# Spacetime Physics: teleportation to Andromeda

1. Sep 12, 2010

### Animastryfe

1. The problem statement, all variables and given/known data
Paraphrase: A Transporter can reduce a person to data and transmits the data by light or radio signal to another location. A person is beamed from Earth to the planet Zircon orbiting a star in the Andromeda Nebula, two million light-years from Earth. Neglect any relative motion between Earth and Zircon, and assume : (1) transmission produces the person identical to the original in every respect except that he/she has traveled two million light-years and (2) the time required for disassembling and assembling the person is negligible as measured in the common rest frame of the Transporter and Receiver.

a. How much does the person age during her outward trip to Zircon?
b. The person spends one Earth-year on Zircon, then beams back to Earth. How much has the person aged during her entire trip?

2. Relevant equations
Interval^2=(ct)^2 - (s)^2

3. The attempt at a solution

The question's wording seems too vague and confusing to me. Am I supposed to assume that the first part of the question, "how much has the person aged during the outward trip", wants me to find the time elapsed from the beamed person's (or her data's) reference frame? If the person is moving at c, then wouldn't that be 0, as the Lorentz interval is 0? If so, then the answer to the second part of the question would be 'one Earth year', as the entire trip from the frame of the person being transported would be just one Earth year, correct?

This is question 1-10 from the second edition of Spacetime Physics by Taylor and Wheeler.

2. Sep 12, 2010

### diazona

I have to agree with you, something seems fishy about this question. But your reasoning mostly makes sense. Given that the data is transmitted by radio or light waves, it will travel at speed c, and for something traveling at the speed of light there is no notion of time. Photons do not age. (As you know)

Even if the data were transmitted at sublight speed, though, I think there would still be something fishy about the question, because although the particles transmitting the data would age, the data itself would not change en route. Since the biological age of the person being teleported is a function of the transmitted data, he/she would be the same age before and after the teleportation. (Also since the problem says the reassembled person is identical to the original: that must mean the reassembled person is the same age as the original.)

P.S. One technicality I'll mention: something moving at the speed of light does not have a reference frame (a.k.a. rest frame), because it can never be brought to rest.

3. Sep 12, 2010

### Animastryfe

Ah, I did not know that. My special relativity course has just started, so I assume we'll get to that in due course. I shall ask my professor about this question next week.

Thank you for the response.