Is Conservation of Momentum Overlooked in Bells Inequality Violations

Click For Summary

Discussion Overview

The discussion revolves around the relationship between conservation of momentum and the violations of Bell's inequalities in the context of quantum mechanics, particularly as it relates to the EPR scenario and the measurement of spin in entangled particles. Participants explore whether a classical explanation could account for these violations, especially under non-parallel detector settings.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation

Main Points Raised

  • Some participants suggest that a more complete understanding of conservation of momentum in the context of spin measurements could potentially explain the violations of Bell's inequalities classically.
  • There is a discussion about whether the conservation laws of classical mechanics apply to the spin correlations observed in entangled particles, particularly under different detector settings.
  • One participant notes that momentum is conserved with perfect anti-correlation at parallel detector settings, raising questions about how this conservation is affected when settings are non-parallel.
  • Another participant questions the completeness of the current understanding of conservation of momentum in these scenarios, seeking clarification on what aspects are considered incomplete.
  • Concerns are raised about the interaction between particles and detectors during measurement, and whether this interaction could lead to changes in spin that violate the expected inequalities.
  • A later reply challenges an earlier claim about conservation, stating that while conservation holds for the system of A and B, it may not apply to individual particles once a measurement is made.
  • There is a suggestion that the measurement process itself might affect the spin of the observation apparatus, which could relate to conservation laws.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of classical conservation laws to quantum measurements, particularly regarding the implications of non-parallel detector settings. The discussion remains unresolved with multiple competing perspectives on the relationship between conservation of momentum and Bell's inequalities.

Contextual Notes

Participants highlight limitations in the current understanding of conservation laws as they apply to quantum mechanics, particularly in the context of measurement interactions and the implications of non-commuting observables. Specific mathematical steps and assumptions regarding the measurement process and its effects on spin are not fully resolved.

Point Conception
Gold Member
Messages
1,157
Reaction score
1,874
In the EPR scenario the correlation results are explained with the conservation laws of classical mechanics as applied to spin. The Bell type inequalities are derived on expected spin values.
But the violations of these inequalities are then explained with QM: That simultaneous knowledge of mutually non commuting observables is forbidden, collapse of wave function , non locality ...
If there were a more complete understanding of conservation of momentum as applied to the physics of spin with non- parallel detector settings could violations of the inequalities be explained classically ?
 
Physics news on Phys.org
morrobay said:
If there were a more complete understanding of conservation of momentum as applied to the physics of spin with non- parallel detector settings could violations of the inequalities be explained classically ?

What's incomplete about our understanding of conservation of momentum in these situations?
 
morrobay said:
In the EPR scenario the correlation results are explained with the conservation laws of classical mechanics as applied to spin. The Bell type inequalities are derived on expected spin values.
But the violations of these inequalities are then explained with QM: That simultaneous knowledge of mutually non commuting observables is forbidden, collapse of wave function , non locality ...
If there were a more complete understanding of conservation of momentum as applied to the physics of spin with non- parallel detector settings could violations of the inequalities be explained classically ?

the spins come opposite (in case of anti-correlated)...momentum is conserved

why do you feel it's overlooked?
 
Momentum is conserved with this inequality with perfect anti correlation at parallel detector settings
n[x-z+] + n[y+z-] ≥ n[x+y+] The spin values derived from entangled particles created at the source with total spin, when measured at A and B, equal to zero.
In accord with the conservation laws.
One of eight:
..A::::::::::::::B..
x y z :::::::::x y z
+ + -::::::::::- - +
But when the above inequality is violated with non parallel settings the total spin at A and B does not equal zero, in conflict with conservation laws. So the question is about the interaction at detector with particle at time of measurement. Given that particles were created with total spin of zero at source and the inequality was violated (spin change ) Then can spin change be related to an interaction with the detector and conservation of momentum for total system ? Again, with non parallel detector settings can the spin be affected by the conservation laws in such a way that the inequality is violated ? And if so then is a particle or classical physics mechanism the explanation?
 
Last edited:
As an example for the above, with a 4 out of 8 table of spins with parallel detector settings
A:::::::::::::::B
x y z:::::::x y z
+ ++:::::::- - -
- + +:::::::+ - -
- - +:::::::+ + -
- - -:::::::+ + +
n[x+y-] + n[y-z+] ≥ n[x-y-] The Bell type inequality with expected spin values is applied in experiments when detector settings are not aligned. If only the spin on axis for x in first term of inequality:n[x+y-] changes spin to n[x-y-] during measurement due to particles interaction with magnetic field in detector and angle of detector, then the inequality is dis proven. Maybe a particle physicist can explain a mechanism for this spin change in terms of state of particle, detector angle/field interaction and the conservation laws.
 
Last edited:
morrobay said:
... But when the above inequality is violated with non parallel settings the total spin at A and B does not equal zero, in conflict with conservation laws. ...

Ah, this is not quite correct. There is conservation for the system of A+B. This system no longer exists after one is measured, say you found A=-1 at 0 degrees. You now know B=+1 at that same angle. But instead you measure B at 15 degrees. The answer may or may not be +1, exactly as you imagine.

But now the question is: is there conservation of spin on a single particle? So you are really asking what happens to the spin of the observation apparatus when a particle's known spin is measured on a different basis. Ie is that somehow affected when it comes into contact with B? I would answer: sure, precisely *because* there is conservation.
 

Similar threads

  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 59 ·
2
Replies
59
Views
8K
  • · Replies 12 ·
Replies
12
Views
2K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 50 ·
2
Replies
50
Views
8K
  • · Replies 73 ·
3
Replies
73
Views
3K
  • · Replies 93 ·
4
Replies
93
Views
8K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 5 ·
Replies
5
Views
3K