Quantum Entanglement from Wikipedia:
When particles decay into other particles, these decays must obey the various conservation laws. As a result, pairs of particles can be generated that are required to be in certain quantum states. For ease of understanding, consider the situation where a pair of these particles are created, have a two state spin and one must be spin up and the other must be spin down. As described in the introduction, these two particles can now be called entangled since you can not fully describe one particle without mentioning the other. This type of entangled pair where the particles always have opposite spin is known as the spin anti-correlated case. The case where the spins are always the same is known as spin correlated.
Now that entangled particles have been created, quantum mechanics also holds that an observable, for example spin, is indeterminate until a measurement is made of that observable. At that instant, all of the possible values that the observable might have had "collapse" to the value that is measured. Consider, for now, just one of these created particles. In the singlet state of two spin, it is equally likely that this particle will be observed to be spin-up or spin-down. Meaning if you were to measure the spin of many like particles, the measurement will result in an unpredictable series of measurements that will tend to a 50% probability of the spin being up or down. However, the results are quite different if you examine both of the entangled particles in this experiment. When each of the particles in the entangled pair is measured in the same way, the results of their spin measurement will be correlated. Measuring one member of the pair tells you what the spin of the other member is without actually measuring its spin.
The controversy surrounding this topic comes in once you consider the ramifications of this result. Normally under the Copenhagen interpretation, the state a particle occupies is determined the moment the state is measured. However, in an entangled pair when the first particle is measured, the state of the other is known at the same time without measurement, regardless of the separation of the two particles. This knowledge of the second particle's state is at the heart of the debate. If the distance between particles is large enough, information or influence might be traveling faster than the speed of light which violates the principle of special relativity. One experiment that is in agreement with the effect of entanglement "traveling faster than light" was performed in 2008. This experiment found that the "speed" of quantum entanglement has a minimum lower bound of 10,000 times the speed of light.[5] However, because the method involves uncontrollable observation rather than controllable changing of state, no actual information is transmitted in this process. Therefore, the speed of light remains the communication speed limit.
en·tan·gle·ment
[en-tang-guh
l-muhnt] 
Show IPA | entanglement (ɪnˈtæŋɡ ə lmənt) | |
| — n | |
| 1. | something that entangles or is itself entangled |
| 2. | a sexual relationship regarded as unfortunate, damaging, or compromising |
Radiolab:
http://www.radiolab.org/blogs/radiolab-blog/2009/jul/13/in-defense-of-darwin/
No comments:
Post a Comment