Quantum Mechanics is both very intriguing and very confusing. First, I must answer the most commonly asked question about quantum mechanics, what is it? Quantum mechanics is the study of the radioactivity and physics of atoms. Another question you may have is why classical mechanics will not apply to atoms. This answer is simple, classical mechanics is imperfect. Quantum mechanics apply to all matter, and so does classical mechanics except for on an atomic level, so the much easier classical mechanics are still used for larger matter even though they are altogether incorrect. There are many things that quantum mechanics can explain that classical mechanics cannot. The first of these is that light acts as both a wave and a light. Quantum mechanics explains that light actually exists as a particle, but the probability of the position of the photon is wavelike. In this way quantum mechanics explains something that classical mechanics never could. Another thing that goes against classical mechanics is the Heisenberg uncertainty principle. This is the belief that exact accurate measurements can not be taken of anything. This is because when you take measurements of what direction and what speed an atom is going, you are hitting it with a barrage of protons. This barrage of photons will change the speed and direction that the particles is going, so truly accurate measurements can never be taken by any modern means. Yet another example of the faults of classical mechanics is that if the laws of classical mechanics were true, the electrons of an atom would spiral into the nucleus almost immediately. This is obviously incorrect because if that were true it would make existence impossible. Quantum mechanics state that every electron exists on a discrete energy level. This can be proven by using a light bulb with multiple energy levels. If you switch from on energy level to another, the light does not get gradually brighter or gradually darker, but shifts immediately.