I am not an active or knwoledgable user of SE Physics, but as person with a light form of color blindness (actually green/blue weakness), I wanted to bring this to Meta's attention:
The Color scheme, while certainly pleasing, relies heavily on subtle hues and I have difficulty in discerning thes...
@barlop I viewed the video. The links I have given say that you can observe the slit the particle came through and still an interference pattern appears if you do not disturb the particle by you measurement,
@DavidZaslavsky copied it to Word and recopied and it works!
@barlop I viewed the video. The links I have given say that you can observe the slit the particle came through and still an interference pattern appears if you do not disturb the particle by you measurement,
i.e the primary interaction with the particle at the slit ( probably a photon exchange). The video is talking about an old experiment and I see no reference. The speaker is obviously biased trying to put consciousness in the picture. I would forget about it since there does not exist a recent experiment reproducing this, but rather the opposite.
@annav ok let's forget that white bearded guy thomas as he didn't provide a source, and indeed you've shown there are experiments where it's possible to measure which slot without it interfering.
@annav Consider the delayed choice quantum eraser experiment en.wikipedia.org/wiki/Delayed_choice_quantum_eraser The detectors presumably aren't special ones that don't disturb the particle. I don't know what happens when a particle in that experiment goes through 2 slits, but for simplicity.. to ask my question.. I understand from that experiment that if a particle goes through a slit, it gets split into two particles, one goes through D0, the other goes through one of D1-D4...
D0 might be a special detector that takes a picture ,, it can tell whether it's an interference pattern or a band/particle pattern.
D0 is always hit. D1 and D2 can get hit if it went through Slit A or slit B. Whereas D3 and D4 are different from D1 and D2, in that D3(which is at the bottom of the diagram) can only ever be reached by a proton that went through slit B, (as wikipedia also says "If it is recorded at detector D3, then it can only have come from slit B.". and we see only a blue line going in). and D4 can only be reached from a proton coming from Slit A
"It is impossible to know which group a photon appearing at Detector 0 at time T1 may belong to until after its entangled partner is found at one of the other detectors and their coincidence is measured at some slightly later time T2. "
One funny thing is that D0 seems to see the correct pattern, Interference or band, even though the other proton hasn't quite reached its detector yet. That's a funny thing, that is mentioned on wikipedia, so I can accept that's meant to be odd.
But what I don't understand and perhaps this has an explanation, is why it is that when a proton hits D3 or D4, i.e. the detectors that can only be reached by a particular slit, and thus detectors that tells us what slit the proton came from. Why when one of those are hit, we get a band/particle pattern (no interference pattern). Whereas when the proton hits D1 or D2 then as those detectors don't tell us which slit it came from, we get an interference pattern.
So it looks from that, as if it's our ability to know which slit it came from, which affects the result - interference or band.
Presumably you disagree with the idea that it's our -ability to know-, so what is it? And why should we get an interference pattern with D1-D2, but not with D3-D4 ? (and as you can see I understand the distinction between D1-D2 and D3-D4)
@barlop Yes, I disagree. When we do an experiment where two slits are in the boundary conditions, the solution of the quantum mechanical equation will give a wave function where the two slits are there
The square of this solution gives the probability of finding the "particle" at a specific (x,y) on the screen. All the correlations and interferences are in this solution. In the usual two slit experiment the boundary conditions, i.e. geometrical boundaries are changed when trying to detect which slit the particle went through, so a different solution applies.
In the links I gave care was taken to set up an experiment whose wave function would be stable against the change of detecting the slit the particles went through, demonstrating the statistical basic quantum mechanical probability. I consider all these elaborations on the basic experiments as “navel gazing.”
The more splitters etc are introduced the more complicated the solution of the QM equations become. Each interaction changes the boundary conditions, imo, and is a new experiment.
. It is our ability to build different experiments that changes the outcome, which always comes in classical physics terms. In my opinion ofcourse.
does anything happened to the stackexchange search? now I see results like this: i.stack.imgur.com/dHBmH.png but before I've seen them like this i.stack.imgur.com/eeuBl.png now the latter only shows up when I do tag search with no added words.
worse, it seems to me like a google search (and I totally dislike the idea that since I find google custom search much inferior to old stackoverflow search, add privacy concerns) I want my old search display back. Is it just me or did SE change?
After the performance problems we have run into with Lucene.NET we've decided to make a change, we're moving the network on to elasticsearch.
The test screen is a little hidden at the moment until we swap all search over, but here's a link to get there. Note that searches via the top box will ki...
@Manishearth thanks @Manishearth ... I now read it. I hope there is/will be a way to get the old features back, doing things like [some-tag1] [some-tag2] +word
by the way is this question better placed here than in "Discussion"? I thought this is for Physics.
@Manishearth I think the new interface is simply awful. Can't help, I feel this, probably compared to the old one. The big Q and A vote counters in colored boxes was a distinct and very useful mark of stackexchange sites.
s/interface/result UI
If the old functionality is kept then I welcome the functionality extensions and the better backend, though.
