Why does time dilation occur?

Question

Time dilation is the phenomenon whereby an observer finds that another's clock which is physically identical to their own is ticking at a slower rate as measured by their own clock. This is often taken to mean that time has "slowed down" for the other clock, but that is only true in the context of the observer's frame of reference. Locally, time is always passing at the same rate. The time dilation phenomenon applies to any process that manifests change over time.

I would like to understand why this occurs...not just the phenomenon itself.

Answer 1

It occurs because all observers measure the speed of light as c. We measure the speed of something by measuring the distance and time covered in moving from point A to point B. If two observers moving at different speeds relative to each other measure the same speed for a single light ray, it must be that their meter sticks and clocks aren't measuring the same things.

In the case of time dilation, consider a clock made of two mirrors with a light ray bouncing between them. It clicks each time the light ray returns to the bottom mirror. If the clock is moving, then the distance the light flash must travel is longer (the vertical separation between plates, and a horizontal displacement of the whole clock) than when the clock is stationary--- but the light flash moves at exactly the same speed! So the flash takes longer to complete its there-and-back motion and the moving clock ticks slower.

Answer 2

These "why is water wet" questions are hard to answer, but I'll take a stab. Einstein started with this "gedanken" (thought experiment)...
imagine riding along a beam of light some distance from a clock. Imagine specifically that the light is the image reflected off the clock striking twelve. As you approach the speed of light, it will take more time for the light from that image to reach you and "tell" you that the clock has struck twelve, thus to you it will *appear* that the clock is slowing down the more you approach light speed (relative to your inertial frame).

Now, this is just a thought experiment that suggests why it would normally *appear* that time runs at different rates in different inertial frames. What Einstein (and numerous experiments, now) proved is that it really IS this way... it doesn't just appear this way.

Answer 3

time dilation is caused by the fact that the speed of light is a constant (in a vacuum) and does not change depending on one's frame of reference, i.e. how fast someone is travelling.
it is because the speed of light does not change, rather it is one of the axiomatic constants of the universe, like the charge of the electron or Planks constant. The extent of the time dilation is based on the Lorentz factor, with the constant "c" as the speed of light. the Lorentz equation says that the faster the object is travelling in relation to its frame of reference, the greater is the time dilation.

click here for more information:

http://en.wikipedia.org/wiki/Time_dilation

Answer 4

It is simply a consequence of Special Relativity, resulting from the fact that information cannot travel instantaneously. It is so counter-intuitive that it is hard to grasp, or to give a "why" that has any meaning other than as a mathematical formula.

Answer 5

Honestly, with the second sentence as simple response would be that the "slower" watch is defective. LOL.