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Quantum Entanglement is an ongoing hot topic in the field of Quantum Mechanics (QM), and has been since Einstein and two colleagues raised it almost ninety years ago with the question: “Can Quantum-Mechanical Description of Physical Reality be Considered Complete?” In a paper which became known as The EPR Thought Experiment, Einstein, Podolsky and Rosen pointed out that, according to QM, Local Realism - the fairly obvious requirement that two interacting particles or systems must have some form of viable connection in spacetime - was not something that could be taken for granted. In fact, according to the equations of QM, two particles or photons of energy could be entangled in such a way that they could interact, regardless of the distance between them, instantaneously - faster than the speed of light.
Einstein referred to this as “Spooky action at a distance”, since it clearly violates the light-speed limit of all communications as decreed by his Theory of Special Relativity (SR). He, and others, proposed that there must be some hidden factor, usually referred to as hidden variables, which enabled particles to give the impression of interaction when this wasn’t the case. In 1964 John Bell proposed a statistical means by which this could be tested: the 2022 Physics Nobel Prize was awarded jointly to three researchers who had shown experimentally, to increasing degrees of certainty, that application of Bell’s proposal ruled out, to a very high level of probability, any possibility of the effects correctly predicted by QM being due to such hidden variables. The “spooky action at a distance” which Einstein regarded as highly questionable, and which in turn calls into question his assertion of the absolute nature of the speed of light, shows every sign of being de facto, very much a feature of our space-time reality.
The debate rumbles on, as it surely must for something which challenges the very foundations of SR, a cornerstone of 21st century physics. The purpose of this post is to look at the evidence, to consider possible explanations and implications. We have already seen in this thread, from various directions, flaws in the conventional view of SR; we have also seen, though, that particles of matter are formed from energy moving at speed c (light speed); clearly it wouldn’t be possible for such particles themselves to move at a speed greater than that of the energy they’re formed from, or for that energy itself to carry information faster than its own speed. So we’re going to have to investigate a little more deeply.
Photon self-entanglement
The first place to look is at the phenomenon of photon self-entanglement. I’ve never heard it referred to in these terms anywhere else, but it is very much a thing and it’s very well known of.
This relates to the well-documented effect whereby a photon communicates with itself (potentially across vast distances) instantaneously - far faster than the speed of light. This is happening all the time, for every photon that gets absorbed anywhere by anything.
For example, let’s think about when you see light from a distant star, say 100 light years away. Each of that small number of photons absorbed by your eye has travelled for 100 years; in that time the wavefront of each photon has spread out over a vast expanse of space in a shape likened by one writer to that of a giant contact lens - covering an area of millions of square miles. When that photon hits your eye, all of its energy, which could register anywhere over that vast area, is poured into your optical receptor and is no longer available anywhere across the wave-surface of that cosmic contact lens. The electromagnetic field effect signalling the availability is - instantly - no longer in evidence anywhere across that huge expanse of space. This must be so, because (obviously!) a photon cannot be ‘spent’ twice.
[Obfuscation alert: There are those who will tell you that light is emitted as a photon, travels through space as a wave (not a photon), then becomes a photon again at the point where it’s absorbed. This is a matter of semantics, not science, to avoid the very point I’m making. That point is unavoidable, and such semantic jiggerypokery doesn’t deserve the label ‘science’. Others admit frankly that yes, this does happen faster than the speed of light - but that’s ok because it can’t be used to transfer information; this completely misses the main point. If you still have doubts, check out the results from Aspect’s sequential-single-photon version of the double-slit experiment and decide for yourself whether or not that pattern was made by photons travelling as waves.]
So, a question: how can a photon registering at your eyeball trigger instantaneous ‘collapse’ of an electromagnetic field effect (call it a photon or just a wave - makes no difference) millions of miles from that eyeball? There is, as yet, no answer to this question (though we’ll consider the implications very shortly). What is very clear, though, is that an effect at any one point on that (potentially humongous-sized) wavefront triggers knock-on effects instantly everywhere else on that wavefront, no matter how distant. In effect, a photon - every photon - is ‘entangled’ with itself, in a way directly comparable to the generally understood relationship between two electrons or photons linked by quantum entanglement.
