## How can you know that the properties of quantum entangled particles weren't determined at the source? - by Mark John Fernee - Quora Question Review

This document contains a review of the answer by Steve Baker on the question in Quora: "How can you know that the properties of quantum entangled particles weren't determined at the source?"
• The text in italics is copied from the article.
• Immediate followed by some comments

### Reflection

This is exactly what Einstein thought and what John Bell sought to test in developing Bell's theorem and the associated Bell's inequality. The experiments conduct so-called Bell measurements, which according to the property of local realism (i.e., that the measured values are predetermined) should yield correlations which fall within a specified bound. What is found is that these correlations generally exceed that bound. This is called a violation of Bell's inequality.
What follows is a simple example that illustrates how this works.
Consider a bag of 100 pebbles. If all the pebbles are white, then the probability of drawing a white pebble is 100%. Easy.
Yes. Too easy?
If half the pebbles are black, then the probability of drawing a white pebble is now 50%.
If there are 75 white and 25 black pebbles in the bag, then the probability of drawing a white pebble is 75%. Simple.
Yes. The probability of drawing a white or black pebble for each draw is resp. 75% and 25%. This has to calculated based on 100 experiments.
Yet in this case the experiment finds the probability to be nearly 85%. How can that be?
That is impossible. This means the chance of white is 85% and black 15%. That means when you are finished you have
The assumption that the pebbles have a specific colour independent of the measurement is the weak link.
This answer is not clear. What means "colour independent"
This analogy actually describes correlations observed in the experiment, not the individual measurement statistics, but the logic of the expected probabilities is the same. If one assumes that the measured properties are fixed, or predetermined, you cannot explain the observed correlation probabilities.
This is what the 2022 Nobel prize was awarded for.

### Reflection 1 - Question Review

If you want to give a comment you can use the following form
Comment form
Created: 1 June 2023

Go Back to Quora Question Review