Is quantum theory supplanted by string theory in 21st century physics?
408267
Quantum theory accurately describes the way things in the universe behave on small scales.  General relativity does the same for large scales.  However, combining the two theories to find equations that work for things like black holes doesn't really work.\n\nString theory is an attempt to find something that accurately describes interactions on both large and small scales.  Another idea is loop quantum gravity.  Neither idea has really been proven yet, although useful insights have been gleaned from both.\n\nThe hope is that future research at places like the Large Hadron Collider that is scheduled to begin operation soon in Europe will eventually prove string theory correct.  Even if that does happen though, the equations for string theory are actually still too complex for mathematicians to accurately solve them.  Currently, physicists use estimates instead of the true equations.  There will need to be a lot of work done in that area as well before string theory will really replace quantum theory.
261464
Additional info: I've talked to Holger Bech, one of the three founding fathers and Danish, and not even he believes in the theory. Basically, this is due to the String Theory postulating the existence of 9 dimensions. We can see that this is pretty far from the case, with there only being 3 physical dimensions and time, equaling 4. Furthermore, S.T. postulates that almost 300 of a specific grouping of particles exist. Experimental testing estimates that only 16 exist.
16307
Quantum physics is a fundamental physical theory 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. Often, it is the answer to questions when general relativity fails.
175717
I've heard of this parallel universe theory..well, it's not a theory really it would be like a conclusion if string theory is someday proved ; there may be infinite universes each with a different law of physics and ours will be just one of many others .\nsounds weird huh? that there are hidden worlds beyond ours, well, that's because there are particles like e- that can stay in more than one place at a time ..so one explanation could be that this particles don't exist just in our universe but in an infinite number of them ( parallel universes)..reality is even more amazing than fiction sometimes :P
91646
String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects (strings) rather than the zero-dimensional points (particles) that are the basis of the Standard Model of particle physics. For this reason, string theories are able to avoid problems associated with the presence of pointlike particles in a physical theory. Studies of string theories have revealed that they require not just strings but also higher-dimensional objects.\n\nThe basic idea is that the fundamental constituents of reality are strings of energy of the Planck length (about 10-35 m) which vibrate at resonant specific frequencies[1]. Another key claim of the theory is that no measurable differences can be detected between strings that wrap around dimensions smaller than themselves and those that move along larger dimensions (i.e., effects in a dimension of size R equal those whose size is 1/R). Singularities are avoided because the observed consequences of "big crunches" never reach zero size. In fact, should the universe begin a "big crunch" sort of process, string theory dictates that the universe could never be smaller than the size of a string, at which point it would actually begin expanding.\n\nInterest in string theory is driven largely by the hope that it will prove to be a theory of everything. It is a possible solution of the quantum gravity problem, and in addition to gravity it can naturally describe interactions similar to electromagnetism and the other forces of nature. Superstring theories include fermions, the building blocks of matter, and incorporate supersymmetry. It is not yet known whether string theory is able to describe a universe with the precise collection of forces and matter that is observed, nor how much freedom to choose those details the theory will allow. String theory as a whole has not yet made falsifiable predictions that would allow it to be experimentally tested, though various special corners of the theory are accessible to planned observations and experiments.\n\nWork on string theory has led to advances in mathematics, mainly in algebraic geometry. String theory has also led to other theories, supersymmetric gauge theories, which will be tested at the new Large Hadron Collider experiment.
117056
String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects (strings) rather than the zero-dimensional points (particles) that are the basis of the Standard Model of particle physics. For this reason, string theories are able to avoid problems associated with the presence of pointlike particles in a physical theory. Studies of string theories have revealed that they require not just strings but also higher-dimensional objects.
106275
These are very thorough answers.  But you asked for "simple," so here goes...\n\nAccording to string theory, "strings" are the fundamental building block of all matter...the old fashioned ones (atoms and/or their consituent parts) are in fact nothing more than strings vibrating a certain way.  If they vibrate one way, they're electrons.  If they vibrate another way, they're protons.  And so on.
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String Theory is only a theory of description of elementary particles based on one-dimensional curves, or "strings," instead of point particles, given by from some theoretical Physicist.\nThe energy-scale at which the stringlike properties would become evident is so high that it is currently unclear how any of the forms of the theory could be tested.\nSo it has not been tested yet and I think it will remain a theory not reality in near future.
