The Quantum Around You with Professor Andrea Morello // Quantum Entanglement

I thought I wouldn't cover much in this post, but since I can imagine the questions you might have after watching the video, I'll dive in. My advice is to read what I wrote after watching the video.

In the video I created the subtitle for, Professor Andrea Morello explains the Bell Inequality and Quantum Entanglement, which shows the difference between the classical physics relation and Quantum Entanglement.

To enable subtitles, there's a subtitle button next to the buttons like "Full Screen." You can enable subtitles by pressing that button.

First, he gives an example of a classical physics relation. So, I write +1 on the left side of a piece of paper and -1 on the right. I fold it in half, making the numbers invisible. I mail the right-hand piece of paper to a friend who's far away. Let's say he's in Canada. I tell him, "My friend, tomorrow at midnight, we'll both open the papers at the same time and read what they say."

Tomorrow, we'll both open the paper. I see it says +1, and I immediately know that my friend's paper says -1. The same applies to him. There's no quantum entanglement here. Since we know the relationship between the numbers I wrote beforehand—that is, the information is in us, not in the papers—there's no problem. Therefore, in the formula Andrea Morello wrote, the infinity in the classical relation is between -2 and +2. The smallest possible sum of the inputs (-1-1=-2) and the largest sum (+1+1=+2) are compatible with the result.

But with quantum entanglement, things change. This time, I don't do anything to the paper. However, this paper is such that, even though it doesn't have anything written on it, when someone observes it, it randomly writes either -1 or +1. The other piece of paper, to which it's related, shows the exact opposite of whatever I observed. In other words, if I observe +1, my friend observes -1. I can also observe -1. In this case, because both the right and left parentheses (i.e., the pieces of paper) are present in both cases in the formula, higher values (+2.8, -2.8) can appear in the result.
At the same time, since the information about what I observe is known in the other paper due to quantum entanglement, the rules of classical physics and general relativity are broken.