# Simultaneity of events

1. Jun 8, 2010

### proculation

Hi,

A friend of mine asked me something about relativistic physics. It's all hypothetical and I told him it's a paradox that cannot be achieved since you cannot go back in time.

Here's his assumption:

Let's say that you pass through a 'wormhole' to a planet near Alpha Centauri (26 lightyears). You send a signal to earth and then you get back into your 'ship' from another worm hole.

From your point of view, it took you about 5 minutes to do all that. You are back on Earth 5 minutes after.

26 years later, you receive the signal you sent from Alpha Centauri. That would mean you are on Earth to receive the signal and also on the planet of Alpha Centauri.

My guess is that it is impossible since when you would get back to Earth, you would be travelling backwards in time.

Am I right ?

Oiivier

2. Jun 9, 2010

### Dmitry67

Wormholes can create close time-like curves.
The same problem exists inside rotating black holes

CTL curve itself is not a contradisction per se, wiki for example novikov self-consistency principle.

3. Jun 9, 2010

### proculation

That's exactly what I think. it's impossible.

You cant go back in time to receive the signal.

4. Jun 9, 2010

### Dmitry67

You dont 'go back in time', you always go forward, but arrive to the past. Like on the globe: you can always go west, but return to the East

5. Jun 9, 2010

### proculation

That's my understanding.

6. Jun 9, 2010

### elibj123

I don't see how recieving the signal means you are on Alpha Centauri.

It's like I will send you a letter, meanwhile go on a trip around the world, but when you'll recieve the letter it will require me to be home.

Maybe I didn't get your question right.

7. Jun 9, 2010

### proculation

That's in a Newtonian world. But in a Einstein world... It can't happen.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook