Prof. Greene says “time itself slows down”, and he mentions the term “time itself” more than once. But, if time is relative, there is no such thing as “time itself”. According to Relativity Theory, “time itself” does not exist. What exists is relative time only.

Prof. Greene says “time itself slows down”, and he mentions the term “time itself” more than once. But, if time is relative, there is no such thing as “time itself”. According to Relativity Theory, “time itself” does not exist. What exists is relative time only.

Prof. Greene says “time itself slows down”, and he mentions the term “time itself” more than once. But, if time is relative, there is no such thing as “time itself”. According to Relativity Theory, “time itself” does not exist. What exists is relative time only.

I agree, good one.

Can the light clock be used for a geometric analysis of time dilation if it is rotated 90-degrees towards the direction of motion?

An excellent point, Bruce.

Relative theory only states, as far as I can make out, that observers will observe clocks that tick at the same rate when moving at the same speed with respect to the observer will be observed to tick at different rates when moving at different speeds with respect to the observer. The rate observed being slower the faster the clock moves with respect to the observer. Whilst speed is relative because it is defined in terms of speed with respect to other objects/observers rates are not. I do not need another clock to define what a rate is. I can, of course, see if one clock has a faster rate than another clock if I put them side by side (and they move at the same speed). A basic assumption of special relativity is that clocks can be synchronised and can be made to run at the same rate. In special relativity “time” (if we want to define it as a concept) is simply the rate of ticking clocks. With this definition we can say that “time slows down” however there is no fundamental underlying physical concept to this expression it is simply shorthand for saying “we observe that the rate of some ticking clock to be slower”. In special relativity, “time exists” means “clocks tick at a particular rate”, no more and no less.

Is a clock measuring the passage of time or is it defining the passage of time? Note we never observe directly “the passage of time”, we only observe clocks that tick. Sometimes the clocks tick faster sometimes slower.

Is a clock measuring the passage of time or is it defining the passage of time? Note we never observe directly “the passage of time”, we only observe clocks that tick. Sometimes the clocks tick faster sometimes slower. It is an assumption that we make of physical reality that the quantity of “time” between two subsequent ticks is always the same.

Is a clock measuring the passage of time or is it defining the passage of time? Note we never observe directly “the passage of time”, we only observe clocks that tick. Sometimes the clocks tick faster sometimes slower. It is an assumption that we make of physical reality that the quantity of “time” between two subsequent ticks of a clock is always the same. What we see is that motion (of observers with respect to clocks) affects the rate of ticking they see on the clocks. It is perhaps somewhat misleading or at least incomplete to say that “motion affects the passage of time” it would be more accurate to state that “motion affects the passage of time as seen by a particular observer moving with respect to the clocks being observed”.

Is a clock measuring the passage of time or is it defining the passage of time? Note we never observe directly “the passage of time”, we only observe clocks that tick. Sometimes the clocks tick faster sometimes slower. It is an assumption that we make of physical reality that the quantity of “time” between two subsequent ticks of a clock is always the same. What we see is that motion (of observers with respect to clocks) affects the rate of ticking they see on the clocks. It is perhaps somewhat misleading or at least incomplete to say that “motion affects the passage of time” it would be more accurate to state that “motion affects the passage of time as seen by a particular observer moving with respect to the clocks being observed”.

“Time itself is running slower on the moving clock” -> an observer watching a clock moving with respect to the observer will observe the clock ticking at a slower rate than a clock that is stationary with respect to the observer.

Is a clock measuring the passage of time or is it defining the passage of time? Note we never observe directly “the passage of time”, we only observe clocks that tick. Sometimes the clocks tick faster sometimes slower. It is an assumption that we make of physical reality that the quantity of “time” between two subsequent ticks of a clock is always the same. What we see is that motion (of observers with respect to clocks) affects the rate of ticking they see on the clocks. It is perhaps somewhat misleading or at least incomplete to say that “motion affects the passage of time” it would be more accurate to state that “motion affects the passage of time as seen by a particular observer moving with respect to the clocks being observed”.

“Time itself is running slower on the moving clock” -> an observer watching a clock moving with respect to the observer will observe the clock ticking at a slower rate than a clock that is stationary with respect to the observer.

“A clock that is in motion will tick off time at a slower rate” ->A clock that is in motion with respect to an observer will be observed (by the that observer) to run at a lower rate.

Is a clock measuring the passage of time or is it defining the passage of time? Note we never observe directly “the passage of time”, we only observe clocks that tick. Sometimes the clocks tick faster sometimes slower. It is an assumption that we make of physical reality that the quantity of “time” between two subsequent ticks of a clock is always the same. What we see is that motion (of observers with respect to clocks) affects the rate of ticking they see on the clocks. It is perhaps somewhat misleading or at least incomplete to say that “motion affects the passage of time” it would be more accurate to state that “motion affects the passage of time as seen by a particular observer moving with respect to the clocks being observed”.

“Time itself is running slower on the moving clock” -> an observer watching a clock moving with respect to the observer will observe the clock ticking at a slower rate than a clock that is stationary with respect to the observer.

“A clock that is in motion will tick off time at a slower rate” ->A clock that is in motion with respect to an observer will be observed (by that observer) to run at a lower rate.