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Local-Program404 t1_j8smu6t wrote

Reply to comment by Chemomechanics in Does refracting light impart momentum onto the object that is refracting it, for the duration of the refraction? by TheFeshy

So when the light speeds up when it leaves the medium, where does that come from? The medium? So the net force on the medium is 0 because if gives it back up to the light when it leaves?

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Chemomechanics t1_j8snwzw wrote

The medium plays a part in the momentum transfer, yes.

The net force on a spherical body isn't zero for a single beam because the beam changes shape moving through it, so the refractive details are different on either side.

But for two counterpropagating beams, which is what I used, the left–right forces do balance out, leaving an internal tensile load that stretches a compliant medium. You don't notice this in everyday situations with macroscale objects because they're stiff and the light is weak.

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Local-Program404 t1_j8sp69c wrote

Honestly, this made me think of the emdrive from a few years ago. Interesting phenomenon.

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