Archive for October, 2012

Entanglement with an Extinct photon?

A recent paper by Megidish et al suggests it is possible to create an entanglement with a photon that no longer exists! The paper, titled ‘Entanglement Between Photons that have Never Coexisted’ documents an experiment of entanglement-swapping between two pairs of photons (

Basically they created two entangled photons. Entanglement means that the two photons instantly affect each other even though they are separated by large distances. While spooky and difficult to explain, this is the accepted reality of physics. Then they allowed one photon to expire. Then they created another entangled pair (photons 3 and 4). Next they swapped the second photon into entanglement with photon 3, and released photon 4. They found that photon 4 was entangled with photon 1, even though the two had never existed at the same time. If this is true, then it raises all sorts of new weirdness for quantum mechanics.

The conclusion is that, ‘This is a manifestation of the non-locality of quantum mechanics … in time.’ The authors presented two explanations for their results, both involving temporal causality (but in different directions): (a) that ‘measuring the last photon affects the physical description of the first photon in the past, before it has even been measured. Thus, the ”spooky action” is steering the system’s past.’ And (b)  the measurement of the first photon is *immediately* steering the future physical description of the last photon. ‘ (emphasis added).  I don’t disagree with the experimental evidence, but I do think the authors have overly dramatised their findings and rushed their interpretations without thinking through all the explanations.

However there is a much simpler explanation that does not require retrospective temporal causality.

First, consider that a particle can have two states of some variable. That variable could be spin, polarisation, etc. (In this experiment they used polarisation.) Label those states BLACK and WHITE. Second, accept that entanglement involves two particles synchronising their states, and having the means to continue to maintain that synchronisation over large distances: this is the spooky part of entanglement. For the present purposes we don’t have to worry about exactly *how* that entanglement occurs, but merely accept that it does. Third,  accept that such synchronisation involves the entangled particles taking complementary states. (This does appear to be the case in the experiment, but it is not totally clear). In this experiment that would correspond to photon 1 taking BLACK, and photon 2 taking the WHITE state.

Then destroy photon 1. Thereafter create two new photons 3 and 4, and entangle them together in a complementary way. Since we are talking about states like polarisation, the absolute orientations will not necessarily be the same as the first pair: call them RED and GREEN for convenience.

Next, swap the entanglement so that 2 and 3 and entangled, and release photon 4. At this point we need a fourth assumption, that the state of photon 2 has been preserved and dominates the 3-4 pair. This is a reasonable interpretation of the experiment. Then, since photon 2 is WHITE, photon 3 adjusts from RED to become BLACK. Now we need a fifth assumption, that in the entanglement-swapping process the released photon 4 also has to transform to a complementary state, i.e. cannot stay GREEN. This is  a sensible assumption for conservation reasons. This means that photon 4 changes from GREEN to WHITE and exits the entanglement.

Now,  compare the first and last photons: photon 1 was BLACK and photon 4 is WHITE. So it is true, photon 1 has influenced the future state of photon 4, in the sense that 4 has become complementary to what 1 used to be.

Thus photon 4 is (inversely) correlated to photon 1, with photon 2 being the temporal carrier of the state.

Finally, note that correlation does not necessitate causality.

Therefore, there is no positive reason to accept the paper’s conclusion that entanglement can occur across time.

Update 16 Oct 2012

This experiment showed that photon 4 had properties complementary to what photon 1 used to have. So what? Some take this view that this constitutes entanglement. However entanglement is usually understood as a two-way effect, where EITHER particle can affect the other. Entanglement involves bi-lateral causality. In this case the effect is decidedly ONE-SIDED in both the object (photon 4) and direction of time. The paper makes no claim that photon 4 resurrects the dead photon 1. Nor is there any evidence provided that the future photon 4 influences the initial creation of photon 1.

The results cannot be interpreted as bi-lateral causality, and hence the observed effect is merely correlation rather than true entanglement.

Interpreting the results as superposition across time, is a position of belief not necessity.



Leave a comment

What is *reality*?

Here is a copy of our post in response to a New Scientist article Reality: Is matter real? byJan Westerhoff

Venture to where the wild things are?

