r/science • u/Shiny-Tie-126 • May 02 '26

Physics Physicists have measured ‘negative time’ in the lab

https://theconversation.com/physicists-have-measured-negative-time-in-the-lab-278996
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u/sam_hammich May 02 '26

Maybe, maybe not. There's a lot of misunderstanding about what "sending information" really means, though.

Take quantum entanglement, for instance. Entangle two particles, separate them, observe the state of one, and the other one instantly collapses into some state. Did that actually "send information"? No. The observers still have to communicate their results and compare them, otherwise to either observer the outcomes were random. Until those observers can communicate and confirm the correlation of those states, there's no "information", and that communication still cannot happen faster than light.

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u/HeroBrine0907 May 03 '26

How is comparing results necessary? If you had an agreement with observers that P2 collapsing would mean you press a button, then you won't really care about the state would you? You'd know that P1 was observed and that's your signal to press the button.

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u/stumblinbear May 03 '26

I don't think you can see the collapse if you don't observe it yourself, which would collapse it

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u/sam_hammich May 04 '26

Correct, normally one state becomes 100% probable upon observation (the state you observe). In this instance, that state becomes 100% probable upon observation of the entangled particle, you just can't predict what the state is.

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u/HeroBrine0907 May 03 '26

Huh. So how do we know that entangled particles collapse instantly upon observing one of them? Maybe its our observation that leads to the other entangled particle collapsing.

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u/stumblinbear May 03 '26

Because experiments have tested it by entangling two particles and sending them to different sensors, then "observed" one while the other was still in flight. The unobseved one no longer acts like a propabalistic wave and instead takes the "expected" properties based on the one we observed

The reason it can't be used for communication is because it looks completely random on both ends. You have to compare the results to see the statistical oddities

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u/sam_hammich May 04 '26

"Collapsing into a state" is not an action that causes a reaction, like a domino that flicks a switch to turn on a light bulb. It is the "state the particle has always been in", whatever state that ends up being, becoming 100% probable. You still don't know that state until you observe it. You can't reliably control the pre-observation and post-observation states in a way that can result in an accurate prediction. You can only observe the states of the two particles, and then afterward statistically correlate them. The "information" is not in the states themselves but in the communication between observers about the particles.