14 ms·

Electromagnetism is a property of spacetime itself, study finds

397 points by egfx 5y ago

fosk 5y ago
I dream of faster than light travel by bending the space time fabric in “U” shape (like pinching a piece of paper) and allowing to travel across the two planes of reference.
- amelius 5y ago
  What if your neighbor wants to bend space time in the other direction?
  - swayvil 5y ago
    Then we would simply fork reality. Everybody's happy.
    - IgorPartola 5y ago
      Everybody is both happy and unhappy.
    - excalibur 5y ago
      Everybody but the TVA.
- koheripbal 5y ago
  folding the paper isnt enough. you also need to reform the paper to make the hole attach at both ends. ripping apart spacetime may not even be possible.
- freshhawk 5y ago
  Sure, it would take an enormous amount of energy to do it though. Oh yeah, and you'd also be annihilated as you were completely turned to energy as you tried to go through it of course. But you'd sure fire a hell of a lot of randomized high energy particles out the other side after the amount of time it would have taken light to get there. Not my preferred kind of "travel", I'll just freeze myself and go the slow way or something.
- psyc 5y ago
  Ah, fond memories of A Wrinkle in Time by Madeleine L’Engle.
- cletus 5y ago
  This common desire for FTL should be an object lesson in how wishful thinking distorts objectivity. We see a constant stream of ideas that spring from simply not understanding the domain of a function. You can put a negative value into mass or energy. That doesn't mean it means anything. There really is no plausible theory for FTL of any kind. Maybe there will be in the future. Personally I'd put everything I have on the speed of light being an absolute limit to causality. Look at it this way: if FTL travel were possible we probably wouldn't exist. Whoever came first would probably colonize the Universe and sterilize it of competition. So there's that.
  - ineedasername 5y ago
    if FTL travel were possible we probably wouldn't exist. Whoever came first would probably colonize the Universe and sterilize it of competition FTL doesn't necessarily mean infinite/instant travel. Also the scenario you propose could be part of the Great Filter, and we just haven't been culled yet. Or FTL civilizations tend to get so large they fracture & turn to in-fighting or encounter other resource bottlenecks that limit exponential expansion. Or C is the law and going FTL spawns a cosmic traffic cop like the meatball head things in Rick & Morty. Or FTL is simply impossible, but perhaps not constant and various factors impact the local C
avmich 5y ago
> Moreover, electric charge relates to some compressibility properties of spacetime. Wonder if somebody could explain this?
- findalex 5y ago
  Maybe something along the lines of regions of charged space time resist compression while charged and non charged regions more spontaneous compress? Attraction/repulsion?
- swayvil 5y ago
  Maybe we could take the same motion in air as a metaphor for what's happening in spacetime. Charge becomes an area of higher or lower air-density. EM Waves become areas of changed air-density, propagated. This is just pulled fresh from my butt, mind you.
calin2k 5y ago
this reminds me of https://en.wikipedia.org/wiki/Philadelphia_Experiment https://en.wikipedia.org/wiki/Philadelphia_Experiment
marsven_422 5y ago
I long for the day they invalidate QM
curt15 5y ago
I come from maths, not physics, but their construction g_{\mu \nu} = A_\mu A_\nu looks a little weird to me. The left side is a tensor, but isn't the electromagnetic four-potential is a gauge field, not a tensor?
- ajkjk 5y ago
  A gauge field is tensor-valued; what's wrong with that? Although it does seems strange for other reasons. Primarily because it seems very unlikely that everyone else who developed this field wouldn't have considered the possibility and then discarded it.
  - curt15 5y ago
    Although a gauge field has multiple components, it transforms differently from tensors under a change of coordinates: A -> O A O^{-1} - dO O^{-1} (O is the Jacobian matrix) The second term is absent for tensors (such as the left side of their equation 4). It also vanishes on a flat spacetime where one only considers linear (Lorentz) coordinate transformations, but based on my cursory reading they don't seem to be making that assumption.
    - codethief 5y ago
      I'm not sure I'm following. In General Relativity, the 4-electromagnetic potential A^μ is simply a vector field on spacetime, so what's wrong with taking the (symmetrization of) the tensor product of A_μ with itself to obtain a symmetric 2-tensor? (Whether or not that 2-tensor satisfies the requirements for a semi-Riemannian metric is another question.)
      - nilaykumar 5y ago
        Why is A_\mu a vector field on spacetime? In the standard treatment A is the (pullback to the base of the) connection 1-form of a connection on a principal U(1)-bundle on spacetime. Technically it's valued in the Lie algebra of U(1), but as that can be identified with i times the real numbers, we can ignore that here. Does the product A_\mu A_\nu happen to transform tensorially? Because as the parent pointed out, the transformation rule for A involves an extra term, so it's not obvious.
ajkjk 5y ago
This article is not really coherent. It seems like a bunch of random statements about physics, strung together without explanation. This paragraph for instance is a bunch of true-ish sentences but overall is gibberish: > The metric tensor of spacetime tells us how lengths determine in spacetime. The metric tensor also thus determines the curvature properties of spacetime. Curvature is what we feel as "force." In addition, energy and curvature relate to each other through the Einstein field equations. Test particles follow what are called geodesics—the shortest paths in the spacetime.
- LegitShady 5y ago
  There’s a paper with equations linked at the bottom. I suspect it sounds like gibberish because its describing a mathematical proof with common language. The paper assumes you have a lot of knowledge as well.
- codethief 5y ago
  > This paragraph for instance is a bunch of true-ish sentences but overall is gibberish: >> The metric tensor of spacetime tells us how lengths determine in spacetime. The metric tensor also thus determines the curvature properties of spacetime. Curvature is what we feel as "force." In addition, energy and curvature relate to each other through the Einstein field equations. Test particles follow what are called geodesics—the shortest paths in the spacetime. Could you elaborate on why you think this is gibberish? I mean, I agree that the article is giving off a pseudo science vibe and the authors should work on their style. (Instead of presenting their results in a matter-of-fact manner, they should rather dedicate more time to explaining their assumptions and their reasoning in a step-by-step manner.) But the paragraph you quoted seems perfectly fine.
  - ajkjk 5y ago
    All of the sentences in the paragraph are real sentences from physics but they're strong together like they were generated by GPT-3 or something. For instance what does "how lengths determine in spacetime" mean? Why is it saying that curvature is what we feel as force? Why is it suddenly talking about test particles without introducing the term? Why does it jump to talking about geodesics in the last sentence? etc. it just feels like it was strung together by an algorithm.
evancox100 5y ago
I’m nowhere near qualified enough in general relativity to evaluate their claims, but when I see something like this: “This is aesthetically pleasing, as nature seems to strive for harmony, efficiency and simplicity.” it makes me think they are not being the most objective evaluators of reality.
- KhoomeiK 5y ago
  Aesthetics, harmony, and simplicity are the guiding principles of mathematical conjecture. This piece is simply hypothesizing about a link while calling for further empirical research.
  - haskellandchill 5y ago
    No, that's just fluff. Occam's Razor is all there is to it.
    - catlifeonmars 5y ago
      Occam’s razor more or less manifests as elegance in mathematics.
- enkid 5y ago
  Aesthetics should have nothing to do with science. Aesthetics is the reason we thought the Earth was at the center of the universe and everything outside the orbit of the moon was made of perfect spheres. It's why the Soviet Union pushed Lamarckian biology instead of Darwinism.
  - bullsbarry 5y ago
    The earth is at the center of the visible universe.
    - mellosouls 5y ago
      Only to observers on earth...
ozankabak 5y ago
IIUC the authors are saying that if we associate the metric with the four-potential via an outer product, they get a picture coherent with the current understanding of how electromagnetism "works" in GR under certain circumstances. I can somewhat see how to interpret the mathematics in free space. But what about when there are massive bodies in the picture? They will result in a non-flat metric... does that imply they create their own electromagnetism?
