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I was looking at the Wikipedia entries on Time Travel and the Grandfather paradox and noticed a paragraph on the so-called Huggins Displacement Theory. I haven't been able to find the source although I assume it's originator was the Victorian astronomer Sir William Huggins. Does anyone know of the precise reference?

Normally sending information into one's past can lead to contradictions. For example based on some condition now I could send a message into my past that prevents that very condition from occurring in my present. Thus sending information into the past, and therefore arbitrarily changing it, seems to be forbidden physically.

However the Huggins Displacement Theory says that there is a loop-hole in this argument (or more accurately a "corner case"!) I could send information along my past lightcone so that if I influence something a year in my past then it must be a light-year away from me. Thus no change in the past has a enough time to travel back to me to cause a contradiction in my present.

For example imagine that I see a stock price going up today. The Huggins Theory says that I can beam knowledge of this stock price rise back in time provided that the message is also displaced by a comparable distance. Thus if I send it back a year in time then it must also travel away from me by a light-year in distance. If my twin gets the message then he might try to profit from the information by sending back a message to me to buy the stock. Unfortunately the message will only get back to me at the instant that the price rises so that neither myself nor my twin will be able to profit from this situation.

Maybe physics does allow information to be sent back in time along a past lightcone so that this effect could be measured. My hunch is that perhaps if one charged up an electrode then electrostatic influences from it might travel back along its lightcone to cause measureable repulsion or attraction on distant electrodes.

I don't think electromagnetic radiation itself could go backwards in time as in principle it could be reflected back onto an observer's past worldline and therefore trigger contradictions in his/her present.

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What is your question? Just the request for the reference? –  user27578 Mar 6 at 1:55
    
I guess so. I'm also interested in what people think of the Huggins Theory. Is there a better forum to introduce a discussion topic? –  John Eastmond Mar 6 at 8:32
    
This doesn't seem to work, for the following reason: the theory says I can send a message back in time one year to you, one light-year away. But you can then relay the message back to me one year ago (and one light-year away) as well. That means I receive the message two years before I sent it, leading to grandfather-type paradoxes. –  Nathaniel Mar 6 at 8:36
    
Huw Price writes about a different loop-hole in his 1996 book "Time's Arrow and Archimedes' Point". Price's loophole is that it's OK to change the past as long as there's no way that change in the past can be measured. He proposes this as an explanation for entanglement in quantum mechanics: in Price's interpretation, a causal influences doesn't travel faster than light between the two particles, but instead travels back in time to the point when the particles were in contact, and then forward again to the time when the other particle is measured. I've always thought that was pretty neat. –  Nathaniel Mar 6 at 8:40
    
Unfortunately this question will be closed. Questions that only ask for discussion are against the rules here. But it's an interesting topic, and if you can come up with some specific questions about it I hope they will be welcome. –  Nathaniel Mar 6 at 8:41

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