Very possible. Something behind our imagination (e.g. Energy, Light based life forms etc.). But it is not unreasonable to expect something similar, based out of Carbon or Si that has a metabolism and senses.
Once I read a suggestion to look for life: look for an entropy source.
I think even this is a bit of an assumption. I have a sort of thought experiment that what we call physics and what our ancestors saw as angels or spirits moving the heavenly bodies _could_ actually both be true.
Life as we know it is a source of entropy but if we take the view of God as an architect/clockmaker who created the universe as a (mostly?) deterministic machine with angels being his agents, it would stand to reason angels would be orderly as well rather than chaotic. Perhaps so orderly we would perceive their invisible involvement as natural laws rather than unusual miraculous intervention people usually expect from that sort of thing.
Of course it's unprovable and even if you proved it it doesn't really contribute much to our understanding of the natural world, but it's interesting to imagine a form of life so orderly that we don't even perceive it as life but as part of the machinery of the universe.
If it can't die it's not alive
And just because life on earth is fragile, it doesn’t mean all forms of life have to be.
When it comes to life made out of molecules, there aren't that many viable options for "base components".
For example, carbon based lifeforms like stuff on Earth can harvest energy from food without spending too much energy while remaining stable enough to avoid falling apart.
Silicon has somewhat similar properties, but its compounds require stricter conditions to be useful for hypothetical life.
Some amount of fragility is actually a good thing. Not for an individual, but for life in general. Animals harvest "building blocks and fuel" for themselves from other life forms that should be "fragile" enough to eat. All the advancements of evolution are possible due to mistakes in DNA replication that should be fragile enough for mutations.
That's why I mentioned silicon.
We have examples in popular culture already that are neither fragile nor organic: sentient machines.
Im not saying that the universe is full of Transformers and Terminators. Just that searching for silicon based life isn’t all that different to search for carbon based life when you consider that life is just a sophisticated machine and you can literally build a machine out of anything.
> digital 'computers' that can replicate themselves
By this definition we are just a few RepRap 3d printer revisions away from creating life.
> can you explain why that is not life?
As far as I know, the answer depends on ability of such a computer to become a competent Starfleet officer.
They included it because one of the scientific definitions of “life” and specifies the ability to reproduce.
https://en.m.wikipedia.org/wiki/Life
A RepRap wouldn’t satisfy every criteria though.
The only way alien civilizations will pick up each others' signals is if they're intentionally directed at those systems with highly focused emitters. If you're intentionally sending a signal in hopes another civilization will see it you're definitely not going to encrypt it. Compression also serves little purpose as there's no shared context to decompress the message.
By the same token, if humanity disappeared but left a bunch of encrypted hard drives around and aliens came and found them, they may have no hope of distinguishing the bits from random bits, but they'd be able to tell that no natural process encodes any kind of bits at all onto magnetic discs or flash drives or whatever else we manage to come up with.
The actual issue is what the other commenter said about the impossibility of detecting such low power radio at all.
historical forms of signal modulation like ook and fm don't look very much like white noise, because they're designed to be demodulated by circuits with 1-10 vacuum tubes, but more modern modulations can look pretty white. they'd look a lot whiter if they weren't constrained by regulation to strongly attenuate bands used by obsolete forms of signal modulation