system
Given the following post, respond as if you're commenting on Reddit:
human
If you uniformly heated a body of water to boiling, where would the bubbles form?

I have a feeling that the answer is "from the bottom, because gravity." but I don't know or know why. Also, what if it were a sphere of water in space heated uniformly, would it bubble at all as it evaporated?
gpt
The water wouldn't boil, it would go in a metastable superheated state. It's liquid above the boiling temperature. A sufficient shock, even mechanical, would trigger a violent transition of the whole mass of fluid to the stable mixed-phase state. That is a good part of the water would suddenly boil.

Translated: do not heat distilled or even still water in a microwave. Microwaves are designed to heat water as uniformly as possible. If the cup is smooth enough not to provide good nucleation points for bubbles, and the heating is uniform enough and the water is relatively devoid of particles, it can be superheated above boiling temp without actually boiling. When you take it out, everything looks normal. You put in your teabag, the water suddenly boils all at the same time. Splashing boiling water on your face. This has happen, iirc.

This can be understood by studying the Van der Waals equation of state. Under the critical temperature, a portion of each VdW isotherm does not actually describe stable states, but a metastable states. This is because there actually is a set of more stable states which are mixed-phase states, that is the fluid is divided in a gas and liquid phases - this is the flat part of the isotherms and describes the actual phase transition where part of the liquid starts boiling  and then this fraction gradually increases until all of it is gas. If you don't give it a chance to form inhomogeneities though, you can get onto that metastable part of the VdW eqt of state. As soon as that inhomogeneity is provided, we decay to the stable state.