For physicists, one of the most complex branches of the discipline is quantum physics. It is often said that this has to do with the fact that, when analyzing any event, our presence influences the outcome. This makes it impossible to reach a “real” conclusion. To understand it better, some experts in the field point out that quantum physics would be like analyze what condensed milk is made of only by touch. And that our fingers were made of condensed milk. That’s how complex and strange this field is.
Entanglement is perhaps one of the most confusing aspects of quantum mechanics. At first glance, entanglement allows particles communicate over great distances instantaneously, apparently violating the speed of light. But, although entangled particles are connected, they do not necessarily share information with each other.
In quantum mechanics, a particle is not really a particle (back to the complexity of condensed milk). Instead of being a hard, solid and precise point, a particle is actually a cloud of fuzzy probabilitieswhich describe where we might find the particle when we go looking for it. But until we make a measurement, we can’t know exactly everything we’d like to know about the particle.
These fuzzy probabilities are known as quantum states. In certain circumstances, we can connect two particles quantumly, so that a single mathematical equation describes both sets of probabilities simultaneously. When this happens, we say that the particles are entangled.
When particles share a quantum state, measuring the properties of one can give us automatic knowledge of the state of the other. For example, let’s look at the case of quantum spin, a property of subatomic particles. In the case of particles like electrons, the spin can be in one of two states, up or down. Once we entangle two electrons, their spins are correlated. We can prepare the entanglement in a certain way so that the spins are always opposite to each other.
If we measure the first particle, we could randomly find the spin pointing up. What does this tell us about the second particle? Since we have carefully organized our entangled quantum state, We now know with 100% absolute certainty that the second particle must be pointing downwards. Its quantum state was entangled with the first particle, and as soon as one revelation is made, both revelations are made.
But what if the second particle is on the other side of the room? Or on the other side of the galaxy? According to quantum theory, as soon as a “choice” is made, the associated particle “knows” instantly what spin it should be. It seems that communication can be achieved faster than light. The solution to this apparent paradox comes from examining what is happening, when, and, most importantly, who knows what and when.
Let’s say we are the ones doing the measurement for particle A, while someone else is responsible for particle B. Once I make my measurement, I know for sure what spin my particle should have, but the other person doesn’t.. The other person only knows when they do their own measurement, or after we tell them.
So, while the entanglement process occurs instantaneously, the revelation of it does not. We have to use good old-fashioned communication methods that are not faster than light to reconstruct the correlations that quantum entanglement requires. The problem is that, in In quantum physics, we see the results, not the process that led to them. And it is the latter that could be faster than the speed of light.