There Have Probably Been Aliens • Hacker News Board

Re: There Have Probably Been Aliens

#141

Post by code777777 » Sat, Jun 11, 2016, 7:45 PM UTC

yoha wrote: post #125

dave_sullivan wrote: post #96

Earlier quoted context omitted.

One of my favorite explanations and counterpoints come from Neil deGrasse Tyson: It took modern astrophysics to determine the origin of the chemical elements. We observe stars (and) we know what goes on in their center. They explode, laying bare their contents. And what we have discovered is that the elements of the periodic table -that which we are made of- derive from the actions of stars that have manufactured the…

Most common elements in the universe [1]: Hydrogen, Helium, Oxygen, Carbon, Neon, Iron, Nitrogen Most common elements in the human body [2]: Hydrogen, Oxygen, Carbon, Nitrogen I agree that we can skip helium and neon since those are noble gases, but I do find the lack of iron interesting. [1] https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elem... [2] https://en.wikipedia.org/wiki/Composition_of_the_human_bod…

Indeed. Iron and other heavy elements sink into the core of planets as they're being formed. This leaves less iron on the surface for chemical reactions that might lead to life.

However, iron does play an important role in life as we know it, even today. Earth's molten and rotating iron and nickle core is what creates our magnetosphere that shields us--and presumably early life--from deadly solar radiation.

Re: There Have Probably Been Aliens

#142

Post by gpsx » Sat, Jun 11, 2016, 7:53 PM UTC

nitrogen wrote: post #135

gpsx wrote: post #126

Earlier quoted context omitted.

I don't know enough to know if the range you specify is right, but I agree that it is silly to say 10^-22 is a ridiculously small number. For one thing, when talking about the size of probabilities, we should talk about the size of the exponent. -22 is not a ridiculously small number. People base the idea that there should be other life in the universe on the fact that life developed at least once, which is here on e…

AIUI the term "observation" in quantum physics has absolutely nothing to do with life.

Yes, my discussion of it was my attempt to say it was not a factor in my point, as I didn't want some people to get caught up in it.

Re: There Have Probably Been Aliens

#143

Post by sangnoir » Sat, Jun 11, 2016, 8:47 PM UTC

code777777 wrote: post #141

yoha wrote: post #125

Earlier quoted context omitted.

Most common elements in the universe [1]: Hydrogen, Helium, Oxygen, Carbon, Neon, Iron, Nitrogen Most common elements in the human body [2]: Hydrogen, Oxygen, Carbon, Nitrogen I agree that we can skip helium and neon since those are noble gases, but I do find the lack of iron interesting. [1] https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elem... [2] https://en.wikipedia.org/wiki/Composition_of_the_human_bod…

Indeed. Iron and other heavy elements sink into the core of planets as they're being formed. This leaves less iron on the surface for chemical reactions that might lead to life. However, iron does play an important role in life as we know it, even today. Earth's molten and rotating iron and nickle core is what creates our magnetosphere that shields us--and presumably early life--from deadly solar radiation.

> However, iron does play an important role in life as we know it, even today

I would have thought the iron in mammal blood would come to mind first, but other aquatic life forms have copper-based blood, so it's not exactly required.

Re: There Have Probably Been Aliens

#144

Post by asamarin » Sat, Jun 11, 2016, 8:57 PM UTC

greggman wrote: post #93

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…

what if life didn't evolve here but arrive on other space debris? Has that theory been ruled out?

That's called panspermia, and no, it hasn't been ruled out. Main problem with it though is that it doesn't explain how life as we know it came into existence, it simply shifts its origin from Earth to somewhere else

Re: There Have Probably Been Aliens

#145

Post by sangnoir » Sat, Jun 11, 2016, 9:01 PM UTC

XorNot wrote: post #71

madaxe_again wrote: post #6

The most likely reason that nobody seems to be out there is the great filter. The author asks if our civilisation will last millenia or millions of years - but I think a more apt scale would be decades or centuries. It just seems pretty obvious that we have an ever increasing set of opportunities to extinct ourselves, and therefore the probability of a civilisation ending disaster only grows. All the aliens either bl…

Conversely, by 2025 there might be living humans on Mars (if Elon Musk gets his way). And while that's not enough to form the basis of a backup civilization, I'm somewhat more interested in the effect on global zeitgeist it's likely to have. The feeling of the times is, I feel, an underestimated factor in how democracies pick their priorities - and the early 21st century has been very down on itself trying to figure…

> And while that's not enough to form the basis of a backup civilization

Or that might accelerate the end of civilization due to our inherent tribalism - the US isn't quite a backup of Europe as a 16th century European would have imagined. Who is to say there won't be a Planetary Mutually Assured Destruction?

