There Have Probably Been Aliens • Hacker News Board

Re: There Have Probably Been Aliens

#101

Post by lisper » Sat, Jun 11, 2016, 2:32 PM UTC

ulmus wrote: post #58

In estimating a probability for the occurrence of life in the universe, the authors essentially claim to know the probability of their own existence. For me, that's a red flag. I can't know the probability of a phenomenon which my existence depends on just by observing my existence alone, because I can't observe all of the cases where the phenomenon does not occur and I do not exist.

The quantity of interest in any probability problem can always be re-cast as the conditional probability of the event given that the person asking the question exists, which is necessarily 1.

Re: There Have Probably Been Aliens

#102

Post by dmfdmf » Sat, Jun 11, 2016, 2:36 PM UTC

If you are interested in these issues a great book to read is called "Rare Earth:Why Complex Life is Uncommon in the Universe" by Peter Ward and Donald Brownlee. They make a convincing argument (to me anyway) that bacteria and simple life forms are probably common in the universe but animals and complex life with intelligence might be exceedingly rare. We, quite possibly, could be the only intelligent life in the universe.

Re: There Have Probably Been Aliens

#103

Post by andrewstuart2 » Sat, Jun 11, 2016, 2:37 PM UTC

Dylan16807 wrote: post #72

andrewstuart2 wrote: post #4

Probably. Assuming they're correct. Our planet is 12,742km in diameter, yet we've only drilled 12.262km deep [1] (and we were wrong about how hot it was gonna be), and sent a human down ~10.900km [2] (and we still can't decide how deep we've actually been). Do we really think we understand the probability of alien life on another planet that well, given the amount of data we have on those planets, and that we're cons…

I like your post for the most part, but "Unless we can make it there in 1.198 years." is just nonsense for the sake of being pithy. We could do a decade easily. And it still doesn't get us to anywhere. No need to act like people die from a year in space.

Could we? 0G is pretty rough on the human body (if you're planning on going back to a gravitational environment). And the truth is that beyond 1.198 years, we can only extrapolate what the effects are, as we have no evidence beyond that amount of time. Yeah, chances are we could go longer, but we don't know what happens until we've actually tried and measured.

Re: There Have Probably Been Aliens

#104

Post by andbberger » Sat, Jun 11, 2016, 3:01 PM UTC

apsec112 wrote: post #9

"In other words, given what we now know about the number and orbital positions of the galaxy’s planets, the degree of pessimism required to doubt the existence, at some point in time, of an advanced extraterrestrial civilization borders on the irrational." This is terribly silly. It reminds me of the Onion talks: "Step 1: Devise an idea to create a car that runs on compost. Step 2: Create the car. We’ve already compl…

Your assumption that the odds of abiogenesis is given by `~1/2^n, where n is the complexity in bits' is utterly, completely false.

Statistical mechanical entropy and information theoretical entropy ('complexity in bits') are not the same quantities! But even if they were, your expression would still be incorrect because living system are definitionally not at equilibrium - so equilibrium statistical mechanics (whose predictions you are using to get that expression) does not apply.

No one is surprised when convection rolls spontaneously form as they boil a pot of water. But equilibrium statistical mechanics predicts that this should be extremely unlikely as convection roll states have very low entropy. That is, of all of the ways that the molecules in that pot of water could be oriented, vanishingly few of them correspond to convection roll states, where several Avogrado's numbers worth of particles conspire to all swirl around in a coordinated fashion to dissipate the heat of the burner faster than would occur just by diffusion.

The origin of life is very much analogous to the formation of convection rolls in the pot. And I believe is far more common than classical predictions imagine it to be - nearly everywhere there is an energy gradient in the universe, you will probably find life.

Citation: I have a degree in physics

Re: There Have Probably Been Aliens

#105

Post by gus_massa » Sat, Jun 11, 2016, 3:03 PM UTC

throwaway_yy2Di wrote: post #56

ThePhysicist wrote: post #30

Earlier quoted context omitted.

I think what will really help us to get at a better estimate is to answer the question whether there exists life in our solar system that evolved independently of that on Earth. If we should find traces of bacteria on Mars or another planet, that would immediately take the corresponding probability factor in the Drake equation to a number close to 1 (i.e. most solar systems with planets in the habitable zone produce…

I think what will really help us to get at a better estimate is to answer the question whether there exists life in our solar system that evolved independently of that on Earth. That's definitely the big question. But you left out the elephant in the room: is there life right here on Earth that's evolved independently? Abiogenesis doesn't simply halt after it's achieved its "goal". Perhaps we take the common-origin h…

I think it's a winner take all task. If you are the first almost live form, you have plenty of time, and can evolved in an environment that has plenty of food. Something like the brown goo of Titan, with lots of hydrocarbons and other small molecules that you can pick up for free. And nobody is trying to eat you. So the reproduction process can be slow and unreliable, perhaps a few reproductions per day/week?/month??

The only way to die if a UV ray split you, or you fall into a volcano (there are no fire, because the atmosphere has very few oxygen), or a nasty oxygen molecule reacts with you, or ...

Well, there are many ways to die, but they are not targeting you, so perhaps you can hide from the sun under a rock. Or to be more clear, since you doesn't have any kind of senses or mobility, perhaps you are lucky and get beached under a rock. Perhaps the rock also makes a nice place to concentrate other molecules during the low tide.

