Quantum mechanicsEntangled particles -- wave function collapse does the other entangled particle collapse too?
361537
the entanglement can only exist if the wave function is undisturbed, so yes. if particle a is observed as having spin +1/2, particle b will be observed as having spin -1/2.
407070
The short answer is that it simply isn't derived. \n\nStandard quantum mechanics is based on a series of postulates which describe something called a wavefunction. One of the postulates states that the wavefunction must obey the Schrodinger Equation.\n\nThe Schrodinger Equation is somewhat analogous to F=MA (Newton's Second Law) from classical mechanics. There really isn't any derivation of F=MA, it just seems to work. If you are doing an experiment with classical mechanics and you plug the right numbers into F=MA, you get the right answer. Likewise with the Schrodinger Equation, except it works on the quantum scale.\n\nThere have been some attempts to derive the Schrodinger Equation from a grand unified field theory, but for all but the most advanced particle physics applications the Schrodinger Equation is simply taken as a postulate. (just like F=MA)
509589
Yes, there are. If you move an object by half an atom's width, the smooth movements added together still make a quantum leap. If there were no quantum leaps, then there could be no space-time, since everything would be constricted to nothing.
855985
Young's double slit experiment does not PROVE that we create our own reality. However, some believe it does offer evidence that perception can affect reality. \n\nIt doesn't simply show the wave/particle duality of quantum particles. When the experiment is set up with no detectors, and a beam of light is sent through, an interference pattern is formed, as is expected wave behavior. However, if a detector is placed at either or both slits in an attempt to differentiate which slit a particular photon travels through, the difraction pattern is not achieved.\n\nThe Copenhagen interpretation takes this to mean that until the photon is detected, it exists at all points in space. In the abscence of detectors, the particle can and therefore does pass through both slits, thus arriving at the grid at the exact same time via both pathways and causing interference with itself. However, when the photon is detected by way of a physical interaction with the placed detector, the photon suddenly exists only in the point in space where it has been detected, and therefore reaches the grid via a single path and causes no interference pattern. \n\nThis does not neccessarily mean that if one chooses to see something, the necessary light waves will form to bring the vision to reality, but it does suggest that the universal reality we rely on may be based on the physical interaction of all its parts.
255127
Quantum theory suggest that no, it doesn't-- the observer affects the Universe.\n\nBut in a Newtonian, objective Universe, all the laws of physics should apply regardless of if there is an observer or not.\n\nI propose the falling tree is in an eigenstate like Shroedinger's cat: it is both making a sound and NOT making a sound.\n\nIf you aren't familiar with Shroedinger's cat, look it up and prepare to have your mind blown!
548070
Every length, or distance, can in theory be divided into a fraction, with the Planck length as the denominator.  Any distance smaller than this is meaningless, immeasurably small.\n\nAs to the ball addendum to your question, I suppose the ball could be thought of as never hitting the wall, as it cannot possibly come closer than this length.  In that case, however, the atoms that compose the ball and the wall are at least that far (actually much much further) from one another, yet they create a solid object.  The mechanics of the ball bouncing off the wall do not change because of this implication.\n\nFYI***The Planck length is approximately 10^-20th the size of a PROTON
481055
Since Einstein is rather inconveniently dead at the moment, I'll have to answer.  \n\n\nWhy we can't simply have a half a photon that goes undetected is a good question, from the information presented in that article, but a reason it can't work like that:\n\nThe energy of light is related to its wavelength, so if a photon split into two equal halves, then each would have twice the wavelength.  Of course, I'm kinda cheating here, since the relationship between energy and wavelength is one of the rules of photon quantization.  However, there's a very good theoretical reason for this: the ultraviolet catastophe.   See links below.\n\nThe "twin" in this case is really the same photon.  So, this is an example of superposition, which is similar to entanglement.  Entanglement is basically when a set of particles are put into superposition such that the outcome of a measurement on one depends on the measurement of the other.  In this case, the photon is simply in two possible paths through the beamsplitter until such time as it's measured.  Superposition is said to occur whenever a particle is put in a state such that it can have more than one observable outcome if measured.  Until such time that the photon hits one detector or another, it's both reflected off the mirror *and* passed through the mirror.  Yes, it seems like it really ougth to be one or another, doesn't it?  However, QM doesn't work that way.   \n\n\nIf there were three paths...  well, then there would be three paths.  It depends on what the detectors and other optical devices put in the path can do as far as how this would affect the whole behaviour of the system. \n\nThe example given there is the classic "interaction free measurement" trick, also sometimes called quantum interrogation.  It's an important function in ideas about quantum computing since it allows information about states to be retrieved without upsetting entangled states.\n\nIt's getting rather late in my current timezone, and I haven't had dinner yet.  I'll answer in more detail and answer your additional comments once I get some dinner in me.\n\nOK, a few additions...\n\nThe screen placed in either path breaks the single particle interference and gives rise to the possibility of detector B finding the photon, but it doesn't rule out the photon still ending up at detector A, and it also gives rise to the possibility that the photon gets absorbed by the screen.  However, the amazing thing is that if the photon does show up at detector B, then it will tell us that something is located in the optical path without ever having interacted with it.  Presto!  An interaction free measurement.  So, this both shows some interesting possibilities for quantum measurement tricks, which have implications for quantum computing, and shows one of the achilles' heels of the technique.  In this case we can do something which is impossible in a classical physics sense, but we also have three possible outcomes of the experiment, only one of which actually does anything interesting.  So, there are a lot of issues in the development of quantum computing that hinge on the ability to take advantage of these strange effects, but also give us good reliability of the answer.  Taking this trivial example, what we'd need is to develop a more complicated system in which the interaction free measurement effect occurs not 1/4 of the time (half the time the photon is absorbed, if not absorbed, half the time it ends up at A, which tells us nothing) but almost every time.  There are ways to do this, but it gets very complicated very quickly.  \n\nAs for how you get a single photon to work with in the first place...   We currently don't have the technology to simply conjure up a single photon reliably.  There are certainly hypothetical ways it can be done, but right now you just take a brief low intensity laser pulse, pass it through a filter that will
1154260
Yes! in the Sub Atomic particle. Photons behave the same way.
730142
Possibly so. Possibly no. I'd say the Heisenberg uncertainty principle comes foremost into play here. Maybe also Schrödinger's cat. Is it dead or still alive? That would make a significant difference, you know. These questions can't just be taken so lightly. And how could you even consider Y!A as a forum to resolve such complex issues as this? More to the point, even assuming Planck scale dynamics can be fully understood with the mathematical tools we have at hand today, where exactly does that get us? We still don't know what topping to put on our pizza this weekend. Or whether a third eye would make a good chick magnet. Or even whether that darn cat is still alive or dead.... 'tis an enduring mystery. And we wouldn't want to take all the mysterious challenge out of life, now would we?....Meow.
663537
Be careful with your statement.  The electrons do not act like both a wave and particle at the same time!  They act like one or the other.\n\nWhen you are not "watching" the electrons, they exhibit wave like behavior because they hit on the screen only in the spots that would correspond to a bright fringe for light.  But, that isn't the coolest part.  \n\nFirst: you can shoot one electron at a time, and each time, each electron will hit at a spot that would be a bright fringe, if you were to shoot light with the same wavelength through two slits.  Now, cover one of the slits and shoot one electron at a time, and the pattern will shift to that of a single slit diffraction. \n\nQuestion: How does the electron "know" if there are two slits or one slit, so that it hits the correct spot on the screen?  Answer: if there are two slits open, it goes through both slits on its way to the screen!  In essence, it interferes with itself!  This is what is known as the sum of histories, where the electron is said to take every path possible on its way to the screen.  \n\nOf course, you might object and say when I shoot a cannon ball into the air, it only takes one path: the parabolic curve.  So, why does an electron take every path and the cannon ball does not?  This is the essence of quantum physics: these bizzare happenings occur with the very small.  However, the sum of histories can still be applied to a cannon ball, but guess what?  All paths cancel except for the parabolic path it will always take on Earth.  For the electron, each path has equal probability, so they do not cancel, thus it goes through both slits at the same time.\n\nSecond: If you try to "watch" the electron go through both slits by using an instrument, the electron stops acting like a wave, and behaves like a particle.  It hits the screen like a particle should.  Stop "watching" it and the pattern goes right back to that of wave interference!\n\nIt's as if nature will not allow us to see such bizarre things.
