this post was submitted on 02 May 2024

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A proposed experiment could bring scientists closer to answering the long-standing question of whether gravity is a classical or a quantum phenomenon. (physics.aps.org)

submitted 4 months ago* (last edited 4 months ago) by [email protected] to c/[email protected]

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[–] [email protected] 25 points 4 months ago (2 children)

For those who are confused. It's an experiment to see if gravity is smooth or lumpy. Relatively assumes it is smooth, quantum mechanics says it is lumpy. By knowing what is happening, we can tell which is more wrong. Both seem hyper accurate in their realms, but neither allows for the existence of the other.

Effectively, 2 pendulums are put close together and left to swing. Relativity says they will slowly move into sync. Quantum mechanics says they will move together in fits and starts. By checking at the end, they can see if the syncing is lumpy or smooth. They will also have to run it a huge number of times, to pull any difference out of the noise.

Previous ideas for experiments relied on forcing 2 masses into a diffuse state, then letting them entangle with each other. Getting matter into such a state is hard however, let alone keeping it there for long enough to work. The new experiment dodges around this problem.

[–] [email protected] 7 points 4 months ago (1 children)

Thanks for this nice explanation. Also, I would underline some of the requirements of the setup :

... "the experiment requires long coherence times, torsion pendulums that lose little energy as they oscillate, and an ultracold environment." ...

[–] [email protected] 8 points 4 months ago (1 children)

It's definitely not an easy experiment, it's an order of magnitude easier than the other ideas though. It might even be within the realms of current equipment.

[–] [email protected] 3 points 4 months ago

Absolutely ! ...and science discoveries often comes from people who are creative and knows technology : both in capacities and limits.

[–] [email protected] 5 points 4 months ago

Thanks for the recap 🙏

[–] Corkyskog 6 points 4 months ago (3 children)

I just want them to prove that C is actually a constant both ways.

[–] [email protected] 13 points 4 months ago

C has const, yes. C++ also has this.

🤡

[–] [email protected] 2 points 4 months ago (1 children)

I want to know if the C constant is the same when not under the effects of a gravity well.

[–] [email protected] 1 points 4 months ago (1 children)

Is that under debate?

[–] [email protected] 1 points 4 months ago (2 children)

for me it does as I know of no meaurement done under those conditions.

[–] [email protected] 2 points 4 months ago (1 children)

As far as I understand, even if c is different in some circumstances or changes over time it would be hard to measure because everything else is expressed with c

It's like trying to measure if your fingers have grown longer, but doing it with only those fingers as a measure

[–] [email protected] 2 points 4 months ago (1 children)

so you believe c was never directly measured?

[–] [email protected] 1 points 4 months ago (1 children)

Well, how would you measure C directly? You can only always get 2C.

[–] [email protected] 2 points 4 months ago (1 children)

I wouldn't but it has been historically. Unsurprisingly with mirrors but always under the not insignificant influence of the suns gravity. Our most recent measurements I believe use cosmic bodies I believe which is what makes me wonder if our measurement is accurate. https://www.speed-of-light.com/historical_measurements.html

[–] [email protected] 1 points 4 months ago (1 children)

Oh sorry, I was talking about measuring C rather than 2C (since that is the only way we can get C, IIRC, you cannot measure C directly since SOME information must be conveyed when measurement begins AND ends, hence 2C). For C in a gravitational field, I have no idea but I suspect it will have something to do with relativity and time dilation if it has any effect at all.

[–] [email protected] 2 points 4 months ago

well we measure it assuming it has no effect and that is why going way back in this chain I said I would like a measurement outside the influence of a gravity well.

[–] [email protected] 1 points 4 months ago (1 children)

Isn't Earth a gravity well, or nah?

[–] [email protected] 1 points 4 months ago (1 children)

when not under the effect and the big gravity well in teh area is the sun. maybe the voyager craft are far enough out for it to be weak enough.

[–] [email protected] 1 points 4 months ago (1 children)

Even then, we are still in the gravitational field of our galaxys black hole.

[–] [email protected] 2 points 4 months ago (1 children)

Good point and black holes are part of make me wonder about that given what it does to light and spacetime. All our measurements of the galaxy and universe is on a speed of light is in our gravity well and even though it drops off so quickly the suns is so huge we have to have quite a distance to get to where its inconsequential is way beyond earth. Knowing there it is the same 1000 au from the sun at high precision would be nice to know. It it showed any difference. Even slightly then it would be massive in our understanding of the universe.

[–] [email protected] 1 points 4 months ago (1 children)

Yeah, this is a teally intresting thought! The observation should be really somewhere outside of galaxies, or where there is almost no gravitation.

[–] [email protected] 2 points 4 months ago

not necessarily but at least far enough away that gravitational forces are way different. the sun contrls orbits for over 1000 au but neptune I think is the farthest circular orbit at 30 au. Our measurements at 1au have no practical gravitational variance at all but we assume light is uneffected by it.

[–] [email protected] 2 points 4 months ago (1 children)

Not sure what are those "both" ways, but yeah isotropic or especially anisotropic speed of light would be nice to know for sure

[–] [email protected] 1 points 4 months ago (1 children)

The speed of light being isotropic has been demonstrated already and I believe I know what they mean when they say "both ways" : since all demonstrations of the speed of light are based on "round way trip" from A to B then from B to A. But, no experiments can measure a one-way trip speed.

[–] [email protected] 2 points 4 months ago (1 children)

Then I was probably incorrect, what would be a correct term for isotropic but depends on direction? Because I also meant one-way speed

[–] [email protected] 3 points 4 months ago

Hi lad,
i was not certain so i double checked :
https://en.m.wikipedia.org/wiki/Isotropy
Physics - - Electromagnetics :

An isotropic medium is one such that the permittivity, ε, and permeability, μ, of the medium are uniform in all directions of the medium, the simplest instance being free space.

... if you read this like i do, they do not care to diferentiate "round trip" and "one way" ... and my vocabulary is not good enough to find a word that would fit.

[–] [email protected] 4 points 4 months ago (1 children)

I understood some of those words.

[–] [email protected] 1 points 4 months ago

"the", "a", "and"?