CrazyNeutrino said:
the universe is 13 billion Years old
the universe will last a quite a few more billion years
what if we are the first?
how old will the universe get before it cannot support life on a planet
> Astronomers unfazed by theory aliens could already be extinct
Not surprised, it’s part of the Drake Equation.
> what if we are the first?
There has to be a first, even in an infinite universe. We certainly could be the first. Also, because of relativity, we may be the first within the visible horizon without being the first overall.
> the universe is 13 billion Years old. How old will the universe get before it cannot support life on a planet?
So far as I can tell, there’s no limit.
Part of the answer depends on whether the proton can decay. The proton can’t have a half life of less than 10^34 years (as compared to 13 billion years which is only 1.3*10^10) and may have a half life that is considerably longer. If a proton happens to have a half life of only 10^34 years then a planet will have shrunk to the size of a comet by 2.5*10^35 years.
If protons don’t decay then atoms lighter than Zr (40) inclusive are forever. A hydrogen atom will remain available as a nuclear fuel for ever. Atoms heavier than Zr may eventually decay by spontaneous fission, but that’s of minor importance here.
So the real issue then on how long a planet can support life comes down to what the minimum energy usage a lifeform is.capable of. Again there seems to be no lower limit for lifeforms such as bacteria. They can survive in suspended animation for an unlimited length of time. When it comes to multicellular eukaryotes things are less certain. Of plants, Verbascum blattaria seeds can survive for extended periods (more than 120 years) with no detectable energy usage.
Another limit might be evaporation, but if that’s the case then the resulting gases can later coalesce to form a new planet in a cyclic manner. It also means that as smaller planets evaporate, the resulting gases would make larger planets grow, at least for a while. How fast planets evaporate ought to be calculable.
Another time-unlimited fuel source is white dwarf stars. If atoms are forever then white dwarf stars are also forever. Any future civilization may be able to get white dwarfs to got Type 1a supernova at extremely long times in the future by adding mass to it, either mass evaporated from smaller objects or mass in the form of collisions. How often do white dwarf stars collide? That would be an interesting calculation.
As for red dwarf stars, like planets and white dwarfs they survive for an exceptionally long period of time containing usable fuel. As time progresses, the distinctions between planets, brown dwarfs, red dwarfs and white dwarfs become less distinct.
