Can John Cramer's Experiment Really Demonstrate Retrocausality?

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In summary: Anyway, I don't think it'll do anything groundbreaking.In summary, John Cramer plans to use a double slit setup to look for an interference pattern between entangled photons. However, this has been previously disproven and is not feasible.
  • #1
Lelan Thara
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Hi folks - here's a link to an article that talks about John Cramer's planned new experiment that's intended to test entanglement and "retrocausality".

http://seattlepi.nwsource.com/local/292378_timeguy15.html

As usual with this kind of article for laymen, it's very hard to decipher the exact experimental setup that Cramer has in mind. The article also seems misleading to me in some ways. For instance, it talks about photons being "either" particles "or" waves, when I thought it was more accurate to say that photons are always waves that express themselves as particles when they strike a detector. (To put it another way, photons always "travel as waves and arrive as particles" - it's not an either/or situation.)

The article also seems to imply that entanglement doesn't have much experimental evidence, whereas I thought it did. And it suggests that in general, physicists have found ways to explain away entanglement, and show no acausal signalling - this is news to me.

My question is - does anyone know where I can find a more complete description of Cramer's planned experiment?

Thanks!
 
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  • #2
Regardless of a philosophical and everlasting question about photons being waves or particles, that guy looks like he is nutz.
He expects to detect signal by a detector before sending it?
I think he has read too many (and bad) SF books.
 
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  • #3
It looks like Cramer is trying to use a double slit setup on one of the entangled photons. The idea is that he will look for an interference pattern depending on whether or not a certain type of measurement is performed on the other photon of the pair.

This idea has been proposed and shot down on this forum a number of times (count me as one of the victims). We have previously determined that an entangled photon does NOT yield an interference pattern when going through a double slit setup. As a result, you cannot use the wave-particle concept like a yes-no bit of information. You can see this in an enlightening article by Anton Zeilinger, p. 290, Figure 2.

Experiment and the foundations of quantum physics
 
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  • #4
DrChinese said:
It looks like Cramer is trying to use a double slit setup on one of the entangled photons. The idea is that he will look for an interference pattern depending on whether or not a certain type of measurement is performed on the other photon of the pair.

Isn't this just what happens in the much-discussed delayed choice quantum eraser experiment? What am I missing?
 
  • #5
DrChinese said:
We have previously determined that an entangled photon does NOT yield an interference pattern when going through a double slit setup. As a result, you cannot use the wave-particle concept like a yes-no bit of information. You can see this in an enlightening article by Anton Zeilinger, p. 290, Figure 2.
I see no reason for a stream of any photons being presented to a double slit not to generate a pattern, regardless of whether or not there exists a beam of correlated photons going someplace else. And no matter what happens to that possible alternate beam; the beam that can see a double slit will still produce a pattern.

Looking at the idea in the Zeilinger figure 2 is just silly, to borrow a term from John Bell.

The problem is in what he does with the two separate beams a and a’. The diagram he gives is clear enough, each is going to only one separate slit! This is a single slit set up not a double slit! Add a mirror to widely separate the two beams a and a’. Give each of them a pair of slits that they both can “see” and there will be a pattern behind both of them, with or without checking on b or b’. (Note that he never actually ran this “test”)

DrC I can’t believe you didn’t catch this flaw.

As to the Cramer experiment, no big deal – I see nothing there that has not already been shown in a traditional polarization entanglement experiments that has been done so many times already. That is Correlation that can only be explained by FTL action OR accepting non-local effects.
 
  • #6
Tehno - not only does Cramer read sci fi, he writes it, apparently. However, as for him being "nutz" - he is at least credentialed enough that John Gribben was writing about him ten years ago in his book, "Schrodinger's Kittens and the Search for Reality". Gribben was quite impressed with Cramer's "Transactional Interpretation" which sees interactions between electrons as having an "advanced" (ftl, backward in time) wave and a "retarded" (forward in time) wave.

Apparently this concept grows out of work done by Feynman in trying to explain radiation resistance in electrons.

So this experiment seems to be Cramer's effort to find more proof for theories he's been working on for at least a decade.

DR Chinese - linkee no workee. :smile: I like your sig saying - "the map is not the territory." I agree.

Anyhow - I can see the basic idea to this experiment in one sense. But overall, I don't understand how the experimental setup in question could test what it intends to test. That's why I was asking if anyone had a better description of it.

