This is a follow up to yesterday’s post about digital time travel, My initial thought as to why it wouldn’t actually work was that it violates the speed of light. However, I’m less sure of that and now think conservation of energy would be the more obvious problem. Obviously its all messed up as far as causality goes but that’s inherent in any time travel device.
To simplify matters, I’ve reduced the scenario to simply a backwards telegraph sending a single Morse code like ‘dash’ a short distance back in time to another telegraph station,
The numbers show the sci-fi time travel sequence and left-to-right shows the normal passage of time.
- The operator uses the telegram key to send a ‘dash’ pulse.
- The time machine sends it backwards in time down the telegraph wires.
- The signal passes along the wires, covering the same distance in the same amount of elapsed time as a regular “dash”.
- The other telegraph signal “receives” the signal. However, to an observer, it will look like the “dash” originated at the past telegram office and is being sent regularly down the wires. They key hasn’t moved but it will look like it made the dash.
- I’ve got the dash appearing on a ticker tape but that would only happen if the telegram office printed out the telegrams they SEND rather than just the ones they recieved.
Because the signal is traveling both backwards in time and backwards in space (so to speak), it actually looks physically conventional. The whole thing looks like a signal going from the past telegram officer to the future telegram office if we just look at the signal going down the wires.
The freaky bit is that the past telegram office appears to send a “dash” without anybody pressing the key. The electricity appears from nowhere! Meanwhile, the future telegram office produces an electrical pulse that to a regular observer just disappears. Those no net gain in energy overall, so you couldn’t build a perpetual motion machine but there is a short term localized violation of the conservation of energy.