And there’s more. Let’s consider Young’s two-slit experiment, where it’s been shown that a sequence of single photons can build up an interference pattern, showing that a single photon passes through both slits simultaneously as a wave (look back to the results of Nobel laureate Alain Aspect’s experiment). If the output from each of those two slits is led away to separate receptors, then that single photon will register at either one of those receptors (apparently randomly) but never both. Again we’re seeing that self-entanglement at work: if the wave from slit A registers at its receptor then the wave from slit B effectively ceases to be - instantaneously, otherwise there’s the possibility of a ‘double-hit’ from that single photon. And vice versa: registration from slit B immediately nullifies the wave from slit A. By whatever the means, every photon ensures that it can only be banked once.
So what exactly is going on?
Well, there’s a big clue in the nature of the photon, the quantum of energy, itself. ‘Quantum’, of course, means ‘how much’ (in Latin) - and ‘how much’ is pretty well exactly what this quantum of energy is all about. Every photon carries within its own form a clear statement of precisely how much energy it’s carrying. That statement is in the form of its frequency; as soon as we know the frequency of a photon, we know how much energy it’s carrying (since the one is proportional to the other).
Anywhere on the wavefront of a photon (or the wave carrying the photon, if you like) - however widespread, however faint - its frequency is the same: the frequency telling the full energy content of that photon. And so that full energy content, the whole of that photon, can be cashed in at any point on that wavefront.
Contrast this with, say, a potato or a broomstick: the weight of that potato or the length of that broomstick can only be measured at one point in space - the place where that potato or that broomstick is (obviously!). More than this, that potato can only be consumed, that broomstick can only be employed, where it is (obviously!). And that ‘where it is’ can only be in one place at any given time.
When one is slicing up potatoes to make chips, it’s easy to tell if you’ve inadvertently switched to a different potato from the one you were chopping up just now. Couldn’t happen: each potato has its own separate presence, its own self-connected being. The same is true of photons, with the essential difference that its self-connectedness isn’t restricted by spatial proximity, its one coherent being can be spread out without limit - even to the extent of (wrongly) appearing to be totally fragmented from the space-time perspective.
Consider a simple analogy: the main auditorium in the Theatre Royal, Plymouth (UK) has 1300 seats; each of those seats can, naturally, be taken by just one person for any given performance. Each of those seats is made available, for any performance, at every computer terminal across the world - potentially many millions of different locations where one particular seat can be ‘bagged’; but each seat, available via so many widely-separated locations around the globe, can only be ‘bagged’ once for a particular performance, from any one of those places; as soon as a particular seat is taken, at any one of those terminals, it instantly becomes unavailable at every other potential booking site around the planet.
So we have a scenario where a resource - a theatre seat - is offered simultaneously at numerous places, at great distances apart - but as soon as that offer is taken up at any one of those widely-separated places it instantly becomes unavailable everywhere else. This requirement doesn’t present a problem, for the simple reason that all of those spatially separated outlets are in fact parts of the same undivided entity: localisation is not an issue. [Note that even physical material connection isn’t an issue: satellite communication works just fine]. Nonlocal distributed access to a single-use resource is a key feature of the system, essential to its success.
Herein is a massive clue to the deeper nature of our physical reality: photons, the raw formative material of matter and the energy-packets that drive every form of action across the universe, are by their very nature non-local entities. A potato, a broomstick or any other material object is (at least to our perception) localised: it can only be measured at one place, is only available in one place at any time. By contrast a photon, like those theatre reservations, is available simultaneously at numerous places; like those theatre seats, its worth can be measured simultaneously at all of those places; and like a theatre seat, once taken at any one of those places it is gone, unavailable at any other place.
And amazingly, the key to this available-everywhere but available-only-once property is that crucial quality, so much talked about but so little understood: every slightest hint of a particular photon, no matter how faint, no matter how many square light years it may be spread out over, carries a clear measure of its full energy content: the frequency of that photon, sounding its worth loud and clear. How much more definitively does this need to be spelt out: a photon is uniquely equipped to be deployed across space to an unlimited degree, then fully employed at any point where it happens to have a presence.
