Telegraph time machine

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,

An act of insubordination to the laws of nature

The numbers show the sci-fi time travel sequence and left-to-right shows the normal passage of time.

  1. The operator uses the telegram key to send a ‘dash’ pulse.
  2. The time machine sends it backwards in time down the telegraph wires.
  3. The signal passes along the wires, covering the same distance in the same amount of elapsed time as a regular “dash”.
  4. 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.
  5. 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.


7 thoughts on “Telegraph time machine

  1. I don’t understand why you think it violates the speed of light. Also my understanding always has been that the causative chain is in the other direction; that violating lightspeed has time travel as a required consequence.

    Also I have seen speculation from physicists, some of it fairly serious, that antimatter is matter travelling backward in time.


    1. I don’t think it does any more. My initial thinking was that for information to reach a destination BEFORE it had left is necessarily faster than the speed of light – the faster you got the smaller the time between departure and arrival, the speed of light prevents that time being zero and if you can’t get to zero then you can’t get to negative values either. However, this set up is a bit like the tachyon set-up, the information couldn’t travel beyond the negative speed of light (I


  2. Strictly speaking, short-term localized violations of conservation of energy happen all the time: that’s basically what virtual particles are in a quantum sense. That said, given delta t times delta E is less than Planck’s constant, that’s some pretty strong restrictions on how much energy you’re dealing with.

    Not to mention that time travel in general tends to play merry hell with the Second Law of Thermodynamics anyway…

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  3. Actually, there are ways in which something might be doable without even violating the first law of thermodynamics at all… have you ever seen how the original Cray computer worked, with Emitter-Coupled Logic? One of the tricks to the Cray, and why it worked as well as it did, was that none of the switches was every actually ‘off’ in the sense of having no power flowing through it; nor are they ever fully ‘on’ in the sense of saturated. Current is just switched from one path to a different path. The end result is that the system draws pretty much the same amount of power no matter what state it is currently in. (The downside, of course, is that this is a fair amount of power, which is why the cooling system was the most problematic part of the thing.)

    The right type of circuitry, where all states draw the same power, could potentially duck the conservation of energy issues. A receiver would just be a random state arrangement waiting to be filled in.


      1. Oh, even information going back in time is pretty much guaranteed to violate the Second Law of Thermodynamics (entropy), even if you do figure out ways to not violate the First (conservation of energy). The second is the one that really defines the ‘Arrow of Time’.

        There might be ways to avoid a direct violation of the Second Law (the Second Law being somewhat probabilistic in nature), but I think only at the expense of being unable to guarantee accurate reception of the signal. It would likely end up being the sort of ‘changing one random value into a different random value’ thing you get into with quantum entanglement, where you could only ever deduce the situation by analysis after the fact, and which would make it rather useless to actually send information.

        None of which makes it any less fun to think about. (And I just finished watching the anime adaptation of Steins;Gate with some friends yesterday. Send text messages back through time to yourself!)

        There’s the whole issue with the idea that ‘Hard SF’ is a bit of a moving target as the advance of science renders previously vague corners to do weird things in no longer available.


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