A Bet Against Quantum Gravity

Is gravity quantum in nature, just like all the other particles and forces? Or is it fundamentally different? For nearly a century, physicists have attempted to define gravity using the framework of quantum mechanics. But it turns out that “quantizing” gravity leads to some thorny dead ends.

To chart a path forward, the physicist Jonathan Oppenheim and his students have proposed a different idea: What if gravity simply can’t be quantized? Building on work from the 1990s, Oppenheim’s theory keeps gravity classical and then searches for a way to couple the quantum and classical realms.

Such hybrid theories could solve long-standing problems in physics. But they also lead to a conclusion that many physicists may find unsettling: the universe is deeply random. To make his point, Oppenheim made a bet with two quantum gravity researchers that he’s right. Upcoming experiments could determine the winner of the bet.

#quantum #blackhole #physics #gravity #spacetime

[jamesking]

All we need is a physicist named Oppenheimest and we're set.

[jessstuart]

Measuring the noise in the gravitational field around a 1kg mass sounds incredibly difficult.

[blackshard]

This is exactly the kind of thinking that, even if it's proven wrong, in doing so it will have contributed massively toward our understanding of the universe.

[thequestion]

This guy taught my Quantum Computation course a long long time ago (2012). So cool to see him pop up here.

[tristanwegner]

Describing an experiment, whose outcome will restrict the possibilities how the universe fundamentally works, is a big scientific accomplishment.

[concernedspectator]

"What we were able to prove is that any consistent theories of coupling between classical degrees of freedom and quantum degrees of freedom have to be fundamentally stochastic." Huge. So exciting to see what these experiments reveal

[abhishekshah]

I have this feeling that gravity is in essence an emergent phenomena, a classical observable and hence, trying to quantize it seems like trying to fit something in a box that doesn't fit. Kudos to him for daring to try this approach.

[Self-Duality]

Penrose (paraphrased): “The trouble is that we’re trying and trying to quantize gravity, but we really need to gravitize quantum mechanics.”

[badlydrawnturtle]

What catches my attention is the throwing out of the information paradox. The notion that information is some sort of fundamental conserved quantity rather than a human-centric descriptor of what we can know has always rubbed me the wrong way, so to see a hypothesis that just chucks it out the window, at least in part, is refreshing.

[greggary]

I’m a huge fan of turning problems on their heads and it’s pretty much a fundamental tenant of human behaviour that over time (what passes for) knowledge becomes tied up with dogma, which is often confused with strings.

Whether ultimately right or wrong this gets a standing o from me on that basis alone.

[purplenanite]

I like how there's already tests of this math - I do think gravity will be quantum, but I cannot wait to see what happens here

[protocol]

I hope he defined the 5, 000 items better than that, otherwise someone's going to give him 8.3e-21 moles of elemental hydrogen and call it done. They might even try giving him a quarter of that, counting the electron and quarks separately. We can only hope they don't start trying to count the gluons. It'd probably be easier just to radically overpay with a glass of water.

[TheBiomuse]

If evidence for noise in gravitational fields is strengthened, it will mean either that 1) gravity may harbor substantial nonquantizable stochasticity; or 2) that we are presently underinformed regarding the abundance and/or energetic states of gravity's discrete units. I'd bet on the latter. Thus far, it sure looks as though the history of physics is that stochasticity is always apparent only until those units are better understood.

[arctic_haze]

I like this approach. In General Relativity gravity is not even a force. In this approach, locally it is a fictitious force just like Coriolis force or centrifugal force. But we do not quantize fictitious forces. So why should we attempt that with gravity?

[mikemines]

If time is quantized what is the frame rate of the universe.

[thomasspeer]

It’s refreshing to hear a different take on gravity for once

[flambambam]

If I'm understanding where he's going with this, his experiments sound a lot like a question I've had for a few years. If an electron cloud is just a probability density function, then we should expect its electromagnetic field to be dispersed throughout this cloud (instead of a point-charge all the way down). If gravity is fundamentally quantum, then we have good reason to believe that its gravitational field should be dispersed in the same manner. The only issue is that gravity is extremely weak, so we have to either get creative with how we would measure something like this, or wait until we have technology sensitive enough to make these measurements.

[Abmotsad]

"If you don't find randomness and noise in a gravitational field, then you can rule out a classical theory of gravity."

That's wrong. In these circumstances, failure to find something is NOT proof that it's not there. It could mean simply that the effect is one decimal point smaller than the sensitivity of your instruments.

[slo]

Random is that which cannot be predicted. So even if something were deterministic, it ramains random as long as you cannot measure it accurately. So basically as long as we dont know everything there will be randomness. And if the universe has true randomness in any form, we cannot know everything.

[GeoffryGifari]

when it comes to experimental measurement in the "randomness of gravity", how can we distinguish a random (but classical) gravitational noise from quantum fluctuations stemming from quantum gravity?