5 ms·

Caveat: I only have a B.Science degree in Engineering Physics (Colorado, USA) and hobbyist-type research in PhD-level physics. I've always found it easier to e

Caveat: I only have a B.Science degree in Engineering Physics (Colorado, USA) and hobbyist-type research in PhD-level physics. I've always found it easier to explain quantum entanglement thusly: Imagine you have 2 cubes that alternate glowing between purple and orange. And they stay in one color for a random amount of time (100s of milliseconds). Holding both in your hands, you would just have randomly color-shifting cubes. But a neat trick of these cubes is that when you close your eyes, hit them together, and quickly put them into separate closed boxes, you know that three things will happen: 1. they will be locked into one color as long as the box stays closed (no more alternating) 2. each cube will be the opposite color from each other (when one is purple, the other is orange, and vice versa) 3. when you open the box and observe the cube, it will stay in the current color for 1 second, and then resume its randomness once again. So you take one of the boxes containing a cube and ship it to your friend on the Moon (greater than 1 light-second away). When she gets the box, you call her on your phone and ask her to wait. Then you open your box and see that your cube is purple. And then the cube starts blinking again because the entanglement is broken on your end. So you wait a few seconds and say to her "open your box and I bet you the cube is orange". She does so and confirms the cube was glowing orange before resuming the random blinking. Now the entanglement is broken on her end, but you "knew" that by having the purple cube in your possession that hers would be orange. Using this system, there is no way to exploit your knowledge of what the colors will be once observed (so sorry, no FTL communication here). The particles no longer influence each other after they are entangled at the start. It's not an active process, but rather a very specific type of setup. But it still bothers physicists (most famously Einstein), that you could "know" something without direct proof. And people in general hope that this un-intuitive phenomenon will open up whole new worlds of sci-fi tech. But no, as the article explained: "Nothing we knew suggested this goal was unachievable. The significance of this news is not that it was unexpected or that it overturns anything previously believed, but simply that it’s a satisfying culmination of years of hard work." If you had shipped the other cube-box to the opposite side of the galaxy, thousands of years after you were long dead, someone would open it and still find an orange cube.

gabrielgoh 9y ago
i fail to see whats mysterious about knowing something without direct proof. You could put a literal orange cube in a box, ship it across the galaxy, and you'd "know" anyone opening the box would be an orange cube. You don't need to be present at the unboxing to know that with certainty. How is this different? Am I missing something?
- im3w1l 9y ago
  Allow me to give a more (but not perfectly) accurate analogy. I give you a magic piece of paper with a two binary digits (00/01/10/11) on it. I also keep such a paper for myself. If we both start by looking at our first digits then those will mysteriosly match, but if we then look at our second digits they will have just a 50% chance of matching. However, if we both start by looking at the last digits, then those will match, and our first digits will have a 50% chance of matching. If you and I start by looking at different digits, then the digits we read are just standard random bits. The cool thing about this is that our magic paper will also work instantly even if we are lightyears apart. However, if you decide to look at the last digit and you see a 1, then that tells you nothing about me or which digits (if any) I have looked at, so I can't send you a message with this paper.
  - kbenson 9y ago
    It sounds like an interesting, if very expensive, way to get around primes for key exchange, in the world where prime factorization is much more efficient. Need a random number, look a bun of shared digits in a predefined order. You now have a shared random number that's perfectly secure, as long as you shipped out your shared state in advance.
- coldtea 9y ago
  That this example has very little to do with entanglement, which is not merely "knowing without direct proof". We do that everyday. The same way, the issue with Shroedigger's cat is not that "the cat is in a single state, but we just don't know whether that's dead or alive unless we open the box" (as many laymen try to explain it). That's just "I don't know yet" and has nothing to do with the issue Shroedigger tried to highlight or quantum mechanics (not to mention that this we encounter everyday and we can replicate perfectly with say, a box and a person that throws a dice and based on that releases or not a gas in the box with a cat -- that's not what the paradox is about). For entanglement, see this: https://www.sciencealert.com/watch-this-is-how-quantum-entanglement-really-works https://www.sciencealert.com/watch-this-is-how-quantum-entan...

gabrielgoh 9y ago

i fail to see whats mysterious about knowing something without direct proof. You could put a literal orange cube in a box, ship it across the galaxy, and you'd "know" anyone opening the box would be an orange cube. You don't need to be present at the unboxing to know that with certainty. How is this different? Am I missing something?

im3w1l 9y ago
Allow me to give a more (but not perfectly) accurate analogy. I give you a magic piece of paper with a two binary digits (00/01/10/11) on it. I also keep such a paper for myself. If we both start by looking at our first digits then those will mysteriosly match, but if we then look at our second digits they will have just a 50% chance of matching. However, if we both start by looking at the last digits, then those will match, and our first digits will have a 50% chance of matching. If you and I start by looking at different digits, then the digits we read are just standard random bits. The cool thing about this is that our magic paper will also work instantly even if we are lightyears apart. However, if you decide to look at the last digit and you see a 1, then that tells you nothing about me or which digits (if any) I have looked at, so I can't send you a message with this paper.
- kbenson 9y ago
  It sounds like an interesting, if very expensive, way to get around primes for key exchange, in the world where prime factorization is much more efficient. Need a random number, look a bun of shared digits in a predefined order. You now have a shared random number that's perfectly secure, as long as you shipped out your shared state in advance.
coldtea 9y ago
That this example has very little to do with entanglement, which is not merely "knowing without direct proof". We do that everyday. The same way, the issue with Shroedigger's cat is not that "the cat is in a single state, but we just don't know whether that's dead or alive unless we open the box" (as many laymen try to explain it). That's just "I don't know yet" and has nothing to do with the issue Shroedigger tried to highlight or quantum mechanics (not to mention that this we encounter everyday and we can replicate perfectly with say, a box and a person that throws a dice and based on that releases or not a gas in the box with a cat -- that's not what the paradox is about). For entanglement, see this: https://www.sciencealert.com/watch-this-is-how-quantum-entanglement-really-works https://www.sciencealert.com/watch-this-is-how-quantum-entan...