Short Note / May 27, 2026
Can physicists send messages to the past? The quantum paper behind the claim
Sabine Hossenfelder's video walks through a recent PRL-linked quantum paper behind headlines about messages sent backward in time. The short version: no working time machine, but a real causality problem.
The headline version is irresistible: physicists found a way to send messages into the past.
The video version is better.
In a new Sabine Hossenfelder video, the claim is pulled back from time-machine territory and put where it belongs: theoretical quantum physics, postselection, and the awkward boundary between a message from the future and a prediction that only looks meaningful after the fact.
The paper discussed in the video is linked to Physical Review Letters. Hossenfelder describes it as a continuation of earlier work from an MIT group. The setup is not a device someone can build today and use to warn last week's self about the stock market. It is a theoretical scenario involving a prepared quantum state, a receiver, a later measurement, and postselection.
Postselection is the key word. Instead of using every possible outcome, the setup keeps only certain outcomes after the measurement. That is where the time-travel language starts to get slippery. If the selected outcome lines up with what later happens, it can be described as information reaching backward. It can also look like a prediction whose failed branches have been discarded.
Hossenfelder uses a simple version of the problem: imagine a screen that seems to receive a future message saying "Buy Nvidia." If the trade works, did the screen receive information from the future, or did it make a good prediction? In general, she says, the two can be hard to tell apart.
The practical catch is blunt. Current quantum experiments do not let a user force the needed outcome onto the universe. Postselection can filter results after the fact; it does not give someone a button marked "send message to yesterday."
That makes the viral headline too strong. The interesting part is not that physicists have built a telephone to the past. They have not. The interesting part is that quantum theory keeps making the order of events less tidy than everyday cause-and-effect language suggests.
This sits under frontier science rather than UAP. It follows a familiar media pattern: a real technical paper, a spectacular headline, and a public explanation that depends on keeping the word "possible" under control.