Can you explain the Twin Paradox?

Question

I am having trouble grasping this concept of time not being the same all around. To me, even though one twin is traveling, they should still age the same amount, it's just that the twin will cover a lot of distance in this time, because he is traveling so fast.

But apparently, the twin who is on the ground will only APPEAR older and more aged, or is he actually more aged then the traveling twin?

I am just having trouble understanding the concept of time in this context and relative time, please help me!

Answer 1

It is true that, at any given instant when the moving twin, is moving at his cruising speed, you could claim that no such thing as absolute motion means that either twin could be considered moving.



However, this isn't a complete picture of the story. There is something unique that the twin in the rocket did, that the twin back on Earth did. And we call it, acceleration. Yes there is such a thing as absolute acceleration, as that is why you feel "heavy" against the back of your chair, when in a vehicle that is speeding up.



It will indeed be true that the twin in the rocket will have barely aged, and the twin back on Earth will have aged the most. Time slows down for the one with the greatest changes in state of motion. Special relativity alone, the equations for constant speed cases, ISN'T ENOUGH to calculate it, precisely because of the acceleration.



My favorite question to ponder about the twin paradox, is, which twin is happier, upon reuniting with his brother? I'd think I'd be happier to end up younger than someone who was originally my age, with plenty of time left to outlive them by 50 years. But, the twin in the rocket, will unfortunately be kind of lonely, in this future world to which he returns. Over half of everyone he knew in his whole life is gone. The remainder are much older, and nothing like he remembers. His much older brother, by contrast, has decades of life experience, and has met generations of people he knows and loves.

Answer 2

OK, the twin paradox is really just about clocks(light clocks, hence any physical system, like biological activity too) tick more slowly when they are travelling close to the speed of light relative to the the stationary clock.



Soo... when jo travels away at close to the speed of light he has been 'ticking' quite slowly. mind you jo needed also very large amounts of energy to even travel anywhere near the speed of light. When jo gets back to twin jo back on earth all jo's biological processes had been going only say half the rate. So jo's twin who stayed on earth IS older. When jo and twin are back together though they now age at the same rate.



THis is the same principle as atomic clocks going out of sync when they have been in an fast jet aircraft for a few hours. The clock from the jet will be slightly out of sync compared with the one that was left on the ground.

Answer 3

I will agree, it is a confusing concept at first! Okay so the twin that is in the rocket ship is actually YOUNGER than the twin on Earth after the trip. This is because of the fact that the speed of light is constant (i.e no matter how fast you are moving in one direction, if you shine a flashlight ahead of you, the beam will travel at light speed (even if you yourself are traveling at 99.99% the speed of light relative to an observer in a different frame of reference). This means that time MUST slow down for the object moving quickly. There are a few ways that time can slow down for an object. The first (I just mentioned) is if the object is moving very fast. We do not notice any time dilation on Earth because, relative to the speed of light 299,792,458 m/s, we are barely moving! The second way that an object can appear to age less than its surroundings is if it is in the presence of gravity! What this implies is that if you live next to a mountain (or other massive object), time will move more slowly for you than where there is less gravitation (however this only would slow time my a few billionths of a second over your lifetime). The last way is similar to gravitational dilation; it is acceleration. This is the most important element in the Twin Paradox. Because the twin in the rocket ship was accelerating for most of the journey (i.e. away from Earth, slowing to a stop, and coming back to Earth), time moved more slowly for the space twin and thereby caused him/her to age LESS than the one on Earth! Crazy isn't it?