Complete Solution To The Twins Paradox

This video is about the famous “Twins paradox” of special relativity, how time can appear to be faster for two different observers at the same time, and which twin really is older (or younger) – the one who stays on earth or the one who flies in a rocket ship to the stars?

REFERENCES

And twitter - @minutephysics

Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!

Created by Henry Reich

[comicstwisted]

"You guessed it" you overestimate my intelligence

[garethhanby]

The twins paradox has haunted me for most of my adult life. Thank you for finally explaining it to me, it is not a paradox at all. I can now die happy.

[lukefirst]

When I watch your videos, I nod my head and I'm like "Yeah, I totally understand that." I watch your videos to feel smart, but it just makes me feel really stupid.

[captainpalegg]

I like how the comments are pretty much an even blend of “This is a nice introduction to the concept, but here’s how I would expand on it” and “…You lost me at ‘setup’.”

[ibrahimhassan]

You lost me the second you said something about moving affecting time speed or something... basically lost me 10 seconds in.

[Cytrillex]

That's quite astonishing that in the time it takes you to very quickly decelerate and accelerate on your return journey, you can observe your twin back at home suddenly experiencing this large amount of time that you had missed due to your notion of time being on a very fast starship.

Imagine this being on a much longer scale where the time was 10 years rather than 10 seconds. Had you, as a space traveler, not watched this video, you would have come home 3.6 years later than you had expected! Thanks for minute physics for preparing the future space travelers to expect this phenomenon :P

[regular-joe]

All the way through I understood what he was saying, but then when it was done I didn't know what I'd understood...

[cennetc]

there is a c square missing under the squareroot

[NandikaRama]

This is very good! On the surface, many paradoxes seem to defy logic, while really, all it requires is some different perspective to probe it and make sense of it. Paradoxes demands reform in the way we think and approach problems.

[christopherramsey]

+MinutePhysics 0:47 "since you're moving"
Wait a sec. How do we know who's moving and who's not?
Isn't that the original argument?
How can we know who's moving if there's no absolute motion?
Can someone please explain this to me?

[GalaxableTV]

"If you can't explain it simple enough, you don't understand it well." - Einstein

[davidsweeney]

Geez, im sure glad I did psychology at university!

[karotix]

Thank you so much my physics teacher had no explanation as to how both people can view each other as having a slower time AND for one to come back older. This has been a HUGE help :)

[rstriker]

But couldn't you say the ship is still and earth is moving away then accelerating then coming back? Why doesn't this work both ways?

[TerryBollinger]

This is the cleverest, most concise, best reasoned, and least noisy Twins Paradox video I've found on YouTube. Alas, it's also wrong. For example, if your spaceship is a muon swarm passing through our atmosphere, it shows continuous verifiable time dilation _without_ bothering to turn around. The gap in your figure works only because you added two _independently_ observable time dilations.

[jeremyplayzxd]

i can tell you want thing. i dont understand

[Adamzychu]

I don't understand one thing. What if we choose person in spaceship as 'static' one and repeat all other steps. Wouldn't that lead us to conclusion that it was the other way around, 10s for spaceship, 8s for the Earth? Leaving us in the very same 'paradox' spot where we started.

[arrccellia]

im still having trouble with, "moving things experience time slower". how? why?

[theolav]

How does this solve the problem with 3 people, in which nobody turns around? In that one, A stays on the earth, B leaves the earth and C leaves the star. B and C travel at the same speed. When B and C meet, they compare times, and when A and C meet, C shows A the time B showed him in their encounter, and the time he used from the encounter with B to the earth. This means A has the time from his own clock and the time B and C measured in their entire journey. Nobody in that example has changed their velocity or reference frame, and both C and A should think the other is older until they meet?

[epiendless]

I find the paradox easier to understand if you look at length dilation instead.
The twin on Earth sees the rocket shrink in the direction of movement, but that makes no difference to the trip time.
The twin on the ship sees the Earth shrink, but also the distance to the turning point shrinks, because Earth and the turning point are both in the same frame of reference. So he gets there faster from his perspective because the distance shrank.
Relating it back to what the clocks show during the journey is more mind-bending. This video _feels_ correct, better than the last 'length dilation' explanation that I read which had the clocks running faster on the return journey.
But I've yet to see an explanation that doesn't amount to needing to do a whole lot more reading.