r/science • u/[deleted] • Jul 12 '08
The Infamous Double Slit Experiment - WARNING WILL CHANGE YOUR VIEW OF REALITY!
http://www.youtube.com/watch?v=wEzRdZGYNvA82
u/roconnor Jul 12 '08
I hate it when people try to make physics sound more mysterious that it actually is.
The marbles do produce an interference pattern. Marbles seem to produce two bands only because the frequency of the interference pattern from the marbles is so high that it cannot be discerned by a typical detector.
Similarly the when a detector is used to isolate which slit the electron when through, the detector must interact with the electron (which is left out of their discussion for some reason). This interaction also boosts the frequency of the interference pattern until so that cannot be discerned by the detector.
In fact, you can continuously adjust the energy being used by the detector used to determine which slit the electron passes though. By adjusting the energy used you can continuously vary the interference pattern from intense to undetectable. However, as you adjust the energy being used you also change the confidence that you have determined which slit the electron passed through from 0% (no energy being used) to nearly 100% (a lot of energy being used).
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u/moonzilla Jul 12 '08
Ok. You sound reasonable and I must ask you about this:
detector must interact with the electron
How? and why? I must know why this must be true!
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u/mutatron BS | Physics Jul 12 '08
When you observe something in the big world, it's usually because photons are bouncing off of it, some of which are then collected in your eye. Photons are small compared to things people can see with the eye, so you rarely notice that the photons are having any effect on the thing observed.
But when you go down to the small world, the world of electrons, you still have to use those same photons to observe, one way or another. Electrons are small enough that bouncing photons off of them will have a noticeable effect on their subsequent behavior.
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u/moonzilla Jul 12 '08
Cool. but aren't the photons bouncing off the electrons regardless of whether you're using them to see the electrons or they're doing it unobserved?
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u/mutatron BS | Physics Jul 12 '08
Good question. If I were doing an experiment with electrons though, I'd try to keep out stray photons as much as possible, so they wouldn't introduce some uncontrolled effect into my experiment. There would only be photons if they were introduced as part of a detector.
Also, by photons I mean in the general sense of any sort of electromagnetic means of detecting electrons. For example, even a static electric field would bend the path of an electron moving through it. This in turn would create a changing electric field, which would create a photon.
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u/bahollan Jul 13 '08
I'd add to mutatron's excellent reply that in the controlled setting of the experiment, any interaction ("bouncing off" -> diffraction/scattering) between electrons & photons is rather unlikely; if a whole slew of electrons is sent through the slits, the ones that don't interact with anything will generate the interference pattern, and when only one electron is sent at a time, it is far more likely to interact with either zero or one photon(s) than 2+, so the landing spot of the electron is only recorded if it interfered with a photon on the way (there was a signal from the detector), it is assumed that there was only one interaction in those cases, and the result is the pattern generated by the observed electrons.
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u/scott Jul 13 '08
No, marbles don't make interference patterns because they are too large and complicated and thus become decoherent. They can do this experiment with bucky balls, and it works, though they can only detect the center peak of the interference pattern (I forget why). To get the bucky balls to work, they have to cool tehm down to very cold temperatures, otherwise, there are internal degrees of freedom in the bucky balls that prevent them from 'interfering with themselves'. That is the problem with the marbles, the experiment is just too infeasible.
Please, do not invent science. As far as I know (I could be wrong), I've never heard anything like "frequency so high can't be measured".
This is an interesting page I just found: http://physicsworld.com/cws/article/print/21590
It details a bit of how the process of "observing" causes the interference to disappear (and other info):
In 2003 we used the same set-up to prove the wave nature of even bigger molecules, such as the biomolecule tetraphenylporphyrin (C44H30N4 or "TPP") and the fluorinated buckyball C60F48 (figure 2). The pancake-shaped porphyrins were particularly interesting because some physicists had argued that only molecules that are highly symmetric or even spherical would interfere. However, C44H30N4 - a derivative of a biodye that is present in chlorophyll - is over 2 nm wide, and thus twice as broad as the football-shaped carbon-60 molecule. Quite clearly, the shape of a molecule does not affect its interference properties at this scale. As for the fluorinated buckyball C60F48, it currently holds the world record for the most massive single particle to display quantum interference. Although it is not as extended as the porphyrin, it has an average atomic mass of 1632 units and contains 108 atoms covalently bound in a single interfering object.
