On 15 Jun 2017, at 06:59, Bruce Kellett wrote:
On Wednesday, June 14, 2017 at 10:19:56 AM UTC+10, Brent wrote
6/13/2017 4:11 AM, Telmo Menezes wrote:
> The reason why it would follow is precisely the point of my
rhetorical
> question above. If you take the wave function seriously, then you
take
> seriously that qubits really do exist in a superposition of states,
> and this explains the exponential increase in computational power as
> you add qubits to the systems in certain configurations. I guess you
> can accept superposition and deny many worlds, but I would say
that it
> is quite an awkward move.
Being in a superposition is just a matter choosing the basis. If
it's a
pure state then there's some basis in which it is not a superposition.
And if it's not in a superposition, then you can choose another
basis in
which it is.
The basis problem is always going to defeat naive accounts of many
worlds.
OK.
That is why most people now see decoherence as central, since that
can give a principle reason for basis selection: the preferred basis
is that which is stable against environmental decoherence.
That was already well explained in Everett's long text. But the
preferred basis is only preferred relatively to a entity/machine. The
big picture does not need to choose a special base. That is proven in
Everett. He insisted that this makes the notion of subsystem into a
relative notion.
Separate worlds can only form after irreversible decoherence.
The decoherence itself is reversible in QM-without collapse, and it
can even been done, theoretically, by memory erasing/discarding. Of
course, to have a decent subjective life for some period, it is better
(FAPP) to consider the decoherence irreversible. Yet, to avoid
conceptual paradoxes, we need to realize that, without collapse, the
decoherence is always a local happening and is *in principle
reversible* in the big picture. The entire universe (assuming this
makes some sense) cannot be subjected to decoherence, as you cannot
leak outside the universe, by definition of "universe".
Bruno
Bruce
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