Schrödingers Katze – Tot oder lebendig? | Harald Lesch

I have a guest today, I really don't know. One of the most famous cats in the world. Erwin Schrödinger's cat. The question is: is she still alive? Is she already dead? Or is she still somewhere in between? Yes, here. I'll open it right away. Come on, let's make it short and concise. Erwin Schrödinger, a great physicist, one of the founders of quantum mechanics, thought the following several decades ago: If you had a radioactive element in a box like this, that is, a radioactive chemical element, it could disintegrate. And the decomposition will cause a hammer to break a vial of poison and the cat here in the box will die as a result.

So the ending would definitely be if I waited long enough until the cat died. But what condition is the cat in? Because there is a big problem. Radioactive decay is a quantum mechanical process. This can happen, but it doesn't have to be that way. Then there is an intermediate state, the entanglement of both/and. And that is somehow clear now. So with radioactive decay it's like this: I can't say when an atomic nucleus will decay. But if I have enough atomic nuclei, then I can make a fairly accurate determination of the half-life. This means that this is the time in which half of the existing atomic nuclei have decayed.

Of course, one must ask: How does the atomic nucleus know that the others are still there, and why does it not simply decay after its half-life, but only statistically? Why is it like this? And that is precisely this element of indeterminacy in quantum mechanics that has given rise to so many mysterious questions, including Erwin Schrödinger's. And he basically just wanted to point out how absurd it is that quantum mechanics can so successfully explain natural phenomena. I'll explain what else you can explain in a moment. But once he said: Okay, I have the indeterminacy, the entanglement in radioactive decay.

If I now add the cat and close everything again, will the cat in turn also be locked? And then you can just say: What conditions can a cat have? She's alive, she's not alive... Yes. Like right now? And in the middle? What is the intermediate state supposed to be? How was it even concluded that such intertwined states must exist? You can basically, well, what should you use? Let's take the simplest one. It's about the question: Why do we exist? Yes, sure. At the beginning of the 20th century it was discovered that the atom is made up of a positively charged nucleus and that these positively charged atomic nuclei are orbited by negatively charged electrons.

And back then, at the time when all this quantum mechanics with its limited and entangled states did not yet exist, we had a big problem. Because opposite charges attract each other and because the electron is much lighter than the proton in the atomic nucleus, the electron would have to rush toward the nucleus gradually and fairly quickly, not so gradually, and would be accelerated by the presence of the atomic nucleus. If accelerated charges are radiated, it would fall even faster, so it would be practically like a transmitter. Yes, what would happen then? Some form of matter, definitely very compact.

Haha, like that. There is no way for that to happen, because molecules, for example, are where atoms connect. We only found out about this much later. But it was already clear that there had to be something completely different here, that is, that the electron could not simply be a particle. So there is a certain path around the core, but at the beginning no-go zones were defined. And then they said: So the electron can only be there! And only there! And nothing more! So, in essence, it is not at all. That couldn't be allowed to happen. This means that it was already suspected, without saying it directly, that the simple definition that the electron is a particle and only a particle is nothing more than a particle.

Yeah? Like that famous phrase “The truth and nothing but the truth.” That can't be right. And in fact there is a famous experiment that casts great doubt on this character, the particle character of the electron. And it was quite early. This experiment is the famous double slit. We have a machine here that emits electrons. And then we have a double slit like this. This is nothing more than two very, very narrow slots and on the back we have a screen. And then, like a photosensitive screen, for example, every time an electron hits this screen, a dark or bright spot would form, depending.

So what would we expect? When we launch particles, we have a gap here, a gap there. We would then expect a maximum directly behind one slit and a maximum directly behind the other slit. Good. The particles pass through it, maximum, maximum. No? It is empty. Do you see? Something completely different: you see an interference pattern whose maxima are exactly where you wouldn't expect them. So it's right behind the gap. Nothing. Between. As if electrons were waves. Yes, what now? After all, we send electrons. They are particles that behave like waves. OH! Yes, and that's exactly where the dog is buried.

