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...
> 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.
Can you please elaborate, the first part of the sentence says graviton is for non-self-interacting gravity, the second part of the sentence says graviton is for self-interacting (if 'its' in 'its self-interaction' refers to the graviton).
I don't intend to nitpick the sentence, just trying to understand the theory and I don't even know if particle means self interaction or the opposite and can't parse it here either...
If the answer is graviton is for non-self-interacting: what is the model for the other case (where gravity does self interact) and what would cause that self interaction if not the graviton?
> Can you please elaborate, the first part of the sentence says graviton is for non-self-interacting gravity, the second part of the sentence says graviton is for self-interacting (if 'its' in 'its self-interaction' refers to the graviton).
The point is, we know gravitation does self-interact. But our best model, the graviton, doesn't model self-interaction. So the model is probably accurate in regimes where you'd expect little self-interaction anyways.
Photon-photon interaction is photon self interaction. Gravity/graviton self interaction then means graviton-graviton interaction. In general relativity, all form of energy would have an effect of gravity, and also react to gravity. Since all matter, including photon and graviton, has energy, then they should self interact.
In QED, photon and photon do interacts too and you can calculate its effect to be small. In GR, you can expect self interaction is small if the space time curvature is small.
(Photon is the particle that mediates QED, and graviton is the hypothetical particle that mediates gravity.)
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
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.
> 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.
I disagree with that part. For the strong force we have the "gluons" and they are considered particles and they have a strong self-interaction. The strong self interaction makes it a huge mess and a lot of things that involve gluons are impossible to calculate.
It's more like:
fake quote> Let's pretend for 30 minutes that the strong field don't self-interact, so we have this nice particles call gluons. Now we add this interaction to the Lagrangian to make gluons interact with other gluons, and now we have a problem.
I agree that that when gravity is small enough, then gravitons give an easy to calculate aproximation. IIRC at high enough energies calculations with gluons get not impossible to calculate too.
The thing is, no particle is defined when it interacts. At our present level of understanding the only defined particles are the individual green's functions that appear in perturbation expansions, the lines in Feynman diagrams.
We see interacting particles in detectors, but since nobody can write down what field configuration they mean by "a photon," I can defend my phrasing - but you can defend yours too because I know what a bird is even if I don't know how they work.
I don't know if it was just sheer luck that your comment fit my particular flavor of ignorance perfectly, but it struck me as great writing! I think I learned a little thing today. When I read the article I thought, too bad I can't ever understand anything of this, but now my personal model of the universe is just a little bit richer.
If you’re young (or if you’re old but your mind remains flexible) i urge you to think hard about this problem.. i do and i will! my mind is already quite inflexible so i’m not going say anything definite about this question out of fear of saying something dumb/misleading. Your q hides monsters ready to snipe any serious mind of the planet!
That said, an easier question to ponder (and many have tried) might be:
Do photons self-interact? With each other? In free space?
After thinking thru this question yourself, you might be more prepared to consider gravitons (=“spin-2 massless bosons”) ditto for me!
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.
> 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.
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.
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.
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?
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.
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?
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.
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.
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
> 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)
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 or 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).
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?
Fwiw gravitational waves were predicted by Einstein himself (Einstein, Albert, Ueber Gravitationswellen, 1918) as a consequence of general relativity.
The core idea is that when you move a mass, its contribution to the spacetime geometry changes, but the effects of the change of the geometry doesn't apply instantaneously to all the universe but instead the change propagates at the speed of light.
So that explains why any sudden movement of a mass creates a "crest" that moves through space at the speed of light.
Furthermore, the sources of fast movement of extremely heavy mass just happen to involve an object that wiggles back and forth in a periodic way because those events involve heavy objects orbiting other heavy objects.
That's the reason we can measure a wave with multiple crests and we can talk about a wave length of the gravitational waves: the wave length of the gravitational waves matches the period of the orbit of the heavy mass.
So the main issue here is how people were presenting it, in Quantum field theory, as stated by other people, each force is associated with a field and has at least one force carrier, the exact number is linked to the specifics of the mathematical framework underlying it
To that extent you can build 3 fundamental forces, electro magnetic, weak (that are called together electroweak) and the strong force. You have an extra force carrier through the Higgs that allows you to give mass to everyone.
Now you need to consider gravity because you know that gravity exist and since everything under the sub is quantised, well so should gravity.
