[jdkee]

Per our new electronic friend:

" The weight of a molecule of water (H2O) is the sum of the weights of the two hydrogen atoms and one oxygen atom that compose it. Here are the atomic weights of these elements:

Hydrogen (H): Approximately 1 atomic mass unit (amu) Oxygen (O): Approximately 16 amu So for a molecule of water:

2 Hydrogen atoms: 2 * 1 amu = 2 amu 1 Oxygen atom: 16 amu Adding these together gives a total of 18 amu for a molecule of water.

This means that a molecule of water has the same weight as the sum of the weights of the two hydrogen atoms and one oxygen atom that compose it, because the molecule is simply a combination of these atoms. There's no loss or gain in weight when the atoms combine to form the molecule.

However, this does not take into account the minor decrease in mass that occurs during the formation of a water molecule due to the conversion of some mass into binding energy according to Einstein's equation E=mc^2. This decrease is incredibly small and generally not considered in standard atomic weight calculations, but it does technically make the water molecule ever so slightly lighter than the sum of its constituent atoms."

[eigenket]

I would say this phrase

> the minor decrease in mass that occurs during the formation of a water molecule due to the conversion of some mass into binding energy according to Einstein's equation E=mc^2

Is highly imprecise at best, and misleading at worst.

It is true that the mass of the water molecule is slightly less than that of the oxygen and hydrogen atoms combined. It is not true that this excess mass is converted into "binding energy", binding energy is negative in stable molecules. That is the binding energy measures how much energy you would have to add to break up the molecule, or conversely, how much energy is lost (as heat/light/whatever) to the environment when the molecule is formed.

The mass is lower because it has been converted into heat in the environment, not because it has been converted into binding energy.

---------------

I would call this an instance of the language model producing convincing sounding nonsense (something that they do quite often when asked about technical stuff).

[Sakos]

Okay, somebody explain these downvotes, because afaik none of these statements in this comment or the other downvoted comments about the mass of water are incorrect. Somebody make it make sense.

[tsimionescu]

I believe this one is downvoted for quoting Chat GPT. The other one is downvoted not so much for the claim about water molecule mass, but because of the combative tone and feeling that it is challenging established physics in a somewhat shallow way, most likely.

[jiggawatts]

It cracks me up that my comment is seen as "challenging established physics" (and being downvoted into oblivion) when literally everything I stated is established physics.

I really don't see what's controversial about what I've said that's riled up people so much...

[rcxdude]

It is factually incorrect in the assertion that the standard model can't explain the reduction in mass (special relativity and quantum mechanics work fine together. It's general relativity that is the problem). In fact mass-energy equivalence is a pretty core part of quantum mechanics.

[jiggawatts]

> In fact mass-energy equivalence is a pretty core part of quantum mechanics.

It may be stated as such, and added in to equations as an external piece of knowledge from relativity, but this is cheating a bit.

Essentially, when we state that H2O has less mass than H+H+O, what we actually mean is that H2O bends spacetime a little bit less than the three atoms individually that made it up. There's no accepted variant of QM or the Standard Model that explains this. The dynamics of spacetime curvature rearranging as the photon is emitted as the hydrogen atoms burn is not explained by modern science. This is fundamentally the "QM is incompatible with GR" issue.

My point was that it isn't just near black holes that a GR-compatible microscopic theory is relevant.

It's relevant even in the flame of a candle. It's a small effect, but it's there. The inconsistency in the theories occurs at all scales.

[tsimionescu]

While you're right about the inconsistency between GR and QM applying at any level, you're wrong about needing GR to talk about the mass of the water molecule.

Even in pure QM, the water molecule will have less inertia than unbonded hydrogen and oxygen atoms. This should in principle be measurable by applying a known force to the water molecule and to the three atoms, and measuring their acceleration. The difference should perfectly match the inertial difference predicted by SR and GR.

GR adds the observation that, if the water molecule has less inertia, it should also bend space-time less, and it is this bending of space time that can't be explained by QM.

Though I should add that I've had a reply to a different comment once that explained that QM is actually compatible with the flat-ish but not perfectly flat space times that GR predicts anywhere not very close to a black hole. They were claiming that in fact modern QFTs can even predict things like the gravitational lensing produced by our sun, and that they only break down when near the event horizon of a black hole.

[naasking]

> Essentially, when we state that H2O has less mass than H+H+O, what we actually mean is that H2O bends spacetime a little bit less than the three atoms individually that made it up. There's no accepted variant of QM or the Standard Model that explains this.

I'm not sure this is correct. It bends spacetime less simply because it's in a lower energy state. It's correct to say that the Standard Model doesn't explain spacetime curvature, but the curvature in GR is implied by the energy which is explained.