Anonymous

# Quantum Mechanics -- Questions?

1.How has special theory of relativity been unified/reconciled with Quatum mechanics?

2. Why, and where, has the general theory of relativity of not been reconciled with Quantum mechanics?

3. What things has Feynman proved in QED?

A 3-4 line answer for each question will be ok too.

Relevance

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.

1. 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).

2. 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.

3. 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.

I would also like to comment on the answers given by other users, such as Smart prash:

1. In question 1 the user is asking about Dirac's relativistic quantum mechanics, and not about Bohr's elementry quanrum mechanics.

2. 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).

1. Actually it was neil's bohr who combined the ideas of quantum mechanics to explain the structure of atom, which was further developed by schrodinger and De broglie.....

3. In QED, what they assumed is that quarks do have some colour.... according to them they combine as if it follows color mixing technique.

Quantum Electrodynamics or QED, a set of equations that accounts theoretically for the interactions of electromagnetic radiation with atoms and their electrons. QED appears to underlie the chemical and readily observable behaviour of matter and to encompass classical electromagnetic theory. The equations, which explain electromagnetism in terms of the quantum nature of the photon, the carrier of the force, were first formulated by Paul Dirac, Werner Heisenberg, and Wolfgang Pauli in the 1920s and 1930s.

there has never een any conflict between quantum mechanics and special relativity. all the formulas hold - and are more accurate - when you factor in the effects of special relativity. relativity makes the math harder, so it is rarely seen until advanced qm.

general relativity deals with the effects of large objects changing spacetime - gravity, and quantum mechanics deals with incredibly tiny objects. it is really tough to measure the effects of gravity in an atom because quantum mechanical forces are so much stronger, so its like looking for a needle in a haystack. the opposite is true for measuring qm in large scales, its like looking for hay in a needlestack. they both involve making different assumptions about the universe. i know i haven't given a real answer, this is partly because i don't know exactly why they don;t fit, and also because nobody really does - if they did, they could fix it.

feynman predicted quarks, among other things. check http://en.wikipedia.org/wiki/Feynman for more