# Time dilation when an object moves [duplicate]

Why does time dilation happens when the object moves, is it just because the physical processes, in the moving objects, happens slower? (this video suggests this: https://youtu.be/Ci4L6myFFng?t=224)

If yes, does this means if a person moves fast, this might alter his brain activity and his thinking process be altered?

Does this means there is no time dilation at all, but just that the physical processes happens slower when moving? This might explain why two atomic clocks are different, when on is taken to space and back.

## marked as duplicate by John Rennie, ACuriousMind♦, Kyle Kanos, Ryan Unger, user10851 Mar 18 '16 at 1:20

• What is the difference between time slowing down and all physical processes slowing down? – lemon Mar 17 '16 at 8:51
• Please see the video link, it suggests the photon travels a longer distance than normal. – user4691 Mar 17 '16 at 8:55
• When you say "happens slower", it would be helpful to say "slower" than what? What are you comparing it to? – tom10 Mar 17 '16 at 13:54

It is always depending on the frame of reference. In the rest frame, time will be just normal. Only relative to a different observer, the elapsed time will be shorter.

The human brain activity is not really altered as all processes are slower for the outside observer. For the human (who is always in his own rest frame), nothing is changed.

I think you contradict yourself in the last sentence. There definitly is the effect of time dilation. You can look at four-vectors, Lorentz transformations and the Minkowski scalar product. This is what makes the two clocks go different.

You might be interested in my essay about the twin paradox where I take the sledgehammer of general relativity formalism to resolve the twin paradox, once in the rest frame of earth and once for the astronaut. Both give the exact same result showing that time dilation is a manifest effect and does not depend on subtle tricks like “the astronaut was the one to turn, therefore he must be the younger one”.

Before Einstein there was a theory that moving objects just got shorter and their processes took longer to complete. Becsuse of this, we still use the words length contraction and time dilation. But they are horrible names, and there is a problem with the whole idea.

If you theorized that moving objects slow down and get shorter. Then the moving objects wouldn't notice they are moving. They would think you are moving. They would think you are shorter and you are running slower.

So they'd think you compute everything with defective slow running clocks (that then don't measure time accurately) and using defective shortened rulers (that then don't measure distances accurately).

So there is a huge problem in that you theory thinks there is a magic frame where clocks at rest measure time accurately. And where rulers at rest measure distances accurately. But there is no experimental procedure to find out which frame is the magic frame.

What we do know from experiment is that two clocks tick different based on how they move. And two rulers measure differently based on how they move.

And our thekries should be based on what we measure and not on undetectable magic frames. After all, in the magic frame time is measured by clocks at rest in that frame and distance is measured by rulers at rest in that frame.

So instead of magic, we could accept that clocks and rulers measure something and that what they measure depends on how they move. And now we don't need to treat any one frame as special as long as we make a theory that predicts accurately and correctly what real clocks and rulers do.

And that theory is relativity. It says there is a thing called a metric. And clocks and rulers measure the metric along the 4d path in spacetime that the clock or ruler takes. One metric. Lots of possible paths. So lots of possible clock and ruler readings. And if we pick the metric right the predictions will agree with what clocks and rulers read.

So we don't measure time. Never have. It's just that clocks that move slowly relative to each other tick at very similar rates. So we conflated a measurement of the metric along those really similar curves with "time".

Now to finally get back to your talk about brains and physical processes. Processes don't ever happen at a certain rate in time. They always happen at a certain rate of the metric as measured along a path. So if you fix a lath, and measure the metric along that path then you get something like a time, and that's what tells everything (clocks, brains, radioactive decay, any process) how often tondo something.