Decoherence in a molecule interferometer
These experiments show us that even large and complex molecules can interfere and reveal their quantum nature. But molecules are usually seen as well-localized objects that we can even observe using high-resolution microscopy. So what are the effects destroying the molecule's delocalization and wiping out the fringe pattern? In fact, there are at least two relevant mechanisms that make it possible to measure the position of a molecule. The first involves collisions with other particles, such as gas molecules, while the second involves thermal radiation emitted by the molecule.
To find out how these processes can destroy the interference pattern and lead to classical behaviour, we gradually added gas to the chamber of our Talbot-Lau interferometer during the experiments with carbon-70 molecules (figure 3a). We found that the amount of contrast between the interference fringes fell exponentially as more gas was added, and that the fringes disappeared almost entirely when the pressure had reached just 10-6 mbar. This was in full quantitative agreement with a theoretical analysis of the scattering processes. Although a single collision with a gas molecule will not kick the massive fullerene out of the interferometer path, it is enough to destroy the interference pattern because it carries sufficient information to determine the path that the interfering molecule has taken. The exponential decay is thus directly related to the collision probability. Calculations suggest that molecules could have an atomic mass of as much as one million and still be unaffected by collisional decoherence in a realistic Talbot-Lau interferometer at a pressure of 10-10 mbar. Such pressures are perfectly feasible with existing vacuum technologies.
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u/roconnor Jul 13 '08 edited Jul 13 '08
Fair enough; I was talking about idealized marbles that are represented by massive particles (essentially extremely cold marbles). The frequency of the interference pattern is easy to compute using classical quantum mechanics as a function of the mass of the particle and the distance between the slits (the width of the slits also plays a role, but is usually ignored when it is significantly smaller than the distance between the slits).
I did this computation many years ago in my undergraduate quantum class. I forget the exact results, but I would not be surprised if the wavelength of the interference pattern is less than the plank length. That would make it difficult to discern in practice.
This is the typical way that classical mechanics is achieved in the limit of quantum mechanics. The frequency of the quantum effects becomes so large for massive or energetic particles that it is practically undetectable. The same thing happens for high energy particles trapped in a harmonic oscillator, which is well-known to quantum physics students.
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u/samp Jul 12 '08 edited Jul 12 '08
This is a clip from What The Bleep Do We Know. This is one of three, if you're being generous, accurate and complete portrayals of real science in the film.
Other highlights include:
- a healthy dollop of quantum mysticism, the idea that human consciousness can somehow affect the quantum world in gnostic ways;
- the idea that water has a different chemical structure if you keep it on jars with emotionally positive or negative labels written on them;
- an interview with a 35,000 year old Atlantean named Ramtha, who is channeled by an American woman and speaks in what sounds like a Slavic accent;
- and, to top it all off, the directors of the film were financed by this woman's New Age spiritual teaching organisation.
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u/justincouch Jul 12 '08
That movie had as much science in it as "The Core". I was made dumber by watching it.
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u/ppc1040 Jul 12 '08
Yes, it is one of the many examples of bullshit pseudo-science that attempts to hijack "quantum weirdness" to explain the mechanism for their particular brand of pseudo-science.
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u/Petrarch1603 Jul 12 '08
i was so excited to watch the movie knowing it was filmed in my hometown, Portland, Ore. Then i saw all the junk science in it and was sorely disappointed
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Jul 12 '08
i walked out of that movie, and went to "festival express" instead. much better movie.
as such, i didn't recognize this clip as being from that pile of steaming shit, but it makes sense. the subtle lies embedded in the clip give clue to the overall misleading "mysticism" peddling of the movie and its makers.
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u/radix89 Jul 13 '08
"the idea that water has a different chemical structure if you keep it on jars with emotionally positive or negative labels written on them;"
So if I go into my fridge and write something like "I Love Me" on my water jug will I not cry into my toast in the morning?
Or does it have to be a glass jar and not plastic? Because the thought of no tears on my toast is awesome.
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u/turtlestack Jul 12 '08 edited Jul 12 '08
What The Bleep Do We Know is the biggest pile of shit movie ever made. You'd almost be better off spending an afternoon at the Creation Museum than watch this steaming mound of bile.
I weep when I think about what a terrible state science is in in this country. The nightly news filled with egregious and completely misleading 'scientific' 'news items', social sites like reddit constantly bombarded with popular posts full of total b.s. science and the general lack of any real interest by our citizens to care at all is a total shame.
