Actually, at least according to Einstein's theory, it would require an *infinite* amount of energy to reach the speed of light. However, in the realm of quantum mechanics, instantaneous communication (of a sort) is apparently common place. See Belle's Theorem, the EPR (Einstein-Podolsky-Rosen) experiment, the Einstein-Podolsky-Rosen Paradox, and/or non-locality (aka "spooky action at a distance", Einstein's term for it)
EPR Paradox
By Andrew Zimmerman Jones
The EPR Paradox (or the Einstein-Podolsky-Rosen Paradox) is a thought experiment intended to demonstrate an inherent paradox in the early formulations of quantum theory. It is among the best-known examples of quantum entanglement. The paradox involves two particles which are entangled with each other according to quantum mechanics. Under the Copenhagen interpretation of quantum mechanics, each particle is individually in an uncertain state until it is measured, at which point the state of that particle becomes certain.
At that exact same moment, the other particle’s state also becomes certain. The reason that this is classified as a paradox is that it seemingly involves communication between the two particles at speeds greater than the speed of light, which is a conflict with Einstein’s theory of relativity.
The Paradox’s Origin:
The paradox was the focal point of a heated debate between Albert Einstein and Niels Bohr. Einstein was never comfortable with the quantum mechanics being developed by Bohr and his colleagues (based, ironically, on work started by Einstein). Together with his colleagues Boris Podolsky and Nathan Rosen, he developed the EPR Paradox as a way of showing that the theory was inconsistent with other known laws of physics.
(Boris Podolsky was portrayed by actor Gene Saks as one of Einstein’s three comedic sidekicks in the romantic comedy I.Q..) At the time, there was no real way to carry out the experiment, so it was just a thought experiment, or gedankenexperiment.
Several years later, the physicist David Bohm modified the EPR paradox example so that things were a bit clearer. (The original way the paradox was presented was kind of confusing, even to professional physicists.) In the more popular Bohm formulation, an unstable spin 0 particle decays into two different particles, Particle A and Particle B, heading in opposite directions.
Because the initial particle had spin 0, the sum of the two new particle spins must equal zero. If Particle A has spin +1/2, then Particle B must have spin -1/2 (and vice versa). Again, according to the Copenhagen interpretation of quantum mechanics, until a measurement is made, neither particle has a definite state. They are both in a superposition of possible states, with an equal probability (in this case) of having positive or negative spin.
The Paradox’s Meaning:
There are two key points at work here which make this troubling:
Quantum physics tells us that, until the moment of the measurement, the particles do not have a definite quantum spin, but are in a superposition of possible states.
As soon as we measure the spin of Particle A, we know for sure the value we’ll get from measuring the spin of Particle B.
If you measure Particle A, it seems like Particle A’s quantum spin gets “set” by the measurement ... but somehow Particle B also instantly “knows” what spin it is supposed to take on. To Einstein, this was a clear violation of the theory of relativity.
No one ever really questioned point 2; the controversy lay entirely with point 1. David Bohm and Albert Einstein supported an alternative approach called “hidden variables theory,” which suggested that quantum mechanics was incomplete. In this viewpoint, there had to be some aspect of quantum mechanics that wasn’t immediately obvious, but which needed to be added into the theory to explain this sort of non-local effect.
As an analogy, consider that you have two envelopes that contain money. You have been told that one of them contains a $5 bill and the other contains a $10 bill. If you open one envelope and it contains a $5 bill, then you know for sure that the other envelope contains the $10 bill.
The problem with this analogy is that quantum mechanics definitely doesn’t appear to work this way. In the case of the money, each envelope contains a specific bill, even if I never get around to looking in them.
The uncertainty in quantum mechanics doesn’t just represent a lack of our knowledge, but a fundamental lack of definite reality. Until the measurement is made, according to the Copenhagen interpretation, the particles are really in a superposition of all possible states (as in the case of the dead/alive cat in the Schroedinger’s Cat thought experiment). While most physicists would have preferred to have a universe with clearer rules, no one could figure out exactly what these “hidden variables” were or how they could be incorporated into the theory in a meaningful way.
Niels Bohr and others defended the standard Copenhagen interpretation of quantum mechanics, which continued to be supported by the experimental evidence. The explanation is that the wavefunction which describes the superposition of possible quantum states exists at all points simultaneously. The spin of Particle A and spin of Particle B are not independent quantities, but are represented by the same term within the quantum physics equations. The instant the measurement on Particle A is made, the entire wavefunction collapses into a single state. In this way, there’s no distant communication taking place.
The major nail in the coffin of the hidden variables theory came from the physicist John Stewart Bell, in what is known as Bell’s Theorem. He developed a series of inequalities (called Bell inequalities) which represent how measurements of the spin of Particle A and Particle B would distribute if they weren’t entangled. In experiment after experiment, the Bell inequalities are violated, meaning that quantum entanglement does seem to take place.
Despite this evidence to the contrary, there are still some proponents of hidden variables theory, though this is mostly among amateur physicists rather than professionals.
Related Articles:
What is Bell’s Theorem?
What is Quantum Entanglement?
There are many different interpretations of quantum mechanics.
