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I am no physics expert, but I read that if someone, the same age as me, travels at near the speed of light time will go a lot slower for them. So that means that I would age quicker than that person. But is that age difference just perceived or real? Let's say that the person traveling at near the speed of light were to stop, relative to me, would the perceived age difference disappear and that person be my age again?

Rodrigo Pina
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  • In addition to the kinetic time dilation that you are bringing up, there is also gravitational time dilation. Time flows relatively slower near a planet than out in space, and the larger the planet, (or star) the slower the time. And time stops all together at a black hole (or very nearly stops depending on what we know about a black hole.) And it is all very real. – foolishmuse Jul 12 '22 at 19:22

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Time dilation is always a real physical effect. Although in the situation presented, known as the twin paradox, there is a difficulty: if someone travels relative to you at a speed close to the speed of light, according to his calculations you would age at a slower rate than he does and live longer than he does. Nevertheless, according to you she travels faster than you and he would stay younger. This is a seemingly paradoxical result, but it is not contradictory since the notion of time is different for both observers. If you perform the experiment of putting both observers together to see who aged more, then it is necessary to apply significant decelerations and changes of direction to one of the observers, in which case the paradox disappears because the traveler who experiences accelerations and decelerations will actually age less, so there is no contradiction.

Davius
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