This question has been bothering me for a while. The title wouldn't do justice with what i asked so let me put forth the scenario.

Suppose a person lives on equator, he has a transmitter that he uses to send information to another person living far but on equator. Suppose that the direction of transmission is opposite to the earth rotation. If the person transmits the signal, then the other person should receive information in less time than what it would have actually taken as the earth revolves in opposite direction and so does the receiver.

Is the statement above true? If so, do we use this fact in our system design? ( i am doing engineering and so far i haven't considered it anywhere) and if no, then why? From what i know inertia couldn't be a factor here as inertia does not work on light (if we ignore particle nature of light for such scenario).

And lastly, if it is true then the relative speed of data transfer would be faster than speed of light?

  • $\begingroup$ What do you mean by relative speed of data transfer faster than light? Are you referring to the speed of transmission plus the angular speed of the Earths rotation? If so, then most certainly not. The speed of light is the limiting velocity in relativity. You should look up the Relativistic law of velocity addition to confirm this. I would type it but I'm on my phone. Furthermore the effect you are referring to is the Sagnac effect. You should also look this up. It's normally discussed with GPS timing systems. $\endgroup$ – Rumplestillskin Jan 18 '17 at 7:28

No, Even though it is true that the receiver will have traveled a tiny distance towards the transmitted wave, and it would receive it minutely faster as compared to if earth was not rotating, or as compared to if you interchange the sender and receiver.

But same will apply to light signal if you send a light signal in the same direction as the info transmission.

This is not making the transmission speed faster or slower than light. It only increase, or reduces the distance the signal has to travel.

In your scenario, time taken by the signal traveling from A to B will be different from that it takes in traveling from B to A. Whether that difference would be material or not, is a different issue. And that would decide whether the difference would be considered in designs or not. And that also, if the thing being designed depends upon time taken by a signal in two directions.

But mentioned earlier, same will apply to light and the transmission will be at same speed as light. No different.


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