The Expanse (books and TV series) explores some themes around planetary identity & politics in a fictional future where Mars and the outer solar system has been colonized and Earth is seen as a meddling 'old country' by some.

Re: There Have Probably Been Aliens

#146

Post by ulmus » Sat, Jun 11, 2016, 9:10 PM UTC

lisper wrote: post #138

ulmus wrote: post #129

Earlier quoted context omitted.

Pardon me, but I'm not sure what you mean by quantity of interest. If the quantity of interest can always be re-cast as a value which is necessarily 1, isn't "quantity of interest" the same for all probability problems?

Sorry, I wasn't very clear. > the authors essentially claim to know the probability of their own existence The "quantity of interest" is the probability of aliens, but not the probability of aliens in all possible worlds, but rather the probability of aliens in this world. In this world, the probability that the authors exist is 1.

I respectfully disagree. I claim the probability of human existence could have been less than 1, just as the probability of heads when tossing a fair coin is less than one, even when heads is observed as an outcome. We simply can't observe "tails" in this case.

Re: There Have Probably Been Aliens

#147

Post by imh » Sat, Jun 11, 2016, 9:17 PM UTC

One in 10^22 seems really easy odds to beat. Basically anything should happen more often than that, right? But if we choose a random 16 letters, the odds that they spell "unscientifically" is less than that. If we gave 16 letters to each of the 10^22 stars, we expect the word to happen on only one star, if even that. It's not too hard to argue that life is more difficult to get by random chance than the word "unscientifically", so we can't simply argue that "of course life will happen with those odds!"

Re: There Have Probably Been Aliens

#148

Post by gilleain » Sat, Jun 11, 2016, 9:36 PM UTC

Houshalter wrote: post #128

cookingrobot wrote: post #127

Earlier quoted context omitted.

Purely hypothetical: where N is the fewest number of bits for a successful virus. There could be 10 different ways to make a virus N bits long. There could be 1000 ways to do it in N+1 bits, and a billion ways in N+2. The relationship between how many possible successful viruses exist to number of bits doesn't have to scale by any obvious pattern.

I don't see why adding more bits would make the program significantly more likely. Yes in theory that is possible, but I don't think it's relevant.

For proteins, at least, there is a lower limit on sequence length below which it is less likely to form a folded structure. Most proteins are around 200-250 amino acids long (see http://www.umich.edu/~zhanglab/publications/1996-2001/Zhang_...).

There is a reasonable theory that I remember discussing/reading once that proteins may have started out as long sequences and were then selected for shorter more stable versions. Presumably the early proteins were partly disordered, and only optimised for having stable cores and domain structures later on.

In any case, it is not as simple as the number of bits in a program, as macromolecules are not 'just' software, but actual physical devices that have to (self)-assemble and carry out functions at various temperatures, pressures, pH, etc.

Re: There Have Probably Been Aliens

#149

Post by gilleain » Sat, Jun 11, 2016, 9:49 PM UTC

cgio wrote: post #108

andbberger wrote: post #104

Earlier quoted context omitted.

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?

I presume the idea is that of 'the other half' of evolution - that is, the spontaneous formation of order through simple physical processes coupled to symmetry breaking.

Of course it can be easy to over-do the analogies between things like convection rolls and the emergence of lipid bilayers (or whatever). However, the origin of life necessarily came about through purely physical processes and only once that bootstrap phase was over did evolution come into play as biological systems took over acting upon themselves.

As I understand it the idea is that a closed system that is driven far from equilibrium by a constant influx of energy can undergo 'symmetry breaking' where the symmetries of the system are changed. So the symmetric situation of the boiling pot is broken such that convection rolls are formed - which is new structure.

Similarly, a uniform soup of primitive chemical compounds could have been broken into less-uniform patches by some energy gradient (black or white smokers, for example). This diversity of chemical conditions then helped to form the initial replicators that could then further exploit various temperature, chemical, or proton gradients to create primitive life.

Re: There Have Probably Been Aliens

#150

Post by drjesusphd » Sat, Jun 11, 2016, 10:07 PM UTC

noiv wrote: post #50

ITT, people start with the assumption live is something incredibly special. Another way of thinking assumes live emerges everywhere an energy gradient and some matter exists. Maybe we are not special at all. https://www.quantamagazine.org/20140122-a-new-physics-theory...

So where is everyone?

If intelligent life is at all likely, there ought to be many civilizations that have had millions of years technological head start on us. Given one species with galactic ambitions, but technology only modestly beyond ours, it would only take them one million years to colonize the entire galaxy. So why do we not see any evidence whatsoever?

This is the Fermi Paradox.