deleted 5y ago
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enoreyes 5y ago
This is interesting and if the experimental evidence confirms this hypothesis, it bodes well for our future. A universe where we can interact with spacetime via engineering is one that allows for a lot of creative freedom. They also have another interesting article claiming that the imaginary structure of QM is the result of stochastic optimization on spacetimes: https://www.nature.com/articles/s41598-019-56357-3 https://www.nature.com/articles/s41598-019-56357-3 Maybe the UAPs really are just secret warp drive tech we made 20 or 30 years ago.
zeteo 5y ago
The idea that strong electromagnetic fields affect the local curvature of spacetime is nothing short of revolutionary. Imagine the possibilities of that! This may be the beginning of the road to a functional warp drive at last.
- nimish 5y ago
  Well good news, we've known that for a century as it follows from incorporating the electromagnetic stress energy tensor into the field equations
  - zeteo 5y ago
    I can do without the sarcasm. Can you point me to any actual experiments?
    - gus_massa 5y ago
      I think there are no experiments in the lab or a direct measurement of this. Anyway, if the light is blended during an eclipse, the that light should have accelerated the Sun just a tiny tiny ... tiny tiny bit in the opposite direction.
    - nimish 5y ago
      I'm not sure what you're looking for. EM fields so strong that they affect spacetime noticeably? We haven't observed any Reissner-Nordstrom/Kerr-Newman black holes iirc. That said, _anything_ with stress-energy-momentum is held to affect spacetime curvature in GR.
    - BlackFly 5y ago
      Controlled experiments are very rare if you are talking about gravity, since the force is so weak. Observational experiments (astronomy) is where most of the evidence comes from. The most obvious inclusion of it for me is the radiative (also known as the photon) component of the matter density in Lambda CDM models (that is, they need to account for the proportion of the energy density of the universe which is related to electromagnetic fields to rule it out as dark matter).
amelius 5y ago
What would the EM field of a photon look like if you moved along with the photon? Would the magnetic part disappear just like it disappears when you move along with a moving electron?
- blamestross 5y ago
  Basically, from the photon's point of view, all travel is the universe distorting until origin and destination are literally the same point. Photon's don't experience movement, the universe does an instant jig around them while they sit still.
- gary_0 5y ago
  You can't "move along with a photon" because, in terms of General Relativity, any particle moving at c doesn't have a frame of reference.
  - deleted 5y ago
    [deleted]
lumost 5y ago
Reading the article, this appears to be a speculative rehash of past theories claiming to unify electromagnetism and general relativity. The article ends on the note that empirical research is needed. I did not see anything novel that would warrant further attention - did I miss something?
- codethief 5y ago
  The article is based on a paper linked at the very bottom of the text.
yummypaint 5y ago
Electromagnetism is already understood to be a special case of the electroweak interaction, which is itself a component of the standard model. The paper mentions Maxwell's equations, but not these more general models.
- codethief 5y ago
  So what? The very first step to unifying GR with quantum mechanics and the standard model might actually be to realize that part of the standard model can be embedded in GR (at least when EM is considered as a classical field theory). I don't think it's a deficiency of the paper that it doesn't present a solution to everything.
gus_massa 5y ago
In particles physics, they have a different explanation of electromagnetism that is also very natural, almost inevitable. https://en.wikipedia.org/wiki/Quantum_electrodynamics#Mathematical_formulation https://en.wikipedia.org/wiki/Quantum_electrodynamics#Mathem... The explanation in particle physics is compatible with Quantum Mechanics and Special Relativity, but no one is sure about how to extend it to General Relativity. I'm not sure how compatible is it with the proposal in the article discussed here. Non technical version (ELI25): In quantum mechanics the wavefunction Ψ is has complex values. If you multiply everything in the universe by -1, nothing changes because all the physical results use ΨΨ* (where * is the complex conjugation). You can also multiply everything by i or -i. Moreover by any other complex number of modulo 1 because ΨΨ* does not change. (The technical term for this is U(1) global gauge symmetry.) But you can be more ambitious and want to multiply each point of the universe by a different complex number of modulo 1. ΨΨ* does not change but the derivatives of Ψ change and they are also important. (When you use the same complex number everywhere, the derivatives is just a multiple of the original derivative. When you use a different number in each point, it changes.) The only way to fix the problem with the derivative is to add a new field A. When you and multiply each point of the universe by a different complex number of modulo 1, then A changes in a simple to calculate but not obvious way. The change in A fix the problem with the derivatives of Ψ. So now the equations of the universe with Ψ and A don't change when you make this change. (The technical term for this is U(1) local gauge symmetry.) When you write carefully how a universe like this look like, the new field A is electromagnetism. (Actually, you can get the electric field and magnetic field using the derivatives of A.) This explanation looks more complicated than the explanation of the article, but the article is full of technical terms that you really don't want to know, like: > Riemann curvature tensor is more than just Ricci curvature—electromagnetic fields stretch and bend the spacetime
- KirillPanov 5y ago
  >_In particles physics ... very natural Er, I'm not sure that things like dressed particles [1] and off-shell matter [2] violating E=mc^2 [3] could be described as even remotely "natural". Perhaps they are valid theories, but "natural" certainly isn't an appropriate description of most of what unavoidably follows from particle assumptions. [1] https://en.m.wikipedia.org/wiki/Dressed_particle https://en.m.wikipedia.org/wiki/Dressed_particle [2] https://en.m.wikipedia.org/wiki/On_shell_and_off_shell https://en.m.wikipedia.org/wiki/On_shell_and_off_shell [3] https://en.m.wikipedia.org/wiki/Virtual_particle#Properties https://en.m.wikipedia.org/wiki/Virtual_particle#Properties
kilodeca 5y ago
I heard people saying the opposite.
lend000 5y ago
I like the idea intuitively (the idea that infinite discrete photons are required to mediate continuous fields from a single electron over infinite distances never sat well with me), so are they claiming here that there is a relativity-version of Maxwell's Equations? Does it require an additional spatial dimension to account for charge, or does it operate it on the same spacetime as gravity? Regardless, if I'm understanding this nontechnical overview correctly, it's a large claim requiring a lot of work. Probably worth a Nobel Prize if it they actually pull it off.
ethn 5y ago
I thought we knew this already since Faraday.
kmm 5y ago
I'm not an expert in GR, but the linked paper seems nonsensical[0]. It postulates a highly degenerate decomposition of the metric tensor, for which they postulate a contrived action which then seems to correspond to the Einstein-Hilbert, through mathematically unsound manipulations (how can you raise indices with the metric being nowhere even close to invertible?). Besides, how can you talk about unifying general relativity and electromagnetism without mentioning Kaluza-Klein theory[1]? And what about one of the most beautiful principles in physics, gauge invariance[2]? I don't want to be rude, but I'm very curious as to how this got through peer review. 0: https://iopscience.iop.org/article/10.1088/1742-6596/1956/1/012017 https://iopscience.iop.org/article/10.1088/1742-6596/1956/1/... 1: https://en.wikipedia.org/wiki/Kaluza%E2%80%93Klein_theory https://en.wikipedia.org/wiki/Kaluza%E2%80%93Klein_theory 2: https://en.wikipedia.org/wiki/Gauge_theory https://en.wikipedia.org/wiki/Gauge_theory
- lamontcg 5y ago
  Yeah first thought that popped into my head was Kaluza-Klein theory, and I'm far from an expert enough to dissect the paper but it has that smell of junk science.
- codethief 5y ago
