# Re: PHYSICS/SPACE: Legitimate time travel proposal

Date: Sun May 20 2001 - 00:11:36 MDT

Lee Corbin wrote:
> One idea I had turns out (so I like to think) isomorphic to
> what David Deutsch suggests! First, DD wrote an article in
> Scientific American five or six years back that purported to
> describe how time travel would really work. You can't imagine
> my anticipation of reading that, only to be rather disappointed.
> It seemed that DD was saying that --- well, you know how anything
> can happen in the multiverse? E.g., your keyboard could suddenly
> turn into a brown rabbit, because there is a small amplitude in
> QM for just such a transformation? --- he was saying, or so it
> seemed to to me, that the appearance of a time traveler from
> the future was exactly such a miraculous transformation. How
> dull.

impossible, the probability of events that would thwart paradox
creation get bumped up in proportion to the probability of the paradox
suceeding. (Or: normally, malfunction A has a 1% chance, malfunction B
has a 3% chance, and success has the remaining 96% chance. But if
success would create a paradox, success automatically has 0%, thus A
has 25% and B has 75%.)

> But here was my idea from many years ago: suppose (to make
> the paradox simpler) we have a Contrarian. This person will
> always say "Yes" if he is supposed to say "No" and vice-verse.
> The Contrarian receives information from the future that he
> is about to say "Yes", so naturally he says "No". Well, then
> after he writes down his answer somewhere, and some time travel
> apparatus gets hold of it, it's now the "No" answer that flies
> backwards in time. This time, the past Contrarian is presented
> with the "He said No" information, and so says "Yes". Then,
> later, when **his** information is written down and then used
> by the time travel apparatus, the cycle repeats.

Unless his information gets mistranscribed, or the wrong (or an
illegible) message gets sent, et cetera.

> But so far as I can make out, this is what David Deutsch is
> in effect saying. If you "go back in time" you are going to
> a different branch of the multiverse, that's all. (The
> multiverse is a continuum, so it would lack my finite recursion
> property that I used for illustration above, but that isn't
> essential.)

It has been hypothesized that, just as particles can only have
multiples of certain quanta of energy, particles can only move in
multiples of certain distances - essentially a universe of voxels, with
resolution far smaller than can be measured by any instrument we have
yet devised. If this turns out to be correct, it would imply that any
real continuum is made up of discreet elements, and thus can do finite
(or countably infinite) recursion as you described.

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