Category Archives: Uncategorised

How quantum teleportation actually works

EDIT: Philip Ball has updated his article on Nature News, correcting the most serious of its errors. While everyone makes mistakes, few actually admit to them, so I think this action is rather praiseworthy. Correspondingly, I’m removing criticism of that … Continue reading

Posted in Uncategorised | Leave a comment

Pure quantum operations

Everybody knows how to derive what are the most general operations one can apply to a quantum state. You just need to assume that a quantum operation Is linear. Maps quantum states to quantum states. Still maps quantum states to … Continue reading

Posted in Uncategorised | Leave a comment

What is the probability of an infinite sequence of coin tosses?

It’s 0, except on the trivial cases where it is 1. But clearly this is the wrong way to formulate the question, as there are interesting things to be said about the probabilities of infinite sequences of coin tosses. The … Continue reading

Posted in Uncategorised | Leave a comment

Crackpots in my inbox

Often people ask me why I’m not more open-minded about ideas that defy the scientific consensus. Maybe global warming is just a conspiracy? Maybe Bell’s theorem is in fact wrong? Maybe the EmDrive does provide thrust without using propellant? Maybe … Continue reading

Posted in Uncategorised | 21 Comments

My shortest research program ever

\[ t=0:00 \] SIMPLICIO: These quantum gravity people! Always claiming that the world is fundamentally discrete! It’s so stupid! INGENUO: Humm why is it stupid? They do have good reasons to think that. SIMPLICIO: But come on, even the most … Continue reading

Posted in Uncategorised | 3 Comments

The sleeping beauty problem: a foray into experimental metaphysics

One of the most intriguing consequences of Bell’s theorem is the idea that one can do experimental metaphysics: to take some eminently metaphysical concepts such as determinism, causality, and free will, and extract from them actual experimental predictions, which can … Continue reading

Posted in Uncategorised | 33 Comments

Understanding Bell’s theorem part 3: the Many-Worlds version

This post is based on discussions with Harvey Brown, Eric Cavalcanti, and Nathan Walk. At least one of them peacefully disagrees with everything written here. After going through two versions of Bell’s theorem, one might hope to be done with … Continue reading

Posted in Uncategorised | 3 Comments

Understanding Bell’s theorem part 2: the nonlocal version

Continuing the series on Bell’s theorem, I will now write about its most popular version, the one that people have in mind when they talk about quantum nonlocality: the version that Bell proved in his 1975 paper The theory of … Continue reading

Posted in Uncategorised | 4 Comments

Understanding Bell’s theorem part 1: the simple version

To continue with the series of “public service” posts, I will write the presentation of Bell’s theorem that I would like to have read when I was learning it. My reaction at the time was, I believe, similar to most … Continue reading

Posted in Uncategorised | 3 Comments

If your interpretation of quantum mechanics has a single world but no collapse, you have a problem

To inaugurate this blog I want to talk about Daniela Frauchiger and Renato Renner’s polemical new paper, Single-world interpretations of quantum theory cannot be self-consistent. Since lots of people want to understand what the paper is saying, but do not … Continue reading

Posted in Uncategorised | 26 Comments