So we thought about it. My God, what conditions. So the electron can do it. This is in canned condition. Here at the end it is in essential condition. For this interference to occur, there must have been a wave, etc. And there begins all the madness to which Schrödinger's thought experiment should lead. What have we sent here? Particles? No, those are waves. People have also tried it the other way around. The waves were sent with light, yes. You can see. The waves were sent, for example, over metal surfaces. And then he discovered that these electromagnetic waves don't behave like waves at all.

They behave like particles. This is the famous photographic effect. Yeah! So where you thought there were waves, apparently there are particle properties. And where I thought there were particles, apparently there are wave properties. In this little world, in this smaller world down there, not everything seems so clear at all. So it's not like it's there and it's there to clearly say that it's something in one place, it's something of this type, but it seems to be in intermediate states. And so it would have been with Schrödinger's cat. He would have been in the intermediate state, in the intermediate realm.

So what is quantum mechanics? In recent years many things have become clearer. That is why now one could say: From now on the demystification of quantum mechanics begins! Forget about collapsing wave functions, many-worlds theories, etc. Let's take a look at reality. Let's do the double slit experiment in a not-so-isolated environment in some lab, but let's put it in a box somewhere and let that box heat up. Yes, that's how an experiment was done. The box got hot. This is where heat radiation occurs. And heat radiation, we must know, is electromagnetic radiation. Yes, electromagnetic radiation can also behave like particles, we have already heard that.

So are they actually electromagnetic waves or not? Well, the concept of photons was discovered or invented. A photon is a certain amount of energy depending on its frequency. Thermal radiation is a relatively long wave. Anyone who has ever tried to warm up their joints, etc. With an infrared device, you know what the radiation does. She warms you up. This means that the radiation passes from the lamp to the body and heats the particles there. That means there is an interaction. So now let's look at the experiment. It's pretty hot here now. What happened to that interference pattern back there?

Fun. The interference pattern has disappeared. You see a maximum behind one slit, you see a maximum behind the other slit. As if the particles we send here remain particles all the way through space to the photographic screen back there. Nothing remains of the properties of waves. Far. What happened there? Oh! The radiation! Exactly. The radiation interacted with the electrons on the way to the gap. And the ghostly, entangled states of quantum mechanics have grown weaker and weaker with each collision between electrons and photons, with electromagnetic radiation. And the faster this happens, the more interaction there is and the fewer quantum mechanical properties are visible.

And in the end everything is classic. Tatatata! This is called decoherence. That through the penetration of reality into a quantum mechanical system these apparently entangled states are obtained, of which I will never be able to know anything until no interaction has taken place. They are even destroyed by interaction. In other words: reality converts the reality of quantum mechanics into classical reality. That's why we exist, that's why the box exists, and that's why there is the cat, which actually interacts with itself in the box as a system of many particles so intensely that the cat, of course, has no entangled states.

There is no intermediate cat. The cat is alive or dead. The number of interactions defines whether I am in a classical world, that is, a many-body system. Even in our brains there is nothing quantum mechanical up there, although of course atoms are constantly interacting with each other. But this decoherence, the disappearance of these entangled quantum mechanical states, is so rapid that there is nothing left of quantum mechanics in our brains. Yes, quantum mechanics is everywhere, but it is not noticeable everywhere because it, so to speak, partially annihilates itself. And only in this way is a world possible in which we can distinguish between cause and effect, saying: This is there and that is there, not being able to go through the wall, etc.

Quantum mechanics is the condition of possibility, being human. But being human is something completely different from pure quantum mechanics. Quantum mechanics is a theory, a mathematical theory, that is very successful. Just think about the technological impact it has had. But it describes a world that has almost nothing to do with us. And in the end probably only Niels Bohr will be able to save someone, about whom it is said that he said a lot, but that he once said: Whoever claims to have understood quantum mechanics, has not understood it.