Originally posted by @metal-brain
You said you would write another post. Did you change your mind?
Someone said that time dilation was predicted as a result of GR theory. Is that true? If so how did that evolve? Was it Einstein himself that predicted that or other physicists?
Big Al in fact made the formula for time dilation:
"
Time Dilation
It turns out that as an object moves with relativistic speeds a "strange" thing seems to happen to its time as observed by "us" the stationary observer (observer in an inertial reference frame). What we see happen is that the "clock" in motion slows down according to our clock, therefore we read two different times. Which time is correct??? well they both are because time is not absolute but is relative, it depends on the reference frame. Let's look at the following classic example. There is a set of twins, one an astronaut, the other works for mission control of NASA. The astronaut leaves on a deep space trip traveling at 95% the speed of light. Upon returning the astronauts clock has measured ten years, so yhe astronaut has aged 10 years. However, when the astronaut reunites with his earth bound twin, the astronauthe sees that the twin has aged 32 years! This is explained due to the fact that the astronaut's twin is traveling at relativistic speeds and therefore his "clock" is slowed down.
Let's see how we can calculate the time "difference". The equation for calculating time dilation is as follows:
t = t0/(1-v2/c2)1/2
where: t = time observed in the other reference frame
t0 = time in observers own frame of reference (rest time)
v = the speed of the moving object
c = the speed of light in a vacuum
so in our problem we will let v = .95c, t0 = 10 years and we will solve for t which is the time that the earth bound brother measures.
t = 10/(1- (.95c)2/c2)1/2
t = 10/(1- .952)1/2
t = 10/ .312
t = 32 years
(the time the earth bound brother measures)"
From this site:
http://www.phy.olemiss.edu/HEP/QuarkNet/time.html
In the example given, the Earthbound twin ages 32 years while the astronaut ages 10 and for the astronaut he effectively (From his POV) is going 3 times the speed of light. Of course that is only for him and the ship, if he goes out 32 light years and stays a year, he then goes back, 65 years will have gone by on Earth but 21 years goes by for the astronaut. That is at .95c. it gets more extreme if you can manage to go say .999c which puts the astronaut going effectively 22 times the speed of light so now say he goes out 22 light years away, stays for 1 year, comes back, he ages 3 years but the Earth bound dude ages 45 years. Great for the astronaut except he comes home to a time where everything changed.
Compare that to a Rip Van Winkle spending 50 years or so starting in 1968, wakes up now in 2018. He would be a bit confused, eh. 'what the hell is a cell phone' and we landed on the MOON?
https://www.scientificamerican.com/article/einsteins-time-dilation-prediction-verified/