Leo Kouwenhoven, professor in Applied Physics discusses “Spooky” Physics at TEDxDelft – Transcript

**Listen to the MP3 Audio here: Spooky physics by Leo Kouwenhoven at TEDxDelft**

**TRANSCRIPT: **

They just told me back there that apparently there is a golden rule in book publishing that says that with every formula you show, you lose half of your audience. And I have two in my first slide.

But I only want to show you these formulas to illustrate that with just a few symbols, like F = m x a, we can describe a wealth of phenomena, from the Earth around the Sun, from a ball game, from your bike ride, everything.

Or if you are a communication person, you may like Maxwell’s equation. Everything we do with our radio or mobile phone, communications or actually the fact that we see each other, is all described by this very simple Maxwell equation that you see here. It is so simple. It describes basically these two equations. It describes basically everything in our daily life.

But there is more. Besides our classical world, there is also a quantum mechanical world. This is the world of atoms, molecules, the very small particles. And again, we have a very simple looking equation. It has a Greek symbol in it, that makes it a little bit obscure, but otherwise it is fairly short.

And please be impressed, that this equation, the Schrödinger’s equation, describes all of Chemistry. So in some sense, because our bodies are big chemical factories, with all the atoms held together by quantum mechanical glue, our existence is thanks to quantum mechanics.

But maybe with this third equation I am losing another half of the audience. Many people think: *“Oh, these small particles are not my things.”* Or *“Formulas, I never have understood them. I am more of the human scale. I feel things or hear things or even touch things.”* In that case, you are the right person for me to talk to because I will not show any more formulas in my presentation. I will actually show you some quantum objects that you can actually see, you can actually hear them, and you can touch them. So let’s start.

It all starts, actually, up to a few minutes ago, before I came on the stage, quantum mechanics was describing very well, very accurately the world of atoms and molecules. Then, at large scale, it had already started at our unit, the biological cell, it kind of stops. The biologist takes the cell as the fundamental unit to build up biology. This is an enormous simplification because it completely ignores quantum mechanics. But it is as best as we can do at this moment. Larger objects like our hair, which is basically the smallest thing we can see with our eyes, or us, you know, that is all classical.

But the small things can be described very accurately. The people who put forward this theory, the quantum theory, actually maybe made the greatest intellectual revolution of mankind. You see a picture here on the first row, very prominent Albert Einstein. You can clearly recognize him in the middle. On his right, left for us, there is Hendrik Lorentz, our Dutch hero. And next to Lorentz, you see Madame Curie. And many of these men in this picture have received a Nobel Price for their great work. There is one person who got the Nobel price twice. And that is actually the only woman in the picture, Madame Curie. So apparently that is true what they say that women have to perform twice as good in order to be part of the gang. She did it. This is a hundred years ago.

What’s new? Well, present day geniuses look like this. This is a group of brilliant people that form our group at the TU Delft. But again, they are at the verge of a new quantum era. We are no longer studying atoms and molecules as given by nature, a concept that we actually design and make, by using very advanced fabrication techniques, new objects, much bigger, but still showed us this absurd quantum mechanical behavior.

So what is actually absurd about quantum mechanics? Why are we so excited about our quantum stuff? Let me give you two examples of absurd quantum mechanics. The first example is quantum superposition. Let’s take a particle, like an electron or something, and bring it into a ring structure. Have the particle then take either the upper arm to get to the exit or take the lower arm to get to the exit.

Now, what actually happens in quantum mechanics is that the electron takes both arms at the same time simultaneously, really sitting in the upper arm as well as in the lower arm at the very same time. And we know this because we follow the particle and we see that at the exit of the ring it actually collides with itself. It bounces into itself. And we observe this as interference. Such a superposition of being at two different locations at the same time has been very thoroughly checked by all kinds of experiments. Quantum superposition.

The next example is an example of entanglement. And we start very simple. We take, say, a red particle and a white particle. Very classical colors. Then the next step is that we bring them together and we make them interact a little bit. So we bring them very close together so they feel each other. By virtue of this interaction they become entangled; they take over each other’s properties. In terms of color they become white-reddish. That’s OK.

The curious thing that happens if we take them, and disentangle them again and bring them apart. And while taking them apart they remain entangled. They are still — the one that is on the left for you, still has some properties of the other particle, which can be at a very large distance, as far as the size of the Universe, in principle. So let’s disentangle them over a very long distance. Particles keep having each other’s properties.