Re: Time Machines, FTL, and P=NP

On Feb 22, 3:45 pm, George W Harris <ghar...@[EMAIL PROTECTED]
> wrote:
> On Fri, 22 Feb 2008 13:44:40 -0500, James Burns <burns...@[EMAIL PROTECTED]
>
> wrote:
>
> :But then, without the wackiness to force consistency in highly
> :unlikely ways, it looks to me not too hard to set up a situation
> :where /no/ possible outcome is consistent. For my simple example,
> :just put the received signal through a NOT gate before sending
> :it back in time. What happens in that case? Hard reboot on the
> :universe?
>
>         Mechanical failure of the time machine, or some
> other break in the chain.

Some further elaboration on that point- what an oracle does is
essentially just manipulate probabilities. There's some (presumably
infinite, but possibly not) set of things that could happen, all with
different probabilities, which all sum up to 1 (i.e., *something* will
happen). Using the oracle allows you to take action which makes the
probability of certain outcomes become 0, which then correspondingly
scales up the probabilities of everything that's left. Seeing as how
just having an oracle does not automatically make you completely
omnipotent, however, there will be things that you cannot control; it
is always possible that, even though you have the information
necessary to plan actions that make certain results impossible, you
may fail in the attempt to carry out those plans, in which case the
oracle does you no good. Since the summed probabilities of all
potential futures must be 1 (because *something* will happen), that
means you already have a zero probability of taking actions that make
all futures inconsistent (i.e., set the probability of all potential
futures to zero). Therefore, if you try to do so, no matter how
incredibly improbable the thing that must happen to cause you to fail
would otherwise be, that set of events has suddenly been promoted to
100% probability (because you eliminated everything else), and so you
*will* fail in some way, and the universe remains consistent.
Mechanical failure in the time machine, quantum-magical
destabilization of the causal loop, you simply happening to forget to
send the back-time message, etc.

-l.