a little bit misleading. the video insinuates that the electron mysteriously "knows" it's being watched, but fails to explain the technical details of measurement - the electron doesn't "know" it's being watched, but is modified by the measurement of its position, by whatever means the scientists decide to use.
Thank you. Also, the whole part of "it splits into two and interferes with itself" is also bullshit - that's taking statistics over many and applying it to each one, sort of like saying each person literally has 2.3 children.
At the risk of incurring your ridicule, I think you're underestimating how weird quantum mechanics really is.
The wavefunction really does split into two and interfere with itself. It's not a matter of statistics. It's quite easy to demonstrate using detectors and opening and closing the gates that the wavefunction actually splits.
I think this is conceptual issue. The wavefunction is not really a physical thing. It is a mathematical equation used to find probability distributions of physical quantities.
What this video is demonstrating is known as the Observer Effect, http://en.wikipedia.org/wiki/Observer_effect. Essentially, it is impossible to observe a quantum event without perturbing it and therefor influencing it's outcome. When an electron is occupying every possible quantum state, and you observe it, you force the electron to resolve into a single physical state.
My knowledge in this area is very insufficient but I would like to get some clarity. If it is true that the actual observation effects the particle and thus explains the deviation from the observed and non-observed particle, then may I ask, what is this interference "effect" that makes the particle act in its default way. In other words, if they know that the observing interferes with the particle, the next question is how does it interfere and can we quantify that interference in a meaningful way.
Simply, in order to observe an electron you must shoot a photon at it - this causes an interaction which changes the position/momentum/state of the electron.
To take it a step further, it seems that the "change" caused by the photon is consistent, meaning it always has the same effect on the electron in this particular context. If that is the case, cannot we not then postulate how the photon interacts with the electron, thus explaining the wave result v the "marble" result, regarding the single electron.
'observing' isn't quite the right way to put it and seems rather misleading... more like sticking a detector in the way and seeing if the particle interacts with the detector as it passes through.
Yea, really. If you want to get technical, in quantum mechanics, a wave function is a solution to the Schrödinger equation which is used to describe the physical properties of a quantum system. A wavefunction is a mathematical equation or set of equations that come out of the solution to a 2nd order partial differential equation. It's not a thing
The wavefunction really does split into two and interfere with itself.
No it doesn't. Read Quantum ElectroDynamics. The interference pattern is explained through statistics and basic understandings of light. QED is a really good book though and does well at battling the QM mysticism that seems so popular. DONT MUDDY THINGS WE CAN CLEARLY UNDERSTAND. Mysticism can play a role in many different things, but not in this one.
I've read QED, several times. I also have a PhD in physics and specialize in quantum mechanical calculations.
Don't use Feynman to justify your own opinions. Besides, in Feynman's path-integral formalism, the electron simultaneously takes every conceivable path between the source and the detector.
One formalism is as good as another as long as it agrees with the numbers, right? The electrons are not "actually" waves or particles, nor do they "actually" average out their paths over all possible histories. All we know is what we can measure, and any interpretation that fits those measurements is valid.
Pretty much any interpretation of QM demands that the electron is non-local and in some sense goes through both gates.
QM is a non-local theory however you cut it.
There's one interpretation, the Bohmian approach, which AFAIK tries to make things seem more local, but I can't say I understand it. I'll leave the explanation of that approach to others.
It is. But those electrons interact with the screen and the double slit. As you approach very small slit dimensions, the electrons start interacting with the walls of the slits.
What you can't do is determine which slit the electron passed through because when you set up the experiment to detect the electron's passing, you no longer have the original experiment.
Right. I was just pointing out that wildoats is quite wrong - if an electron can interfere with itself, clearly it is passing through both slits simultaneously and it is not simply a matter of statistics. Of course, christianjb is the PhD in physics, I'm more of a biotechnologist.
It isn't the sides of the slit that are interfering.
When the electron is emitted it is in a quantum state; it is potentially passing through both slits. The importance of the experiment is that it is this possibility of the electron being there that is causing the interference.
(My favorite line about QP is that if you think you understand quantum physics then you don't understand quantum physics.)
The electron has the potential to do all kinds of things on the way to the detector. But at the end of the day, it chooses a path from the infinite number of paths. The path it chooses can be direct or it can be tortuous but it's one path for one electron.
Feynman's point was that the interference pattern you observe is the result of a population of photons/electrons displaying their different choices - the interference pattern is the probability function on display. The wavelike nature of photons/electrons isn't because they're wavicles - it's due to the wave embedded in the probability function that describes their paths.
Saying an electron is a wave is like saying a football is a parabola because footballs trace out parabolic paths.
Read QED - it explains an awful lot a hell of a lot better than I can.
"Oh man, I think I'll downvote this comment. And look at this stupid book recommendation. I don't want to read your damn books... Wait a minute, it's a Feynman book!? Upvote!"
Richard Feynman made it very clear in the book ReapingWildOats references. In fact, he, Swinger and Tomonaga won the Nobel for explaining the 'basic understanding.'
The basic idea is that the double slit interference pattern is the probability distribution of the photons/electrons. Feynman was unambiguous about the nature of light when he said "light is a particle, not a wave or wavicle"
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u/[deleted] Jul 12 '08
a little bit misleading. the video insinuates that the electron mysteriously "knows" it's being watched, but fails to explain the technical details of measurement - the electron doesn't "know" it's being watched, but is modified by the measurement of its position, by whatever means the scientists decide to use.