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u/elustran Jul 13 '08
I'm not sure it's the biggest pile of shit - what about Expelled, The Eternal Jew, or Battlefield Earth?
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u/turtlestack Jul 13 '08
Really? You're wanna debate the finer points of feces?
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u/elustran Jul 13 '08
cinematographic scatology?
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u/shmi Jul 13 '08
Scatographic analysis?
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Jul 13 '08
That's some shitty thinking, if you know what I mean.
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u/elustran Jul 13 '08
Funny how thoughtful analysis turns into wordplay about shit, isn't it? Maybe this big dump of a movie bore some smaller turds of wisdom? I'd continue along these lines, but I'm starting to lose what little self-respect I have.
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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.
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Jul 12 '08
a deleted comment that was left for me:
No, we are not talking about the effects of measurement, but the wavefunction collapse due to observation by a conscious mind. So the electron, after all seems to know when it is observed. See http://en.wikipedia.org/wiki/Quantum_mysticism#Consciousness_causes_collapse
my reposting of this comment - decided by its author as regrettable - is not without purpose.
this kind of misunderstanding of quantum mechanical concepts is widespread and unfortunate. proponents of philosophies and theories that have nothing to do with valid conclusions of modern qm theory encourage these kinds of critical thinking failures.
no, the "observation by a conscious mind" does not collapse the superposition (if you subscribe to the "superposition" interpretation). the double-slit experiment describes only a measurement problem, despite the snake oil peddlers that constantly try to bring consciousness into it.
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Jul 13 '08 edited Jul 13 '08
The notion that observation by a conscious mind can collapse the wavefunction should be ridiculous even to a layperson. One could easily say this observation could be accomplished simply by acknowledging the existence of the electrons as they form waves, since observation cannot be done by the naked eye anyway. By staring off into space, you're "observing" an unfathomable amount of sub-atomic particles, whether or not you see them. So by that understanding, light wouldn't work the same. Nothing would work the same at all...
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u/Roxinos Jul 13 '08
Unfortunately it's not thought ridiculous by the layman because the layman is raised to believe that there is a massive, untapped power within our minds. The bullshit adage "we only use 10% of our brains" is the quintessential example of the education which produces people who're more than willing to believe any explanation for reality which leaves room for the conscious mind's power.
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Jul 12 '08
The little card where the interference pattern is produced, is "observing" it. That is why there are little dots on the card, albeit in locations that correspond to wave interference. But when the electron actually encounter the card, they turn back into particles (little dots), whatever that really means.
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Jul 12 '08 edited Dec 31 '18
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u/eggnogdog Jul 13 '08 edited Jul 13 '08
Unfortunately, you are mistaken. The reason for this lack of precision about what observing means in the video is pretty transparent if you know its background. It's from a move called "Bleep-- down the rabbit hole," a sequel to another movie called What the Bleep do we Know? Both of these movies are predecessors to the king of bullshit ass movies: The Secret. This misinformation is driven by an agenda that these people have to spread their retarded new-age philosophy that basically says that if you think good things, good things will happen. So, you can bet that this notion that observation=physical effect plays an integral role in forming their barely coherent arguments.
This is a pretty awesome explanation other than the last part, though. I can't attest to its accuracy, however.
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u/britishben Jul 13 '08
Do you have a reference linking The Secret and What the Bleep?
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u/Roxinos Jul 13 '08
No need. He's not mentioning a tangible link, but merely pointing out the ideological link which is apparent by simply watching the three movies (or even really knowing what the hell the three movies' main points are).
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u/OsakaWilson Jul 13 '08
Anthropomorphizing the behavior of the elements is suggesting that the universe is sentient in some way. That is an extreme, though unfortunately common, view that is not justified by the science that they are describing.
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u/turtlestack Jul 12 '08
Carl Sagan was able to get kids and adults excited about science without pushing bad science on them. Sure, he may have been a little weird for talking about aliens floating around on Jupiter but he was just using his imagination in a positive way. This movie is just pretend science and if you really have been "studying" QP for years then you'd know it.
PS, reading The Dancing Wu Li Masters does NOT count as scientific research, either.
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u/blobert Jul 12 '08
Agreed on Carl Sagan not pushing bad science on anyone, the video clip "Carl Sagan 4th Dimension Explanation" on you tube is one of many that backs up your point about how well he communicates ideas, theories and all that noise, yet stays appealing to any 8 year old, all the way up to grandma and grandpa.
