[HN Gopher] Physicists discover that gravity can create light
___________________________________________________________________
Physicists discover that gravity can create light
Author : wglb
Score : 165 points
Date : 2023-04-19 21:02 UTC (2 days ago)
(HTM) web link (phys.org)
(TXT) w3m dump (phys.org)
| mitthrowaway2 wrote:
| We know that light can create gravity, so it stands to reason
| that there should be a reciprocal relationship!
| cocoa19 wrote:
| "We know that light can create gravity"
|
| I've never heard of light creating gravity, where did you learn
| this?
| nimish wrote:
| Concentrate enough energy in a small area and baby, you got a
| black hole going!
| monstertank wrote:
| Obviously gravity works on particles to condense into stars,
| which create light...so I'm guessing it's not talking about that?
| jacquesm wrote:
| You added 'particles'.
| joadha wrote:
| The authors added "electromagnetic field", which also happens
| to involve particles.
| jacquesm wrote:
| To create one, yes. But to propagate it, no.
| stared wrote:
| All quantum fields have their vacuum energy fluctuations. When we
| change the parameters of the space (e.g. stretch or compress it),
| the current state is no longer the ground state but becomes a so-
| called squeezed vacuum state.
|
| This effect is used in laser physics to "split photons" in
| spontaneous parametric downconversion. That is, an intense laser
| changes the refractive index of a medium periodically. These
| oscillations generate a squeezed vacuum state.
|
| https://en.wikipedia.org/wiki/Squeezed_coherent_state
| westurner wrote:
| Is there a corollary SQG Superfluid Quantum Gravity fluidic
| description of squeezed coherent states?
|
| And what of a Particle-Wave-Fluid triality?
| westurner wrote:
| > _Is there a corollary SQG Superfluid Quantum Gravity
| fluidic description of squeezed coherent states?_
|
| > _And what of a Particle-Wave-Fluid triality?_
|
| Today, ChatGPT said maybe. Google Bard said yes, in 1990. And
| Particle-Wave-Fluid triality might be a thing.
|
| From Google Bard, in full:
|
| > _Yes, there is a corollary SQG Superfluid Quantum Gravity
| fluidic description of squeezed coherent states. This was
| first proposed by Kibble and Turok in 1990. In their paper,
| they showed that it is possible to describe squeezed coherent
| states in terms of a fluid of gravitons. This fluid is known
| as the superfluid quantum gravity (SQG) fluid._
|
| > _The SQG fluid is a quantum fluid that is made up of
| gravitons. Gravitons are massless particles that mediate the
| gravitational force. The SQG fluid is characterized by its
| long-range correlations and its non-zero ground state
| energy._
|
| > _The SQG fluid can be used to describe a variety of
| phenomena in quantum gravity, including the formation of
| black holes and the evolution of the early universe. It can
| also be used to describe squeezed coherent states._
|
| > _A particle-wave-fluid triality is a proposed relationship
| between particles, waves, and fluids. This relationship
| suggests that particles, waves, and fluids are all
| manifestations of a single underlying entity._
|
| > _The particle-wave-fluid triality has been proposed by a
| number of physicists, including David Bohm and David Mermin.
| Bohm proposed that particles are actually fluids,_ and that
| waves are just the way that these fluids propagate. _Mermin
| proposed that fluids are actually particles, and that waves
| are just the way that these particles interact._
|
| > _The particle-wave-fluid triality is still a controversial
| idea, but it has the potential to revolutionize our
| understanding of the physical world. If it is correct, then
| it would mean that the fundamental building blocks of the
| universe are not particles, waves, or fluids, but something
| else entirely._
|
| > _It is too early to say for sure whether or not the
| particle-wave-fluid triality is correct. However, it is an
| intriguing idea that is worth exploring further._
| qikInNdOutReply wrote:
| So the trick to creat this light in todays environment would be
| to make a gravity amplifying device similiar to a
| https://en.wikipedia.org/wiki/Gravity_laser and overlay the
| amplitudes? That can be easy. Just have a microscopic black hole
| particle go back and forth in a field..
