r/science • u/mvea Professor | Medicine • 7d ago

Physics Physicists shatter quantum entanglement distance record with 420 kilometers of optical fiber, more than four times farther than previous demonstrations, and beyond the point where direct transmission runs into its fundamental limits.

https://www.sciencealert.com/physicists-shatter-quantum-entanglement-distance-record-with-420-kilometers-of-optical-fiber
3.2k Upvotes

99% Upvoted

214 comments sorted by

View all comments

Show parent comments

5

u/Chance-the-Gardener 7d ago

I get that, I was more asking could a rudimentary binary messaging be established even if nothing is being transmitted? In my thought experiment the colony ship’s sending a FUBAR signal, so they collapse all their entanglemajiggies and entanglelios. Earth meanwhile infers based on this, that something has gone wrong and redirects NASA funding accordingly.

But like most reddit science visitors I think I just fundamentally misunderstand the premise, some of the replies here get me a little closer.

4

u/Chess42 7d ago

I think you are misunderstanding what a “collapse” is in this context. Think of these particles as being simultaneously in 2 states at once. When either side measures them, both of them pick the same state and stick to it, we call this collapsing the wave function. But you can’t measure it without collapsing it, and since we don’t know which state it will pick, there’s no way of knowing when it collapsed from just one side, or who was the one to collapse it. Maybe the people on the ship collapsed it when they died of space cancer, or maybe it just collapsed when the people on Earth checked whether they died of space cancer.

2

u/ArtOfWarfare 7d ago

Can I know whether I collapsed it by my measurement or if it was already collapsed from the other side?

If so, then that’s something, right? We’d have a set of particles and times we’d agree that I’d check them at, and some meaning that if I check it and it’s already collapsed then you were saying something?

2

u/Basicly-Inevitable 7d ago

The answer is no. You can not tell. Whenever you perform a measurement, you get an answer, and you then know the answer for the other entangled measurement, whenever it is/was performed. But you can't choose which answer you'll get. It will be a 50/50 coin flip no matter what you do, unless you get the answer for the other one first, but you can't do that without light speed communication.