How Quantum Physics Explains the Invisible Universe
Copenhagen interpretation - “textbook” explanation of quantum physics
Measurement Problem
What is Schroedinger’s Cat?
http://physics.about.com/od/physicsetoh/g/EPRparadox.htm
What is Bell’s Theorem?
By Andrew Zimmerman Jones
One of the most curious elements of physics is the principle of quantum entanglement in quantum physics, where two seemingly independent particles appear to be connected to each other in a strange way. This behavior - which was famously debated by Albert Einstein and Niels Bohr - was called “spooky action at a distance” by Einstein. However, physicist John Stewart Bell developed a way of determining whether this “action at a distance” (or non-local behavior, in more physics-like jargon) actually takes place.
What was Bell’s Theorem?
Answer: Bell’s Theorem was devised by Irish physicist John Stewart Bell (1928-1990) as a means of testing whether or not particles connected through quantum entanglement communicate information faster than the speed of light. Specifically, the theorem says that no theory of local hidden variables can account for all of the predictions of quantum mechanics. Bell proves this theorem through the creation of Bell inequalities, which are shown by experiment to be violated in quantum physics systems, thus proving that some idea at the heart of local hidden variables theories has to be false.
The property which usually takes the fall is locality - the idea that no physical effects not move faster than the speed of light.
Quantum Entanglement:
In a situation where you have two particles, A and B, which are connected through quantum entanglement, then the properties of A and B are correlated. For example, the spin of A may be 1/2 and the spin of B may be -1/2, or vice versa. Quantum physics tells us that until a measurement is made, these particles are in a superposition of possible states. The spin of A is both 1/2 and -1/2. (See our article on the Schroedinger’s Cat thought experiment for more on this idea. This particular example with particles A and B is a variant of the Einstein-Podolsky-Rosen paradox, often called the EPR Paradox.)
However, once you measure the spin of A, you know for sure the value of B’s spin without ever having to measure it directly. (If A has spin 1/2, then B’s spin has to be -1/2. If A has spin -1/2, then B’s spin has to be 1/2. There are no other alternatives.) The riddle at the heart of Bell’s Theorem is how that information gets communicated from particle A to particle B.
Bell’s Theorem at Work:
John Stewart Bell originally proposed the idea for Bell’s Theorem in his 1964 paper “On the Einstein Podolsky Rosen paradox.” In his analysis, he derived formulas called the Bell inequalities, which are probabilistic statements about how often the spin of particle A and particle B should correlate with each other if normal probability (as opposed to quantum entanglement) were working. These Bell inequalities are violated by quantum physics experiments, which means that one of his basic assumptions had to be false, and there were only two assumptions that fit the bill - either physical reality or locality was failing.
To understand what this means, go back to the experiment described above. You measure particle A’s spin. There are two situations that could be the result - either particle B immediately has the opposite spin, or particle B is still in a superposition of states.
If particle B is affected immediately by the measurement of particle A, then this means that the assumption of locality is violated. In other words, somehow a “message” got from particle A to particle B instantaneously, even though they can be separated by a great distance. This would mean that quantum mechanics displays the property of non-locality.
If this instantaneous “message” (i.e., non-locality) doesn’t take place, then the only other option is that particle B is still in a superposition of states. The measurement of particle B’s spin should therefore be completely independent of the measurement of particle A, and the Bell inequalities represent the percent of the time when the spins of A and B should be correlated in this situation.
Experiments have overwhelmingly shown that the Bell inequalities are violated. The most common interpretation of this result is that the “message” between A and B is instantaneous. (The alternative would be to invalidate the physical reality of B’s spin.) Therefore, quantum mechanics seems to display non-locality.
Note: This non-locality in quantum mechanics only relates to the specific information that is entangled between the two particles - the spin in the above example. The measurement of A cannot be used to instantly transmit any sort of other information to B at great distances, and no one observing B will be able to tell independently whether or not A was measured. Under the vast majority of interpretations by respected physicists, this does not allow communication faster than the speed of light.
http://physics.about.com/od/quantuminterpretations/f/bellstheorem.htm
Here is are the problems I have with quantum entanglement.
They say that entanglement between two particles can occur over millions of miles. But just the distance part makes the theory untestable.
The big bugaboo , to me, is how do they know they have found ‘a pair’ ? Let’s say that a particle could be in one of six states. Up, Down, Left, Right, Top, Bottom. Assuming an infinite Universe, and an even distribution of states, then the number particles that could be in the same state as the ‘source’ particle is INFINITY/6. Or another way to look at it would be that you had a 1 in 6 chance of finding a matching pair between any two particles in the Universe, whether they are ‘entangled’ or not.
The last problem is that they say that determining the state of the source particle makes it change. Then they say that the other entangled particle changes instantly.
When they check the other particle, it’s state matches the original particle. But... if checking it causes it to change, then it wasn’t identical to the source and didn’t change in response to the source particle ‘instantly’. It didn’t change until it was checked. I don’t see how they can claim the second changes instantly to match the first when (1) they can’t verify it instantly, and (2) verifying it causes it to change and doesn’t even prove what state it was in before it was changed. The two ‘entangled’ particles may have been in different states, and the fact that after being tested, they match means nothing... really.