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Comment by darkwater | Hacker News Reader

I really find hard to believe how people can say "well, maybe it's not that easy to have other forms of life in the Universe". I mean, we have a cluster with thousands of galaxies, which make it for millions of stars, 240 MILLION light years away. Which means that there is a 240 million years window in which we are basically blind. Any communication from there will never reach the human race, most probably. Philosophically we can say there is no life there as we are concerned, because we will never be able to see any proof of it, but that doesn't mean that there was anyway, or there currently is, and maybe in more than one planet.

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People underestimate how dead and hostile the space is to life in general. First of all, you can just swipe most of the available galaxy space off the table because of radiation - the center of the Milky Way, close to our "core" black hole, is just pure hell. This is why we inhabit a remote neighborhood of the galaxy. You can extrapolate that most spiral galaxies are like that and only a small sliver of them are "in play".

Earth won multiple jackpot lotteries in a row, and that's only the variables we are aware of:

* Right-sized star

* Right-sized planet

* Not too far and not to close to the star

* Not too little and not too much water

* Oxygen

* Iron core (magnetic field protects from radiation)

* Right-sized moon (keeps rotation stable, tides)

* Gas giants absorbing a lot of debris coming our away

* A single-star system, with nearly circular, stable planetary orbits (very rare)* ... and so on

Yes, I know there are permutations that might also work, but in general it does not look good for spontaneous life.I like a theory that states that the Universe is just the right size where one single Earth has only a single probability to spring up randomly. The Maker covered their tracks well, if you believe in higher intelligence.

This doesn't seem like the right calculation to me. Doing some quick lookups, I find that the number of galaxies in the universe is estimated to be between 200 billion and 2 trillion. As for stars in a galaxy, there are around 100 billion stars in the milky way galaxy, so lets go with that.

If we guess that only about a quarter of any given galaxy is potentially habitable, that leaves 25 billion possibilities per galaxy. If we go with that and a middling estimate for the number of galaxies then we have maybe (25 billion * 1 trillion) stars, which is a number so big I don't even know how to say or comprehend it.

Even if we take an extremely conservative view that each galaxy only has at most 25 stars with potentially habitable planets (cutting the 1/4 galaxy estimate down by a factor of one BILLION) then we are still left with 25 trillion possibilities, which seems like a pretty good chance to me.

Space... is big. Really big. You just won't believe how vastly hugely mindbogglingly big it is...

Aka Drake's equation, with sufficiently large numbers, gives a decent chance of habitability. We just don't know what the numbers really are. Those big enough numbers with small enough other names make for a low enough number that it might as well be zero since we can't observe or interact with them.

Oxygen doesn’t belong on that list, I think - the earth’s oxygen was made by the first living things.

The didn't make the oxygen, they unlocked it from various molecules and minerals etc. It had to be here first.

But I don't think there is anything special on there being oxygen in the cloud of gas that formed the solar system. The distribution of elements following a supernova probably follows some law, and oxygen is low enough on the periodic table that probably quite a bit of it is expected.

True - oxygen is very abundant, though, so its presence is not surprising.

You are making a few (?wrong) assumptions here:

- that we are first

- oxygen is needed for all life forms

- the habitable zone that is ideal for us the only one that can give birth to intelligent life

- magnetic field is needed for life to exist/radiation kills off all life

"I'll tell you one thing about the universe, though. The universe is a pretty big place. It's bigger than anything anyone has ever dreamed of before. So if it's just us... seems like an awful waste of space. Right?"

-- Contact (1997)

Waste of space seems like a poor phrase. It seems to imply it should be used by intelligent life, and if it isn't, then it's a waste.

It’s a game of numbers. There may be 10^n opportunities for life potentially forming, with the average likelihood for life actually forming being 10^-m for each. The question is, is n (much) larger than m, or vice versa? We really have no idea, in particular with regard to m. It doesn’t help if n is 100 when m may be 1000. And the human brain is really bad at estimating such likelihoods.

If the universe is infinite like we think it is, then there is life somewhere, in fact, there is an infinite number of copies the earth exactly like or own, with a copy of you and me on it. We are just "blinded" by the limits of the observable universe.

So, we are almost 100% sure that there is extraterrestrial life somewhere in the universe, but if there is no possible causal relationship between us, what's the point? It is also the same reason why "the universe" is often shorthand for "the observable universe". There is probably something beyond it, but we have no way to know what it is, so it might as well not exist.

I am not aware of any models of the universe that posit an infinite mass.

Edit: Also, "observable universe" is a frequently misunderstood concept. Just because something is now outside the observable universe (the distance between them and us is big enough so that the rate of expansion of the universe between us and them is higher than the speed of light) doesn't mean that we aren't, today, receiving light from a long time ago when the object was closer. If you go far enough back in time you can "see" the entire universe . As time passes, more and more mass moves outside of the observable universe since the size of the sphere is constant relative to the rate of expansion.

That would imply there’s an edge to be closer to, which doesn’t align with my understanding of it.

> If the universe is infinite like we think it is, then there is life somewhere, in fact, there is an infinite number of copies the earth exactly like or own, with a copy of you and me on it.

This requires more assumptions than just infinite scale.

Right, like in math, not all infinite sequences contain every finite subsequence. For example, a non-repeating sequence of 2's and 7's contains no sequence "4". The further condition is that the number be normal[1].

Also, TIL we don't know whether π is normal thus the popular claim that "every string of numbers eventually occurs in π" is not known to be true

[1] https://en.wikipedia.org/wiki/Normal_number

this is such a commonly-repeated fallacy. just because something is infinite, doesn't mean everything is possible. the sequence 1,3,5,7,9,... is infinite, and yet it contains no even numbers. there are many such cases.

In this case, the existence of earth is an even number, so I don't see how this is a fallacy.

Take the sequence of prime numbers, with Earth = 2. ;)

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