  > Besides, how can you talk about unifying general relativity and electromagnetism without mentioning Kaluza-Klein theory[1]? No offense but the very first paragraph of the article's introduction mentions Kaluza's work: > The earliest attempts can be reasonably traced back to the German physicist Gustav Mie (1868-1957) and the Finnish physicist Gunnar Nordström (1881-1923). Fruitful efforts came, for example, from David Hilbert (1862-1943), Hermann Weyl (1885-1955), Theodor Kaluza (1885-1954), Arthur Eddington (1882-1944) and of course also from Albert Einstein (1879-1955). It is less well-known that, for example, Erwin Schrödinger (1887-1961) had such inclinations as well, see [1]. For a thorough historical review, see [2].
- onhn 5y ago
  Are you sure it was peer reviewed at all? It looks like a conference proceedings.
trhway 5y ago
mass/energy conversion (in particular to/from photons, i.e. EM waves) is a kind of huge hint that there is really only energy and spacetime (and with energy being just a configuration of spacetime we're left with the spacetime only really). The only issue is the nature of electric charge - what is it really, i.e. can it be reduced to gravity? can it be just an emergent property of energy/spacetime? And in particular the repelling property of the charge which at first seems to not exist for gravity - then where it comes from? I think it is some spin based effect along the lines of the [non-charged] black holes spin-spin interaction based repelling effect, something like this https://arxiv.org/abs/1901.02894 https://arxiv.org/abs/1901.02894 Another commenter https://news.ycombinator.com/item?id=27943428 https://news.ycombinator.com/item?id=27943428 talks what basically looks to me as an emergence of EM field from rotation - "to multiply each point of the universe by a different complex number of modulo 1" - ie. as an artefact emerging by changing the frame to the one where the system is rotating (ie. gets a spin). Kind of similar how magnetic field is just emergent artefact in the frame where charge is linearly moving.
edem 5y ago
Wait, we know this since QED, no?
zwaps 5y ago
It’s really interesting to see other fields trying to explain research. Here, I feel the authors are not entirely clear who the audience is supposed to be. At first, they seem to target people who need the difference between Einstein and Maxwell explained. The section is titled:“ Maxwell's equations and general relativity—what are these all about?“ Then when they reveal the missing link, the uninformed reader is presented with a logical progression that is obviously written towards somehow for whom the statement:“the Lagrangian of electrodynamics is just the Einstein-Hilbert action“ is self explanatory. You know, people who say, yes of course, if you say:“ keep the spacetime manifold Ricci-flat.“ Writing about science is hard
- zwaps 5y ago
  And all I, the non technical reader, want to know is which of these theories give us Warp technology by the time the Vulcans pass by the solar system
- yesenadam 5y ago
  That reminds me of Roger Penrose's 1100pp The Road to Reality: A Complete Guide to the Laws of the Universe, which I was very excited about reading when I bought it years ago. Lots of lovely diagrams. Turns out I could learn almost nothing from it, although I really tried: The first half of the book was basic stuff I already knew, but I could understand nothing of the second half, it passed so quickly from the elementary to the super-advanced. I ended up wondering who it was written for—I imagined everyone would have a similar experience, whatever their level—it's stuff you already know until suddenly it's stuff you can't understand, and no way of passing beyond. It covers so much ground so quickly, with no time for enough explanation—if you didn't already understand the current topic. Maybe that was just me! But it was extremely surprising putting so much (money,) time and effort into a book with rave reviews by a leading physicist, and learning virtually nothing.
  - JohnHaugeland 5y ago
    " yesenadam 1 day ago | parent [–] | on: Electromagnetism is a property of spacetime itself... That reminds me of Roger Penrose's 1100pp The Road to Reality: A Complete Guide to the Laws of the Universe, which I was very excited about reading when I bought it years ago. Lots of lovely diagrams. Turns out I could learn almost nothing from it, although I really tried: The first half of the book was basic stuff I already knew, but I could understand nothing of the second half, it passed so quickly from the elementary to the super-advanced. I ended up wondering who it was written for—I imagined everyone would have a similar experience, whatever their level—it's stuff you already know until suddenly it's stuff you can't understand, and no way of passing beyond." This is nearly universally an answer to the request" tell me you don't understand something you think you understand without telling me that you don't understand something that you think you understand" The ramp isn't steep. It's just that if you think you're on it but aren't, then the second floor looks like a wall
LinAGKar 5y ago
>On the other hand, the theory of gravitation is rather well understood I thought it was the other way around. Gravity is not well understood.
- Sharlin 5y ago
  Gravity is extremely well described by general relativity. What we do lack is a quantum version of GR, but that does not change the fact that we understand gravity very well, at least in the sense of the word that physicists are used to.
  - codethief 5y ago
    > we understand gravity very well, at least in the sense of the word that physicists are used to (emphasis mine) As someone with a background in mathematical relativity, I would like to note that GR actually is not very well understood at all. Physicists seem to focus on the few simple solutions to Einstein's field equations that people have found through educated guessing, but there a ton of questions about the field equations that are open to this day.
akomtu 5y ago
Here's about the same idea with formulas: http://estfound.org/quantum.htm http://estfound.org/quantum.htm. TL;DR if we assume that the ds2 invariant oscillates a bit, and apply the lorentz transforms, we'll get the stationary Schrodinger equation. I can't judge the math or physical soundness of the approach, but it looks legit.
immmmmm 5y ago
just read the abstract, seems meh wrote two very well cited articles [1,2] on this in the context of string theory. but this was just extending kaluza klein, where by adding one compact dimensions (with some assumptions) you get maxwell out of einstein for free. this result is from 1919, 102 years old. i'm glad i can write all gravitation, electromagnetism, yang mills and string theory in two equations (1.6 in [2]]) but honestly i don't that's a breakthrough. i might be wrong, yet it smells more like PR than important discovery. btw you can as as well find solutions of GR that are dual to navier stokes equs. [0] https://en.m.wikipedia.org/wiki/Kaluza–Klein_theory https://en.m.wikipedia.org/wiki/Kaluza–Klein_theory [1] https://arxiv.org/abs/1109.4280 https://arxiv.org/abs/1109.4280 [2] https://arxiv.org/abs/1304.1472 https://arxiv.org/abs/1304.1472
orbifold 5y ago
This paper is seriously flawed. I'm surprised it was published.
- LegitShady 5y ago
  Please go on
MichaelZuo 5y ago
There seems to be something tantalizing in the relation between the EM and gravity field. Whether this is an accurate description of that remains be seen. Some interesting potential tie-ins https://en.wikipedia.org/wiki/Abraham–Minkowski_controversy https://en.wikipedia.org/wiki/Abraham–Minkowski_controversy and https://en.wikipedia.org/wiki/Casimir_effect https://en.wikipedia.org/wiki/Casimir_effect
drran 5y ago
EM is math. LOL.
codethief 5y ago