382672
In Physics there is a sub-field called Quantum Physics... this field is the study of motion patterns by the smallest particles of matter.  The Quantum Physicists say that they have got a particle that is so small that even with the Super Collider they cannot SEE this particle... they only can see the energy pattern of this "particle."  They say... they... "have a dance, but no dancer."  This is getting close to Metaphysics... which some may call the spiritual realm... or maybe the "ethers."  Some of the physicists call this small unseen particle... "The God Particle."  There is a book by a physicist named Leon Lederman with the title:  "The God Particle."  Interesting reading... I have no knowledge of this Theory = Quantum Aether Dynamics or of J R RedBourne.  So I cannot comment on that part of your question.  But I like Leon Lederman's book. Go to your local library and see if it is there... it is an interesting book, and very understandable as it was written for the layman with no great foundational knowledge in Physics.  Hope this helps!
471221
I am trying to give just a brief idea about these questions. Actual explanations need a lot of space. In any case, one can easily search the internet for these things.\n1. Special theory of relativity was combined with quantum mechanics to produce a new branch of physics called 'relativistic quantum mechanics'. This was done mainly by Dirac. He considered the wave functions of particles moving with very high velocities, and used Lorentz transformation equations in his mathematics. He considered also the imaginary (complex) solutions to the basic equations of motion (such as the Schrodinger equation, for example). The main contribution of this 'unification' was the theoretical discovery of anti-particles (which was varified later on from the experimental discovery of positrons).\n2. The 'unification' of general theory of relativity and quantum mechanics leads to the branch called 'quantum gravity'. The basic problem with this unification is the matching of length scales at which these two theories work. Quantum mechanics is designed and valid for subatomic length-scales, whereas, the general theory of relativity, which is the theory of gravity, deals with massive objects and large (astronomical) length-scales. Presently, scientists are looking for a suitable wavefunction for the universe, which is expected to provide information about the universe in the same way as the wavefunction of an electron gives many information about it.\n3. Feynman reconstructed almost the whole of quantum mechanics and electrodynamics in his own way, deriving a way to analyze atomic interactions through simple diagrams (now known as Feynman diagrams), a method that is still used widely. QED was the theory to which Feynman diagrams were first applied. For his work on quantum electrodynamics, Feynman was one of the recipients of the Nobel Prize in Physics for 1965, along with Julian Schwinger and Shin-Ichiro Tomonaga.\n\nI would also like to comment on the answers given by other users, such as Smart prash: \n1. In question 1 the user is asking about Dirac's relativistic quantum mechanics, and not about Bohr's elementry quanrum mechanics.\n2. Please don't get confused. Quarks are not coloured at all (how can they be?). Colour of a quark is just one of the many quantum numbers that is used in a way to number them in terms of their different energies. Moreover, the question is about QED (quantum electrodynimics), and the colour quantum number is a concept from QCD (quantum chromodynamics).
333510
Yes, any object can, in theory, be treated as a single "state" that is scattered from some potential, with some probability that it ends up in a given direction.  Of course, for an object (such as a billiard ball) of macroscopic size, the only final states with any reasonable probability are those for which the result is near "classical".  And writing the initial state of a collection of ~10^23 particles that make up a macroscopic object as a single state (without approximation) is essentially impossible.\n\nIn other words, you COULD treat an everyday collision involving macroscopic objects as a quantum scattering problem, but you'd certainly be better off with classical mechanics for such situations; the probability of the actual result deviating from the classical result by even a tiny amount is pretty much zero.
