[safety1st]

It's super fun to consider, but one problem with ammonia-based biochemistry is that everything would be so cold. In temperatures that are cold enough to liquefy ammonia you just have a lot less energy going around, and life requires energy to thrive. We can see this principle at work on earth where the tropics have the most biodiversity and the interior of Antarctica is almost totally barren of life. So it seems to me that while an ammonia-based biochemistry might be plausible, it may be a sort of evolutionary dead-end where nothing can progress beyond being simple and microscopic.

Or maybe it can at the bottom of an ocean where the pressures are higher and the ammonia is warmer due to geothermal effects...? but then it has no access to energy from the sun, and it's very hard for us to detect something that lives at the bottom of our sea, let alone an extraterrestrial one

[dylan604]

This kind of gets to what I was implying. Chemistry is chemistry, and physics is physics. The same elements are available throughout the universe even if they are not all brought together in the same quantities.

I get that it's fun to consider, but things are beyond credulity thinking that chemistry will be different elsewhere in the galaxy. Of course the weasel words "based on our current understanding" are a great way to keep the fun going

[bee_rider]

It seems like there ought to be a sweet-spot where life will consume the right amount of energy for an environment. Consume too much energy, you starve. Consume too little, you are out-competed by other life forms which consume more, and move faster as a result. But that’s environment-specific, maybe it is possible that ammonia life evolved on a lower-energy planet everybody just moves slower?

[safety1st]

If you move slower, you evolve slower. If less energy is available you have fewer organisms, there's less reproduction, therefore there is less evolution and less mutation.

That's why when we drilled down to Lake Vostok we found some single celled life forms that had interesting properties because they'd been cut off from the rest of the world for millions of years, but we didn't find Jules Verne's Lost World. There's just not enough energy down there under the ice to power a lot of biology. The less abundant/accessible energy is, the less probable complex life becomes, regardless of the biochemistry.

I buy that there's a good chance weird things on the complexity scale of bacterium are dotted all over the cosmos, but the big problem is those are functionally impossible for us to study (and even conclusively detect) unless mayyyyybe if they're in our solar system.

[hansvm]

> if you move slower, you evolve slower

In the plank limit maybe. Large-scale "organic" farms speed up evolution 100,000x with the right drug cocktail to circumvent the current legal definitions of "GMO." They aren't pumping 100,000x more energy into the system. Our base rate of evolution is naturally selected for complicated reasons which _involve_ the available entropy supply but aren't simply monotonically dependent on it.

[peddling-brink]

The Dragons Egg explores this in a fun way. Life on the surface of a neutron star.

[seventytwo]

It’s possible that a sentience dependent on a colder chemistry could operate more slowly, too.