On Wed, Jan 1, 2014 at 4:33 AM, LizR <lizj...@gmail.com> wrote:
> On 1 January 2014 21:34, meekerdb <meeke...@verizon.net> wrote:
>> On 12/31/2013 7:22 PM, LizR wrote:
>> On 1 January 2014 13:54, meekerdb <meeke...@verizon.net> wrote:
>>> Of course in Hilbert space there's no FTL because the system is just
>>> one point and when a measurement is performed it projects the system ray
>>> onto a mixture of subspaces; spacetime coordinates are just some labels.
>> I thought there was no FTL in ordinary space, either? (I mean, none
>> required for the MWI?)
>> Right, but the state in Hilbert space is something like |x1 y1 z1 s1 x2
>> y2 z2 s2> and when Alice measures s1 at (x1 y1 z1) then s2 is correlated at
>> (x2 y2 z2). As I understand it the MWI advocates say this isn't FTL
>> because this is just selecting out one of infinitely many results |s1 s2>.
>> But the 'selection' has to pair up the spins in a way that violates Bell's
> If I understand correctly ... actually, let me just check if I do, before
> I go any further, in case I'm talking out my arse. Which wouldn't be the
> first time.
> I assume we're talking about an EPR correlation here?
> If yes, I've never understood how the MWI explains this.
The thing to remember is entanglement is the same thing as measurement.
The entangled pair of particles have measured each other, but they remain
isolated from the rest of the environment (and thus in a superposition, of
say UD and DU). Once you as an observer measure either of the two
particles, you have by extension measured both of them, since the position,
which you measured has already measured the electron, and now you are
entangled in their superposition.
> I've see it explained with ASCII diagrams by Bill Taylor on the FOAR
> forum, and far be it from me to quibble with Bill, but it never made sense
> to me. Somehow, the various branches just join up correctly...
> The only explanation I've come across that I really understand for EPR,
> and that doesn't violate locality etc is the time symmetry one, where all
> influences travel along the light cone, but are allowed to go either way in
> So although I quite like the MWI because of its ontological implications,
> this is one point on which I am agnostic, because I don't understand the
>> In fact, it's generally assumed to be very, very STL (unless light
>>> itself is involved). At great distances from the laboratory, one imagines
>>> that the superposition caused by whatever we might do to cats in boxes
>>> would decay to the level of noise, and fail to spread any further.
>>> That's an interesting viewpoint - but it's taking spacetime instead of
>>> Hilbert space to be the arena. If we take the cat, either alive or dead,
>>> and shoot it off into space then, as a signal, it won't fall off as 1/r^2.
>>> No, but it will travel STL!
>> Sure. I was just commenting on the idea that the entanglement has a kind
>> of limited range because of 'background noise'. An interesting idea,
>> similar to one I've had that there is a smallest non-zero probability.
>> But if you want to get FTL, that's possible if Alice and Bob are near
>> opposite sides of our Hubble sphere when they do their measurements. They
>> are then already moving apart faster than c and will never be able to
>> communicate - with each other, but we, in the middle will eventually
>> receive reports from them so that we can confirm the violation of Bell's
> Hmm, that's a good point. That would, however, fit in nicely with time
> symmetry (which really needs a nice acronym, I'm not sure "TS" cuts it). I
> tend to evangelise a bit on time symmetry, but only because everyone else
> roundly ignores it, and it seems to me that it at least has potential.
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