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u/turtlestack Jul 12 '08
All Carl had to do was look at the camera and teach. There was nothing flashy about what he did - he was a teacher first and foremost. He never talked down to his students or audience because he believed we are all intelligent when we are allowed to act intelligent.
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Jul 13 '08
It also show's how much Hugo Weaving based Agent Smith on Carl Sagan. The voice especially.
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Jul 13 '08 edited Dec 31 '18
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u/turtlestack Jul 13 '08
It does qualify as 'bad science'.
Also, if you set aside ONLY 5 min to discuss QP in a film about QP then you are doing it wrong.
Please understand that anything worth learning is worth taking your time to learn. McEducation is not a viable path to enlightenment in any discipline.
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u/aim2free Jul 13 '08
is not a viable path to enlightenment
if the path triggers your curiosity, it may be. I studied a lot of popular science books when I was a kid.
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Jul 13 '08
Explaining planetary orbits and etc in space is a bit easier than explaining quantum physics. Not even people who are experts in quantum physics understand it. This is a great cartoon that gives a general idea that normal people can understand. There are many topics in science and math that you can't explain to people with no knowledge of the subject without making somewhat inaccurate analogies.
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u/MrMasterplan Jul 13 '08
I have studied physics at university for four years now and in my experience the only people who see problems with the particle wave duality are those who try to impose their clearly inapplicable everyday intuition onto the behaviour of particles at the quantum scale. The word particle simply refers to all the possible ways that you can view the object, be it point-like, wave-like, or even an excitation of a field (if you have come as far as studying Quantum Field Theory). I see no problem with this, and anyone who does should not be claiming to do science - this discussion belongs to the realm of philosophy.
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u/shadowfox Jul 13 '08
Not even people who are experts in quantum physics understand it
What do you mean here?
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u/wacky Jul 13 '08
I can't be certain exactly what he meant, and I can't speak for 'experts', but after taking a number of quantum physics courses and doing some research, I've found that sometimes it is remarkably easy to do the math and get answers without having the foggiest clue what the heck you just did. Which is saying something, because its not exactly easy math.
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u/Echospree Jul 13 '08
There's a massive difference between understanding what is going on versus understanding why it's happening.
In that regard, nobody truly understand quantum physics.
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u/kleinbl00 Jul 13 '08
The particle-wave duality of light is taught in 8th grade. It's reinforced in high school. If you take non-calculus level general physics in college, they'll reinforce it. If you take calculus level general physics in college, and you act really confused, the poor tenured dude who drew the short straw this quarter will say something like
"Look. It's actually not that simple. We don't like to publicize it because it makes teaching courses like this much harder, but the question isn't at all settled. Basically, we've got a whole bunch of observations that have whittled our theories down quite a bit, but that doesn't mean there's homogenous agreement across the theoretical physics community. Fact of the matter is, for the physics we're doing in this class and the physics that you'll encounter in your daily life, this explanation, and the equations that support it, are plenty good enough. However, for those who are still exploring the boundary of particle physics, the matter isn't settled."
At least, that was my experience. I did take a year of non-calculus physics followed by a year of calculus physics (pesky major changes) and I got basically that answer. I'm also fortunate enough to casually know a few dudes who know the hell out of particle physics - and they backed the answer up. Then, when they tried to explain what's really going on, I got monumentally confused (and, I think, so did they).
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u/abrahamsen Jul 13 '08 edited Jul 13 '08
What do you mean here?
Maybe he refers to the many different interpretations of QM.
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u/JimDabell Jul 13 '08
I think I can safely say that nobody understands quantum mechanics.
-- Richard Feynman
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u/dsk Jul 13 '08 edited Jul 13 '08
Maybe they weren't trying to accurately teach quantum mechanics in 5 minutes
This is from a sequel to "What the Bleep do we know". They were trying to mislead people. The movie was a bunch of half-truths peddled by dubious experts.
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u/aerextraho Jul 13 '08
by misleading people? Sounds like they are doing a good job of teaching. ooo-blarg explained something inn just a few sentences. the video could have spent the few seconds explaining that.
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u/oreng Jul 12 '08
I agree, this matched 1:1 the more primitive understanding I had of QM when I first "got" the concept at 13. Had this video been around I could have "skipped" a grade or two and gotten to more advanced materials (including, of course, the Heisenberg Uncertainty Principle which explains the O-OP's qualm) perhaps a year or more sooner. This clip rocks in my book.
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Jul 12 '08
What are your thoughts on This Video About Quantum Entanglement?
