On 29/05/2017 6:26 pm, Telmo Menezes wrote:
On Mon, May 29, 2017 at 3:26 AM, Bruce Kellett
<bhkell...@optusnet.com.au> wrote:
On 29/05/2017 9:45 am, Pierz wrote:
WRT to this whole multi-coloured T-Rex business, there is a simpler point to
be made. My original argument was in favour of MWI. Now whether, in MWI,
macroscopic histories can merge is surely an interesting puzzle. But without
MWI, there cannot be any ambiguity about the colour of T-Rexes. In a single
universe interpretation of QM, T-Rexes were blue or they were red and they
can't exist in a superposition of both. The past can't turn back into a mush
of probabilities, because that would imply either that there is some "3p"
significance to the concept of "now", or that the past consists of many
worlds. In other words I am asserting that, sans MWI, any ambiguity about
the past is a matter of ignorance, not of quantum uncertainty. Otherwise you
are saying that past moments which once were well defined are somehow
dissolved back into ambiguity by the passage of time. But that would be
privileging the now with some kind of absolute significance, which is
untenable. All nows are equal.
Another way of stating my argument is that the following three propositions
are mutually incompatible:
There is a single history
There is no objective significance to the concept of the current moment
("now")
The future is objectively uncertain
You can take your pick which of those propositions you reject, but it's
logically impossible to support all three.
I would say that there is only one history leading to our present state.
Whether you take an MWI view or a collapse view, the wave function branches
deterministically at every point, so if you follow your current twig back
down to the main trunk etc, there will be a unique path.
I don't think we can say we are in a specific twig. Many things about
out present state are unknown/undefined. I can imagine that there are
many well-defined present states that are compatible with my current
subjective state.
Sure, but we are talking about wave functions, not subjective states.
In fact you can perform a quantum erasure experiment, and be sure that
your current state goes through at least two different shortest paths
to the root, and it becomes nonsensical to say that one is the
"correct" one. I don't think anyone knows how far this can go into the
macroscopic world, but I don't see any reason to believe that it
doesn't.
I don't understand what you think you are getting in a quantum erasure
experiment. If the "which way" information that was gathered is erased,
normal interference patterns are seen in the double slit situation. The
two paths (through the separate slits) are in unresolved superposition
until they hit the detector, when decoherence takes over. There are not
two separate worlds, and your state is the result of the superposed
paths, not of either path separately. There is no ambiguity about which
the the "correct" path -- neither is, both contribute equally.
Bruce
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