I had a quick look at their paper. I haven't understood everything and looked into all steps in detail but I think what they doing is (roughly) the following: Let g be the spacetime metric, and A be the electromagnetic 4-potential. 1. Suppose you could write the metric as g_{μν} = A_μ A_ν, i.e. the symmetric product of A with itself. 2. Conclude that the Einstein-Hilbert action is just the electromagnetic action plus a correction term A_μ ∇^μ ∇_ν A^ν = g(A, grad(div A)). 3. Assume that J^μ = ∇^μ ∇_ν A^ν = grad(div A). 4. The correction term from step 2 then becomes the usual electromagnetic coupling A_μ J^μ. As a consequence, the Einstein-Hilbert action for g is just the usual full (non-vacuum) action of electrodynamics on a background curved by g = Sym(A⊗A). 5. Consider the vacuum Einstein equations and, thus, a Ricci-flat spacetime. Show that this is equivalent to ∇² A^μ = J^μ which are the inhomogeneous Maxwell equations in Lorentz gauge. The fact that we're in a vacuum spacetime but still considering electromagnetism seems odd but I guess their idea is that if electromagnetism is a purely geometric property of spacetime, then the electromagnetic action (including any potential electric current) shouldn't appear on the right-hand side of Einstein's equations in the first place – because the Einstein equations are Maxwell's equations. 6. Identify the 4-current J^μ with terms involving the electromagnetic field tensor and the metric's Weyl curvature. (Meaning, once again, that J^μ can be non-trivial even though we're considering a vacuum/Ricci-flat spacetime.) 7. Identify the remaining (homogeneous) Maxwell equations with the first Bianchi identity for the Riemann tensor. 8. Impose the continuity equation ∇_μ J^μ = 0, i.e. assume conservation of charge. 9. Conclude from 3) and 8) that div(A) fulfills a homogeneous wave equation. ----- Comments and observations: - In step 5, I don't see how Maxwell's equations (18) are supposed to follow from equation (17). But it's late, maybe I'm just being blind. - As other comments have already pointed out, step 1 seems unreasonable because the metric will no longer be of Lorentzian type (with determinant -1) but instead will be positive-semi-definite. (To see this, diagonalize the metric at a given point => g = (A_μ)² (dx^μ)².) In particular, the metric might even be degenerate(!) It seems section 2.1 in their paper is supposed to address the signature issue but from my POV it's insufficient. - The paper basically claims that gravity is just the theory of a vector 4-potential. That doesn't seem right, given that much effort was spent in the past 100 years to find such a theory. AFAIK it's pretty much ruled out these days. - Given step 5 and the fact that the EM field no longer seems to contribute to the field equations, I have even more doubts this theory could ever turn out to be true. There are lots of solutions to the Einstein-Maxwell equations and I'm sure some of them have been confirmed experimentally by now. (I'm thinking of black hole jets etc.) - For instance, IIRC there's a paper showing that from Einstein-Maxwell's equations it follows that photons move along null geodesics (which in the beginning of GR was merely an axiom of the theory). I wonder what would happen to this result. Hypothetically, photons might no longer move along geodesics in this new gravito-electromagnetic theory but the theory might still reproduce gravitational lensing. I don't think that's very likely, though. - More generally, I think their theory is even difficult to reconcile with classic electrodynamics in the first place. In the absence of strong gravitational and quantum effects, we know that Maxwell's equations describe ED very well. However, the equations ∇² A^μ = J^μ above no longer are the classic (linear!¹) vacuum Maxwell equations we know – they are now highly non-linear since the covariant derivative ∇ now also involves the vector potential A. To reobtain classic ED in flat space one would basically need to ensure that in every-day situations A is "constant enough" not to produce any significant curvature through g = Sym(A⊗A) but still dynamic enough to reproduce the classic wavey nature of light. This doesn't seem likely. Plugging any known (experimentally proven) solution to the Maxwell equations into the equations here should invalidate the theory. ¹) in the absence of charges, i.e. J^μ = 0
dr_dshiv 5y ago
"John Wheeler, the famous physicist, put forward the idea that all of the material world is constructed from the geometry of the spacetime. Our research strongly supports this kind of natural philosophy. It means that the material world always corresponds to some geometric structures of spacetime." This is also the Platonic-Pythagorean perspective, that the world is literally made of math.
avsteele 5y ago
No opinion on this paper but I'll note something related of interest: You can see how special relativity is true by just taking Maxwell's equations seriously. They show the speed of light is the same in every reference frame.
sethc2 5y ago
> In a way, spacetime itself is therefore the aether. This somehow reminds me of C.S. Lewis’s “Out of the Silent Planet”, where the narrator says regarding the protagonist “He wondered how he could ever have thought of planets, even on Earth, as islands of life and reality floating in a deadly void. Now, with a certainty which never after deserted him, he saw the planets - the 'earths' he called them in his thought - as mere holes or gaps in the living heaven - excluded and rejected wastes of heavy matter and murky air, formed not by addition to, but by subtraction from, the surrounding brightness.”
- snet0 5y ago
  That's a wonderful quote. I've only read Mere Christianity by CS Lewis, would you recommend reading the book you quoted?
  - sethc2 5y ago
    I love the space trilogy. Out of the silent planet helped me think of what the “heavens” are. I’d definitely recommend them, though I love thinking of t he symbolic nature of things.
fallingfrog 5y ago
Link to the paper: https://iopscience.iop.org/article/10.1088/1742-6596/1956/1/012017/pdf https://iopscience.iop.org/article/10.1088/1742-6596/1956/1/...
fallingfrog 5y ago
I can’t follow the math but he seems to be talking about general relativity in empty space, and he seems to be talking about classical electromagnetism not quantized. So it doesn’t seem to be the holy grail of quantum general relativity, in any case.
nsoonhui 5y ago
The idea of combining electromagnetism into space time field isn't exactly new; Weyl's theory of the combined gravitational-electromagnetic field [0], proposed by Hermann Weyl, some 100 years ago, did just that. [0]: http://www.weylmann.com/weyltheory.pdf http://www.weylmann.com/weyltheory.pdf
- codethief 5y ago
  Yes, and the paper the article is based on does mention Weyl: > The earliest attempts can be reasonably traced back to the German physicist Gustav Mie (1868-1957) and the Finnish physicist Gunnar Nordström (1881-1923). Fruitful efforts came, for example, from David Hilbert (1862-1943), Hermann Weyl (1885-1955), Theodor Kaluza (1885-1954), Arthur Eddington (1882-1944) and of course also from Albert Einstein (1879-1955). It is less well-known that, for example, Erwin Schrödinger (1887-1961) had such inclinations as well, see [1]. For a thorough historical review, see [2].
johndoe42377 5y ago
Property of what?
codethief 5y ago
Since the comments here keep addressing the (machine-generated?) article, not the research paper it is based on, here's the paper: https://doi.org/10.1088/1742-6596/1956/1/012017 https://doi.org/10.1088/1742-6596/1956/1/012017
ijidak 5y ago
GPT-3?
icf80 5y ago
This explains why speed to light = speed of gravity
PaulDavisThe1st 5y ago
There are some great comments here, incredibly enlightening. Yet somehow, I still find myself on Wolfram's side, suspecting that the entire QM/GR formulation is going to turn out to be the wrong way to understand the universe and that something quite different (e.g. cellular automata) will eventually be seen as much better. The situation seems quite analogous to the one with fluid mechanics: we can use the continuously valued models that involve concepts like rate, turbulence, friction, etc. and be happy that we can reason about the system even though we fundamentally do not know what these properties are and can reasonably doubt that they are real. Or we can use cellular automata models, which use discrete math and have no "properties" that we can reason about. The outcomes are broadly similar in terms of prediction, but the approaches are totally different. I will not be alive in 300 years, but if I were to be, I'd be willing to wager right now that most of the QM/GR formalisms will have been replaced by something entirely different.
nazrulmum10 5y ago
Maxwell's equations and general relativity—what are these all about? Maxwell's equations are the key linear partial differential equations that describe classical electromagnetism. The equations relate the electromagnetic field to currents and charges. On the other hand, in general relativity, the Einstein field equation is a set of nonlinear partial differential equations describing how the metric of spacetime evolves, given some conditions, such as mass density in the spacetime. Both equations are ultimately of second order, if seen properly. Therefore, we thought that perhaps we are talking about the same governing equation, which could describe both electromagnetism and gravitation. Indeed, it becomes clear that Maxwell's equations hide inside the Einstein field equations of general relativity. The metric tensor of spacetime tells us how lengths determine in spacetime. The metric tensor also thus determines the curvature properties of spacetime. Curvature is what we feel as "force." In addition, energy and curvature relate to each other through the Einstein field equations. Test particles follow what are called geodesics—the shortest paths in the spacetime.