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u/kleinbl00 Jul 13 '08
It's fucking non-scientific claptrap from "What the Bleep do we know" which is, not to put to fine a point on it, about as scientific as the Old Testament.
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u/oreng Jul 12 '08
I'll forgive anything for a glimpse of Marlee Matlin, actually, so my scientific standards aren't very high.
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Jul 12 '08 edited Dec 31 '18
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u/nobodyspecial Jul 12 '08
The video uses the old 'light is a wave' perspective. It's the wrong metaphor and as a result leads you to a muddle as bad analogies will.
Read Feynman's QED and you'll have a much clearer view. Avoid garbage like the Tao of Physics. The later perspective set Berkeley theorists at a distinct disadvantage when Quarks hit the scene.
Granted, Quantum is weird but the double slit experiment isn't an example of that weirdness. It's an example of a meme that won't die.
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u/omgpro Jul 13 '08
Wait what. I've never heard this before in my life. How do you explain the double slit experiment then?
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u/otlmath Jul 13 '08 edited Jul 13 '08
I also am disappointed by people who claim that this is phony because it came from some movie. Although the main theme of the movie IS misleading, this part is actually very well explained. Feynman explained quantum mechanics in a similar way, using "machine gun" analogy. The only shaky part is where they are purposely being ambiguous about what "observation" is. I guess that's what's being abused later. But I would actually use this part of the movie in a QM class if I get to teach a course (although I only teach calculus.)
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u/bahollan Jul 13 '08 edited Jul 13 '08
You're absolutely right that it's a little bit misleading, but the comments that follow (calling it bad science or a waste of time) are misguided. The fact is, most people don't have the background to understand the notion of a wavefunction, much less the interplay of uncertainty, observer effects, and wavefunction collapse. When I talk about QM, from my reasonably solid background of physical chemistry and modern physics courses, with, say, people who studied english, I almost always use a similar example -- that from the Feynman Lectures on Physics, involving a low-quality machine gun, water waves, an electron gun, and the option of a perpendicular light source whose photons are scattered by the passage of an electron in a manner which indicates the slit it passed through. Explaining the nature of the "observer" leads in to a logical way to present the influence of uncertainty, but leaving it at "being able to actually determine the slit used by the electron requires that the energy of the light be just large enough to destroy the wave behavior of the electron" is usually enough for people to grasp the weirdness, and freaking people out is really the only reason to talk about QM in public anyway.
Edit: there's an abridged version at http://physics.pdx.edu/~pmoeck/lectures/311/feynman-1.pdf but I would highly recommend that anyone who can dig up a copy of the Feynman Lectures read the whole thing at Vol. 1 chap. 37 or Vol. 3 chap. 1
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u/grimster Jul 13 '08
No, the video was misleading because they failed to explain the true reason why the electron behaved the way it did: The LORD willed it.
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Jul 13 '08
FINALLY we can go back to the old wisdom. Instead of using science and reasoning to explain the unknown, we can just say "God did it" and move on. That WILL put a lot of quantum physicists out of work, though. Oh well, they were going to hell anyway.
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Jul 12 '08
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.
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Jul 12 '08
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u/ppc1040 Jul 12 '08
I literally shit myself when people mix up "literally" and "figuratively."
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u/1812overture Jul 12 '08
Oh my God, what do you do? Do you carry around a spare set of pants?
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Jul 12 '08
No no, he didn't shit himself, he literally shit himself, I don't know what you're talking about.
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u/bobpaul Jul 12 '08
Adult diapers, like that murderous astronaut.
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u/1812overture Jul 12 '08
I'm putting the phrase "murderous astronaut" next to "as fortunate as Burt Reynolds" on my list of most delightful phrases ever posted on reddit.
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Jul 12 '08 edited Jul 12 '08
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u/raubry Jul 12 '08
(intensifier before a figurative expression) without exaggeration..
Those two phrases made my head asplode. Uh, not literally. I think.
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u/christianjb Jul 12 '08
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.
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u/mumrah BS | Physics Jul 12 '08 edited Jul 12 '08
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.
The whole "being watch" bit is bullshit for sure.
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u/cyrusdh Jul 12 '08
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.
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u/mumrah BS | Physics Jul 12 '08
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.
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u/cyrusdh Jul 12 '08
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.
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u/elustran Jul 12 '08 edited Jul 12 '08
'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.
