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Glom
2004-Mar-24, 11:47 AM
More to eburacum:

In the wormhole example on OA, where you had a ship travelling at near c hauling a wormhole mouth on a 100ly journey that only took a little over 1 year relative to the ship, you said that this would mean that after a year, the people left back on Earth would be able to step through the wormhole to the destination even though they'd only see the ship 99 years away from destination.

Wouldn't this lead to a potential paradox? Let's say that upon arrival at the destination, a child was born. This child grows up to be in his twenties and travels through the wormhole back to Earth. From Earth, the ship still appears to have over seventy years left of its journey. Couldn't this kid jump on a much faster ship, catch up with the colony ship and blow it up, therefore preventing him from being born?

eburacum45
2004-Mar-24, 01:29 PM
Yes, it does!

Matt Visser has proposed that virtual particles will start to travel around any closed time like loop which forms; these particles cause the wormhole (s) to collapse
and prevent any paradox from becoming established.

So you have to keep thw wormhole mouths further apart than the temporal displacement caused by relativity...

Normandy6644
2004-Mar-24, 01:43 PM
More to eburacum:

In the wormhole example on OA, where you had a ship travelling at near c hauling a wormhole mouth on a 100ly journey that only took a little over 1 year relative to the ship, you said that this would mean that after a year, the people left back on Earth would be able to step through the wormhole to the destination even though they'd only see the ship 99 years away from destination.

Wouldn't this lead to a potential paradox? Let's say that upon arrival at the destination, a child was born. This child grows up to be in his twenties and travels through the wormhole back to Earth. From Earth, the ship still appears to have over seventy years left of its journey. Couldn't this kid jump on a much faster ship, catch up with the colony ship and blow it up, therefore preventing him from being born?

This paradox has been addressed many times in the so-called "grandfather paradox" in time travel where someone goes back in time to kill his own grandfather, thus preventing his birth. The thing is, he was born, so he couldn't kill his grandfather! Thus something will happen to prevent him from doing it.

eburacum45
2004-Mar-24, 01:47 PM
Thus something will happen to prevent him from doing it.

Yep; that something has been called the Chronological protection Conjecture.

http://www.orionsarm.com/intro/WhyNoTimeTravel.html
http://www.orionsarm.com/intro/ftl-paradoxes.html
http://www.orionsarm.com/whitepapers/wormholes.html

Glom
2004-Mar-25, 04:50 PM
So how far away would the wormholes mouths in that example have to remain in order to avoid CPC blowing them up?

eburacum45
2004-Mar-26, 08:50 AM
Gamma.

As long as they are the same distance apart as the difference in time frames expressed as a distance-

so a wormhole with a time dilation factor (gamma) of one year stays more than one light year away-

no paradoxes are possible.

Luckily most stars are several light years distant from each other; so it is not as restrictive as you might think at first.

Glom
2004-Mar-26, 12:18 PM
So I guess in that example, the convenience of doing a 100ly trip in one year wouldn't actually be possible.

eburacum45
2004-Mar-26, 12:32 PM
One wormhole by itself would not normally be a problem, as long as the mouths are kept far enough apart; but it would be difficult to avoid paradoxes if you built a whole network of them.