397 points by egfx 5y ago

fosk 5y ago

I dream of faster than light travel by bending the space time fabric in “U” shape (like pinching a piece of paper) and allowing to travel across the two planes of reference.

amelius 5y ago
What if your neighbor wants to bend space time in the other direction?
- swayvil 5y ago
  Then we would simply fork reality. Everybody's happy.
  - IgorPartola 5y ago
    Everybody is both happy and unhappy.
  - excalibur 5y ago
    Everybody but the TVA.
koheripbal 5y ago
folding the paper isnt enough. you also need to reform the paper to make the hole attach at both ends. ripping apart spacetime may not even be possible.
freshhawk 5y ago
Sure, it would take an enormous amount of energy to do it though. Oh yeah, and you'd also be annihilated as you were completely turned to energy as you tried to go through it of course. But you'd sure fire a hell of a lot of randomized high energy particles out the other side after the amount of time it would have taken light to get there. Not my preferred kind of "travel", I'll just freeze myself and go the slow way or something.
psyc 5y ago
Ah, fond memories of A Wrinkle in Time by Madeleine L’Engle.
cletus 5y ago
This common desire for FTL should be an object lesson in how wishful thinking distorts objectivity. We see a constant stream of ideas that spring from simply not understanding the domain of a function. You can put a negative value into mass or energy. That doesn't mean it means anything. There really is no plausible theory for FTL of any kind. Maybe there will be in the future. Personally I'd put everything I have on the speed of light being an absolute limit to causality. Look at it this way: if FTL travel were possible we probably wouldn't exist. Whoever came first would probably colonize the Universe and sterilize it of competition. So there's that.
- ineedasername 5y ago
  if FTL travel were possible we probably wouldn't exist. Whoever came first would probably colonize the Universe and sterilize it of competition FTL doesn't necessarily mean infinite/instant travel. Also the scenario you propose could be part of the Great Filter, and we just haven't been culled yet. Or FTL civilizations tend to get so large they fracture & turn to in-fighting or encounter other resource bottlenecks that limit exponential expansion. Or C is the law and going FTL spawns a cosmic traffic cop like the meatball head things in Rick & Morty. Or FTL is simply impossible, but perhaps not constant and various factors impact the local C

avmich 5y ago

> Moreover, electric charge relates to some compressibility properties of spacetime. Wonder if somebody could explain this?

findalex 5y ago
Maybe something along the lines of regions of charged space time resist compression while charged and non charged regions more spontaneous compress? Attraction/repulsion?
swayvil 5y ago
Maybe we could take the same motion in air as a metaphor for what's happening in spacetime. Charge becomes an area of higher or lower air-density. EM Waves become areas of changed air-density, propagated. This is just pulled fresh from my butt, mind you.

calin2k 5y ago

this reminds me of https://en.wikipedia.org/wiki/Philadelphia_Experiment https://en.wikipedia.org/wiki/Philadelphia_Experiment

marsven_422 5y ago

I long for the day they invalidate QM

curt15 5y ago

I come from maths, not physics, but their construction g_{\mu \nu} = A_\mu A_\nu looks a little weird to me. The left side is a tensor, but isn't the electromagnetic four-potential is a gauge field, not a tensor?

ajkjk 5y ago
A gauge field is tensor-valued; what's wrong with that? Although it does seems strange for other reasons. Primarily because it seems very unlikely that everyone else who developed this field wouldn't have considered the possibility and then discarded it.
- curt15 5y ago
  Although a gauge field has multiple components, it transforms differently from tensors under a change of coordinates: A -> O A O^{-1} - dO O^{-1} (O is the Jacobian matrix) The second term is absent for tensors (such as the left side of their equation 4). It also vanishes on a flat spacetime where one only considers linear (Lorentz) coordinate transformations, but based on my cursory reading they don't seem to be making that assumption.
  - codethief 5y ago
    I'm not sure I'm following. In General Relativity, the 4-electromagnetic potential A^μ is simply a vector field on spacetime, so what's wrong with taking the (symmetrization of) the tensor product of A_μ with itself to obtain a symmetric 2-tensor? (Whether or not that 2-tensor satisfies the requirements for a semi-Riemannian metric is another question.)
    - nilaykumar 5y ago
      Why is A_\mu a vector field on spacetime? In the standard treatment A is the (pullback to the base of the) connection 1-form of a connection on a principal U(1)-bundle on spacetime. Technically it's valued in the Lie algebra of U(1), but as that can be identified with i times the real numbers, we can ignore that here. Does the product A_\mu A_\nu happen to transform tensorially? Because as the parent pointed out, the transformation rule for A involves an extra term, so it's not obvious.

ajkjk 5y ago

This article is not really coherent. It seems like a bunch of random statements about physics, strung together without explanation. This paragraph for instance is a bunch of true-ish sentences but overall is gibberish: > The metric tensor of spacetime tells us how lengths determine in spacetime. The metric tensor also thus determines the curvature properties of spacetime. Curvature is what we feel as "force." In addition, energy and curvature relate to each other through the Einstein field equations. Test particles follow what are called geodesics—the shortest paths in the spacetime.

LegitShady 5y ago
There’s a paper with equations linked at the bottom. I suspect it sounds like gibberish because its describing a mathematical proof with common language. The paper assumes you have a lot of knowledge as well.
codethief 5y ago
> This paragraph for instance is a bunch of true-ish sentences but overall is gibberish: >> The metric tensor of spacetime tells us how lengths determine in spacetime. The metric tensor also thus determines the curvature properties of spacetime. Curvature is what we feel as "force." In addition, energy and curvature relate to each other through the Einstein field equations. Test particles follow what are called geodesics—the shortest paths in the spacetime. Could you elaborate on why you think this is gibberish? I mean, I agree that the article is giving off a pseudo science vibe and the authors should work on their style. (Instead of presenting their results in a matter-of-fact manner, they should rather dedicate more time to explaining their assumptions and their reasoning in a step-by-step manner.) But the paragraph you quoted seems perfectly fine.
- ajkjk 5y ago
  All of the sentences in the paragraph are real sentences from physics but they're strong together like they were generated by GPT-3 or something. For instance what does "how lengths determine in spacetime" mean? Why is it saying that curvature is what we feel as force? Why is it suddenly talking about test particles without introducing the term? Why does it jump to talking about geodesics in the last sentence? etc. it just feels like it was strung together by an algorithm.

evancox100 5y ago

I’m nowhere near qualified enough in general relativity to evaluate their claims, but when I see something like this: “This is aesthetically pleasing, as nature seems to strive for harmony, efficiency and simplicity.” it makes me think they are not being the most objective evaluators of reality.