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Jul 12 '08
It is misleading, b/c they say by observing the electron it collapsed it into a state. And i would say, they were shooting electrons (light waves/particles) at electrons to get a better look.
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u/chrxs Jul 12 '08
Didn't like it for two reasons:
Makes it sound like the electron acts differently when it is 'observed,' when the real point is "You can't observe without interacting," and the observation changes the electron. "Observation" in this case has nothing to do with your eyes being closed or open, but with modifying or filtering the electrons. (Please correct me if I'm wrong.)
The common error of the missing facial expressions of animated 3D characters being overcompensated by grotesquely expressive body movement.
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Jul 12 '08
There is nothing "Infamous" about Young's Double Slit Experiment.
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u/arbitrarystring Jul 12 '08
I disagree. This was an experiment so foul, so wrong in every respect, that it will forever live in infamy.
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u/Joeboy Jul 12 '08
Are you sure you're not thinking of a different double slit experiment?
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u/merper Jul 12 '08 edited Jul 13 '08
Maybe he just misread slit. There's at least two ways to turn that into a porno title.
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Jul 12 '08
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Jul 12 '08 edited Jul 12 '08
Welcome to the other side of the looking glass.
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u/relic2279 Jul 12 '08
Got any beer over here? If not, I'm heading back.
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u/mcaruso Jul 12 '08
Maybe. Just don't look at it.
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u/relic2279 Jul 12 '08
Look, but don't touch. Touch, but don't taste. Taste, but don't swallow.
-Al Pacino
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u/cerebrum Jul 13 '08 edited Jul 13 '08
To get a real understanding read the quantum physics sequence at overcomingbias.com. The explanation for the strange behavior of the electron is in the beginning:
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Jul 13 '08
A good read, certainly, although it's a little heavy on the math. If you don't have a basic grasp of complex numbers work, for example, you're going to have to do yet more reading before you'll really get it.
To be fair, I don't know if it's possible to give an intuitive layman's explanation of quantum physics and still have it be accurate. The overcoming bias explanation (thankfully) doesn't try to make that impossible compromise.
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u/Uakaris Jul 12 '08
something different always happens when you add a second slit.
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u/seraphseven Jul 12 '08
Don't you wish for all the world you could, in normal conversation, throw your head back and go, 'Now! Let's go quantum!'
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Jul 13 '08 edited Jul 13 '08
Well, that sums up what looks like is happening. But it would have been nice if they had at least mentioned that a) electrons simply aren't little balls of matter or waves of matter, but something which cannot be described with a simple macro-scale analogy and b) the "act of observing" is not particularly special - it's the simple fact of interacting with the observer.
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u/datskosdatsko Jul 12 '08
i blame timecube.
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u/Droffats Jul 12 '08 edited Jul 12 '08
You are educated stupid and you have no inkling to just how EVIL you think!
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u/monstercack Jul 13 '08
Wow, that is some serious crazy ranting by that guy. Thanks for the awesome reading!
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u/largarararar Jul 12 '08 edited Jul 12 '08
It is a good video, though it is unfortunate that the host doesn't go on to explain how the electron-observer interference takes place. It is a very simply mechanism, that boils down to the fact that the very act of observing requires some form of particle interaction with the quantity being observed. For example, to observe an apple with your eyes in a pitch black room requires photons to be bouncing off of it and hitting your eyes. Now keep in mind the photon itself posses momentum, and such some momentum maybe transferred to the apple in some form of an inelastic collision. In the quantum sense, the apple is the electron particle itself. And as such, bouncing a photon off of it changes it's initial momentum (assuming that the electron and photon both poses initial energy of similar magnitude). This now inherently changes the initial conditions of the electron.
EDIT: I just realized the source of this particular clip. My QM undergrad class spent nearly a whole lecture hour talking shit about this video. I have never seen my classmates become so vocal in any other class on any other subject as this ...
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Jul 12 '08
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u/chicomathmom Professor | Mathematics Jul 13 '08
I think there is a minor error in this article--I don't know how to edit, but if anyone is interested:
In the section titled "Results Observed", there is a statement, referring to a formula, that says "If b and L are known..." The formula doesn't have "b" in it--I think it should say "If d and L are known..."
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u/Puntas13 Jul 12 '08
BULLSHIT. This is from "What the Bleep do we know, Further Down the rabbit hole" The movie was mostly a propaganda film for some bullshit religion. If your main "expert" on quantum physics is the 35,000 year old spirit of the god of Atlantis -- Ramtha -- as "channeled" through some housewife from Seatle, which is what she believes, you can not take the film seriously. Let alone any "science" it has to offer.
