How a cat changed the world
Are you ready for a bit of mind bending? I have to admit the first time when I put together the puzzle pieces below, I had a bit of a strange feeling in my stomach. So, you decide for yourself if you wanna read on or not.
Ok, enough teaser. Let’s start.
Did you ever hear about Schrödinger’s cat? It’s a famous example to show the absurdity of quantum phisics. But today we put it up a notch and try to do an interpretation of the results.
What is quantum physics
Well, explaining quantum physics or quantum mechanics in one or two sentences is probably mission impossible. The only thing that you need to know is that quantum physics ‘describes’ the world/universe on a very small scale. The atomic scale. The building blocks we’re all made of and everything around us.
So why do we need another theory since we already have Einstein’s general relativity, you ask? Well, Einstein’s general relativity is kinda the opposite. It works very well on the large scale. How planets, stars, galaxies or even super clusters behave. But it has its limitations. It is kinda Newton’s theory with much more precision. However, when we are going to smaller and smaller scales general relativity breaks down. One of the most prominent examples is in the center of a black hole.
Both theories (quantum mechanics and general relativity) are correct (in the sense of they were never falsified) and many examples showed that they work in nature. So, why not combining those two you ask? Well yes, that is the ultimate goal and it is called ‘quantum gravity’. One approach towards quantum gravity is ‘string theory’ which is a theoretical framework where we replace point-like particles with one-dimensional objects, ‘strings’. But this is not todays topic.
If you struggled with understanding Einstein’s general relativity where time is not a constant, and we can bend space-time, then good luck imagine what is going on in quantum mechanics. But we are here for a ride, so let’s do this!
What is the problem of quantum mechanics?
Well ‘the’ problem is maybe a bit simplified. There are many (for us humans at least), but mainly because of how our brains work. Nature or the universe has no problem at all with the laws of quantum mechanics. To summarize the problem in one sentence:
We can never be sure about the position and the momentum of a particle (like an electron). – Uncertainty principle
Momentum is the product of velocity (speed and direction) and mass (how heavy). So, a truck with 100 km/h has much more momentum than a motorbike with 100 km/h because of its mass. We can also think of it like ‘how hard is it to stop’.
So, if you now think why is that a problem. Let me give you an example. When we measure the toss of a basketball thrown by a player, we can easily measure the position and momentum of the ball and therefore calculate if the ball will hit the basket. If we wanna do the same with an electron (instead of a ball) we get very strange results. It is basically not possible. But why you ask? What is so different form a basketball to an electron? Both are round, one is just a bit smaller. Well that is the problem, old-school or school physics taught us to imagine the electron like a point-like particle. Quantum physicists however describe an electron not like a point-like particle but more like a cloud. So, when I ask you: can you tell me at what single point a cloud is? You begin to understand the problem.
But it gets even weirder. Quantum physicists describe the electron as a ‘cloud of probability’. So, the cloud kind of shows you where the electron can be when you measure it. Because if you do, you get a clear result (not a cloud). So, is it just an uncertainty problem? And when we measure, we know exactly where it is and what momentum it has but not in advance? Well not really. According to quantum physicists the electron is in a ‘superposition’ and therefore in all locations (of the cloud) at the same time. But only if we are not measuring or looking…
Yes, I told you, it gets weirder. And I just got started…
So, what is Schrödinger’s cat?
Schrödinger’s cat is an example of Erwin Schrödinger where he tried to show how ridiculous the math of quantum mechanics is if we map it to our reality. He did not like his own equation (Schrödinger equation) which is the main ingredient to cook a quantum meal. In other words, it tells you how the electron cloud (the wave function) will evolve in the future. Ok, sounds very abstract, but just imagine it as the solver algorithm for a Rubik’s cube. If you execute it, your Rubik’s cube will be solved along the way but you don’t really have to know why.
So, what Schrödinger did, is he came up with an example that shows how his equation works if we would apply it to a macroscopic scenario (one we can relate to). So, he came up with the idea of Schrödinger’s cat, and it goes like this:
Before we start it is important to understand, that the decay of a radioactive atom is a stochastic (quantum) effect and can therefore not be predicted. Meaning if you just have one atom you don’t know when it will decay. If you have two atoms you can take your chemistry textbook and find the half-life period of the atom and know exactly when one of the two atoms decayed. But again, you don’t know which one in advance.
