6 EPR Table of Contents Previous Next

The EPR thought experiment explained.

This thought experiment was designed by Einstein, Podolski and Rosen (EPR) to show that something basic (a hidden variable?) was missing from quantum theory.

Details of EPR: In the EPR thought experiment you start with two quantum mechanical particles or photons that are entangled. Let us say we have two photons, one red and the other blue. We fire the two photons into something that will make them indeterminate at the same time. A beam splitter will do the job and entangles the two photons and puts them into a state of superposition according to standard physics. See below for a notion of how superposition is supposed to work:

from: http://plato.stanford.edu/entries/qm-copenhagen/

The Measurement Problem and the Classical-Quantum Distinction

Apparently, we are living in a quantum world since everything is constituted by atomic and subatomic particles. Hence classical physics seems merely to be a useful approximation to a world which is quantum mechanical on all scales. Such a view, which many modern physicists support, can be called quantum fundamentalism (Zinkernagel forthcoming). It can be defined as a position containing two components: (1) everything in the Universe is fundamentally of quantum nature (the ontological component); and (2) everything in the Universe is ultimately describable in quantum mechanical terms (the epistemological component). Thus, we may define quantum fundamentalism to be the position holding that everything in the world is essentially quantized and that the quantum theory gives us a literal description of this nature. The basic assumption behind quantum fundamentalism is that the structure of the formalism, in this case the wave function, corresponds to how the world is structured. For instance, according to the wave function description every quantum system may be in a superposition of different states because a combination of state vectors is also a state vector. Now, assuming that both the quantum object and the measuring apparatus are quantum systems that each can be described by a wave function, it follows that their entangled state would likewise be represented by a state vector. Then the challenge is, of course, how we can explain why the pointer of a measuring instrument enters a definite (and not a superposition) position, as experience tells us, whenever the apparatus interacts with the object. In a nutshell this is the measurement problem.

In the standard quantum interpretation the photon that is detected first (lets say it turned out to be red) became red at the instant of measurement which collapsed the wave-function (when things become observable and not probabilistic) and ended the superposition and entanglement, when this happens information becomes instantly available to the other particle so that it can be blue. Prior to discovery of the red particle, it was a superposition (of probabilities) of red and blue and its discovery caused it to appear in reality as red.

Einstein and crew pointed out that this thought experiment could not in reality be performed because information would need to go faster than the speed of light to tell the remote blue particle to appear. Alain Aspect and others have shown that this experiment could really be done and that when the red particle is detected the blue shows up instantaneously. This apparent contradiction of EPR tended to verify the standard interpretation of quantum mechanics (superposition, uncertainty and entanglement).

DWT agrees with the result of the Aspect experiment, and also agrees with Einstein and crew that information does not travel faster than light. So, what is going on?

What is going on? John S. Bell theorized that no “hidden variable” could exist that would not make quantum mechanics “grossly non-local”. So, a (continuous) hidden variable would not help explain the quantum mechanical result. Alain Aspect went on to prove Bell’s inequalities and said “The experimental violation of Bell’s inequalities confirms that a pair of entangled photons separated by hundreds of metres must be considered a single non-separable object — it is impossible to assign local physical reality to each photon.”

Bell and Aspect came to a very interesting conclusion but it did not answer Einstein’s objection about information traveling faster than the speed of light. And we are left in the interesting position that everybody is right and something is wrong. That something is uncertainty and superposition and the very big assumption that quantum mechanics is a continuous phenomena.

There is no EPR paradox: DWT thinks that Aspect’s entangled photons are one connected thing that has to λ-hop together. A proton and an electron are quantum particles that are entangled when they are together in a hydrogen atom. The hydrogen atom itself is a quantum particle that λ-hops with a hop that is shorter than either the electron or proton that are its parts. If we measure a hydrogen atom (without imparting too much energy to it) it does not become an isolated proton and electron that have to reunite. So, entangled particles that do not expand are commonplace.

Is it possible to make an entangled particle that does expand? DWT thinks that Alain Aspect made an entangled particle that expands during its hop. Entangling the polarizations of two photons as done by Aspect has turned them into a particle (a photon thingy). The photons have become dependent upon each other to exist (they hop together), and they cannot be separated from each other without the application of energy. The particle that is the entangled photons is dramatically different from the particle that is the hydrogen atom in that the two entangled photons (taken as a whole) can be made to have a net low velocity (even though they are moving apart at the speed of light). This is not true for the proton and electron in the hydrogen atom which cannot be made to propagate away from each other. The entangled photons taken as a single particle (the photon thingy) has a net velocity very close to zero, but the photons themselves are moving apart at the speed of light. This photon pair is easy to disentangle because the energy holding it together is small. When the entanglement is broken between the two photons they both appear (out of nowhere) at each end of their former combined particle. Entangled particles that are expanding on a hop are not commonplace but they can be made as Alain Aspect has demonstrated.

The difference between superposition and λ-hopping:

In superposition each particle exists continuously as a probability mix of both red and blue particles until they are measured. The measurement is a wheel of fortune event where the result can be red or blue.

In DWT theory we can think of the particles as never loosing their identity (even if they are not manifest) one hops down the fiber in one direction the other hops down the fiber in the other direction. We have arranged the experiment so that we do not know which one went which way (by using a beamsplitter), but one went one way and the other went the other way. When we look and find a particle it was what nature intended to be there.

To visualize the DWT concept think of sending a red and a blue particle via UPS to a destination. The two particles are put randomly into a small box and the box is sent off (λ-hops). At the destination the box arrives as an elongated weird shape with a lump at each end (sometimes that happens when we ship things). The box is opened and the particle at one end is red and the other end is blue. DWT sees no reason to postulate that observing one particle caused the appearance of the other. Both particles were present at their respective locations when the package arrived. When the box arrived and was opened the red particle was found first. As soon as we see that it is red, we know that the other is blue, no measurement is needed and the speed of light has no bearing in what is going on.

The concept of λ-hopping may seem to be as strange as uncertainty and superposition but it makes physics understandable. In this case non-existent is better than uncertain.

Einstein’s intuition was correct: Einstein was correct in that there is something “goofy” about quantum mechanics, and it is that all quantum mechanical objects (photons and particles) do not have a continuous existence. Einstein’s missing hidden variable is humanity’s insistence that all particles including photons must manifest continuously.