- #1
Sonden
- 7
- 0
While making calculations of FTIR/tunneling isn't that hard, I don't understand the phenomenon, and therefore there are some predictions I'm unable to make. So I have some questions (or it's probably just one).
If you have a prism with refractive index n in vacuum, total internal reflection occurs if the angle of incidence is greater than arcsin(n). But if you have a second prism at some distance from the first one, the wave will not be completely reflected, a part of it will be transmitted to the second prism. If the wavelength is large (eg microwaves) you'll get substantial transmission even if the distance between the prisms is "macroscopic".
This is probably "thinking classically" when I should be thinking quantum physically, but how does the wave "know" there's a second prism at some distance away? If the distance is d, and the wave is partially reflected in the first prism at time t, when is the wave transmitted into the second prism? It should be at T=t+d/c?
What if d is large (which should allow transmission if the wavelength is large) and there's no second prism at this distance at t, the second prism is being put there at, for example, t_2=t+d/(3c). Will the wave be transmitted to the second prism as if the second prism had been there all along (that is, at time T)? Or not at all? What if you measure the part of the wave that was reflected in the first prism (at some time, before t_2, between t_2 and T, or after T, that shouldn't matter, if it's just a short wave packet), then you could predict (if you make the measure before t_2) that someone will, in the future, put a second prism at some distance to the first! Which must be nonsense.
On the other hand, if the second prism is there from the start, and you measure the reflected wave, the you can draw the conclusion that the wave "knew", at t, that there's a second prism at distance d! And that no one will remove it prior to T! Which, to me, sounds equally ridiculous.
So, what's wrong here? I don't think it should have anything to do with relativity. The uncertainty principle - but how? Something else - what?
I'd be very grateful to get an answer (not too advanced, this is my first course in quantum physics), as this is making me more frustrated than the Frustrated total internal reflection...
If you have a prism with refractive index n in vacuum, total internal reflection occurs if the angle of incidence is greater than arcsin(n). But if you have a second prism at some distance from the first one, the wave will not be completely reflected, a part of it will be transmitted to the second prism. If the wavelength is large (eg microwaves) you'll get substantial transmission even if the distance between the prisms is "macroscopic".
This is probably "thinking classically" when I should be thinking quantum physically, but how does the wave "know" there's a second prism at some distance away? If the distance is d, and the wave is partially reflected in the first prism at time t, when is the wave transmitted into the second prism? It should be at T=t+d/c?
What if d is large (which should allow transmission if the wavelength is large) and there's no second prism at this distance at t, the second prism is being put there at, for example, t_2=t+d/(3c). Will the wave be transmitted to the second prism as if the second prism had been there all along (that is, at time T)? Or not at all? What if you measure the part of the wave that was reflected in the first prism (at some time, before t_2, between t_2 and T, or after T, that shouldn't matter, if it's just a short wave packet), then you could predict (if you make the measure before t_2) that someone will, in the future, put a second prism at some distance to the first! Which must be nonsense.
On the other hand, if the second prism is there from the start, and you measure the reflected wave, the you can draw the conclusion that the wave "knew", at t, that there's a second prism at distance d! And that no one will remove it prior to T! Which, to me, sounds equally ridiculous.
So, what's wrong here? I don't think it should have anything to do with relativity. The uncertainty principle - but how? Something else - what?
I'd be very grateful to get an answer (not too advanced, this is my first course in quantum physics), as this is making me more frustrated than the Frustrated total internal reflection...