Aliens and the Fermi Paradox

First time accepted submitter sayhem (1842674) writes Various explanations for why we don't see aliens have been proposed—perhaps interstellar travel is impossible or maybe civilizations are always self-destructive. But with every new discovery of a potentially habitable planet, the Fermi Paradox becomes increasingly mysterious. There could be hundreds of millions of potentially habitable worlds in the Milky Way alone. This impression is only reinforced by the recent discovery of a "Mega-Earth," a rocky planet 17 times more massive than the Earth but with only a thin atmosphere. Previously, it was thought that worlds this large would hold onto an atmosphere so thick that their surfaces would experience uninhabitable temperatures and pressures. But if this isn't true, there is a whole new category of potentially habitable real estate in the cosmos.

Comments

Progenitors?

[jythie]

Well, it is always possible we are simply the first. We do have an unusually old population I star and it still took billions of years for humans to come on the scene, so it is possible that the typical case simply takes longer and many suns are younger then our's.

Re:Progenitors?

[Cryacin]

You know what? All very nice, but how about this? We are not all that interesting, nor special, and in the last 35,000 years when we could comprehend what we're looking at, no-one's bothered to swing by and ask for a cup of sugar.

It may also be possible that we are part of a nature preserve, or that there are more than enough planets with similar conditions to inhabit, to not have to displace or destroy an entire culture.

Another possibility is that we're left alone, because other civilizations have been contacted before, and once given technology, have self immolated themselves akin to giving firearms to the natives.

That, or we're won the interstellar lottery, and we are indeed the first who will learn a lot of lessons as we swarm across the galaxy once we figure out how to get off this damn rock.

Re:Progenitors?

[AthanasiusKircher]

That, or we're won the interstellar lottery,

THIS.

So far, we have precious little evidence one way or another about this. Lots of people make up all sorts of numbers for the Drake equation, but frankly it's almost entirely speculation. There seems to be this assumption nowadays that life will inevitably evolve on planets with similar conditions to Earth, but how do we possibly know that? What counts as sufficiently "similar"?

Go back before Carl Sagan and a few other such scientists, and the idea that the cosmos was littered with life was treated only by imaginative science fiction writers -- the presumption that something like SETI should turn up something would have been seen a little weird, certainly not based on any scientific evidence.

And what evidence exactly have we accumulated since then? Other than 40 years of Star Trek finding civilizations everywhere, do we have anything scientific to base our estimates on?

No. Not really. In particular, while there has been some work in self-organizing systems and theories about how we get from basic amino acids to the first "living" cells, there's a whole lot of steps to fill in to explain how life begins.

And frankly, until we sort that out, let's just not pretend we're doing anything other than speculating from a single data point -- which means we have absolutely no evidence at all to decide whether the universe is teeming with life in every star system, or whether the situation on Earth was so specific that we're alone (or nearly so).

These articles about the Fermi Paradox always bother me a bit because of this. There's nothing "scientific" about them. I'm not saying we shouldn't look for aliens (and it would be truly interesting if we found anything), but we simply have no clue whether life is likely to evolve on 1 in 10 planets or 1 in 100 trilllion planets. Until we find life somewhere else or we can figure out the details of how to manufacture it in a lab (and determine how likely such conditions are to occur naturally), this is all idle speculation. Thus, there's really no "paradox" to resolve, since the probability estimates are meaningless.

Re:Progenitors?

[Anonymous Coward]

All stars and stellar generations are not the same. As the Universe ages, every generation of supernovae introduces more metals (which in astro means 'anything except hydrogen and helium') into the galactic medium. Stars significantly older than our sun are unlikely to have had enough metals to form lots of rocky planets. Or if they did, any intelligent life there would find many of the metals that we consider fairly rare to be virtually nonexistent.

Conversely, in the far future when a large fraction of the ISM is heavier elements, the freak exception will the formation of rocky worlds small enough that the inhabitants on their surface can escape into space at all...

Re:Progenitors?

[AthanasiusKircher]

The old biology rule is: if you have a sample of one, you make the assumption that it is "average."

Yes, I'm very familiar with this assumption. In exobiology arguments it's known as the principle of mediocrity.

The problem is that it's simply an assumption. It can be wrong. We simply don't know. Moreover, in biology this often makes a little more sense when you're, say, dealing with a single fossil specimen or something. In that case, you're at least dealing with an interdependent ecosystem of life, and based on evolutionary principlles, most specimens we encounter are likely to be ones that survived and multiplied and existed as species with more than one exemplar.

There's no such data or evidence for extraterrestrial life, because we're not part of a common ecosystem with known evolutionary principles. Again, we have just one data point.

There are 88 objects (known) in our solar system larger than 200 miles in diameter. We know one has life, we believe 3 others have a promising chance to have life (Enceladus, Titan. Europa), as well as the possibility of subterranean life on Mars (methane venting).

