Quantcast
  • Register
PhysicsOverflow is a next-generation academic platform for physicists and astronomers, including a community peer review system and a postgraduate-level discussion forum analogous to MathOverflow.

Welcome to PhysicsOverflow! PhysicsOverflow is an open platform for community peer review and graduate-level Physics discussion.

Please help promote PhysicsOverflow ads elsewhere if you like it.

News

New printer friendly PO pages!

Migration to Bielefeld University was successful!

Please vote for this year's PhysicsOverflow ads!

Please do help out in categorising submissions. Submit a paper to PhysicsOverflow!

... see more

Tools for paper authors

Submit paper
Claim Paper Authorship

Tools for SE users

Search User
Reclaim SE Account
Request Account Merger
Nativise imported posts
Claim post (deleted users)
Import SE post

Users whose questions have been imported from Physics Stack Exchange, Theoretical Physics Stack Exchange, or any other Stack Exchange site are kindly requested to reclaim their account and not to register as a new user.

Public \(\beta\) tools

Report a bug with a feature
Request a new functionality
404 page design
Send feedback

Attributions

(propose a free ad)

Site Statistics

180 submissions , 140 unreviewed
4,534 questions , 1,819 unanswered
5,159 answers , 21,954 comments
1,470 users with positive rep
720 active unimported users
More ...

  What does Bohr mean by "applied at least twice"?

+ 0 like - 0 dislike
38 views

In an interview one day before his death, Niels Bohr said that "the spacetime or energy-momentum relations must be applied at least twice otherwise they are not defined."

If we send an electron through a diaphragm with a slit, the location where it hits the screen can be predicted by measuring the momentum transferred to the diaphragm. However, If the diaphragm is fixed to a support, we lose the ability to predict the location of the collision with the screen.

In one of his papers, he writes that

"In an arrangement suited to measure the momentum of the diaphragm, it is further clear that even if we have measured this momentum before the passage of the particle, we are after this passage still left with a free choice whether we wish to know the momentum of the particle or its initial position relative to the rest of the apparatus. If the diaphragm is sufficiently heavy in comparison with the particle, we may even arrange the procedure of measurements in such a way that the diaphragm after the first determination of its momentum will remain at rest in some unknown position relative the rest of the apparatus. If we choose to measure the momentum of the particle, we lose through the uncontrollable displacement inevitable in such a measurement any possibility of deducing from the behavior of the particle the position of the diaphragm relative to the rest of the apparatus, and have no basis whatever for predictions regarding the location of the collision."

Does anyone understand this argument?

asked Oct 12 in Chat by duhitasx (0 points) [ no revision ]
recategorized Oct 14 by Arnold Neumaier

Your answer

Please use answers only to (at least partly) answer questions. To comment, discuss, or ask for clarification, leave a comment instead.
To mask links under text, please type your text, highlight it, and click the "link" button. You can then enter your link URL.
Please consult the FAQ for as to how to format your post.
This is the answer box; if you want to write a comment instead, please use the 'add comment' button.
Live preview (may slow down editor)   Preview
Your name to display (optional):
Privacy: Your email address will only be used for sending these notifications.
Anti-spam verification:
If you are a human please identify the position of the character covered by the symbol $\varnothing$ in the following word:
p$\hbar$ys$\varnothing$csOverflow
Then drag the red bullet below over the corresponding character of our banner. When you drop it there, the bullet changes to green (on slow internet connections after a few seconds).
To avoid this verification in future, please log in or register.




user contributions licensed under cc by-sa 3.0 with attribution required

Your rights
...