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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

#41

Post by light_hue_1 »

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 has nothing more going for it than that.

Practically, the most "likely" situation, if you want to define likely as what most researchers think and how they behave, is that most people are fans of "shut up and calculate". QM is what it is. That's it. We don't need crazy interpretations, particularly ones that don't contribute anything to our understanding.

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

#42

Post by outlace »

FollowingTheDao wrote: post #32
outlace wrote: post #6

Earlier quoted context omitted.

Genuine question here, when was the last time a total outsider made a significant contribution to physics?

Ask yourself; why are they outsiders in the first place? It's like asking why hasn't anyone who is not a player in major league baseball ever won a world series?

Those are disanalogous in the case of theoretical physics where you don’t need access to any expensive equipment. There’s nothing in principle preventing someone from learning math and physics on their own or from a traditional university and then coming up with new theories alone. And in fact this happens all the time and most of those people get called crackpots.

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

#43

Post by archibaldJ »

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…

Now I'm curious: does the refraction that happen within our eyes has anything to do with the processing and the consequent experience of sight in a way that it utilizes quantum mechanics that we don't understand?

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

#44

Post by LatteLazy »

AnimalMuppet wrote: post #23

Somewhat off topic, and somewhat related: I don't think there actually is such a particle as a graviton. General relativity says that you can't tell the difference between being unaccelerated, and being in free fall. But in one case you have no gravitons coming in, and in the other you have gravitons. I can change whether gravitons are there or not by a (general) relativistic transformation. But that's not possible.…

In relatively gravity is not a force like Electromagneticism etc. Instead, space time is curved and as a result the object itself is travelling in a straight, in accelerated line and only looks like it is accelerating to an observer outside of the curved space.

So relativity has no gravitons and instead curves space.

In quantum physics the opposite is true: space is flat, and gravity is like other forces, the result of particle exchange.

This is one way that the two systems are incompatible.

Again, happy to be corrected...

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

#45

Post by semi-extrinsic »

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…

This. So much this. And also https://xkcd.com/1240/

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

#46

Post by bowsamic »

phkahler wrote: post #35
bowsamic wrote: post #14

Earlier quoted context omitted.

I’m a quantum physicist and yeah you’re totally right. It’s already obvious that a quantum theory of gravity is needed because we need a way to talk about superpositions of spacetime curvatures. Either QM is wrong in general or we need a way to treat spacetime that is in a quantum superposition Also my old supervisor actually suggested an experiment to observe this gravity induced entanglement but it would require ex…

>> 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.

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

#47

Post by goatlover »

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…

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.

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

#48

Post by eterevsky »

contravariant wrote: post #39
eterevsky wrote: post #8

(Not a quantum physicist. Please correct me if I am misunderstanding.) From what this article says, his assumption is that gravity is classical, but "fuzzy" or probabilistic: you can't precisely measure the gravitational field of a sufficiently small object. In the last years we've seen progressively bigger objects being put in quantum superposition. The theory from this article is incompatible with this process cont…

> possibly even without creating a particle accelerator the size of the solar system. Sure, you just need to entangle two objects big enough to exert a noticeable amount of gravity on one another but somehow do not interact gravitationally with the rest of the set up. Anyway, let's try a cat sized object first, then we'll finally know if Schroedinger had a point.

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).

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

#50

Post by tauwauwau »

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…

I watched it a long time ago. I just put it here because it presents the idea visually, not because I support or even understand it :)
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