Talk:Transactional interpretation
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Pavel V. Kurakin (Keldysh Institute of Applied Mathematics, Russian Academy of Sciences, me).
John Cramer is very accurate and delicate in his formulations (as far as I can judge). He specially points, that TIQM is a kind of methodological or pedagogical trick to make understaning of quantum mechanics easier, and not an model of quantum phenomena.
(Last experiment by S. Afshar changes this situation, according to John Cramer. As John Cramer argues, Afshar's experiment verifies TIQM to be more consistent with quantum mechanical formalism and predictions as compared to Copenhagen interpretation.)
I am sorry, but I suppose that I am the only person on Earth to use publicly the term model as applied to quantum mechanics. I work in mathematical modeling team and this term is so natural to me. John Cramer delicatly prefers to say "underling picture".
Contrary, well-mannered physicists imply that quantum mechanics is the "underlying picture" by itself. The idea to explain quantum amplitudes is sometimes assumed as a characteristic feature of crackpots (crackpot index by John Baez).
So, what prevents TIQM to become a model of quantum-mechanical behaviour of particles? In my view, there are 2 crucial points here:
1. back-in-time is unconcieveble. One can endeed crack his pot trying to understand it.
2. why one transaction? Many possible detectors send their retarded conformation waves to one single source. So how a single transaction (i.e., a full pair of waves -- offer wave and confirmation wave) happens?
The problem of "back-in-time-propogation" can be solved, I believe. Hidden time concept puts both offer wave and confirmation wave in hidden (not physical!) time, while physical time is when transaction finally ends.
I assume my model as a direct development of John Cramer's TIQM and I ask for any criticism.
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[edit] TI's standing wave is unobserveable
"To an observer, this standing wave in space-time looks as if a particle has travelled through space."
This standing wave doesn't "look like" anything anybody has ever, or could ever, actually observe in any experiment. If anyone could actually observe "particles travelling through space" quantum theory wouldn't be neccesary in the first place.
Furthermore, this unobservable standing wave, unlike the wave function of the Copenhagen interpretation (which is also unobservable), can't be used to predict anything as the data necessary to compute the wave is not available until the measurements it might have predicted have already been obtained.
That said TI remains very interesting.
It reminds me of the guy in the film The Matrix, who having escaped the simulated reality, regrets the choice, and desires a return. To such an end he does a deal with the artificial intelligensia who control the boundarys of this reality.
The standing wave of TI can be imagined as that "reality" bounded by the matrix - a neo-classical universe in which "particles travel through space".
But can an observer in such a reality observe what we are able to, in fact, observe - namely interference patterns!
Perhaps we are, indeed, inside the TI matrix. But since we are modelling the TI matrix from within the TI matrix the interference patterns we might have hoped to see (in the TI) get cancelled out. That would explain the "paths through space" effect that we see in the model. We would have to invert the model (eg. into the Copenhagen one) in order to see the interference patterns (in our TI model) that we otherwise, in fact, observe from within the TI matrix.
Perhaps we would.
Carl Looper 16 January 2006
[edit] Standing waves in Heim's multidimensional space
Consider a universe where waves of distortion in multiple dimensions propagate forwards and backwards in time, interacting to create a complex interference pattern. From this complex pattern emerge the observable phenomena we see, such as particles (the standing waves of the TI) and forces (momentum exchange).
In this hypothesis, knowing the underlying wave motion does not help us derive the physical laws obeyed by the emergent phenomena. It's like trying to derive analytically a formula describing the motion of objects in the n-body problem. It can't be done, even though Newtons laws are pretty simple. You have to simulate the system in a computer and see what happens.
It would be interesting to compute the propagation of advance and retarded waves in a 6 dimensional universe, and see if the familiar effects of gravity and electromagnetism emerge. Maybe other, previously unknown phenomena would emerge, giving the experimenters something new to look for.
Why 6 dimensions? An obscure mathematical theory developed by Burkhard Heim links gravity and electromagnetism by adding additional dimensions to spacetime. This is also described in Michio Kaku's "Hyperspace". With 6 dimensions you get gravity and electromagnetism. With 8 dimensions you (apparently) get the remaining forces, plus some new ones. The new forces seem to produce effects like the accelerating expansion of the universe currently attributed to dark energy.
Quantoid 06:32, 21 January 2006 (UTC)
[edit] Retrocausality
Both Cramer's standing wave and the probability wave of conventional quantum theory can only function as a model of what might be imagined as taking place behind experimental data. But unlike the probability wave, Cramer's standing wave has no use value other than to satisfy a philosophical preference for classical models. The retrospectively constructed standing wave - whether retrocausally constucted by Nature herself and/or by our theorisation, can't be used to predict future data. It can only be used to put a classical spin on how we imagine the past. This is okay. If it doesn't change the facts and establishes a possible domain of compatibility with, for example, relativity theory, we should not be concerned by it's otherwise redundant decoration of the facts.
The trap is that we run the risk of confusing this redundant model with "reality". Indeed I suspect Cramer himself has fallen into just such a trap. An article in New Scientist (30 Sept 2006, page 36, "What's done is done") suggests that Cramer (and others) are on the verge of sending mesages back in time - not just in theory but in fact.
In any case such an experiment is very important because although it won't succeed in sending messages back in time (am I the only one who understands why?) it will succeed in showing how retrocausality is both a redundant model and a trap. It could also establish why the sought after compatibility between relativity and quantum theory can be seen as redundant - but that's another story.
