Physicists discover that gravity can create light
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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.
And what of a Particle-Wave-Fluid triality?
FWIR there are Degrees of curl: convergence, divergence
But are paths of photon particles always non-intersecting?
"""Explain how specific (for example Fedi and Turok's) theories of gravitons and superfluidity differ from General Relativity, the Standard Model, prevailing theories of Quantum Gravity and dark matter and/or dark energy non-uniform correction coefficients, classical fluid dynamics, and quantum chaos theory in regards to specific phenomena in the quantum foam.
Also, are is there one wave function or are there many; and are they related by operators expressible with qubit quantum computers or are qudits and qutrits necessary to sufficiently model this domain of n body gravity gravitons in a fluid field?
If graviton fields result in photons, what are the conservation symmetry relations in regards to the exchange of gravitons for photons?"""
And then (though apparently currently one must remove "must use `dask_ml.model_selection.GridSearchCV`" presumably due to current response length limits of Google Bard):
"""Design an experiment as a series of steps and Python code to test (1) whether Bernoulli's equations describe gravitons in a superfluidic field; and also (2) there is conservational symmetry in exchange of gravitons and photons. The Python code must use `dask_ml.model_selection.GridSearchCV`, must use SymPy, define constants in the `__dict__` attribute of a class, return experimental output as a `dict`, have pytest tests and Hypothesis `@given` decorator tests, and a `main(argv=sys.argv)` function with a pytest `test_main`, and use `asyncio`."""
In the actual summation, does the calculation of vacuum energy take into account a cross section of neutrinos and extended "particles". I've always found the concept of vacuum energy lacking in that most(even physicists) do not fundamentally conceptualize a permanent neutrino and elementary particle flux in all but the most astoundingly shielded vacuum.
If there is a medium in which to effect the refractive index, then isnt this an interaction of the molecular structures therein?
My main take away is something like "gravity" is ~ death / extensional pain of life & the "rainbow" is the beauty that exists/we make under that
But we only find out if we try, I guess.
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.
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.
In physical cosmology (and especially considering alternatives to General Relativity) it is very common to consider the possibility that some effect is strong in the very early universe and so weak as to be undetectable at present times (or even as early as the first galaxies or the surface of last scattering). Examples include auxiliary gravitational fields ("bimetric" theories, for example) that decay in the early universe, variable-speed-of-light/variable-Newton's-constant theories, and so forth.
Although one might think "hm, it's very convenient that an important effect only happens so early that we cannot use telescopes to see it", there is very good evidence for electroweak unification and cosmic inflation, both of which terminated (in different ways) in the very early universe, and are (or arguably were) too difficult to directly observe this late in the universe's history. Additionally there is ample indirect evidence that (if it exists) is within our reach.
That the hypothesized graviton-photon mechanism cannot work in vacuum makes it at least very difficult to test (or observe with telescopes) today, however the final section of the paper does suggest that if it happens in nature, where it happens is likely to become accessible to us in due course. This is not a theory that has a hard cut-off in the early universe; it is just a hypothesis that to be realized requires a configuration of e.g. binaries and molecular clouds that is not very close to what we commonly observe. (Double-binary compact objects in dusty environments might end up being commonplace though, and in those settings one could expect changes in "multimessenger" signals if the authors' ideas are correct. It's amazing how many star systems are turning out to be triples, and we know of triple-compact-star systems; there are a number of known quadruples like DI Chamaelontis; and Gamma Cassiopeiae is a system of at least seven ~stellar mass bodies.)
AFAIK there exists no popular belief that physics was different in early universe. The physics was the same, the only thing that was different was physical conditions. Meaning everything was densely packed together.
If you, even for a moment, assume that laws were different in early universe then you essentially lost any possibility to predict anything.
