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First let's look at the classic Clauser-Aspect experiment. Too simple
for a complex signal.
The photons were in a maximally entangled spin triplet
http://www.roxanne.org/epr/aspect2.gif
http://www.roxanne.org/epr/qmS.html
http://www.roxanne.org/epr/eprS.html
Bottom line, although you can code a message S(t) in the nonlocal
correlation relative phase (mutual orientation at times of passage) ~
cos^2(2Theta(t)) that can be detected in hindsight by comparing data
from both ends via classical retarded at most luminal signals you cannot
decode the signal locally because the local detection probabilities ~
1/2 (ideally) independent of the orientation of the sender at one end
that codes the message.
Now, the idea behind Cramer's experiment is that there is some complete
set of spatial transverse modes fk(x,y t) along line of flight z where,
each photon pair is maximally entangled as, to a good approximation,
Psi(1,2) ~ Sum over k fk+(x,y,t)fk-(x'y't')e^iEk(t - t')
Where fk+(x,y,t)and fk-(x'y't') have the same shape in their respective
transverse planar coordinates.
Now, what the "stencil"
http://qedcorp.com/APS/URstencil.jpg
Does on the time delayed future (b) sender photon is to MODE SELECT or
filter a set of the initial modes into the UR shape, for example as
above. This means the wave function collapses to a new state
Psi(1,2)' ~ Sum over k A(k)kfk+(x,y,t)fk-(x'y't')e^iEk(t - t')
With the set of filter coefficients {A(k)} encoding the shape of the UR
stencil above.
This is a completely different kind of measurement than previous
experiments.
The intuitive idea then is that the stencil inserted in the future by
Wheeler delayed choice will be shadowed or imaged in the past for the
twin photon. This is essentially the idea in Cramer's mind I suspect.
That is, the retroactive nonlocal signal image is essentially the set {A(k)}
One then has to assume that the amplification at the past receiver
photon can be done faithfully with a sufficiently good signal to noise
ratio to clone a large number of photons with the same {A(k)} pattern
without violating the no-cloning theorem.
Note what is seen at the receiver (x,y) image plane is the nonlocal
signal set
{|A(k)|^2}
because we need to integrate the orthogonal modes over the entire source
(x'y') plane.
Note, we can encode more info using scale-dependent wavelets.
The effective "amplification" is to use intense enough entangled very
short laser pulses so that a large enough number of pairs are detected
in each short burst to get enough statistics to see something.
Begin forwarded message:
From: Jack Sarfatti <sarfatti@pacbell.net>
Date: January 22, 2007 7:54:49 PM PST
To: Sarfatti_Physics_Seminars <Sarfatti_Physics_Seminars@yahoogroups.com>
Subject: Re: Cramer's Upcoming Retrocausality Experiment Back From The
Future - new twist
On Jan 22, 2007, at 9:31 AM, Jack Sarfatti wrote:
Ah, yes, here it is.
Begin forwarded message:
From: ANTIGRAY@cs.com
Date: January 21, 2007 10:14:26 PM PST
To: marssouthpolereturns@yahoogroups.com
Cc: sarfatti@pacbell.net
Subject: Researchers condense entire image into single photon
Researchers condense entire image into single photon?
OK the photon quantum field operators are a sum over "modes" fk(x,y,z,t)
i.e.
A = Sum over k [fk(x,y,z,t)a + fk*(x,y,z,t)a*]
where a and a* destroy and create a photon respectively
aa* - a*a = 1
The mode function need not be small. It can be quite large! Indeed the
surviving mode function can be shaped by a "stencil" so that the
"message" would be that filtered mode function
fk(x,y,z,t) = http://qedcorp.com/APS/URstencil.jpg
Thus, the single mode "message" pattern can be large in space and last
in time for a significant duration - it's that the energy in the single
photon is tiny and one needs to amplify that energy with a laser in such
a way that the modal shape is not distorted since the "nonlocal signal"
or "message" is in the shape of the single future filtered mode. The
point of all this is that we should not need to use hindsight in after
the fact time correlations between future sender and past receiver. The
conventional wisdom of "signal locality" is that this is impossible in
orthodox quantum physics.
