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Comment by realo | Hacker News Reader

When I look at this, it is hard to believe that life (and intelligent life) only exist on planet Earth...

Very hard to believe.

There are roughly 10^23 stars in the observable universe. We really have no idea how likely intelligent life is to evolve. It could be 1/10^10 per star, in which case intelligent life would be a fairly typical thing (dozens in the milky way), or it could be just 1/10^100, in which case we could be the only ones. Unlikelihoods can compound very quickly.

Thats not hard to believe once you understand how unprobable life seems to be and especially in the very long term. The universe is a very violent place and cosmic events act as great filters all the time.

Then again, this photo mosaic spans just one arm of one galaxy in the visible universe.

We know that life only emerges in very specific conditions, that most planets do not have. We also know that even in very stable Earth, we have had billions and billions of species that developed and disappeared and we now only have a single specie with technological capabilities - and for a very short time at that, all things considered.

If the universe is 'rich in life', most of it is probably micro-organisms that get wiped out every now and then by drastic changes on the planetary scale.

Agreed. It’s a minuscule probability per planet multiplied by a vast number of planets and it’s hard to say which factor carries greater weight. The fact that we haven’t detected any signals from space also sets a limit on the likelihood/duration of intelligent life in our area of the universe.

What are the chances that, from an outside perspective, that we are just one variety of life form on the planet?

Sure, they can make distinctions about which variety of us (e.g. humans, not dogs) have the most intelligence or something--but perhaps from an outside perspective, we all started from the same spontaneous event or whatever, and we're just many, many generations of that same lifeform.

In other words, maybe we're just being "racist," sort-of.

As an aside, is this a named theory or something? I'd like to read about it.

You might well be undercounting there, according to a 2016 study[0]:

> Earth could contain nearly 1 trillion species, with only one-thousandth of 1 percent now identified, according to a study from biologists. The estimate is based on the intersection of large datasets and universal scaling laws.

[0]: https://www.sciencedaily.com/releases/2016/05/160502161058.h...

When I look at this I feel life must be common. Maybe some dot in there must be planet full of dinasaurs.

If we would find a huge natural mirror or similar - far away, maybe we would be able to see our past earth still populated with dinosaurs.

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