Spontaneous symmetry breaking has been at the root of at least three Nobel prizes, and is crucial to understanding the differences in physical systems at very high energies both in laboratories and in extreme astrophysical settings, at both early and approximately present times in the universe.
https://en.wikipedia.org/wiki/Spontaneous_symmetry_breaking
The early universe was in a high energy state, being very much hotter and denser than the later universe, as you say. There are several epochs -- notably the https://en.wikipedia.org/wiki/Electroweak_epoch -- where symmetry breaking is important, and using the lower energy theory (electromagnetism, in this example) simply does not work: results are (if even calculable) manifestly wrong, leading to a universe with a very different cosmic microwave background, and very different chemistry and nuclear physics.
I think at best one might say that theories with broken symmetries could still have those symmetries (i.e., the breaking may be reversible under "different ... physical conditions", like if our universe surprisingly evolved to a Big Crunch), however treating that as a denial of the possibility of different physics in the early universe is probably something you'd have to take up with philosophers or lexicographers for now.
Additionally, there is no reason to just assume (and refuse to trace out implications if wrong, or to validate) that physical constants are constants everywhere and everywhen. Putting some spacetime-location-dependent function on constants like G, k_B, \alpha, \Lambda, c has at the very least proven instructive in further understanding the concordance (standard) models of particle physics and cosmology, where those constants are taken as constant everywhere and at all times in the universe. Indeed paramaterizing apparent constants is outright productive science. See e.g. <https://en.wikipedia.org/wiki/Test_theories_of_special_relat...> for a scratch-the-surface set of details, and additionally <https://en.wikipedia.org/wiki/Variable_speed_of_light#Relati...> are at least [a] interesting [b] testable and [c] improves testability of the families of theories in which these constants are assumed truly constant (i.e, everywhere and everywhen).
> popular belief
Well, I guess your popular is could outweigh a literature search. But for scientists:
<https://duckduckgo.com/?q=%22spontaneous+symmetry+breaking%2...>
<https://duckduckgo.com/?q=%22new+physics%22+early+universe+s...>
etc.
Finally,
> lost any possibility to predict anything
It's been about half a century since Kenneth Wilson and Nikolay Bogolyubov explored rescaling and renormalization, and nowadays practically every physical theory is written down as, considered as, or is being adapted towards <https://en.wikipedia.org/wiki/Effective_field_theory> (EFT). It is common that different EFTs apply to the same physical configuration as some characteric scale is crossed, and it is possible that physical theories will be EFTs all the way down (and all the way up), with the concept of fundamental becoming a relation between families of theories. (For example, Newtonian gravitation is less fundamental than General Relativity, because the former can be derived from the latter (and not the reverse), not because General Relativity is known to be correct at all scales).
To be pedantic, we don't know this. Hawking radiation has never been observed.
If anything seems like due to dark energy total energy dissipation per area is increasing until death of universe.
Related, I posted a paper on William Sidis earlier today where he explored the idea of a black hole before they were theorized or discovered: https://www.sidis.net/animate.pdf
Maybe I'm just not a fan of strong language, making it appear we know something, where we don't.
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.
https://skullsinthestars.com/2009/03/06/michael-faraday-gran...
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".
Any virtual particle pair which appears along that horizon can potentially be caught on the wrong side of it - i.e. one virtual particle is in a part of space which is now far enough way to be expanding faster then light, whereas the other particle is at a location close enough that it is not.
At the moment that happens, there's a particle or photon which is now inside the light cone of a distant object, paired with a particle that it will never meet again because it's outside of it.
As a result, you get Hawking radiation: because one particle can go off and interact with your universe, but it's partner will never be able to causally effect anything inside that horizon again. So the virtual particle has to become real.
Broadly Hawking radiation intensity goes with curvature - i.e. a more curved surface has a better chance of separating a particle pair then a flatter one. This is because a sharper curve means more vectors which carry you away from the event horizon.
This is also why small black holes evaporate faster then big ones - as the black hole shrinks, the Hawking radiation intensity increases because it's curving more and more (hence why microscopic black holes don't devour everything).
In 1976, Bill Unruh published "Notes on black-hole evaporation"[1], in which he showed that "an accelerated detector even in flat spacetime will detect particles in the vacuum" - now known as the Unruh effect This means that an observer in an accelerated reference frame will observe particles in the vacuum where an inertial observer will observe none. The presence of certain particles - the ones we call Hawking radiation in the context of a black hole - is a relative phenomenon. This is known as the Unruh effect. The equation for the Hawking temperature is essentially the same as the equation for the Unruh temperature, where the acceleration value is the acceleration due to gravity of the black hole.
Then in 1977, Gibbons and Hawking published "Cosmological event horizons, thermodynamics, and particle creation"[2], which showed that "the close connection between event horizons and thermodynamics which has been found in the case of black holes can be extended to cosmological models with a repulsive cosmological constant" and that "An observer with a particle detector will indeed observe a background of thermal radiation coming apparently from the cosmological event horizon." This is known as the Gibbons-Hawking effect.
There's a fairly complex relationship between the two effects which I won't try to describe, but if you're interested then [3] discusses it. The abstract itself gives some sense of the connection.
[1] https://journals.aps.org/prd/abstract/10.1103/PhysRevD.14.87...
[2] https://journals.aps.org/prd/abstract/10.1103/PhysRevD.15.27...
Bb --- Earth --- molecular cloud --- B'b'
where Bb and B'b' are very similar (from the molecular cloud's perspective) inspiralling binary black hole pairs, and Earth is where LIGO (and Virgo and other detectors) are, then we will see characteristic bright flashes from within the molecular cloud and a change in the B'b' detected waveform because it will have lost some energy to the production of the flashes of light.
(The light flash will trail behind the dampened B'b' waveform detection because this hypothesized mechanism only works when a refractive medium slows light from c (its speed in vacuum) but does not slow gravitational waves from c. Although the authors do not touch on the matter, I suspect that we would also be interested in <https://en.wikipedia.org/wiki/Light_echo>s.)
The paper focuses on an analysis of water as the dominant molecule. There are known astrophysical water megamasers (see second paragraph at <https://en.wikipedia.org/wiki/Megamaser>), so this is far from ridiculous.
Trying to match detected flashes of light (including gamma rays) and neutrinos with gravitational wave detections is part of multimessenger astronomy <https://en.wikipedia.org/wiki/Multi-messenger_astronomy>.
I've never heard of light creating gravity, where did you learn this?
Alternatively, we can consider the active and passive gravitational charges of a given mass, also commonly called the active gravitational mass and the passive gravitational mass. The passive charge describes a mass's response to a known source of gravitation; the active charge describes the strength of the gravitational effects generated by an object. In General Relativity the version of the equivalence principle that says that all objects fall identically no matter what their internal composition is ("universality of free fall") ensures that the passive and active charges are identical for all matter. Moreover, in the approximately three hundred years before General Relativity was first written down, there were many successful tests of the equality of the active and passive gravitational charges for many masses; many of these tests were motivated by the work of Newton.
In both Newtonian gravity and General Relativity, light is deflected around large masses (e.g. light from distant stars, or radio beams from <https://en.wikipedia.org/wiki/MESSENGER> grazing the sun, and also lunar laser ranging experiments), so in both theories light has a passive gravitational charge (or passive gravitational mass). If passive and active gravitational charges are identical or at least totally equivalent, light must also source gravitation.
Some discussion here: https://physics.stackexchange.com/questions/22876/does-a-pho...
I don't think we have to consider the photons as such because large-photon-number beams sent from, to, and between spacecraft have been shown to deflect around masses in our solar system, sunlight generates measurable radiation pressure (and greybody radiation contributes to the Yarkovsky effect), and because your parent comment just asked about "light".
If we take a look at <https://en.wikipedia.org/wiki/Stress%E2%80%93energy_tensor#/...> and change the 0 indices to "t" (for time), T^{tt} represents quantities conserved across a purely timelike translation, and thus "energy".
However, your t and my t can differ if we are in a quasilocally-different gravitational field, or accelerated or boosted with respect to each other. In that case one of us may prefer coordinates where some of the quantity in T^{tt} is instead in T^{tj} (the latter being momentum), or even in the pressure diagonal T^{ij}, i == j, i != t.(e.g. when considering a Shapiro test setting, or a "mirrored box of light").
