Quantum Mechanics Reveals a Faster-Than-Light Effect

Derek Muller begins his new Veritasium video with a basic question on what happens if the sun suddenly vanishes. That’s the big question because Earth would just keep orbiting for around eight minutes, or the time it takes for light to reach us. Sir Isaac Newton believed that gravity was an immediate force that works over space, but Albert Einstein’s general relativity changed that. He demonstrated that gravitational changes propagate at the speed of light through ripples in space-time. This law keeps the universe in order and prevents all kinds of paradoxical situations from occurring.

Muller then delves into the mysterious domain of quantum mechanics. Now, in this world, you face identical issues. In reality, Einstein was the first to express misgivings about what he dubbed “spooky action at a distance.” In quantum mechanics, a particle’s probability of being in a specific state is defined by its wave function, which spreads like a wave across the entire cosmos.When you measure that wave function in one location, the entire wave function collapses suddenly, everywhere at once. That’s strange because it implies that a particle in one location can instantly influence a particle on the opposite side of the universe, regardless of how far away it is.

Einstein was not at all comfortable with that idea. He co-authored the EPR paradox article with Boris Podolsky and Nathan Rosen in 1935. They basically devised a thought experiment utilizing two particles, such as electrons and positrons. These particles were entangled, which implies they were formed simultaneously with opposite spins. You distance them by thousands of light years and then measure one of their spins; the other particle’s spin is instantly fixed.

The problem is that measuring the spin of one particle is equivalent to sending an instant communication to the other particle, despite the fact that they are thousands of light years apart. Einstein referred to this as spooky action at a distance since it appears to require a signal traveling faster than the speed of light, implying that the universe contains some hidden details that we are unaware of. He preferred the concept of local hidden variables, which are particles with predetermined instructions that explain why they always appear to be related, without the necessity for immediate action at a distance.

However, Niels Bohr’s interpretation of quantum theory denies the concept of local hidden variables. Instead, the wave function contains all of the probabilities that something will occur, and when you measure it, reality changes quickly. Einstein and Bohr had a major argument about all of this. They participated in many heated disputes in conferences in the 1920s and 1930s, including the Solvay conference. Einstein would come up with ingenious thought experiments that appeared to expose weaknesses in quantum theory, but Bohr would always find a way to react, even if his reasons weren’t always obvious. History appears to have come down on Bohrs’ side, as all of quantum theory’s predictions have proven correct in the experiments we’ve undertaken.

It is worth noting that a single breakthrough occurred in 1964 by a man named John Bell. Bell developed a theorem that enables us to test the entire debate mathematically. He suggested thinking about entangled particles being measured from various angles. Consider measuring one particle at 0 degrees, another at 120 degrees, and another at 240 degrees. Quantum theory predicts that we will detect mismatches in these results around 25% of the time. However, if these particles contain local hidden variables, they should have approximately 33% mismatches. So let’s do some experiments to see which one is correct.

That’s exactly what many researchers did beginning in the 1970s and 80s. Alain Aspect was a crucial figure in this effort. They discovered that the data perfectly matched the expectations of quantum mechanics. The concept of local hidden variables just did not stand up when tested. So, what does this mean? It indicates that quantum mechanics requires that when you measure one particle, the other particle is immediately influenced. This is the phenomena of non-locality that Einstein was so concerned about, but in this case, it is a rather safe and benign impact.

Muller argues that this impact, this immediate transmission between particles, conveys no valuable information. It’s not like you can flip a coin and send a message to the other side of the cosmos; the outcome is still utterly unpredictable. You can’t utilize these entangled particles to deliver a message since causality remains intact, and we don’t have to worry about breaching the principles of relativity.