We are the only life form of the univers. Not even the only intelligent, but the only one. My arguments are:
Life is absolutely everywhere on earth. There is not a single isolated island or deep trench in the ocean that is not covered by life. If life can live elsewhere, univers would be covered by life. Some bacteria would have been ejected into space by some cataclysme and had colinized nearby planets. Kind of Fermi’s paradoxes.
Antropic argument. Our universe is suitable for life because if it weren’t, we simply wouldn’t be there. Add it to Okam razor. If a smaller, simpler, universe could handle life, we would be in that one. Not our current one.
“Our universe is so huge, so there must be other life form” is not the right statement. Our universe is so huge because it is the smallest universe where life could potentially appear.
Only my opinion, not a scientific demonstration.
Sure, all of this should be taken with “current state of science”. But if we start saying “we don’t know anything, we may be wrong”, then we just cannot discuss about anything.
Estimation of size of universe vary depending on the models. I’ve read it’s ~10^80 atomes. Let’s makes it 10 times bigger. It would gives 10^81, what a big deal. One billion time bigger, 10^89. You see what I mean ?
But as I know there are currently no scientific model that suppose an infinite universe.
Sometimes, “we don’t know anything” is the most honest discussion that can be held.