The article's description of the second entangled photon being able to turn the first into a particle or wave doesn't make sense to me. I can grasp that this is supposed to be some kind of delayed-time two slit experiment, but I'd like to learn more before I either dismiss it or accept it.

RandalB - you've hit on my major objection to the whole experiment - I don't really see why the extra 'entangled" photon is going to make any difference. If the experimental setup allows for wave interference patterns, then even a one-photon-at-a time setup, with no paired photons, should produce interference patterns - right?
 
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  • #7
We should set up a vote. I think that the interference will occur.

Cramer is a professor at U. Washington, Seattle. Here's his personal website, which links to recent papers. I looked briefly but didn't see any exact descriptions of the experiment:
http://faculty.washington.edu/jcramer/

Carl
 
  • #8
CarlB, I don't really feel I have enough info for an informed vote. But on the limited info I have - my vote is that interference will always occur - or never occur - depending on the experimental setup - and the entanglement part of the experiment won't affect the outcome.
 
  • #9
It's kinda funny.. Cramer seems to have been a fairly expert kinda guy in this field, but the popular account of this experiment sounds like the kind of ridiculous thing people propose on various physics forums. Will definitely be good to get further detail on this one.
 
  • #10
cesiumfrog said:
It's kinda funny.. Cramer seems to have been a fairly expert kinda guy in this field, but the popular account of this experiment sounds like the kind of ridiculous thing people propose on various physics forums. Will definitely be good to get further detail on this one.
When I first read about Cramer's proposal I assumed he wasn't expecting to be actually transmit messages back in time, but just to do a certain experiment which in some loosely-defined way would be "easiest to understand" in terms of his own http://www.npl.washington.edu/ti/ of QM, where the backwards-in-time signalling is real but it's hidden from us in such a way that we can't use it to send meaningful signals (much like the FTL interaction between particles in Bohm's interpretation is hidden); however, one of the quotes in the article from Cramer himself suggest he is talking about violating causality with real intelligible signals:
Besides altering our concept of time, the signaling finding alone would almost certainly revolutionize communication technologies.

"A NASA engineer on Earth could put on goggles and steer a Mars rover in real time," said Cramer, offering one example.
 
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  • #11
Besides altering our concept of time, the signaling finding alone would almost certainly revolutionize communication technologies.

"A NASA engineer on Earth could put on goggles and steer a Mars rover in real time," said Cramer, offering one example.
Probably he's desperately trying to have funds for an experiment in order to drive people's attention on his Transactional Interpretation theory, which is very interesting, on the other hand.
 
  • #12
lightarrow said:
Probably he's desperately trying to have funds for an experiment in order to drive people's attention on his Transactional Interpretation theory, which is very interesting, on the other hand.

Tell that to http://kathryncramer.typepad.com/" ; she'll probably punch you out:devil:

Added: Don't miss http://www.kathryncramer.com/kathryn_cramer/2006/11/my_dad_is_coole.html" : My Dad is Cooler than Your Dad, with really great pictures!
 
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  • #13
While I think that the entangled photons will determine whether or not interference is seen, I should mention that I don't think that this can be used to send information faster than light. It's just a statistical effect, I believe. But I haven't thought deeply about this.
 
  • #14
Lelan Thara said:
DR Chinese - linkee no workee.

If the experimental setup allows for wave interference patterns, then even a one-photon-at-a time setup, with no paired photons, should produce interference patterns - right?
The DrC link worked fine for me before and still does, if you need to cut and paste use:
hep.yorku.ca/menary/courses/phys2040/misc/foundations.pdf (add www.)[/URL]

For quantum analysis any experiment must use “one-photon-at-a time” or when dealing with EPR type experiments one photon split into one pair of photons. There is no point to be made otherwise. I’m sure if had a double slit with one slit only by one laser and the other slit only eliminated by a second laser patters could be seen depending on the frequencies and phase differences between the two lasers.

The problem with Cramer is not if interference will occur or not, I have no doubt he can adjust the set up to give either result. That is not the problem, with what he claims he will do. Any pattern will take the time of many photons passing to build up and confirm it shape.
Problem is he claims from a “pattern” he can determine if “a” (as in one individual) photon is a “wave” or a “particle”? What kind of new definition of attribute to an individual photon is that supposed to be!
NOT that it is both but it must only be one or the other??
Quoting from the article:
[Quote] one of the entangled photons will be sent through a slit screen to a detector that will register it as either a particle or a wave -- because, again, the photon can be either. The other photon will be sent toward two 10-kilometer (6.2-mile) spools of fiber optic cables before emerging to hit a movable detector, he said.

