4 ms·

You forgot about conservation of momentum. Photon cannot change it's direction without interaction with something to exchange momentum. "Bending of spacetime"

You forgot about conservation of momentum. Photon cannot change it's direction without interaction with something to exchange momentum. "Bending of spacetime" is just computational trick to increase precision of the model. Bending of trajectory because of change of speed of light is negligible, yes. It's only visible on light-year long distances. Photon is very wide. Dual slit experiment show that single single photon interacts with two slits up to millimetre apart. Even small difference in speed/frequency at such large distance will accumulate to noticeable change of course at light year long distances. I can calculate bending radius, if you wish.

LegionMammal978 2y ago
> Photon cannot change it's direction without interaction with something to exchange momentum. Doesn't the entire photon simply exchange momentum with the star, without needing to invoke any higher-order effects? Just as the star exerts a gravitational pull on the entire photon, the entire photon exerts a (very miniscule) gravitational pull on the star.
- oneshtein 2y ago
  Photon is massless, so it cannot use the same physical process as non-massless particles. For example, when photon will aim at a object, it will not «fall» and increase it speed, like a regular particle.
cyberax 2y ago
> You forgot about conservation of momentum. Photon cannot change it's direction without interaction with something to exchange momentum. No. I'm not forgetting anything. Photons _do_ _not_ change direction. They always move in straight lines (from their "point of view"). It's just that if you step a bit away, these straight lines are not actually "straight" globally. A classic example is a 2D ant crawling on a surface of a sphere. From the ant's point of view, it moves in a straight line, but a 3D observer will see that a straight line is actually a 3D circle. Conservation laws are not violated. A photon (or another particle) will cause its own slight bending of the space-time, that in turn will slightly bend the star's trajectory. It does sound like an interaction between gravitational fields, but the models give different numeric predictions. > "Bending of spacetime" is just computational trick to increase precision of the model. It really is not. > Photon is very wide. Facepalm. Sorry dude, but you have no idea what you're talking about. Lensing and time dilation also happen for point-like particles like electrons.
- oneshtein 2y ago
  > Conservation laws are not violated. A photon (or another particle) will cause its own slight bending of the space-time, that in turn will slightly bend the star's trajectory. It's not possible, because EM field doesn't affect all particles. > Lensing and time dilation also happen for point-like particles like electrons. If we stick 2E15 electrons together in a long line, then it will start to rotate too due to differences in gravitational field at inner and outer segments of the line. Something like that must happen to an 1mm wide photon too. I'm not talking about orbit of those electrons around object, but about rotation alone.
  - cyberax 2y ago
    > It's not possible, because EM field doesn't affect all particles. It's not the EM field, but gravity. > If we stick 2E15 electrons together in a long line, then it will start to rotate too due to differences in gravitational field at inner and outer segments of the line. Just look at an individual electron. Why would it curve? It's sufficiently point-like for the gravitational field gradient to be negligible.

LegionMammal978 2y ago

> Photon cannot change it's direction without interaction with something to exchange momentum. Doesn't the entire photon simply exchange momentum with the star, without needing to invoke any higher-order effects? Just as the star exerts a gravitational pull on the entire photon, the entire photon exerts a (very miniscule) gravitational pull on the star.

oneshtein 2y ago
Photon is massless, so it cannot use the same physical process as non-massless particles. For example, when photon will aim at a object, it will not «fall» and increase it speed, like a regular particle.

cyberax 2y ago

> You forgot about conservation of momentum. Photon cannot change it's direction without interaction with something to exchange momentum. No. I'm not forgetting anything. Photons _do_ _not_ change direction. They always move in straight lines (from their "point of view"). It's just that if you step a bit away, these straight lines are not actually "straight" globally. A classic example is a 2D ant crawling on a surface of a sphere. From the ant's point of view, it moves in a straight line, but a 3D observer will see that a straight line is actually a 3D circle. Conservation laws are not violated. A photon (or another particle) will cause its own slight bending of the space-time, that in turn will slightly bend the star's trajectory. It does sound like an interaction between gravitational fields, but the models give different numeric predictions. > "Bending of spacetime" is just computational trick to increase precision of the model. It really is not. > Photon is very wide. Facepalm. Sorry dude, but you have no idea what you're talking about. Lensing and time dilation also happen for point-like particles like electrons.

oneshtein 2y ago
> Conservation laws are not violated. A photon (or another particle) will cause its own slight bending of the space-time, that in turn will slightly bend the star's trajectory. It's not possible, because EM field doesn't affect all particles. > Lensing and time dilation also happen for point-like particles like electrons. If we stick 2E15 electrons together in a long line, then it will start to rotate too due to differences in gravitational field at inner and outer segments of the line. Something like that must happen to an 1mm wide photon too. I'm not talking about orbit of those electrons around object, but about rotation alone.
- cyberax 2y ago
  > It's not possible, because EM field doesn't affect all particles. It's not the EM field, but gravity. > If we stick 2E15 electrons together in a long line, then it will start to rotate too due to differences in gravitational field at inner and outer segments of the line. Just look at an individual electron. Why would it curve? It's sufficiently point-like for the gravitational field gradient to be negligible.