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So I thought gravity was basically the curvature of spacetime. But if there's a "gravity" particle, those two things seem mutually exclusive? Can someone who u

• deleted 2y ago
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• gary_0 2y ago
  Electromagnetism is both a continuous wave and a discrete particle, so it makes sense to me that a continuous spacetime curvature could also be a discrete particle at the same time. (Keeping in mind we're not talking about tangible shapes but mathematical models that describe aspects of reality that are hard for humans to intuitively conceptualize.) Of course, our idea of how to reconcile quantum gravity with general relativity is much less developed than our understanding of electromagnetism and the nuclear forces.
  • Willingham 2y ago
    When you mention nuclear forces, are you referencing weak force and strong force? Do we understand these forces at the same level that we understand electromagnetism?
    • deleted 2y ago
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    • btilly 2y ago
      Yes. The Standard Model has completely explained all experiments involving them for around 50 years now. In fact the outstanding success of the Standard Model has posed its own problems - the lack of deviations from it makes it hard for experiments to point in a useful direction for better theories to be developed along.
      • elashri 2y ago
        > the lack of deviations from it makes it hard for experiments to point in a useful direction for better theories to be developed along. We have anomalies (deviations from standard model) in many measurements done by several experiments. This is a good summary [1] from them up until now (sorry for the pay-walled) [1] https://www.nature.com/articles/s42254-024-00703-6 https://www.nature.com/articles/s42254-024-00703-6
      • jcranmer 2y ago
        That's not quite accurate. There are a few things that the Standard Model doesn't exactly account for--neutrino oscillation being the most famous. The trouble is that these issues aren't really big enough to suggest new physics, and the experiments aren't good enough to really suggest how much patching actually needs to be done.
        • jraines 2y ago
          Also the unexpectedly large mass of the Higgs, which suggested (to string theorists), super symmetry. Which unfortunately turned out to not exist unless it’s at some configuration that’s quite different from what was suggested
          • pfdietz 2y ago
            I thought the Higgs had an unexpectedly small mass. https://home.cern/news/news/physics/incredible-lightness-higgs https://home.cern/news/news/physics/incredible-lightness-hig...
        • btilly 2y ago
          Yes, there are some deviations. But minor adjustments to the Standard Model handles those. And don't really point in the direction of a better theory. More relevantly to the previous question, I'm not aware of any of those which affect interactions with the strong or weak nuclear forces.
          • jcranmer 2y ago
  • somat 2y ago
    My understanding is the particle model of electromagnetism, the photon, really only shows up where the em field interacts with matter(electrons really), the em field itself is not quantized, or at least not quantized at the level of the photon. Not that this really matters(intentional), we can only interact with the em field as matter so that is what matters.
    • alkonaut 2y ago
      > matter so that is what matters At first I thought this was a great pun. But then this is perhaps also the reason the word is actually "matters"? Where "matters" is what means something? What matters is what has an observable effect?
  • dist-epoch 2y ago
    The most elegant description of electromagnetism is also in terms of curvature, but the curvature of a certain mathematical structure called "connection on fiber bundles" and the math field is called differential geometry.
• whatshisface 2y ago
  Our ability to solve integrals is much more limited when the dx represents a slight change in a function, rather than a small change in a real number. As a result, a lot of things that are easy to say in English such as "quantized curvature in spacetime," or "strongly coupled gauge theory," turn into a big mess when they're written down more precisely. One of the consequences of this limitation is that we have a model for quantized vibrations in spacetime that only works when they do not interact with each other. General relativity says that no, gravitational fields do interact with each other - so the picture we have at present is incomplete. The model of non-self-interacting gravity is a particle we call a "graviton," and it probably describes reality very well when the gravitation involved is so weak that its self-interaction is undetectable. String theory and loop quantum gravity fit into this picture by trying to replace the integral over something we can't handle with an integral that matches it at large scales, but turns into something more tractable at small scales. Maybe the fact that we still can't make sense of the integral is Nature's way of telling us that she does not do the integral either...
  • gradschoolfail 2y ago
    This needs to be emphasized more, by the TFA too — most (theoretical) physicists think that detecting gravitons is an engineering exercise that has no implications* for quantum gravity (as understood by the public) >The model of non-self-interacting gravity is a particle we call a "graviton," This needs to be emphasized even more, because it has >when the dx represents a slight change in a function *see the discussion around sharikous’ comment below https://news.ycombinator.com/item?id=42003116 https://news.ycombinator.com/item?id=42003116
    • lazide 2y ago
      Because they don’t want to run the risk of being wrong, eh?
