Doppler effects and relativity

arnesinnema
Messages
13
Reaction score
0
I’ve got a question.

Say we have a medium traveling through a pipe at speed v. The soundspeed of the medium is vs. The speed of the wavefronts to an stationary are approximately v-vs and v+vs when both v and vs are much smaller than the lightspeed c. However what happens when v=c? Do the wavefronts move with apparent speed v-vs and v+0 or do they appear to be frozen i.e. v-0 and v+0.

On a similar note, say an electron is traveling around one of the medium atoms in a plane parallel to the direction of movement of the atom. Say the electron is first placed at the front, can it than move backwards? But will stay there? I.e. it cannot move forwards since than the combined speed (relative to the stationary observer) would exceed the speed of light.
I.e. what happens to the Doppler effect at relativistic speeds?

Admittedly I’m not an expert ;).

Regards Arne Sinnema
 
Physics news on Phys.org
However what happens when v=c?

For a medium like water?
Water consists of massive particles (molecules/atoms), which cannot travel at the speed of light.
Nothing massive (m > 0) can reach the speed of light.

If your water goes at ##v_{sound}##, your sound wave should "stand still".

For combined speed you might want to check http://en.wikipedia.org/wiki/Velocity-addition_formula#Special_theory_of_relativity.

traveling around one of the medium atoms

That is not easy to answer, you will probably need quantum mechanics for that.
 
OK, so this has bugged me for a while about the equivalence principle and the black hole information paradox. If black holes "evaporate" via Hawking radiation, then they cannot exist forever. So, from my external perspective, watching the person fall in, they slow down, freeze, and redshift to "nothing," but never cross the event horizon. Does the equivalence principle say my perspective is valid? If it does, is it possible that that person really never crossed the event horizon? The...
ASSUMPTIONS 1. Two identical clocks A and B in the same inertial frame are stationary relative to each other a fixed distance L apart. Time passes at the same rate for both. 2. Both clocks are able to send/receive light signals and to write/read the send/receive times into signals. 3. The speed of light is anisotropic. METHOD 1. At time t[A1] and time t[B1], clock A sends a light signal to clock B. The clock B time is unknown to A. 2. Clock B receives the signal from A at time t[B2] and...
From $$0 = \delta(g^{\alpha\mu}g_{\mu\nu}) = g^{\alpha\mu} \delta g_{\mu\nu} + g_{\mu\nu} \delta g^{\alpha\mu}$$ we have $$g^{\alpha\mu} \delta g_{\mu\nu} = -g_{\mu\nu} \delta g^{\alpha\mu} \,\, . $$ Multiply both sides by ##g_{\alpha\beta}## to get $$\delta g_{\beta\nu} = -g_{\alpha\beta} g_{\mu\nu} \delta g^{\alpha\mu} \qquad(*)$$ (This is Dirac's eq. (26.9) in "GTR".) On the other hand, the variation ##\delta g^{\alpha\mu} = \bar{g}^{\alpha\mu} - g^{\alpha\mu}## should be a tensor...
Back
Top