# Is time dilation real

## Is the time dilation real or apparent?

RELATIVITY PRINCIPLE.INFO

A very common question that is not easy to answer is the question of the reality of time dilation. Is the slowing down of the clocks and all physical processes in a system that is moving relative to the observer real or is it apparent?

This question is very easy to answer for the twin paradox: If you load a watch onto an airplane and fly it around the earth, it can be checked a little behind. One can easily compare the clock with a stationary clock and get a real, measurable deviation.

### One way flight

The question is more difficult to answer for a one-way trip. If you move two clocks apart at high speed and then slow them down again so that they are at peace with one another, you cannot absolutely specify which clock is ahead and which is behind. This is a consequence of the relativity of simultaneity. Which clock goes depends on what kind of inertial system you are using. But here, too, it is not arbitrary: If you have decided on a coordinate system, the relativistic calculation clearly shows which clock is ahead. This can be checked experimentally with the help of a clock synchronization. Here, too, the statements of the theory of relativity are clear and verifiable. They are therefore just as real as all other physical measurands.

### kinetic energy

There are, by the way, many analogies to Newtonian physics. There, too, there is already relativity according to Galileo Galilei. The kinetic energy of an object depends, for example, on the choice of the coordinate system. Nevertheless, the effect in the event of a collision is real and independent of the coordinate system. The total energy also depends on the coordinate system, but in any inertial system it is a real, because measurable, conservation variable. So one should carefully choose between relative and any distinguish.

Last change: April 13, 2007