Getting closer to perpetual motion!

[hiriskpaul]

You'll find the two chapters, albeit without the catchy titles in many standard texts, e.g. at
libretexts.

My point is that Bohr's atom was the last model where the electron actual orbited like a planet. In later models the electron not "moving" it's just sitting in a ground state, so "perpetual motion" comes from applying the wrong semantics.

There's a lot of bad semantics going around. There's a good explanation using math. But people convert it into some English and then complain about the math. Math is not the problem here.

For example IIRC we explained Compton scattering fully using wave equations. Original system has a wave equation for the electron and photon, the wave equation evolves over time. If you collapse it some time later you get the results of the scattering, which includes many occurrences of missing the electron. You do not need to collapse to particles in the middle.

Also lots of bad statements about the second law of thermodynamics. This is fundamentally statistical in nature. Nobody should be surprised that the statistics of a two-particle system manifest differently than a billion-particle system.

Sorry for the delay, just extremely busy at the moment.

The problem with the idea that electrons in atoms are standing waves is that for many aspects the electrons in hydrogen behave as though they are in a S-wave, angular momentum l =0, spherically symmetric distribution around the nucleus at a distance of 10**5 times the size of the nucleus, proton in this case. If one does an experiment one can collapse the electron to a specific point but how you go from a continuously variable standing wave to a condensed electron is easy in the maths but not easy conceptually. It is the argument about Schrodinger and his cat, how can a cat be both alive and dead? If one then goes on to consider atoms, one has various forms of ground states with non zero angular momentum, p,d,f... (l=1,2,3...) with various forms of electronic binding that lead to molecules and these then lead to macro parameters such as compressibility via Van de Waals forces that one can measure etc. One can also consider the added complications of intrinsic angular moment or spin with all fermions having half integer spin, all bosons having integer spin. In super conductivity one has Cooper pairs of Fermions that behave like bosons. Analogous processes exist in nuclei too. The concept of wave function or particle get applied where they work but as to understanding, that is beyond what we currently know.

Thermodynamics is a complicated business if one moves from macroscopic systems and begins to consider small or isolated or fluctuations in the vacuum it gets very complicated and it is not clear, at least to me, if we understand what is going on here as in the rest of quantum mechanics.

Regards,

To get better understanding you need to move beyond the "classical" quantum physics of Heisenberg/Schrödinger and study quantum field theory. Again, understanding meaning being able to explain observed behaviour in terms of mathematical models, not understand in being able to fully conceptualise.

The macroscopic laws of thermodynamics can be better understood in terms of the fundamental particle physics through study of statistical physics.

[odysseus2000]

I tend to think of quantum mechanics as being understood at the engineering level: We have maths that allows us to calculate properties that agree with experiment.

At a physics level I don’t understand quantum mechanics. I have no idea what the physics is that allows the collapse of a smoothly varying wave function into a discrete value by the act of observing.

I do not understand how entanglement works. How can entangled entities, photons or electrons allow one to know what the other component is by measuring its entangled pair over distances that are too large to be transverse by information, traveling at the velocity of light, to permit this knowledge to be obtained essentially instantaneously?

Sure all of these things come out of the maths and perhaps that is all we will ever know, but there seems to be some underlying mechanisms that operate & allow the mathematics to work. If we can understand that there would likely be a revolution in our understanding.

In terms of fields the debate goes back to Newton’s critics who described gravity as witch craft, no mechanism to allow the transmission of force of attraction. One can postulate that this force occurs by the exchange of gravitons, but as far as I know there is no evidence for that. Alternatively one can argue along the lines of general relativity that mass distorts space time & it is this distortion that creates gravity & we do experimentally see gravitational waves, both with earth based telescopes & with the fluctuations in pulsars, although the latter is not, as far as I know, universally accepted.

There is the huge success of quantum electrodynamics, but whether this is limited to the small or extends across all dimensions is not clear from experimental results. String theory is often brought out to explain all manner of stuff, but the energy levels involved are far beyond what we can reach, so whether it is a true description of matter or beautiful mathematics is not experimentally testable.

Regards,

[9873210]

Do you have any explanation for why inertial and gravitational mass are the same? Or why there are no magnetic monopoles?

