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I've always naively assumed gravity to be a facet of momentum/movement through time. The math between acceleration, gravity, and time dilation are all too cute

by iaw 3y ago

I've always naively assumed gravity to be a facet of momentum/movement through time. The math between acceleration, gravity, and time dilation are all too cute to be coincidental in my book. I suspect that gravity manifests as a force but does not stem from the same underlying drivers as other forces.

m3kw9 3y ago
Yeah gravity seem to have a time dimension to it
- ars 3y ago
  Gravity itself does not have a time dimension - if you had a highly changed particle acting on another one, the time dilation would be identical to that caused by gravity acting with the same force. i.e. it's force and acceleration that cause it, not gravity.
magicalhippo 3y ago
Lee Smolin is working on an idea where the building blocks are events where momentum is exchanged.Space, and hence position, is an emergent phenomena. Here's a colloquium talk[1] and here's a recent paper[2]. Not exactly what you said but perhaps interesting. As mentioned it's work in progress so remains to be seen if the idea pans out. [1]: https://pirsa.org/21030005 https://pirsa.org/21030005 [2]: https://arxiv.org/abs/2303.15546 https://arxiv.org/abs/2303.15546
- nemo44x 3y ago
  I love how this word “emergent” has become popular by people that want to pretend they have an answer but it’s really just the “…” thing. There is no such thing as “emergent”. The motion of an automobile isn’t an “emergent” thing you can claim because you don’t know how engines and transmissions work. Everything we can’t explain recently has people, who I assume don’t know how to say I don’t know, proclaiming “it’s emergent”. As if that’s an answer to anything. Much less a claim to knowledge. Might as well claim “god made it happen”.
  - lanstin 3y ago
    System availability is an emergent property - I can build five nines of availability out of components with just two nines. Retries, algorithmic handling of failure, and the like.
  - Dylan16807 3y ago
    > The motion of an automobile isn’t an “emergent” thing you can claim because you don’t know how engines and transmissions work. That's the opposite of what emergent means, isn't it? Because of force on the transmission, you can say that the motion of the vehicle is emergent rather than needing its own framework or explanation.
  - CaptainNegative 3y ago
    Seems like pretending to know what the word emergent means in physics is an emergent phenomenon on HN. It's not wishy washy, it has a precise meaning that can be both derived and, typically, refuted.
  - nextaccountic 3y ago
    Emergent just means that it's not the basic building block; it's made up of other, more fundamental things. So for example thermodynamics is emergent (even though it is fully studied and relatively well understood) because it arises from interactions of particles. If you say that spacetime is emergent that is a big deal: it means that, while it can be studied on its own, it's actually composed of other, more fundamental things. But you still need to show that a) this other fundamental thing actually exists, and b) we can show mathematically how the spacetime works, in terms of those other fundamental thing (just like you can show how thermodynamics works in terms of statistical mechanics) And that's where your "because you don't know how it works" thing breaks apart: one can't claim to have solved this problem without tacking b).
    - nemo44x 3y ago
      > it's made up of other, more fundamental things Then explain those things and prove they exist. Otherwise this just sounds like bullshit. There’s a difference between observing thermodynamics (and not trying to answer why but rather how we observe it - big difference!) and writing equations we can measure and just saying “it’s emergent” to “…” things we are unable to answer “I don’t know to”.
wiml 3y ago
That is the basic idea that gives rise to the theory of general relativity — that gravity isn't really a force, it's just the observable effect of being in curved spacetime. (Take a look at the "equivalence principle" and its role in the development of GR as a theory.)
- denton-scratch 3y ago
  > gravity isn't really a force Yeah, this fact made me cringe at explanation #2: the guy keeps saying things like "gravity is the only force that is felt by all kinds of matter". Stuff doesn't "feel" gravity; it's not a force, it's just the shape of spacetime. Also, gravity doesn't just affect matter; photons are not matter, but are affected by the curvature of spacetime (i.e. gravity). /me not a physicist; but I'm not a baby either, and I don't appreciate babytalk oversimplifications.
alanfalcon 3y ago
Gravity is an effect of the curve of space and relativity coming together in what we now call spacetime. Right? Einstein told us so. But... Maybe not? There's promising math behind the idea that there are multiple additional dimensions, but where are they? How can we perceive them? What do they have to do with gravity? The unifying theory of dimensional geometry and interaction: https://youtu.be/fvqXshyuvOg https://youtu.be/fvqXshyuvOg

by iaw 3y ago

m3kw9 3y ago

Yeah gravity seem to have a time dimension to it

ars 3y ago
Gravity itself does not have a time dimension - if you had a highly changed particle acting on another one, the time dilation would be identical to that caused by gravity acting with the same force. i.e. it's force and acceleration that cause it, not gravity.

