Re: Time Machines, FTL, and P=NP

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.

In other words, your machine outputs "12345" or it outputs "54321" and 
this causes you to act differently and gives you a different outcome. But 
this isn't going to influence a cosmic ray, and you're not going to end up

in a future where the woman of your dreams materializes in front of you 
due to spontaneous quantum tunneling of CHON and trace elements out of 
your walls and the contents of your refrigerator. Unless outputting a 
different value is somehow the deciding factor in this event.

You made me realize that I've been assuming a deterministic universe. In 
other words, if you start with identical conditions you'll get identical 
conditions at every point in time afterwards. But this doesn't have to be 
true, and in fact I believe that current physics assumes that it's not. 
Quantum events are inherently probabilistic and this is real 
can't-know-ahead-of-time randomness, not just can't-be-predicted 
randomness. Is there anything in known physics which is *incompatible* 
with a deterministic universe, rather than just not requiring one? Anyway,

if physics really is probabilistic then this whole idea will fail for any 
problems where such effects influence the outcome. You'll be able to crack

that lock but may not be able to bed that woman if the low-level quantum 
noise ends up changing conditions in the brain enough to cause a different

result. I guess you would have your free will in that case.

> [...]
>> Pretend for a moment that we're not talking about time
>> machines, but instead about faeries. The discussion is
>> based around the question of what we could do if faeries
>> exist. Could we build faerie-powered starships?
>> Faerie-powered lockpicks? What design would you use to
>> construct a 200 mile-per-gallon faerie-catalyzed Cadillac?
>> 
>> It may be fun speculation but from a scientific standpoint
>> it's all garbage. The term isn't defined well enough to
>> discuss it in any context other than fun.
>> 
>> Thus it is with causality, I think. Fundamentally it's
>> outside our understanding, so discussion of the consequences
>> is necessarily non-scientific.
> 
> Sorry, I don't see causality as fundamentally outside our
> understanding. I understand that talk using the word
> "causality" and its cousins has been frowned upon for much of
> the twentieth century, but it looks to me as though the
> actual use of the ideas never went away.
> 
> There has been some very good work in dealing with causality.
> Judea Pearl's home page, highly respect researcher in this area
> http://bayes.cs.ucla.edu/jp_home.html
> A couple of "gentle intruductions"
> http://singapore.cs.ucla.edu/LECTURE/lecture_sec1.htm
> http://singapore.cs.ucla.edu/IJCAI99/index.html
> 
> I understand that there is some controversy to the idea that
> everything we need about causality can be modeled by Bayesian
> nets, but the argument that there is something uncapturable
> about causality reminds me too much of all the arguments
> that /consciousness/ has something uncapturable.
>
http://www.uni-konstanz.de/FuF/Philo/Philosophie/Spohn/preprints/pdf/PS62-Spohn.pdf
> Bayesian Nets Are All There Is To Causal Dependence

You're right, that was a very bad analogy, because removing causality 
isn't adding faeries, it's.... removing them. Which doesn't work, because 
we don't have them.

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.

-- 
Michael Ash
Rogue Amoeba Software