The issue then is:
Can we shape this "UR" mode function with the "future" delayed (6.2
miles of coiled fiber optic cable) sender photon passing through the
stencil and will that act back in time to select that same "UR" mode
function in the past in the twin entangled receiver photon even before
the choice is made in the future of what "stencil" message to insert in
the future?
http://qedcorp.com/APS/in_laser_1.jpg
If we can do that, then can we amplify that stencil image in the past
receiver photon with a good enough signal to noise ratio and not violate
the no cloning theorem at the receiver?
Then, if we succeed in the above, what happens when we attempt to make
an autocidal time travel paradox? What prevents the loop from being
disturbed?
Posted Jan 21st 2007 4:06AM by Conrad Quilty-Harper
Filed under: Storage A team of researchers has managed to find a way to
store a large amount of data in a single photon of light. Although the
first stored item -- an image of the characters "UR" -- implies that the
inventor was a 13 year old girl dealing with an extremely low text
messaging limit, the image was in fact intended to signify the
institution which developed the technology, the University of Rochester
(either that or it's the shortest example of the "UR IN MY ... " meme
that we've seen in the while.) Apparently the system works because
"instead of storing ones and zeros" (a la binary code), the team has
figured out how to store an entire image in a single photon, which
sounds sort of impossible to us. Funny, because that's exactly what John
Howell, the leader of the team said about the system. One of the key
components of the process is the particle-wave duality nature of light:
by firing a single photon of light through a stencil -- we presume one
heckuva small one -- the wave carries a shadow of the image along with
it at a very high signal-to-noise ratio, even with low light levels. The
light is then slowed down in a cell of cesium gas, where it is
compressed to 1 percent of its original length. This is where the
storage aspect of the device comes in, as the researchers hope to be
able to delay a single photon almost permanently, resulting in a device
that can store "incredible amounts of information in just a few
photons": an enticing thought for a world currently satisfied with a
maximum of 1TB hard drives based on physical platters. A pity then that
the world is completely distracted by the potential for "Photon on
photons" jokes that this throws into the ring.
http://hdtv.engadget.com/2007/01/21/researchers-condense-entire-image-into-single-photon/
On Jan 22, 2007, at 9:00 AM, Jack Sarfatti wrote:
There was also a report of being able to imprint a complex image on a
single photon!
Well, if that is true then what happens if that is done one photon pair
at a time to the delayed photon in Cramer's experiment? Will that
complex image be transmitted backwards in time to the undelayed twin
photon. Since, it's one photon pair at a time the usual argument of the
late H.Pagels et-al of the random washing out of the nonlocal signal in
the statistical accumulation (e.g. local probabilities stay at 1/2)
would be side-stepped, completely irrelevant to this new kind of total
experimental arrangement seemingly permitted by the new technology
beyond the wildest dreams of the creators of quantum theory almost 100
years ago now.
On Jan 22, 2007, at 12:19 AM, Jack Sarfatti wrote:
Begin forwarded message:
Go to
http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2007/01/21/ING5LNJSBF1.DTL&type=printable
Science hopes to change events that have already occurred
- Patrick Barry
Sunday, January 21, 2007
Ever wish you could reach back in time and change the past? Maybe you'd
like to take back an unfortunate voice mail message, or rephrase what
you just said to your boss. Or perhaps you've even dreamed of tweaking
the outcome of yesterday's lottery to make yourself the winner.
Common sense tells us that influencing the past is impossible -- what's
done is done, right? Even if it were possible, think of the mind-bending
paradoxes it would create. While tinkering with the past, you might
change the circumstances by which your parents met, derailing the key
event that led to your birth.
