- [Narrator] It was the nature of fundamental particles which make up the world we see around us that Einstein had come to Brussels to discuss.

And it was here that Einstein entered into a heated debate that would lead to the discovery of quantum entanglement.

(thrilling music) A concept that would trouble him for the rest of his life.

- This is the original Solvay Institute Building, and this is the place back in October 1927, where the Fifth Solvay Conference was held.

This amazing week long series of discussions on really what the world is made of, on the nature of matter and the new quantum theory.

And these steps are the very steps on which this famous group photograph was taken.

It is a collection of some of the most brilliant people in the world.

Here in the front row, we see Albert Einstein and the great Marie Curie and Max Planck.

In the back row standing the dapper Erwin Schrodinger.

And these sort of brash 20-year-olds or mid-20s, Werner Heisenberg and Wolfgang Pauli.

- [Narrator] These scientists were the pioneers of quantum mechanics.

I had a huge version of this photograph up on the wall.

It was a poster in my college dorm room.

My roommates had their favorite bands, and I had the 1927 Solvay Conference, which says a lot.

- [Narrator] This was one of the greatest meetings of minds in history.

More than half were or would become Nobel Prize winners.

Their experiments were showing that deep inside matter, tiny particles like atoms and their orbiting electrons were not solid little spheres.

They seemed fuzzy and undefined.

- So, this group here, these were the folks who had just been plumbing deeper and deeper and deeper to find what they hope would be a bedrock of what the world is made of.

And to their surprise, they found things less and less solid as they dug in.

This world was not tiny little bricks that got smaller and smaller.

At some point, the bricks gave way to this mush.

And what looked like solidity solidness, in fact became very confusing and kind of a whole new way of thinking about nature.