Doppler effect

[caledonia]

If I travel at high speed towards a clock, do I see it as running fast? If yes, how does this square with the assertion of Time Dilation viz. "each observer sees the other's clock as running slow".

[Schrödinger's hat]

If I travel at high speed towards a clock, do I see it as running fast? If yes, how does this square with the assertion of Time Dilation viz. "each observer sees the other's clock as running slow".

 

There is an important distinction between see (how the light around you interacts with you) and measure (what you perceive of the world once you take that into account, or otherwise work around).

You will see the clock running fast, but you will measure the clock running slow.

The doppler shift is a result of you moving through the light that the clock has previously emitted (so every second you get some fraction of a second closer to the clock, so the light you see is more recent, thus the clock appears to be ticking faster). Once you acocunt for this (by calculating what time the clock showed in your frame of reference at various times after taking into account light delay) you see that it is running slow (in your frame).

[caledonia]

There is an important distinction between see (how the light around you interacts with you) and measure (what you perceive of the world once you take that into account, or otherwise work around).

You will see the clock running fast, but you will measure the clock running slow.

The doppler shift is a result of you moving through the light that the clock has previously emitted (so every second you get some fraction of a second closer to the clock, so the light you see is more recent, thus the clock appears to be ticking faster). Once you acocunt for this (by calculating what time the clock showed in your frame of reference at various times after taking into account light delay) you see that it is running slow (in your frame).

 

many thanks for clear explanation