The delayed choice quantum eraser, debunked
http://backreaction.blogspot.com/2021/10...raser.html
INTRO: A lot of you have asked me to do a video about the delayed choice quantum eraser, an experiment that supposedly rewrites the past. I haven’t done that simply because there are already lots of videos about it, for example Matt from PBS Space-time, the always amazing Joe Scott, and recently also Don Lincoln from Fermilab. And how many videos do you really need about the same thing if that thing isn’t a kitten in a box. However, having watched all those gentlemen’s videos about quantum erasing, I think they’re all wrong. The quantum eraser isn’t remotely as weird as you think, doesn’t actually erase anything, and certainly doesn’t rewrite the past. And that’s what we’ll talk about today... (MORE)
https://www.youtube-nocookie.com/embed/RQv5CVELG3U
What should everyone know about quantum mechanics?
https://bigthink.com/starts-with-a-bang/...mechanics/
EXCERPTS (Ethan Siegel): Before there was quantum mechanics, we had a series of assumptions about the way the universe worked. We assumed that everything that exists was made out of matter, and that at some point, you’d reach a fundamental building block of matter that could be divided no further. In fact, the very word “atom” comes from the Greek ἄτομος, which literally means “uncuttable,” or as we commonly think about it, indivisible. These uncuttable, fundamental constituents of matter all exerted forces on one another, like the gravitational or electromagnetic force, and the confluence of these indivisible particles pushing and pulling on one another is what was at the core of our physical reality.
The laws of gravitation and electromagnetism, however, are completely deterministic. If you describe a system of masses and/or electric charges, and specify their positions and motions at any moment in time, those laws will allow you to calculate — to arbitrary precision — what the positions, motions, and distributions of each and every particle was and will be at any other moment in time. From planetary motion to bouncing balls to the settling of dust grains, the same rules, laws, and fundamental constituents of the universe accurately described it all.
Until, that is, we discovered that there was more to the universe than these classical laws.
1.) You can’t know everything, exactly, all at once. If there’s one defining characteristic that separates the rules of quantum physics from their classical counterparts, it’s this: you cannot measure certain quantities to arbitrary precisions, and the better you measure them, the more inherently uncertain other, corresponding properties become...
[...] 2.) Only a probability distribution of outcomes can be calculated: not an explicit, unambiguous, single prediction.
[...] 3.) Many things, in quantum mechanics, will be discrete, rather than continuous...
[...] 4.) Quantum systems exhibit both wave-like and particle-like behaviors...
[...] 5.) The act of measuring a quantum system fundamentally changes the outcome of that system.
[...] 6.) Entanglement can be measured, but superpositions cannot...
[...] 7.) There are many ways to “interpret” quantum physics, but our interpretations are not reality. This is, at least in my opinion, the trickiest part of the whole endeavor. It’s one thing to be able to write down equations that describe the universe and agree with experiments. It’s quite another thing to accurately describe just exactly what’s happening in a measurement-independent way.
Can you? I would argue that this is a fool’s errand. Physics is, at its core, about what you can predict, observe, and measure in this universe. Yet when you make a measurement, what is it that’s occurring? And what does that means about reality? Is reality:
http://backreaction.blogspot.com/2021/10...raser.html
INTRO: A lot of you have asked me to do a video about the delayed choice quantum eraser, an experiment that supposedly rewrites the past. I haven’t done that simply because there are already lots of videos about it, for example Matt from PBS Space-time, the always amazing Joe Scott, and recently also Don Lincoln from Fermilab. And how many videos do you really need about the same thing if that thing isn’t a kitten in a box. However, having watched all those gentlemen’s videos about quantum erasing, I think they’re all wrong. The quantum eraser isn’t remotely as weird as you think, doesn’t actually erase anything, and certainly doesn’t rewrite the past. And that’s what we’ll talk about today... (MORE)
What should everyone know about quantum mechanics?
https://bigthink.com/starts-with-a-bang/...mechanics/
EXCERPTS (Ethan Siegel): Before there was quantum mechanics, we had a series of assumptions about the way the universe worked. We assumed that everything that exists was made out of matter, and that at some point, you’d reach a fundamental building block of matter that could be divided no further. In fact, the very word “atom” comes from the Greek ἄτομος, which literally means “uncuttable,” or as we commonly think about it, indivisible. These uncuttable, fundamental constituents of matter all exerted forces on one another, like the gravitational or electromagnetic force, and the confluence of these indivisible particles pushing and pulling on one another is what was at the core of our physical reality.
The laws of gravitation and electromagnetism, however, are completely deterministic. If you describe a system of masses and/or electric charges, and specify their positions and motions at any moment in time, those laws will allow you to calculate — to arbitrary precision — what the positions, motions, and distributions of each and every particle was and will be at any other moment in time. From planetary motion to bouncing balls to the settling of dust grains, the same rules, laws, and fundamental constituents of the universe accurately described it all.
Until, that is, we discovered that there was more to the universe than these classical laws.
1.) You can’t know everything, exactly, all at once. If there’s one defining characteristic that separates the rules of quantum physics from their classical counterparts, it’s this: you cannot measure certain quantities to arbitrary precisions, and the better you measure them, the more inherently uncertain other, corresponding properties become...
[...] 2.) Only a probability distribution of outcomes can be calculated: not an explicit, unambiguous, single prediction.
[...] 3.) Many things, in quantum mechanics, will be discrete, rather than continuous...
[...] 4.) Quantum systems exhibit both wave-like and particle-like behaviors...
[...] 5.) The act of measuring a quantum system fundamentally changes the outcome of that system.
[...] 6.) Entanglement can be measured, but superpositions cannot...
[...] 7.) There are many ways to “interpret” quantum physics, but our interpretations are not reality. This is, at least in my opinion, the trickiest part of the whole endeavor. It’s one thing to be able to write down equations that describe the universe and agree with experiments. It’s quite another thing to accurately describe just exactly what’s happening in a measurement-independent way.
Can you? I would argue that this is a fool’s errand. Physics is, at its core, about what you can predict, observe, and measure in this universe. Yet when you make a measurement, what is it that’s occurring? And what does that means about reality? Is reality:
- a series of quantum wavefunctions that instantaneously “collapse” upon making a measurement?
- an infinite ensemble of quantum waves, were measurement “selects” one of those ensemble members?
- a superposition of forwards-moving and backwards-moving potentials that meet up, now, in some sort of “quantum handshake?”
- an infinite number of possible worlds, where each world corresponds to one outcome, and yet our universe will only ever walk down one of those paths?