The main issue with gravity is that it is interpreted so far as a curvature of space time, it's mainly fine for big items, but the implications for quantum field theory is that you should modify the small integral element that you use (space shouldn't have the same size) except that you look locally at space that is mainly flat... And changing the integral does not lead to well behaved behaviours.
You can start to introduce new fields but doing so also causes an issue...
Funnily enough even in the standard model something is missing, everything mostly fits, but that's the trick, mostly, neutrinos have mass and this in itself is a problem because the Higgs mechanism doesn't provide mass to them ...
Long story short, people take shortcut when explaining the messy gritty part of it, which is "fine" but not really, and from a simple standpoint one would like to have a simple field from which gravity is born, which might be but so far, to my simpleton understanding, this hasn't been too successful, unless some form of string theory is realised. But the pre requisite for this is a form of supersymmetric theory existing which is currently disfavored, but could exist in the unproved energy scales from here to the plank energy scale.
Sorry this ended being a tad long and I'm not sure this is clarifying things.
> The main issue with gravity is that it is interpreted so far as a curvature of space time,
Yes, that is the main issue. It doesn't have to be that way though. If you look at the Einstein field equations, and solutions like the Schwarzschild and Kerr metrics, the key component is a metric tensor that is nothing more than a mapping from flat spacetime to curved spacetime. We have the ability to choose which interpretation to use. The metrics are nothing more than Mercator-like projections.
If you take the curved spacetime view then you get distortions of spacetime. If you take the flat spacetime view then you get other distortions like that the speed of light -though always seen as the same locally- varies according to the gravitational potential (there are other distortions as well).
We seem to have a bit of a fetish for the curved spacetime view. But oddly when you look for animations depicting interactions with black holes and photons or particles / small bodies what you almost invariably find are of two types: a) flat spacetime representations, or b) the funnel representation, and (b) often comes with a flat spacetime representation above the funnel. How do you think the authors produce the flat spacetime representations? A: By applying the metrics to go from curved spacetime to flat! And why do they use flat spacetime for their animations? A: Because it's easier for humans to understand!
The reality is that flat and curved spacetime are two sides of the same coin. If curved spacetime is the sticking point for quantizing gravity, then switch to flat spacetime.
> neutrinos have mass and this in itself is a problem because the Higgs mechanism doesn't provide mass to them ...
The Higgs mechanism doesn't provide all mass, even of the things that it provides mass for. They each have a "bare" mass, that is, a mass without any Higgs interactions. They just have a much greater mass because of the Higgs interaction. (And maybe that's why neutrinos have so little mass...)
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.
My naive understanding is that forceless spacetime distortion predicts somewhat different things than the old model. That's how general relativity finally explained the procession of Mercury's orbit for example.
GP means that you can take the Einstein field equations (and their solutions) and use the metric tensors to map between flat and curved spacetime, with either way being equivalent. GP did not mean that those tools map from Newtonian flat spacetime to curved.
Consider centrifugal force. In a non-rotating reference frame, it doesn't exist. In a rotating reference frame, it does, that is, it shows up as a term in the equation of motion.
You wouldn't expect to find quantums of centrifugal force in a rotating frame of reference, and no quantums of centrifugal force in a non-rotating frame of reference. They're both describing the same situation; either quantums exist in both frames, or they exist in neither.
So either gravity really exists as a force, or it doesn't. If it does, then I would expect gravitons, and expect them in all frames of reference. If it doesn't, then I would expect no gravitons in any frame of reference.
Except... If I understand correctly, static electric and magnetic fields are not carried by photons - they just sit there. It's only changing E/M fields that are carried by photons. So maybe only changing gravitational fields are carried by gravitons, and the static fields are just curved space-time?
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.
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.
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.
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.
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.)
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.
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.
> 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.
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?
> 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.
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.
> if there is a force carrying "gravity" particle?
There is not. Or maybe there is not. At least so far there is not. We have never observed one. "Graviton" particle is just a hypothesis. Outside of some people theorizing that graviton could exist, there is no observations that it exists.
"In theories of quantum gravity, the graviton is the hypothetical quantum of gravity"
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.
we keep moving the goalposts, and that's not a bad thing.
remember when Doom came out? How amazing and "realistic" we thought the graphics were? How ridiculous that seems now? We'll look back at ChatGPT4 the same way.
