Can someone explain Quantum Physics? Or the Quantum theory?
962631
that's a very broad question. because all the branches of physics are intertwined with each other.\nUmm.. a basic principle of quantum theory is the observation that the smallest pieces of matter, electrons,  exhibit properties of both particles and waves. What an electron is doing at any given moment is a mystery to all of us. We can't just "look" at what the electron is doing to find out, though. The problem is that when we look at something, we're bombarding the electron with photons (light particles that have no mass, but carry momentum & energy).  Hitting the electron with a photon changes the path, speed, etc of the electron and defeats the whole purpose of looking at it.\nInstead we have to look at the end results of what electrons do - so there is an experiment called the double slit experiment which shows us where electrons hit a detector after passing through two small slits. \nYou might imagine that throwing electrons that passed through two holes would create two big blotches on the detector. \nBut the results of this experiment showed that the electrons hit the detector in a particular way - one that demonstrated that the path the electrons took was determined by wave-like motion, not like particle motion (diffraction).\nWierd - so actually, what we conclude is that the electrons took EVERY possible path from the source to the detector, and then upon observation, the resulting pattern arranged itself according to a probability distribution.  Strange, yes.\nAnyway, exploiting the fact that electrons' actions are governed by probability, we are able to conclude a lot of rules about electrons. Where they are, what their energy is, what their momentum is, .. all related to probability. And also all related to "standing waves."  (very very complicated mathematics go here) \nThe thing about standing waves (imagine a violin string) is that they can vibrate at certain harmonics - either one half wave across the whole string, or one, or one and a half, as long as both ends are clamped down.  But they can never be in between those. (Try it by shaking a rope faster and faster)\nANYWAY so this tells us that the amount of energy that electrons can carry can only be in certain amounts and never in between. When an electron gains or loses energy, it can only be enough to send it to the next lowest/highest energy level. Never in between.  This is known as quantization, and you may know this as the "energy states" of electrons.
284320
Time-Travel, silly it may sound, has genuine science behind it. Quantum physics is such an interesting and revolutionary science that it shows the possibility of Time-travel (Theoritically NOT Practically). So, as of this moment, saying "Time Travel is possible" or "Time travel is Impossible" will be wrong. I think that answer could be... "we just dont know yet".\n\nOfcourse there are Time-Travel Paradox that scientists debate on, which i have to tell you is extremely interesting. \n\nJust the word "Time-Travel" initiates so much of discussions and some of them are very deep. When theoritical physicists debate about Time-Travel, its always about the possibilites, contradictions, logic, science and  paradox behind Time Travel. These debates and discussions bring about new science just by discussing Time-travel. So its worth exploring that science. As of this moment, may be we can't even comprehend travelling in time but hey....who knows what the advances in quantum physics and String theory will bring about.
961835
Quantum gravity is the field of theoretical physics attempting to unify quantum mechanics, which describes three of the fundamental forces of nature, with general relativity, the theory of the fourth fundamental force: gravity. The ultimate goal of some is a unified framework for all fundamental forces—a "theory of everything".\n\nclick here:http://en.wikipedia.org/wiki/Quantum_gravity#Overview
660849
http://www.joot.com/dave/writings/articles/entanglement/\n\nhttp://en.wikipedia.org/wiki/Quantum_entanglement\n\nim not sure about your level of expertise on the subject but some goods books are in search of Schodinger's cat by Gribbins and a basic level introduction introducing Quantum theory from the introduction series
36589
That previous answer is wrong.  The reconciliation between classical physics and quantum mechanics is intrinsic to quantum mechanics itself.  One thing we require of quantum mechanics is that, in the limit of large quantum numbers, we recover classical mechanics.  Schrodinger, Ehrenfest and some others demonstrated from the outset that quantum mechanics does indeed give rise to classical mechanics in such a limit.\n\nString theory is, rather, an attempt to reconcile the general theory of relativity with the standard model for particle physics.  For the most part, string theory is an attempt to do two things: 1) Provide a quantum theory of gravity 2) Provide an account of physics which explains both gravity and the standard model of particle physics (when dealing with particle physics at our current level of understanding, we have to introduce the effects of gravity by hand.  The standard model of particle physics and the general theory of relativity are completely separate theories right now).\n\nBefore going further, it's probably a good idea to make sure that everyone understands what a dimension is.  Think of a piece of thread with a black dot painted on it somewhere.  To find that dot, I really only need to know how far it is from the end of the thread in inches.  It requires one number to find anything on a piece of thread, so we say that the thing is one dimensional.  A piece of paper has length and width, so it's two dimensional.  To find something on a cube, for example, I need 3 coordinates.  Finally, if I were to ask you to meet me for dinner, I'd need to supply you with a location (which takes 3 numbers) and a time (which is another).  At first appearance, our universe seems to be 4 dimensional.\n\nIn string theory, we define something called a Planck length by taking the sqaure root of the quantity obtained by multiplying the gravitational constant by Planck's constant and then dividing by the cube of the speed of light.  We actually know all three of these, and we obtain something like 1.61 x 10^(-33)cm as the Planck length.\n\nNow, once the mathematics behind the central hypothesis of string theory have been developed, we can actually derive values for the gravitational constant.  As a strange artifact of the mathematics, this value changes based off of how many spatial dimensions the universe is made out of.  There is no comparing, for example, a four dimensional gravitational constant to a five dimensional constant because their units are different.  We can, however compare Planck lengths, which always carry units of centimeters.  I'll come back to this in a second.\n\nIn order for this superstring business to work, someone had to work out the way they vibrate.  For whatever reason, they use the Ramanujan function to do this, and it spits out the number 10 as the number of dimensions required for string vibrations.  As for your question, the 11 dimensions were part of a previous theory (called supergravity), and it has since been roundly disproven.  The current developments of string theory call for 10 dimensions.\n\nThe problem is the Planck length... it's one we get out of four dimensional spacetime, not 10 dimensional spacetime.  If string theory is right, then somehow our universe is 10 dimensional, and looks 4 dimensional.  How can this be?\n\nThink of a cardboard tube, but one that's actually hundreds of miles long.  Up close, you need two numbers to tell where a small dot of ink might lie on the surface of this tube.  From far away, though, you wouldn't really be able to distinguish between a tube and a very thin piece of string, and you'd begin to talk only about where something lies with respect to the end of the tube, and you'd only need one number.  It's possible that space has this kind of topology, with several small dimensions, and that's why it looks 4 dimensional, but might actually have more dimensions than that.\n\nThere is no experimental verifi
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).
