I have googled for „definition of proper time“
This source https://www.collinsdictionary.com/dictionary/english/proper-time gives the following definition:
- proper time … measured by a clock that has the same motion as the observer. Any clock in motion relative to the observer … will not, according to the theory of relativity, measure proper time.
However, according to this answer
Confusing time dilation – proper time is higher?
„In other words, it is the time registered by a clock that is carried from one event to the other“ exactly the moving clock measures proper time interval and this time interval is the shortest due to time dilation.
Is definition in Collins Dictionary wrong? Please help resolve this contradiction.
Best Answer
The definitions are both trying to say the same thing, but they are not quite managing to avoid all scope for misunderstanding. For a non-technical appreciation of the meaning of proper time you should start with the principle that proper time is the time experienced at any point in one's own reference frame. As you sit at your desk marvelling at the clarity of my answer you are experiencing proper time in the reference frame in which you are stationary. Any clocks that are stationary relative to you will record time at the same rate you experience it.
Anybody moving relative to you will experience their own proper time, which will be faithfully recorded by any clocks moving with them (ie clocks that are stationary in that person's reference frame).
The Collins definition was insufficiently precise. It should have said that any clock moving with respect to an observer will not measure proper time in the observer's frame of reference.
If a clock is moved between two other clocks that are stationary relative to each other, the time it records is a proper time for that clock's frame of reference, and it will be shorter than the time that appears to have elapsed according to the stationary clocks.