lucas_ said:
Theoretically how many billions of years after the Big Bang when life could theoretically exist in any star system?
Nobody can say for sure. But it probably can't. At a very fundamental level, life requires heavier elements than just hydrogen and helium (because life requires complex chemistry, and hydrogen and helium can't produce anything more complicated than ##H_2##), and temperatures low enough for matter solids/liquids to exist (gases and plasmas are too chaotic for stable structures). And there's no guarantee that such heavy elements will ever exist outside of the stars themselves in every solar system.
If you want to know how long it will take until every solar system that might ever result in life will, then that number is probably close to the time it takes for star formation to cease, which occurs sometime around 1-100 trillion years from now (per
this Wikipedia article).
lucas_ said:
I am thinking how old they are now. And how big the accelerator they had built to probe the Planck scale. Couldn't very advanced civilization created solar system size accelerators for instance? How can these be detected if they don't give of light and don't orbit around the sun?
It's highly unlikely that it's possible to produce a pocket universe in a particle accelerator. At least, not one that can ever be probed. The reason for this is the detection of ultra high-energy cosmic rays which impact atoms in our atmosphere at in excess of ##10^{20}##eV, which is tens of millions of times the energies probed in current particle accelerators (see
here)
Thus if a measurable "universe" can be created by high-energy particle collisions that are remotely measurable, it would already be happening in our atmosphere as these ultra high-energy particles impact it. Creation of particle accelerators which allow for substantially higher energies are likely impossible. But we'd never be able to know even if it was possible at higher energies even if such accelerators were possible: either there would be (most likely) no measurable consequences, or it'd destroy the universe.
There are two general ways in which such a universe would be produced. If its vacuum energy was higher than the vacuum energy in our universe, then it would present as a microscopic black hole that is created and instantly evaporates. As I understand it, it is plausible that such pocket universes could continue to exist, but they would forever be disconnected from our universe. If we ever did measure such a microscopic black hole, we'd never have any way of knowing whether it initiated a new universe or not (barring some as-yet-unknown discovery which allows that experimental determination: it's hard to say for sure that it will always be impossible, but it probably is). This concept is related to the idea of Lee Smolin's
fecund universe. This idea is probably impossible to verify experimentally.
The other option is if the new universe has a lower vacuum energy than ours. In that case it would start to expand rapidly, with the boundary between our universe and the new one reaching near the speed of light within about a second. It would result in the complete destruction of everything within the future horizon of the event (meaning all galaxies for tens of billions of light years).
Such events, though theoretically possible, must be incredibly rare or else our universe would not have lasted as long as it has. The plausibility of this means that it's probably a bad idea to attempt to probe energies above those of ultra high-energy cosmic rays, even if the technology to do so does exist sometime in the future. This process is known as
Vacuum decay, and would be plausible if our universe was in a false vacuum state and the interaction energy was greater than the amount required to efficiently access other vacuum states (likely somewhere between the Planck scale and the GUT scale, i.e. ##10^{25}##eV to ##10^{28}##eV).