191997
The very best explanation to this is a video I watched in my Philosophy class called "The String Theory" - it is amazing, and makes complete sense. If you looked it up on the internet, it goes into deep detail and is confusing. The video is by Nova (the science channel), and maybe someone else, but it is perfect. Unexplainably mind boggling and amazing.
849239
my favorite is quantum physics, it explains so much about the way our universe works right down to the atomic level
376295
For those who understand mathematics, and dare to imagine beyond the usual, quantum mechanics could easily be the most beautiful branch of physics.\n\nQuantum mechanics is a fundamental branch of theoretical physics that replaces Newtonian mechanics and classical electromagnetism at the atomic and subatomic levels. It is the underlying framework of many fields of physics and chemistry, including condensed matter physics, quantum chemistry, and particle physics. Along with general relativity, it is one of the pillars of modern physics.\n\nQuantum mechanics was developed in the first part of the 20th century and was highly successful in explaining the behavior of atoms, molecules and nuclei. Developed between 1900 and 1930 and later combined with the general and special theory of relativity, it revolutionized the concepts of physics. The new concepts, which were the particle properties of radiation, the wave properties of matter, quantization of physical properties and the idea that one can no longer know exactly where a single particle such as an electron is at any one instance were necessary to explain all of the new experimental evidence that was available at the time. For example, quantum mechanics explains the behavior of semiconductors which are used to make the myriad of devices we use every day.\n\nFollowing are the important contributors to the foundation of quantum mechanics and the principles they uncovered.\n\nYear  Researcher    Quantum Mechanics Concept\n1901  Planck        Blackbody radiation\n1905  Einstein      Photoelectric effect\n1913  Bohr          Quantum theory of spectra\n1922  Compton       Scattering of photons off electrons\n1924  Pauli         Exclusion principle\n1925  de Broglie    Matter waves\n1926  Schroedinger  Wave equation\n1927  Heisenberg    Uncertainty principle\n1927  Davison and Germer  Wave properties of electrons\n1927  Born          Interpretation of the wavefunction\n\n[The answer given by the first user (theswarm666x) is foolish. Although, one gives such examples in order to explain students of quantum mechanics what is actually meant by the terms like 'tunneling', you could not and should not use quantum mechanics in such a situation. Quantum mechanics talks about the wave aspect of objects (which is significant only for very small bodies) and waves can travel through walls.]
810838
Quantum Physics:\n\nThe science of manipulating the inner parts of atoms, to create worm holes, warp spacetime etc. the science attempts to get the atom dissected until you arrive at its smallest component, and then split that.
18056
actually, physicists are still looking for the law of everything that connects the different theories of things and stuff.  String theory is pretty interesting although it doesnt provide definitive answers, it gets closer.  You seem interested in this stuff, you should read "The Elegent Universe" by Brian Greene.  It will explain a lot and help with your understanding.  Be warned though, you might find it too interesting and get too curious like me and end up being a physics major just to get some questions answered, and more do get answered the farther you go in physics haha. Read that book though, it will blow your mind.
507841
Quantum theory and its relation with general theory of relativity
484329
see this link\nhttp://www.colorado.edu/physics/2000/quantumzone/index.html
838195
Good question - it depends on which theory you want to use. Currently, it is estimated that there are 5 hydrogen atoms per cubic metre. But this does not necessarily mean that there is "nothing" between these atoms.\n\nAccording to quantum physics, even the space that we most often referred to a a vacuum, may be composed of various exotic unobservable (for now) components.\n\nIn quantum physics a vacuum is not the same thing as "nothing." One theory supposes that all space is filled with the Higgs Ocean composed of an undetected Higgs field.\n\nThe current idea in quantum physics is that the only place where there is "nothing" is between the strings making up all matter and energy. The concept of "nothingness" is a complex and extensive subject and very difficult for us to visualize.\n\nOf course there is much more to these concepts than a few words in a brief paragraph can relay.\n\nGood Luck
453143
http://computer.howstuffworks.com/quantum-computer.htm
475801
A good book is called the new quantum universe.  You'll need to give yourself a bit of time to absorb all that information.  But it contains all the basic ideas, formulations and explanations to get started
756937
for sure.\n\nbible is descriptive.... quantum physics is a snap.\n\naren't you glad..\n\nthat way its cover 11 or 12 diminsions where you only think in 3 or 4.