A really, really, REALLY long-term scenario
Lawrence Krauss says we know more about where the universe came from right now than beings in the far-distant future possibly could.
But first, some great quotes that seem to apply directly to scenario planning, from his book A Universe from Nothing:
"...As a theorist, I feel that speculation is fine, especially if it promotes new avenues for experiment. But I believe in being as conservative as possible when examining real data, perhaps because I reached scientific maturity during a period when so many new and exciting but tentative claims in my own field of particle physics turned out to be spurious."
"...Of course, speculations about the future are notoriously difficult. I am writing this, in fact, while at the World Economic Forum at Davos, Switzerland, which is full of economists who invariably predict the behavior of future markets and revise their predictions when they turn out to be horribly wrong. More generally, I find any predictions of the far future, and even the not-so-far future, of science and technology to be even sketchier than those of the 'dismal science.' Indeed, whenever I'm asked about the near future of science or what the next big breakthrough will be, I always respond that if I knew, I would be working on it right now!"
Now to his prediction about the far far future, which was delivered with the latter caveat that he could be horribly wrong.
There are three evidentiary bases for our knowledge of the origins of the universe, according to Krauss:
- The cosmic microwave background radiation (CMBR) from some 300,000 years after the Big Bang (which took place 13.72 billion years ago), which comes at us from all directions (almost) uniformly, and emanates from the point at which the universe finally cooled down enough so that the roiling primordial plasma of subatomic particles of the initial expansion suddenly coalesced to form hydrogen atoms. (Plasma is opaque, hence we cannot see any farther out/farther back in time than some 300,000 years after the Big Bang.) (For the most recent map of the CMBR, see the New York Times from 3/21/13. The maps on that page massively overstate the actual variation in heat across the universe; if they had been rendered in actual proportion to their variation across the sky, the human eye would not have been able to detect any variation at all.)
- The Hubble Expansion of galaxies outside the Milky Way, which we know about from the Doppler red-shift of light from "standard candles" such as supernovae in those galaxies. Since supernovae explode when they get to a certain exact size and collapse, they are all the same size and brightness; so from their relative dimness we can tell how far away their galaxies are. It turns out that the Doppler "red shift" of their light spectra is directly correlated to how far away they are - in other words, the farther away the galaxies are, the faster they are receding from us. So we can surmise that all of it was once much closer together.
- The "observed agreement between the abundance of light elements - hydrogen, helium, and lithium - we have measured in the universe with the amounts predicted to have been produced during the first few minutes in the history of the universe."
So we have these three things we can see right now that tell us that a Big Bang almost certainly took place.
But "on a timescale of less than a trillion years or so," the cosmic background radiation will no longer be visible, because it will be too weak to penetrate the plasma barrier surrounding our galaxy. The Hubble Expansion will no longer be visible because all other galaxies (aside from the locals like Andromeda, which will have merged with the Milky Way due to local gravitational attraction) will have accelerated away from us so much that they will be receding from us at more than the speed of light.* And the relative abundance of elements in a trillion years will correspond far more to what could be created within ordinary stars (with more emphasis on heavier elements), rather than the relative amounts to be expected from a Big Bang (the lightest elements - hydrogen, helium, lithium - dominant).
Bottom line: Any future civilization that evolves on some planet in the Milky Way in a trillion years will presumably have zero idea of the Big Bang, because none of the evidence for it will exist anymore. They will look out and see no galaxies outside of ours - just empty space. There will be no cosmic background radiation detectable. And the elements will correspond to those to be expected from the burning of stars.
So right now, if Krauss is right, we know more about why we are here than any beings in the far, far distant future could possibly know.
But much good all this unique knowledge will do for us. Because ultimately, in a hundred trillion years, star formation will have ceased. In 10,000,000,000,000,000,000,000,000,000,000,000,000,000 years, all protons and neutrons in the universe may have decayed into sub-subatomic particles, and our galaxy, and all other galaxies, will, due to local gravitational attraction, collapse into black holes, with all the black holes continuing to expand faster and faster away from one another due to the (anti-) gravitational "dark energy" of empty space. Eventually, even the black holes, after 10,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,
000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 years, will have evaporated, expelling some particles and light as they do. And gradually, the energy density of the universe will decline further and further and even the remaining few particles will almost never run into one another... and of course no one will be left to know what special special snowflakes we all were who knew exactly how our universe started all those trillions and trillions of years ago.
...Have a great week, everybody!!!
*Impossible, you say? Not according to Krauss, and the General Theory of Relativity. Because while objects cannot move away from one another faster than the speed of light, the space that those objects inhabit is allowed to move faster than the speed of light... so we're out of luck.