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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

#351

Post by ImHereToVote »

lgas wrote: post #344
ImHereToVote wrote: post #301

Earlier quoted context omitted.

Unless one of the observers accelerates for some reason. Now his observation is privileged.

Doesn't relativity mean there's no difference between that observer accelerating in one direction and everything else accelerating in the opposite direction? So wouldn't everyone's observation be equally privileged? I'm asking honestly as am (obviously) not a physicist.

You would think so, but no. There is something magical about acceleration, specifically how much spacetime you increasingly or decreasingly traverse.

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

#352

Post by SpaceManNabs »

wholinator2 wrote: post #334
SpaceManNabs wrote: post #308

Earlier quoted context omitted.

Time doesnt slow down for them. They reach the center in their time as normal. We never see them reach the center. You can use kruskal coordinates and other tools to understand this.

Right, time doesn't slow down for them, but it would appear so for an outside observer. So would the "experience" of a particle sent in to be that it circles closer and closer for some time on the order of years and at some point when it is arbitrarily close to the center it just pops out some billion or trillion years later once the black hole has evaporated? Assuming it isn't destroyed and somehow can experience it…

It would be more than a few trillion years I think, but that is the thinking unless you are a certain contentious Berkeley astrophysicist.

The particle does see itself “reach” the black hole though. And so would an outside observer if they had infinite time.

The black hole dissipating sure would make some of the experience odd. I would need to revisit my notes to make a claim about that, but discontinuities like that arent uncommon.

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

#353

Post by eterevsky »

audunw wrote: post #278
eterevsky wrote: post #48

Earlier quoted context omitted.

If they are close enough to each other and far enough from everything else, then why not. The smallest objects for which we measured their gravitational interaction weighed just 90 mg ( https://arstechnica.com/science/2021/03/researchers-measure-... ). The biggest object put in quantum superposition weighed around 1 mcg ( https://physics.aps.org/articles/v16/s45 ).

I think the comparison you're giving here is quite misleading. You're implying that we "only" need to scale up the objects we put in quantum superposition by tens of thousands of times. But that's not all there is to it. You'd have to put it in a kind of superposition that affects its mass enough to be measured. For instance, having the whole object be in superposition of one position, or another position several cen…

I do understand that there's more to it than just closing the gap of 90'000x. That said, the fact that these numbers are on roughly the same order of magnitude makes me cautiously optimistic.

If anything, to me both measuring the gravity of 90 mg weight and putting a crystal that you could see with your naked eye into quantum superposition already seem borderline unthinkable.

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

#354

Post by eigenspace »

AnimalMuppet wrote: post #339
eigenspace wrote: post #110

Earlier quoted context omitted.

Compton scattering with a space-like separation for the absorption and emission points are a well known phenomenon in quantum field theory. Classically these events would be causally disconnected, but in a QFT the propagator is non-zero and instead has an exponential suppression in the space-like interval. This is a phenomenon with experimental consequences and uses: https://arxiv.org/abs/1301.3819 https://www.nature…

Interesting. I did not know that. Still, we were originally talking about gravitons. "Exponential suppression in the space-like interval" means that it cannot apply to gravitons (or at least, it cannot apply to gravitons on astronomical scales). So, backtracking the argument a ways: Do you have any examples of the numbers of particles being different in different frames or coordinate systems that works at all distanc…

What makes you think this cant apply to gravitons, or more generally, what makes you think that gravitons are relevant over large distance scales?

> Do you have any examples of the numbers of particles being different in different frames or coordinate systems that works at all distance scales?

Sure, it’s called the Unruh effect. Any accelerated frame (or observer in a gravitational field) will see a different particle vacuum than observers in a inertial frame.

This means that if you start in empty space and then accelerate, the space will suddenly not look so empty and will be at a higher temperature with more fluctuating particles.

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

#355

Post by mrguyorama »

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.

You are asserting that there is something fundamentally "unsimulatable", un"real" about consciousness.

If we are going to give up and turn to religion for our understanding of the universe then I pick "last tuesday-ism". It physically cannot be distinguished from any other compatible interpretation of the data.