Such are the perils of retrocausality, the idea that the present can
affect the past, and the future can affect the present. Strange as it
sounds, retrocausality is perfectly permissible within the known laws of
nature. It has been debated for decades, mostly in the realm of
philosophy and quantum physics. Trouble is, nobody has done the
experiment to show it happens in the real world, so the door remains
wide open for a demonstration.
It might even happen soon. Researchers are on the verge of experiments
that will finally hold retrocausality's feet to the fire by attempting
to send a signal to the past. What's more, they need not invoke black
holes, wormholes, extra dimensions or other exotic implements of time
travel. It should all be doable with the help of a state-of-the-art
optics workbench and the bizarre yet familiar tricks of quantum
particles. If retrocausality is confirmed -- and that is a huge if -- it
would overturn our most cherished notions about the nature of cause and
effect and how the universe works.
Dating back to Newton's laws of motion, the equations of physics are
generally "time symmetric" -- they work as well for processes running
backward through time as forward. The situation got really strange in
the early 20th century when Einstein devised his theory of relativity,
with its four-dimensional fabric of space-time. In this model, our sense
that history is unfolding is an illusion: The past, present and future
all exist seamlessly in an unchanging "block" universe.
"If you have the block universe view, the future and the past are not
any different, so there's no reason why you can't have causes from the
future just as you have causes from the past," says David Miller of the
Centre for Time at the University of Sydney in Australia.
With the advent of quantum mechanics in the 1920s, the relative timing
of particles and events became even less relevant. "Real temporal order
in general, for quantum mechanics, is not important," says Caslav
Brukner, a physicist at the University of Vienna, Austria. By the 1940s,
researchers were exploring the possibility of time-reversed phenomena.
Richard Feynman lent credibility to the idea by proposing that particles
such as positrons, the antimatter equivalent of electrons, are simply
normal particles traveling backward in time. Feynman later expanded this
idea with his mentor, John Wheeler of Princeton University. Together
they worked out a theory of electrodynamics based on waves traveling
forward and backward in time. Any proof of reverse causality, however,
remained elusive.
Fast forward to 1978, when Wheeler proposed a variation on the classic
double-slit experiment of quantum mechanics. Send photons through a
barrier with two slits in it, and choose whether to detect the photons
as waves or particles. If you put up a screen behind the slits, you will
get a pattern of light and dark bands, as if each photon travels through
both slits and interferes with itself, like a wave. If, on the other
hand, you take a snapshot of the slits themselves, you will find each
photon passes through one slit or the other: it is forced to pick a
path, like a particle. But, Wheeler asked, what if you wait until just
after the photon has passed the slits to make your choice? In theory,
you could suddenly raise the screen to expose two cameras behind it, one
trained on each slit. It would seem that you can affect where the photon
went, and whether it behaved like a wave or particle, after the fact.
In 1986, Carroll Alley at the University of Maryland at College Park,
found a way to test this idea using a more practical set-up: an
interferometer which lets a photon take either one path or two after
passing through a beam splitter. Sure enough, the photon's path depended
on a choice made after the photon had to "make up its mind." Other
groups have confirmed similar results, and at first blush this appears
to show the present affecting the past. Most physicists, however, take
the view that you can't say which path the photon took before the
measurement is made. In other words, still no unambiguous evidence for
retrocausality.
That's where John Cramer comes in. In the mid-1980s, working at the
University of Washington in Seattle, he proposed the "transactional
interpretation" of quantum mechanics, one of many attempts to relate the
mathematics of quantum theory to the real world. It says particles
interact by sending and receiving physical waves that travel forward and
backward through time. In June, at a conference of the American
Association for the Advancement of Science, Cramer proposed an
experiment that can at last test for this sort of retrocausal influence.
It combines the wave-particle effects of double slits with other
mysterious quantum properties in an all-out effort to send signals to
the past.