KhoomeiK 5y ago
Aesthetics, harmony, and simplicity are the guiding principles of mathematical conjecture. This piece is simply hypothesizing about a link while calling for further empirical research.
- haskellandchill 5y ago
  No, that's just fluff. Occam's Razor is all there is to it.
  - catlifeonmars 5y ago
    Occam’s razor more or less manifests as elegance in mathematics.
enkid 5y ago
Aesthetics should have nothing to do with science. Aesthetics is the reason we thought the Earth was at the center of the universe and everything outside the orbit of the moon was made of perfect spheres. It's why the Soviet Union pushed Lamarckian biology instead of Darwinism.
- bullsbarry 5y ago
  The earth is at the center of the visible universe.
  - mellosouls 5y ago
    Only to observers on earth...

ozankabak 5y ago

IIUC the authors are saying that if we associate the metric with the four-potential via an outer product, they get a picture coherent with the current understanding of how electromagnetism "works" in GR under certain circumstances. I can somewhat see how to interpret the mathematics in free space. But what about when there are massive bodies in the picture? They will result in a non-flat metric... does that imply they create their own electromagnetism?

deleted 5y ago

[deleted]

enoreyes 5y ago

This is interesting and if the experimental evidence confirms this hypothesis, it bodes well for our future. A universe where we can interact with spacetime via engineering is one that allows for a lot of creative freedom. They also have another interesting article claiming that the imaginary structure of QM is the result of stochastic optimization on spacetimes: https://www.nature.com/articles/s41598-019-56357-3 https://www.nature.com/articles/s41598-019-56357-3 Maybe the UAPs really are just secret warp drive tech we made 20 or 30 years ago.

zeteo 5y ago

The idea that strong electromagnetic fields affect the local curvature of spacetime is nothing short of revolutionary. Imagine the possibilities of that! This may be the beginning of the road to a functional warp drive at last.

nimish 5y ago
Well good news, we've known that for a century as it follows from incorporating the electromagnetic stress energy tensor into the field equations
- zeteo 5y ago
  I can do without the sarcasm. Can you point me to any actual experiments?
  - gus_massa 5y ago
    I think there are no experiments in the lab or a direct measurement of this. Anyway, if the light is blended during an eclipse, the that light should have accelerated the Sun just a tiny tiny ... tiny tiny bit in the opposite direction.
  - nimish 5y ago
    I'm not sure what you're looking for. EM fields so strong that they affect spacetime noticeably? We haven't observed any Reissner-Nordstrom/Kerr-Newman black holes iirc. That said, _anything_ with stress-energy-momentum is held to affect spacetime curvature in GR.
  - BlackFly 5y ago
    Controlled experiments are very rare if you are talking about gravity, since the force is so weak. Observational experiments (astronomy) is where most of the evidence comes from. The most obvious inclusion of it for me is the radiative (also known as the photon) component of the matter density in Lambda CDM models (that is, they need to account for the proportion of the energy density of the universe which is related to electromagnetic fields to rule it out as dark matter).

amelius 5y ago

What would the EM field of a photon look like if you moved along with the photon? Would the magnetic part disappear just like it disappears when you move along with a moving electron?

blamestross 5y ago
Basically, from the photon's point of view, all travel is the universe distorting until origin and destination are literally the same point. Photon's don't experience movement, the universe does an instant jig around them while they sit still.
gary_0 5y ago
You can't "move along with a photon" because, in terms of General Relativity, any particle moving at c doesn't have a frame of reference.
- deleted 5y ago
  [deleted]

lumost 5y ago

Reading the article, this appears to be a speculative rehash of past theories claiming to unify electromagnetism and general relativity. The article ends on the note that empirical research is needed. I did not see anything novel that would warrant further attention - did I miss something?

codethief 5y ago
The article is based on a paper linked at the very bottom of the text.

yummypaint 5y ago

Electromagnetism is already understood to be a special case of the electroweak interaction, which is itself a component of the standard model. The paper mentions Maxwell's equations, but not these more general models.

codethief 5y ago
So what? The very first step to unifying GR with quantum mechanics and the standard model might actually be to realize that part of the standard model can be embedded in GR (at least when EM is considered as a classical field theory). I don't think it's a deficiency of the paper that it doesn't present a solution to everything.

gus_massa 5y ago

In particles physics, they have a different explanation of electromagnetism that is also very natural, almost inevitable. https://en.wikipedia.org/wiki/Quantum_electrodynamics#Mathematical_formulation https://en.wikipedia.org/wiki/Quantum_electrodynamics#Mathem... The explanation in particle physics is compatible with Quantum Mechanics and Special Relativity, but no one is sure about how to extend it to General Relativity. I'm not sure how compatible is it with the proposal in the article discussed here. Non technical version (ELI25): In quantum mechanics the wavefunction Ψ is has complex values. If you multiply everything in the universe by -1, nothing changes because all the physical results use ΨΨ* (where * is the complex conjugation). You can also multiply everything by i or -i. Moreover by any other complex number of modulo 1 because ΨΨ* does not change. (The technical term for this is U(1) global gauge symmetry.) But you can be more ambitious and want to multiply each point of the universe by a different complex number of modulo 1. ΨΨ* does not change but the derivatives of Ψ change and they are also important. (When you use the same complex number everywhere, the derivatives is just a multiple of the original derivative. When you use a different number in each point, it changes.) The only way to fix the problem with the derivative is to add a new field A. When you and multiply each point of the universe by a different complex number of modulo 1, then A changes in a simple to calculate but not obvious way. The change in A fix the problem with the derivatives of Ψ. So now the equations of the universe with Ψ and A don't change when you make this change. (The technical term for this is U(1) local gauge symmetry.) When you write carefully how a universe like this look like, the new field A is electromagnetism. (Actually, you can get the electric field and magnetic field using the derivatives of A.) This explanation looks more complicated than the explanation of the article, but the article is full of technical terms that you really don't want to know, like: > Riemann curvature tensor is more than just Ricci curvature—electromagnetic fields stretch and bend the spacetime

KirillPanov 5y ago
>_In particles physics ... very natural Er, I'm not sure that things like dressed particles [1] and off-shell matter [2] violating E=mc^2 [3] could be described as even remotely "natural". Perhaps they are valid theories, but "natural" certainly isn't an appropriate description of most of what unavoidably follows from particle assumptions. [1] https://en.m.wikipedia.org/wiki/Dressed_particle https://en.m.wikipedia.org/wiki/Dressed_particle [2] https://en.m.wikipedia.org/wiki/On_shell_and_off_shell https://en.m.wikipedia.org/wiki/On_shell_and_off_shell [3] https://en.m.wikipedia.org/wiki/Virtual_particle#Properties https://en.m.wikipedia.org/wiki/Virtual_particle#Properties

kilodeca 5y ago

I heard people saying the opposite.

lend000 5y ago

I like the idea intuitively (the idea that infinite discrete photons are required to mediate continuous fields from a single electron over infinite distances never sat well with me), so are they claiming here that there is a relativity-version of Maxwell's Equations? Does it require an additional spatial dimension to account for charge, or does it operate it on the same spacetime as gravity? Regardless, if I'm understanding this nontechnical overview correctly, it's a large claim requiring a lot of work. Probably worth a Nobel Prize if it they actually pull it off.

ethn 5y ago

I thought we knew this already since Faraday.

kmm 5y ago

I'm not an expert in GR, but the linked paper seems nonsensical[0]. It postulates a highly degenerate decomposition of the metric tensor, for which they postulate a contrived action which then seems to correspond to the Einstein-Hilbert, through mathematically unsound manipulations (how can you raise indices with the metric being nowhere even close to invertible?). Besides, how can you talk about unifying general relativity and electromagnetism without mentioning Kaluza-Klein theory[1]? And what about one of the most beautiful principles in physics, gauge invariance[2]? I don't want to be rude, but I'm very curious as to how this got through peer review. 0: https://iopscience.iop.org/article/10.1088/1742-6596/1956/1/012017 https://iopscience.iop.org/article/10.1088/1742-6596/1956/1/... 1: https://en.wikipedia.org/wiki/Kaluza%E2%80%93Klein_theory https://en.wikipedia.org/wiki/Kaluza%E2%80%93Klein_theory 2: https://en.wikipedia.org/wiki/Gauge_theory https://en.wikipedia.org/wiki/Gauge_theory

lamontcg 5y ago
Yeah first thought that popped into my head was Kaluza-Klein theory, and I'm far from an expert enough to dissect the paper but it has that smell of junk science.
codethief 5y ago
> Besides, how can you talk about unifying general relativity and electromagnetism without mentioning Kaluza-Klein theory[1]? No offense but the very first paragraph of the article's introduction mentions Kaluza's work: > The earliest attempts can be reasonably traced back to the German physicist Gustav Mie (1868-1957) and the Finnish physicist Gunnar Nordström (1881-1923). Fruitful efforts came, for example, from David Hilbert (1862-1943), Hermann Weyl (1885-1955), Theodor Kaluza (1885-1954), Arthur Eddington (1882-1944) and of course also from Albert Einstein (1879-1955). It is less well-known that, for example, Erwin Schrödinger (1887-1961) had such inclinations as well, see [1]. For a thorough historical review, see [2].
onhn 5y ago
Are you sure it was peer reviewed at all? It looks like a conference proceedings.

