The Twin Paradox in Special Relativity

In the ’time dilation’ post, I left off with this question….

The reason I left off was because of length contraction,

to answer the twin paradox….^^ hehe

So again,

about that last question from that time, very briefly,

what exactly is the twin paradox! Let’s quickly go over it

In the previous post, talking about Interstellar, I said this

Our father, who left his daughter on Earth,

relative to the daughter who is stationary on Earth, time passes more slowly for him,

so when they meet again later, the daughter has become much more of an old lady….

This made sense after learning ’time dilation',

but what if someone asks this????

“From the father’s perspective inside the spaceship, the daughter on Earth would look like she’s moving in the opposite direction~~~~

So wouldn’t the opposite also make sense, that time flows relatively slower for the daughter than the dad, so the opposite result — the daughter being way way way younger than the dad — should also be possible?????????”

Great confusion

-_-

What on earth is this lol lol lol lol lol lol

The answer to this question

will be done with ’length contraction'.

But first, length contraction or whatever, we can just explain it simply hehehehe

“What the picture above is saying is that there’s no way whatsoever to tell who is the one moving.”

“However, the fact that somehow the two of them met up afterwards”

“means that one of the two changed direction.”

“During the process when one of them changes direction (the accelerated motion process), we can figure out who was the one moving.”

“Ahh!!! I was the one moving!!! Sorry for getting mad^^” is what they can say.

The summary above is so simple it doesn’t seem like an answer,

but fundamentally that’s the right answer…hehehe

And now, it’s a matter of explaining by how much, by what amount, using “length contraction”.

So now, let me explain this according to the situation in our book.

I’m going to tell the story again using ’length contraction'.

There are twins, and the older twin brother is making a fuss about going on a space trip in a spaceship at 0.8c to the star ‘Kkerakkurukkung star’ which is 20 light-years away.

The older brother went 20 light-years in the spaceship, and came back……hehe

After returning from the trip, he says this…..

“The distance wasn’t that long??????????????20 light-years my foot~~~~it was only 12 light-years????????”

The decrepitly aged younger twin brother majored in physics while his older brother was away,

and is now a physics professor…. So that guy says he understands what he’s saying.

“Dude –”

“Your spaceship speed was 0.8c, that’s why you’re saying that kind of nonsense–…..”

Since the older brother traveled round-trip at 0.8c over a distance of 12 light-years,

he thinks it was 15 years each way, 30 years round-trip,

but the twin younger brother on Earth saw him traveling round-trip over 20 light-years at 0.8c,

so on Earth he was watching 50 years.. (now call me older brother punk)

Originally written in Korean on my Naver blog (2015-08). Translated to English for gdpark.blog.