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An old theory of quantized gravity is gaining new life

quantamagazine.org

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Re: An old theory of quantized gravity is gaining new life

#31

Post by ars »

clauraform wrote: post #26
RuggeroAltair wrote: post #16

Earlier quoted context omitted.

From a physics perspective, the many-world, as ridiculous as it sounds, is a more sound theory (believed to be correct by some top physicists) than negative gravity. The explanation of why gravity is only positive is a complex one, but physicists believe it's almost axiomatic. This doesn't mean that you can't have repulsive type of effects, similar to one of the contributions that's believed to make the universe expa…

> The explanation of why gravity is only positive is a complex one, but physicists believe it's almost axiomatic Isn't that a consequence of relativity, the speed of light being constant by definition? I'm not sure that makes any sense, though, what is the physical unit of gravity N? Jf you mean classical mechanics, than there has to be a negative counterforce by the three axioms of newtonian mechanics and it's just…

> Isn't that a consequence of relativity, the speed of light being constant by definition?

No, because if it was then there would not be negative electric charge, and there is.

Re: An old theory of quantized gravity is gaining new life

#32

Post by ars »

Taniwha wrote: post #28
goldenkey wrote: post #3

I think it is relevant to consider gravity from a more abstract standpoint as well by looking at Le Sage's theory and particularly Hyugens' comments. [1] Whether gravity is mediated by a graviton, and the intricacies that QM brings to bear, one interesting idea I took from the above hundreds of years of thought on the subject -- gravity may be a pushing force mediated by constant spherical wave emission (quantized as…

Dumb question: how do you exchange gravitons with a black hole?

A graviton would have to be both massless and energyless. Thus it would be unaffected by gravity.

It also means it can not have a "frequency" like light does (because lacking any energy there is no frequency to change).

It must also always move at the speed of light, and could not exist at any slower speed. (Because to slow down, would imply a change in its energy, which it can not do.)

But that means it can't interact in a way that is detectable, other than gravity.

Because you can not give it energy, you can also never create it artificially. If you did, you would be creating gravitational force out of nothing, which is impossible because it violates conservation of energy, and you can not pay for that violation because you can not give it energy.

It's pretty much the ultimate impossible to study particle.

Re: An old theory of quantized gravity is gaining new life

#33

Post by Maro »

rubber_duck wrote: post #25
jpeg_hero wrote: post #12

> The theory called asymptotically (as-em-TOT-ick-lee) safe gravity was proposed in 1978 by Steven Weinberg. Would a person interested in an article about quantum gravity not be familiar with the term asymptotically?

Maybe author hears it mispronounced often and it bugs him.

It's a her :)

Re: An old theory of quantized gravity is gaining new life

#34

Post by goldenkey »

Taniwha wrote: post #28
goldenkey wrote: post #3

I think it is relevant to consider gravity from a more abstract standpoint as well by looking at Le Sage's theory and particularly Hyugens' comments. [1] Whether gravity is mediated by a graviton, and the intricacies that QM brings to bear, one interesting idea I took from the above hundreds of years of thought on the subject -- gravity may be a pushing force mediated by constant spherical wave emission (quantized as…

Dumb question: how do you exchange gravitons with a black hole?

Its very likely that gravitons are not affected by other gravitons -- just as photons generally do not affect other photons unless at very high energies. This is the case for typical bosons.

So to answer your question: the same way they would normally.

https://en.wikipedia.org/wiki/Two-photon_physics

Re: An old theory of quantized gravity is gaining new life

#35

Post by T-A »

ars wrote: post #23
T-A wrote: post #11

Earlier quoted context omitted.

You would observe the theory not blowing up. :) The key feature she never names is known as a "UV fixed point". UV = UltraViolet, which in this context simply stands for "high energy". Fixed point... for that you need to know that the effective values of coupling "constants" aren't actually constant in quantum field theory; they depend on the interaction energy (i.e. how hard you bang your particles together). So the…

This helps, but doesn't say what the theory says gravity will do at higher energy levels. To me it seems to imply gravity will get weaker at higher energies? Something about that makes me feel like it violates conservation of energy, so maybe that's not it.

Having the theory behave at all, in the sense that calculations do not result in infinities, is big enough.

But there is a prediction which has been made pretty much since Reuter et al. picked up asymptotic safety again in the mid-2000s, and which is directly related to the way it supposedly tames those infinities: at higher resolution, i.e. when spacetime is probed at higher interaction energies, its dimensionality is reduced, going from 4 at the macro scale to 2 at the microscopic scale [1].

[1] https://arxiv.org/abs/hep-th/0508202

Re: An old theory of quantized gravity is gaining new life

#36

Post by Retra »

goldenkey wrote: post #14
Florin_Andrei wrote: post #8

Earlier quoted context omitted.

This is one of the many kinetic theories of gravity. It's very old. No scientist nowadays believes that kinetic theories could really work in this realm. This is mostly of historic interest only.

I'm aware of that-- but no one is sure about how the graviton operates. So though the kinetic part might not be very realistic or all that relevant anymore, the other parts still are.

The 'non-kinetic' parts are just geometry, which we already understand and incorporate into general relativity.

Re: An old theory of quantized gravity is gaining new life

#37

Post by goldenkey »

Retra wrote: post #36
goldenkey wrote: post #14

Earlier quoted context omitted.

I'm aware of that-- but no one is sure about how the graviton operates. So though the kinetic part might not be very realistic or all that relevant anymore, the other parts still are.

The 'non-kinetic' parts are just geometry, which we already understand and incorporate into general relativity.

Just as there is a huge difference between Maxwell's laws and QED -- the same gap lies with relativity and the graviton. Knowing the gravitational field as full fidelity partial differential equations based on the stress energy tensors is a great achievement. But it alone does not tell the full story as to how that field is mediated. Just as EM is mediated via virtual photons, we wish to know more..

Re: An old theory of quantized gravity is gaining new life

#38

Post by virgilp »

goldenkey wrote: post #29
ars wrote: post #23

Earlier quoted context omitted.

This helps, but doesn't say what the theory says gravity will do at higher energy levels. To me it seems to imply gravity will get weaker at higher energies? Something about that makes me feel like it violates conservation of energy, so maybe that's not it.

Also begs the question of how that reaction could even take place if gravitons are totally unreactive with anything other than their source - mass. How would you accelerate a graviton. Gravitons always move at C just like light. Do we have any idea what kind of production and annihalation products will give us gravitons? Just a guess - dark matter/energy might be the only way to create a graviton without associated m…

Are gravitons a thing - i.e.a generally accepted concept in the scientific community? I thought their very existence was highly controversial...

Re: An old theory of quantized gravity is gaining new life

#39

Post by gnulinux »

sago wrote: post #27
intrasight wrote: post #19

Earlier quoted context omitted.

That bothered me as well (pronouncing rather than defining)

Particularly as the pronunciation is strange. Strange place to break syllables, and I'm not sure the second vowel is a 'e' in most pronunciations. /a-sim-TOT-i-klee/

This is how I pronounce it in IPA: /a.sim'to:.ti.kli:/ Why is TOT one syllable?

Re: An old theory of quantized gravity is gaining new life

#40

Post by jsmthrowaway »

gnulinux wrote: post #39
sago wrote: post #27

Earlier quoted context omitted.

Particularly as the pronunciation is strange. Strange place to break syllables, and I'm not sure the second vowel is a 'e' in most pronunciations. /a-sim-TOT-i-klee/

This is how I pronounce it in IPA: /a.sim'to:.ti.kli:/ Why is TOT one syllable?

The weird thing about IPA is that the non-IPA pronunciation you’re replying to seems easier to understand.
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