What Earth Tells Us About Life, Intelligence and the Universe | Hacker News Reader

What Earth Tells Us About Life, Intelligence and the Universe

nautil.us

34 pointsdnetesn23 comments

> Earth is about 4.5 billion years old, and early forms of life were definitely on the planet by 3.7 billion years ago. That bare fact seems to imply that it wasn’t hard to get life going on Earth; if initiating life was really improbable, then we should have had to wait a long time before its appearance.

I think that's a big leap to make in drawing conclusions exactly because of the N=1 problem. If we had managed to reproduce a process by which a bunch of organic compounds turn into a the simplest cell type then we could start talking about probabilities of this process happening elsewhere in the universe. It might very well be true that life would start just as easily elsewhere but that conclusion can't be based on the amount of time it took life to appear on earth. The fact that someone wins the lottery the first time they buy a ticket does not mean its easy to win the lottery...

"Earth is about 4.5 billion years old, and early forms of life were definitely on the planet by 3.7 billion years ago. That bare fact seems to imply that it wasn’t hard to get life going on Earth; if initiating life was really improbable, then we should have had to wait a long time before its appearance."

I think it's a significant observation that there's just a single origin of life -- that after a 4.5 Gy sample time, we only observe one type of biochemistry. If you predict abiogenesis happens easily, you should expect it to have happened again independently, many times, and expect to find distinct classes of radically different, "alien" life on earth.

Not necessarily. It might have happened that different types of chemistry appeared, but as life evolved, one type pushed out the other. So we can't really tell if life happens easily or not from the fact that there's one type of biochemistry here.

It is a big leap to draw if life has to exist for a long time before intellegence can emerge. Given how close we are to the end of the carbon cycle on Earth (in geological terms) it implies that it takes a very long time for intelligent life to evolve. This requires that life appears early.

What I think is better proof that intelligent life is rare is the existence of stars. Stars are like finding gold coins on the street - they both only will be there if intelligent life is not.

Can you expand on your idea about the stars? I follow why gold coins aren't found in the street, but not how intelligent life would scoop up stars.

It is not my idea (I wish it was), but the basic idea is that any intelligent life a little more advanced than us would build Dyson spheres [1] around each star to capture the energy being released. This would shift the stars EM spectra heavily into the red. Combine these with von Neumann machines [2] and the stars soon cease to shine.

Interestingly while we are not really capable of searching for such stars right now we have found few possible candidates [3]. I personally think these are likely to all be false positives because any civilisation capable of building a Dyson sphere will be able to capture all the energy being emitted and so the black body temperature of the sphere will be only be a little above 2.73K. These we would not be able to detect.

1. http://en.wikipedia.org/wiki/Dyson_sphere

2. http://en.wikipedia.org/wiki/Self-replicating_machine

3. http://home.fnal.gov/~carrigan/infrared_astronomy/Other_sear...

Awesome, thanks for writing this up for me.

I wonder if there's reason to think that all or many stars would need capturing.

Also, is there perhaps an alternative situation, where, put simply, there power needs can be sufficiently met without capturing all that available? (Lower power tech, or some very efficient power capture / production?)

Once you have von Neumann machines spreading they will take over each new star system pretty much as soon as they reach it. Assuming the von Neumann machines are small and are being powered by an energy source (i.e lasers) from their origin star system they will spread through the galaxy at close to the speed of light. This spread method creates an interesting effect in that we would not see the stars go out until the von Neumann machines had almost reached us if the origin star was within our galaxy - basically the von Neumann machines would be traveling only a little behind the light front from the origin star system (this would make a good science fiction story).

If the origin star system was far enough a way, then the slightly slower speed that the von Neumann machines would travel at should allow us to see them progressing though a distance galaxy. Such a galaxy would look to us like part of the galaxy had a chunk taken out of it. It would be worth looking through the galaxy classification data set [1, 2] to see if there are any galaxies like that out there that look like this. My feeling is we won't find any as I think intellegent life is near unique within the visible universe, but it is at least a testable hypothesis.

1. http://www.galaxyzoo.org

2. http://en.wikipedia.org/wiki/Atlas_of_Peculiar_Galaxies

You sound like you want to believe that the emergence of life is difficult (by comparing it to winning in a lottery). Then the N=1 evidence that we actually have says, the emergence of life was easy (or, at least, quick). But you brush this off by saying blah, it's just N=1. But the evidence for your emergence-of-life-is-difficult is N=0.

Granted, N=1 is not much. But it's still more than N=0.

I don't want to believe anything until there's evidence for it. My intention was to show there's a problem with the logic that assumes it's easy when there is not enough evidence to support either that it is easy or that it is difficult. The example of the lottery was meant to illustrate how it could be difficult while seeming easy, not to convince anyone that it is in fact difficult. I wouldn't agree with someone claiming that the development of life is difficult for exactly the same reasons.

Isn't the discussion about extraterrestrial life pretty much entirely speculation?

Perhaps you can fill me in on that subject ? I googled it a while back, totaly unable to find out if " physical drag seining " has ever been done in space. Small samples are taken from Moon, Mars, etc. How about drifting micro-organisms in space itself? I know this isn't "/R/askscience", but there you go

This is why Europa exploration is important. If we discover life there, there is a good chance life is common in the universe. Just add water and you get life.

I guess in the same way the Higgs Boson was speculation, or string theory is speculation. It is a valuable hypothesis that is not proven yet.

IANAP, but I think the hypothesis is more that it's incredibly likely that life exists.

We have no evidence that it does, only that Earth-like conditions are not unique.

A serious question: why are earth-like conditions suggestive of extraterrestrial life and not, say, extraterrestrial McDonalds? The observed frequency is identical so far.

I think the answer must be a bias towards believing in some essential specialness or uniqueness of life, which isn't supported scientifically.

No, because intelligent life exists outside of Earth. It is a matter of time until we find it. Just like it's a matter of time until religion is no more.

So, speculation, then.

You used zero evidence in your statement, just a couple of beliefs.

I believe, too, but I'm not willing to assert it as fact.

It tells us very little, there are more stars in the universe than sand grains on earth http://www.npr.org/blogs/krulwich/2012/09/17/161096233/which... and we don't even have the technology to properly search our solar system, our sand grain.

Considering prospects of living, stars in other galaxies are irrelevant, because they are unreachable. We should, at least now, look at the closest stars around us, which are very few. There's reason to believe even these might be unreachable for us. https://en.wikipedia.org/wiki/Great_Filter

There could be other filters not listed. I sometimes wonder why on the Earth the observed sizes of the Sun and the Moon are the same, and recently wondered if the effect is far better eyesight in some land animals, including humans, than would otherwise be the case. If the Moon looked larger than the Sun, the Sun would disappear more frequently and for a longer time in the daytime, and there'd be no corona; if vice versa, the eclipse would only ever be partial. Because the corona lasts 5 minutes only, once a lifetime, animals will stare at it in surprise. Only animals with eyes which won't be damaged by sustained bursts of daylight will pass on their genes. Perhaps it also gives rise to animals which can see both in the dark and in the bright light. Is such type of eyesight essential for higher intelligence? If so, it's part of the Great Filter, reducing the odds of intelligent life by orders of magnitude.

Do you mean reachability in terms of a spaceship? If so, wouldn't intergalactic communication be pretty incredible, even if it was only one-way?

But all the intermediate steps suffer from the same n=1 problem. In fact, those difficult hoops themselves cannot be identified when there's just one experiment.

How are we to know that our experiment is not just an outlier in some way?

I guess there will be more data when we have a closer look at some of these exoplanets.

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