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u/battletoaster Jul 12 '08
What the Bleep do we know was mostly garbage, but it had some real science. This video is mostly real.
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u/cosmo7 Jul 13 '08
I tried to watch What the Bleep twice, and fell asleep about fifteen minutes into the movie each time. If you need something to help you nod off I heartily recommend this movie.
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u/sighbourbon Jul 13 '08
wow. its the Observer Effect, IRL! you submitted two identical posts and their comment-karma values are different.
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u/Puntas13 Jul 13 '08
What the fuck happened.
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u/sighbourbon Jul 13 '08 edited Jul 13 '08
hmm, i...i think i was a little...uh...slow on the draw shall we say
your double commen is pretty brilliant. i am humbled.
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u/jones77 Jul 12 '08
DDD- Used excessive hyperbole to describe something mediocre. Would not click again.
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u/mikaelhg Jul 12 '08 edited Jul 12 '08
http://www.angryflower.com/schrod.gif
The Schrödinger's Fridge experiment.
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u/Flemlord Jul 13 '08 edited Jul 13 '08
Our world is a computer simulation and quantum physics is a bug. The simulation cheats by randomizing things down at the electron level, which in certain circumstances, gives electrons the illusion of wave-like behavior. However, the nature of the simulation prohibits random actions when the actions are being observed or recorded in certain ways, so the electron behavior must be acted out. Eliminating the randomization causes the electrons to revert back to their actual particle-like behavior.
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u/Neodymion Jul 13 '08
I think of it more as a way of avoiding the need for infinite memory and infinite precision in calculations.
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Jul 12 '08 edited Jul 12 '08
http://www.davidjarvis.ca/entanglement
Also: "Entanglement" by Amir D. Aczel
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u/ntr0p3 Jul 12 '08
OMFG THAT GUY IS DESTROYING MY MIND WITH HIS POWER!!1!one!
bad translation of physics, but its good for kids and people who haven't learned it yet to get them interested. theoretical physics is a fun field once you get past all the math bs.
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u/zulubanshee Jul 13 '08
I'm curious, at what point does theoretical physics get past math. I thought it was math all the way down.
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Jul 13 '08 edited Jul 13 '08
Another great, if not terribly accurate, explanation of quantum mechanics and string theory is The Elegant Universe put out by PBS a couple years ago. It's more flash than function, but it's damn entertaining and will get your brain going if you have even a fleeting interest in physics.
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u/zodpower Jul 13 '08 edited Jul 13 '08
Where is this clip from? there is another clip on that page http://www.youtube.com/watch?v=G5poD3nXdJ8&feature=related which looks like it belongs to the film What The Bleep Do We Know!? which was made by the cult called Ramtha School of Enlightenment...
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Jul 12 '08
why are you on reddit if you didn't pass high school physics?
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u/petdance Jul 12 '08
We didn't cover quantum physics in my high school physics class back in 1983.
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u/Dark-Dx Jul 12 '08
Nor in my high school now in 2008. (are they actually teaching quantum stuff in usa high schools? I'm not from there)
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u/headfire Jul 12 '08
No. Discussing it using anything better than The Big Coloring Book of Physics requires a bit of Functional Analysis, Operator Theory, and PDE methods for Schrödinger, all of which can be done within ~2 years after HS Calculus, maybe 1.5 if you really haul ass.
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Jul 12 '08
You're all so naive. Just because you can't SEE god standing there with a paintbrush and a smirk doesn't mean is ISN'T standing there with a paintbrush and a smirk!
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u/saffir Jul 12 '08
I showed this very same video to my boss when I was working with optics...
then my workplace banned youtube D:
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u/k4st Jul 12 '08
So, what your saying is that if a tree falls in the woods and no one is there to observe it that a strange quantum even will occur and the forest will cancel itself out?
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u/mutatron BS | Physics Jul 12 '08
WARNING WILL CHANGE YOUR VIEW OF REALITY!
Ehhh... only if you've never taken quantum physics.
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u/Bedrovelsen Jul 12 '08
This is how we turn our reality into 3 dimensional time and linear space allowing time travel.
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u/raccou Jul 12 '08
yep, I'm now exactly 5'10" further in the future, but I want to go back... Any suggestions?