      • gus_massa 2y ago
        Probably because the number of detection will be too few to test old theories or make new theories with the experimental results. Physicists love to be wrong! If there is an experiment that disagree with the current theory, then is like the will west and everyone can publish their own pet theory that "fix" it. It's like raining free paper for them, their graduate students and everyone. Also, it's fun! When experiments and theory agree, they have to use imagination to get a new "interesting" tweak that can be published. In some case the the tweak may be interesting, but most of the times it's not. I remember a talk about a 2-sigma "particle". There was a small disagreement in some experiment, so someone did a thesis about a possible fix adding a new particle. A lot of hard work and hard calculations. It was a nice talk, and someone asked what what happened then. The sad new was that later the 2-sigma disappeared, it was only a fluke :( . This kind of work is important, but it's more boring that looking for new particles.
• yarg 2y ago
  To my understanding (not the best) there's a huge disconnect between the physics of the very small (quantum mechanics and the standard model) and that of the very large (general relativity). The disconnect seems to be unresolvable (I don't understand this part at all) and so efforts are being made to quantise gravity and incorporate it into the standard model.
• LeoPanthera 2y ago
  In theory, if gravitons exist, they should reproduce the same effects as the curvature of spacetime at larger scales. So, while they seem contradictory, they're actually complementary. Gravitons would be the "quantized" particles that, in large numbers, create the effect we observe as curved spacetime. The problem is that nobody has successfully combined these two views into a single unified theory, known as "quantum gravity". General Relativity and quantum mechanics don't naturally fit together, and that's why we don't yet fully understand gravity in a way that reconciles both the spacetime curvature and graviton perspectives.
• 1024core 2y ago
  Sort of like how light is both a wave and a particle...?
• ajkjk 2y ago
  Not an expert, but: the curvature of spacetime is modeled as a tensor field (the metric tensor). That field can have (classical) waves in it, which is what LIGO detects (I believe). Then you can certain hypothetically quantize that field, in which case it definitely has to be a spin-2 particle and it seems likely that there will be a way to do it since all the rest were. The "geometry" comes from the fact that the way we measure distances (or, well, experience time) uses the metric tensor field to do it. But it is still ultimately just a value attached to every point like any other field.
• dcl 2y ago
  Yes. I've seen lots of twitter/X posts lately about how Gravity is not actually a force. But how can that be true if there is a force carrying "gravity" particle? Or is the word 'force' being used loosely here?
  • XorNot 2y ago
    You can make a lot of pseudo particles in semiconductors which definitely exist, but also aren't "real" - i.e. semiconductor electron holes are capably modelled as positive particles which can move freely with momentum/position within a semiconductor.
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  • cyberax 2y ago
    > Yes. I've seen lots of twitter/X posts lately about how Gravity is not actually a force. That is true. Classically, gravity is a fictitious force, merely a result of inertia from moving in a curved space-time. > But how can that be true if there is a force carrying "gravity" particle? Or is the word 'force' being used loosely here? Because we _suspect_ that the classical view is not correct. And there's a quantum description that may or may not involve curved space-time. It's not impossible that the spacetime curvature is a mathematical artifact of a deeper theory. Merely a kinematic explanation, just like epicycles. It's also possible that the space-time _is_ really curved, and gravitons simply cause the curvature by somehow coupling with it. And then other matter experiences this, in the manner described above.
  • InDubioProRubio 2y ago
    In a sim, it would fall into the "configurable parameter" category and dynamically altered parameter whos laws depended on locations are function lookups. And to execute performant, it would be a constant factor field only updated onAlteration with fun(x) So you have a thing, that gets interpolated updated with various functions, that overlap, and those functions only get updated at lightspeed, cause caching. Cachesize limit should show as farway gravity sources getting bundled into lower density information functions.
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• pdonis 2y ago
  > I thought gravity was basically the curvature of spacetime. Classically, it is. But most physicists believe that there is a quantum theory of gravity that underlies the classical theory, and that that quantum theory will include, at some level of description, a spin-2 gauge boson that mediates the quantum gravitational interaction, called the "graviton". Our classical theory of gravity, General Relativity, would then be the classical limit of that quantum theory, just as classical Maxwell electrodynamics is the classical limit of quantum electrodynamics.
