What does the universe being not locally real mean?

Question

I just saw a comment that linked to an article explaining how Nobel prize winners recently discovered the universe is not locally real. My brain isn’t functioning properly today, so can someone please help me understand what this means?

In: 2860

Answer 1

Entangled particles change spin without any possible idea which way they will spin, because they don’t spin like a ball and because nothing near touches it to make the spin change.

Get a ball.

Local means if you push the ball, the ball moves. Your hand, your foot, a stick, the wind, something nearby that touches the ball moves the ball. Not something far away that can’t see or touch the ball.

The ball is real because it reacts to pushes and pulls and kicks and things that move it. We can say the ball is right there, it is moving or not moving, spinning or not. If you want, you could say the ball knows this too.

The ball is made of small particles. Sometime the particles can move like the ball. But when we look at particle spin, it is different. The ball can spin one way or another, but it is only spinning one way at a time until something local touches the ball and changes its spin. The ball changes based on how it was spinning and how it was last touched. In math and physics, we can say the ball has a local spin property.

When we look at entangled particles, we notice the spin is either one direction or the other. After we look.

Before we look at entangled particles, they spin every possible way, until we look to see which way they spin. Entangled particles are common, not weird. Spin is everywhere too.

Now the weird not locally real part.

With two entangled particles, before you measure spin on one particle, you don’t know the direction and you don’t know the direction of the particle either. After you measure one particle, you know its spin, and immediately know the other entangled particle has the opposite spin. But you never know which direction the particle you measure will spin.

So the locally not real part is that the particle does not know which way it is spinning before measure, and does not know which way it will spin after measure, and no other particle or known force locally touched the particle we measured.

So the particle is not locally real. Sort of.