On 29/05/2017 3:33 pm, Pierz wrote:
Russell, do you believe that Schrödinger's cat is in a superposition
of dead and alive before we open the box?
That depends a little on your point of view. For the 'bird' view from
outside the wave function, all superpositions exist timelessly, so the
cat is both dead in one world and alive in another, but these worlds are
both part of the same universal wave function, so there is still a
superposition.
But in the 'frog' view from within, we only ever experience just one
branch, so the superposition has been reduced as far as we are
concerned. In fact, from our perspective, there is never a superposition
of live and dead cats because decoherence will have reduced the decayed
and non-decayed radioactive atom to separate worlds long before the
canister of cyanide is crushed. The cat is alive in one such world, and
dead in the other, and we, as decohered observers, are in one world or
the other, not in any superposition.
For the case of the colour of T. Rex, even if both red and yellow are
possible colours, the split between the worlds in which such different
evolutionary trees are possible would have occurred long before either
T. Rex or we appeared on the evolutionary stage. So again, no
superposition in any effective sense.
Bruce
On Monday, May 29, 2017 at 3:26:49 PM UTC+10, Bruce wrote:
On 29/05/2017 2:52 pm, Russell Standish wrote:
> On Mon, May 29, 2017 at 11:26:18AM +1000, Bruce Kellett wrote:
>> There is another question as to whether we are in a superposition,
>> of say red and green T.Rexes, but that they are in separate
>> decohered worlds and the overlap function is zero FAPP, as Russell
>> says. I don't think such a question has a definitive answer.
Despite
>> what some people say, viz., that in the QM MWI, everything that is
>> possible happens in some branch or other, I don't think that the
>> branches of the quantum tree necessarily pass through every
point in
>> the possibility space. Quantum evolution in the Everettian picture
>> is strictly deterministic, so if some apparently possible state of
>> affairs is not consistent with the initial conditions, then if
will
>> never appear anywhere. Given any particular imagined possibility,
>> one cannot say whether it occurs in some world or other, or in no
>> world whatsoever.
>>
> It is true that you have laid bare an unstated assumption - that
the
> two different coloured T. Rexes are compatible with the universe's
> initial conditions, as we know them. Obviously, if it possible to
> deduce the colour of T. Rexes from first principles without
making any
> further measurements, then we don't live in such a
superposition. But I
> still think that if it requires a measurement (no matter how
indirect)
> to determine the fact of colour, than we do live in a
superposition.
I don't think that follows. If the initial conditions are such
that only
red T. Rexes can evolve, it would still require a colour
measurement to
determine that colour. There would be no superposition of different
coloured T. Rexes, with or without any necessary measurement. The
point,
I think, is that colour, in the sense that we are using that concept
here, is really a classical property that does not necessarily
exist in
superpositions.
Bruce
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