Solution to the Twin Paradox
One clever solution to this paradox is that E's conclusion is right:
T will be much younger indeed.
The reason is that one of special relativity's conditions is a uniform motion.
The spaceship needs acceleration and deceleration, thus T's conclusion is not right.
This solution has a little problem. Just let T travel more and we will see.
Suppose T travels double the distance at the same speed. How old will E and T be?
Following the original thought, T will be 40 and E will be 60,
because both of their clocks would have passed double amount of time.
Here is another thought, let's call it thought B.
T's new journey can be thought of as the old journey plus an extra journey in a uniform motion.
For this extra part of the journey, E and T are in exactly the same kind of relative state,
so their clocks should not add any difference during this part.
This will give us a different result: T will always be 10 years younger than E,
no matter how much longer he travels further.
Let's continue thought B in another direction.
Instead of traveling longer, let T travel shorter this time,
so that all the uniform motion part is cut out.
Due to the same reason, this cut-out should not cause any time difference.
T will still be 10 years younger than E, even if the acceleration and deceleration causes T only 10 hours!
So, the clever solution does not work.