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New theory claims to unite Einstein's gravity with quantum mechanics

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Re: New theory claims to unite Einstein's gravity with quantum mechanics

#121

Post by chasd00 »

dataflow wrote: post #17
dotnet00 wrote: post #16

Earlier quoted context omitted.

If it were simply a matter of losing particles, I'd expect that one of the many very capable metrology labs around the world would've devised an appropriate experiment, e.g. storing two exact same masses at slightly different temperatures near absolute zero and characterizing the difference in mass (since presumably the higher temperature sample would lose slightly more mass if it were down to high energy particles).…

I mean I just gave one example of how it might lose mass. There are other obvious ways (like when they're picked up etc.). My point wasn't to present a hypothesis for people like myself here to rebut. I can do that just fine myself. I was trying to understand what about this has been confusing for scientists.

> like when they're picked up etc.

Wouldn’t just moving an object change its mass? Any change in potential energy would mean a change in mass from good old e=mc^2

Re: New theory claims to unite Einstein's gravity with quantum mechanics

#122

Post by throwaway4PP »

Exciting times! Any physicist here aware of how these two papers would impact the applicability or validity of Modified Newtonian Dynamics (MOND)?

background: my lay understanding of MOND is that it modifies the gravitational interaction parameter over cosmological distances. the force exerted on objects due to gravity is currently accepted to scale with distance in a certain manner (ex. 1/distance^2) while MOND postulates a different scaling relation (ex. 1/distance^3). Those are just examples, not actual values. The currently accepted gravitational interaction force scaling is what gives rise for the need for dark matter, and the corresponding lambda cold dark matter (LCDM) theory. Of course, we have not been able to observe dark matter, which is a problem for a theory. That is what has given rise to MOND, amongst other things. There are prominent, esteemed physicists who have recognized many issues with LCDM, some of which are addressed by MOND (https://astro.uni-bonn.de/~pavel/kroupa_SciLogs.html)

previous HN posts with interesting discussions / links re: MOND

https://news.ycombinator.com/item?id=37012052

https://news.ycombinator.com/item?id=33261981

https://news.ycombinator.com/item?id=23982814

Re: New theory claims to unite Einstein's gravity with quantum mechanics

#123

Post by Timeroot »

maho wrote: post #99

After skimming the second paper, I still don't understand how precision mass measurements come into play here. They mention Cavendish-type measurements, but they are used for measuring the gravitational constant. Of course, you can turn the formula around, plug an unknown mass into the apparatus and then call it a mass measurement, but it's going to be a very imprecise measurement. A Penning trap can give you 11 to 1…

(I went to a talk by Oppenheim author a couple weeks ago on this topic.) The idea is that gravity, as a force, only operates classically. More precisely: there is a classical state describing the curvature of space time, and then a quantum state describing the configuration of particles on that spacetime. But then, that quantum state needs to affect the classical state again (mass bends space), which would usually lead to the classical half becoming quantum and entangled with the other half.

You can keep the classical half (the shape of spacetime) classical, if the effect of the quantum part is partially stochastic. There's a minimum amount of random noise you need for it to be mathematically consistent. So, you set up an experiment where a particle is acting on another via gravity. There's a quantity of noise you should expect to see in the gravitational force.

"Inertial Mass=Gravitational Mass" now only holds on average. The gravitational mass will effectively have a Brownian noise term added in.

Re: New theory claims to unite Einstein's gravity with quantum mechanics

#124

Post by stjohnswarts »

Animats wrote: post #18
hn_throwaway_99 wrote: post #2

> A second paper, published simultaneously in Nature Communications and led by Professor Oppenheim's former Ph.D. students, looks at some of the consequences of the theory, and proposes an experiment to test it: to measure a mass very precisely to see if its weight appears to fluctuate over time. Definitely don't know enough to comment about the overall proposal, but given how many grand physics theories over the pas…

It's good that it's testable. This is one of those ideas which either wins a Nobel Prize or is totally bogus. So what does it take to test it?

Bogus usually implies something meant as a fake or counterfeit, I think a better way to describe it would be "incorrect", I don't think these scientists are trying to fake anything.

Re: New theory claims to unite Einstein's gravity with quantum mechanics

#125

Post by jerf »

maaaaattttt wrote: post #28

This is a question I've been asking myself (probably due to a lack of understanding and knowledge) and this theory seems to hint at something similar: why do we assume spacetime to be homogenous in its nature? Here they seem to say that on some quantum level spacetime could vary drastically. Couldn't then dark matter be explained by some variations on a large scale? Like giant "wrinkles" in spacetime? They would then…

"Here they seem to say that on some quantum level spacetime could vary drastically."