magicalhippo 3y ago

Lee Smolin is working on an idea where the building blocks are events where momentum is exchanged.Space, and hence position, is an emergent phenomena. Here's a colloquium talk[1] and here's a recent paper[2]. Not exactly what you said but perhaps interesting. As mentioned it's work in progress so remains to be seen if the idea pans out. [1]: https://pirsa.org/21030005 https://pirsa.org/21030005 [2]: https://arxiv.org/abs/2303.15546 https://arxiv.org/abs/2303.15546

nemo44x 3y ago
I love how this word “emergent” has become popular by people that want to pretend they have an answer but it’s really just the “…” thing. There is no such thing as “emergent”. The motion of an automobile isn’t an “emergent” thing you can claim because you don’t know how engines and transmissions work. Everything we can’t explain recently has people, who I assume don’t know how to say I don’t know, proclaiming “it’s emergent”. As if that’s an answer to anything. Much less a claim to knowledge. Might as well claim “god made it happen”.
- lanstin 3y ago
  System availability is an emergent property - I can build five nines of availability out of components with just two nines. Retries, algorithmic handling of failure, and the like.
- Dylan16807 3y ago
  > The motion of an automobile isn’t an “emergent” thing you can claim because you don’t know how engines and transmissions work. That's the opposite of what emergent means, isn't it? Because of force on the transmission, you can say that the motion of the vehicle is emergent rather than needing its own framework or explanation.
- CaptainNegative 3y ago
  Seems like pretending to know what the word emergent means in physics is an emergent phenomenon on HN. It's not wishy washy, it has a precise meaning that can be both derived and, typically, refuted.
- nextaccountic 3y ago
  Emergent just means that it's not the basic building block; it's made up of other, more fundamental things. So for example thermodynamics is emergent (even though it is fully studied and relatively well understood) because it arises from interactions of particles. If you say that spacetime is emergent that is a big deal: it means that, while it can be studied on its own, it's actually composed of other, more fundamental things. But you still need to show that a) this other fundamental thing actually exists, and b) we can show mathematically how the spacetime works, in terms of those other fundamental thing (just like you can show how thermodynamics works in terms of statistical mechanics) And that's where your "because you don't know how it works" thing breaks apart: one can't claim to have solved this problem without tacking b).
  - nemo44x 3y ago
    > it's made up of other, more fundamental things Then explain those things and prove they exist. Otherwise this just sounds like bullshit. There’s a difference between observing thermodynamics (and not trying to answer why but rather how we observe it - big difference!) and writing equations we can measure and just saying “it’s emergent” to “…” things we are unable to answer “I don’t know to”.

wiml 3y ago

That is the basic idea that gives rise to the theory of general relativity — that gravity isn't really a force, it's just the observable effect of being in curved spacetime. (Take a look at the "equivalence principle" and its role in the development of GR as a theory.)

denton-scratch 3y ago
> gravity isn't really a force Yeah, this fact made me cringe at explanation #2: the guy keeps saying things like "gravity is the only force that is felt by all kinds of matter". Stuff doesn't "feel" gravity; it's not a force, it's just the shape of spacetime. Also, gravity doesn't just affect matter; photons are not matter, but are affected by the curvature of spacetime (i.e. gravity). /me not a physicist; but I'm not a baby either, and I don't appreciate babytalk oversimplifications.

alanfalcon 3y ago

Gravity is an effect of the curve of space and relativity coming together in what we now call spacetime. Right? Einstein told us so. But... Maybe not? There's promising math behind the idea that there are multiple additional dimensions, but where are they? How can we perceive them? What do they have to do with gravity? The unifying theory of dimensional geometry and interaction: https://youtu.be/fvqXshyuvOg https://youtu.be/fvqXshyuvOg