Schrödinger’s cat setup:
- Take a box
- Put a cat inside
- Put a closed glass with poisonous gas inside
- Put a detector that will detect the decay of the atom (after it happened)
- Plug the detector to a hammer that destroys the glass with the poison when the detector detected the decay
So, you can easily see that: When the atom decays the detector will go off and triggers the hammer and therefore destroys the glass with the poisonous gas. And as an effect the cat dies.
If I would ask you a simple question like:
Me: The atom did decay, what is the state of the cat?
You would easily tell me:
You: It is dead.
Or
Me: The atom did not decay, what is the state of the cat?
You would easily say:
You: It is alive.
Without ever opening the box.
But since we are now in the quantum “world”, things get a bit more complicated. But let us first start with the easy part. If we open the box in the quantum world, everything behaves as we would expect in our world. We can see the atom, detector, hammer, poison and cat and check how the cat is doing. It only gets weird when we do not open the box but ask some questions.
So, let me ask you the following:
Me: You cannot open the box, what is the state of the cat?
You would probably tell me:
You: I don’t know.
I would then ask you. Ok, but what do you guess? What is possible? You would tell me, either the cat is alive OR dead. You know from your world that the cat must have either of those states. But the right answer in a quantum world would be: It is alive AND dead.
Ok, wait a second. How can a cat be alive and dead at the same time? This was exactly the point of Schrödinger. It is not possible (in our world). However, in the quantum world it is as normal as the sun rising. Schrödinger hated the fact so much, that his equation does make such ridiculous statements in our everyday world, that he once said:
If your mind is not bent enough, let us try to go into another realm and try to interprete what this could mean.
What does Schrödinger’s cat example tell us about ‘reality’?
There are actually two popular parties in the quantum mechanics field.
- the ‘Copenhagen interpretation’ (Bohr/Heisenberg), that basically says: do not try to understand what the math means in reality and
- the ‘Many-world interpretation’ (Everett) that says that everything that can happen, happens but just in another branch/world.
The Copenhagen interpretation is not complete because we cannot really explain what happens when we open the box (and the wave function collapses). And therefore, we cannot use it as an ‘explanation’ of Schrödinger’s cat. It is also better known as: ‘Shut up and calculate’. Which basically means: Stop trying to interpret the results.
I wanted to change your world today, so let me give you the most promising version of a working explanation what could happen when we open the box:
The Many-worlds interpretation
DISCLAIMER I will not be able to explain this with simple words, because I would probably need another wall-of-text like this. If you are interested in the details, ask me next time we are having a beer together.
In the above example you clearly saw that the atom, the detector, the hammer and the poison where somehow connected with each other. Meaning that when the atom decayed the detector triggered the hammer and the poison leaked. What happens next is, that the cat would die from the leaked poison. So therefore, the cat is connected to all of the above. In quantum mechanics we call this ‘entanglement’. Meaning that the atom, detector, hammer and cat are entangled with each other. Precisely, the quantum systems (because all of them are quantum systems on their own) are entangled with each other and therefore from one combined quantum system (of the whole box).
This could be the end of the story and a pretty happy world. However, we have one problem that in reality these quantum systems are not isolated. Not isolated from the environment. The box stands somewhere. In a room, full of other quantum systems (atoms, electrons, …), and the room is in a house and the house is in a world, … (you get the point). We might be able to know the quantum system of the atom, detector, hammer, poison and cat, but for sure we can never know all states of the environment. Basically, we would need to know everything about the universe to make the math work. Since we cannot do that the math gives us luckily another solution: The quantum system of the atom, detector, hammer, poison and cat decohere with the environment. And according to the math the wave function will therefore branch (split in two). And this means our universe (world) also branches (clones) into two. And so will the cat. And so will we. And in one of the two universes the cat is alive and in the other the cat is dead. And when we open the box, one version of us sees the cat alive and the other sees the cat dead.
So, how is that not insane? Well, following the math this theory makes total sense. Just because our brains do not want to accept the fact that decoherence (branching of the universe) happens at a very frequent and high rate and there are large numbers of us existing in different ‘worlds’, does not mean it is insane.
Or how the famous physicist Neil deGrasse Tyson put it:
The Universe is under no obligation to make sense to you.
Well, I’ve warned you.
Until next time . . .