# Effect before Cause: Is it possible?

1. Aug 14, 2008

### BioCore

Hi,

I once read a book that stated that scientists had somewhere a couple of years or decades ago (not sure) performed an experiment in which they had somehow proven that an effect occurred or could basically occur before the cause even happened.

I was wondering if this actually is true and if there is some place where just results could be read about. Now I have read about Special Relativity and how according to Einstein's theory nothing is faster than the speed of light which was necessary for this experiment. But I have heard from my Professor recently and have also read this that some scientist and theoretical physicists are on the verge of proving that the speed of light is not the maximum speed. So is this also true. If so then there could actually be a possible result where effect could come before cause.

2. Aug 14, 2008

### ShaneS

An effect preceding its cause is analytically illogical. Causes and effects are obviously temporal distinctions, with the cause being a priori.

Of course, determining causal relations depends not just on the phenomena, but the observer. This means that I can certainly observe an effect prior to observing its cause: I hear my wifes voice prior to seeing her person...I see the ball smash the window prior to seeing who kicked it...etc. But determining who caused the vocal sounds and who kicked the ball is necessitated by my being able to relate two observations/events. That is, I have a notion that my wife spoke, and that the ball was kicked. My wife and the ball kicker must precede the speech act and the smashed window.

Without a notion that someone-kicked-the-ball-which-caused-the-window-to-smash occuring in that temporal order, then on what grounds would I have for asserting the one necessarily preceded the other? To say that the smashing of the window as an event occured before the ball kicking event is illogical IF the window was indeed smashed by the kicked ball. Again, this is because our concept of causality is based on linear temporal events: this, then that. Our concept of causality is also based on observed phenomena: state of affairs 'X', then state of affairs 'Y'. I dont think I have ever seen a window smash ('X') then seen the window-smashing-ball kicked at it ('Y'). As far as 'X' is concerned, the window is currently smashed. But as far as 'Y' is concerned, the window is yet to be smashed. How can a smashed window precede its being smashed?

3. Aug 14, 2008

### ZapperZ

Staff Emeritus
Please read https://www.physicsforums.com/showthread.php?t=249970" about the need to provide a more complete citation. It is difficult to address something when it is unclear if what you wrote here is the same as what you read. Always pay attention to the source and make a complete citation for someone else to double check.

Zz.

Last edited by a moderator: Apr 23, 2017
4. Aug 14, 2008

### Usaf Moji

5. Aug 18, 2008

### evidenso

hmmm. If you read the detailed litterature about the Raman effect. It's proven that the scattered photon can be emitted before the incoming photon is absorbed. Well I dont understand it either

6. Aug 18, 2008

### peter0302

One has to be very careful when discussing "effect" and "cause" in quantum mechanics. We have, for example, the delayed choice quantum eraser where it might appear that the behavior of photons is being influenced by what happens at a later time.

The simple definition - "cause comes before effect" - clearly is insufficient to capture the nuances of what happens in QM because we don't really know what the "cause" is of any quantum event. On the other hand, we know that outcomes cannot be determined prior to measurement and still give us the results we see. Thus, if there is a "cause" it must come at the time of measurement or later.

Perhaps in QM the cause does precede effect, but the effect is not actually manifested until much later than we think - i.e., in an entanglement experiment, perhaps the "effect" is not the detection, but the comparison of the two detections.

And there is also difficulty in defining the term "cause" itself. Does cause mean that but for an event, the other would not happen? Well, no - one can still cause someone's death by shooting them even if they would've had a heart attack moments later. Does cause mean that you have altered the odds of an event? No - again, death might have been certain in both cases.

So we can't really have the discussion - can cause precede effect - until we know exactly what it means to cause an event. We see correlations all over the place - and they need not be in any temporal sequence. But causation is difficult to identify and even harder to define.

7. Aug 19, 2008

### wawenspop

Along the lines in this thread, here is an interesting situation:
Say one of a pair of entangled particles went in a rocket at very high speed on a long journey, so that when it returned it would be younger than the first particle. Lets say you changed the state of the older one, would the younger one already have changed?

Last edited: Aug 19, 2008
8. Aug 19, 2008

### peter0302

Because there is no apparent correlation until measurements are compared, the states will be observed in whatever reference frames they're observed in, and no one will agree on who observed first. But they will agree, when they compare measurements, that there was entanglement.

9. Aug 19, 2008

### DaveC426913

I do not believe it is valid to talk about particles "aging". Particles that were created 15G years ago have not changed in 15Gy.

Now, if you're thinking about particle decay, that's an effect that can only be predicted in groups of particles. I do not believe a single particle has any "ticking clock" in it that says "I will decay soon".

