Ask Science

8716 readers

211 users here now

Ask a science question, get a science answer.

Community Rules

Rule 1: Be respectful and inclusive.

Treat others with respect, and maintain a positive atmosphere.

Rule 2: No harassment, hate speech, bigotry, or trolling.

Avoid any form of harassment, hate speech, bigotry, or offensive behavior.

Rule 3: Engage in constructive discussions.

Contribute to meaningful and constructive discussions that enhance scientific understanding.

Rule 4: No AI-generated answers.

Strictly prohibit the use of AI-generated answers. Providing answers generated by AI systems is not allowed and may result in a ban.

Rule 5: Follow guidelines and moderators' instructions.

Adhere to community guidelines and comply with instructions given by moderators.

Rule 6: Use appropriate language and tone.

Communicate using suitable language and maintain a professional and respectful tone.

Rule 7: Report violations.

Report any violations of the community rules to the moderators for appropriate action.

Rule 8: Foster a continuous learning environment.

Encourage a continuous learning environment where members can share knowledge and engage in scientific discussions.

Rule 9: Source required for answers.

Provide credible sources for answers. Failure to include a source may result in the removal of the answer to ensure information reliability.

By adhering to these rules, we create a welcoming and informative environment where science-related questions receive accurate and credible answers. Thank you for your cooperation in making the Ask Science community a valuable resource for scientific knowledge.

We retain the discretion to modify the rules as we deem necessary.

founded 2 years ago

MODERATORS

What if the measurement device in the double slit experiment were a light year away? (self.askscience)

submitted 1 year ago by AB7ORH7D to c/askscience

8 comments fedilink hide all child comments

In the famous double slit experiment, setting up a measurement device that watches which slit an electron passes through changes the eventual outcome on the screen, causing the wave function to collapse.

If the measurement device were a light year away and were precise enough to "zoom in" and see which slit the electrons went through, what would happen on the final screen?

Surely, if the measurement device were off, then the electrons would behave like waves and not particles. An interference pattern would appear on the final screen as there is no observer. On the other hand, if someone a light year away turned on the measurement device, this far-away person (and the measurement device) wouldn't know which slit the electrons went through until a year later. And, the electrons going through the slits wouldn't "know" they are being observed because no information (ie the measurement device turning on) can travel faster than the speed of light.

you are viewing a single comment's thread
view the rest of the comments

[–] [email protected] 11 points 1 year ago* (last edited 1 year ago) (1 children)

There is a great article on space.com that covers this exact scenario.

https://www.space.com/667-quantum-astronomy-cosmic-scale-double-slit-experiment.html

First, though, your premise is a bit off. Zooming in still wouldn't change the speed of light or change how fast the photons take to get from point A to your zoom lens. Zooming doesn't give you a time or distance shortcut - all zooming does is decrease the angle of view of whatever you are pointied at. The only thing that matters in the double slit experiment is whether you observe them enroute or if you observe the screen after impact. If the screen were between you and the photon sources and you zoomed in, the photons would still hit the screen first and the photons you observe through the lens would come after.

The TL/DR of that article I cited earlier is that we still know the field would collapse. The more interesting question (and the one they pose in the article that remains unanswered) is: how fast does the collapse propagate back to the source? Is the propagation delay of the collapse instant/infinite (like what would be described by entanglement) or is the speed of the collapse still subjected to the speed of light (which is the same for the propagation delay of gravitational waves)?

[–] VoterFrog 2 points 1 year ago* (last edited 1 year ago)

The links to the older articles are dead in that link. Here's an archive of the 3rd essay (and it links to the second and first). The 3rd essay presents a thought experiment very close to what OP is asking. If we delay the choice of inserting a detector then would we still get an interference pattern when we're not supposed to? It seems that the question is still unanswered but theoretically, no, because the universe is not locally real and quantum effects seem to happen faster than light in plenty of other experiments.