- #1

Sophrosyne

- 128

- 21

- TL;DR Summary
- Elaborating on the the twin paradox to help understand it

I am looking at some of the threads on the twin paradox, and getting even more confused. I have been trying to run through the details of what each twin is seeing, and was wondering if I could get some help. I am just trying to imagine how each twin is “seeing” the other twin at each step as the scenario unfolds. Please tell me if I am going wrong at any step in this scenario.

So in my scenario, we have the two twins, each with a powerful telescope through which they can see each other, and also an electromagnetic beacon which emits a pulse every second which the other can receiver. They bid each other farewell and the traveling twin takes off and in short order achieves near-light-speed velocity.

Step 1, the outward journey: the traveling twin travels to a planet 20 light years away. He notes time dilation from the stationary twin’s electromagnetic pulses, so they slow to, say, every 2 seconds instead of one. As he looks back at his twin through his telescope, he sees that his twin has only aged 10 years instead of his 20.

The stationary twin, in the meantime, sees the same thing: he has aged 20 years while the traveling twin has only aged 10, and his electromagnetic beacon frequency also halved for most of the trip. (I am just making up these numbers qualitatively- the exact numbers don’t matter too much- I am looking for a qualitative, intuitive understanding).

Step 2, the return trip: So now, on the return trip, the traveling twin begins to see the electromagnetic pulse speed up to faster than every second, due to the Doppler effect, but tempered by relativistic time dilation). The stationary twin sees the same thing, but at presumably less of a rate, so that at some point he sees that his stationary twin is older than him.

So now, some questions:

1) At what point do the twins realize the stationary twin has aged more? It has to be somewhere as the traveling twin anpproaches Earth again, right? Somewhere mid-flight at some point. Would they both agree that it happened mid-flight as they see each other through their telescopes and keep track of the number of EM pulses, even if they don’t agree on exactly when? IOW, they can both agree that the time for the stationary twin has moved faster on the return trip than for the traveling twin, correct?

2) The traveling twin picks up an alien on that planet on which he he had stopped- one who is used to seeing time dilation when traveling at near light speeds. Wouldn’t this alien be a little surprised to see that the time as measured by the EM pulse at their destination is actually speeding up instead of slowing down? As two objects approach each other at relativistic speeds, the every-second EM pulse from the stationary twin should be slowing down, not speeding up. I am not sure why this should be observed differently by the returning twin as opposed to the alien he picked up who never made the first leg of the journey, but is on the same ship.

———————

Sorry if I am sounding confused here- but that’s because I am!

So in my scenario, we have the two twins, each with a powerful telescope through which they can see each other, and also an electromagnetic beacon which emits a pulse every second which the other can receiver. They bid each other farewell and the traveling twin takes off and in short order achieves near-light-speed velocity.

Step 1, the outward journey: the traveling twin travels to a planet 20 light years away. He notes time dilation from the stationary twin’s electromagnetic pulses, so they slow to, say, every 2 seconds instead of one. As he looks back at his twin through his telescope, he sees that his twin has only aged 10 years instead of his 20.

The stationary twin, in the meantime, sees the same thing: he has aged 20 years while the traveling twin has only aged 10, and his electromagnetic beacon frequency also halved for most of the trip. (I am just making up these numbers qualitatively- the exact numbers don’t matter too much- I am looking for a qualitative, intuitive understanding).

Step 2, the return trip: So now, on the return trip, the traveling twin begins to see the electromagnetic pulse speed up to faster than every second, due to the Doppler effect, but tempered by relativistic time dilation). The stationary twin sees the same thing, but at presumably less of a rate, so that at some point he sees that his stationary twin is older than him.

So now, some questions:

1) At what point do the twins realize the stationary twin has aged more? It has to be somewhere as the traveling twin anpproaches Earth again, right? Somewhere mid-flight at some point. Would they both agree that it happened mid-flight as they see each other through their telescopes and keep track of the number of EM pulses, even if they don’t agree on exactly when? IOW, they can both agree that the time for the stationary twin has moved faster on the return trip than for the traveling twin, correct?

2) The traveling twin picks up an alien on that planet on which he he had stopped- one who is used to seeing time dilation when traveling at near light speeds. Wouldn’t this alien be a little surprised to see that the time as measured by the EM pulse at their destination is actually speeding up instead of slowing down? As two objects approach each other at relativistic speeds, the every-second EM pulse from the stationary twin should be slowing down, not speeding up. I am not sure why this should be observed differently by the returning twin as opposed to the alien he picked up who never made the first leg of the journey, but is on the same ship.

———————

Sorry if I am sounding confused here- but that’s because I am!

Last edited: