Does anyone know or have an interest in finding out how exactly physicists detect if a particle goes through one slit or the other in the double-slit experiment? Every book and article I read seems to elude this part.
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Does anyone know or have an interest in finding out how exactly physicists detect if a particle goes through one slit or the other in the double-slit experiment? Every book and article I read seems to elude this part.
That's something I'm curious about as well. At one point I started a thread (in the wrong forum I think) about it, but learned very quickly that my understanding of the technology used was completely wrong. I assumed they used an electron microscope, which I reasoned would be like observing a pool ball by shooting a stream of pool balls at it. Apparently they don't use an electron microscope. Somebody directed me to a massive Wiki page listing dozens if not hundreds of different technologies that can be used to observe such particles, but I have no idea which one was actually used for that experiment.
http://www.youtube.com/watch?v=B9xM2...yer_detailpage
The experiment is actually explained in detail in Brian Greenes the Elegant Universe and you would probably come to a better understanding of it by reading about it than watching a video.
Still didn't mention what type of device was used to make observations as the photons are going through the slits. That's what I'm interested in. If I get the book, will that be explained there?
Cause what I can't understand is - how would it even be possible to "observe" photons in motion without disrupting them at the same time?
I've also seen that video. Very good basic explanation, but they just show this generic "camera" looking thing that the scientists used to make observations with. WTF is it??!!?? :panic:
Wheeler's delayed choice experiment - Wikipedia, the free encyclopedia
^^^In this version it says they use a telescope... other than that it just says 'particle detector'. I'm not sure what type they meant. Sorry if that didn't help :(
Well thanks - I do appreciate the effort!
A Telescope!!?? :shock:
I suppose if I really want to know in-depth info like this I need to get crackin' and read some books about it, huh?
But the way they set that experiment up - so the observation takes place AFTER the photon has passed through the slit - does seem to remove the possibility that the observing device disturbs the behavior of the photons.
I believe that the mechanical interference doesn't actually matter as such, and stuff like the delayed choice experiment proved it. Basically with that experiment, even if you measure which slit the particle went through with some device, if you then irrevocably destroy the information, the interference pattern returns.
That clip is from a bullshit religious propaganda film, so watch out.Quote:
Originally Posted by Seroquel
Haha... if you ever find out for certain, let me know. I'm now curious, but not curious enough to read books on the subject. My 'to read' list is way too long already.
The implications are mind-boggling-
http://www.chanarchive.com/content/4...5745587903.png
... What kind of crazy mixed-up world do we live in?!!?? :shock:
If I find out, I'll post here about it. I just can't believe any kind of camera could be used to record a photon, with any degree of magnification.
Apparently the telescope version was more of a thought experiment to show that interference patterns are not affected by the 'short' distance between the slits and the detector screen.
Ok, that does make sense - a telescope allows you to get it far enough away.
Mark my words - the ultimate finding of these experiments will be that subatomic particles actually float in the Aether....
The implications are mind boggling.
But isn't that what cameras do? Record light? A photon doesn't seem much of a stretch from that. Maybe I'm missing something.
If it turns out they actually use cameras I'll bang my head on the wall!!!
the whole reason I got obsessed with this in the first place is, I reasoned (assumed) that you can't see anything that small with anything short of an electron microscope. But I did see mention in that article you posted that what they're looking for is a "flash" in the slit. I suppose a camera could pick that up. In which case everyone can say derp to me and I'll be forced to ask "Why didn't somebody just explain that to me??!!!"
Which makes what the information is actually made up of all the more interesting haha.Quote:
Originally Posted by Xei
I'm really not sure if a camera can be used, don't quote me on it. But if it is just a matter of measuring light then it seems at least plausible to me. It definitely isn't a bad question but there is a big difference between 'seeing' something in the detailed scale of an electron microscope and simply 'detecting' something's presence.
That's interesting because if that's true then I can't see anyway a camera could pick up information from a particle that ends up at the screen unless it behaved like a wave lolQuote:
Originally Posted by Darkmatters
o.O
well apparently when you measure things like this you 'get' the 'result' you're looking for in a sense.
