Exploring Proxima Centauri: The Effects of Light Speed and Time Travel

[bluemanta9]

I am a physics "layman", so please forgive me if these questions seem basic.

Let's say we can travel at light speed, we send a crew to Proxima Centauri, & it's exactly 4 light years away. They explore for exactly one day, then return.

1. Since it takes 4 years for light to reach it & 4 years to return it, would we not see our crew arrive for 8 years? Also...

2. Would we see them both leaving Proxima Centari & arriving back at Earth at the same time on the next day?

 

[phinds]

I am a physics "layman", so please forgive me if these questions seem basic.

Let's say we can travel at light speed

No, let's not, since it is impossible.

 

[Dale]

Let's say we can travel at light speed,

Well, it is not possible even in theory to travel at light speed. However, we could travel at nearly light speed (say 0.9999999 c). Would you accept an answer to that slightly modified question?

 

[bluemanta9]

Well, it is not possible even in theory to travel at light speed. However, we could travel at nearly light speed (say 0.9999999 c). Would you accept an answer to that slightly modified question?

Sure.

 

[Dale]

Ok, so to keep things simple, let's say that they travel just under light speed so that the 4 light year trip takes 4 years plus 1 minute.

1. Since it takes 4 years for light to reach it & 4 years to return it, would we not see our crew arrive for 8 years? Also...

Yes. They would arrive in 4 years and 1 minute, so we would see them arrive after 8 years and 1 minute.

2. Would we see them both leaving Proxima Centari & arriving back at Earth at the same time on the next day?

Almost. We would see them leave PC at 8 years 1 day and 1 minute, and then we would see them arrive at 8years 1 day and 2 minutes

 

[bluemanta9]

Ok, so to keep things simple, let's say that they travel just under light speed so that the 4 light year trip takes 4 years plus 1 minute.

Yes. They would arrive in 4 years and 1 minute, so we would see them arrive after 8 years and 1 minute.Almost. We would see them leave PC at 8 years 1 day and 1 minute, and then we would see them arrive at 8years 1 day and 2 minutes

Thank you! :-)

 

[sophiecentaur]

Someone needs to point out that, as far as the ship's crew (their body cells) and all the ship's clocks are concerned, their whole journey may have taken only a few minutes. They wouldn't have aged more than that.
The given example is too extreme to contemplate but, given a suitable drive and enough fuel to accomplish a 'very fast' journey, we could observe a significant difference in the ageing process for the ship's crew and the rest of us on Earth over the (more realistic) ten Earth years that they were away for.

 

[nitsuj]

Someone needs to point out that, as far as the ship's crew (their body cells) and all the ship's clocks are concerned, their whole journey may have taken only a few minutes.

Dale did, 2min -1min =1min

 

[sophiecentaur]

Dale did, 2min -1min =1min

Yes. I read it but my point was about the fact that they would actually experience the changed time. People often think (wrongly) that the way the clock works is not the same as the way their brain and other cells would age. (I think my point was a valid addition.)