Although I don't think that much of that particular stack exchange discussion, the accepted answer is right to aim readers at <https://en.wikipedia.org/wiki/Electromagnetic_stress%E2%80%9...>, which is almost wholly classical in its outlook. If one were really keen on thinking about gravitation and sufficiently small numbers of photons, it can get a bit messy or drive one towards the canonical quantization and canonical quantum gravity. As far as I can see nothing at your link goes anywhere close to that, or even really discusses the active or passive gravitational behaviour of an individual photon.
There's better in the sense of correctness, and there's better in the sense of "words that will be useful to someone who has never heard that light can create gravity". My inference is the GGP does not already have a deep technical background in general relativity. This guides the words I choose.
But I'll always upvote for technical correctness!
Light can also be used to push objects. Interestingly, sunlight exerts a pressure of 6.56e-10 [psi = lbs/in^2] or 4.53e-6 [N/m^2] on the Earth. This is roughly 5.75e8 [N] or 46 Space Shuttle SRBs. The gravitational force between the Earth and Sun is 3.52e22 [N], or + ~14 orders-of-magnitude.
Objects on Earth at the rotational equator at MSL weigh 0.2% less than at the rotational poles due to the centrifugal force.
That might not answer all of your or my question. But maybe we didn't give enough time to ponder on that line.
https://en.wikipedia.org/wiki/Geodesics_in_general_relativit...
The basic idea is that depending on your frame of reference, you might experience what is called a fictitious or psuedo force that disappears in a more simple frame of reference. Examples of these include centrifugal force, the Coriolis effect.
https://en.wikipedia.org/wiki/Fictitious_force
Einstein's great revelation in the theory of general relativity was that there was no difference between gravity and free fall - which is called the equivalence principle.
https://en.wikipedia.org/wiki/Equivalence_principle
In special relativity, einstein's theory had a preference for inertial frame observers where the observer essentially became the origin of coordinate system to map space by, but in general relativity einstein does away with inertial frames as privileged, and an observer is literally decided by what light it can see, and their coordinate system cannot be universal because of curved space.
https://en.wikipedia.org/wiki/Inertial_frame_of_reference#Sp...
https://en.wikipedia.org/wiki/Observer_%28special_relativity...
Just as centrifugal force is a relative effect that you only observe in a rotating (i.e. accelerated) reference frame, the force of gravity is also a relative effect that you only observe in an accelerated reference frame.
Standing on Earth, we're accelerating towards the center at 9.8 m/s^2, and we feel that as weight due to a force of gravity that we experience in our reference frame.
If you jump out of a plane, though, you feel weightless (especially if you can arrange to do so in a vacuum), because you're in "free fall" - you're following the curvature of spacetime. In your reference frame, you're not experiencing the force of gravity.
This demonstrates that gravity, like centrifugal force, is a "fictitious" force - which doesn't really mean that it's not real, but rather that it's a secondary effect that depends on your reference frame.
General Relativity posits that gravity embodies both of those qualities you mentioned.
It is a force that bends space and dilates time.
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]
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 .
I really don't, because it really isn't. All I need remember is that you are wrong.
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.
This is precisely where GR doesn't work, so using it to declare with confidence what gravity "is" is as silly as using QM to do it. They don't work on this matter. General Relativity is definitely not a complete description of how the universe works. It's a good approximation, even a very good one.. but no more than that.
We know this. It is well understood. This is not some sort of whacky Time Cube position. The whacky Time Cube position is really the one that says GR is correct so we can declare with confidence that gravity isn't a force.
In the end I don't expect gravity to be different from electromagnetism and the other forces. There's been plenty of efforts to build GUTs from nothing but geometry in which case nothing is a "force". Efforts from the QM side tend to incorporate "gravitons" as the force mediation particle just like the other forces have mediation particles. It seems very likely to me that GR's "gravity is specially not a force" will end up being an error, in that either all the other forces turn out not to be forces either, in which case we'll change the meaning, or it will be a force like every other. I don't think there's a lot of reason to expect this to be anything other than an artifact of GR being an approximation.