I really don't know what I'm talking about haha I'm just thinking it through now so hopefully I'm not messing things up for anyone. It is a cool experiment to read about.
I just can't help thinking that somebody will figure out one day that it was all a basic misunderstanding of the data and really it doesn't mean anything profound, and then physicists will have to say:
http://www.youtube.com/watch?v=V3FnpaWQJO0
:cackle:
hahahaha
Even if it was a misinterpretation of some sort it most likely still leads to some important discovery. But that would still be really funny.
Scientific 'discoveries/facts' are proven wrong all the time.
I was replying to a reply that has now vanished o.O it made my browser very unhappy. Oh well.
sorry :embarrassed: I had a thought that made me doubt what I said because it's hard to imagine Einstein's theory of gravitation being revolutionized into something completely different. Maybe his theory will be modified and built upon but will the bending of space and dilation of time ever be an outdated concept? Like science found out that the earth is round, I don't think that's gonna be outdated anytime soon lol.
Ahhh okay.
No worries, it just made me do a reality check and I was sad to discover I wasn't dreaming :(
hahaha
I was basically going to agree with you that no scientific theory can be classified as right. I think we are more approaching (but not reaching) the limits of right with every new theory that is developed. But you have to classify the 'outdated' discoveries as wrong or inaccurate in order to move on to a more 'correct' understanding.
To address a post that was never posted :P (maybe I just like to hear myself think)
You can't 'prove wrong' models for existing data or qualified hypotheses. Science never asserts anything.Quote:
Originally Posted by Jenny5
You can 'prove wrong' an existing theory/hypothesis, or at the very least, prove the evidence the hypothesis was based on was incorrect (or incorrectly interpreted). Science could not advance if scientists didn't constantly question what they 'believe' to be true.Quote:
Originally Posted by Xei
Maybe in an ideal world "Science" never asserts anything, but in that space between hypothesis and explanation Scientists can make a mistake.
All evidence used to suggest the earth was flat, that life spontaneously generated, that the earth was the center of the universe, that Pluto was a planet, that proteins were the basis of heredity, etc etc I can list more examples if you really need them. You could argue that these theories were not proven wrong, just 'corrected' according to new data, but at that point it is all semantics. The fact is our understanding of how everything works is continuously advancing and improving.
I don't think any of those ideas were arrived at scientifically in the first place, were they? More like they were assumptions based on "common sense", and as soon as we turned the scientific eye on them they evaporated.
It does seem harsh to me when people say a theory was "disproved" rather than improved upon. It gets my goat a little when people dismiss Freud that way - "Oh, his ideas were all disproved".
Actually they were never asserted as facts... only put forth as working hypotheses in the ongoing search for knowledge. It's funny how people don't say that about Alexander Graham Bell... his ideas for the original telephone look ludicrous to us today compared to the iPhone!! His invention has been improved upon so many times the new version doesn't even remotely resemble it anymore, and yet nobody says "Oh, he was a fool - his ideas were proven wrong long ago".
Yes, Freud had some weird notions about sexuality and stuff... hardly surprising considering his ultra-repressive venue. But he invented psychotherapy!! And without his amazing insight into the human unconscious nobody would have had any theories to work against in the first place! :mad:
Sorry, I get a little bent about this subject! :lol:
I can see your point. I just don't personally think the difference between 'proven wrong' and 'improved upon' is significant. I'm not saying older theories should be dismissed as insignificant or ludicrous based on what we know today, we are constantly building off older ideas and wouldn't be where we are today without them. Todays ideas will be built on and replace by new ones 'tomorrow'.
well... valid point. But my understanding is there was significant suport early on for proteins being the unit of inheritance. However scientfic or unscientific you want to call earlier observations it is the path to discovery that is important. We didn't jump from 'earth as the center of the universe' to our current understanding. There were intermediates based on newer and newer information (the sun was the center of the universe). If you can't acknowledge that the original idea was incorrect in some manner then I don't think you can fully move forward.Quote:
I don't think any of those ideas were arrived at scientifically in the first place, were they?
I can definitely see your point. But I don't mean anything harsh or insulting to the original theory when I say it was wrong. I don't take it as a negative thing. Although I can see how saying it was 'improved' has more positive connotations, to me they mean the same thing.
Oh I totally agree with that!! But I feel it only really applies to ideas that weren't arrived at scientifically in the first place, or that were misconstrued by media and the public as fact rather than theory. When scientists put forth a theory they're simply saying "according to data we've been able to collect, we believe _________ is the most likely probability". This then becomes known as "the theory of ___________". Media and the public then begin to talk about it as if it's a well-known or "proven" fact, and when new experiments are done, often using new technology, and new data collected and studied, the theory then changes to reflect that. I don't think the scientific community really considers anything to be proven or fact.Quote:
If you can't acknowledge that the original idea was incorrect in some manner then I don't think you can fully move forward.
Example, people sometimes say Einstein proved Newton wrong. Not true. He simply modified Newton's theories in light of new data demonstrating special circumstances in which it didn't apply.
Okay... so I basically agree with you 100%
I'm just a bit loosey goosey with the word wrong apparently. My bad :panic:
It's ok!
I just wanted to explain it before Xei did... he's not as nice as I am! :lol:
And that's one thing you'll find very quickly n this website - especially if you get involved in scientific political or religious/spiritual discussions... you have to be so careful with wording!!
meh... you forget already, I'm loose with the word wrong.
I think being proven wrong is a good thing, a learning experience. Even if I'm the only person learning. I'm sure I would have survived whatever Xei could have said.
But thanks for explaining :D so nicely
That's a good thing. I'm finding most of the serious discussions I enter around here are knocking me on my ass. All my ideas are being seriously challenged. It sometimes feels like I'm being broken down. But then, that's the starting point for growth, isn't it? :upsidedown:Quote:
I think being proven wrong is a good thing, a learning experience.
So another answer I got was that mostly electrons are used and something like circuits with current flows can be placed at each slit and detect moving charges.
I wouldn't know how to set that up but it sounds reasonable :) Probably makes more sense then a camera.Quote:
So another answer I got was that mostly electrons are used and something like circuits with current flows can be placed at each slit and detect moving charges.
Yeah... I love serious discussions for that very reason. They make you analyze your current ideas. If I think I'm right and can support my beliefs, I'll defend them until proven otherwise. But after much experience with being proven wrong it has lost a lot of sting. I'd rather learn and move forward.Quote:
That's a good thing. I'm finding most of the serious discussions I enter around here are knocking me on my ass. All my ideas are being seriously challenged. It sometimes feels like I'm being broken down. But then, that's the starting point for growth, isn't it?
I don't think you can get a picture of an electron. It wouldn't reflect photons I believe, and it doesn't emit them without colliding with something.Quote:
Originally Posted by Jenny5
And you couldn't use a circuit with current, as that would create a magnetic field that would change the direction the electron was headed. It's possible you could run a loop around one slit and hook it up to an extremely sensitive voltmeter of some kind, but the energy the voltmeter detects would have to come from the electron, and so that set-up would also affect it, though perhaps to a lesser degree.
Yeah, electrons emit and absorb photons through changing orbits and speed when bound to an atom and when striked with the appropriate wavelength of photon. Or through heat but that's another topic. Also photons don't have mass, yeah. But they have an impulse and hence watching electrons with photons wouldn't really work since you'd kick it around. Nevertheless as far as I know you can detect electrons like mentioned above. Though obviously that affects the electron, if it wouldn't, chances are observing and not-observing wouldn't make any difference and if that were the case this whole thing wouldn't happen. At that point you force the electron to decide where it is, breaking it's wave-state, hence getting it to behave like an particle.
Know that you can never perfectly define location AND speed for any existing object, since defining one means always changing the other. That's also why you can't bring anything to absolute zero in terms of temperature.