trhway 5y ago

mass/energy conversion (in particular to/from photons, i.e. EM waves) is a kind of huge hint that there is really only energy and spacetime (and with energy being just a configuration of spacetime we're left with the spacetime only really). The only issue is the nature of electric charge - what is it really, i.e. can it be reduced to gravity? can it be just an emergent property of energy/spacetime? And in particular the repelling property of the charge which at first seems to not exist for gravity - then where it comes from? I think it is some spin based effect along the lines of the [non-charged] black holes spin-spin interaction based repelling effect, something like this https://arxiv.org/abs/1901.02894 https://arxiv.org/abs/1901.02894 Another commenter https://news.ycombinator.com/item?id=27943428 https://news.ycombinator.com/item?id=27943428 talks what basically looks to me as an emergence of EM field from rotation - "to multiply each point of the universe by a different complex number of modulo 1" - ie. as an artefact emerging by changing the frame to the one where the system is rotating (ie. gets a spin). Kind of similar how magnetic field is just emergent artefact in the frame where charge is linearly moving.

edem 5y ago

Wait, we know this since QED, no?

zwaps 5y ago

It’s really interesting to see other fields trying to explain research. Here, I feel the authors are not entirely clear who the audience is supposed to be. At first, they seem to target people who need the difference between Einstein and Maxwell explained. The section is titled:“ Maxwell's equations and general relativity—what are these all about?“ Then when they reveal the missing link, the uninformed reader is presented with a logical progression that is obviously written towards somehow for whom the statement:“the Lagrangian of electrodynamics is just the Einstein-Hilbert action“ is self explanatory. You know, people who say, yes of course, if you say:“ keep the spacetime manifold Ricci-flat.“ Writing about science is hard

zwaps 5y ago
And all I, the non technical reader, want to know is which of these theories give us Warp technology by the time the Vulcans pass by the solar system
yesenadam 5y ago
That reminds me of Roger Penrose's 1100pp The Road to Reality: A Complete Guide to the Laws of the Universe, which I was very excited about reading when I bought it years ago. Lots of lovely diagrams. Turns out I could learn almost nothing from it, although I really tried: The first half of the book was basic stuff I already knew, but I could understand nothing of the second half, it passed so quickly from the elementary to the super-advanced. I ended up wondering who it was written for—I imagined everyone would have a similar experience, whatever their level—it's stuff you already know until suddenly it's stuff you can't understand, and no way of passing beyond. It covers so much ground so quickly, with no time for enough explanation—if you didn't already understand the current topic. Maybe that was just me! But it was extremely surprising putting so much (money,) time and effort into a book with rave reviews by a leading physicist, and learning virtually nothing.
- JohnHaugeland 5y ago
  " yesenadam 1 day ago | parent [–] | on: Electromagnetism is a property of spacetime itself... That reminds me of Roger Penrose's 1100pp The Road to Reality: A Complete Guide to the Laws of the Universe, which I was very excited about reading when I bought it years ago. Lots of lovely diagrams. Turns out I could learn almost nothing from it, although I really tried: The first half of the book was basic stuff I already knew, but I could understand nothing of the second half, it passed so quickly from the elementary to the super-advanced. I ended up wondering who it was written for—I imagined everyone would have a similar experience, whatever their level—it's stuff you already know until suddenly it's stuff you can't understand, and no way of passing beyond." This is nearly universally an answer to the request" tell me you don't understand something you think you understand without telling me that you don't understand something that you think you understand" The ramp isn't steep. It's just that if you think you're on it but aren't, then the second floor looks like a wall

LinAGKar 5y ago

>On the other hand, the theory of gravitation is rather well understood I thought it was the other way around. Gravity is not well understood.

Sharlin 5y ago
Gravity is extremely well described by general relativity. What we do lack is a quantum version of GR, but that does not change the fact that we understand gravity very well, at least in the sense of the word that physicists are used to.
- codethief 5y ago
  > we understand gravity very well, at least in the sense of the word that physicists are used to (emphasis mine) As someone with a background in mathematical relativity, I would like to note that GR actually is not very well understood at all. Physicists seem to focus on the few simple solutions to Einstein's field equations that people have found through educated guessing, but there a ton of questions about the field equations that are open to this day.

akomtu 5y ago

Here's about the same idea with formulas: http://estfound.org/quantum.htm http://estfound.org/quantum.htm. TL;DR if we assume that the ds2 invariant oscillates a bit, and apply the lorentz transforms, we'll get the stationary Schrodinger equation. I can't judge the math or physical soundness of the approach, but it looks legit.

immmmmm 5y ago

just read the abstract, seems meh wrote two very well cited articles [1,2] on this in the context of string theory. but this was just extending kaluza klein, where by adding one compact dimensions (with some assumptions) you get maxwell out of einstein for free. this result is from 1919, 102 years old. i'm glad i can write all gravitation, electromagnetism, yang mills and string theory in two equations (1.6 in [2]]) but honestly i don't that's a breakthrough. i might be wrong, yet it smells more like PR than important discovery. btw you can as as well find solutions of GR that are dual to navier stokes equs. [0] https://en.m.wikipedia.org/wiki/Kaluza–Klein_theory https://en.m.wikipedia.org/wiki/Kaluza–Klein_theory [1] https://arxiv.org/abs/1109.4280 https://arxiv.org/abs/1109.4280 [2] https://arxiv.org/abs/1304.1472 https://arxiv.org/abs/1304.1472

orbifold 5y ago

This paper is seriously flawed. I'm surprised it was published.

LegitShady 5y ago
Please go on

MichaelZuo 5y ago

There seems to be something tantalizing in the relation between the EM and gravity field. Whether this is an accurate description of that remains be seen. Some interesting potential tie-ins https://en.wikipedia.org/wiki/Abraham–Minkowski_controversy https://en.wikipedia.org/wiki/Abraham–Minkowski_controversy and https://en.wikipedia.org/wiki/Casimir_effect https://en.wikipedia.org/wiki/Casimir_effect

drran 5y ago

EM is math. LOL.

