Relativity in Ender's Game

[ChromePony]

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This is partly science fiction, and definitely goes against the theory of relativity, but there is also a point where relativity breaks down. Quantum mechanics predicts that there are things which "travel" faster than light.


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This is partially true if youre talking about quantum teleportation, but unlike it sounds there is actually no way for any information to travel faster than light. If you separate particles that have are quantum entanlged then it is true that a measurement on one with instantaneously affect the results of a measurement on the other no matter how far away it is. However, in order to convey useful information you need to know the states of each particle and this can only be shared classically and such classical information is limited by the speed of light.

Of course without this fancy communication thing Card's plots would have completely broken down and the books wouldnt be nearly as entertaining, so Im alright with granting him a freebie here.

[Requin]

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No. Radio waves always travel at the same speed.

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I don't know the exact physics of it, but anything on your ship must be travelling in the direction that your ship is traveling. You want to send it back to earth. So clearly you must chance its current velocity. The fact that light always travels at the same speed makes this hard to explain, but trust me whatever you use to send information must undergo acceleration.

[Sharkey]

What precisely do you think is changing velocity, and in which frame of reference?

[bunny]

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A different version of the Twin Paradox:

1. The twins begin at rest on Earth.
2. They embark on separate voyages which are identical except in opposite directions.
3. Both voyages include accelerating to near the speed of light from the point of view of Earth.
4. They meet again back on Earth.
5. They compare ages.

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They are the same age - as they recede from each other they witness their twin's clock running slow. At the furthest point of separation each of them thinks they are older than their twin. They then turn around and speed back together - here it seems their twin's clock is running faster than their own and they "catch up". When they return to Earth they will be the same age.

[Sharkey]

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They then turn around and speed back together - here it seems their twin's clock is running faster than their own and they "catch up".

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Caused by what specific physical phenomenon?

(If that’s not an impolite question.)

[bunny]

It's a consequence of the speed of light being constant for all observers.

[Sharkey]

Clarify something if you would. Do you mean time dilation is dependent on relative direction? If that is the case, then how can several observers positioned all around a linear accelerator observe the same lengthening of lifespan for an unstable relativistic particle?

[bunny]

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Clarify something if you would. Do you mean time dilation is dependent on relative direction? If that is the case, then how can several observers positioned all around a linear accelerator observe the same lengthening of lifespan for an unstable relativistic particle?

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Dont they observe it using the same instruments at rest in the accelerator? I havent thought about this and dont know the answer, hopefully metric/borodog or someone clever will stick their nose in soon...

In the twins example it doesnt seem a problem to me as the spacetravellers have heaps of photons all "banked up" waiting to hit them as they speed back to earth, the only way I can understand this is that they see time running faster on the other ship (as they have to observe the light moving at constant speed).

Edit: I guess I am claiming time dilation is dependant on relative direction but I dont know if perhaps the solution isnt actually the periods of acceleration...it's been too long since relativity courses I'm afraid. I'll have to withdraw from answering. [img]/images/graemlins/confused.gif[/img]