[dguest]

I'll always remember my middle school science teaching telling us that nuclear fusion violates conservation of mass because the 2 protons in a pair of hydrogen nuclei combine to make helium with 4 nucleons. It's not true, but that's not the point.

But he was a great teacher anyway. He was engaging and kept the kids in line and learning. I eventually learned the truth, and most of my classmates forgot about it. Teaching, like flying a plane or driving a train, might become more about keeping watch over a small group of people and ensuring that things don't go off the rails, and that's fine.

[3form]

This one feels less sinister than some other things at least to me, personally. You can reasonably doubt that the conservation of mass is violated and find out the truth based on that. But understanding more complex biology or historical context for some things? Granted, many of these things seem to be low stakes, but I'm sure there are some there are not (sex ed comes to mind).

[zem]

to be fair, fusion does violate conservation of mass, just not the way the teacher explained it. the loss of mass is where the energy comes from.

[3form]

Yes, together with mass-energy equivalency it would form a coherent argument, and then also a correct one - but the thing is that if incomplete, it still might sound funky enough to you to research it if you care.

I think it helps that it's a very narrow field to look at, compared to fuzzy and big-picture view of social studies, for example. So much room to be confidently wrong... And sadly I can't think of a solution, LLMs or not.

[mr_mitm]

Yes, there is no law of conservation for mass like there is for energy. Fusion is a good example for why it's not conserved. The teacher was right.

[dguest]

He was right that it violates conservation of mass. He was completely wrong that it violated it by adding 2 atomic mass units when hydrogen fuses.

In reality heavier isotopes of hydrogen fuse, conserving the total number of nucleons, but the resulting hydrogen has a lower rest mass than the parent particles. The extra mass is released as energy and the total energy is conserved.

By his logic the system either violated energy conservation (by creating nucleons while releasing energy) or was endothermic (creating nucleons from the surrounding energy).

[tardedmeme]

There actually is a law of conservation of mass (it's the same law, because mass is energy) and it only appears violated if you forget about the particles that are zooming away at the speed of light. Of course the mass of a system changes if mass can flow in and out.

[mr_mitm]

Mass is not the same as energy. Mass can be converted to energy or has energy, but a photon, for example, is massless while carrying energy.

[tardedmeme]

That is incorrect. Photons have mass. They have no rest mass. They also cannot rest, so you might wonder how relevant that is.

[bernds74]

I had a chemistry teacher who told us that hydrogen reacts violently with oxygen, and this is how the hydrogen bomb works.

[daymanstep]

I had a chemistry teacher who insisted that the fissile isotope of Uranium was U-238 not U-235. I challenged him on this multiple times and he refused to budge on this. I get that it's a simple mistake to make (it seems like U-238 is bigger so intuitively ought to be less stable) but he could have just looked it up and he didn't, I guess he was just so confident about it that he thought there was no way he could have been wrong about it.

[dreamcompiler]

Well you can make a hydrogen "bomb" that way. Just not the hydrogen bomb.

[dguest]

Hey it's a bomb made out of hydrogen! Also the deployment system for a thermonuclear bomb might involve that reaction in the rocket engine.

[saagarjha]

I had one that mentioned this too :(

[BobaFloutist]

I mean fusion and fission do violate conservation of mass and conservation of energy, they just don't violate conservation of mass and energy, right? We thought mass was strictly conserved until Einstein, and then we updated our understanding.