Do Entangled Particles Communicate Faster Than Light?
Quantum entanglement works in a very simple way, that can be described using a simple example.
Let’s say you have two balls — one red, and one blue. These are placed in a bag, and you pick one of them randomly. When you see it is red in color, you realize instantly that the other ball is blue in colour.
No matter how far the second ball is, you will know it’s colour as soon as you see the first ball! But this does not violate any law does it? The second ball is not “sending” you any information, is it?
The above is an example of classical entanglement. The colour of the two balls are entangled with each other. Note that changing the colour of one ball externally by painting, won’t change the colour of the second ball.
Now let’s take a look at an example of quantum entanglement. You have two hydrogen atoms, which are bonded together as a hydrogen molecule. The two electrons are sharing the same molecular orbital, and thus have opposite spins, by Pauli exclusion principle.
One of them is spin up and the other is spin down. Now as in the previous case, if you measure the spin of one of the electrons, and find that it is up, you will instantly realize that the spin of the other electron is down, no matter how far it is. Here, the spin of the two electrons are in quantum entanglement.
Note that, in this case too, changing the spin of the first electron to down, using an external magnetic field, will not change the spin of the second electron — it will stay down.
What is the difference between classical and quantum entanglement? Superposition. In the classical case, the red ball always stays red, and the blue one always stays blue, no matter how many times you see them.
In the quantum case however, the probability of getting up or down spin is always 50–50, regardless of all previous measurements. The spin of the first electron may come out to be up the first time, down the second time, and up the third time again!
So what have we learnt?
- Quantum properties, like spin, strangeness, charm, parity, flavour, etc, are in a state of superposition, and are not permanent.
- Each of the above properties can take different values. For example, spin can take the value “up” or “down”.
- When one of the properties of two particles are in a state of quantum entanglement, measuring the value of one of these particles will reveal the value of the other immediately, regardless of distance.
- Changing the value of one of these particles externally, won’t change the value of the other. Hence, entanglement does not violate special relativity.
I hope you have understood!
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