I’ve seen people explain it before but I have absolutely no idea what they are talking about. An example of what I’m saying would be the movie interstellar or the old planet of the apes movie. It makes absolutely no sense.
In: Physics
I have a B.S. in biophysics, and one of my favorite college classes was “modern physics” where we learned about this. This is a special relativity concept known as “time dilation”. The ELI5 version of special relativity is: nothing can go faster than the speed of light, and the laws of physics do unintuitive things when you go really really fast (near the speed of light). The faster you go, the slower time moves for you with respect to someone moving slowly (time dilation).
You seem to be curious about the actual mechanism of this, which is really hard to explain in an ELI5 version, but I’ll try to go step-by-step.
On Earth, we perceive speeds “relatively” in a pretty simple way: if I am going 70mph in a car and there are cars whizzing past me going 70mph the opposite direction, they appear (from my POV or “reference frame” in physics terms) to be going 140mph straight at me. That’s makes decent enough sense. However, in 1887, physicists Michelson and Morley found something extraordinary: the speed of light is constant, whether you are moving towards it or away from it. In other words, the speed of light (c) is constant in all reference frames.
This result shocked the world of physics because it seemed irreconcilable with the world we know. Imagine you are in a car going 90% the speed of light (0.9c) and someone outside the car shone a laser pointer back at you, you would expect to measure the speed as additive: 0.9c you are racing toward it + 1.0c the light travels at you = 1.9c the light appears to be traveling from your frame of reference. However, this is not the case. You will still measure the light as traveling 1.0c. More than this, physicists found that nothing with mass can ever go faster than the speed of light (or even appear to go faster than the speed of light) in any frame of reference.
So now what? What if you are going 0.9c in one lane and a car was traveling 0.9c in the other lane as you… how could the math work out that you not perceive them as going 1.8c??? Well Hendrik Lorentz worked out the math to properly “transform” frames of reference going at very high speeds–“the Lorentz transformations”. They are equations that “fix” the math so that at even in frames of reference going high speeds, we will still perceive the speed of light as c, and even if two people are going high speeds on a collision course, neither will perceive each other’s speed as higher than c. One natural consequence of the Lorentz transformations is time dilation. When changing high speed frames of reference, there is a “Lorentz factor” that needs to be taken into account: 1/sqrt(1- v^2 / c^2 )
As crazy as this is, it is absolutely true. In 1941, Rossi and Hall showed that muons (heavy electrons) in cosmic rays decayed much much slower than they do when they are stationary because they were traveling at 0.99c, and the difference in their lifetime was exactly predicted by the Lorentz equations, showing that time is slower for extremely fast things. In 1979, Bailey et al. redid this experiment with even better controls in the CERN particle accelerator and got the exact same results.
The Lorentz transformations were essential to Einstein correctly theorizing Special Relativity in 1905. Then in 1907, he also described that time dilation can also occur due to gravitational effects of large bodies–what you see accurately depicted in *Interstellar*.
I know that was a lot, but I find it fascinating and this it is a great question as well. If you want to read further, the history of special relativity Wikipedia page is a good start: https://en.wikipedia.org/wiki/History_of_special_relativity
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