyson, published in 1979 and which are online. Then Dyson took the optimistic view of life’s survival prospects, at least in an open universe. Temperatures would fall, energy would become scarce and everything would slow down, but he was prepared to toy with the prospect of life adapting to these conditions and continuing indefinately.
For a closed universe, Dyson saw nothing surviving through to the late stages of the collapse. But, ever the optimist:
The topology of the universe? Can we change it, …
However, there’s been a crucial twist to our understanding of the expansion since 1979 and it’s a major fly in the ointment. The expansion appears to be accelerating, an effect attributed to the mysterious “dark energy”. This might lead the universe into a Big Rip, whereby everything ends in about 50 billion years.
Even if that’s avoided, there’s the prospect that the acceleration makes everything colder and thinner too fast for the sort of survival schemes that Dyson was envisaging in 1979 to work. Even before the Big Rip was proposed, he had become pessimistic - see this 2002 NYT article where he’s one of the experts inverviewed on the topic.
It should be noted here that the Big Rip is a real theory being seriously considered by physicists, but it’s still speculative. In the simplest models, everything on the scale of galaxy clusters or smaller still holds together, it just gets really boring after a while.
To elaborate further: There’s a parameter describing the dark energy called alpha, which appears to have a value very close to -1. If it’s exactly -1, then the dark energy takes the form of the cosmological constant hypothesized by Einstein, the simplest case. If it’s between -1 and zero, then we have what’s called quintessence, which is a sort of dark energy which effectively gets weaker with time. There are a few theoretical models which predict that what we have ought to actually be quintessence. If it’s less than -1 (i.e., more negative), then we have what’s called phantom energy, which would eventually lead to the Big Rip. We understand very little about dark energy, but in the context of what we do know, it’s a lot harder to come up with a theoretical prediction of phantom energy than it is for cosmological constant or quintessence. Observationally, the best fit to the data thus far shows a value of alpha that’s less than -1 (i.e., supporting phantom energy), but only slightly: -1 exactly is still well within the error bars. So all three models are consistent with the data, and so the simplest one (cosmological constant) is preferred.