Adjusting the position of the detector that captures the second photon (the one sent through the cables) determines whether it is detected as a particle or a wave. [/quote]
The whole idea of confirming "retrocausality" depends on being able to first detect this wave vs. particle attribute with the passing of just one photon!
AND even more significantly he is claiming that by adjusting the position of the second detector he can force the attribute of one of the entangled pairs as he desires, thus forcing the attribute of the detection of the other one to his desire even though that detection took place 50 microseconds before!

I see no explanation in [PLAIN]http://www.kathryncramer.com/kathryn_cramer/2006/09/retrocausality.html" (See diagrams on his daughter’s web site) that explain how he intends to define a photon without taking more than 50 microseconds to do so.

If he presented what I’ve seen so far on this experiment for posting under “Independent Research” here on PF; I doubt he would get approval for it to be taken seriously. I wouldn’t, even if his daughter might punch me.
 
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  • #15
RandallB said:
I see no reason for a stream of any photons being presented to a double slit not to generate a pattern, regardless of whether or not there exists a beam of correlated photons going someplace else. And no matter what happens to that possible alternate beam; the beam that can see a double slit will still produce a pattern.

Looking at the idea in the Zeilinger figure 2 is just silly, to borrow a term from John Bell.

The problem is in what he does with the two separate beams a and a’. The diagram he gives is clear enough, each is going to only one separate slit! This is a single slit set up not a double slit! Add a mirror to widely separate the two beams a and a’. Give each of them a pair of slits that they both can “see” and there will be a pattern behind both of them, with or without checking on b or b’. (Note that he never actually ran this “test”)

DrC I can’t believe you didn’t catch this flaw.

Zeilinger is not a figure to be taken lightly. He has probably run the experiment, but that is just a guess. Entangled photons behave somewhat differently than other photons because they are in a different wave state.

Cramer is asserting the opposite of Zeilinger, at least that is the premise of the experiment. So I also agree with Zeilinger because I doubt that FTL signalling is possible.
 
  • #16
selfAdjoint said:
Isn't this just what happens in the much-discussed delayed choice quantum eraser experiment? What am I missing?

That is exactly how I saw the setup as well. :smile:
 
  • #17
DrChinese said:
Zeilinger is not a figure to be taken lightly.

Cramer is asserting the opposite of Zeilinger
Zeilinger and part III of his paper you linked us too – didn’t know I was dis’n someone that has his photo on Wikipedia.

But, I’ve never agreed with the idea of concept of three entangled particles, and I see he was part of the trio that put that together. That is one strike against him for me.
And for a second strike, looking closely at page S290 of his paper in the first column the second full sentence agrees with the notes in FIG 2; but the very last column sentence is nonsense or a pretty bad error/typo to let slip through.

However, based on your rep here on PF, and sticking by him, that gets him on base if not a double.
So, I’m going to have to print it out and go over Part III with care to see if I’m missing something.
Need to find just how a Heisenberg Lens and Detector work.
Plus I’d like to find a ref. on what the output of a Type I parametric down-conversion looks like compared to a type-II as shown in FIG 8.

I agree with you on the Cramer position – I consider that effort pointless.
 
  • #18
Lelan Thara said:
Gribben was quite impressed with Cramer's "Transactional Interpretation" which sees interactions between electrons as having an "advanced" (ftl, backward in time) wave and a "retarded" (forward in time) wave.

Apparently this concept grows out of work done by Feynman in trying to explain radiation resistance in electrons.

So this experiment seems to be Cramer's effort to find more proof for theories he's been working on for at least a decade.
I think Feynman never believed anything being actually radiated "backward in time".At least,not in such sense what we usually consider a past.
IMO,wrong interpretations evolved from trick which was purely mathematical ,based on symmetry of Maxwell equation where included also -t sign.QM entanglement seems to experience no space-time dimensions.

Here are words of mr. Cramer himself in regard to his expeiment with lasers and splitting photons:

"I want people to know what it's like to do science, what makes it so exciting," he said. "If this experiment fails in reality, maybe I'll write a book in which it works."