10. Aug 21, 2008

### wawenspop

Another slant on this is to think of a photon as a record of a past event as it travels into the future. So in this sense, it if an event has already happened, then it cannot be altered in the future.

But for entangled photons, the record in the future is of an ambiguous event (the production of the entangled pair) in the past. So in the future, the event remains ambiguous (i.e. which particle has which state etc).

11. Aug 21, 2008

### Jon_Trevathan

A discussion of effect before cause somehow seem incomplete in a quantum physics forum if the paradox of delayed choice quantum erasure is omitted from the discussion. In this context, numerous delayed choice quantum erasure experiments have been conducted and are reported in the literature (See generally http://en.wikipedia.org/wiki/Quantum_eraser; [Broken]
http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser and
http://en.wikipedia.org/wiki/Wheeler's_delayed_choice_experiment).

In their “peer reviewed” paper, “Random Delayed-Choice Quantum Eraser via Two-Photon Imaging” (The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics, Volume 44, Number 1 / July, 2007 (see also http://arxiv.org/abs/quant-ph/0512207v1), the authors: Giuliano Scarcelli, Yu Zhou, Yanhua Shih; provide a brief summary of such experiments and report on their experimental contribution to this literature. For those who are not familiar with these experiments, I have copied their introduction below:

“Quantum erasure was proposed in 1982 by Scully and Druhl [1]. After two decades the subject has become one of the most intriguing topics in probing the foundations of quantum mechanics [2,3]. The idea of quantum erasure lies in its connection to Bohr’s principle of complementarity [4]: although a quantum mechanical object is dually particle and wave; its particle-like and wave-like behaviors cannot be observed simultaneously. For example, if one observes an interference pattern from a standard Young’s double-slit interferometer by means of single-photon counting measurement, a photon must have been passing both slits like a wave and consequently the which-slit information can never be learned. On the other hand, any information about through which slit the photon has passed destroys the interference. In this context Scully and Druhl showed that if the which-slit (which-path) information is erased, the interference pattern can be recovered; the situation becomes extremely fascinating when the erasing idea is combined with the delayed choice proposal by Wheeler and Alley [5,6]: i.e. even after the detection of the quantum itself, it is still possible to decide whether to erase or not to erase the which-path information, hence to observe the wave behavior or the particle behavior of the quantum mechanical object.

In the past two decades, a number of experiments demonstrated the quantum eraser idea by means of different experimental approaches and/or different point of theoretical concerns [7–17]; in particular Kim et al. [12] have realized an experiment very close to the original proposal by using entangled photon pair of spontaneous parametric down-conversion (SPDC). The experiment demonstrated that the which-path information of a photon passing through a double-slit can be erased at-a-distance by its entangled twin even after the annihilation of the photon itself. The choice was made between the joint detection of a single two-photon amplitude that involved either the upper slit or the lower slit (read which-path information) or the joint detection of a pair of indistinguishable two-photon amplitudes involving both slits (erase which-path information).

Unlike all previous experiments the present work takes advantage of two-photon imaging. A photon passes through a standard Young’s double-slit for its complementarity examination. The quantum correlation between this photon and its entangled twin allows the formation of a “ghost” image of the double-slit on the side of the entangled twin. Thus, the which path information is completely passed to the entangled twin photon and can be erased by the detection of the twin. After the detection of the photon which passed through the double-slit, a random choice is made on the Fourier transform plane of the “ghost” image between “reading complete information” or “reading partial information” of the double path.

The new approach shows clearly that any attempt to interpret the physics of the quantum eraser in terms of complementarity examination on a single photon leads to counterintuitive results and paradoxical conclusions ..."

The authors, Giuliano Scarcelli, Yu Zhou, and Yanhua Shih, go on in their paper to describe the Klyshko model as a potential theoretical explanation for the phenomena as follows:

"As we pointed out in the introduction, the interpretation of the quantum eraser results in terms of complementarity examination on a single photon is troubling. On the other hand, the straightforward calculation presented here can be intuitively captured if it is based on the concept of nonlocal two-photon amplitudes and their coherent superposition. In this sense, the physics behind entangled two-photon phenomena seems having no classical counterpart in electromagnetic theory. In order to help clarifying this physics, Klyshko proposed an “advanced-wave model” [20] that forces a classical counterpart of the concept of two-photon amplitudes and the associated two-photon optics. In his model, Klyshko considered the light to start from one of the detectors, propagate backwards in time until the two-photon source of SPDC and then forward in time towards the other detector. The two-photon source is thus playing the role of a mirror to keep the proper transverse momentum relation of the entangled photon pair.”
arXiv:quant-ph/0512207v1

Please take special note of the next to last sentence of the above quote, which is from a peer reviewed journal. Does time reversal explain this experimental result?