Based on what, exactly? A whole truckload of assumptions about how common life MUST be and what conditions make it LIKELY. But we have no evidence for most of those assumptions. Call me when you find life on one of those places with a "promising chance" -- then we'll have EVIDENCE to talk about and more than one data point. Until then, this is idle speculation.

So lets do some math.

There's only one number that matters: P (chance of life evolving on a random planetary body).

Do you know that number? I certainly don't. You can make a bunch of stuff up about how "unique" or "not unique" the Earth is, but you simply don't know.

You do the math on how many objects that are out there. Again, anyone who doesn't think the odds are there's any life out there don't understand how fucking big an "out there" it is.

The universe could have 10^100 planets in it that are earthlike, but it wouldn't mean crap about finding life if P (chance of life evolving on a random planetary body) is 10^200. You still can't estimate a probability from one data point.

This all reminds me of a discussion in Richard Dawkins's Blind Watchmaker. He talks about how unusual it would be for four players to simultaneously get a royal flush in poker (or something like that). And then he says -- let's imagine some creatures that lived for millions of years (I can't remember the exact amount, but he gives something more specific). And he then concludes -- with all that time playing poker, these creatures would obviously not find it unusual if they all drew royal flushes at the same time occasionally.

It's a fun argument, but just for kicks I actually ran the numbers, and it turns out that Dawkins was off by many orders of magnitude for the lifespans of these creatures in order for this occurrence to be likely for them to experience.

Dawkins was obviously being sloppy there, and I don't fault him a lot for it since he was just making a casual analogy -- but his flawed methodology is PRECISELY what you are doing here. He simply assumed, "Yeah -- creatures who live millions of years" and assumed the numbers would make it likely for the poker hand to show up. Except the number that matters is P(weird poker situation), and he obviously didn't bother to compare that to his hypothetical giant lifespans of these long-lived poker-playing creatures.

It doesn't matter how big the numbers are for things in the universe. What matters is the chance of life evolving. Do I think it's likely we're unique in the universe? Well, if I had to state my BELIEF, I'd say "no." But that's NOT SCIENCE.

Science says we have one data point, and there's nothing else to extrapolate fro

Re: Progenitors?

[O('_')O_Bush]

Well, as has been pointed out before, just because life appears to stem from one thing, doesn't mean there wasn't a "Second Genesis" (or multitudes of them, even happening today). However, those other lifeforms have to compete for the same resources as better adapted ones (per natural selection). And then there are things that are "arguably life" that seem awfully close to life and awfully orthogonal to the existing tree, like viruses.

But besides that, what amazes me is that we are not only the most intelligent life on earth (for some values of intelligence), but as far as we can tell, the most intelligent life to have ever developed on earth.

This seems odd, given that there are so many other intelligent life (but nowhere near our level) like cetaceans, some birds (which are descended from Dinos, which had a longer time to evolve in interesting forms- not like early, ratlike mammals, to boot), other primates, some species of octopuses, and I am sure I can think of more examples.

Maybe the trick is having a big brain and a body plan that is flexible enough to do many things, starting with a high metabolism. I would think that a therapod with human intelligence levels would have an awfully hard time building spaceships.

And the brain consumes a lot of energy, which is why human muscles are relatively weak and energy efficient (also for endurance).

In that sense, it is my opinion that life is probably common, but intelligent life is rare, maybe even extraordinary, and probably not inevitable for a planet or system.

We have already contacted alien civiliations.

[Anonymous Coward]

At a certain point that starts looking like an attractive option. If NASA announced that they've managed to create a warp bubble, no matter how small, then I'd say the low hanging fruit is that aliens are in contact with certain elements of humanity and that this isn't widely known because a huge percentage of the world would freak the fuck out.

At Los Alamos, right around the time of the Fermi Paradox, everyone was agog at the green fireball phenomenon. One of the greatest collections of scientists ever assembled were pretty evenly split on the subject. Some though the the green balls of fire flying through the sky and changing direction as if being intelligently guided were some kind of secret earthly craft, while many other were certain they were extraterrestrial in origin. No one doubted they were real, however, and no one thought they were natural.

You don't really hear about this, but it's part of what started Fermi along the way towards his paradox.

As for the usual "OMG, nobody could keep that secret!" meme. Even if someone had 100% proof of alien encounters, the signal to noise ratio is assumed to be no signal and all noise. Someone could have been shouting the truth from the rooftops for forty years and nobody would care because they'd be lost in the din of people seeing little green men and anal probes.

Between "every civilization eventually kills itself" and a high level conspiracy to keep the world from shitting their pants at alien life, I'll pick the conspiracy. The fact that half of humanity isn't really ready to stop killing one another over five thousand year old superhero stories is kind of telling. Hell, half of humanity is confused by shoes.