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Comment by roenxi | Hacker News Reader

I don't see it mentioned on wikipedia, but one tin-pot theory I heard once and quite liked was:

* The universe at the moment is on average large, cold and quite hostile to life.

* At some point in the past all the energy in the universe was concentrated roughly at one point

* So, in between, the universe was a soup of energy that would have been, on average, warm, comfortable and conducive to life.

It dovetails with this because it is a plausible "why would life have evolved somewhere else but not here" counterargument. I wouldn't buy it though, it seems likely to me that earth's life is a local phenomenon.

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From https://en.wikipedia.org/wiki/Chronology_of_the_universe:

> Between about 10 and 17 million years the universe's average temperature was suitable for liquid water (273 – 373K) and there has been speculation whether rocky planets or indeed life could have arisen briefly, since statistically a tiny part of the universe could have had different conditions from the rest, and gained warmth from the universe as a whole.

But temperature alone isn't sufficient for life as we know it. Here on Earth we enjoy an atmosphere providing us with oxygen, a large planet protecting us from most meteor impacts, and a magnetic shield against radiation.

Life didn't start out breathing oxygen, oxygen was actually a waste product and the introduction of oxygen into the atmosphere was a disaster for a lot of the life existing at that time... https://en.m.wikipedia.org/wiki/Great_Oxygenation_Event

What do you think the probability of each of those factors is? Even if they're each 1 in 100, there leaves an enormous likelihood of those conditions existing many times over in the vastness if the universe.

This has received some serious consideration in Loeb's "The Habitable Epoch of the Early Universe" https://arxiv.org/abs/1312.0613

Proxima and Ultima by Stephen Baxter hit along this theme and are a pretty good read.

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