5 ms·

If you were watching their lives out the window of your spaceship you’d see them in fast forward vv. they’d see you in slow motion. Everything is relative. The

If you were watching their lives out the window of your spaceship you’d see them in fast forward vv. they’d see you in slow motion. Everything is relative. The main ”paradox” found by experimention is that the speed of light is a constant, regardless of your velocity. The only way this could be true, if you do a thought experiment, is if time was dialating for you. As for the physical and mathematical “why is this happening”, that’s where Einstein comes in. It’s an exponential. At 0.5c 100 years to you would be 115 years elasped to an observer, 0.9c 229 years, 0.999c 2,236 years, etc. Here’s an online calculator for the dilation effect https://www.omnicalculator.com/physics/time-dilation https://www.omnicalculator.com/physics/time-dilation

lurquer 5y ago
> If you were watching their lives out the window of your spaceship you’d see them in fast forward vv. they’d see you in slow motion. Everything is relative. Both observers, looking at one another, would see the other moving near c. Neither would know who was ‘actually’ moving. Yet, you assume there would not be a symmetry in their respective views of the other’s passage of time. Explain why. In simpler terms, a twin in a c-speed rocket could very well assume he was still and the earth was moving away. He should expect to find a younger twin when the earth ‘returned.’ Yet the examples only have the earth twin age, so to speak, and not the rocket twin.
- deleted 5y ago
  [deleted]
- jeffwass 5y ago
  The symmetry is broken in your twin example because the travelling twin had to accelerate to depart, accelerate to turn around, and accelerate to stop again at earth.
  - platz 5y ago
    It has nothing to do with acceleration. You can play games with acceleration and start to get "wrong" answers with the twin paradox. What actually matters is who travels the longest World Line a.k.a. the longest path in 4-d spacetime https://en.wikipedia.org/wiki/World_line https://en.wikipedia.org/wiki/World_line . That is all. A person on a non-curved geodesic spacetime path ages more quickly than a person on a curved non-geodesic spacetime path
- wruza 5y ago
  It’s still a hard topic related to the rotational “symmetry”. https://m.youtube.com/watch?v=cPEwkMHRjZU https://m.youtube.com/watch?v=cPEwkMHRjZU (7 minutes) It doesn’t answer your question directly, but the tricky part of a twin paradox is not that the earth twin observes his brother in a slow motion (the space twin also does that, thus a paradox). It’s because a space twin actually changes direction by acceleration at some point B, and at that time he skips over a big part of earth’s timeline. The video above only addresses why it’s NOT the earth twin who changes direction by acceleration, which you’re reasonably questioning. The universe somehow knows who is really “steering” and what remains more or less inertial. The pendulum example at the end may give a hint on why. Edit: also, the space twin doesn’t have to experience any additional acceleration from the “engines” - looping around some gravity well would work too. E.g. an entire trip could be that the space twin goes to the orbit around the earth, gets slung away by a quickly passing blackhole, loops around a distant blackhole and returns, all in a complete free fall.
- iaw 5y ago
  I asked this in physics when I first heard the twin experiment. The answer comes from more complicated relativity based on acceleration and depends entirely on which reference frame you meet in. If you travel back to earth you age slower, if the twin catches up to you they aged slower.... It's not intuitive but time actually warps and there is no true concept of "simultaneous" in a special relativity world.
  - doctor_eval 5y ago
    > there is no true concept of “simultaneous” in a special relativity world This did my head in. Wikipedia has a great explanation. https://en.m.wikipedia.org/wiki/Relativity_of_simultaneity https://en.m.wikipedia.org/wiki/Relativity_of_simultaneity
- danielsju6 5y ago
  The one who experienced the force of acceleration is the one who shifted their inertial frame w/re to the reference.
- caf 5y ago
  This TEDEd video works through the thought experiment, with messages sent from each twin to the other at 1-year interval (in the sender's frame of reference). https://www.youtube.com/watch?v=h8GqaAp3cGs https://www.youtube.com/watch?v=h8GqaAp3cGs

lurquer 5y ago

> If you were watching their lives out the window of your spaceship you’d see them in fast forward vv. they’d see you in slow motion. Everything is relative. Both observers, looking at one another, would see the other moving near c. Neither would know who was ‘actually’ moving. Yet, you assume there would not be a symmetry in their respective views of the other’s passage of time. Explain why. In simpler terms, a twin in a c-speed rocket could very well assume he was still and the earth was moving away. He should expect to find a younger twin when the earth ‘returned.’ Yet the examples only have the earth twin age, so to speak, and not the rocket twin.

deleted 5y ago
[deleted]
jeffwass 5y ago
The symmetry is broken in your twin example because the travelling twin had to accelerate to depart, accelerate to turn around, and accelerate to stop again at earth.
- platz 5y ago
  It has nothing to do with acceleration. You can play games with acceleration and start to get "wrong" answers with the twin paradox. What actually matters is who travels the longest World Line a.k.a. the longest path in 4-d spacetime https://en.wikipedia.org/wiki/World_line https://en.wikipedia.org/wiki/World_line . That is all. A person on a non-curved geodesic spacetime path ages more quickly than a person on a curved non-geodesic spacetime path
wruza 5y ago
It’s still a hard topic related to the rotational “symmetry”. https://m.youtube.com/watch?v=cPEwkMHRjZU https://m.youtube.com/watch?v=cPEwkMHRjZU (7 minutes) It doesn’t answer your question directly, but the tricky part of a twin paradox is not that the earth twin observes his brother in a slow motion (the space twin also does that, thus a paradox). It’s because a space twin actually changes direction by acceleration at some point B, and at that time he skips over a big part of earth’s timeline. The video above only addresses why it’s NOT the earth twin who changes direction by acceleration, which you’re reasonably questioning. The universe somehow knows who is really “steering” and what remains more or less inertial. The pendulum example at the end may give a hint on why. Edit: also, the space twin doesn’t have to experience any additional acceleration from the “engines” - looping around some gravity well would work too. E.g. an entire trip could be that the space twin goes to the orbit around the earth, gets slung away by a quickly passing blackhole, loops around a distant blackhole and returns, all in a complete free fall.
iaw 5y ago
I asked this in physics when I first heard the twin experiment. The answer comes from more complicated relativity based on acceleration and depends entirely on which reference frame you meet in. If you travel back to earth you age slower, if the twin catches up to you they aged slower.... It's not intuitive but time actually warps and there is no true concept of "simultaneous" in a special relativity world.
- doctor_eval 5y ago
  > there is no true concept of “simultaneous” in a special relativity world This did my head in. Wikipedia has a great explanation. https://en.m.wikipedia.org/wiki/Relativity_of_simultaneity https://en.m.wikipedia.org/wiki/Relativity_of_simultaneity
danielsju6 5y ago
The one who experienced the force of acceleration is the one who shifted their inertial frame w/re to the reference.
caf 5y ago
This TEDEd video works through the thought experiment, with messages sent from each twin to the other at 1-year interval (in the sender's frame of reference). https://www.youtube.com/watch?v=h8GqaAp3cGs https://www.youtube.com/watch?v=h8GqaAp3cGs