The experiment builds on work done in the late 1990s in Anton
Zeilinger's lab, when he was at the University of Innsbruck, Austria.
Researcher Birgit Dopfer found that photons that were "entangled", or
linked by their properties such as momentum, showed the same
wave-or-particle behavior as one another. Using a crystal, Dopfer
converted one laser beam into two so that photons in one beam were
entangled with those in the other, and each pair was matched up by a
circuit known as a coincidence detector. One beam passed through a
double slit to a photon detector, while the other passed through a lens
to a movable detector, which could sense a photon in two different
positions.
The movable detector is key, because in one position it effectively
images the slits and measures each photon as a particle, while in the
other it captures only a wave-like interference pattern. Dopfer showed
that measuring a photon as a wave or a particle forced its twin in the
other beam to be measured in the same way.
To use this setup to send a signal, it needs to work without a
coincidence circuit. Inspired by Raymond Jensen at Notre Dame
University, Cramer then proposed passing each beam through a double
slit, not only to give the experimenter the choice of measuring photons
as waves or particles, but also to help track photon pairs.
Instead of the "double slit" use the "stencil" on the delayed photon!
See what happens.
<Untitled01.jpeg>
One of the key components of the process is the particle-wave duality
nature of light: by firing a single photon of light through a stencil
The double slits should filter out most unentangled photons and either
block or let pass both members of an entangled pair, at least in theory.
So a photon arriving at one detector should have its twin appear at the
other. As before, the way you measure one should affect the other.
Jensen suggested that such a setup might let you send a signal from one
detector to another instantaneously -- a highly controversial claim,
since it would seem to demonstrate faster-than-light travel.
If you can do that, Cramer says, why not push it to be
better-than-instantaneous, and try to make the signal arrive before it
was sent? His extra twist is to run the photons you choose how to
measure through several kilometers of coiled-up fiber-optic cable,
thereby delaying them by microseconds. This delay means that the other
beam will arrive at its detector before you make your choice. However,
since the rules of quantum mechanics are indifferent to the timing of
measurements, the state of the other beam should correspond to how you
choose to measure the delayed beam. The effect of your choice can be
seen, in principle, before you have even made it.
That's the idea anyway. What will the experimenters actually see? Cramer
says they could control the movable detector so that it alternates
between measuring wave-like and particle-like behavior over time. They
could compare that to the pattern from the beam that wasn't delayed and
was recorded on a sensor from a digital camera. If this consistently
shifts between an interference pattern and a smooth singleparticle
pattern a few microseconds before the respective choice is made on the
delayed photons, that would support the concept of retrocausality. If
not, it would be back to the drawing board.
If the experiment does show evidence for retrocausation, it would open
the door to some troubling paradoxes. If you could see the effects of
your choice before you make it, could you then make the opposite choice
and subvert the laws of nature? Some researchers have suggested
retrocausality can occur only in limited circumstances in which not
enough information is available for you to contradict the results of an
experiment.
Another way to resolve this is to say that even if the present can
influence the past, it cannot change it. The fact that your hair is
shorter today has as much influence on your going to the barber
yesterday as the other way around, yet you can't change that decision.
"You wouldn't be able to talk about altering, but you could talk about
causing or affecting," says Phil Dowe, an expert on causation at the
University of Queensland in Australia. While it would mean we cannot
change the past, it also implies that we cannot change the future.
If all that gives you a headache, then consider this: if retrocausality
does exist, it says something profound about how the universe works. "It
has the potential to solve what is one of the biggest problems in modern
physics," says Huw Price, head of Sydney's Centre for Time. It goes back
to quantum entanglement and "nonlocality" -- one particle
instantaneously affecting another, even from the other side of the
galaxy. That doesn't sit well with relativity, which states that nothing
can travel faster than light. Still, the latest experiments confirm that
one particle can indeed instantaneously affect the other. Physicists
argue that no information is transmitted this way: Whether the spin of a
particle is up or down, for instance, is random and can't be controlled,
and thus relativity is not violated.
