The Original Double Slit Experiment

What is light?

What is light? Light is... light is... what is light? That's a good question, isn't it? What is light?

Isn't it an element?

Light is brightness, I guess.

- We have auras? - We all have auras.

- Which are light? - Yes, they are.

It lights up the room, it makes it... not dark.

- What's the difference between blue light and red light? - The color.

It goes in your eyes and then you see stuff.

The range from white to red to orange to green, it's like the chakras of your body.

- Can you see my aura? - No, not particularly right now.

- Is it too bright out? - It's very sunny out here today.

- Does that make it harder to see someone's aura? - Not necessarily.

If I was to explain it to a blind person, I'd... It would be... It would be the difference... You see nothing whatsoever as a blind person, whereas I see things in front of me.

To be fair, the question of what light is, is not an easy one. For centuries, the greatest minds in science debated this issue.

In the late 1600s, Newton proposed that light was a stream of particles or corpuscles. He proposed this in his treatise, Opticks.

But at the same time, a dutch physicist named Huygens proposed that light was a wave.

And this debate raged on until it was settled by the experiment I've recreated today, Thomas Young's double slit experiment.

To make sure I got the experiment right, I went to the original source. With a help of Brady Haran, I managed to get into the vault, underneath the Royal Society in London.

We're in!