"God does not play dice with the universe.ý A. Einstein Quantum mechanics and general relativity: the two great theory (or philosophy?) are still puzzling physicist all around the world to unresolved the conflict between them. Quantum phenomena, for example, seem to require that observations made at one place affect what will be observed in another place at the same instant (no delay at all), thus violating the relativity principle that a signal cannot travel faster than the speed of light. Though both the theories were able to explain many phenomena in this world to make it less strange, there are many things still we are not sure about the theory. Both theory introduced the ideas which baffled the minds of great thinkers and philosophers for long time; yet both have made the universe more explicable and predictable than it ever was before. Newtonian mechanics on the other hand permitted physicists to calculate the motion of cannon balls or planets with great accuracy, but it cannot account for the behavior of atomic particles traveling at nearly the speed of light. Both the theories are today introduced to college freshmen and everybody is familiar with the mysterious "action at a distance," in which gravity acts instantaneously across the universe. Which doesnýt matches the idea of cause and effect. Einstein's general theory of relativity replaced action at a distance with a simple idea of the curvature of space-time, which resolved the paradox. It is the same idea as if you put two heavy balls on a soft bed, they both disturb the area around them and move towards each other. Based on the same idea, in Einstein's general theory, space-time is deformed by the presence of a massive object (like earth, sun), much as the surface of the bed is deformed by the heavy balls On the time scale we are used to live, the universe appears continuous and quantum mechanical effect cannot be seen or observed. Proper scientific instruments can allow us to explore the universe on a sufficiently small scale, far from human experience, the universe turns out to be discontinuous, divided into discrete bits. Its like water stream, if you just see a water flowing in the river, it looks very continues, but if see it finely, it is made up of discrete water molecules. Same thing was found true for light wave and was a completely unexpected discovery. Quantum mechanics deals with that discreteness by treating matter or energy (they are the same according to relativity) either as particles or as waves. The idea that matter or energy could be both a wave and a particle seemed at first to be so strange as to be ridiculous. Thinking it philosophically, waves and particles, of course, are simply images drawn from everyday experience. We use them to describe the subatomic world because we find it impossible to imagine that which we cannot experience. One of the most popular beliefs about the "strangeness" of quantum mechanics has to do with the Heisenberg uncertainty principle, which states that it is impossible to know with total precision both the momentum (or velocity) and the position of an object at the same time. This can be understood by the idea that by measuring any quantity, for example the position of an electron, you will disturb the state of an electron, because you need to hit the electron with light (photon) to see it. This effect cannot be seen on daily life because photon energy is very small to give any significant effect on a for example a marble or any heavy object. One can conclude from the Heisenberg principle that the world is unpredictable, but the opposite is true: The uncertainty principle is actually a recipe for making measurements with incredible accuracy. (If you want to know the position of an object as precisely as possible, for example, then don't try to determine its velocity at the same time.) Because its predictions are faithfully borne out by experiment, quantum mechanics has made the scientist's universe much less strange cont.......