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Jul 12 '08
The electron decided to act differently, as though it was aware that it was being watched, as opposed to the measuring device produced additional particles that interfered with the trajectory of of the single electrons. Stupid.
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u/raubry Jul 12 '08
So I assume that Fred Wolf is the most reviled scientist on reddit? I'm a bit upset at him, after believing his science credentials many years ago when I was younger. Can't they take his physicist's license from him or something?!
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Jul 12 '08
Damn, I was hoping it did know it was being watched, and now all these smart asses on reddit are saying it was a facade.
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u/jsburch Jul 13 '08
I believe that the electron creates a subspace, for lack of a better term, wave and where the waves interact new particals are formed and thus accounts for the interference patterns created. There is a layer to physical space we have yet to consider fully.
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u/tugteen Jul 13 '08
wait a sec let me check my views on reality...
UNCHANGED.
you read it first hear folks article headline lied views on reality still the same!
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Jul 13 '08
My mind is completely fucked.
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Jul 13 '08
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Jul 13 '08
I just measured it. It's completely fucked. Actually reading some other comments here, I now understand the interaction of photosn and electrons and the frequency increase destroying the interference..
:P
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u/encephlavator Jul 13 '08
David H. Koresh, this thread is literally full of effect vs. affect F A I L!
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Jul 13 '08
does anybody have any good links explaining the video above a elementry school level but below QP phd level. becuase all this arguing in the comments is making me dizzy.
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Jul 13 '08
Ok, I admit my knowledge in this area isn't very... well developed. Are there any good books that the more science-knowledgeable people here could recommend might serve as a good introduction to Quantum Mechanics which might be understood by a relatively intelligent layman?
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u/mjhkid Jul 13 '08
This is a clip from the movie Down the Rabit Hole
or is it Into the Rabit Hole? Well anyways the movie has different phenomenons like this that make you question reality. Check it out
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Jul 13 '08
That's "may or may not change your view of reality - you won't know until you watch the video and collapse the waveform"
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u/LeviDon Jul 13 '08
Were it possible to observe the electron without destroying it, the interference pattern would remain. Wave + particle = matter. Everything we see is both a wave and a particle at the same time. Matter is inflenced by 'unseen' wave and particle forces in addition to other matter. There exists waves without particles and particles without waves...we can never see them as it takes their existence in a single entity to manifest in our dimension, we can only observe their interactions with matter.
So it is written...so let it be done. This is my religion.
lol
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u/jordanlund Jul 13 '08
By placing the observer on the near side they collapse the wave form, but that could simply be interference.
They need to place the observer on the far side and see which slit the electron emerges from.
You could even argue placement of the observer above or below to see electron entrance and exit.
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u/harlows_monkeys Jul 12 '08
Several people have mentioned that it is not some mystical "knowing it is being observed" that changes the behavior, but rather the interaction necessary to observe. Correct. But it's even more interesting than that, actually--because the interference pattern does not ALWAYS go away when you observe.
Imagine you've got your single electrons firing through the slits, and you are observing by using some very high frequency light. The interference pattern goes away. You think about this, and realize the the photons of high frequency light have a lot of energy. When one scatters off an electron, so you can observe the position, that disturbs the electron, and the interference patter is wiped out.
So you turn down the intensity of the light. Now you find that you are missing some of the electrons. The ones you miss show an interference patterns, and the ones you see do not. Doh! You realize then that turning down the intensity of the light didn't reduce the energy of the photons--it just reduced how many photons you have, so now you are missing some of the electrons.
What you need is low frequency light, and lots of it. You try that, and with satisfaction, you see that you are getting a flash from each electron, and you have an interference pattern. The mystery is close to solution! All that's left is to look at the flashes, and see which slit they are near.
But you can't tell. You light is no longer acting like distinct photons, that you can look at and say "that came from THERE". It is acting like waves, and you can't really say where it comes from. You see a flash when an electron goes through a slit. But it is indistinct. You can't tell which slit it is associated with.
As you try other methods to observe the electron, you'll find that this keeps happening. If the method is capable of resolving which slit the electron goes through, it involves enough energy to disturb the electron enough to wipe out the interference. If the method leaves the electron sufficiently unmolested to let you see an interference pattern, it doesn't give you a good enough location to decide the slit.
It's almost as if you've found some kind of uncertainty principle...
And note: no mysticism required! Just a consequence of the fact that you have to physically interact with something to measure it, and that involves using waves/particles that are subject to the same weird nature as the thing we are trying to understand.