The inescapable conclusion from this, surely the only meaningful conclusion, is that the photon is intrinsically a nonlocal entity, its role in the workings of the universe is nonlocal. What does this say about matter, if matter is composed of such entities? (Clue: Clint Davisson won a Nobel prize for proving that matter travels through space as waves). Equally to the point, a photon is a coherent entity, in the everyday sense of having a structure and boundaries: the integrity of a single photon is no less well-defined than the integrity of a single theatre seat, potato, or broomstick. The self-entanglement of a photon, its management of its own energy content over potentially vast distances (or across separated outputs from a two-slit experiment), is simply a demonstration of that integrity - though deeply puzzling when viewed from a temporo-spatial mindset.
And there’s the rub: consideration of the behaviour of photons takes us beyond the temporo-spatial mindset, since photons don’t fit in the temporo-spatial paradigm. Put simply, photons are a key element of the deeper reality underlying that paradigm, giving it its form. This is a subject for further consideration in a later post; for the time being it’s enough to note that a photon is a coherent structure, so formed as to operate outside the confines of spatial dimensionality which we regard as a given in our view of reality - the nonlocal measure of photons is clear evidence of this.
[In fact we can go one step further: ‘nonlocal’ means ‘not subject to localisation’, or ‘not limited in respect of spatial position’; with regard to photons, the term ‘spatial position’ doesn’t even have any meaning, ‘space’ is a meaningless concept. In this context the term alocal is sometimes used; photons are alocal.]
Two (or more) entangled photons (or electrons)
A pair of entangled photons or electrons have shared destinies, until and unless that entanglement is broken. In some ways they may be thought of as quantum-level Siamese twins: they’re birthed from the same event, they share combined resources, in very real terms they are one composite entity; whatever shared assets are taken by one of the pair (such as spin characteristics), what remains becomes part of the other. Energetically they are one.
I was recently describing the weird relationship between two entangled electrons to my mother-in-law, who is ninety-one. She immediately responded, from pretty much a zero background in physics, with: “Well surely that means they’re actually parts of the same thing?” And she was absolutely right.
Once we recognise that photons are alocal, in the terms described above, then its no great leap to see that interaction between two conjoined photons (and by extension, constructs of photons such as electrons), could similarly demonstrate alocal behaviour outside the terms of reference of normal space-time interactions. In particular, if one part of that joint entity exhibits a particular mode of behaviour then it’s totally to be expected that its partner will exhibit complementary behaviour; spatial separation shouldn’t be expected to in any way inhibit such a response.
Numerous attempts have been made to explain away these ‘beyond spacetime’ interactions, majoring on those ‘hidden variables’ referred to near the beginning of this post. Most of these proposed explanations have been put to bed by those findings that led to award of the 2022 Nobel prize, though some variations are still mooted. The real crunch, though, comes from practical applications of quantum entanglement - in sensing, cryptography, quantum computing. All of these applications yield real tangible results; none of these applications would provide meaningful results if that quantum interaction were not happening. Agreed, none of these applications actually depend on intercommunication at superluminal (faster-than-light) speed, but if it’s happening at all - and these applications show clearly that it is - then QM tells us that it’s happening independently of degree of separation, ie. superluminally.
The Bottom Line
The bottom line, then, isn’t just that information between photons or material particles is being transferred at superluminal speeds - though that’s pretty much beyond question now. Neither is it that entities vast distances apart are able to communicate with one another, singling each other out from untold numbers of the same across sometimes many parsecs with the unerring recognition of a parent penguin finding its own chick among thousands of others on returning from an ocean foraging expedition - though this galactic-level recognition, too, is a wonder that’s beyond comprehension.
No, the bottom line to beat all bottom lines is that our universe is fashioned, in every part, from energetic building blocks that pay no regard to the niceties of spatial separation; indeed, for these wisps of energy that form everything from you and me to the towering walls of galactic clusters across the cosmos, spatial separation isn’t even a concept worthy of consideration. At the foundational level of physical reality the keyword is alocality: the three spatial dimensions are just an architectural rendering thrown up - quite possibly by our own minds - to provide a scaffolding on which to hang our experience of spacetime. Who knows what wonders we might be capable of, were we able to get a glimpse behind that scaffolding? Who knows what we might discover about ourselves and our own true purpose in this many-layered miracle of which just the top layer is what we experience through our physical senses, mediated by our sensory filtering circuits?
And then, what about time?
Watch this space.