Quantum Quack

• What is this App?

Quantum Quack makes a decision from a list of options you provide, using quantum random numbers, which are fundamentally different than ordinary random numbers.

Making a decision based on quantum randomness has fascinating implications that vary depending on the various interpretations of quantum mechanics. The two main ones are detailed here, within the hypothetical and highly relevant example of choosing between an Italian and a Chinese restaurant.

• In the Copenhagen Interpretation: This is historically the first dominant interpretation, and is therefore still presented as the standard one in most textbooks. In this interpretation, a quantum measurement "collapses" the quantum state onto one of its possible outcomes. The collapse is fundamentally random, as opposed to ordinary random processes. Indeed, the result of a dice roll for example, appears random to us only because it is a complex process to predict. However, it is in principle perfectly predictable, knowing the laws of mechanics and all the dice’s properties. The randomness here is emergent, not fundamental. All randomness at human scale is of this sort, and in principle every human-scale phenomena are determined in advance, even you reading this text right now! Making a quantum choice then breaks this deterministic chain of events. In other words, if some supernatural intelligence knew everything about the universe at the moment of your birth, it could predict everything about your future life, except if you’re going to that Italian or Chinese restaurant.

In summary: you escape determinism.

• In the Many-Worlds Interpretation: This is a popular interpretation among researchers working on the foundations of physics. In this interpretation, during a quantum process, the state of the universe splits into all possible outputs of the process, called "branches", each of which behaves as an independent universe. We then have two branches, one in which you go to the Italian restaurant, and one in which you go to the Chinese restaurant. Both exist simultaneously in the abstract state space of the universe. If the result turns out to be the Italian restaurant, you can take confort in the idea that, somewhere, you are also enjoying the Chinese restaurant. Lucky you!

In summary: you end up doing all the options at once.

• How does it work?

Mobile phones contain an element that can measure quantum processes: the camera! The detection of light by a pixel is subject to quantum fluctuations (known as shot noise), and constitutes a quantum measurement as discussed above. When you tap "Quack it", the app takes a picture and uses these fluctuations to produce a random number, which is then used to pick one of your options with equal probabilities.

Shortcuts are available for common entries, such as yes/no, directions (for quantum exploring), or digits.