My prediction:he is going to write another SF book:biggrin:
 
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  • #19
DrChinese said:
Zeilinger ... He has probably run the experiment, but that is just a guess. Entangled photons behave somewhat differently than other photons because they are in a different wave state.
To avoid confusion with the Cramer issues,
I’ve moved comments on the Anton Zeilinger article and Dopfer thesis paper to a new thread:
https://www.physicsforums.com/showthread.php?p=1166941#
as a Separate Subject.
 
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  • #20
RandallB said:
If anyone comes across a English translation of the 146 page Dopfer paper I'd like to read it.

Aside from the abstract, the linked paper appears to be in English.
 
  • #21
selfAdjoint said:
Isn't this just what happens in the much-discussed delayed choice quantum eraser experiment? What am I missing?

I didn't read though all the stuff, but from what I can make from the text, yes, this seems to be exactly a delayed-choice quantum eraser experiment. So, it probably *will* work, and has no specific implications for any interpretational scheme - as in fact no observational experiment can distinguish between *interpretations*, them all being empirically equivalent. Many people fall in that trap. Deutch does so, too. There's no experimental way to demonstrate "Bohmian mechanics" from "MWI" or "transactional interpretation" or whatever, as they all are empirically equivalent to "standard quantum mechanics". We also know from standard quantum mechanics that no information can be transmitted using entangled systems. So the best Cramer can do is to suggest an experiment that will violate the predictions of standard quantum theory.
 
  • #22
RandallB said:
Not when I follow my link to the web page holding the Birgit Dopfer paper. If you see a English version link there or some other English link to the Dopfer thesies please post it, or detail where you found it.

Sorry - I had accidentally looked at the wrong paper.
 
  • #23
Cramer builds on absurdity

RandallB said:
As to the Cramer experiment, no big deal – I see nothing there that has not already been shown in a traditional polarization entanglement experiments that has been done so many times already. That is Correlation that can only be explained by FTL action OR accepting non-local effects.

Yes, Cramer’s proposed set-up adds a time-delay to Zeilinger’s two-crystal experiment, to allow the observer at a km-distant detector to choose how to observe the photon within the 3 microseconds between a nearby measurement on the conjugate photon and his own. His choice is alleged to affect the nearby prior detection, whose result he would not know.

Recall that ingenious experiment had two identical crystals illuminated by the pump laser, and aligned so that a second tuned laser passed through both crystals successively. It found interference fringes between the two conjugate emissions – a double-crystal experiment akin to the famous double-slit one. Zeilinger et al. deduced that the first photon was affected not by the act of observing but of being able to choose to observe the second conjugate photon. This introduced subjectivity that Zeilinger admitted# is “absurd”.

One absurdity can beget another – in this case, Cramer’s subjective retrocausality.

The natural explanation of light-conversion in crystals is given by maxwellian wave theory*. The first non-linear terms have sum and difference frequencies of the two lasers, though Zeilinger’s experiments used only the difference (‘down-converted’ photons).

As the conjugate beams in the two-crystal experiment are phase correlated, wave theory naturally implies interference fringes. What produces absurdity (Faster-than-Light / non-local effects) is forcing the photon description onto the phenomenon of light splitting by crystals.

# Bouwmeester and Zeilinger, Nature 388, 827-8, 1997
* R.W. Boyd, Nonlinear Optics (Academic Press, Boston, 1992);
Marshall, http://arxiv.org/abs/quant-ph/%209711030
 
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Related to Can John Cramer's Experiment Really Demonstrate Retrocausality?

1. What is the purpose of John Cramer's new experiment?

John Cramer's new experiment aims to test the theory of retrocausality, which proposes that the future can influence the present.

2. How does John Cramer's new experiment work?

The experiment involves sending particles through a series of devices that can either act as a detector or a switch. The order in which the particles pass through these devices is determined by a random number generator. The results of the experiment will be compared to the predictions of quantum mechanics to see if there is evidence of retrocausality.

3. What makes John Cramer's new experiment unique?

Unlike previous experiments on retrocausality, John Cramer's experiment uses a delayed-choice setup, where the decision to measure or switch the particles is made after they have already passed through the devices. This eliminates the possibility of any hidden variables influencing the results.

4. What are the potential implications of the results of John Cramer's new experiment?

If the experiment confirms the existence of retrocausality, it could challenge our current understanding of causality and the nature of time. It could also have implications for technology, such as improved quantum computing and communication.

5. When will the results of John Cramer's new experiment be released?

The experiment is currently ongoing and the results are expected to be published in the near future. However, further analysis and confirmation from other experiments may be needed before any definitive conclusions can be drawn.

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