Retrocausality offers an alternative explanation. Measuring one
entangled particle could send a wave backward through time to the moment
at which the pair was created. The signal would not need to move faster
than light; it could simply retrace the first particle's path through
space-time, arriving back at the spot where the two particles were
emitted. There, the wave can interact with the second particle without
violating relativity. "Retrocausation is a nice, simple, classical
explanation for all this," Dowe says.
While Cramer last week prepared to start a series of experiments leading
up to the big test of retrocausality, some researchers expect reverse
causality will play an increasingly important role in our understanding
of the universe. "I'm going with my gut here," says Avshalom Elitzur, a
physicist and philosopher at Bar-Ilan University in Israel, "but I
believe that when we finally find the theory we're all looking for, a
theory that unifies quantum mechanics and relativity, it will involve
retrocausality."
But if it also involves winning yesterday's lottery, Cramer won't be
telling.
Did we reach back to shape the Big Bang?
If retrocausality is real, it might even explain why life exists in the
universe -- exactly why the universe is so "finely tuned" for human
habitation. Some physicists search for deeper laws to explain this
fine-tuning, while others say there are millions of universes, each with
different laws, so one universe could quite easily have the right laws
by chance and, of course, that's the one we're in.
Paul Davies, a theoretical physicist at the Australian Centre for
Astrobiology at Macquarie University in Sydney, suggests another
possibility: The universe might actually be able to fine-tune itself. If
you assume the laws of physics do not reside outside the physical
universe, but rather are part of it, they can only be as precise as can
be calculated from the total information content of the universe. The
universe's information content is limited by its size, so just after the
Big Bang, while the universe was still infinitesimally small, there may
have been wiggle room, or imprecision, in the laws of nature.
And room for retrocausality. If it exists, the presence of conscious
observers later in history could exert an influence on those first
moments, shaping the laws of physics to be favorable for life. This may
seem circular: Life exists to make the universe suitable for life. If
causality works both forward and backward, however, consistency between
the past and the future is all that matters. "It offends our
common-sense view of the world, but there's nothing to prevent causal
influences from going both ways in time," Davies says. "If the
conditions necessary for life are somehow written into the universe at
the Big Bang, there must be some sort of two-way link."
-- Patrick Barry
Retrocausality: Can the present affect the past?
<in_laser_1.jpg>
Researchers have devised an experiment using laser light to demonstrate
a property of quantum mechanics: That pairs of entangled photons show
identical properties as either a wave or a particle. By using this
knowledge, they hope to demonstrate how to influence an event that has
already occurred.
1. A laser beam is directed into a crystal that makes two streams of
photons.
2a. One stream of photons travels through a screen with two slits.
2b. The other stream of photons travels through an identical screen with
two slits BUT is routed through six miles of fiber-optic cable that
delays the light by microseconds.
3a. A detector captures the light and records it as a wave-like or
particle-like photon (you don't know which yet).
3b. The delayed light is sensed by a movable detector. If the detector
is closer to the lens it's recorded as a wave-like interference pattern.
If its farther from the lens it is recorded as a particle.
What is happening here: By choosing to measure the delayed photon as
either a wave or particle photon, the experimenter forces the other
photon to appear in the same way - because they are entangled - even
though it reaches the detector earlier.
Sources: John Cramer, University of Washington; NewScientist, Sept. 2006
Patrick Barry wrote this piece for the New Scientist, where it first
appeared. Contact us at insight@sfchronicle.com.
Page E - 1
URL:
http://sfgate.com/cgi-bin/article.cgi?file=/c/a/2007/01/21/ING5LNJSBF1.DTL
Jack Sarfatti
sarfatti@pacbell.net
"If we knew what it was we were doing, it would not be called research,
would it?"
- Albert Einstein
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