From a philosophical point of view Cramer has already succeeded in sending a message back in time. The message, in this case, is his concept of a particle's history as a retrocausally well defined path in space over time (the standing wave). But nobdody in the past can ever receive this message.
Or to put it another way, if we imagine ourselves in the past, Cramer's message (the particle possessing a neo-classical path) has yet to be retrocausally constructed - if only for us.
We must use the probability wave of conventional quantum theory to represent the particle's otherwise pre-causal status. We can allow that this is an approximation and that the present "really" holds a Crameresque well defined path for us to retrospectively appreciate at a later time but until such time we have no other choice.
In other words it is only when the future finally arrives (and the particle is detected), that Cramer's model becomes appreciable. But it's too late. We will have already predicted, using conventional quantum theory, the probable location for the paricle's detection (it's future), and we will have already represented it's history (by the probability function), and we will have already satisified predispositions for classical models by disposing of the probability function (wave function collapse) at the moment we have a detection. What's left?
All that's left for Cramer's model to do is reinscribe an unreachable past as classically conceivable.
And risk deluding oneself that this is not just theoretically or experimentally demonstratable but experimentally exploitable - that we can send messages back in time - or otherwise convince science journalists we can.
Carl Looper carllooper@hotmail.com 1 October 2006
[edit] Back to the past
Cramer's original formulation was well conceived and rigourous. He expressly emphasised that his interpreatation (TI) was experimentally indistinguishable from that underlying the well worn Copenhagen Interpretation (CI). At the level of fact (the data) no distinction was possible. The distinction was at the level of theory - about how we think or otherwise "philosophise" the data and the math.
All this meant was that TI and CI were experimentally compatible. The experimental success of one would always be the experimental success of the other. TI would work wherever CI worked because the underlying math was the same.
But then an an otherwise interesting experiment by Afshar implied (for Cramer) that an experimental distinction could be demonstrated between TI and CI. In other words Cramer reinterpreted his own interpretation as not just distinguishable in terms of thought but experimentally distingishable in terms of fact.
The origin of this "error" (for want of a more diplomatic term) is philosophical. On one side of the philosophical divide, we find theorys (models, interpretations) are treated as if they were candidate descriptions for what is "really" happening out there in the world, so to speak. It's as if all that's required for a theory to succeed/fail is to be experimentally tested and found either correct, incorrect or the "jury out" on such. But some theorys, such as Cramer's original one, fall under a fourth category - untestable. Until recently Cramer's theory was just such a theory.
On the other side of the philosophical divide are theorys (such as quantum theory and CI) that are purely utilitarian. They make no implicit or explicit claim about being right or wrong. Their success is measured in terms of the correlation found between the data predicted by the theory and that which is experimetally derived. But as Dirac once said, it could still be just a coincidence. There is a radical disclaimer underlying quantum theory. The model is purely fictious. Any resemblance to Nature either living or dead is purely coincidental. This robs the classical opponent of any amunition in the criticque of quantum theory.
It also puts the classical opposition in the unfortunate position of reinforcing their assumption that theorys should not be just utilitarian but about what is "really" there. That is why Cramer was excited when Afshar's experiment implied possible testability.
Up until then Cramer's model was in the same camp as the Copenhagen Interpreation - purely utilitarian. But it's use value was a little different. It's utility was not measured in terms of experimental data - that stayed the same as CI (due to the common mathematical basis). Rather, it's utility was in the the philosophical bridge it provided between the data and predispositions for classical (rational) models. In this respect Cramer's original philosophical formulation is great.
But the ground has shifted.
Cramer has retrospectively (retrocausally?) recouched TI in classical terms - as correct, incorrect or the "jury out".
This is very brave. It is also very unfortunate. Cramer has rewritten the past. TI is now - was always - not a utilitarian theory. It is now (was always) about what was/is "really there". And we're going to test it. And if we're right then it's not only possible to build a time machine but we're going to build one.
If we're right.
The lure of classical philosophy is tantalising. The hold it has on us is the result of thousands of years as Heisenberg puts it. But Bohr and Heisenberg were are able to replace this grip with a virtual handshake - a loosely defined "wave function collapse". If Cramer elaborated this into a standing wave model it was no more or no less virtual.
But now it has become more than a virtual handshake. It has become a firm grip. And Cramer has been yanked over the line into the classical or neo-classical camp.
Lets do the same.
Let's suppose that a time machine or retrocausal messaging system is not just a utilitarian construct but experimentally possible - that we can - in factum - send messages into the past. Or to put it another way - receive messages from the future. I for one would love to see such happening - not out of any philosophical predisposition for such but because I'm a fan of classical science fiction.
OK. Could we use retrocausally constructed messages from the future to selectively interrupt the channel (slit) through which the standing wave function has not been realised? In other words, if the standing wave is retrospectively computed post factum (in the future) to describe a photon "path" through slit A (in the present) could we then use such computation (from the future) to "interupt" slit B?
Is slit B supposed to be (in the present) retrocausally empty?
That's the question. If our future informed intervention of slit B, despite being informed by the future (that the standing wave is in slit A), fails to have nill effect on that future then what does it mean to compute this standing wave in the first place (in the future) - even if we don't send it back in time?
What sort of past are we computing?
Carl Looper
