If you pressurize a sealed cavity with a gas, it's not going to move due to the internal pressure regardless of what shape you make it. If you sum all of the collisions of the gas atoms along with the container, the sum momentum will be zero. Momentum is mass x velocity.
Contrast this with pressure created via light. Velocities with light don't add that way. Instead there is a red/blue shift in the frequency.
I can't put my finger on how this could work, but it seems there is a discontinuity here between the speed of light being constant in all reference frames and summing velocities to calculate momentum.
Maybe with light, only energy conservation matters and momentum can be changed via redshift/blueshift relative to the container.
Contrast this with pressure created via light. Velocities with light don't add that way. Instead there is a red/blue shift in the frequency.
I can't put my finger on how this could work, but it seems there is a discontinuity here between the speed of light being constant in all reference frames and summing velocities to calculate momentum.
Maybe with light, only energy conservation matters and momentum can be changed via redshift/blueshift relative to the container.