• cryptonector 2y ago
  That gravity is curvature of spacetime is one view of two equivalent views, but it is the standard view. The other view is that you have flat spacetime with different distortions (of things other than spacetime) than the distortions you get in curved spacetime. The Schwarzschild metric essentially lets you do exactly that projection of curved spacetime to flat, and vice-versa. When you watch an animation like https://www.youtube.com/watch?v=hF7zltx7Ecc https://www.youtube.com/watch?v=hF7zltx7Ecc or https://www.youtube.com/watch?v=E1mD4C7dBKc https://www.youtube.com/watch?v=E1mD4C7dBKc you're watching a flat spacetime representation of GR's effects, and the reason for using flat spacetime in these representations is <drum-roll/> that that is what us humans understand. So if you take the gravity curves spacetime view, then gravity is not a force and all that. But if you take the alternative view then gravity is a force. Now, I'll leave what the distortions are that gravity produces in flat spacetime for another time, or for the reader. But I'll say this: this view is both controversial (perhaps replies will show this) and not (see above -and many other- animations).
  • NitpickLawyer 2y ago
    I last took a physics course when Pluto was a planet, so excuse my possibly outdated question, but isn't the detection of gravitational waves proof of gravity being a force? I follow a few educators/communicators in this field and I have a feeling they're using this "gravity isn't really a force" to bridge the gap between their deep understanding and us mortals that don't poses the language / understanding to get the entire meaning behind it. Is that feeling correct or am I missing something?
    • whatshisface 2y ago
      It's a bit of an internet meme, gravity can take momentum away from one object and transfer it to another, and that's what Newton said a force was. The meme is that the way it happens makes "changing momentum" (3-momentum, the one Newton was talking about) and "going straight" (geodesically, in curved space-time) hard to separate in English.
    • stouset 2y ago
      My naïve understanding is that you can model gravity as a force in a flat, static spacetime. Equivalently you can model gravity as a forceless distortion of curved spacetime. Both models can be translated faithfully into one another, so you can solve problems related to gravity in either domain.
• swayvil 2y ago
  Maybe all particles are twists in spacetime.
• ruthmarx 2y ago
  > So I thought gravity was basically the curvature of spacetime. That's just part of the picture. I always thought that Veritasium video did more harm than good.
• renegade-otter 2y ago
  I just watched this a few days ago on the Space Matters channel about gravitational waves: https://www.youtube.com/watch?v=9bg2NINW8a0 https://www.youtube.com/watch?v=9bg2NINW8a0 Not just some dumbed down Discovery show - it pushes the limits of what a layperson can understand.
  • gosub100 2y ago
    The YT algorithm is so damn bizarre sometimes. I'm subscribed to probably a dozen different astronomy and physics channels, some for 8 years, and never once saw this channel you recommended. It recommends plenty of AI-TTS bunk too. But somehow didn't decide to show me that channel. Thanks for recommending it.
• exe34 2y ago
  it's important to realise that particles are an artefact of living in a monkey sized body. at the basic level, the equations are useful if they match observations, not if they make sense intuitively. https://arxiv.org/abs/1204.4616 https://arxiv.org/abs/1204.4616
• blenderob 2y ago
  > So I thought gravity was basically the curvature of spacetime. But if there's a "gravity" particle, those two things seem mutually exclusive? It does not have to be either or. It can be both. Both models can be useful to understand the nature of gravity and make predictions about natural phenomenon.
• gpsx 2y ago
  Gravity is similar to an electric field here. A wave function for a field consists of an amplitude for each field configuration, where a “field configuration” refers to a value for the electric field for each point in space. In GR each field configuration would correspond to a space time geometry for the universe. We have quantized excitations as distinct “valid” solutions to the wave function, which we call a particle, though it is nothing like an electron. The notion of space time geometry holds throughout. (Edit: in practice, people never calculate wave functions for fields like electric fields. That would be too hard. Different methods are used in calculations. Second edit: the wave function wouldn’t be composed of complete space-time configurations, histories of the universe, but time slices from it, like space geometries. Maybe this can be expanded in responses/comments.)
• philipov 2y ago
  There are some ideas that spacetime is an emergent phenomenon. One such proposal is that it is produced by the large-scale presence of entanglement between particles: that entanglement creates spacetime. Where entanglement between regions of spacetime is stronger, the space is closer together, and where that entanglement is cut things get farther apart. This idea is known as "ER=EPR" [0]. That's the link bridging gravity as a particle (small-scale) and gravity as a feature of a manifold (large-scale). Physicists are trying to find a way to make spacetime emerge from quantum field theory, or make both emerge from some common framework. 0: https://en.wikipedia.org/wiki/ER_=_EPR https://en.wikipedia.org/wiki/ER_=_EPR