Any theory is a summary of a lot of observations and an assumption that those observations are repeatable. There are always "whys" that have no answers.

As for needing math to do quantum mechanics and claiming this meaning we don't understand. Math is simple describing something precisely. That's why all fields of physics use math. English (or other languages) only have words for things that are commonly experienced and are quasi-classical. The lack of a simple explanation not using math is because the world is not quasi-classical. For that matter many popular explanations of special or general relativity are flat out wrong. But people don't care, they absorb the incorrect explanation and assume they have some sort of insight.

[odysseus2000]

Do you have any explanation for why inertial and gravitational mass are the same? Or why there are no magnetic monopoles?

Any theory is a summary of a lot of observations and an assumption that those observations are repeatable. There are always "whys" that have no answers.

As for needing math to do quantum mechanics and claiming this meaning we don't understand. Math is simple describing something precisely. That's why all fields of physics use math. English (or other languages) only have words for things that are commonly experienced and are quasi-classical. The lack of a simple explanation not using math is because the world is not quasi-classical. For that matter many popular explanations of special or general relativity are flat out wrong. But people don't care, they absorb the incorrect explanation and assume they have some sort of insight.

There are many things that we have no answers for such as why no magnetic monopoles have been detected & whether div B = 0 is universally true & if so why.

The argument over maths & physics is a very old one. Mathematicians have problems with things that are not quantified. Physicists have problems with things that they can’t understand at a qualitative level. Both sides like to feel they are superior, but there is a long tradition of physics thinking leading to understanding which then gets put on a mathematical frame work by theoretical physicists & mathematicians, the latter often getting upset at the lack of mathematical rigour & tricks of hand like renormalisation, summing infinite series etc which physicists justify by it giving a correct description of experiment.

It may be that there are somethings we can only understand by mathematics, or maybe the mathematics is obscuring some underlying physics. Einstein liked to argue that imagination was the most important tool in a physicists armory.

Regards,

[9873210]

The argument over maths & physics is a very old one. Mathematicians have problems with things that are not quantified. Physicists have problems with things that they can’t understand at a qualitative level.

Whoa there.

The bulk of mathematics is non-quantitative. Logic, group theory, topology, category theory, ... , anything that begins "there exists a ... ". The quantitative stuff is mostly on the applied side at the behest of engineers, physicists and other practical folk.

But the distinction here should not be between qualitative v. quantitative. It's between simple enough to explain to a five-year old (or a grad student) and a theory that is as simple as possible and no simpler. It's the universe that dictates how complex the theory has to be, and the universe doesn't care whether or not you can understand it without four years of tensor calculus; or understand it at all. You can and should try to simplify, but if experiments turn up the monster group instead of, say, SU(2) you won't have much luck; you'd need to get comfortable with the monster.

[odysseus2000]

The argument over maths & physics is a very old one. Mathematicians have problems with things that are not quantified. Physicists have problems with things that they can’t understand at a qualitative level.

Whoa there.

The bulk of mathematics is non-quantitative. Logic, group theory, topology, category theory, ... , anything that begins "there exists a ... ". The quantitative stuff is mostly on the applied side at the behest of engineers, physicists and other practical folk.

But the distinction here should not be between qualitative v. quantitative. It's between simple enough to explain to a five-year old (or a grad student) and a theory that is as simple as possible and no simpler. It's the universe that dictates how complex the theory has to be, and the universe doesn't care whether or not you can understand it without four years of tensor calculus; or understand it at all. You can and should try to simplify, but if experiments turn up the monster group instead of, say, SU(2) you won't have much luck; you'd need to get comfortable with the monster.

The interesting thing is that nature has not in general turned up the monster, but has instead mostly created things that are simple. Indeed Dirac often argued that if something was too complicated it was wrong; paraphrasing what he said.

Mathematics is indeed in its pure form abstract thought & can exist within that abstract thought as a stand alone discipline that may or may not have any practical use, but in that form it is only mathematicians who are interested. Sometimes things are found that can then be described by some mathematics that was developed for interest only & then more folk get interested.

There is often no interaction between mathematicians & physicists, neither discipline having interest to the other as they address very different areas & there is often friction when the two disciplines meet.

Regards,