10601
This is one of those wierd questions in Quantum Mechanics where there is no way to visualize the answer. Our brains, understandably, have evolved to handle falling rocks, jumping tigers, and other macroscopic objects. We have numerous hardwired responses to these things which follow classical, Newtonian Physics.\n\nOn the atomic and subatomic scales where objects behave according to the laws of Quantum Mechanics things are different. An electron can behave like a wave in this experiment, but a particle in another experiments. According the classical physics (and our macroscopic-loving brain's "common sense) nothing can be *both* a particle and a wave. \n\nSo what is an electron? A wavicle? A partiave? \n\nNope. An electron is a, well, an electron. Sometime it will behave *exactly* like a wave, other times it will behave *exactly* like a particle. Never will it behave like some intermeditate or mixed state.\n\nThe problem - to the extent there is a problem - is that we cannot visiualize this. There is no way to form a picture in our heads the same way we can form a picture of a ball flying though the air. Our brains are meant to operate on macroscopic phenomena, and subatomic phenomena just behave differently.\n\nPresumably some other alien species could have some sort of mind, or mind-like thing, for which the whole wave-particle duality thing just makes perfect sense! But presumably this aliens would be confused by what are to us the simple motions of a ball flying through the air.\n\nSo, in the Copenhagen Interpretation of Quantum Mechanics, there is no sense in which the "other forms" of an object change after a wavefunction is collapsed. That this seems to be a problem is more a function of our brains and how they have evolved.\n\n\n(As an aside, it should be said that it is possible to understand the mathematics underlying Quantum Mechanics. And to be able to use this math to make extremely accurate predictions of how electrons, atoms, etc. will behave. These predictions can be tested experimentally and Quantum Mechanics holds up extremely well. \n\nSo while QM is very wierd, there is an enormous amount of evidence that it is correct.)
340205
In quantum communication, the information to be transmitted is encoded on individual\nphotons that are sent either in free space or through low loss optical fibres. Of special interest\nin quantum communication are light beams where twin- and multiple photons become\nentangled (correlated more strongly than permitted by pure classical effects) in such a way\nthat any measurement one on photon in one beam immediately, irrespective of distance,\naffects the possible outcomes of measurements on other photon(s) in the other beam(s). It is\nlike having a pair of dice, miraculously prepared in such a way that whenever one of the two\nshows a certain number, its twin partner will always show the same number, even if one is in\nMonte Carlo and the second in Las Vegas. "Spooky action at a distance" was the phrase\nAlbert Einstein used to describe the quantum mechanical correlation in entangled beams.\nSuch special light beams (in physics language - quantum states) can be generated using nonlinear\noptical effects when intense laser pulses hit special crystals. In IST-QuComm,\nentangled twin-photons, or even triple- or quadruple-entangled photons has been used for\nquantum cryptography and to teleport quantum states. The latter process refers to\ntransferring the full information content of a quantum state from one place to the other\nwithout sending the state itself. It should be stressed that two particles in the same quantum\nstate are identical; they are indistinguishable even in principle. Thus if we transfer the\nquantum state from one particle to another we have indeed transferred-"teleported" the\nparticle itself. The requirement of quantum mechanics in the process is that the "identity"-the\nquantum state of the original particle is destroyed in the teleportation process. Besides being\nof fundamental interest, quantum teleportation may also play a role in quantum computation,\nand could also be a way to transfer quantum information between separated quantum\n"processors".
797659
Yes. A quantum of energy is invariant unless it interacts with another particle. A certain photon of a given frequency and wavelength has invariant energy.
870020
While photons don't have any force-mitigated interactions, there can be interference.  Matter (fermions) has the Pauli Exclusion Priniciple preventing, say, two electrons from being in the same spin-state in the same sub-orbital...there's a destructive interference term in the probability wave equation that comes from their half-spin states.  \n\nSimilarly, there's an inverse sort of "Pauli Inclusion Principle" for bosons (which have integral spin states and includes photons) to constructively interfere in the wave equation such that there's an increased probability for them to be in the same place at the same time.  \n\nOne might be able to, as you say, 'channel' this and force them to work together by creating an energetic population inversion of electrons ready to emit, then sending through a photon of the proper wavelength to produce a cascade of stimulated emission...Oh wait, that's a laser.