Quantum entanglement is another concept of quantum theory that has no physical equivalent. It lets quantum entities merge into one system, so changing one instantly affects the others at any distance. Particles can also aggregate into bigger objects if they are close enough but entanglement doesn’t depend on distance at all, as photons remain entangled even if they are light years apart.
For example, when a Cesium atom emits two photons in opposite directions, they entangle into one system with a net zero spin. Yet both photons still spin up or down randomly, so if one is measured to be spin up, the other should be spin down. Experiments show it is always so, but if a photon’s spin is random, how does the other instantly know to be the opposite, at any distance?
Einstein called this spooky action at a distance because it implied a faster-than-light effect, and so suggested an experiment to disprove it (Einstein, Podolsky, & Rosen, 1935). When the test was finally made, called Bell’s inequality, it proved that entanglement occurs, even for photons too far apart to communicate at the speed of light (Aspect, Grangier, & Roger, 1982). This was one of the most careful experiments ever done, as befits the ultimate test of quantum theory, and it found that entanglement occurs, even when there is no physical way it could happen!
How can an event at one location affect another at any distance? For particle physics, the problem is that it can’t, but the evidence is that it does. Two photon particles heading in opposite directions are separate, so if they spin randomly, as they do, why can’t both spin up, or both spin down? Quantum theory just says the initial spin is conserved, but gives no clue as to how. Nature could conserve spin by making one photon spin up and the other down from the start, but apparently this is too much trouble, so it lets both have both spins until one is measured, then instantly adjusts the other to be the opposite, regardless of where they are in the universe. Entangled states that have no physical basis are now common in physics (Salart, Baas, Branciard, Gisin, & Zbinden, 2008).
A processing model explains entanglement as follows. Physics assumes that two photon particles leave the Cesium atom (Figure 3.23a) but really, processing just spreads. The Cesium atom creates the two photons in a physical event that restarts both at the same place, to merge the processes. Rather than pick a direction, both photon processes just spread in both directions. When light travels, it takes every path and lets a later physical event decide the one it took. In this case, the merged photons go both ways and let a later physical event decide which one went which way. In effect, both servers support both wave front clients as they go opposite ways, so the photon going left is run by two servers, as is the one going right (Figure 3.23b).
Why then is spin conserved when either photon is observed? To recap, the photons entangle when their processes merge, so both servers jointly handle the client requirements until a physical event restart. The entangled photons look and act like photons, but each is in effect half spin-up and half spin-down. When either photon is observed, one server restarts leaving the other to run the other photon, so they have opposite spin. Which server restarts is random, as it depends on which instance accesses a server first, but the result is always photons with opposite spin. Spin is always conserved because the processing after a restart is identical to that before, so the net spin must stay zero (Figure 3.23c).
Entanglement is then non-local for the same reason quantum collapse is, that client-server effects ignore the point-to-point transfer rate we call the speed of light. By analogy, a processor producing a screen pixel doesn’t have to go to that point to do it. It links to any screen point directly and likewise photon servers act regardless of how far apart entangled photons are on the screen of our space.
If the photons leaving a Cesium atom are particles that spin randomly, the spin of one can’t affect the other without some message between them, so how can it occur instantly? In contrast, if two servers are sharing both wave fronts, they are already in place to adjust to any physical event. Nothing then has to go anywhere to achieve the entanglement effect, as when one server restarts one photon, the other instantly carries on running the other. How entangled photons interact is thus solved.
Entanglement also underlies super-conductivity where many electrons entangle, so every electron is run by all their servers. They then move with no resistance because, in effect, nothing moves in a superconductor metal. Bose-Einstein condensates let any number of quantum entities merge in this way. Chapter 6 explores the implications of this unique feature for consciousness.