Perhaps it's not a good idea to be near the surface and it's better to be lucky and get near a underwater sea vent with tasty hydrogen. I think the details of the first steps are not clear for anyone (in particular for me).

Once a stupid life for appears, the first thing it would do is eat all the free food. In particular, before the first life form the half of the amino acid were L and half D. We have used all the L amino acids (and created many more than the original supply), and we have also eaten all the original D amino acids. So there are very few of them floating around freely, it would be very hard to start an alternative D-tree.

A new life form will be targeted by the existing life form, like the free D amino acids. The competition will be extremely hard. So I think it's a winner take all task.

Moreover, then some moron decides to release a lot of oxygen to the atmosphere. Oxygen is extremely toxic for most life forms, and more toxic for isolated molecules that are barely alive ...

About the shadow biosphere: Perhaps we (humans) can't detect or identify them, but the bacteria and archaea can probably live there and eat them barely-alive. Our cousins can keep all the out-of-tree competition at bay.

Re: There Have Probably Been Aliens

#106

Post by [deleted] » Sat, Jun 11, 2016, 3:10 PM UTC

apsec112 wrote: post #9

"In other words, given what we now know about the number and orbital positions of the galaxy’s planets, the degree of pessimism required to doubt the existence, at some point in time, of an advanced extraterrestrial civilization borders on the irrational." This is terribly silly. It reminds me of the Onion talks: "Step 1: Devise an idea to create a car that runs on compost. Step 2: Create the car. We’ve already compl…

[deleted]

Re: There Have Probably Been Aliens

#107

Post by tim333 » Sat, Jun 11, 2016, 3:35 PM UTC

apsec112 wrote: post #9

"In other words, given what we now know about the number and orbital positions of the galaxy’s planets, the degree of pessimism required to doubt the existence, at some point in time, of an advanced extraterrestrial civilization borders on the irrational." This is terribly silly. It reminds me of the Onion talks: "Step 1: Devise an idea to create a car that runs on compost. Step 2: Create the car. We’ve already compl…

An alternative is if you believe in the principle of terrestrial mediocrity, that we are on a fairly average planet in a fairly average bit of the universe where fairly average things happen, the fact that life popped up on our planet in less than a billion years implies it probably has done so in loads of other places.

Quote Martin Amis's The Information:

“The history of astronomy is the history of increasing humiliation. First the geocentric universe, then the heliocentric universe. Then the eccentric universe – the one we’re living in. Every century we get smaller. Kant figured it all out, sitting in his armchair. What’s the phrase? The principle of terrestrial mediocrity.”

Re: There Have Probably Been Aliens

#108

Post by cgio » Sat, Jun 11, 2016, 3:44 PM UTC

andbberger wrote: post #104

apsec112 wrote: post #9

"In other words, given what we now know about the number and orbital positions of the galaxy’s planets, the degree of pessimism required to doubt the existence, at some point in time, of an advanced extraterrestrial civilization borders on the irrational." This is terribly silly. It reminds me of the Onion talks: "Step 1: Devise an idea to create a car that runs on compost. Step 2: Create the car. We’ve already compl…

Your assumption that the odds of abiogenesis is given by `~1/2^n, where n is the complexity in bits' is utterly, completely false. Statistical mechanical entropy and information theoretical entropy ('complexity in bits') are not the same quantities! But even if they were, your expression would still be incorrect because living system are definitionally not at equilibrium - so equilibrium statistical mechanics (whose…

How do you substantiate the analogy between origin of life and convection rolls formation?

Re: There Have Probably Been Aliens

#109

Post by [deleted] » Sat, Jun 11, 2016, 3:59 PM UTC

andbberger wrote: post #104

apsec112 wrote: post #9

"In other words, given what we now know about the number and orbital positions of the galaxy’s planets, the degree of pessimism required to doubt the existence, at some point in time, of an advanced extraterrestrial civilization borders on the irrational." This is terribly silly. It reminds me of the Onion talks: "Step 1: Devise an idea to create a car that runs on compost. Step 2: Create the car. We’ve already compl…

Your assumption that the odds of abiogenesis is given by `~1/2^n, where n is the complexity in bits' is utterly, completely false. Statistical mechanical entropy and information theoretical entropy ('complexity in bits') are not the same quantities! But even if they were, your expression would still be incorrect because living system are definitionally not at equilibrium - so equilibrium statistical mechanics (whose…

[deleted]

Re: There Have Probably Been Aliens

#110

Post by ChuckMcM » Sat, Jun 11, 2016, 4:08 PM UTC

I can't recommend "The Vital Question" by Nick Lane enough for people who are really interested in the question of life elsewhere. It does such a wonderful job of show how mechanically "life" can be started as a way of simply reacting chemicals to a lower energy state. It neatly ties together biochemistry and geochemistry in a very plausible (and testable) way.

Given the analysis, I would expect that bacteria and archaea, are present on any world with liquid water and a threshold amount of heat. Which would include Mars, Europa, and probably Io as well. There are a number of forms of bacteria living in the ionosphere which could be dropped on to Mars and they would do just fine there.

The odd bit comes from the origin of eukaryotes. Which, according to Lane, might arise if archaea were endosymbiotically living inside bacteria. That works but he doesn't offer any suggestion of what caused it to happen the first time. And he makes a reasonably good case that what ever it was that caused it, happened exactly once in the 4+ billion years of the planet and 3+ billion years of bacterial life roaming around.