| soylentcola wrote:
| And I just upgraded all of my bulbs to LED...
| kgwxd wrote:
| This made my fucking day
| badrabbit wrote:
| Isn't gravity just a fundamental force? Could it be matter
| reacting to gravity? Light is energy but gravity is not energy
| and has no mass so how can it create something out of nothing?
| How is hawking radiation even possible unless something else was
| involved?
| habibur wrote:
| Or gravity is just bending of space around a mass. And not a
| force.
| joadha wrote:
| I used to share your confusion on this topic, but I think I
| got it:
|
| General Relativity posits that gravity embodies both of those
| qualities you mentioned.
|
| It is a force that bends space and dilates time.
| narag wrote:
| https://www.youtube.com/watch?v=ZHxoM9lvzVA
| cronix wrote:
| Not a physicist, but how do you get something to bend without
| a force exerted upon it?
| scotty79 wrote:
| The cool thing about gravity is that it doesn't bend
| anything it just alters space so that straight things are
| bent.
| habibur wrote:
| They attribute it to the fact that space around the object
| is bent. Which is causing the other object to drop,
| accelerate or bent. Check General Relativity's explanation
| of Gravity.
|
| That might not answer all of your or my question. But maybe
| we didn't give enough time to ponder on that line.
| a_wild_dandan wrote:
| It's just unfortunate nomenclature. Space(time) is a set of
| dimensions. It's not a substance, like a ruler, anymore
| than temperature is a substance in a thermometer. The word
| "bend" misleads us by equivocating "bending" a ruler
| (forcefully rearranging its atoms into a new shape) with
| "bending" spacetime (e.g. changing how fast someone's clock
| ticks).
| Maursault wrote:
| > Isn't gravity just a fundamental force?
|
| Not really. Gravity is most accurately
| described by the general theory of relativity... which
| describes gravity not as a force, but as the curvature of
| spacetime, caused by the uneven distribution of mass, and
| causing masses to move along geodesic lines.[1]
|
| [1] https://en.wikipedia.org/wiki/Gravity
| badrabbit wrote:
| Ok, so how does curvature cause light and radiation on its
| own?
| jerf wrote:
| You have to remember that General Relativity is wrong. We
| don't know exactly how it's wrong, but it's wrong. In light
| of that fact, it's not really a proper answer to say that
| "General Relativity says it isn't so it isn't." It is true
| that GR says gravity isn't a force, but the implication
| doesn't follow. We don't know whether a Grand Unified Theory
| would have gravity as a force or not. Given that a great deal
| of the answer to "Is gravity a force?" depends heavily on the
| definition of _force_ being used, we don 't even know what
| the final definition will be in light of a GUT. There may or
| may not be a meaningful distinction between gravity and other
| forces in the real universe.
|
| In QM, gravity isn't a force because gravity doesn't _exist_.
| Clearly this is wrong as well. Saying "GR says gravity isn't
| a force" is effectively the same thing as saying "Gravity
| doesn't _exist_ because QM says it doesn 't." This is exactly
| where both theories break, so we can't use them to answer
| this question.
|
| See also https://www.youtube.com/watch?v=EmrZ3ZaXmS4 .
| Maursault wrote:
| > You have to remember that General Relativity is wrong.
|
| I really don't, because it really isn't. All I need
| remember is that you are wrong.
| a_wild_dandan wrote:
| I'm not seeing how these distinctions are helpful. Maybe
| there's a miscommunication?
|
| When we say "gravity isn't a force", it's shorthand for
| "our best understanding of gravity, with the widest
| explanatory power that most accurately matches experimental
| results, says that gravity isn't a force." But that's an
| exhausting, verbose way to talk. Knowing that GR is
| incomplete doesn't change that.
|
| No falsifiable theory is 100% guaranteed Truth. Not GR, QM,
| evolution, or any widely accepted future Grand Unified
| Theory. Science is one big exercise in affirming the
| consequent, verifying contrapositives, and finding
| surprises. Maybe _all_ mental models are wrong. Maybe we
| 're brains in vats. Aaaah!...so what?