Indeed the behaviour of particles is peculiar. They behave as waves or points, depending on how one interrogates them. The article follows that path and then shows how usual explanations about contextual measurement lead to absurdities: the role of the conscious observer in collapsing quantum indeterminacy is an unsatisfactory model.

The article then relentless pursues a reductive explanation for physics, and shows that pure mathematics would be the underlying reality if that path is taken. (I am not sure that I followed or agreed with all the logic though). Hence likewise back to mental entities and an observer.

I loved these circular concepts, for their philosophical wrangling and the stark conclusion that philosophy does not give an answer either way. However, perhaps those are not the only two options? Could there be others? There was one such candidate, which I did not miss. This is the usual escape hatch by which physics evades the effort of thinking about meaning, namely the many worlds theory. What a relief not to have that given an airing!

There may be other candidates, more deserving of consideration. The article might have gone on to discuss locality and local realism, hence also entanglement, and how solutions might emerge from that direction.

In particular, a logical case may be made that weird interpretations result, not as the article implies from the choice of solution path taken, but because there is something very broken with one of the fundamental tacit premises.

We note that the entire weight of the ontology of QM’s physics rests on a zero-dimensional point. It is thus hardly surprising that QM gives us weird explanations, singularities, and circular reasoning. What is even more surprising is the persistent adherence to the ontology, instead of a serious questioning of whether such premises might be wrong. But if not a point, then what? And don’t the Bell-type inequalities preclude anything but a 0-D point at the root of all matter?

They would seem to, though there is reason to believe that those inequalities might be based on circular reasoning of their own. They start by implicitly assuming a 0-D point structure and then conclude that matter can have no internal structure. Duh! Is that not circular?

If so then that opens the possibilities for other concepts for matter. String theory being one, though it yields only mathematical solutions rather than physical interpretations and therefore seems more in the reductionist line of thinking. But there are other non-local hidden variable solutions, and some of these already provide physically natural explanations, devoid of metaphysical weirdness, for all the paradoxes here mentioned and more besides: Airy patterns, wave-particle duality, entanglement interferometers, among others.

Expectedly, there is cost, which is that the 0-D point construct would have to be abandoned. And locality too. Some would say these are very light costs, to be gaining so much more explanatory power than extant theories.

My point is therefore that the article only explores two of the possible solutions to the reality question, and finds answers in neither of them. My criticism then is that the article stays too close to the campfire of the safe orthodoxy, which we already knew is beyond weird. What will physics have? Stay with the orthodoxy and accept the weirdness and epistemic stasis? Or venture to where the wild things are, and explore the raw new ideas?

For example, have a look at the FQXi essays on ‘Which of Our Basic Physical Assumptions Are Wrong?’

Our own work in the wild side is readily available at

, , ,

Leave a comment

Does the Proton decay?

What is proton decay?

Some theories of physics predict that the proton decays, i.e. it breaks down into other products. There is no experimental evidence that this actually occurs. If it does occur, it is expected to be a very rare event. The life of the proton, according to those theories that predict it to decay, is longer than 10^33. So there is no danger of the atoms in our world suddenly breaking up in an immediate end of the universe scenario.

Still, the question of proton decay is important to the grand unified theories (GUTs), those theories of physics that seek to unify the electric, magnetic, weak, and strong forces (interactions). Their idea is that the proton decays into a positron (antielectron) and pion. Quite how they might decay depends on the theory under consideration, and might involve the Higgs particle or other exotic particles that are not yet observed.

Does the Cordus conjecture have anything to add about proton decay?

Yes, it predicts that hitting it with two antineutrinos should remanufacture it to an antielectron and two photons. This prediction may be testable and falsifiable.

Cordus model of the PROTON. Showing the proposed internal geometry and external fields (which are discrete).

This result also implies that proton decay would not be fundamentally random, but rather a result of a specific coincidence of antineutrinos. In the Cordus model decay is a conditional event, which is an unorthodox position. By comparison conventional explanations consider decay rates to be fixed, and therefore the events are merely spontaneous and random. Read more …

What this means is that the proton could unravel back into a positron and two photons, with the right kind of forcing by antineutrinos. But realistically that is not expected to be a common occurrence given that antineutrinos do not react much with matter.

Other articles

, , , , , , , , ,

Leave a comment