One more thing is certain: some beginners will trip up on physics concepts. It’s a new way of thinking, and it takes getting used to.

Dot Physics: Constant Force and Constant Motion

It seems that every semester when this discussion comes up, someone says this:

“Well, I think that a constant force will make the thing go at a constant speed. It just makes sense. Look at your car. You push on the gas pedal with a constant force and the car goes at a constant speed.”

For some reason, the students think of pushing the gas pedal with a constant force as the same as pushing the CAR with a constant force. Perhaps this is because the gas pedal is part of the car. Maybe they are just trying to bring one of their own experiences into the discussion.

I don’t think that this is unreasonable — a constant amount of gas to the engine should mean a constant force. But it’s not the only force, since there is air resistance and rolling friction balancing the effect of the engine. I think that the problem is more the difficulty in conceptualizing a single force without any other forces on the object — we don’t have much experience driving in a vacuum.

The kerfuffle is not dead yet. First, here’s a piece from The Guardian, specifically Jon Butterworth’s Life and Physics column: On Pauli and the interconnectedness of all things

Now, declaration of interest, Brian and Jeff are both old friends of mine, and I even starred briefly in “Night of the Stars” as “elbow behind Jonathan Ross’s head”. I have never met Sean, though I have read some of his work (and used his links) and I have a lot of respect for him. Anyway, this is about physics, not about taking sides in a celebrity scientist face-off.

My celebrity non-status must be why my contribution(s) are only hinted at (“some previous blogs” and “**it”; I guess you can call me et. al) but the main objections, or more precisely, my main objections (which I delineated) were the claim that a response to change in one electron’s energy would be instantaneous, and that the cause would be the Pauli Exclusion Principle. It seems to me that Jon admits that Brian Cox was incorrect on both of these points, though there’s some hedging on the instantaneous part — he gives an example of the electron in a potential well, i.e. an electromagnetic interaction, but then cites the phenomenon as being nonlocal, which I don’t understand. (Yet somehow he manages to conclude this was a “high-score draw”, which brings the Black Knight’s “We’ll call it a draw!” to mind)

So in principle one has to treat the potential of the whole universe, all the atoms, as a single system (a single Hamiltonian). All agree on this, as far as I can tell.

This already means that saying “it’s in a different place” is not sufficient reason to say of an electron “it’s in a different quantum state”.

This is something I don’t accept as given. I still point to my example of composite Fermions. Nature thinks that individual atoms are identical, because Fermionic atoms obey Fermi-Dirac statistics. If the electron energy levels were different, they would no longer be identical and would not do this. Nature seems to be saying that this assumption is incorrect.

Another issue has been pointed out by Dr. Skyskull in Pauli, “armchair physicists”, and “not even wrong”, in which he walks you through some of the background before discussing the problem, which is useful. (Part of the post concerns some of the remarks that have been made, and I’m happy to skip over that and focus on the physics, as I have already noted).

The additional argument comes near the end, regarding a claim that while the splitting is there, it’s so small that we can’t measure it, which garners a “physics fail” epithet.

Here Cox explicitly acknowledges that his “universal Pauli principle” consequences are something that not only cannot be measured today, but in principle can never be measured, by anyone

There a notion in science that can be summarized as: pics (i.e. experimental results) or it didn’t happen. You simply can’t make a claim in science without some kind experimental evidence to back it up — without that support it’s merely hypothesis or conjecture. You come to expect this from the fringe folks, but not from actual scientists. It’s hard to fathom that argument being brought up.

If you want to ruminate on the implications of treating the universe as a single system, fine — there’s a lot to discuss, such as “what does ‘identical’ really mean in this context?” Much of it will be interesting and some of it quite subtle. But presenting it as accepted science, to a lay audience? No.

In an advanced physics class.

Ice Sliding Off a Bowl: When Does It Leave the Surface?

A small block of ice is placed on the top of an inverted spherical bowl. The ice is then given a slight nudge so that is slides down the side of the bowl. At some point, the ice will speed up enough to leave the bowl. At what angle does this happen?

Quantum entanglement is a topic that often gets mangled in the popular press (much my to my torment), so it’s nice when a physicist writes about it.

Tangled Up in Quantum Mechanics

[H]ere’s the problem: the first measurement does not cause anything to happen with the second system: they cannot be in communication in any way, because the distance between them is arbitrary. In other words, they could be separated by several parsecs without changing the outcome, so if they were actually passing information, that would be in violation of relativity. You can’t send signals faster than light using entanglement as a result: the only way you could kinda-sorta communicate is if you had two groups of researchers who agreed in advance on what the settings of their instruments would be before they parted company; no new information would be available, since the real communication takes place at light-speed or slower, before the measurements are even performed.

Fair warning: at the end of the post, under the heading of “What Entanglement Is Not”, the discussion loops back into the “everything is connected” kerfuffle.