As far as I think you can take this to the next step with a thought experiment. Imagine an definite void with absolutely nothing existing there and repeat the experiment with large matter, such as molecules or hell even an chair, as long as the slits are positioned according to the wavelength of the object. I'd think that if you could erradicate all means of information exchange, hence eradicate all means of defining the position (just like that's the case with photons) you'd be able to reproduce the results. Obviously that wouldn't work in normal life though since Information is constantly exchanged between matter through several means, light being one of them. That's also part of what keeps micro- and macrocosmos apart. I'd tend to say Quantummechanics defy themselves in greater scales with high entropy.
Just my own thoughts on this topic there.
Alright- so if I understand what you're saying, then the detectors themselves must physically affect the photons they're observing, right? And that's what causes the state-change?
Because a lot of people seem to be saying that it's the knowledge itself causing the change... just the fact that scientists are thinking about it or observing it. If the problem is caused simply by the detecting equipment itself, then that means something entirely different - it simply means that it's impossible to make any finer observations at that scale and that we've probably hit the limit of observable facts at a quantum scale.
Exactly, that is because photons/electrons and the likes are the smallest bundles of existence we can detect so far. Hence using them to detect them doesn't quite work.Quote:
Originally Posted by Darkmatters
Yet it really is the observing that's doing the job (also thinking about it won't affect the experiment). Because in the microcosmos, observing always goes along with changing what you observe, not like in the macrocosmos where you can use light to determine the position of any object, that is because the impulse of light is by far to small to affect such large matter.
Even assuming it doesn't really physically affect the said matter. While matter knows both wave and particle as state it is one or another. Photons are waves while traveling and particles upon impact, or in other words, upon interfering with something. Likely the same counts for electrons, upon impact they are particles, yet upon interfering with an electromagnetic field, they are also particles, while not interfering with their surroundings, they are waves. Hence the observation, the information exchange with the outside determines the state.
My theory above is my own thought, to myself I explain it in systems and their contact with each other, two systems in contact with each other will appear as particles to the other, seperated they are superpositioned waves to each other. Through unmeasurable amounts of photons and other stuff the macrocosmos is connected as one system, constructed out of dozens of several seperated subsystems, namely photons and the likes again. Thus I recon you could repeat the experiment under certain circumstances with larger amounts of mass than an electron, however it is easier said than done to produce such circumstances. It already is proven however to work with atoms like helium. Thus at a position far enough outside, the universe we are currently in would also be a wave. Hence we are both particles and wave the same time, we have definite positions yet are in superposition. It depends from where you look and if you look at all. I have obviously no means of saying wether this is right or wrong but to me it made sense with everything I heard about the matter and it condenses it in an for me easy to understand and yet information full form.
This obviously excludes phenomena like water particles that imitate the behaviour of waves. This is something else again.
That's not quite what I was saying, if the question was directed at me. I'm saying that observing an electron must physically affect it, and that it might be what causes the state change. But if whoever said it was right, and they have tried doing the same experiment where they irreversibly discard the information and that then the interference pattern re-emerged, then... something else might be going on.Quote:
Originally Posted by Darkmatters
I'm so confused!!
My question was directed at StaySharp really, but I appreciate any responses. Ok, it looks like if I want to try to understand any of this I just need to get some books and really dig in. I can't understand what it means to "irreversibly discard the information". Would that mean bringing in new observers who were unaware of the previous results? And what about stored data?
Hm, maybe you're missing something else, in that case it might be good to pick something and work it through. I know there is one really decent set of videos on the topic, far better than the two posted above, but it's in german. There might still be some good videos out there in english but I don't know of any so far so I guess you'll better stick to something to read.
You might also want to look into quantum entanglement, and how that's used for quantum encryption.
You seem to have some knowledge on the subject but do you know how they detect the particles?
