Is it likely that there could be other life somewhere in the universe?

Since we’ve never detected any life beyond Earth - it’s possible that we are completely alone.

But since we’d likely be unable to detect life (say) 200 light years away on some other remote planet - it’s possible that life is present on billions of planets throughout the universe and we could be completely unaware of each other.

That said - we may have finally detected signs of ancient life on Mars - and if that’s the case then life should be found on hundreds of planets that we could detect them on with a bit more study.

The one key fact that we don’t yet know is how the very first living thing arose on Earth.

It’s almost 100% certain that some kind of random chemical process (probably in the early oceans) resulted in a self-replicating molecule (like DNA or RNA) that appeared by chance alone.

From that moment on - we’d have a LOT of those molecules - and evolutionary processes that we understand very well would kick in - and the rest is history.

So this all comes down to one very simple-seeming question:

• Under the conditions found in Early Earth - what is the probability of a self-replicating chemical forming by chance alone.

And we have no idea what that probability is. If we ask:

“What are the odds of a self-replicating chemical appearing once in a million years on a habitable zone planet?”

Then the situation is going to depend on what that number is:

• 1 in 10 per million years: If the odds are that high then we’d expect to see forms of life that are unrelated to our DNA/RNA structures right here on Earth. We don’t see that - so it seems that the odds are not that high.
• 1 in 100 per million years: If the odds are that high - then our existence on Earth isn’t too surprising. There should be life *EVERYWHERE* - and it would be surprising if we didn’t detect signs of life (past or present) on Mars. Recent announcements from NASA make it possible that we’ve found evidence of bacteria on Mars - but like “The Boy Who Cried Wolf” - we’ve heard this claim half a dozen times - and each time, the finding has been largely debunked.
• 1 in 1,000 per million years: It would be likely for there to be life beyond Earth - but not in our solar system - we should be able to detect them by radio signals - and it would be rather strange if we could not.
• 1 in 100,000 per million years: Then there should be life on distant stars - and it would be surprising if we couldn’t either communicate with them (if they’re intelligent) - or at least detect chemical signatures.
• 1 in a million per million years: Then there is life elsewhere in our galaxy - but it’s unlikely that we could detect it.
• 1:1 billion per million years: If the odds of it happening are that low - then we’re probably alone in our galaxy - but there will be life in at least some other galaxies - that are far too distant for us ever to find them.
• 1:1 quadrillion per million years: Then it’s possible that there has been - and could still be life other than us out in the universe - but it’s going to be very unlikely that they’d exist during the lifespan of our Sun - so we definitely couldn’t find them no matter what.
• 1:1 quintillion per million years: There’s probably no life beyond Earth within the observable universe - but maybe the universe is infinite and there are infinitely more places with life - but none of them will ever meet each other.
• BUT - our existence here on Earth can be at much longer odds than that - because there are an insane number of stars with planets in an insane number of galaxies - and it only had to happen once - and we would be that one time fluke.

MY BEST GUESS:

Because we don’t know of any simple self-replicating molecules that could possibly form at random - it’s unlikely that any do actually exist - and if the shortest possible one is (say) 2,000 base-pairs long - then the odds are already too long for there to be alien life that we can detect.

So - we await with some degree of optimism that maybe biochemists discover such a molecule - perhaps the one that formed spontanously to create life on Earth? When we know how long it is - we can make intelligent guesses as to the likelyhood that we’re just an insanely unlikely fluke - or whether there are almost certainly aliens everywhere.

Finding life on Mars - which we can analyse and determine did not travel to Earth - or come from Earth - would also indicate that there are aliens everywhere.

But if we don’t find either of those things - then we’re alone in the universe.