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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

#31

Post by 317070 »

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.…

> There's not two sets of reality of what particles exist for two different coordinate systems.

Look up Unruh radiation for an example of such particles. Gravitons wouldn't be the first.

https://en.m.wikipedia.org/wiki/Unruh_effect

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

#32

Post by FollowingTheDao »

outlace wrote: post #6
sandworm101 wrote: post #3

>> Jonathan Oppenheim, who runs a program exploring post-quantum alternatives at University College London, suspects that’s because gravity simply can’t be squeezed into a quantum box. So... he is still part of the Orthodoxy. He is challenging ideas, but as an employee of University College London he is hardly any sort of outsider to the physics community.

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?

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

#33

Post by FollowingTheDao »

x3n0ph3n3 wrote: post #5
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 has been done, and we only see the gravity from the cannon ball that we placed, and not the alternate location it might have been placed at. Doesn't this presume that your brain deciding where to place the cannon ball was an uncertain quantum event? Doesn't it also presume quantum gravity does not exist?

Your brain is not deciding where the cannon ball is, it is predicting where it is and them making that prediction a certainty. That is the collapse of the wave function, turning a probability into a certainty.

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

#34

Post by FollowingTheDao »

treeman79 wrote: post #4
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…

Where would energy come from for creating each universe?

"Where would energy come from for creating each universe?"

Why does it have to come from somewhere? What if it just is?

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

#35

Post by phkahler »

bowsamic wrote: post #14
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…

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 save classical gravity?

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

#36

Post by rvcdbn »

bowsamic wrote: post #16
srejk wrote: post #7

Earlier quoted context omitted.

You have to be trained in physics to theorize about it. Thinking otherwise is the realm of the crackpot. https://www.youtube.com/watch?v=11lPhMSulSU

I’m a quantum physicist and you wouldn’t believe how many people try and sell me on their theory that solves everything that is literally just an idea in their head and can’t even produce any quantitative predictions. The levels of self delusion that these people display is astounding and we need to mock it more openly imo

if i have a crackpot theory and i’d like a real physicist to look it over and am willing to pay for their time where would i find one? asking for a friend

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

#37

Post by legel »

bowsamic wrote: post #16
srejk wrote: post #7

Earlier quoted context omitted.

You have to be trained in physics to theorize about it. Thinking otherwise is the realm of the crackpot. https://www.youtube.com/watch?v=11lPhMSulSU

I’m a quantum physicist and you wouldn’t believe how many people try and sell me on their theory that solves everything that is literally just an idea in their head and can’t even produce any quantitative predictions. The levels of self delusion that these people display is astounding and we need to mock it more openly imo

Agreed. Those who confuse “astronomy” and “astrology” are confused.

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

#38

Post by captainclam »

tgv wrote: post #10
treeman79 wrote: post #4

Earlier quoted context omitted.

Where would energy come from for creating each universe?

Among other problems. It's just bollocks on the level of "but you didn't say it couldn't be this, nanananana."

I think because of the abuse of "many worlds" in science fiction media (especially as of late) as a convenient plot device, people develop this idea that it's an unserious proposal wrt the foundations of physics. As far as I have read, it strikes me as perhaps the most parsimonious interpretation of QM out there.

Genuinely curious, what do you mean by "but you didn't say it couldn't be this, nanananana...?" The Everett interpretation isn't some fantastical notion spun up by a scifi writer...it is simply the consequence of removing collapse of the wavefunction as an objective event from the picture. And if it turns out our observations wouldn't be changed by removing this feature, then perhaps it was an extraneous feature in the first place!

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

#39

Post by contravariant »

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.

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

#40

Post by javajosh »

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 were caused a multitude of miniature Shapiro delays [0]?)

0 https://en.wikipedia.org/wiki/Shapiro_time_delay

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