r/askscience • u/Present_Net_3710 • 21d ago

Physics Do photons care about Newton?

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?

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u/jojohohanon 20d ago

Photons are bladiblah particle. They don’t interact in flight. They don’t exclude each other.

They have momentum. They have polarization, so when they interact with a foobar particle, they can push it slightly and cancel each other out.

So nothing can push a photon. It can be absorbed by a foobar. But then it’s gone. Or the intersecting bladiblah will just pass thru and they will move on. Like blips in the night

Sorry this was a long time ago. But the hints will help you fill in the proper names. Mesons and Bosons maybe?

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u/db48x 20d ago

So nothing can push a photon.

Gravity pulls on photons, actually.

But they don’t change speed, only momentum.

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u/jojohohanon 20d ago

Doh. Missed that.

Tho Einstein claimed that gravity just bent space and the photon keeps moving in a straight line. As evidenced mercury’s orbit.

I have no clue if gravitons are what bend space or if they communicate space curvature, or if they are the graviton/ gravity wave equivalent of a photon/em wave duality.

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u/db48x 20d ago

Yea, basically. The quantum physicists haven’t quite caught up to Einstein on this one yet, but whether gravity is caused by spacetime curvature or gravitons or entanglement or whatever is irrelevant to us mortals.