In the now defunct chain titled “Superluminal Communication” (see https://www.physicsforums.com/showthread.php?t=250578), I had attempted to raise another paradox – one in which experimental results (which I still think was good science) seemed to challenge our common conceptions of special relativity. The common theme in that chain and in this chain is the possibility that through one universal concept, (e.g. time reversal) a “particular” paradox of quantum physics could potentially be understood.

Do you feel time-reversal theories might have explanatory value? If so, I would hope that this chain and the chain on Cramer’s theories (See https://www.physicsforums.com/showthread.php?t=177506) might become more substantive in their content. As to the Cramer chain, may I proffer the apologetic update on John Cramer’s Transactional Interpretation of Quantum Mechanics (TIQM) that Dr. Ruth Kastner of the University of Maryland provides in her paper titled: “Cramer’s Transactional Interpretation and Causal Loop Problems” (See http://arxiv.org/PS_cache/quant-ph/pdf/0408/0408109v1.pdf) (Yes, Dr. Kastner’s paper is not peer reviewed but, in my opinion, it should be considered)
[For those that are not familiar with Cramer’s work, it is built on Wheeler-Feynman emitter-absorber theory of radiation (see http://en.wikipedia.org/wiki/Wheeler–Feynman_absorber_theory)

As to this chain, I would again like to proffer (as I had intended in the aborted “Superluminal Communication” chain) the TSQM model of Yakir Aharonov and Jeff Tollaksen for Forum consideration. (see New Insights on Time-Symmetry in Quantum Mechanics; Non-statistical Weak Measurements; Weak measurements, weak values, and entanglement; Pre-and post-selection, weak values and contextuality; and Robust Weak Measurements on Finite Samples). And, in order to comply with Forum Rules please consider also Jeff Tollaksen’s paper titled “Pre- and post-selection, weak values and Contextuality, 2007 J. Phys. A: Math. Theor. 40 9033-9066 doi: 10.1088/1751-8113/40/30/025 (see also: http://arxiv.org/PS_cache/quant-ph/p.../0602226v3.pdf [Broken] for those of us who do not have free subscriptions to this journal)

Last, please consider M. S. Leifer and W. Spekkens paper titled "Pre- and Post-selection paradoxes and contextuality in quantum mechanics" [Physical Review Letters, 2005] in which they state: the "study of quantum systems that are both pre- and post-selected was initiated by Aharonov, Bergmann and Lebowitz (ABL) in 1964 and has led to the discovery of many counter-intuitive results, which we refer to as pre- and post-selection (PPS) effects [2], some of which have recently been confirmed experimentally [3]." ABL foundations the research that Aharonov and Tollaksen are currently conducting. As you will note from any review of the literature, the topic is not without some controversy. In fact, when Drs. Leifer and Spekkens go on to note that ABL’s experimental confirmations “have led to a long debate about the interpretation of the ABL probability rule [4]”, it is Dr. Ruth Kaster’s paper titled “The Nature of the Controversy over Time-Symmetric Quantum Counterfactuals” that they were citing [see R. E. Kastner, Phil. Sci. 70, 145 (2003)].

Last edited by a moderator: May 3, 2017
12. Aug 22, 2008

### LaserMind

Information has no 'mass' and as such could travel faster than light. The barrier is the causality inferred in special relativity - most thread readers already know this very well. i.e. If FTL information transmission is possible, then information could be sent that 'prevents' something that has already happened.

- MWI may get round this - guess where 'events' that were prevented from happening end up?

This reference puts anti-FTL information transfer arguments quite well IMO (for those readers that don't already know):
http://www.phy.duke.edu/research/photon/qelectron/pubs/GauthierCompendiumPreprint2006.pdf

13. Aug 22, 2008

### Jon_Trevathan

Dear LaserMind:

Thank you for your post. In a way you have brought the “Superluminal Communication” chain back to life (see https://www.physicsforums.com/showthread.php?t=250578)

In that chain I affirmed that “as conventionally understood, superluminal communication is an impossibility yet I also affirmed my belief that the thought experiments I proffered in starting the Superluminal Communication chain give every indication that this conventional understanding might be violated. We had a paradox of some very interesting, and well-done science, with an impossible implication.

Niels Bohr one said “How wonderful that we have met with a paradox. Now we have some hope of making progress.”

I am grateful for you post, for as it and the paper you cited brought some additional paradoxes of QM to our attention.

