Time Dilation: SR Basics & Confusion

thrush
Messages
5
Reaction score
0
Hi everybody,

I'm learning Special Relativity, and probably ok with four vectors, the metric equation, the Lorentz Transform, and the Doppler shift, etc., but enough about me.

I'm still a little confused about time dilation. In several hypothetical examples of SR that I have seen, two spaceships, call them A, and B, are traveling apart. From A's frame, B's velocity is 0.9C, and B's spaceship has contracted in length and increased in mass. From B's frame, A's velocity is 0.9C, and A's spaceship has contracted in length and increased in mass. When both slow down so that the relative velocity becomes zero, all is back to 'normal' and they then occupy the same reference frame (with standard orientation, as some say).

But what about time? From A's frame, time is slowed on B's spacecraft . But from B's frame, time is slowed on A's spacecraft . Would it not then be the case that their clocks would read identically even until their relative velocities became zero again? Which astronaut aged more slowly? Do not these examples about an astronaut aging more slowly on a high speed round-trip imply that she is moving with respect to some more fundamental frame upon which we sit back here on Earth? And does not SR imply that there is no "fundamental frame?"

I know this must be a thread many times here, apologies, but clearly I am missing something. Thank you.
 
Physics news on Phys.org
You need to find out about the so called 'twin paradox'. http://en.wikipedia.org/wiki/Twin_paradox.[/PLAIN]

Relativity is not about time-dilation and length contraction. These are just linked coordinate effects of the Lorentz transformation that connects any two inertial frames' coordinates. The important things are those that are *not* dependent on which observer measures them.

The most important ( for some) is the fact that every clock measures its own time, which is a mathematical function of the spacetime length of its four dimensional path through spacetime.
 
Last edited by a moderator:
Thanks for the pointer Mentz114! No need to beat a dead horse here, close this thread/delete it. You have given me plenty to chew on!
 
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...
In this video I can see a person walking around lines of curvature on a sphere with an arrow strapped to his waist. His task is to keep the arrow pointed in the same direction How does he do this ? Does he use a reference point like the stars? (that only move very slowly) If that is how he keeps the arrow pointing in the same direction, is that equivalent to saying that he orients the arrow wrt the 3d space that the sphere is embedded in? So ,although one refers to intrinsic curvature...
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...
Back
Top