mankind has been extremely lucky with our environments, among others:
- Jupiter & Saturn pick out most of the comets, so we encounter massive reset only very rarely
- thanx to hitting other planet long time ago, we have a spinning molten metal core inside planet generating magnetic shield for all nasty radiation
- moon gives us tides & stability
- our sun is just the right size and age to be stable
- we're located at quiet part of the galaxy, which itself is pretty stable
I think some primitive life (ie stromatolytes equivalent) can exist on many places, simply because it happened on our planet very early when it was very violent place to be - so random arrangement of matter into self-reproduction is feasible.
But to evolve into specialized multi-cellular organisms took more than billion of years, a step that might not happen at all.
And to create an intelligent life is another massive step up (or accident). There is Drake equation to manifest it, but basically all variables in it can be anything including 0, so it's kind of useless.
So from my perspective there are couple of options:
- universe is too young (if you consider average star age compared to estimated universe age), so we're one of the first sentient arrivals, others are behind in evolution
- we're just not interesting enough to be contacted by superior races - just look at the news, I wouldn't blame them. We're 'meh' category at best, although most like to think of themselves in very different perspective
- we're fucking alone, weird random anomaly (by far the most scary option of them all)
There is a wonderful TV series from BBC called Earth: Power of the Planet, which explores this topic to great details, highly recommended!
A good book that explores some of these factors for our environment is Rare Earth by Peter D. Ward and Donald Brownlee.
While it's true that life "out there" may look vastly different, I feel like sometimes ET-optimists use that as a hand-wavy defense that overlooks two curious details: First, we haven't found any different-looking-life-out-there on, say, Venus, or Mars... so clearly even in a solar system with some "lucky" aspects for life there are plenty of environments where life just doesn't "find a way." Second, the relative quickness with which our kind of life appeared in Earth's history suggests an oddity that we haven't even found other examples of our-general-kind-of-life out there.
A good book that explores some of the proposed solutions to the Fermi Paradox is Where is Everybody? by Stephen Webb. (It does a good job using math to explain why it's a little surprising that we haven't found ET life even within our own galaxy, and it does a good job knocking down most of the sociological explanations by noting that it would require every other civilization in the galaxy to behave that way with no exceptions.)
Our solar system is +-4bn years old, so there have been only cca 3 previous generations of similar stars (and it's kind of nice to have heavier elements from the first generations of stars in abundance - I would expect forming life just from He and H wouldn't work well).
Let's ignore the 'bn' part - this place is 14-old. Our system is 4-old. Life is 3-old. Multi-cellular is 2-old. Sentient is 0.00001 old. With usual star life has +- 10 to escape, or it will be destroyed. It doesn't sound so far-fetched to me.
But maybe it's all different - plenty of life all around the place, even super smart & evolved, but maybe speed of light simply can't be broken no matter what. That would dampen any rise of galactic civilization. Or some other unbreakable constraint.
> there have been only cca 3 previous generations of similar stars
That assumes they're consecutive, not overlapping. Assume it takes 4-old, space them out by 0.1-old, and you could have 100+ generations between the first and us.
Maybe, but unlikely. Life as we know it depends on some rare chemistry.
Carbon is the only atom [I know of] that can form long chains of double bonds (even triple though they tend to be unstable enough to not matter). Nothing else allows the chemical complexity needed for self reproduction.
Water is a weird molecule. Many chemical reactions happen in water that would be uncontrolled or not happen at all without water. The polar properties, the fact that is expands when it freezes (that is frozen water floats on liquid), and acid/bases are all interesting properties that are very useful for life. I suppose that something else could fill this role, but since water is common in the universe I doubt it.
Yes life elsewhere is unknown and so we cannot say for sure it will not look like our, but chemistry is a known.
• Robots that perform all the functions humans do, including making copies of themselves and teaching each other.
• Hive-mind species where there are no individuals.
• Species without any gender or sexual reproduction, whose individuals are spontaneously "born" in specific locations and conditions on their planet.
• "Species" consisting of a single, massive/long-lived individual.
• Parasitic intelligences that "infect" various other, unrelated species and direct them towards the goals of the parasites.
• Lifeforms floating around in gas giants or even in nebulas.
• Life-bearing planets themselves being a lifeform; that "reproduces" when the civilizations it supported upon itself go on to terraform other planets to become like their home planet.
The fundamental thing about life as we know it is not just that it's made of the few particular elements it uses. It's about those elements being a sweet spot for molecular nanomachinery. It's not clear that any other combination of elements might be able to form a stable replicator and bootstrap itself into large-scale complex system. In fact, it might be that life can only arise by itself using materials our life is made of, directly because of laws of physics in our universe.
Or put in another way - if abiogenesis of our life is improbable, a spontaneous creation of robots - large scale machines with digital brains - is orders of magnitude less likely still.
When dom96 said "there could be very many ways for life to exist" I understood that to mean there could be very many different "biological substrates" (for want of a better term), nothing to do with how the species organises itself socially. The challenge is to come up with a hypothesis for "life" that's not based on long carbon chains.
I agree that only our imagination is the limit when discussing potential life. If matter that is not completely frozen (ie atoms stop moving) will eventually organize into some self-replication, any energy source could be enough.
It could be on the surface on active star, neutron star (someone already tackled that in sci-fi), all kinds of dwarfs, nebulas, maybe even something living off dark energy? Or black hole.
Energy means movement, and if matter/energy will eventually arrange into something 'alive', it might be enough.
- Jupiter & Saturn pick out most of the comets, so we encounter massive reset only very rarely
- thanx to hitting other planet long time ago, we have a spinning molten metal core inside planet generating magnetic shield for all nasty radiation
- moon gives us tides & stability
- our sun is just the right size and age to be stable
- we're located at quiet part of the galaxy, which itself is pretty stable
I think some primitive life (ie stromatolytes equivalent) can exist on many places, simply because it happened on our planet very early when it was very violent place to be - so random arrangement of matter into self-reproduction is feasible.
But to evolve into specialized multi-cellular organisms took more than billion of years, a step that might not happen at all.
And to create an intelligent life is another massive step up (or accident). There is Drake equation to manifest it, but basically all variables in it can be anything including 0, so it's kind of useless.
So from my perspective there are couple of options:
- universe is too young (if you consider average star age compared to estimated universe age), so we're one of the first sentient arrivals, others are behind in evolution
- we're just not interesting enough to be contacted by superior races - just look at the news, I wouldn't blame them. We're 'meh' category at best, although most like to think of themselves in very different perspective
- we're fucking alone, weird random anomaly (by far the most scary option of them all)
There is a wonderful TV series from BBC called Earth: Power of the Planet, which explores this topic to great details, highly recommended!