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Quantum particles feel the influence of gravitational fields they never touch

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Re: Quantum particles feel the influence of gravitational fields they never touch

#61
post #58

Earlier quoted context omitted.

"The key point is that the potential, rather than the field, has an observable effect. In classical gauge theories, the potential itself is not considered to be observable; only the field (the gradient of the potential) is. However, in QM, the potential itself can have observable effects." That comment is short, succinct and understandable, it's the best summary of the physics involved that I've heard in so few words…

> in QM, why exactly does potential have observable effects? The simple answer is that it's right there in the Hamiltonian, and the Hamiltonian is the central operator in QM, the one that determines time evolution. The fact that the EM potential appears there has been known almost as long as QM itself. Much of the recent QM experimentation in gravitational fields has been making use of recent technological advances t…

I suppose I fell foul of AE's warning about oversimplification but it's sometimes difficult to avoid in HN posts. Also, I am not a professional physicist which means I don't have the depths of understanding at the edges of the subject that I wish I had, this essentially limits my comments to the accepted orthodox understanding of the subject.

It's a while since I last looked at Aharonov and Bohm's '59 paper but if I recall your point about the Hamiltonian is covered there. My understanding is that in this paper the key difference from the earlier work to which you also refer is that their new solution to the Hamiltonian now involves a phase factor.

The point I should have made was that I wasn't thinking so much about the mathematical explanation of the Aharonov-Bohm effect but in more general terms where perhaps this new experimental work may reinvigorate interest in the subject and in related areas.

Whilst QFT provides us with an exquisitely accurate mathematical account for the purposes of calculation, it says little about the underlying physics per se. Thus, it seems to me that we stil have a limited understanding about the nature of say virtual particles, ZPE, etc. and essentially no understanding of why the electric, magnetic and fine structure constants and others are the values they are.

Research into the Aharonov-Bohm effect, could eventually lead to a deeper more fundamental understanding of the subject although, given past history, I fully accept that coming up with a major breakthrough in the near future is probably unlikely. (It's even more unlikely that we'll resolve the constants problem anytime soon, if at all.)

It seems to me that the most significant aspect of this work is that we now have more than just a theoretical framework that connects EM and gravity/the gravitational field at a QM level (or seemgly so). Tenuous it may be but it seems like a good start.

For my part, I still worry about why, say, the electric and magnetic constants have the value they do or why our understanding of ZPE is seemingly at odds with reality given the ludicrous value of the calculated zero-point radiation of the vacuum. But then, this is more about philosophy than it is about physics.

Re: Quantum particles feel the influence of gravitational fields they never touch

#62
post #21

Earlier quoted context omitted.

As is unfortunately common in pop science writeups, the article gives a garbled description of what the Aharonov-Bohm effect actually is. The key point is not that "the field never touches the particles". The key point is that the potential , rather than the field, has an observable effect. In classical gauge theories, the potential itself is not considered to be observable; only the field (the gradient of the potent…

You're right, most descriptions of Aharonov-Bohm fail to mention Electromagnetic Potential , and just describe it as quantum woo. I'd love to have an actual quantum detector, like a SQUID, to do some physics experiments with.

You'll recall that Feynman whinged about the lack of potentials when he was trained (there bring too much emphasis on fields and almost nothing on potentials). And I reckon he was right to do so for the same reasons, as it took me a considerable amount of time to shift my thinking around to thinking potentials and not fields.

Re SQUIDs, likewise, I could amuse myself for ages if I had several to play with.

Re: Quantum particles feel the influence of gravitational fields they never touch

#63
post #23
post #20

Earlier quoted context omitted.

They measured a bigger gravitational effect on the particle, because the superpositional pair of the particle flew closer to a mass than the actually measured particle. Regarding the "never touch", gravity decreases with distance squared, so it diminishes quickly with distance. There is a big difference in being near the mass, as opposed to feeling the dimished effect of it from far.

> They measured a bigger gravitational effect on the particle No, they didn't. They measured a phase shift in the particle's wave function. There is no "gravitational force" in free fall, and the particles were in free fall. > gravity decreases with distance squared The Newtonian gravitational force does, but the Newtonian gravitational force is irrelevant for an experiment conducted in free fall, as this one was. Th…

"The gravitational potential is the key thing being measured, and it's not the potential due to the Earth, it's the potential due to a 1-kg "source mass"."

Right, it seems that for many the 'potential' worldview is hard to grasp (it was for me too until it drawned on me that it's important).

I blame this on poor training and poor textbooks, they don't emphasize the importance of potentials. Also, we seem to grow up with a 'fields' perspective, electric fields and so on.

Maxwell was on the 'right' path with his original formulation of his equations where potentials were involved. However, when Heaviside reformulated them to the 'vector' view we quickly lost the 'potential' one.

No doubt, Heaviside's formulation is incredibly useful in electrical engineering and eleconics and as you'd know that's how they usually appear in textbooks. Trouble is, outside advanced physics texts the 'potential' view is usually omitted. Educators really need to fix this.

Another problem is that the description of a potential is not up to scratch. All too often we seem to be stuck with highschool physics descriptions - those that involve pith balls. The concept that we never measure absolute energy, but only differences often gets lost when describing potentials.

You'd reckon that after Feynman's well documented whingeing about the fact he wasn't taught about potentials early enough that you'd think by now educators would have had sufficient time to have rewritten their notes but apparently they've not.

Re: Quantum particles feel the influence of gravitational fields they never touch

#64

I know this is a trope that comes up in half of the posts involving a journal article, but scientific journal pricing is so confusing to me. I can pay $30 for digital access to a 4 page article (it says Vol 375 pg 226-229). Or I can pay $15 and get the entire issue of Vol 375 in print? Or I can pay $80/yr to join AAAS and get "50 issues of Science", but which issues? I assume they mean the upcoming year of issues, bu…

i think a possible startup idea would be to start a "Github for science" (replace "science" with any academic or interest area really). Encourage folks to post their papers in latex or markdown. Post their data, code, mechanical and electrical drawings, videos and pictures of their experimental setup, videos explaining their research, videos performing the experiment?, and so on. Allow others to comment on research w…

The problems with this are overcoming the startup inertia and coming to a common agreement about how to implement it.

In my view, the latter is by far the most difficult and failing to come up with a common objective or view is likely to either scuttle the project or render it ineffective or inefficient.

Let me give you a real world example: Linux. We've so many distros that it's hard for anyone of them to get real traction. As we've seen for decades, Linux has never managed to take on Windows on the desktop for the reason that there are so many disparate views about how tackle the problem. Both businesses and ordinary users want certainty not constant variation.

We see the same problem in other areas of the net, for instance copyright reform. The only way to tackle that is on a worldwide basis - as the forces against it are aldo already very well organized on a worldwide basis and have been so for some 140 years (since the original Berne Convention).

I've often thought that we need a worldwide union of computer users to tackle these issues and take on Big Tech, etc. but how does one start something as big and significant as this let alone hold it altogether for any length of time?

I wish I knew.

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