codethief 5y ago

I had a quick look at their paper. I haven't understood everything and looked into all steps in detail but I think what they doing is (roughly) the following: Let g be the spacetime metric, and A be the electromagnetic 4-potential. 1. Suppose you could write the metric as g_{μν} = A_μ A_ν, i.e. the symmetric product of A with itself. 2. Conclude that the Einstein-Hilbert action is just the electromagnetic action plus a correction term A_μ ∇^μ ∇_ν A^ν = g(A, grad(div A)). 3. Assume that J^μ = ∇^μ ∇_ν A^ν = grad(div A). 4. The correction term from step 2 then becomes the usual electromagnetic coupling A_μ J^μ. As a consequence, the Einstein-Hilbert action for g is just the usual full (non-vacuum) action of electrodynamics on a background curved by g = Sym(A⊗A). 5. Consider the vacuum Einstein equations and, thus, a Ricci-flat spacetime. Show that this is equivalent to ∇² A^μ = J^μ which are the inhomogeneous Maxwell equations in Lorentz gauge. The fact that we're in a vacuum spacetime but still considering electromagnetism seems odd but I guess their idea is that if electromagnetism is a purely geometric property of spacetime, then the electromagnetic action (including any potential electric current) shouldn't appear on the right-hand side of Einstein's equations in the first place – because the Einstein equations are Maxwell's equations. 6. Identify the 4-current J^μ with terms involving the electromagnetic field tensor and the metric's Weyl curvature. (Meaning, once again, that J^μ can be non-trivial even though we're considering a vacuum/Ricci-flat spacetime.) 7. Identify the remaining (homogeneous) Maxwell equations with the first Bianchi identity for the Riemann tensor. 8. Impose the continuity equation ∇_μ J^μ = 0, i.e. assume conservation of charge. 9. Conclude from 3) and 8) that div(A) fulfills a homogeneous wave equation. ----- Comments and observations: - In step 5, I don't see how Maxwell's equations (18) are supposed to follow from equation (17). But it's late, maybe I'm just being blind. - As other comments have already pointed out, step 1 seems unreasonable because the metric will no longer be of Lorentzian type (with determinant -1) but instead will be positive-semi-definite. (To see this, diagonalize the metric at a given point => g = (A_μ)² (dx^μ)².) In particular, the metric might even be degenerate(!) It seems section 2.1 in their paper is supposed to address the signature issue but from my POV it's insufficient. - The paper basically claims that gravity is just the theory of a vector 4-potential. That doesn't seem right, given that much effort was spent in the past 100 years to find such a theory. AFAIK it's pretty much ruled out these days. - Given step 5 and the fact that the EM field no longer seems to contribute to the field equations, I have even more doubts this theory could ever turn out to be true. There are lots of solutions to the Einstein-Maxwell equations and I'm sure some of them have been confirmed experimentally by now. (I'm thinking of black hole jets etc.) - For instance, IIRC there's a paper showing that from Einstein-Maxwell's equations it follows that photons move along null geodesics (which in the beginning of GR was merely an axiom of the theory). I wonder what would happen to this result. Hypothetically, photons might no longer move along geodesics in this new gravito-electromagnetic theory but the theory might still reproduce gravitational lensing. I don't think that's very likely, though. - More generally, I think their theory is even difficult to reconcile with classic electrodynamics in the first place. In the absence of strong gravitational and quantum effects, we know that Maxwell's equations describe ED very well. However, the equations ∇² A^μ = J^μ above no longer are the classic (linear!¹) vacuum Maxwell equations we know – they are now highly non-linear since the covariant derivative ∇ now also involves the vector potential A. To reobtain classic ED in flat space one would basically need to ensure that in every-day situations A is "constant enough" not to produce any significant curvature through g = Sym(A⊗A) but still dynamic enough to reproduce the classic wavey nature of light. This doesn't seem likely. Plugging any known (experimentally proven) solution to the Maxwell equations into the equations here should invalidate the theory. ¹) in the absence of charges, i.e. J^μ = 0

dr_dshiv 5y ago

"John Wheeler, the famous physicist, put forward the idea that all of the material world is constructed from the geometry of the spacetime. Our research strongly supports this kind of natural philosophy. It means that the material world always corresponds to some geometric structures of spacetime." This is also the Platonic-Pythagorean perspective, that the world is literally made of math.

avsteele 5y ago

No opinion on this paper but I'll note something related of interest: You can see how special relativity is true by just taking Maxwell's equations seriously. They show the speed of light is the same in every reference frame.

sethc2 5y ago

> In a way, spacetime itself is therefore the aether. This somehow reminds me of C.S. Lewis’s “Out of the Silent Planet”, where the narrator says regarding the protagonist “He wondered how he could ever have thought of planets, even on Earth, as islands of life and reality floating in a deadly void. Now, with a certainty which never after deserted him, he saw the planets - the 'earths' he called them in his thought - as mere holes or gaps in the living heaven - excluded and rejected wastes of heavy matter and murky air, formed not by addition to, but by subtraction from, the surrounding brightness.”

snet0 5y ago
That's a wonderful quote. I've only read Mere Christianity by CS Lewis, would you recommend reading the book you quoted?
- sethc2 5y ago
  I love the space trilogy. Out of the silent planet helped me think of what the “heavens” are. I’d definitely recommend them, though I love thinking of t he symbolic nature of things.

fallingfrog 5y ago

Link to the paper: https://iopscience.iop.org/article/10.1088/1742-6596/1956/1/012017/pdf https://iopscience.iop.org/article/10.1088/1742-6596/1956/1/...

fallingfrog 5y ago

I can’t follow the math but he seems to be talking about general relativity in empty space, and he seems to be talking about classical electromagnetism not quantized. So it doesn’t seem to be the holy grail of quantum general relativity, in any case.

nsoonhui 5y ago

The idea of combining electromagnetism into space time field isn't exactly new; Weyl's theory of the combined gravitational-electromagnetic field [0], proposed by Hermann Weyl, some 100 years ago, did just that. [0]: http://www.weylmann.com/weyltheory.pdf http://www.weylmann.com/weyltheory.pdf

codethief 5y ago
Yes, and the paper the article is based on does mention Weyl: > The earliest attempts can be reasonably traced back to the German physicist Gustav Mie (1868-1957) and the Finnish physicist Gunnar Nordström (1881-1923). Fruitful efforts came, for example, from David Hilbert (1862-1943), Hermann Weyl (1885-1955), Theodor Kaluza (1885-1954), Arthur Eddington (1882-1944) and of course also from Albert Einstein (1879-1955). It is less well-known that, for example, Erwin Schrödinger (1887-1961) had such inclinations as well, see [1]. For a thorough historical review, see [2].

johndoe42377 5y ago

Property of what?

codethief 5y ago

Since the comments here keep addressing the (machine-generated?) article, not the research paper it is based on, here's the paper: https://doi.org/10.1088/1742-6596/1956/1/012017 https://doi.org/10.1088/1742-6596/1956/1/012017

ijidak 5y ago

GPT-3?

icf80 5y ago

This explains why speed to light = speed of gravity

PaulDavisThe1st 5y ago

There are some great comments here, incredibly enlightening. Yet somehow, I still find myself on Wolfram's side, suspecting that the entire QM/GR formulation is going to turn out to be the wrong way to understand the universe and that something quite different (e.g. cellular automata) will eventually be seen as much better. The situation seems quite analogous to the one with fluid mechanics: we can use the continuously valued models that involve concepts like rate, turbulence, friction, etc. and be happy that we can reason about the system even though we fundamentally do not know what these properties are and can reasonably doubt that they are real. Or we can use cellular automata models, which use discrete math and have no "properties" that we can reason about. The outcomes are broadly similar in terms of prediction, but the approaches are totally different. I will not be alive in 300 years, but if I were to be, I'd be willing to wager right now that most of the QM/GR formalisms will have been replaced by something entirely different.

nazrulmum10 5y ago

Maxwell's equations and general relativity—what are these all about? Maxwell's equations are the key linear partial differential equations that describe classical electromagnetism. The equations relate the electromagnetic field to currents and charges. On the other hand, in general relativity, the Einstein field equation is a set of nonlinear partial differential equations describing how the metric of spacetime evolves, given some conditions, such as mass density in the spacetime. Both equations are ultimately of second order, if seen properly. Therefore, we thought that perhaps we are talking about the same governing equation, which could describe both electromagnetism and gravitation. Indeed, it becomes clear that Maxwell's equations hide inside the Einstein field equations of general relativity. The metric tensor of spacetime tells us how lengths determine in spacetime. The metric tensor also thus determines the curvature properties of spacetime. Curvature is what we feel as "force." In addition, energy and curvature relate to each other through the Einstein field equations. Test particles follow what are called geodesics—the shortest paths in the spacetime.