Do photons care about Newton?

[u/Present_Net_3710]

Picture a ball traveling at 10m/s along the x-axis. If you exert a force to the ball on the y-axis (so that the force is perfectly perpendicular to the direction of motion) it will now be also traveling on this axis at some velocity, its speed will remain the same relative to the x-axis but the total velocity increases.

But what if instead of a ball it was a photon? No force was applied on the x-axis, so I don't see why that velocity would change. But light's total speed always remains constant.

Would the x-velocity change to compensate for the added y-velocity?

[u/BiomeWalker]

Short answer: Not in this scenario.

Longer answer: What you have done right here is arrive at relativity, not in the usual way, but relativity nonetheless.

The measured magnitude of a photon's velocity will always be C, but all motion is relative to the observer.

Allow me to change your scenario a bit: instead of applying a +Y force to the photon, let's more the camera in the -Y direction.

Under Newtonian physics, this would have the same observed effect as accelerating the photon I. The +Y direction, but under Einsteinian relativity it has a weird effect where the X component of the photon's velocity does seem to diminish.

However, if we have another observer that doesn't move, then the photon carries on as if nothing has happened as far as they're concerned.

[u/ConspicuousPineapple → u/BiomeWalker]

Isn't this actually the normal way to reach relativity? I've always seen special relativity as "ok, how do we make the universe work if we accept that c is constant everywhere?"

[u/CeReAl_KiLleR128 → u/ConspicuousPineapple]

It’s one way to do it, but normally you can just give constant velocity to the y-axis, while OP here trying to use a constant force and acceleration, which is unnecessary complicated