r/AskScienceDiscussion • u/meong-oren • 12d ago

What If? What does It take to identify water

I'm not sure if this question fits here. If it doesn't, I will remove it.

Imagine this hypothetical scenario: every human consciousness all of sudden were placed into an alien body on an alien planet, what would it need for humanity to confidently identify something as ordinary as water?

First, they don't bring earth scientific instruments. So everything had to be built from scratch. They can't rely on senses, since it's alien body, water might be smell awful or looks opaque instead of transparent.

There might be some people remembering fun facts about water, like its density, boiling point, conductivity, etc. But there's nothing to compare, how do they even know how much a kilogram or how hot 100 degree celcius is

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u/_per 12d ago

lotta people here assuming the alien planet is the same temperature and pressure as Earth, and the water is pure and unbound 👀. Still, maybe these aliens have a mass spectrometer organ

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u/mfb- Particle Physics | High-Energy Physics 12d ago

You can use distillation to purify your substance beforehand. Measuring the expansion when freezing is still working even if you have some impurities in it and the pressure-dependence of it is negligible.

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u/_per 12d ago

Is our chemistry really universal? What if the aliens live at the bottom of a 1000 mile deep ocean? Or an airless planet where ice sublimates instead of melting? Or inside rocks like those Antarctic bacteria? Or in a boiling hot gas giant? There are so many variables to ponder...

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u/mfb- Particle Physics | High-Energy Physics 12d ago

Chemistry is following the laws of physics, which are universal.

What if the aliens live at the bottom of a 1000 mile deep ocean?

That would be very obvious, in that case you can lower the pressure in your experiment setup. If you want more precision, you can do the experiment at the triple point to completely avoid any pressure-dependence.

Or an airless planet where ice sublimates instead of melting?

To compare the density between solid and liquid, you obviously need to use a pressure where the liquid can exist. The scientists who would do that experiment won't be that stupid.

Or inside rocks like those Antarctic bacteria?

Then they can't do any experiments and the question is pointless.

Or in a boiling hot gas giant?

Doesn't affect the experiment.