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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

#241

Post by urinotherapist »

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.

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

#242

Post by scrubs »

rapjr9 wrote: post #114

I wonder if the recent news about the background gravitational hum of the universe has any bearing on this: https://www.sciencealert.com/breaking-news-physicists-have-d... It essentially means that gravity is always in flux everywhere, at all frequencies of gravity waves, so there is noise in gravity. This is in addition to the background EM radiation in the universe. Gravitational and EM fields are infinite are they…

The hum is merely the change in the shape of space time by all the gravitational events like block hole creation, mergers, and novae. In that sense it's not random certainly not in the sense of quantum measurement say of position or momentum.

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

#243

Post by cornel_io »

Gordonjcp wrote: post #236
jfengel wrote: post #171

Earlier quoted context omitted.

That's not what Planck's Constant is. Planck's Constant connects energy to length (in space or time). It's just a way of shifting units around. You're thinking of the Planck Length, which is the result of combining the Planck Constant with the speed of light. It also happens to be the wavelength of a photon so short that its energy makes it a black hole, connecting it to gravity. It's often presented as if it were th…

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I think it didn't land because so many people are in the comments seriously arguing almost exactly what you were saying as a joke. Tough environment for parody to thrive in, alas...

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

#244

Post by danbruc »

tlb wrote: post #107
marcosdumay wrote: post #77

Earlier quoted context omitted.

> μg is too easily mistaken for mg Is that some joke about medical writing? Anyway, I just noticed that table doesn't have rules for nanogram. There is also no mega-anything. (On a serious parenthesis, I think I actually understand their rationale; but changing the abbreviation of only one of them is still confusing.)

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.

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

#245

Post by squirtlebonflow »

Aardwolf wrote: post #227
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…

If gravity is not quantized, would that not mean that it has infinite information (the accuracy to represent its values to infinite digits of precision), and thus cause a black hole due to such high information density?

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

#246

Post by mr_toad »

chownie wrote: post #229
Aardwolf wrote: post #227

Earlier quoted context omitted.

If gravity is not quantized, would that not mean that it has infinite information (the accuracy to represent its values to infinite digits of precision), and thus cause a black hole due to such high information density?

Is that not what it does?

General relativity requires singularities, QM prohibits them. It’s a puzzle.

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

#248

Post by XorNot »

mr_toad wrote: post #246
chownie wrote: post #229

Earlier quoted context omitted.

Is that not what it does?

General relativity requires singularities, QM prohibits them. It’s a puzzle.

Keep in mind in GR singularities don't really make sense either: i.e. when you pass the event horizon of a black hole, under GR the rules say that you must always been traveling towards the singularity. But the corollary of this is that it's not actually possible - mathematically - to arrive at the singularity (because then you'd be moving parallel with it rather then towards it).

So while we can define what happens very well under GR for the "most" of the inside of a black hole, we can't actually explain what happens to objects which reach the center. There has to be some type of discontinuity whatever happens - i.e. if the object disappears, that's still a discontinuity even if it would resolve the paradox.

EDIT: Which is of course where GR and QM need to reconcile as well - as you get infinitely close to the singularity, the size scale is getting small enough that QM should be well in play.

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

#249

Post by EvgeniyZh »

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…

There are some pretty strict limitations on emergent phenomena, like Weinberg–Witten theorem. It doesn't rule out emergence of gravity but it makes it less likely

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

#250

Post by jojobas »

feoren wrote: post #57
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 ).

So 90,000 times smaller. At first glance you made it look 90x smaller because I couldn't tell if "mcg" was a typo for "mg" or not (without clicking the link). I've never seen anyone use "mcg" to mean "microgram" before and I feel like it's misleading. Use "ug", or "μg" if you're feeling fancy.

That's not it. The mass difference of entangled states should be over the 90mg, suggesting much, MUCH heavier entangled object.
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