Quantum Madness

[abfandango]

If quantum particles all exhibit these weird phenomena when you get them on their own (behaving like a wave AND a particle, deciding what to do depending on whether they're being observed or not, communicating between each other faster than the speed of light, etc), why do they stop this and start behaving normally when you group them into real things? Real things are only made up of quanta, after all.

[Squirrel]

With the information I currently have on the subject (albeit very little) the observation that certain particles can act as a wave or a particle depending on how they are observed sounds stupid, wrong. I don't know if the particles actually do freely change between particles / waves or not but this would certainly not be dependent on whether or not someone is looking. From the way you phrased your question, I gather you already thought this.

More accurate observations and measurements of photons etc. are obviously possible when the numbers involved are large. This suggests to me that instead of the duality problem being real, the measuring techniques of such ridiculous quantities as one photon are flawed and the results are ambiguous. (I apply similar reasoning to question whether relativity is even real.) Sorry for the inadequate answer, but you ask a difficult question, and I am told that no one can prove conclusively one theory over another.

[incitatus]

squirrel, not only is it inadequate, it is plain wrong. the particles do do that stuff, and observer participation is a real effect as far as can be measured. and it works in bulk properties too, provided you set it up right. you can prove this by doing a combined youngs slits/photoelectric detector experiment with a simple beam of light. Some of these weird phenomena are observed on the bulk scale but people dont recognise them for what they are. radiation, for example can ONLY be explained in terms of uncertainty (one of those quantum things) but people dont often clock that. The point behind duality is in terms of the conditions needed for things to behave wavishly. smaller things behave more wavishly, larger things like particles. thus photons (pretty small things) can be diffracted by a diffraction grating (diffraction is a wave thing) but electrons (a bit bigger) need to have a grating made of atoms. You could probably diffract motorbikes but the grating would be very small indeed. because they are bigger. The uncertainty principle is often quoted. This is not an experimental flaw, but a process of the universe. the ultimate resolution possible is on the order of 10 exp-34 metres. you cannot measure it smaller. ever.

[incitatus]

the problem you face is enormous squirrel. if quantum mechanics does not work, how does the computer in front of you work, because classical electric theory doesnt really cover it? what about the black body catastrophe? line spectra? the shapes of molecules? molecular bonding? radiation? atomic structure? classical physics cannot explain any of these and yet quantum does. (as for relativity- there are slightly different versions of it but no educated person seriously proposes that the effects it points out are not real. the evidence is too strong.) You are right that theories cannot be proven, but they can be easily disproven. the idea that wave particle duality is false has been disproven many times. so has newtonian gravity. and classical thermodynamics. and the idea of the clockwork universe. Please read a physics book beyond gcse standard.

[Squirrel]

Now I am placed in a difficult situation. I have to choose between the opinion of people that I know and have been taught by, and the opinion of words on a screen. I'll offer no more of my own thoughts based on ignorance at the moment, but just point out that, at AS level, the facts are excessively simplified and often not explained (even by our tutors). For example: "The diffraction of laser light through a grating, and the alternating dark/light lines seen on the screen, is proof that photons can cancel each other out." My unanswered questions included: "what happens to the 'cancelled-out' photons' energy?", "do photons trace a snake-like path through the air?", "what is a peak?" "what is a trough?", "how does a diffraction grating split photons apart?", 'how does a laser work and how do you know that the photons are in phase with each other?''the list goes on and on. I naturally assumed that, seeing as these questions could not be answered by degree level knowledge, then no one knows for certain. I would find it very useful to learn the true answers from you, incitatus, because the temptation is for me to form my own unjustified theories!

(Apologies if this answer appears twice, or in the wrong location.)

[incitatus]

you are rather assuming that the people teacing you payed attention. In terms of electromagnetic radiation....this consists of a variation in an electric field and a variation in a magnetic field in phase but at right angles to each other and orthogonal to the direction of motion. "peaks" and "troughs" are the high and low points of these variations. Photons travel in straight lines through the air. thinking of them as snakish patterns of waves is to miix metaphors and is confusing. A diffraction grating operates on light as a wave, this is the only way to think of it and make sense. if you think of the wave-tank experiments that you have done with water waves you know that waves are diffracted by openings close to the size of their wavelength. So diffraction is a wave property of light. as to how it does it this is rather complex, but think of it as the energy reflecting from the sides of the opening. If you think back to the wave models you use at gcse you know that waves are a perturbation from a mean position. when waves cancel the energy level returns to the mean....i.e. the sum of the perturbation is zero. as to what happens to the energy, nothing. because the light in the light bands is twice the brightness of the light in the dark ones, so the sum of energy remains the same. Lasers are complex, and the physics is rather frightening. but what essentially happens is that you start with a substance into which you pump energy. when all the atoms are in an excited state you pass some llight into it. As this light passes the atoms they emit a photon, in phase with the passing photon. This is an effect called stimulated emission. As i say the proof as to why it happens is very complex, but lasing is quite well understoood.

[incitatus]

electromagnetic radiation....this consists of a variation in Degree level isnt always all its cracked up to be, you know. If you have further queries feel free but you will have to start a new question so i can see it. Sorry about the delay btw, Ive been in hospital for a bit.

[Squirrel]

I am very sorry to hear that, incitatus, and I hope you are well. As for your answer, it is excellent and has warned me well never to get into this topic again! For me, understanding this is like trying to ride a unicycle whilst juggling eels.

[abfandango]

What can I say? Thanks so much for the incredibly informed answers. I saw a guy on the motorway doing your experiment to show his bike's wave like properties by passing through a tiny gap between myself and a nearby driver... By the way, when I said "(behaving like a wave AND a particle, deciding what to do depending on whether they're being observed or not, " these were supposed to be separate items, I'm not suggesting that the wave/particle duality of anything is selected by observation. By the way (2) can quantum theory explain consciousness/free will? Bit cheeky of me, but trying to get a psychology paper out :-). Thanks so much once again! Paul

[abfandango]

By the way (3) sorry to hear of your illness, here's to a speedy recovery!

[mattyai18]

I always found this bit of physics really strange (I am about to start university in 2 weeks). Stranger still is the fact that an electron can be in two different places at the same time, they are a pain to explain. Another odd thing is that you could in theory pass directly through a wall as the position of all of the atoms comprising your body are slightly random and so (although almost impossible) it is possible. I find it hard to believe a lot of physics (i do believe all of this though) as physics tends to be invented for convenience and later proven - e.g. light travelling through a vacuum, I think ether was "invented" or something.