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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

#261

Post by fallingfrog »

btilly wrote: post #2

If you believe in the Everett Interpretation, then he is wrong. The Everett Interpretation, aka Many Worlds, holds that both observer and observed are quantum mechanical systems. From this it follows that the act of observation does not produce a "collapse", but it does separate the observer into multiple observers that can't interact with each other again. So Schrödinger's cat is in a superposition of alive and dead…

This is a good summary. I like to put it the following way as an alternative: instead of imagining that you are the researcher, imagine that you are the cat.

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

#262

Post by fallingfrog »

slowmovintarget wrote: post #28
btilly wrote: post #2

If you believe in the Everett Interpretation, then he is wrong. The Everett Interpretation, aka Many Worlds, holds that both observer and observed are quantum mechanical systems. From this it follows that the act of observation does not produce a "collapse", but it does separate the observer into multiple observers that can't interact with each other again. So Schrödinger's cat is in a superposition of alive and dead…

In Everettian Mechanics, decoherence occurs long before the box is opened. The photons in the box interact with the cat. That entanglement with the environment which causes the branching of the wave function occurs then. The observer that opens the box is already either in a branch where the cat is asleep (to borrow from Sean Carroll) or awake. The interesting thing to come to understand is that probability doesn't a…

The cat is all entangled with the other stuff in the box, but by assumption the stuff inside the box is not entangled with the stuff outside the box.

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

#263

Post by Timwi »

strogonoff wrote: post #208
kromem wrote: post #185

In the decades since the establishment of these theories, both the continuous (classical) spacetime of general relativity and discrete matter of quantum mechanics, the world has changed in rather significant ways. One of those has brought forth advances in technology which led to creating virtual world geometry with continuous function derivation which then gets converted into discrete voxels in order to track state…

A simulation produces philosophical zombies, yet you are not one.

The idea of a philosophical zombie is logically incoherent. The only way to even get the idea is to make unscientific assumptions such as souls or a metaphysical life force, which is itself incoherent as it can't even decide what is “real”.

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

#264

Post by im3w1l »

jiggawatts wrote: post #251

Fields aren't quantised, that's the problem , that's why gravity can't be quantized. It's a field! Immediately, dozens of people are about hit the reply button and say something like: "But all of modern physics is based on quantization!" or something to that effect. The issue is that there's two ways to think of quantization, and for almost all practical experiments, there's no way to distinguish between the two. Ess…

> Unfortunately, those experimental results are cheerfully ignored and hand-waved away. But stop and think about it: how exactly would you model a five kilometre long radio wave quanta as a point? How could something like that be instantaneously absorbed?

Well there are are manu acausal things in quantum world right? So it would work same as any other "spooky action at a distance". Somehow it turns out fine because it can't be used to transmit information.

As for the rest of the comment I'm not well-read enough to have an opinion.

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

#265

Post by causality0 »

Out of curiosity, what's the quantum angle limit? If position is quantized and all fundamental particle are isotropic, there must be a minimum "angle of turn" for all objects, and by extension, a "maximum angular accuracy" for something like, say, orienting the face of a macroscopic object to face a particular direction. How many of those fit in a circle?

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

#266

Post by cryptonector »

eigenket wrote: post #146
bowsamic wrote: post #46

Earlier quoted context omitted.

The problem is that it doesn't act like a mass distribution, it acts as two non spatially overlapping possibilities. I think that the only way to save classical gravity would be superdeterminism. If quantum states correspond to anything other than our ignorance, i.e. if superposition states are actual physical states of reality, then gravity will need to be quantum.

I attended a talk by Jonathan Oppenheim a while back on this subject, and my understanding based on that is that in his model something (very) roughly like this happens. You put your massive object in superposition, it interacts with space-time and "tries" to put space-time in superposition but since space-time is fundamentally classical (in his model) what happens is space-time ends up in a probabalistic mixture of…

Spacetime observing massive objects.

