A physicist who bets that gravity can’t be quantized • Hacker News Board

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

#291

Post by goatlover » Tue, Jul 11, 2023, 4:23 AM UTC

tsimionescu wrote: post #139

goatlover wrote: post #127

Earlier quoted context omitted.

> 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 helps translate the wave function values into testable probabilities (the Born rule). The distribution of worlds/branches is determined by the wave function. A more likely outcome means there are many more worlds with that outcome. Y…

> A more likely outcome means there are many more worlds with that outcome. You can calculate the percentage of worlds that have that outcome. First of all, this is a new postulate of QM, you can't derive it from the Schrodinger equation. It is perfectly equivalent with the measurement postulate. > Measurement, observer and classical shouldn't be part of a physical theory. The answer as to why things appear that way…

Measurements are interactions that result in entanglement. Atoms radioactively decaying in your body are interactions. The environment is the entire universe as it becomes entangled with a quantum event.

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

#292

Post by archgoon » Tue, Jul 11, 2023, 4:25 AM UTC

eternityforest wrote: post #283

bobbylarrybobby wrote: post #254

Earlier quoted context omitted.

IIUC, quantized doesn't mean finite, it just means discrete. Energy being quantized in bound states in quantum mechanics means that the eigenvalues are discrete, but a state can still be any linear combination whatsoever of the eigenstates. And since spacetime is continuous, it's determines by its values on a dense subset, in particular a countable sense subset, which would make both sets of possibilities, gravity an…

What determines the amount of information? Is it the total values the gravity could have had with unlimited mass? The number of values that are less than the one it is observed to be? All the values in the probability distribution for some uncertainty thing? If you have a carbon atom, does it have unlimited information because it theoretically could instead have been some other number of atoms?

> What determines the amount of information?

Noise. Your ability to distinguish between states.

> If you have a carbon atom, does it have unlimited information because it theoretically could instead have been some other number of atom

You don't even need that. A single hydrogen atom has an infinite number of bounded energy states. In principle, you could store infinite information by putting an electron in the nth energy state and keeping it there.

In practice, you can't, due to noise.

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

#293

Post by light_hue_1 » Tue, Jul 11, 2023, 4:41 AM UTC

goatlover wrote: post #124

light_hue_1 wrote: post #59

Earlier quoted context omitted.

> Shut and calculate is putting your head in the sand and avoiding that physics should be telling us what the world is. It's how physics is done. PhD students don't sit in physics departments getting ideas from their interpretation of QM. The interpretations people have are so meaningless and useless they never appear in physics publications. You don't like it, but it's what physics is. > You’re wrong about MWI in th…

> It's how physics is done. PhD students don't sit in physics departments getting ideas from their interpretation of QM. The interpretations people have are so meaningless and useless they never appear in physics publications. They do if they're going into foundations of physics. There's a sociological problem where the Copenhagen interpretation won out in the past and resulted in the shut up and calculate orthodoxy…

> They do if they're going into foundations of physics

People don't do PhDs on this topic because it's not productive. Famous/bored/tenured/rich people pitch in arguments for fun. Anyway, the vast majority of work in foundations of physics has nothing to do with these interpretations https://link.springer.com/journal/10701/volumes-and-issues This is a niche inside a niche in a mostly irrelevant field.

No advance in physics has ever been made based on QM interpretations. No Nobel has ever been won. No phenomena have ever been discovered this way. It's just not what people work on and it's not how physics is done.

You're determined that your view of the world is right, and that of actual working scientists is somehow blind orthodoxy that's missing the point. There's nothing I can say to fix that. It's like arguing with an antivaxer. You think you know more than the people doing the work. Bye stranger! But.. it's worth considering that here and elsewhere in life your probably don't know better.

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

#294

Post by goatlover » Tue, Jul 11, 2023, 4:43 AM UTC

consilient wrote: post #178

FollowingTheDao wrote: post #150

Earlier quoted context omitted.

First, thank you for responding. I’m not saying there’s anything special about our mind, it’s just a function of our mind. And is it misinterpretation or is it my interpretation that you disagree with? How can one rationalize the fact that a photon can be a wave and a particle at the same time? I do not believe, for example, that the moon exist, only because I look at it. I think it exists in a probabilistic state in…

> How can one rationalize the fact that a photon can be a wave and a particle at the same time? Photons are not particles or waves. They are similar to classical particles in certain respects and similar to classical waves in other respects, but what they're really like is a localized excitation of the electromagnetic field. Because that's what they are. Physics by analogy simply does not work. If you understand the…

Depends the interpretation. Bell thought the most straight forward conclusion was that quantum systems are both quantum waves and particles, where the wave guides the particle (Pilot Wave/Bohmian Mechanics). In MWI, particles are superpositions of every possible quantum value. We can understand that as branching worlds thanks to entanglement and decoherence.

Saying we can't understand the mathematical formalism is a kind of Copenhagen interpretation.

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

#295

Post by arpowers » Tue, Jul 11, 2023, 4:55 AM UTC

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…

If I understand you correctly, Ive long thought about this as well!

Note you should clarify that by "slowing of light" you mean a lowering value of the absolute speed of light.

While Einstein assumed it was constant, yet said speed and time we're changing. It's actually simpler to say the opposite; speed and time change because speed of light (c) changes .

