Thursday, 3 November 2016

Spooky Action At a Distance and Superluminal Information Transmission?

- Bruce Long

 A warning before you commence reading this article. Physicists are not in agreement about the status of superluminal information transmission (faster than light information transmission) and the possibility of harnessing action at a distance for instantaneous information transmission any more than they are in agreement about the veracity of string theory.

Some physicists interpret the problem using a particular adaptation of Shannon's statistical theory of information (which is certainly salient to the problem domain), such that there can be no information transmitted between two entangled quantum systems (very small atomic or particle systems that are separated by distance but somehow linked causally) because of what one system already 'knows' about the other. However, this approach favours one kind of subjectivism about the nature of information.

Different interpretations of the definition of probabilities and information can point to different results. Importantly, if there is a physical causal link or pathway of any kind between any two entities or points, then there exists a signal pathway, and therefore there exists an information channel.

Another important point to note is that there are not only multiple interpretations of information theory and probability theory, but of course there are also many debates about the true nature of quantum theory and quantum uncertainty, as well as entanglement. The current view of the possibility of entanglement based superluminal information transmission may change with a change in understanding of decoherence and the measurement effect, for example.

Recent loophole free confirmation of John Bell's test results for confirming spooky action at a distance mean that the question of instantaneous information transmission is a live issue. It has serious practical and philosophical ramifications.

For example - Nick Bostrom's simulation arguments may be reinforced by the idea that the substrate of the physical world is configured such that a physical variable at one point is associated with a physical variable at what we would empirically detect as distant, but with no detectable finite causal interaction via causal structures between them, and with apparently instantaneous synchronisation. This is just the kind of thing that one can bring about in a 3D computer game: two objects can be synchronised by the underlying code in a way that would be considered unnatural in the physical world.
The popularization of the shortcomings of string theory (significantly reduced since M-Theory was introduced by Ed Witten in 1995) and the work of science popularisers like Lawrence Krauss, Peter Woit, John Gribbin, and  Neil DeGrasse Tyson have co-incided with a mounting interest in metaphysics and the philosophy of physics among physicists and philosophers alike. The loophole free confirmation of Bell's theorems, however, may well be more significant than Hawking's discovery of black hole radiation.
Spooky Action At A Distance
When Einstein produced his theory of special relativity and work on quantum mechanics, he made a disturbing discovery - what he called "spooky action at a distance" (from terminology used by Newton). Einstein's Spooky action at a distance is better known among physicists as non-local effect or quantum entanglement.
What is entanglement and what does it have to do with information transmission? Information transmission depends upon cause and effect. If you can make cause and effect happen instantaneously, then arguably so does information transmission.
Briefly, Einstein's theory predicted that two quantum systems (very small systems) like photons or electrons or other particles would affect each other's states instantaneously even if they we separated by large distances. The systems (particles) start out together in the same place in space and time, and then can become widely separated.

After they are separated by a significant non-trivial distance - a measurement of one that changes its state will necessarily result in an instantaneous change in the state of the other in the opposite direction (quantum particles have different rates of spin and what is called angular momentum, and there is a direction of that spin - usually up or down.) If one particle is spin up, and you measure it and it becomes spin down - then the other particle will do the opposite even if has traveled a long way off.  Instantaneously - with no delay at all. Spooky, said Einstein.
Now, instantaneously here literally means instantaneously. Not at the speed of light, or near it, but much much faster. In fact - speed or velocity is not even the right thing to talk about. The cause-effect of entanglement or non-local effects is immediate. It would be like the pitcher throwing the baseball, while the batter hits exactly the same ball at exactly the same time - and the pitcher is on Earth and the batter on the moon.
There is theoretically and practically no speed - just instantaneous change of the state of one physical system based upon the change in the state of the other (usually when the other system is physically measured.) It's almost like if a fan watches the baseball pitcher, then the action at a distance will automatically happen. If the pitcher is pitching, you know the batter is batting at that moment - with the same ball. If the fan goes and hands the pitcher a bat, there is extremely high likelihood (virtual certainty) that the distant batter will have become a pitcher at that exact same moment. It is THAT weird.
Einstein did not like spooky action at a distance at all because it suggested that the usual understanding of cause and effect and causal chains in physics was largely wrong for quantum mechanics. Either something was wrong with the mathematics, said Einstein, or there was something very weird going on in the universe.

Einstein came to the conclusion that there must be intermediate causal structures between the entangled quantum systems that had not been detected physically yet. This theory is called hidden local variable or local realism theory. The realism means that there is really something there doing the entangling, and local means that spooky action at a distance just does not happen but instead there is a hidden intermediate causal structure that is local to the quantum systems.
A Speed for Entanglement After All

Now many readers will be aware of Einstein's maxim that no body without zero rest mass (no mass when not moving relative to any spatiotemporal frame of reference) can move faster than the speed of light. That's an immutable law of the universe - right? Well - maybe. It is action at a distance. Einstein's hidden local variables have not been found - and in fact the theory has turned out to be unsupported by empirical experimental findings.
Recently some Chinese physicists have tried to measure the speed of non-local effects (refer to the list of reference at Physics News.) I have just said that there is no speed involved - so what is this experiment about? Well, their findings don't provide much comfort. What they proved experimentally - assuming no discovery of errors in the future - is that if there is a speed of entanglement then it has to be at least 10 000 times the speed of light. They do not know if it is the limitations of their equipment that is causing the measurement value. The speed might be even higher - or no speed at all as suggested above.
Bell Theorems- Is Spooky Action at a Distance Real? Or are there hidden local intermediate causal structures?
The theoretical physicist John Bell made things even worse for Einstein in 1964 with a theory that suggested that the mathematical predictions of quantum mechanics did not fit with the mathematical theory of hidden local variables that he himself had developed.
Things got worse still for the hidden local variable theory when Bell's findings were supported by experiment in 1972 by John Clauser and Stuart Freeman. Alain Aspect did it again with experiments in 1981.
What Now - Superluminal Information Transfer?
In the best mathematical and scientific theories of information, information transmission involves loss due to signal noise and is limited by the transmission rates permitted by the transmission medium. Some information theorists assert that information transfer is only about the covariance - the simultaneous changing - of one structure with another in such a way that the state of one system (an information receiver) tells one something about the state of the other (the information source) with a certain degree of probability.
Now, normally entanglement is not regarded by physicists as an information channel on a statistical basis since there is no uncertainty about the state of one system if the state of the other is known. For statistical formal measures of information one requires statistical uncertainty - because according to those measures information just is a reduction in uncertainty or an increase in probability about the next state of the source based on the current state, or else based upon signals received that were caused by the current state. (See John Gray's text Information Theory and Entropy: ; See also Warren Weaver's introduction to Claude E Shannon's The Mathematical Theory of communcation.)

I will put aside this consideration of the statistical conception of information as an impediment to quantum entanglement channels for information transmission. This is because the statistical conception is only one (albeit very important) element of the transmission of information, and only one conception of information transfer.
Whither the Second Law of Thermodynamics: Entropy defeated?
The point is that if entanglement is a real physical causality - if it really involves some kind of instant physical cause effect interaction, then that means that information can be transferred instantaneously. If that is true, then many things are unclear. Because of entropy and the second law of thermodynamics, causality is limited in a causally closed universe. Energy loss and impedance limit transmission speeds in predictable ways.

However, if non-local quantum information transmission is true, then it looks very much like we might be able to send information without any signal loss at all. Even weirder - information might be transmissable with no intermediate causal pathway or structure. This is spooky indeed.
J. S. Bell, (1966On the problem of hidden variables in quantum mechanics, Rev. Mod. Phys. 38, 447.