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

#267

Post by xmcqdpt2 »

javajosh wrote: post #202
amelius wrote: post #189

Earlier quoted context omitted.

Ok, I confess that I didn't read the entire comment. But you have a second problem, as you should explain why the conventional explanation does not hold or is canceled by your theory.

I'm already convinced[0] the effect is small, if it exists at all. However I thought of another experiment that might be easier to perform, to see if there is any effect at all: take two crystals, as similar in depth as one can make them, with two different isotopes, and measure the difference in index-of-refraction. Silicon (28 and 30?) would probably be good for this, as would laser interferometry. (Maybe the Gravi…

Isotopes are not 100% chemically equivalent and they form chemical bonds with different vibrational resonances because the vibrating masses are different. You can see those differences in spectroscopic line shapes including in refraction (which is related to absorption by the Kramers-Kronig relation). My guess is that those effects would swamp out any relativistic ones by a lot, and because you can't tune the isotopic mass you wouldn't be able to isolate a gravitational effect.

In fact it appears that the isotopic dependence for silicon isotopes is known,

https://arxiv.org/abs/1105.0822

and the refractive index of Si 30 is lower than Si 28 in the IR, because of the different absorption lines.

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

#268

Post by cryptonector »

causality0 wrote: post #265

Out of curiosity, what's the quantum angle limit? If position is quantized and all fundamental particle are isotropic, there must be a minimum "angle of turn" for all objects, and by extension, a "maximum angular accuracy" for something like, say, orienting the face of a macroscopic object to face a particular direction. How many of those fit in a circle?

Between space quantization (Planck length) and the size of the visible universe, the minimum angle is fantastically small.

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

#269

Post by consilient »

xmcqdpt2 wrote: post #260
nocoolnametom wrote: post #182

Earlier quoted context omitted.

When you say superdeterminism are you referring to something like Pilot Wave theory, where what appear to our measurements as probabilistic yet random interactions are merely expressions of a more complex yet non-random underlying system that we cannot, as yet, measure? (I don't even know if that's the proper description of the hypothesis.)

Superdeterminism is simply the idea that all quantum experiments results could have been known before performing them, assuming a perfect knowledge of the state of the universe. It's one of those things that could be true and explain all of QM but also is kind of a cop out. "Of course your two detectors are giving correlated results, they were tightly coupled 13.8 billion years ago and now they are forever linked lik…

> Superdeterminism is simply the idea that all quantum experiments results could have been known before performing them, assuming a perfect knowledge of the state of the universe.

That's just determinism. Superdeterminism additionally posits that the results of those experiments are all correlated so as to make it appear to us as if local hidden variable theories were false. Pick the settings on two polarimeters for a Bell-type experiment by measuring the spins on photons emitted 10 billion years ago from two different galaxies, and you'll find (or rather, won't find, because it's being hidden from you) that they were arranged, long before the Earth was formed, just so as to trick you. The universe is conspiring against us, and the whole scientific project is a farce.

That, or superdeterminism is false.

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

#270

Post by incompatible »

bowsamic wrote: post #46
phkahler wrote: post #35

Earlier quoted context omitted.

>> It’s already obvious that a quantum theory of gravity is needed because we need a way to talk about superpositions of spacetime curvatures. Is that because of things like the double slit experiment they mention? A particles could be monitored via its gravitational effect on spacetime to determine which slit it went through. What if the particles mass behaves as a mass distribution in such an experiment? Does that…

The problem is that it doesn't act like a mass distribution, it acts as two non spatially overlapping possibilities. I think that the only way to save classical gravity would be superdeterminism. If quantum states correspond to anything other than our ignorance, i.e. if superposition states are actual physical states of reality, then gravity will need to be quantum.

These distributed "particles" are passing through both slits simultaneously before somehow transferring their energy at a particular position at the target screen. If gravitation is non-quantum, I suppose I'd expect that a gravitational measurement would show it passing through both slits, half of its total mass through each.
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