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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

#331

Post by tsimionescu »

consilient wrote: post #118
tsimionescu wrote: post #65

Earlier quoted context omitted.

> 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…

> 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 individual observer, and that we can compute its probability based on how many observers would see a particular state versus the total number of observers.

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.

You are right about the CI though, it's not really a useful term.

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

#332

Post by xmcqdpt2 »

zmgsabst wrote: post #271
xmcqdpt2 wrote: post #260

Earlier quoted context omitted.

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…

How is it a cop out? We know two things: - universe was small enough everything was tightly coupled - non-local phenomena occur Insisting that our beliefs reflect an ideology (eg, you can segregate off portions of reality to study in isolation) which seem contrary to observed reality (eg, the points above) is religion — not a scientific investigation of the universe.

Superdeterminism sidesteps interpretational questions by arguing against reductionism, which is pretty much the core of all physics. Where is this hidden information stored? What causes the specific outcomes in a destructive measurement?

To say that QM is in fact a local hidden variable theory because everything was once touching billions of years ago, without positing any mechanism for it is a cop out.

At least instrumentalism admits that there are interpretational questions, even if we don't need to answer them.

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

#333

Post by GoblinSlayer »

mr_toad wrote: post #255
CuriouslyC wrote: post #97

Earlier quoted context omitted.

If I were a betting man I'd say black holes have no singularity, but rather a core of extremely dense exotic matter (probably formed from top/bottom quarks) which we haven't detected because it decays quickly under less extreme circumstances.

I think it’s true that once an event horizon forms no physical force (known or hypothetical) can stop a singularity forming. There may be some form of very dense matter that stops large stars from collapsing to the point where an event horizon forms in the first place, but that doesn’t seem to apply to super massive black holes. For super massive black holes the event horizon grows too fast.

It takes infinite time for event horizon to form, before that it's just dense. It's time dilation that stops formation.

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

#334

Post by wholinator2 »

SpaceManNabs wrote: post #308
richardw wrote: post #259

Earlier quoted context omitted.

Can they reach the center? And how long would that take? I ask because time will slow down for them as they accelerate towards the center.

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's own time.

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

#335

Post by xmcqdpt2 »

javajosh wrote: post #277
xmcqdpt2 wrote: post #267

Earlier quoted context omitted.

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 isotopi…

Perfectly applicable paper, thanks! I skimmed it, but I didn't see an explanation for the lower refraction index for the heavier isotope. It had the lower RI at all wavelengths they looked at. I think it's useful to ignore the "phonon resonance" wiggle in the middle of their tested range on page 4, around 600nm, if looking for some other effect. (it's crazy that an electron that weighs like 10^-31 kg could actually j…

The off-resonance curves look exactly like what you expect from the Kramers-Kronig relations

https://en.wikipedia.org/wiki/Kramers%E2%80%93Kronig_relatio...

which have very far reaching effects in term of refraction (the real part of the permittivity decays as 1/w).

In term of resonances, it's important to note that the nuclei themselves are not neutral either. In the IR, the time dependence of the field is slow enough that the nuclei can follow it resonantly. Those fields are much below electronic resonances so the electrons aren't even contributing much beyond making the crystal stable!

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

#336

Post by bowsamic »

tsimionescu wrote: post #330
bowsamic wrote: post #325

Earlier quoted context omitted.

> Sure, it's not part of the math, but it is part of the physics. "the physics" here is a specific interpretation > Decoherence helps explain certain things directly from the math without appealing to the extra Born rule, but not fully, and not quantitatively (not the specific probabilities). You can derive the Born rule using decoherence

> "the physics" here is a specific interpretation No, "the physics" here is the way we are supposed to tie the math to physical observations. You can't explain all of our experiments if you don't make a distinction between interactions which preserve quantum properties and measurements which lead to classical observations. For a specific example, you can't explain the double-slit experiment with a detector at one sli…

> the way we are supposed to tie the math to physical observations

Again, that's a matter of interpretation. The different quantum interpretations say different things here.

> No, you can't.

Yes, you can. Look up Quantum Darwinism.

PS. throwing "nuh uhs" back to a professional in the field is not appropriate. Get your respect in order.

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

#337

Post by GoblinSlayer »

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…

Photoeffect shows quantization and doesn't depend on qantization of orbitals.

Quants are absorbed in a finite time, not instantaneously.

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

#338

Post by goatlover »

Timwi wrote: post #263
strogonoff wrote: post #208

Earlier quoted context omitted.

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”.

Not true. Property dualism and panpsychism are neither of those things. There are other ideas as well that don’t involve souls or life forces.

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

#339

Post by AnimalMuppet »

eigenspace wrote: post #110
AnimalMuppet wrote: post #103

Earlier quoted context omitted.

If the events in frame 1 are causally connected, then to see the events in frame 2 in reverse order takes a boost of velocity greater than c, which is not a valid boost. Sure, you can do all kinds of things with a boost like that. It's not physically realizable, though. Can you show me an actual experiment to the contrary?

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 distance scales?

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

#340

Post by tsimionescu »

bowsamic wrote: post #336
tsimionescu wrote: post #330

Earlier quoted context omitted.

> "the physics" here is a specific interpretation No, "the physics" here is the way we are supposed to tie the math to physical observations. You can't explain all of our experiments if you don't make a distinction between interactions which preserve quantum properties and measurements which lead to classical observations. For a specific example, you can't explain the double-slit experiment with a detector at one sli…

> the way we are supposed to tie the math to physical observations Again, that's a matter of interpretation. The different quantum interpretations say different things here. > No, you can't. Yes, you can. Look up Quantum Darwinism. PS. throwing "nuh uhs" back to a professional in the field is not appropriate. Get your respect in order.

> Again, that's a matter of interpretation. The different quantum interpretations say different things here.

In my view, a physical theory has two parts: a mathematical model, and a series of rules to relate the model physical experiments. For example, the theory of Newtonian mechanics isn't just F=m×a, it also includes the observation of how to measure the mass of an object and its speed etc.

Without these extra rules, you just have a mathematical theory, not a physical theory.

> Yes, you can. Look up Quantum Darwinism.

I did, and as far as I understand (e.g. from here [0]), it is an exciting candidate for explaining the Born rule based only on the other equations, but it's not fully accepted and it has its own limitations so far. Still, very interesting, thanks for pointing me to it.

> PS. throwing "nuh uhs" back to a professional in the field is not appropriate. Get your respect in order.

I did not throw a "nuh uh", I explained what I looked for and why I came to my conclusion, including a citation from a professor in the field. I think that's about as far from disrespecting you as I can get, while still disagreeing. Not to mention, I didn't know you were a professional in the field.

[0] https://www.quantamagazine.org/quantum-darwinism-an-idea-to-...

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