> In QM ... gravity doesn't exist
The Standard Model of Particle Physics, a particular relativistic quantum field theory, is Lorentz-covariant by design (and with good reason; Lorentz symmetry is a highly-tested feature of our universe). General Relativity as a physical theory of our universe is defined on a Lorentzian spacetime. Where the radius of curvature is larger than the Compton wavelengths involved, adapting the flat-spacetime Standard Model to curved spacetime is straightforward textbook stuff. (Wald 1995 ISBN 0-226-87025-1; Birrell & Davies 1982 ISBN 0-521-23385-2 and several others).
For smaller radiuses of curvature, of if the semiclassical approach is unsuitable because of nontrivial superpositions, one can take a second-quantization approach ("CQG", very definitely a QM theory in which gravity "exists" as a quantum field with potentials and dynamics, and which admits the correspondence principle) or <https://webspace.science.uu.nl/~hooft101/lectures/erice02.pd...> both of which match General Relativity as effective theories (the characteristic energy cutoffs are usefully large and/or the characteristic cut-off lengths are transplanckian) are verified to high precision in manifestly relativistic systems (e.g. triple PSR J0337+1715). Are these "wrong"? Prove it. You'll likely need to look into a region of strong gravity, and for that you have to deal with a cosmic censorship conjecture.
> General Relativity is wrong.
Prove it?
I'm with Clifford Will <https://en.wikipedia.org/wiki/Clifford_Martin_Will> on this; penultimate paragraph of his 2020 book with Nicolas Yunes ISBN 9870198842125, <https://global.oup.com/academic/product/is-einstein-still-ri...>: "It would not surprise me if the solution to the universal acceleration turned out to be simply Einstein's original cosmological constant, a constant of nature like Planck's constant or Newton's constant of gravitation ... And it would not surprise me if general relativity turned out to be absolutely correct according to any future experiment accessible to humankind." The authors' following paragraph is a challenge to you which is not met by your bold assertion at the top of your comment.
General Relativity may be wrong, but that is not proven. Will would be happy to be surprised by it being proven wrong experimentally. (A huge amount of his research has been aimed at what exactly it means for General Relativity to be wrong).
What I would agree with is that we do not know at present how to avoid divergences of the curvature scalars in the limit of strong gravity, and that this means we can't always fully solve a whole spacetime from initial values. But we also don't have any idea how to test whether that actually happens in our universe (that such divergences occur in stellar remnants or at the centres of galaxies is untested hypothesis) so GR is a perfectly sound, mathematically complete effective field theory at the very least. And moreover the answer may come from new physics in the matter sector, rather than new gravitational physics. What does the Standard Model say about particle energies above YeV? Discovering more about the mechanisms that generate the stress-energy tensor is not the same task as changing the theory of General Relativity.
Meanwhile, there are hundreds of pages in Will & Yunes's excellent book which explain to lay readers the match between GR and observation and experiment, and a wide body of specialist literature on a century's worth of experimental and observational tests of General Relativity, every single one of which has supported the theory or was inconclusive.
And can someone help me understand in layman terms how current physics posits that gravitation is generating light or even hawking radiation?
https://www.researchgate.net/figure/Tree-level-Feynman-diagr...
There you can see different ways in which a pair of gravitons can interact leading to a pair of photons. If you want to dig deeper in the math behind it: https://physics.stackexchange.com/questions/335917/how-do-i-...
Regarding Hawking radiation, it's not gravity itself that causes it. It's a consequence of the existence of an event horizon. In fact, you can have a similar effect in flat spacetime (i.e. no gravity), an accelerating observer will see an event horizon and it will feel itself immersed in a thermal bath of particles at certain temperature that has to do with its acceleration. This is called the Unruh effect. Further reading: https://en.wikipedia.org/wiki/Unruh_effect
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.