# Einstein's Clock: See What at Speed of Light?

• John S
In summary: So in summary, if you were traveling towards a stationary clock at the speed of light, you would see the clock's hands moving faster than they would appear if you were standing still, and if you were traveling away from it at the speed of light, you would see the clock's hands moving slower than they would appear if you were standing still.
John S
Question: If the hands on a stationary clock will appear to stop when traveling away from it at the speed of light, what would you see if traveling towards it at that speed?

John S said:
Question: If the hands on a stationary clock will appear to stop when traveling away from it at the speed of light, what would you see if traveling towards it at that speed?
Clocks don't travel at the speed of light and neither do you.

John S said:
Question: If the hands on a stationary clock will appear to stop when traveling away from it at the speed of light, what would you see if traveling towards it at that speed?

As @phinds says, nothing can travel at the speed of light. But for traveling near the speed of light, the relevant equation for how things "appear" is the Doppler shift formula:

$f' =f \sqrt{\frac{c-v}{c+v}}$ for travel away from the clock

$f' =f \sqrt{\frac{c+v}{c-v}}$ for travel toward the clock

where $f'$ is the rate that the clock's hands appear to be moving (in degrees per second, or whatever units you like), and $f$ is the rate in the rest frame of the clock, and $v$ is your speed relative to the clock, and $c$ is the speed of light. So when you're moving toward a clock, it seems to be running faster than a clock at rest relative to you, and if you're moving away, it seems to be running slower.

The Doppler shift is not the same thing as time dilation, although the two effects are related (in the sense that the Doppler shift formula takes into account time dilation).

Buzz Bloom and m4r35n357

## 1. What is Einstein's Clock?

Einstein's Clock is a thought experiment proposed by Albert Einstein to illustrate the effects of time dilation at the speed of light.

## 2. How does Einstein's Clock work?

Einstein's Clock consists of a light clock, which is a hypothetical clock that uses the speed of light to measure time. The clock has two mirrors facing each other, with a beam of light bouncing back and forth between them. The time it takes for the light to travel between the mirrors is used to measure time.

## 3. What does Einstein's Clock demonstrate?

Einstein's Clock demonstrates the concept of time dilation, which is the phenomenon where time appears to slow down for objects moving at high speeds. This is one of the key principles of Einstein's theory of relativity.

## 4. How does Einstein's Clock relate to the speed of light?

The speed of light is the fastest possible speed in the universe, and according to Einstein's theory of relativity, the laws of physics are the same for all observers moving at constant speeds. This means that no matter how fast an observer is moving, the speed of light will always appear to be the same. Einstein's Clock uses this principle to illustrate the effects of time dilation at the speed of light.

## 5. What is the significance of Einstein's Clock?

Einstein's Clock is significant because it helped Einstein develop his theory of relativity, which has had a profound impact on our understanding of the universe. It also demonstrates the strange and counterintuitive concepts of time dilation and the constancy of the speed of light, which have been confirmed by numerous experiments and observations.

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