If you never heard of Sabine Hossenfelder, read my older post about her. This short one is meant to come with updates on her obsession and her raison d’être.

On X: “I finally got a chance to explain why entanglement is not a spooky action, or any action for that matter.”

Here’s the paper, in Nature (DOI: 10.1038/d41586-025-02638-z): Einstein hated entanglement — and five other quantum myths (barrier-free), by Maria Violaris, Estelle Inack, Sabine Hossenfelder, Norma G. Sanchez, Shweta Agrawal & Emily Adlam.

SABINE HOSSENFELDER: Did Einstein reject the idea of entanglement?

You might have heard that what Albert Einstein referred to as ‘spooky action at a distance’ is technically known as ‘entanglement’, and that he insisted that entanglement couldn’t exist. Neither is true.

The ‘spooky action’ quote is a direct translation of the German phrase spukhafte Fernwirkung, which Einstein wrote in a 1947 letter to fellow physicist Max Born. He was referring to an idea that had long intrigued him — how to interpret the measurement process in quantum mechanics, which he had earlier described as relying on a “peculiar mechanism of action at a distance” (G. Bacciagaluppi and A. Valentini Preprint at arXiv https://doi.org/p2ns; 2006).

Mathematically, the measurement process in quantum mechanics is instantaneous. Say you want to measure the position of a particle. Before you do so, the equations allow the particle to be in several places at the same time. Observe or measure it, however, and suddenly it is in only one place.

This issue of reality apparently suddenly materializing out of uncertainty when you observe it is known as the measurement problem. The update happens faster than light, seemingly violating Einstein’s special theory of relativity, which says that no signal can exceed light speed. Of course, Einstein didn’t like it. That is why, together with physicists Boris Podolsky and Nathan Rosen, Einstein argued in 1935 that quantum mechanics must be an “incomplete” theory (A. Einstein et al. Phys. Rev. 47, 777; 1935), in which measurement is just a probabilistic description of an underlying physical reality.

That same year, Erwin Schrödinger coined the term ‘entanglement’ to describe a correlation between two or more objects about which one has incomplete knowledge. You could, for example, have two particles, one on the left and one on the right, that can each have a state (usually physicists consider the property of ‘spin’, but it could be something else, such as momentum) of either +1 or –1, and both values must add up to 0. So, either the left particle has spin –1 and the one on the right spin +1, or the other way around.

In an experiment, you can flip the spin of one particle, say the left one, even without knowing what it is. If it was –1, it is now +1; if it was +1, it is now –1. If you do that, what happens to the particle on the right side? Nothing. The other particle itself has not changed, and the two particles are still entangled — just the correlation between them has changed. You have changed an entangled system into a different, also entangled system. There is no ‘spooky action’ in entanglement, no exchange of information that is faster than the speed of light.

I think the reason why even some physicists get this mixed up is that in their 1935 paper, Einstein, Podolsky and Rosen used what we now call ‘entangled particles’ to illustrate the problem with the instantaneous update of a system on measurement. The two concepts — measurement and entanglement — became entangled, so to speak.

Einstein never claimed that entanglement, or quantum physics itself, is wrong. What he did was question the physical interpretation of the measurement: that a quantum system seems to exist in several possible superposed states but updates to a different state as soon as you observe it. That is an issue that still hasn’t been resolved.

The replies to her tweet are an exercise in absurdity, but I won’t quote any of them here. Various people seem to have solved all the unsolved issues of quantum physics. It is my perception that quantum physics is more and more quackery and less and less science.

On YT, she allows herself to examine more trivial (and ludicrous) matters: “Recently, a member of U.S. Congress claimed that military officials have seen evidence for interdimensional beings. Apparently, these military officials believe that interdimensional aliens are the only explanations for various unidentified objects that we humans have spotted over the years. Let’s take a look.”