I tried to get some source on what I was thinking and stumbled across a fairly easy method which I should've imagined myself: Polarisation. Putting a polarisation filter in one of the slits allows you to detect witch slit a photon took, without necesserily stopping the photon. Eh I'll assume you all know what polarisation is, right?
Also as far as I can tell any kind of transparent matter (how about glass) should do the trick, because that would cause some sort of interference as well.
I've alse read that single atoms can be used for detection, the more I know about this though, the less sure am I how I would go about doing that. I recon it's absorbt into the atom and re-emitted, hence the interference.
I'm not absolutely certain about the last two points, but I am certain about the polarisation.
How? By causing a flash when it passes through?Quote:
Putting a polarisation filter in one of the slits allows you to detect witch slit a photon took, without necesserily stopping the photon.
Causing a flash would be sorta strange, because a flash would be light and the photon itself is light, and under normal circumstances a photon doesn't split in two, that's however possible, the result would be quantum entanglement, but that's a different story.
Explaining polarisation through words alone is a bit tricky... If you imagine a photon, as a wave, and it passes your vision from right to left it'd look sorta like this-> VVVVVVVVVVV Just more sinus like. If the same wave would come right in your eye it'd look like this | let's call this vertically polarised.
If you'd rotate it by 90° it'd look like this -
Likewise it can look like this / or this \ or whatever orientation. Light of a specific orientation is called polarised. And there are filters that only let light of a certain orientation pass through.
If you don't get what I'm talking about, scrap my idea and rather take a look at this dude: Polarisation - Sixty Symbols - YouTube
He does an awesome job at explaining what's going on there.
Once you understood what polarisation is about, back to the original question, imagine both slits with a polarised filter, the left | and the other -
Now when we receive the photons at the end of the experiment we can definitely say that if the photon is polarised | it passed through the left slit. If it is polarised - it passed through the right slit.
Hence the polarised filter takes the role of the observer, the thing that's asked about here.
Ah ok, thank you!! I actually did know how polarization filters work, but failed to understand until you explained it. Also, this made me laugh ridiculously loud:
Quote:
If the same wave would come right in your eye
Yeah it doesn't quite work and it sounds strange :P
I had a hard time finding the right words but what counts is that I was able to express it in an understandable way.
:? If I understand that correctly, how would you irrevocably discard/disregard the knowledge and observe the interference pattern return? It sounds like you would get an immediate answer... an then you would never not know.
I've heard about the polarization method but I was hesitant to post it because I don't really know what to believe and I have some trouble with it. I heard that you can put things at each slit that changes the polarization of the photon. Then there is another thing that either detects or blocks the photons according to their polarization. If you detect the photon, you know what slit it went though. I was just wondering if this method of polarization detection can show an interference pattern to confirm that the detected particles are actually collapsing a wave function.
Remove the filter?Quote:
Originally Posted by Jenny5
You can record how the particles hit the back wall, but not save the data on which slit they passed through. But I don't know if that would cause the interference pattern to return.Quote:
Originally Posted by Jenny5
I think you and StaySharp are talking about different things. The original question in this thread was how to detect a particle, like an electron, while StaySharp is talking about photons (what makes up light). Particles do not have a polarisation.Quote:
Originally Posted by Wayfaerer
Right, particles in the sense of matter with mass do not have a polarisation like light.Quote:
Originally Posted by khh
However photons are also particles, just without mass. And just like electrons they can be in both the state of an distinct particle and a wave. Otherwise it wouldn't be possible to use both for the DS-experiment.
I've never heard anyone state that photons are particles before, only that they can behave like them.Quote:
Originally Posted by StaySharp
No, they're actually particles. See the Photoelectric Effect.Quote:
Originally Posted by khh
No, they're actually waves. See double slit interference.
WHAT IS HAPPENING
Actually they're wave-particles. See wave-particle duality.
^ I was just pointing out that someone saying "well they're not really particles" is incorrect. They have just as much right to be called particles as waves, and vice versa.
No, we're talking about the same thing. Photons are included in the OP as they exhibit wave-particle duality.Quote:
Originally Posted by khh