|
| Evolution naturally developed eyeballs in mammals. My niece
| just turned 5. The atoms composing me won't rearrange into
| a facsimile of Abraham Lincoln tomorrow. I'm not going to
| add "to our best understanding, given the evidence,
| granting my incomplete knowledge, etc" about these facts in
| service of reality obviously being unknowable. It's
| pointless.
|
| Gravity isn't a force. That's a perfectly "proper answer"
| -- no need to pontificate about philosophical relativism.
| scotty79 wrote:
| We don't have a single test that shows that GR is wrong in
| any way and we have many tests that show that it is exactly
| right to any arbitrary precission we can dream of
| achieving.
| TheOtherHobbes wrote:
| Now make it work with QFT.
| Maursault wrote:
| It already works. Contrary to vacuous and uninformed
| popular belief, there is no fundamental incompatibility
| between QFT and GR.
| brad0 wrote:
| How does this not have more upvotes? This is a great find!
| yarg wrote:
| phys.org can be a bit sensationalistic.
|
| Quanta takes their time getting to the point, but is a bit more
| reliable in terms of the summary provided.
|
| So if there's a popular physics article, it generally seems to
| be quanta.
| uoaei wrote:
| phys.org re-publishes press materials from universities. The
| writers at Quanta write their own articles.
| aaron695 wrote:
| [dead]
| jordann wrote:
| Thomas Pynchon was ahead of his time with his book title
| https://en.wikipedia.org/wiki/Gravity%27s_Rainbow
| avmich wrote:
| The title is about gravity, but the first line is about wave of
| gravity. Hmm. We know that gravity alone can create radiation -
| the Hawking one. We also know that gravitational waves - the
| spacetime curvature changes with time - carry energy, so can be
| transformed into light. Do we still know if spacetime alone can
| create light?.. I'm not sure we know it today. So... we have a
| great experiment here, which shows something known in a different
| way - is it correct?
| antonvs wrote:
| > We know that gravity alone can create radiation - the Hawking
| one.
|
| What does "gravity alone" mean here? Hawking radiation depends
| on a black hole that has energy to radiate. The radiation is
| not due to "gravity alone".
| XorNot wrote:
| Hawking Radiation didn't depend on gravity either, it depends
| on an event horizon. Any phenomenon which would separate
| virtual particle pairs would produce it - i.e. the edge of
| the observable universe would do it too.
| adastra22 wrote:
| > We know that gravity alone can create radiation - the Hawking
| one
|
| To be pedantic, we don't know this. Hawking radiation has never
| been observed.
| mfer wrote:
| Not only has Hawking radiation not been observed but the
| article starts with a "may have" and concludes by pointing
| out that there aren't conditions to observe the phenomenon
| described today.
|
| Maybe I'm just not a fan of strong language, making it appear
| we know something, where we don't.
| PartiallyTyped wrote:
| Relevant: https://phys.org/news/2021-02-stationary-hawking-
| analog-blac...
| dogma1138 wrote:
| Not particularly. This isn't an actual observation, this is
| just an experiment that attempts to create some analogous
| phenomena.
| deciplex wrote:
| to be even more pedantic, hawking radiation isn't exactly
| _created by_ gravity
| chasd00 wrote:
| didn't the LHC create a black hole that immediately
| evaporated due to Hawking radiation? ..maybe it was only a
| theory that the LHC could do that but i thought it actually
| did create one.
| twawaaay wrote:
| No. That's far beyond our capabilities. Somebody calculated
| that LHC would have to be over 1000 light years in diameter
| to do this (and then still we would have to wait for
| thousands of years for particles to get accelerated).
| raattgift wrote:
| The preprint of the paper that is the subject of the (not so
| great) phys.org article at the top is
| <https://arxiv.org/abs/2205.08767>. An accessible HTML5 version
| is available at <https://ar5iv.org/abs/2205.08767>
| (arxiv->ar5iv, the latter expands to a link within
| ar5iv.labs.arxiv.org).
