On 1/9/2014 4:19 PM, Jesse Mazer wrote:
On Tue, Jan 7, 2014 at 7:57 PM, LizR <lizj...@gmail.com
<mailto:lizj...@gmail.com>> wrote:
On 8 January 2014 12:53, Jesse Mazer <laserma...@gmail.com
<mailto:laserma...@gmail.com>> wrote:
On Tue, Jan 7, 2014 at 4:35 PM, LizR <lizj...@gmail.com
<mailto:lizj...@gmail.com>> wrote:
On 8 January 2014 08:59, Jesse Mazer <laserma...@gmail.com
<mailto:laserma...@gmail.com>> wrote:
Well, most physicists already agrees physics is time-symmetric
(well,
CPT-symmetric, but the implications are the same for Bell's
inequality
and thermodynamics),
Yes, they do, but it doesn't appear to be taken into account when
discussing
Bell's inequality.
but I don't see how this alone can explain violations of the
Bell
inequality.
No, you need to work out the consequences mathematically, and I
dare say
that is quite difficult. This is simply a /logical/ demonstration
that
Bell's inequality can be violated while retaining locality and
realism,
which is otherwise impossible.
As I said in another comment, if you allow information about the state
of
complex systems like detectors to flow back in times as well as
forwards, it's
not clear that this really counts as preserving locality.
Nothing is flowing either way in time. (Assuming a block universe, nothing
/can/
flow in time - the notion doesn't make sense).
I think you're reading something into my talk about information "flowing back in time"
that I didn't intend. I certainly didn't mean to deny the block universe view of time or
suggest that an imaginary observer viewing all of spacetime "from the outside" (like we
might observe 2D flatland) would see spacetime itself "changing" (as opposed to just a
set of frozen worldines as one would expect in a block universe). But the notion of
information flowing from one point in spacetime to another doesn't imply any such denial
of the block universe, for example David Deutsch, who argues forcefully for the block
universe view in his book "The Fabric of Reality", wrote a paper at
http://arxiv.org/abs/quant-ph/9906007 titled "Information Flow in Entangled Quantum
Systems". The notion of information flow just requires some type of logical ordering,
with one point in spacetime being the event of the information first being "transmitted"
and another point being the event of it being "received".
There might be no way to define transmission vs. reception of a message at a fundamental
quantum level, but if we're dealing with macroscopic transmitters and receivers of some
kind that have a local thermodynamic arrow of time, there shouldn't be a problem
distinguishing them...for instance, the transmitter has to *first* compose the message
(perhaps after observing some local event, like the outcome of an election, that the
message is supposed to convey information about) and *then* transmit it, relative to the
local thermodynamic arrow of time, while the receiver *first* has a sequence of bits
come in which are *then* made sense of. So as long as we can locally define transmission
vs. reception in this way, my talk of information flowing backward in time just means
that the reception-event is on the past light cone of the transmission-event, and
information flowing forward would just be the ordinary case of the reception-event being
on the future light-cone of the transmission event. The point is that if both sorts of
information-transmission are possible, then I should be able to transmit a message back
to be received by a relay, then the relay can transmit a copy of the message forward to
a friend light-years away from Earth, such that the friend receives the message on the
same day I sent it (relative to our mutual rest frame), despite being light-years away.
It's not obvious that a universe where such things were possible would really count as
one that respects "locality", even if each individual message travelled at the speed of
light.
I don't think that follows. You're imagining yourself moving forward in cosmic entropic
time and composing a message that you're going to transmit back in time. But that's
inconsistent. What T-symmetry implies is that there is a message whose receipt by you
entails that the transmitter in the past who sent it to you also had to send that message
to your friend. In a block universe picture is just requires a certain consistency
between the messages at the transmitter, you, and your friend. In EPR we're just sending
a few particles one-at-a-time. They have to look random to you, which means the "message"
you're sending to your friend is random.
Of course for this to work there has to be determinism - it would look like this in a
Newtonian universe - MWI is in principle deterministic but T-symmetry means reversing all
the "worlds" whereas outside of some exotic laboratory situations we only have access to one.
Locality is preserved so long as no physical objects travel faster than
light.
I don't think physicists use such a narrow definition--if the equations of QM were
modified so that the EPR experiment could be used to transmit *information* FTL, then
even if no measurable particle or wave was observed to move FTL this would still
probably be seen as a violation of locality. And the pilot wave in Bohmian mechanics is
arguably just a sort of rule for coordinating the behavior of distant particles rather
than a "physical object", but its ability to coordinate them instantaneously is
typically seen as a violation of locality. Unfortunately I have not been able to find
any very precise definition of locality that would give a totally clear answer about
cases like this, it tends to be stated in terms of imprecise terms like "effects" and
"influences".
Think of it in terms of Feynman's path integrals. The path can go from the source to you,
back to the source, to your friend, back to the source,...and a lot of other places. But
it only reenforces positively along a few paths and those are the ones that show up in one
block of the multiverse.
Brent
Jesse
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