On Mon, Apr 14, 2008 at 10:24:12PM -0700, nichomachus wrote:
> Hi, Russell,
> Surely the framework of the Many Worlds interpretation would say that
> the likelyhood of measuring a quantum observable in state A rather
> than B reflects the number of histories in which the observable is
> measured as being in state A divided by number of histories in which
> either is seen. Molecules in a gas chamber may not be the best
> example, as I am personally unclear as to whether the macroscopic
> behavior of the aggregate is reduceable to probabilistic quantum
> events. But the point remains that it is impossible to adhere to the
> MWI without also affirming not only the existence of histories in
> which unlikely events happen, but also ones in which *only* unlikely
> events happen.

Absolutely - there are histories in which entropy decreases
continuously. This doesn't contradict the second law, because the
second law is probabilistic. Many, many more histories exist with
increasing entropy than decreasing entropy. The chance of an observer
observing continuous decrease in entropy is negligible, but small
exceptions to the second law can be observed in our world. IIRC, some guys
at ANU showed this a few years back, which got a bit of press,
although its not surprising when you understand what the second law
really is - I think it was Ken Baldwin's group, but you can try Google
for details.

> This includes universes where the cat never dies,
> uranium never decays, and (perhaps) the second law does not hold. Is
> it right to think that this is unproblematic? 


> Or perhaps we should
> regard the Many Worlds formalism as merely an instrumentalistic
> interpretation, similar to how Bohr and Heisenberg regarded their
> Copenhagen interpretation, rather than granting full ontological
> significance to alternate possible histories.

I take the Many Worlds as ontologically significant, unlike Bohr or Heisenberg.

> >
> > In any case, QTI does not change the observed outcome of likely versus
> > unlikely events, it just changes the set of possible outcome on which
> > to apply the second law.
> What does QTI stand for?

Quantum Theory of Immortality. What you are talking about with
Tegmark's suicide experiment.

> So our suicidal physicist would have enabled himself to observe the
> extremely scenario of seeing radioactive elements never decay, by
> killing himself in all histories where decay ocurred and thereby
> selecting only the ones where it did not take place to continue his
> awareness in.Of course, those branches of his identity would still
> have observed the same outcomes even if the gun was unloaded, so he
> doesn't really have to kill himself in nearly all universes in order
> to get to see it.
> But if I accept the above as true, then I must also accept that there
> are histories that have been experienced in which no atom of an
> unstable element has decayed since Jan. 1, 1900. (or any date you
> prefer)


> When Thomas Young performed his double slit experiment, were there any
> versions of himself that did not observe an interference pattern?

Probably. There were others where his apparatus blew up, or a cat peed
on a vital component and so on. 

> Why not?
> I appreciate the replies as I am more questions than answers at this
> point on these topics.


A/Prof Russell Standish                  Phone 0425 253119 (mobile)
UNSW SYDNEY 2052                         [EMAIL PROTECTED]
Australia                                http://www.hpcoders.com.au

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