For the work that I do, ChatGPT accuracy is still garbage. Like it makes obvious factual errors on very simple technical issues which are clearly documented in public specifications. I still use it occasionally as it does sometimes suggest things that I missed, or catch errors that I made. But it's far from "good enough" to send the output to co-workers or customers without careful review and correction.
I do think that ChatGPT is close to good enough for replacing Google search. This is, ironically, because Google search results have deteriorated so badly due to falling behind the SEO spammers and much of the good content moving off the public Internet.
I am going to offer you some tips for using ChatGPT.
1. Just because something is in a public specification does not mean that GPT knows about this specification. If you want to work on something, and that something is documented, share the document with the AI. Don't just assume it has read it!
2. Share your existing code, don't just ask for one-off functions. You can do this with a tool like Aider.
3. Context is king. Do you have code (in a different language?) which does what you want? Do you have ideas/comments from JIRA tickets? GitHub discussions? Include it all. Ask questions. Don't just ask for code, but ask for a plan to implement a given feature or refactor. Add the plan to the context. Work from the plan. Have the AI update the plan as it works.
4. AIs are really good at prompting AIs. Ask Claude for help writing your prompts. Tell it what you want to do. Tell it the things you're concerned about, or possible issues you expect to have.
Here's an example of augmenting a prompt before you use it:
Original prompt: Help me write a prompt for a smart AI to review a webaudio library and find bugs.
Result:
You are an expert developer specializing in web technologies, with deep knowledge of the Web Audio API and common pitfalls in audio programming. Your task is to thoroughly review the provided WebAudio library code and identify potential bugs, performance issues, and areas for improvement.
## Instructions:
1. Analyze the library's architecture and overall design.
2. Review each function and method for:
- Correct implementation of Web Audio API concepts
- Proper error handling and edge cases
- Memory leaks or performance bottlenecks
- Browser compatibility issues
3. Check for common WebAudio-specific bugs, such as:
- Incorrect audio graph connections
- Timing and synchronization issues
- Sample rate and buffer size mismatches
- Potential audio glitches or artifacts
4. Evaluate the library's handling of:
- Audio context creation and management
- Node creation, connection, and disconnection
- Parameter automation and scheduling
- Audio worklet usage (if applicable)
5. Assess the library's documentation and API design for clarity and consistency.
## Output:
Provide a detailed report including:
1. A summary of the overall code quality and architecture
2. A prioritized list of identified bugs and issues
3. Specific code examples highlighting problematic areas
4. Recommendations for fixes and improvements
5. Suggestions for additional features or optimizations
Please be thorough in your analysis and explain your reasoning for each identified issue or suggestion.
Thanks, I appreciate you trying to help but I was already aware of those tips and they don't help. Either the accuracy is still bad, or going through the extra steps takes so long that it's faster to just do everything myself. Maybe the next version will be better.
I am not dealing with code or code reviews but rather complex written specifications where understanding what's going on requires integrating multiple sources.
I don't think we're at a plateau. There's still a lot GPT-4 can't do.
Given the progress we've seen so far with scaling, I think the next iterations will be a lot better. It might even take 10 or even 100x scale, but with increased investment and better hardware, that's not out of the question.
And now we have the LLMs self feeding their models (which may be either good or bad). This shouldn’t lead to short-term wide (as in AGI) efficiency. I bet this is a challenge.
I live in a very hot location, and I also happen to like going for long runs. I've long known, if I took my dog with me on my run, it would kill him. Even though he's a fit young dog, there's no way he can handle the heat at running pace for that length of time.
The whole point of Replicants is that they look exactly like humans in person. Even if we assume AI and robotics advance 100 times or more in the next 10 years to allow the technical part of this, we are not even close to any makeup and prosthetics tech that could make a robot even slightly resemble a human in-person.
And I have to mention, Tesla robots are way behind the competition, it's not even clear if their robot does anything really on its own, given how much they fake their videos of it with "creative" editing.
“It shows that he, to some extent, has the cognitive capacities that he needs to treat the wound with some medically active plants,” she said. “But we really don’t know how much he understands.”
This could apply to many humans too. Many people don't know why they're doing what they're doing, and don't have any understanding of how what they're doing works.
lets say we did this, and we got the tiny probes up to even ~speed of light... then what are they going to do when they get there? what sensors can they carry and report back. And we wouldn't be able to slow them down, so they're going to transit through the target solar system relatively quickly (days even).
Can someone who understands this please explain it to me, thanks!