Non-locality, quantum teleportation and the EPR paradox
Posted by majutsu on January 20, 2008
Einstein, Podolsky, and Rosen wrote a paper in 1935 to try to prove that quantum mechanics was not a complete theory. In classical mechanics, reality consisted of billiard balls rolling around on the pool table of space-time. If the position, weight and speed of every particle were known at once, it would be possible to predict the future with perfect accuracy. But quantum mechanics had replaced this clockwork view of the universe with a gambling God. In quantum mechanics, a measurement on the same exact state did not produce the same result, half the time one thing would happen, half the time another. Instead of definite variables with definite values, quantum mechanics had a roulette wheel of random outcomes in a given situation. Furthermore, that inaccuracy seemed not to be due to some incompleteness of the theorem, but rather this vagueness was a fact of reality itself, made necessary by some sort of barrier to the depth to which we can peer into reality. This barrier appeared to be caused by some sort of interaction between the measuring mind and the objective world, and this interaction was not open to investigation through physical experimental means. This barrier is known as the Heisenberg Uncertainty Principle. As noted above, in the classical view, if the position and momentum (mass times speed) of every particle were known at once, then everything from then on would be known with no uncertainty. But nature places limits on us so that we cannot have such certainty. It turns out that if we know the position, we cannot know the momentum accurately. Or, vice versa, if we know the momentum, we cannot know the position accurately. This necessary uncertainty has something to do with the fact the we are trying to gather all this information for our mind’s use. Without a mind trying to correlate the momentum and the position, both can be measured accurately with no problem, but it is the mind’s involvement in the process that makes the variables we are trying to measure entangled. These seemingly unrelated physical properties become entangled with mind stuff and are no longer free events. Reality and outcomes of its measurement have been molded somehow by interaction with the observing mind. Absolute determinism of the future is avoided because of this interaction with our universe. Or another way to see it, without the mind there would be no free will.
So Einstein, Podolsky, and Rosen wrote a paper which set up an experimental situation known as the EPR paradox. Certain types of radioactive particles will decay into mirror image twin particles going in opposite directions. So the twin particles resulting from the decay will have the same mass but equal and opposite momentums. So let us imagine Alice on the west coast and Bob on the east coast. We will put a radioactive emitter in the Midwest halfway between them so that the particles reach Alice and Bob at the same time. So if Alice measures mass, she knows Bob’s particle has the same mass, so we know the mass of Bob’s particle from Alice’s measurement. If Bob measures the momentum of the particle he gets, then we know the mass and momentum of Bob’s particle, violating the Heisenberg Uncertainty Principle, right? It turns out that Bob is unable measure his momentum correctly. Somehow Alice’s measurement of a particle on the west coast has an instant non-local effect on Bob’s measurement of a different particle on the east coast. If Alice doesn’t make any measurement, then Bob is able to measure the position or the momentum as he pleases. This is called a paradox because it violates our simple ideas about reality.
The EPR paradox is not just a what-if, but has been verified several times experimentally in the laboratory using polarized photons. The EPR paradox and non-locality are a fact. Quantum reality exists in states. In the example we gave above, there are two states: [Alice knows momentum, Bob can’t know position], [Alice knows position, Bob can’t know momentum]. Either one of these states is possible initially. It is Alice’s intent to correlate these two measurements, to have forbidden knowledge of the future, that instantly affects physical reality on the east coast where Bob is, so as to prevent that trespass of Alice’s. It is therefore Alice’s will and mind that glue together at once points across the country and around the globe. If we instead put Bob on Alpha Centauri, we can see that Alice actually affects the reality of the whole universe at once.
The non-locality and entanglement illustrated by the EPR paradox also make teleportation possible. Another set of entangled variables (besides position and momentum) is the quantum spin on the x axis and the quantum spin on the z axis. If we know the quantum state occupied by a particle, we may make a copy of that particle. Knowledge of the full quantum state of a particle includes knowledge of its spin states. If we can teleport one particle, we can do it with many, then a mouse, a dog, a cat or a human! Normally we cannot know x and z spin at the same time because of their entanglement. But instead of seeing entanglement as a barrier to an outdated view of the universe, we can use entanglement to achieve teleportation. Here is how we can use quantum entanglement to make a copy. Alice performs a x-spin measurement on her particle. She sends the result of the measurement to Bob by classical means like a laser pulse (this can only be done at the speed of light or less so as to not violate relativity). After Bob receives the measurement information, he opens his particle box, and performs his z-axis measurement. The measurement itself will make a perfect copy of Alice’s particle appear in Bob’s locality after the proper quantum transformation. This is called quantum teleportation. Two papers of theory were written on this subject in 2004, and successful teleportation of atoms has occurred in the lab already.
To understand the EPR paradox and quantum teleportation, it is necessary to abandon the view that reality is made of chunks of space-time with the four forces (gravity, electromagnetism, strong and weak nuclear) acting between two local, touching points in space-time. Instead, all of reality is a complex vibration that may condense locally into certain physical objects with discrete bands of measured variables. Like acoustic frequencies, the quantum state waveforms of reality are separated into discrete bands of frequencies by this condensation into physical objects and measurement by the mind, much like the equalizer on a stereo separates an audio frequency into response bands. This discrete banding of waveforms makes measure variables in quantum physics have certain jumps in value which has been confirmed experimentally and is the source of the term quantum (meaning chunk, not smooth). From the EPR paradox and non-locality, we learn that the whole universe is vibrating in unison at once, and at any point where mind acts, the color and sound of this wave changes at once in the whole universe, and the objects and measured properties that condense from this song are also changed at once to some degree at every point in space from then on.