@Manishearth well I've tried to upvote some relevant reasons in the comments here: meta.stackoverflow.com/a/161577/188599 I've even tried to add something but I think I've failed miserably. :$
I'm not good enough separating my emotions from my, well, reasons :(
(actually I'm quite awful at it :P but I'm trying to improve )
well maybe that's why I've upvoted that question... Maybe I should do hand-drawn circles :)
@annav No doubt each of these clumsy detectors disrupts things Mathematically, but they don't all collapse the wave function. Why is it that the detectors at D0 and D1 and D2, do not change the pattern, when a proton passes through D0, or when/if a proton passes through D1 or D2, they are clumsy detectors that would I suppose disrupt things mathematically but they do not collapse the wave function.
Whereas D3 and D4 (which are built the same as D1 and D2), do collapse it when a proton passes through ?
A simpler example, with just one detector, that might demonstrate what I mean. Suppose you have 2 slits, and a great big detector that a proton going through either slit will hit. The theory claiming that It's our ability to know that affects it, says you'll get an interference pattern. Suppose you now change it to a small detector that just covers one slit. The theory would say, now we'll get particles. The question there would be the same.
In both cases, the case of the simpler example(run with a big clumsy detector, and run with a small clumsy detector), (that example probably hasn't been done)
I think you're right, it's in the Mathematics. And however the Mathematics knows, is how the proton knows. And in principle, it shouldn't be a mystery. But it's not naval gazing, as it helps refute quackery, and the answer would be in the Mathematics.
As long as the Mathematics doesn't involve inputting things about our ability to know
Granted, you've shown that it doesn't have to act on our ability to know(as we can build detectors that don't interfere). But that doesn't explain what is happening in the examples with the clumsy detectors not affecting things.
@annav Maybe that Math question is very tricky it's worth me making a question of it. You've helped a lot though, I didn't know about the new developments with detectors that don't interfere with things for example. Thanks
@barlop One has to put quotation marks around "collapse" as well as around "particle" . Collapse is a mathematical output too. It is the same for all probability distributions. The life expectancy for example as a probability distribution for an individual does not mean that the individual when alive is spread all over in some mystic manner
and elementary particles are not the same as billiard balls. They have quantum mechanical behaviors because nature in the microcosm is quantum mechanical. We call them "particles" when they behave like billiard balls, but they are just "entities" describe by qm equations that sometimes allow them probabilities close to billiard ball trajectories and sometimes probabilities with interference patterns, depending on the boundary conditions.
is there a quotation around "wave" too? ('cos it's not like a macro wave). It can't just be a probability distribution though because, as you say, it is an entity. or they are entities. I suppose quantum wave and quantum particle, don't need quotes do they?
I considered posting this on http://mechanics.stackexchange.com/, but I think it's more suited here.
My SUV has the ability to switch between four-wheel and front-wheel drive at any time during operation with a little dial next to the handbrake.
I feel that I can somehow "perceive" a differen...
@annav By the way, apparently they've got it working on a large scale. http://www.nature.com/news/2010/100317/full/news.2010.130.html if I recall from an interview with scott aaronson(who spoke uninformatively at a ted conference), the process included taking large objects, putting them in a vacuum and making the temp to near 0 Kelvin.
@barlop The "wave" is the mathematical description of the probability behavior, that is all. We should call them entities which when measured they behave as billiard balls, i.e. thei probability is 1 on a specific trajectory, and sometimes like probability waves, i.e. the probability has a spatial dependence.
The link is interesting. I would like to observe though that superconductivity and superfluidity are quantum mechanical effects on large scale. At the LHC in Cern they have kilometers of superconducting wires.
First of all, sorry for my knowledge of physics. Maybe my question is too obvious but I want to ask it.
I am thinking about fate and if it exist or no.
According to my assumption if I take any system, for example cube, throw into it some atoms and I will know all the laws which exist at this c...
@DavidZaslavsky It is also confused. What does he.she mean by "fate"? luck? destiny? If destiny it is philosophical. Also not clear where sh.cat and parallel universes are in the argument. It possibly is a language problem.
I've got a question for anyone that cares and knows how to help. I'm a third year physics student, currently enrolled in the "regular", straight-up physics stream. However, since I've realized I don't want to go into the experimental side of physics, I am trying to avoid having to take a lab cour...
I considered posting this on http://mechanics.stackexchange.com/, but I think it's more suited here.
My SUV has the ability to switch between four-wheel and front-wheel drive at any time during operation with a little dial next to the handbrake.
I feel that I can somehow "perceive" a differen...
First of all, sorry for my knowledge of physics. Maybe my question is too obvious but I want to ask it.
I am thinking about fate and if it exist or no.
According to my assumption if I take any system, for example cube, throw into it some atoms and I will know all the laws which exist at this c...