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.
1095974
this is sort of trival, dimensions can be thought of as derivatives, and you can take a formula and make any number of derivatives of the original derivatives and still end up with a line that bends, indicating no limit to the number of dimensions we can really conceive..   \nModern string theory is a bunch of hoo haa,   such a sub-atomic idea makes no sense, the reality we know could not have order if there were "strings".  "strings" have no way of organizing themselves into different sub-atomic particles, the universe would just be a bunch of "strings"
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.
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The answer is a definite Maybe.\nAs for the space elevator, my understanding is that to complete one, we would need an ultrathin, ultralight, flexible material wit a tensile strength surpassing all we have now. Quantum Physics is THE tool for people who design new materials. Without using quantum physics, it would all be simply trial and error.\nTime travel is a very slippery subject and I can't comment on that. Right now we have no idea how to begin thinking about it.\nMolecular transport, as in beaming stuff the Star Trek way?\nI'd say there's a lot of problems with that, but quantum physics is the very starting point. All that happens to molecules is subject to quantum laws. Therefore I don't know if qf can bring those things abot. However, nothing else can.
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
561193
You do have a point. Of course Schrodinger's equation was a brilliant breakthrough but these theories necessarily have a mathematical foundation and sometimes that foundation is not as secure as generally perceived. Mathematics is evolving and some of the stuff coming out is very weird, paradoxes and all, and this ends up affecting the way scientists formulate their theories. Put it this way: most physcists are not expert mathematicians and they are often a step behind with respect to rigor. As far as quantum mechanics is concerned, one has to consider its real and significant successes as a useful theory but with the realization that any developing theory  will necessarily have growing pains and it will need to be adjusted, finetuned and sometimes overhauled in the light of new info. in order to be incorporated in a more general theory of which it is a special case much like classical mechanics had to adjust to both quantum mechanics and the special and general theories of relativity. I think the greatest revision to quantum mechanics and General relativity will occur when the large and the small, and the uncertain and the deterministic, are finally 'married' in a breakthrough theory of quantum gravity. The problem with general relativity is that it is deterministic field theory and it is based on the concept of a space-time 'continuum'. I think the concept of continuum upon which the formalism of general relativity is based, is counter-productive and it needsto be replaced with a quantized 'granular' space-time structure that would allow things to get unified. On a philosophical note, you are right, in a sense, concerning questionable foundational definitions since if you keep asking the question: and what precisely do you mean by that? It doesn't take that many questions before you are reduced to axioms which are based on presumptuous perceptions of the human mind: In otherwords we could be missing a lot.
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Nope - String theory was created as a way to make the laws of the universe apply in all situations.  Without string theory, we use one set of laws for sub-atomic particles and another set for everything larger.  Because laws of the universe need to be true everywhere for them to really be "laws," string theory was developed as a way for everything to be governed by one set - the laws remain constant no matter what level you are looking at.
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Like so many things in physics, string theory came about by accident, and was not entirely unrelated to the fact that physicists don't get laid often enough.\n\nGaspard LaRoche was a physicist in Bonne in 1948. He was experimenting with particle deceleration, on the basis that by selectively weakening electrochemical bonds within steel molecules, you could essentially make "stretchy bridges" - bridges that wouldn't break but would only use about a third of the raw steel to make - you'd basically just have to stretch them out long enough.\n\nIt wasn't going well.\n\nGaspard made his own lunch, because like many physicists, he was a truly lonely, blinkered individual. He traditionally made himself cheese sandwiches, and ate them, miserably, in the lab.\n\nThe rest is history - the result of boredom and that dark curiosity that makes physicists wonder 'what will happen if I press this button'. Gaspard zapped his sandwich with a stream of decelerated protons, threw in a handful of deconstructed proteins just for show, and voila - cheese sandwiches that could be bounced, stretched, split and strung across the lab as a party piece.\n\nSadly, Gaspard died alone, uncelebrated for his single contribution to the world outside the laboratory. His stretchy bridges never came to anything, and it wasn't until two years after his death that string cheese was reinvented as a childhood food.\n\nIncidentally, all this pre-dated the string theory of the universe by some years. The scientists behind the theory have always fought shy of acknowledging Gaspard's work as being their inspiration...but we know the truth.
554170
Read Michio Kakuo's book.  He is the "inventor" of strings theory, not Hawking.