This is not a result of this theory. Our best current theories say this too: https://en.wikipedia.org/wiki/Quantum_foam Spacetime getting distinctly different at very small scales is a vital part of all modern theories and I doubt it's going away. Even if spacetime is shown to be continuous itself, which I tend to personally doubt [1], getting close to the scales where the uncertainty principle becomes a major influence rather than an almost academic curiosity will inevitably have major impacts on the behavior of things.

"Like giant "wrinkles" in spacetime?"

Giant wrinkles in space time don't act like dark matter. They either smooth themselves out basically instantly (on cosmological scales) or form something other than a giant wrinkle, such as a cosmic string: https://en.wikipedia.org/wiki/Cosmic_string

In fact one of the low-key mysteries extant in the universe today is that our best theories say cosmic strings really ought to exist, but we don't see them. Though I think the confidence in our theories being pushed to that extent is low enough that this is not generally considered the biggest problem, and very unlikely to be the thing that cracks the mystery, so it isn't something that gets talked about a lot. So you could say that we actually don't "expect" space time to be homogeneous and one of the mysteries is why it observationally is!

[1]: https://news.ycombinator.com/item?id=38433917

Re: New theory claims to unite Einstein's gravity with quantum mechanics

#126

Post by Timeroot »

throwaway4PP wrote: post #122

Exciting times! Any physicist here aware of how these two papers would impact the applicability or validity of Modified Newtonian Dynamics (MOND)? background: my lay understanding of MOND is that it modifies the gravitational interaction parameter over cosmological distances. the force exerted on objects due to gravity is currently accepted to scale with distance in a certain manner (ex. 1/distance^2) while MOND post…

It's of no relevance to MOND, at least none that I can see.

MOND gives a different scaling relation, and is therefore contradicting general relativity. Its goal is to explain the effects we associate with dark matter, without the need for dark matter.

General relativity is (we are pretty sure) inconsistent with quantum field theory. String theory tries to fix the issue by replacing the particles in field theory with strings. Oppenheim is trying to fix it by putting general relativity as a classical phenomenon that lives "outside" of quantum field theory.

They're trying to solve different problems. And, Oppenheim's classical gravity picture could be used just as well with MOND instead of standard general relativity, if that's what you wanted.

MOND is getting less popular every year as evidence for dark matter piles up. The Bullet Cluster is a particular instance where we can actually "see" the dark matter flying around, in a way MOND couldn't hope to explain. LIGO has also given us a lot of confidence we have the right theory of gravity, at least up to the quantum scale.

Re: New theory claims to unite Einstein's gravity with quantum mechanics

#127

Post by trinsic2 »

3cats-in-a-coat wrote: post #117
yathaid wrote: post #33

The article mentions the 5000:1 odds bet, but reading the text of the bet itself is hilarious: >>> Whereas Carlo Rovelli and Geoff Penington firmly believe that gravity is better described by a quantum theory. >>> And whereas Jonathan Oppenheim is more sympathetic to other possibilities (i.e. doesn’t have a clue) ... [1] - https://www.ucl.ac.uk/oppenheim/pub/quantum_vs_classical_bet...

It's heartwarming to see these people have fun while still sticking to serious work. Everything should be like that.

When it comes to science, only the British seem to be able do that.

Re: New theory claims to unite Einstein's gravity with quantum mechanics

#128

Post by edgyquant »

mvdtnz wrote: post #6
dataflow wrote: post #4

Earlier quoted context omitted.

What made them mysterious? Aren't there always some fraction of atoms or molecules with sufficiently high energy to escape the object?

The fact that you, a random internet guy, knows this makes me believe that the world's top experts on measuring this exact thing probably thought of it, and if there is a mysterious divergence this probably doesn't account for it.

[flagged]

Re: New theory claims to unite Einstein's gravity with quantum mechanics

#129

Post by gcr »

yetihehe wrote: post #55
dataflow wrote: post #10

Earlier quoted context omitted.

I figure as much, but that's kinda why I'm asking what made it mysterious. I actually hadn't heard of it being seen as mysterious until today - that comment is the first time I've seen that. Until today I thought it had been was unsurprising for scientists.

> I figure as much, but that's kinda why I'm asking what made it mysterious. You expect simple explanations to VERY complex problems from random internet commenters. I think you expect too much.

One reason why questions like this are important is because it gives the audience around the asker an opportunity to learn something new. Isn't it important to be able to express curiosity, especially for the benefit of others?

Re: New theory claims to unite Einstein's gravity with quantum mechanics

#130

Post by curation »

What if universality is a name for a kind of antagonism? What comes first is not a wholeness that is disturbed, but difference itself. Reality itself is unfinished and built in parallax. This new theory alongside current metaphysical theories of everything is inspiring.
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