Re: Time Machines, FTL, and P=NP

Michael Ash wrote:
> James Burns <burns.87@[EMAIL PROTECTED]
> wrote:
> 
>>I think we're in agreement on a lot here, although I
>>don't think of using the causal loop as "bending their mind"
>>I think of it as selecting one of the the vanishingly
>>rare futures in which she would have changed her mind
>>on her own. Probably just a difference in terminology,
>>but let me point out that your way of putting things
>>implies some sort of influence flowing from me to her
>>that will just not be found, if looked for.
> 
> The key thing to remember here is that you aren't selecting
> from all available futures. You're only selecting between
> futures differentiated by what your machine outputs.

Whether that's true depends on the details of the implementation
of the causal loop.

I think I see how if, for example, one bit were sent back
one second, then the bit could only distinguish between
two universes. I can see how a lot of wackiness could be
avoided under this view of what's going on, because
(extending my horse race analogy) only one horse can be
shot, so whatever's left will be relative high in probability
and non-wacky.

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?

The view I'm more comfortable with is that, even though the signal
sent back in time may be interpreted by us as a digital signal,
it really is an analog signal. ("All signals are analog signals.")

I understand that there is no apparent reasonable connection between
some woman's frame of mind and the 17th decimal place in a voltage
in a detector receiving a signal from the future. But that is
looking at things the boring, every-day, non-wacky way. Limiting
ourselves to consequences that flow in the usual way from a message
from the future will leave us sometimes having to do a hard reboot on
the universe, even if we include the analog nature of the signal received.

I will go out on a limb some at this point (yes, even compared to
the rest of my argument). Recent work in quantum entanglement and
such stuff seems show a universe in which in influences can flow from
one point to another without regard to what we see as the usual
rules of behavior, breaking speed of light limits, even temporal
order. It's true that these influences are not the sort of thing
we can use under normal conditions, but causal loops are not normal.
Perhaps the quantum connectedness combined with the extra
consistency conditions that a causal loop would require would
be able to "bend minds."

I'd really like a time machine, if only to test out this aspect of
my ideas re time machines.

Another possibility is that the problem is avoided by there
not being any causal loops. It is, I have to admit, a reasonable
solution, if a bit boring.


> So, imagine a conversation in which we discuss how the universe
> would look if your favorite fundamental force were to go away.
> Let's say electromagnetism. We can discuss it to a certain
> extent, theorizing about what the equivalent of atoms might be,
> and the nature of the universe in such a scenario, much like we
> can discuss very low-level events in a universe with no
> causality. But then try to scale it up and figure out how many
> legs the life in this universe will have, you just can't get
> there, not even close. Likewise, we can't really discuss much
> beyond particle physics in a universe with no causality. Any
> discussion of humans in such a universe is either raw speculation
> (as I've been doing) or philosophy, not science.

Okay. I haven't really been considering what I've been doing
science, although that's a very fuzzy line. I don't have a
problem with calling it either raw speculation or philosophy.

I don't think your analogy here captures the situation very
well, though. The problem with thinking of a universe without
electromagnetism is filling in the scads of details, such as
how many legs to expect. We're taking a universe with all the
details filled in, this universe, and adding one more thing
to it: causal loops.

I will grant you that there are questions about causal loops
very hard or impossible to answer without a real world
example to examine. The nature of causality itself is one
I would put at the top of the list.

(But, how will we ever create a causal loop until
we already understand causality itself?)

Jim Burns