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A physicist who bets that gravity can’t be quantized

quantamagazine.org

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Re: A physicist who bets that gravity can’t be quantized

#121

Post by javajosh »

tlb wrote: post #112
javajosh wrote: post #40

I think it would be funny if we discover that refraction is caused by the slowing of light in close proximity to mass. That is, one of the most common and observable phenomena in physics is a quantum gravity phenonema! (The usual explanation for refraction is that light as an EM wave causes sympathetic vibration in the electrons (and the protons, a little) which slows it down. But what if light's proximity to protons…

This can be refuted by observing that the refractive index isn't proportional to density, but is accurately predicted by charge mobility. Also, how refractive index changes with wavelength is related to the resonant frequencies of electrons.

Yeah, I was thinking about it and also lasers wouldn't work if it was 100% mini-Shapiro delays. I was thinking that maybe there's a small GR component to refraction, but the experiment would be tricky. You'd need to pin the electrons in the refractor down in a strong magentic field and then shoot some high energy photons at it, probably at least X-rays, and see if they still refract. (The high energy photons would be necessary to bring their wavelength closer to the diameter of the nucleus).

Re: A physicist who bets that gravity can’t be quantized

#122

Post by TillE »

light_hue_1 wrote: post #41
tauwauwau wrote: post #20

Putting it here, as it seems relevant. Veritasium: Parallel World Probably Exist: Here's Why https://www.youtube.com/watch?v=kTXTPe3wahc

The word "probably" there is completely meaningless. There are many interpretations of QM and there is no compelling reason to choose one over the others. In particular the many worlds interpretation makes no testable predictions, it's just a story. There's absolutely nothing "elegant" about it. There's no math, no experiment, no explanation. A story like you read in some religious text or science fiction novel. It h…

The "popular science" takes on QM have generally been an enormous failure, focused on irrelevant fluff like this. I mean, I get it, it's a subject that you can't seriously understand without a degree in physics or chemistry. I had plenty of trouble with the math even at the undergrad level.

But surely there's more interesting stories to tell of eg particle accelerator research, rather than fantasies.

Re: A physicist who bets that gravity can’t be quantized

#123

Post by bdamm »

rapjr9 wrote: post #114

I wonder if the recent news about the background gravitational hum of the universe has any bearing on this: https://www.sciencealert.com/breaking-news-physicists-have-d... It essentially means that gravity is always in flux everywhere, at all frequencies of gravity waves, so there is noise in gravity. This is in addition to the background EM radiation in the universe. Gravitational and EM fields are infinite are they…

Do we actually know that the fields are infinite? I thought it was just the easiest way to model what we know and can observe.

Re: A physicist who bets that gravity can’t be quantized

#124

Post by goatlover »

light_hue_1 wrote: post #59
goatlover wrote: post #47

Earlier quoted context omitted.

Shut and calculate is putting your head in the sand and avoiding that physics should be telling us what the world is. You’re wrong about MWI in that it’s a more elegant interpretation because it adds nothing extra to the wave equation and treats the universe as fundamentally quantum with no arbitrary dividing lines for classically scaled objects.

> Shut and calculate is putting your head in the sand and avoiding that physics should be telling us what the world is. It's how physics is done. PhD students don't sit in physics departments getting ideas from their interpretation of QM. The interpretations people have are so meaningless and useless they never appear in physics publications. You don't like it, but it's what physics is. > You’re wrong about MWI in th…

> It's how physics is done. PhD students don't sit in physics departments getting ideas from their interpretation of QM. The interpretations people have are so meaningless and useless they never appear in physics publications.

They do if they're going into foundations of physics. There's a sociological problem where the Copenhagen interpretation won out in the past and resulted in the shut up and calculate orthodoxy in teaching physics. But there are physicists like Sean Carol who think that's a historical mistake and based on failing to think about QM correctly.

https://www.preposterousuniverse.com/podcast/2023/06/26/241-...

> That's the thing about most QM interpretations, and in particular the many worlds interpretation, and why they aren't science just stories: you're right, they add nothing. So they are untestable!

Some make testable predictions like the collapse theories. For the others, it's more about the proper way to understanding what the mathematical formalism and experimental results are telling us about the world, and how we can use that to advance future physics.

> What can I say to "should"? I can only report what physics is in the real world.

And there have always been physicists like Einstein, Everett, Bohm and Bell who pushed back.

Re: A physicist who bets that gravity can’t be quantized

#125

Post by TheOtherHobbes »

CraftingLinks wrote: post #22
edgyquant wrote: post #12

Earlier quoted context omitted.

Why would anyone believe such a thing?

Because that's what quantum mechanics in it's purest form tells us. Avoiding the many worlds requires tagging on extra stuff not in the equations.

As opposed to tagging on a literally incalculable number of extra universes for every possible quantum interaction.

Re: A physicist who bets that gravity can’t be quantized

#127

Post by goatlover »

tsimionescu wrote: post #65
goatlover wrote: post #47

Earlier quoted context omitted.

Shut and calculate is putting your head in the sand and avoiding that physics should be telling us what the world is. You’re wrong about MWI in that it’s a more elegant interpretation because it adds nothing extra to the wave equation and treats the universe as fundamentally quantum with no arbitrary dividing lines for classically scaled objects.

> You’re wrong about MWI in that it’s a more elegant interpretation because it adds nothing extra to the wave equation and treats the universe as fundamentally quantum with no arbitrary dividing lines for classically scaled objects. That's how it's often presented, but this is wrong. In fact, it does add something to the theory, and that's a measure of how many "worlds" there are after a quantum measurement, which he…

> That's how it's often presented, but this is wrong. In fact, it does add something to the theory, and that's a measure of how many "worlds" there are after a quantum measurement, which helps translate the wave function values into testable probabilities (the Born rule).

The distribution of worlds/branches is determined by the wave function. A more likely outcome means there are many more worlds with that outcome. You can calculate the percentage of worlds that have that outcome.

> Also, the MWI has to somehow define a formal notion of an observer/a classical world, which runs into questions of scale just as much as the measurement postulate of CI.

Measurement, observer and classical shouldn't be part of a physical theory. The answer as to why things appear that way to us is decoherence.

Re: A physicist who bets that gravity can’t be quantized

#128

Post by Gordonjcp »

fsh wrote: post #109
Gordonjcp wrote: post #101

Earlier quoted context omitted.

But space is quantised, that's what Planck's Constant is. The oddity we see with things at relativistic energies is simply because - as with all discretised representations of continuous-time systems - things get a bit fucky close to Nyquist, and the maths breaks down.

There is zero evidence that space is quantized, and this would contradict the Standard Model, as well as General Relativity. The Planck constant gives the relation between the energy of a photon (or more generally a harmonic oscillator) and its frequency. It has nothing to do with the structure of space.

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Re: A physicist who bets that gravity can’t be quantized

#129

Post by consilient »

guerrilla wrote: post #102
CuriouslyC wrote: post #89

Earlier quoted context omitted.

People talk about how space time can't be quantized as if the universe was made up of tiny little cells like minecraft because there is some evidence against that hypothesis. An alternate hypothesis, that a particle is "virtual" and its position/momentum "vector" contains a finite amount of information, is actually both extremely plausible and explains odd paradoxes like the Heisenberg uncertainty principle. That wou…

I was told that this is exactly what the Bekenstein bound ultimately means. It seems reasonable to me, but then why is that not conclusive? Also if anyone who knows wants to explain why the Bekenstein bound is even a thing, I'd love to hear that too.

Exceeding the Bekenstein bound would mean having less-than-equilibrium free energy. See https://arxiv.org/abs/1802.07184
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