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

#296

Post by tlb » Tue, Jul 11, 2023, 4:56 AM UTC

danbruc wrote: post #244

tlb wrote: post #107

Earlier quoted context omitted.

Before Unicode, 'μ' was typically entered as an 'm' in a Greek font. This can go wrong in several ways, like if you converted the document to plain text, or if your laser printer didn't have the font and it substituted a regular font, you're suddenly off by a factor of 1000. 'mc' is ugly but safe.

What time period, system and region are we talking about? For some characters using a specific font was certainly necessary but for µ? It is in the original IBM PC character set from 1981 and could easily be put into plain text files. I would guess that most extended ASCII character sets contain it but I don't know for sure. Every [German] keyboard I ever used had it on the M key.

I remember having to get a µ that way using FrameMaker on SunOS 4 in the mid-90s.

Mac had a µ from the beginning. And some PC code pages did. But PCs in Canada (where I'm from) used code page 850, which had an Á (for French) where µ would be. Just the sort of thing that would hose you if you tried printing a Mac document on a school printer.

Here's a howto article that suggests using an 'm' in the Symbol font in Word: https://www.officetooltips.com/word_2016/tips/how_to_insert_...

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

#297

Post by tsimionescu » Tue, Jul 11, 2023, 5:13 AM UTC

consilient wrote: post #104

tsimionescu wrote: post #83

Earlier quoted context omitted.

Quantum mechanics tells us that, in order to predict the outcome of a measurement, we have to compute a specific probability based on the amplitude of the wavefunction. We can explain this probability as some kind of collapse, or we can explain it as some measure of the number of observers making the measurement in parallel "worlds". Neither is inherently closer to the math.

> Quantum mechanics tells us that, in order to predict the outcome of a measurement, we have to compute a specific probability based on the amplitude of the wavefunction Even this is already wading into interpretational waters. The math says nothing about whether a given POVM should be thought of as a measurement or an interaction (or both, or neither).

Sure, it's not part of the math, but it is part of the physics. There is a very clear distinction in the theory between "interactions", governed entirely by the Schrodinger equation (or its relativistic versions, or QFT), and a "measurement", where you have the apply the Born rule not only to predict what the measurement device will show, but also to correctly predict what will happen in a subsequent experiment on the same particle.

Without the Born rule, QM makes nonsensical predictions that don't explain what happens. 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).

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

#298

Post by nologic01 » Tue, Jul 11, 2023, 5:23 AM UTC

Surely gravity must be quantized at Planck scale. The question is whether that remote scale is the only relevant one and whether there might not be interesting phenomena governing the interplay of the quantum universe with gravity and geometry at larger scales, lower energies.

The footprint of fundamental forces across scales is definitely not uniform. Strong and weak forces are confined to the quantum regime: no long range manifestations. Electromagnetism differs in that it has both a quantum regime and a classical field limit. Gravity may exhibit its own quirky behavior across scales.

The enormous intellectual effort to unify all fundamental forces into a grant scheme may have been a case of premature optimisation.

The most exciting would be if we could break with endless paper universes and device experiments probing the interplay of gravity with quantum.

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

#299

Post by tsimionescu » Tue, Jul 11, 2023, 5:23 AM UTC

edgyquant wrote: post #154

tsimionescu wrote: post #83

Earlier quoted context omitted.

Quantum mechanics tells us that, in order to predict the outcome of a measurement, we have to compute a specific probability based on the amplitude of the wavefunction. We can explain this probability as some kind of collapse, or we can explain it as some measure of the number of observers making the measurement in parallel "worlds". Neither is inherently closer to the math.

Why should we not just take it as a probability based abstraction for something we don’t have a true understanding of and move on? Anything else seems like weird theology to me.

Sure, it's perfectly valid to say we don't understand it - but the ambition of physics is to actually understand things like that. So if we agree that it is something that we don't know yet, then it remains a target for new theory development or new experiments.

Physics is ultimately not about predicting the outcomes of experiments. It goes farther than that: it is about coming up with a model of the world that humans can understand. The experiments and predictions are just there to validate that the model actually corresponds to the world, but they are not an end in itself.

And all of this speculation about what the Born postulate actually means has in fact lead to new experiments and new theories. If we had only ignored it, we probably wouldn't have discovered Bell's theorem, and we probably wouldn't have discovered decoherence.

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

#300

Post by ethn » Tue, Jul 11, 2023, 5:38 AM UTC

hughesjj wrote: post #175

codethief wrote: post #105

> It’s become dogma. All the other fields in nature are quantized. There’s a sense that there’s nothing special about gravity — it’s just a field like any other — and therefore we should quantize it. I keep on citing Stephen Hawking here on HN, but it again seems very appropriate: > It would be rather boring if this were the case. Gravity would be just like any other field. But I believe it is distinctively different…

I'm definitely into the "it's an emergent phenomena" camp. I think it's inherently relational, as that's a more efficient way to encode geometry rather than space itself being a quantized "thing". Afaik this theory is the "leading"/imho most promising theory of "quantum gravity", that being the "gravity = entanglement" conjecture and the related ideas of "Complexity= action/volume/whatever" that susskind and many oth…

It's not relational. There's several rigorous proofs against Spinoza's relational theory. Namely that of Kant and Einstein:

"even if space is composed of nothing but relations between observers and events, it would be conceptually possible for all observers to agree on their measurements, whereas relativity implies they will disagree" [0]

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