|
| Hawking radiation is a semiclassical result: the curved
| spacetime is classical General Relativity and the scalar field
| (in which Hawking quanta arise near the central black hole) is
| quantum.
|
| The dynamical spacetime creates -- through the equivalence
| principle -- an acceleration between past observers and future
| observers, and this acceleration corresponds with the Unruh
| effect. The Unruh effect rests on the definition of a vacuum as
| a state in which an observer sees no particles, and that when
| an observer accelerates a no particle state may be transformed
| into a state with particles. Equivalently, differently-
| accelerated observers will count different numbers of particles
| in a spacetime-filling quantum field. (A family of observers
| may count no particles, i.e., it's vacuum.)
|
| The important part here is that a dynamical spacetime
| ("gravity") _and_ a relativistic quantum field is needed for
| Hawking radiation.
|
| So, "[can] spacetime alone ... create light?" No. There must be
| a matter field filling the spacetime. That matter field, if
| quantum, can look like it has no particles in it to some
| observers, but not all observers. The dynamical evolution of
| the spacetime can cause observers' counts of particles to
| evolve.
|
| > gravitational waves ... carry energy, so can be transformed
| into light
|
| The paper is about how, given:
|
| * a massless quantum field theory proxying for light
|
| * a quantum field theory in which gravitation is mediated by a
| massless spin-2 boson
|
| * a dense medium with a (light-) refractive index greater than
| 1
|
| * standing gravitational waves of significant amplitude occur
| in cases where gravitational radiation from widely separated
| sources converge within the dense medium and somehow [a] cancel
| out polariation and [b] are within a wide (compared to the
| wavelength) patch of flat spacetime
|
| * the non-light massive _and_ massless particles within the
| medium couple very weakly to the incoming gravitational
| radiation
|
| * the particles of the refracting medium couple weakly to the
| "light" field, and generate practically no spacetime curvature
| even in bulk
|
| then the light-proxying particles may be produced via a process
| which the authors compare with electron-positron pair
| production and Cherenkov radiation. (Although they do the
| latter comparison very very breezily, not delving into the
| cross section of light-by-light scattering).
|
| There are weaknesses in this list of requirements, some of
| which the authors admit requires further study.
|
| The key point though is that their mechanism _cannot work in
| vacuum_. It absolutely requires that the light travels
| significantly slower than the gravitational radiation (which in
| turn is assumed to travel at c, even in the non-vacuum in which
| light travels slower than that) and that a far-from-negligible
| momentum is lost by the incoming gravitational radiation as it
| passes through the refracting medium.
|
| > great experiment here
|
| The last paragraph in the Conclusions and Discussion section
| suggests there may be avenues for experimenting with the ideas
| in the paper.
| twawaaay wrote:
| > The key point though is that their mechanism cannot work in
| vacuum. It absolutely requires that the light travels
| significantly slower than the gravitational radiation
|
| I am not a physicist, but I understand we are talking about
| Universe so early after Big Bang that it wasn't yet
| transparent to light. There simply wasn't vacuum yet if by
| vacuum you mean electromagnetic waves being able to travel
| long distances.
| marginalia_nu wrote:
| If gravity would quantize into photons, that would have _very_
| weird implications for the standard model. It would threaten to
| equate gravity with the electromagnetic force, and mass with
| charge.
| pa7x1 wrote:
| Gravity cannot be exchanged by photons or any other spin 1
| particle, for that matter. Spin 1 particles lead to repulsive
| forces for like charged particles.
|
| This leaves you with spin 0 and spin 2 as the simplest
| alternatives. Spin 0 doesn't result in light bending and
| gives a wrong result for Mercury's perihelion precession.
| Spin 2 gives you General Relativity.
| methods21 wrote:
| Thought LIGO can detect these waves?
| https://www.ligo.caltech.edu/
___________________________________________________________________
(page generated 2023-04-21 23:00 UTC)