There's something unbearably poignant about scientific discoveries that delineate the limitations of science. Dennis Overbye explains:
Our successors, whoever and wherever they are, may have no way of finding out about the Big Bang and the expanding universe, according to one of the more depressing scientific papers I have ever read.
If things keep going the way they are, Lawrence Krauss of Case Western Reserve University and Robert J. Scherrer of Vanderbilt University calculate, in 100 billion years the only galaxies left visible in the sky will be the half-dozen or so bound together gravitationally into what is known as the Local Group, which is not expanding and in fact will probably merge into one starry ball.
Unable to see any galaxies flying away, those astronomers will not know the universe is expanding and will think instead that they are back in the static island universe of Einstein. As the authors, who are physicists, write in a paper to be published in The Journal of Relativity and Gravitation, "observers in our 'island universe' will be fundamentally incapable of determining the true nature of the universe."
This is like the cosmological version of Heisenberg's infamous uncertainty theorem. In both cases, we get glimpses of our ignorance, fleeting snapshots of our limited epistemic perspective. The universe wasn't designed to be understood. We understand reality in spite of reality. Physicists of the (distant) future won't be able to see beyond our Local Group of galaxies. What can't we see?
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Hrmm, is the universe still going to exist in 100 billion years? Also, doesn't it imply that the only way to judge our universes expansion is via galaxies, in 100 billion years there might be other phenomenon that can be observed?
What can't we see? That is a beautiful and excellent question.
We are equipped to navigate our own local world of rivers and streams, and rocky hills, and meadows, and forests, so that we can find a little food, and make shelters for ourselves. But, it turns out, we have an intelligence that has overcompensated a little, and we can envision a little beyond the local world in which we dwell, the true nature of the ground on which we walk, not as a flat world, as it would seem, but as a spherical world, one, among the many other planets, and stars.
We can evision the reality of many things that are not readily apparent, and infer with a high degree certainty that our scientific speculations on many things are true.
Yet, what can't we see? I am sure there are physical phenomena beyond the extension of any of our senses or imagination, to which access is forbidden. On these things, even speculation, is by definiton, impossible.
Realizing this is a big to deal, at least, it is to me. Once I thought that I knew so much, and was so smart. But now I know, that I definitely, am not.
It isn't a secret that our observations are affected by our technology and theories, as well as feasibility limits. Boltzmann Brains prevents us from claiming guaranteed certainty that we really observe nature as it is, for example.
But while I haven't read Krauss and Scherrer's paper, I doubt the picture is quite as bleak as they perhaps want to paint it. Einsteins static universe is a contrived ad hoc solution.
What's not to understand?
That all we pursue recedes beyond our questions?
That all that is, has been or will be can perish?
That our only chance to learn what we need to learn is always now?
Last I heard the Universe was some 13 billion years old, give or take a couple of billion. And our sun is about 5 billion years old.
If it's only taken us 5 billion years to get to the scientific level we are at it seems to me there may be human like consciousness, out at the "edge" of our universe, that has 8 billion years on us.
Maybe in our distant future those lonely scientists looking out into that great nothingness will see galaxies coming toward them...the result of those advanced beings efforts to maintain a universe to live in.
One thing to think about is that we use galaxies to see the expansion of the universe (as I understand it) because it is so easy. Perhaps with no galaxies there is another underlying way to prove the expansion of the universe that we haven't really put any time into because we already have this excellent method. It seems to me that billions of years ago you could probably have made a similar argument using some obvious indicator of the expansion of the universe that doesn't exist today.
Clearly I have no evidence for this, but I feel optimistic that science, while possibly slow sometimes, finds a way, I hope I'm not wrong.
In my comment above, I said the question "what can't we see?" is a beautiful and excellent question. I think it apealed to me very much, because it has tapped into my own recent thinking, about the fundamental limitations of our human abilities ever to acquire anything but a superficial and speculative understanding of the universe. I do not think this question is bleak or sad.
The question arises thus:
That we can envision, a future world, similar to our own, inhabited by people similar to ourselves, who will not be able to perceive or understand aspects of the universe which we do perceive and understand; and that if we can envision such other people who cannot know things which we do know, then maybe the same could be true of us, that there are aspects of the universe which could be knowable to others, but not to us. I am sure the answer is yes.
The overriding problem in discussing the fate of the universe is that we lack sufficient understanding of its very nature. While no one can predict when the next breakthrough in our comprehension of the physical world will occur, it will surely render much of the current speculation moot. We will look back on the present discussion with some amusement, in the same way as we now view some ancient notions of our place in the universe.
It seems that confronting the limitations of our species, or indeed of any possible species, even off at incredible distances in time, is something that fills us with incredible fear and dread.
Yet, as numerous commentators have indicated, we all live -- indeed, have always lived -- with the immutable fact that much of the universe, and of "the nature of ultimate reality", if that phrase is even meaningful, is necessarily completely beyond the horizon of the knowable. This is a given based on the nature of human consciousness.
Our lives are enveloped in impenetrable mystery. It is fundamental to the nature of being human. The fact is, that we know practically nothing of the world as it is in itself. This awareness may fill us with an overwhelming sense of vertigo, but there it is. What choice have we got but to live with this as courageously as we can? To learn all that we can, as thoroughly as we can, certainly. Nonetheless, ultimately, we have to accept our humanity and our finitude.
I think it's hubristic to think that in 100 billion years our slim concept of the universe will be sorely missed. What can't we see? We can hardly see ourselves for what we are, let alone the universe. It makes me think of Terence McKenna's observation: "When you consider this model of exploding galaxies, colliding quasars, and mega this and mega that, it's worth noting that these distant parts of the universe register only as faint tracings on our instruments, . . . And where is our data sample coming from? Radio telescopes . . . All the energy that has fallen on all the radio telescopes on this planet since the invention of radio telescopy is less energy than would be generated by a cigarette ash falling a distance of two feet. It's pretty flimsy stuff folks . . ."