Hey, so I just watched the Veritasium video “Something Strange Happens When You Trust Quantum Mechanics” (https://www.youtube.com/watch?v=qJZ1Ez28C-A), and it got me thinking.
The video talks about how light takes every possible path and ends up following the one with the least action. Super cool concept. But then, around the 30-minute mark, there’s this wild experiment where a laser is aimed at one side of a mirror, and there’s a diffraction grating placed on the other side. Even though the laser isn’t hitting the grating directly, you still see light coming out from that side. That part really tripped me up.
So here’s my question: Where is the energy for that “other path” coming from?
My gut says energy has to be conserved, so if light is somehow taking a new path via the grating, does that mean the original laser beam is losing energy? Maybe it just gets dimmer?
But then I thought… what if you could make a really clever diffraction setup that always pulls light along some super-efficient path? Could you, in theory, siphon off light energy from a bulb on the other side of the planet without anyone near the bulb noticing?
And if the original beam’s intensity is not lowered, then we would have generated free energy!
So is this really about energy moving along a new path, or are we just bending scattered light in a clever way to make it look like something more mysterious is going on?
Ah so my intuition was correct that the laser experiment was wrong, the extra light we see was from the scattered light and not from the laser beam. So if we were to somehow minimize the scattering from the source and just keep the beam, we would not see the light on diffraction grating.
If we had to really bend the main beam, we would have to introduce potentially some medium where light travels slower(glass/water) to beam on one side of the reflection… in which case the original path would have almost 0 energy and almost all energy has been transferred to a new path.