An interactive podcast - how does it work?
Start with the intro, listen to the story and - as it progresses - decide how you want to continue ...
Scientific commentary
By Nikolai Kiesel and Mario Ciampini
We hope you enjoyed this short story. If you stick with us for a few more minutes, we'll talk a bit more about its background. As you noticed, our story splits up occasionally. Here we exaggerate a concept that is at the core of quantum physics:
The famous double slit experiment
„Superposition principle”
Say an object is shot at a plate with two holes. Now there are two different „paths “ through the plate. The superposition principle tells us that if the paththough hole 1 is allowed, and the path through hole 2 is allowed, then also a combination -we call it superposition -of the two is in principle allowed. Often people say that the particle passes through „both at the same time“. This is not accurate, butmaybe the best we can do without referring to a „quantum superposition“.
A quantum superposition is a fragile thing: If information about the path of the particle is leaking to the surroundings, the superposition of paths is destroyed
Physicists can verify the existence of such quantum superpositions in the laboratory. In experiments we need isolate the particle from its environment as well as we can to achieve that. This becomes harder as the system we deal with becomes larger. Researchers continue to push this boundary to even larger systems
In our story, the superpositions expand over a large part of the macroscopic world: if there ever was an exaggeration, this is one. Not only that: the characters of our story find that the different paths in the superposition interact, changing the course of the events. This happens for example when Linus thanks to an intuition saves his brother. This is fiction. There‘s nothing about this in standard quantum physics: the events of one “story” cannot influence the others.
This brings us to the Box, the real “deus ex machina” of our story, which magically enables these events: When connected to the Box, after a chance experiment like throwing a coin, the paths of all possible outcomes are evolving. Opening the Box would destroy the other stories leaving only the one where the box opened a reality. Everett’s sees that this allows him to select the most favorable event. One could ask whether that idea can be translated to more realistic situations in actual quantum experiments and what the implicationsare. We’d say that, altogether, Everett‘s trick seems quite forbidden, doesn‘t it?
We discussed the fragility of superpositions before and how leaking the information to the surroundings destroys the superposition. There is a concept that exists in Thermodynamics, which links how much you know about a system (its information) and how much energy it costs to manipulate it. This is called “entropy”. It is often loosely referred to as a quantity that represents how “messy” a system is.
Lyra's intuition as a child is that entropy MUST be produced while the parallel stories proceed and in order not to destroy the superposition there is a price to be paid: she finds it in the devastated landscape around the box. Clever kid! She refers to the second law. She must be referring to an extension of the Second Law of Thermodynamics, as it was originally formulated long before quantum physics. The law exists in many equivalent forms and in the context of our story, we refer to Planck's version, which roughly says, “Every process spontaneously occurring in Nature will increase the total entropy of the Universe.”
In our story, the intricate machinery built around the Box supports a huge superposition, but to obey the Second Law, it needs to dump a huge amount of entropy into the surrounding. To clarify again –such a machinery is pure fiction. Yet, the interplay of thermodynamics and quantum physics is intriguing. The relation between our ability to control a quantum system, and thermodynamic quantities like entropy is part of the young and highly active field of research called “Quantum Thermodynamics”.
By the way, did you know that Decoherence is what scientists call the effect that kills the superposition of a quantum state? Quite ironic that the company who uses quantum mechanics to rule the world would choose such a name, don't you think?