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This entry was prepared for Suesa's science challenge.

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Popular misconception

The speed of light limits us so much. If we could transfer information faster than light travels, we would be able to have faster computers, better communication not only on the Earth, but also across the whole universe. But is it possible? According to Einstein's special relativity - no.

A lot of people say - when they hear about quantum entanglement for the first time - that it provides an easy way to increase a speed of information sending. It, unfortunately, isn't true and it really annoys me. Ehhh, wouldn't it be great if we could transfer information faster than the speed of causality?

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^{image credits: Antonin Allegre on Unsplash}

What is quantum entanglement?

Quantum mechanics is really weird, so its element - quantum entanglement - has to be also weird, right? Oh yea, exactly. Imagine two particles that are somehow connected, we call it entangled pair. If these particles weren't entangled, we - according to quantum mechanics - wouldn't be able to say much about their state before measurements, because they would be in superposition and if we measured one of them the other one would still be in this superposition.

What quantum entanglement changes is that if we measure the state of one particle of the entangled pair we instantly have information about the state of the other. The word instantly is really important, because, if one particle would be, let's say, on Earth and the other in a different galaxy, measuring one gives us information about the state of the other, faster than light needs to travel distance between them.

There are of course different levels of entanglement - sometimes only one property is entangled (spin, polarization etc.), sometimes more, but for thousands of people (you can count me from less than a year ago) conclusion is clear - it allows us to communicate faster than light…

Why it is actually not true?

The answer is simple - we can't force particle to be in a state in which we want it to be! You might ask - why? The answer again isn't complex - nature is probabilistic and measurement gives us random states. Although we know the state of both particles, we can't do anything with this information, at least we can't communicate using them. So there is no faster-than-light communication possible.

Let's say Alice wants to send information to Bob. They have entangled pair of particles (singlet state - spins of particles are opposite - if one's spin is up, the other must be down), one is on the Earth with Alice and the second on the Mars with Bob. They both agreed that spin up means 'yes' and spin down 'no'. So Alice measures her's particle's spin. She realized that spin of her particle is up, so "information" she had sent to Bob was 'no'. What can they do with that? Exactly, nothing that would let them communicate. Without additional traditional communication (limited with speed of light) this is kind of useless.

So there is no faster-than-light sending information in this case. As long as we don't discover a way to influence the state of particles, we won't be able to communicate using quantum entanglement.

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^{image credits: William Bout on Unsplash}

Conclusion

We can't communicate faster than light using quantum entanglement and it really annoys me. What a great opportunities it would cause! Just imagine - immediate communication with any place in the universe! We have to keep searching, unfortunately ;)

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References:

• theory.caltech.edu
• curious.astro.cornell.edu

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