“Two paradoxes are better than one; they may even suggest a solution.” Edward Teller

As example, the paper you cited mentions wave function collapse. This simple reference involves two paradoxes.
First, the von Neumann collapse postulate wherein the state of a particle changes instantaneously along the t=0 hyperplane from a momentum eigenstate to a position eigenstate (e.g. collapse). How is one “position” selected from among all of the “non-zero probable locations for the “particle”) I don’t have time to address this now but will cite and quote from several TSQM papers that address this issue.

The second paradox involves observers in relativistic motion. TSQM is a non-relativistic theory which means not only will the observed collapse along the t=0 hyperplane not be instantaneous for observers in other frames but that observers in different frames will also disagree about temporal order, length, energy and all other physical quantities that are covariant but not invariant. I am still working on a speculative explanation of this paradox that I am not prepared to share at this time.

As the paper you cited spent most of its time discussing the EPR Paradox, I will share an analysis of this paradox in my next post. Also, as I felt from your post that there may be some fundamental misunderstanding over the limits QM places on time reversal, this analysis will also implicitly illumine how boundary conditions operate within the TSQM model.

As we embark, keep in mind: “Every great and deep difficulty bears in itself its own solution. It forces us to change our thinking in order to find it.” Niels Bohr

Best wishes,

Jon Trevathan

14. Aug 22, 2008

### wawenspop

TSQM seems to offer a lot to explain entanglement IMO at a conceptual level, but I must check out the papers as I have only just read your post (I think one post may have been banned by the Zapper, unfortunately).

I say that because I cannot see a problem with time reversal in 'wave packets' - at the quantum level. The problem is when it presents itself in the 'real world' - but in the 'superpositioned' world it would not be transgressing SR, AFIK.

I view entangled particles - for the sake of my sanity - as though they are, in a sense, still together, as at birth (when twinning commenced) even when spatially separated - so the TSQM idea of 'reflected wave packets' going back in time is not too far away from that. Both ideas keep them in 'contact'.

15. Aug 22, 2008

### Jon_Trevathan

For those who care about these thing:
On August 19, 2008, I transmitted a PM to ZipperZ that included the post he had now banned.
On August 19, ZipperZ transmitted a PM to me which gave no hint that he might object to the material.

The deleted post began with introductory materials which to a significant degree involved quotations from and citations to Wikipedia articles. It is hard to conceive that there could be a rational objection to these materials. Accordingly, they will comprise my next post—if permitted.

The materials that I believe will be of interest to physicists were largely drawn from the graduate school text book for a Quantum Paradox class taught by Yakir Aharonov and Jeff Tollaksen at George Mason University. The book, titled “Quantum Paradoxes: Quantum Theory for the Perplexed”, was written by Yakir Aharonov and Daniel Rohrlich. As a professional courtesy, I and a number of others were invited to attend this class during its inaugural semester. There was nothing in my post that to the best of my recollection was not directly drawn from the Quantum Paradoxes book and/or presented and discussed in class. I would encourage any interested readers to assure themselves of Dr. Aharonov’s reputation (Aharanov-Bohm Effect) and the reviews Quantum Paradoxes: Quantum Theory for the Perplexed” has received.

It would be inconceivable that this source material could be found objectionable at a Physics Forum. If ZipperZ had afforded me the courtesy of disclosing his objections, this embarrassment might have been averted.

In any event, I play by the rules, even arbitrary ones. Accordingly, I will go over the substantive portions of the post so that only quotes from the Quantum Paradoxes book or directly citable materials from the book and/or peer reviewed papers remain.

It is with great regret that I now realize we, in the present environment, will never get to some truly astounding work. I had thought my post on TSQM and the EPR Paradox would serve as an almost trivially obvious introduction to TSQM’s explanatory value. I am astounded that it was censored.

Last edited: Aug 22, 2008
16. Aug 23, 2008

### ZapperZ

Staff Emeritus
Since you decided to do this in the open, then it shall be.

The "objection" was to the fact that you were "cutting-and-pasting" wholesale articles from another source which I found by looking for it, not from your post. In this case, it came from a comment you wrote in a blog which you never even mentioned. You recycled the exact, identical comment into a post here.

The objection had nothing to do with the source material from Aharonov and Rohrlich text, which I had already mentioned to you is not a problem! If what you want to say has already been written, and the content follows the rules that we have, then show the LINK to it. There has been WAY too many wholesale quotes out of copyrighted material in your posts. In post #11, almost half of that very long post is nothing but a quote from another source!

And before this gets misinterpreted again, I am NOT telling you that making exact quotes out of another source is prohibited. However, it gets to the point where this is all it seems that you are doing.

Zz.

17. Aug 23, 2008