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Feb
7
comment Is the video “How to Reveal Subatomic Particles at Home”'s explanation of its experiment misleading?
A very fast electron or muon has enough energy that it can ionize atoms it passes by without significantly affecting its trajectory, just as a bullet can stir the air without the bullet being "shot into a different path." Also, in the experiment in question the Heisenberg uncertainty principle is only relevant to much smaller distances than what is visible to the naked eye when looking at the condensation trail.
Feb
7
comment Decoherence and interpretations
@Jke, by taking the wave function "seriously", you are inadvertently making the philosophic commitment that the wavefunction is "ontic," i.e. "real," and not "epistemic," i.e. just a tool for accounting for our lack of knowledge about the state of a system. These are useful google keywords to help you understand the situation. Under Everett et al there is indeed an explanation for how superposed states can appear to reduce to a definite state despite not admitting that state reduction is "real": that is just the many worlds argument. But decoherence does not commit one to that position.
Feb
6
comment Decoherence and interpretations
Decoherence doesn't at all explain "collapse." It only explains the loss of coherence (ie interference effects). State reduction is still a "mystery" given an understanding of decoherence, and as such, all the various interpretational issues are still relevant. Long before Zurek et al even Bohm (of pilot wave theory) and Everett (of Many Worlds) had a basic development of decoherence in order to explain the loss of coherence in their interpretations. The main interpretational dichotomy comes into how you explain state reduction and whether you take the wave function as 'epistemic' or 'ontic'.
Feb
2
accepted What is the physical intuition behind the Bragg peak?
Feb
1
comment What is the physical intuition behind the Bragg peak?
But doesn't the number of electrons encountered per unit time increase with the velocity, and wouldn't that cancel out the 'v' on the bottom of your delta-p expression above?
Jan
31
comment What is the physical intuition behind the Bragg peak?
@Ernie, thanks. The Bethe-Bloch formula itself isn't helpful, but above the formula is a line that comes close to what I am looking for: "The faster the particle is, the less energy is given to the electron (the less time it has to spend imparting energy to the electron)," although while this makes sense for a single electron, I still am left wondering why this effect is still true in a material where the faster the particle the more electrons per unit time are encountered, such that a faster particle should be subject to a similar average field strength as a slower particle.
Jan
31
asked What is the physical intuition behind the Bragg peak?
Jan
22
reviewed Approve Do we need wires for current conduction in ionosphere?
Jan
21
comment From the photons perspective
It is instructive to go through the motions of calculating what the perspective of a scientist made out of parallel-moving photons would look like, and to find the root of the inconsistency. Hint: parallel-moving photons have zero invariant mass and therefore have zero interaction cross-section.
Jan
21
comment From the photons perspective
This is a common but unsatisfying answer: one can surely imagine an observer who is made out of photons. Therefore the repetition "there is no such perspective" is incomplete. The reason such observers don't constitute a valid reference frame is because of the subtle fact that the notion of a reference frame is only valid for bodies whose observational interactions to a good approximation do not affect their motion. Generally speaking, for photons any observational interaction non-negligibly affects its direction of motion (though one can imagine interactions that only change its frequency).
Jan
20
awarded  Popular Question
Jan
13
awarded  Yearling
Jan
11
comment Confusion about quantum probabilities depending on how coarsely grained the measurement apparatus is
Oh, you're right, I mis-read what you were doing.
Jan
11
comment Confusion about quantum probabilities depending on how coarsely grained the measurement apparatus is
Wait, actually, it doesn't work in the general case, for example if you had 5 states, and wanted to compare the probability of getting a 2-state degenerate subset to a 3-state degenerate subset... you would need to add an additional item to your list to be able to treat such cases in general, no?
Jan
11
comment Confusion about quantum probabilities depending on how coarsely grained the measurement apparatus is
I did do those steps, but you are "cheating" by using the fact that you know the probabilities have to add up to one, so you used the Born rule for the non-composite piece (|100>) in order to infer the probability for the composite piece (|211>+|210>). I guess maybe that is OK (and maybe you can always do that in more general cases), but that's what I meant by it not being in your list.
Jan
11
comment Confusion about quantum probabilities depending on how coarsely grained the measurement apparatus is
If you can't parse it then I better try to make sure you understand, because it seems to be a pretty big assumption. When you write "Then afterwards you end up with |100⟩⊗|13.6eV⟩ 50% of the time," how do you justify that statement using any of your nine steps?
Jan
11
accepted Confusion about quantum probabilities depending on how coarsely grained the measurement apparatus is
Jan
11
comment Confusion about quantum probabilities depending on how coarsely grained the measurement apparatus is
...both LR and ABC have the same amplitude when x is in the respective domain. I hope that you're willing to answer that confusion, but as a sign of good faith I'm awarding you the accepted answer. Thanks!
Jan
11
comment Confusion about quantum probabilities depending on how coarsely grained the measurement apparatus is
...thing that is missing, however, is that you do not do what I was asking, that is, explicitly show that if you write the eigenvectors of LR in terms of the eigenvectors of ABC, that you end up with the required 1/sqrt(2) proportionality factor that gave rise to all of my conceptual confusion (and which made me worry the factor was added in an "ad-hoc" manner in order to circularly insure that you up with the expected probability). Looking at the definition of your eigenvectors, it's not clear to me how one would derive that relationship, since the eigenvectors of both...
Jan
11
comment Confusion about quantum probabilities depending on how coarsely grained the measurement apparatus is
Your new edit is truly wonderful and goes a long way. I really do want to thank you for how much work you've put in, despite that there has been some difficulty communicating. I think the biggest thing that helped was going from your first to second equation in the H atom. I had never heard that the Born rule includes the provision "if the experimental outcome doesn't distinguish between states A and B, then the probability for that outcome is the sum of the corresponding probabilities for A and B." If that's really part of the Born rule then I agree everything else follows. One major thing...