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

#356

Post by lossolo »

meindnoch wrote: post #224
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…

>virtual world geometry with continuous function derivation which then gets converted into discrete voxels in order to track state around free agent interactions What?

Video games basically, you only render what's user is looking at.

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

#357

Post by consilient »

guerrilla wrote: post #307
consilient wrote: post #129

Earlier quoted context omitted.

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

Hmm so that would be a system being out of equilibrium but in a "negative" direction, which is nonsense since any amount of non-equilibrium is a positive amount of free energy. So, I don't understand any of the math in that paper but is there any easy/intuitive way to explain why a higher information density would require negative free energy? I guess I need to understand the relationship between information density…

> So, I don't understand any of the math in that paper but is there any easy/intuitive way to explain why a higher information density would require negative free energy?

Not really, no. If you don't have the equivalent of a good undergraduate education in physics very little about QFT is going to be accessible to you.

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

#358

Post by naasking »

GoblinSlayer wrote: post #329
naasking wrote: post #119

Earlier quoted context omitted.

> Oh no I get that, but two comments above inciampati was suggesting that we will end up in a situation where some variable will have to have an infinite value The black hole information paradox from that article presumably fits. The conclusion from GR is that no information can escape, which is ultimately incompatible with QM, and that conclusion ultimately depends on the infinite density of the singularity. I think…

Problems 1-3 there are caused by point particles, not by space. They mention ultraviolet catastrophe was caused by continuous space, but it was caused by non-quantum radiation, so there's no classical electrodynamics with discreet space, instead there's quantum electrodynamics with continuous space.

I'm not sure what "problems 1-3" are referring to here, but all of these problems fundamentally trace their roots to issues with the foundational assumption of continuity.

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

#359

Post by consilient »

tsimionescu wrote: post #331
consilient wrote: post #118

Earlier quoted context omitted.

> 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). All interpretations need to induce a measure over observations ( not "worlds") to produce meaningful results. Without that all you have is an abstract mathematical object. > As you can see, the two interpretations require the same amount of extr…

> All interpretations need to induce a measure over observations (not "worlds") to produce meaningful results. Without that all you have is an abstract mathematical object. Agreed, but the MWI in particular does so by applying frequentist probabilities over all versions of an observer, the so-called worlds. The argument goes that there is an apparent non-deterministic process from the point of view of every individua…

> For some reason, many MWI adherents want to claim that this is not an additional postulate, that MWI only needs the Shrodinger equation, but it clearly is a postulate in addition to that equation, just as much as the collapse idea in other interpretations.

I think you're misinterpreting them (us). The claim is that MWI requires one additional postulate, whereas collapse interpretations need at least two: they both need a way to make distributions into probability distributions over observations, but collapse additionally requires some way of dodging Wigner's Friend type scenarios: an objective classical transition, extra state beyond the wavefunction, outright antirealism, etc.

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

#360

Post by consilient »

kgwgk wrote: post #304
consilient wrote: post #221

Earlier quoted context omitted.

Depends on whether you're talking about the "perspective" of the whole joint |Rock>|Interaction Eigenstate 1> + |Rock>|Interaction Eigenstate 2> ... system or just one of its components. > Decoherence doesn't make things "look classical" by itself - at least until you define what "looking" is. Of course; but that's true of every scientific theory. Decoherence solves the preferred basis problem, not the hard problem o…

> Decoherence solves the preferred basis problem, not the hard problem of consciousness. Ok, I guess I misunderstood the scope of "There's also nothing special about observing." It's not clear to me if you (MWI) would say that rocks had defined positions when nobody was observing them - or whether the question of things having definite positions (and the very existence of those things) wouldn't even make sense in the…

> Ok, I guess I misunderstood the scope of "There's also nothing special about observing."

There's nothing special about the physical processes constituting a scientific experiment. They're unitary evolution like everything else. Whether there's anything special about conscious experience (for my money: obviously yes) is outside the scope of physics.

> or whether the question of things having definite positions (and the very existence of those things) wouldn't even make sense in the absence of consciousness.

If you want to be perfectly precise, the MWI does not contain discrete things at all, any more than the Earth objectively has discrete continents and seas. But the most accurate map is not always the most useful one.

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