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It so happens that last night I was rereading Einstein's famous 1905 paper On the Electrodynamics of Moving Bodies. I think this is one of the most fascinating scientific papers in history, but some people say it's not at all clear. In any case I love reading Einstein's papers.

Clocks obviously play a major role in this paper. I was thinking about the types of clocks that existed in 1905. As a patent clerk in Switzerland, which is famous for its clocks, he may have seen many new ideas for clocks. Perhaps he dreamed about clocks.

His clock seems to be a sort of idealized perfect clock. He of course goes into no details concerning its construction. Although he does mention it has "hands."

I would be interested in reactions to how Einstein defines time in the first section of this paper. Is it clear? Is it confusing?

First he describes clock A and clock B, and the fact that each clock can only indicate the time for events in its immediate proximity, which happen "simultaneously" with a specific position of the hands on a clock. Of course we normally define "simultaneous" to mean "at the same time" and we have not yet defined "time." So I take this to mean we perceive the hands on a clock to be at a certain position, and the event to occur, in a way the brain perceives as "simultaneous." It's a matter of perception.

Thus we have the A time and the B time. But we need to define a common time for A and B.

Then he says that in order to establish this common time for A and B, we must say by definition that the time required for a ray of light to go from A to B equals the time required for a ray of light to go from B to A. Note that this is a definition, not an inference.

Then he defines what he means by synchronized clocks. We have a clock at A, and another clock at B which is "similar in all respects" to the one at A. In accord with his earlier definition, he states that clock A and clock B are synchronized if the time for light to travel from A to B equals the time for light to travel from B to A.

The thought experiment to make this clear is that the ray leaves A, the time being recorded. Then the ray arrives at B, where it is reflected back to A. The arrival/reflection time at B is recorded. Then the arrival time back at A is recorded.

In other words, let T

Then clock A and clock B are synchronized if T

Now he says we can define the time of an event in a stationary system. He says that if a clock is stationary, and is located at the place of an event in a stationary system, then the time of the event is that given simultaneously by the clock, which is synchronized with another specified stationary clock.

This "time" is what he calls the "time of the stationary system."

He also assumes "in agreement with experience" that c = 2AB/(T

Of course this is only the beginning of this paper.

Clocks obviously play a major role in this paper. I was thinking about the types of clocks that existed in 1905. As a patent clerk in Switzerland, which is famous for its clocks, he may have seen many new ideas for clocks. Perhaps he dreamed about clocks.

His clock seems to be a sort of idealized perfect clock. He of course goes into no details concerning its construction. Although he does mention it has "hands."

I would be interested in reactions to how Einstein defines time in the first section of this paper. Is it clear? Is it confusing?

First he describes clock A and clock B, and the fact that each clock can only indicate the time for events in its immediate proximity, which happen "simultaneously" with a specific position of the hands on a clock. Of course we normally define "simultaneous" to mean "at the same time" and we have not yet defined "time." So I take this to mean we perceive the hands on a clock to be at a certain position, and the event to occur, in a way the brain perceives as "simultaneous." It's a matter of perception.

Thus we have the A time and the B time. But we need to define a common time for A and B.

Then he says that in order to establish this common time for A and B, we must say by definition that the time required for a ray of light to go from A to B equals the time required for a ray of light to go from B to A. Note that this is a definition, not an inference.

Then he defines what he means by synchronized clocks. We have a clock at A, and another clock at B which is "similar in all respects" to the one at A. In accord with his earlier definition, he states that clock A and clock B are synchronized if the time for light to travel from A to B equals the time for light to travel from B to A.

The thought experiment to make this clear is that the ray leaves A, the time being recorded. Then the ray arrives at B, where it is reflected back to A. The arrival/reflection time at B is recorded. Then the arrival time back at A is recorded.

In other words, let T

_{A}be the "A" time the ray leaves A. Let T_{B}be the "B" time the ray is reflected from B. Let T^{'}_{A}be the "A" time the ray arrives again at A.Then clock A and clock B are synchronized if T

_{B}- T_{A}= T^{'}_{A}- T_{B}.Now he says we can define the time of an event in a stationary system. He says that if a clock is stationary, and is located at the place of an event in a stationary system, then the time of the event is that given simultaneously by the clock, which is synchronized with another specified stationary clock.

This "time" is what he calls the "time of the stationary system."

He also assumes "in agreement with experience" that c = 2AB/(T

^{'}_{A}- T_{A}) is a universal constant, namely the speed of light in empty space.Of course this is only the beginning of this paper.

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