Light is NOT constant relative to the source.

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SUMMARY

The discussion centers on the calculation of light travel time from two sources, A1 and A2, to Earth, considering the relative motion of the sources. The participant proposes that the time for light from A1 should be calculated as d/(u-c) and from A2 as d/(u-c) + T/2, leading to a difference in arrival times. However, they question whether the correct approach should involve using d/(u+c) for A1, as the star is moving towards Earth. This indicates a misunderstanding of the relativistic effects on light propagation.

PREREQUISITES
  • Understanding of special relativity concepts, particularly time dilation and simultaneity.
  • Familiarity with the equations of motion for light in a relativistic context.
  • Knowledge of the variables involved: distance (d), speed of light (c), and relative velocity (u).
  • Basic grasp of periodic motion and its relation to light travel time.
NEXT STEPS
  • Study the principles of special relativity, focusing on the implications of relative motion on light speed.
  • Learn about the Lorentz transformation and its application to time and distance calculations in relativistic scenarios.
  • Explore the concept of Doppler effect in light and how it affects perceived frequencies and travel times.
  • Investigate the mathematical derivation of light travel times in moving reference frames.
USEFUL FOR

Students of physics, particularly those studying special relativity, educators explaining light propagation, and anyone interested in the implications of motion on light travel times.

glover_m
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Homework Statement



earth.jpg


Homework Equations



How do you come up with 2ud/(c^2-u^2)

The Attempt at a Solution



Here's my issue with this problem: I would expect that for the light from A1 to reach Earth it would be d/u-c, and the time for the light of A2 to reach Earth would be d/u-c + T/2 = d/(u-c)
+ pir/u

Therefore Delta A would be (pi)(radius)/u

This isn't the case however, am I missing something? Shouldn't the difference in times be equal to half the period of rotation?
 
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glover_m said:
Here's my issue with this problem: I would expect that for the light from A1 to reach Earth it would be d/u-c, and the time for the light of A2 to reach Earth would be d/u-c + T/2 = d/(u-c)
+ pir/u

shouldn't it be d/(u+c) from A1, since the star is moving towards the earth.
If you use that you get the difference from your text.
 

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