MAIN CONCEPTS.

1) Physics involves the study of an enormous number of length

scales from the Planck length to macroscopic distances, going

from particle physics, nuclear physics, atomic physics, mesoscopic

(nano and micro) physics. At all levels, there are problems

which require the quantum mechanical treatment of MANY DEGREES OF FREEDOM.

2) Many TECHNIQUES are common to all these fields, since

they involve the quantum mechanics of many degrees of freedom.

Techniques and ideas from one are sometimes useful in other

areas even if the scales are quite different (atomic and nuclear physics)

(Higgs phenomena and superconductivity). Different degrees of freedom

are usful at different lenght scales (strenght of a material is determine

by dislocations at distances of 1000 A), cohesive properties of a material

are determined by short distance properties, binding on a scale of 1-10 A.

3) At each level of description, at each length scale, there are

different EFFECTIVE DEGREES OF FREEDOM. NEW laws of physics

for those effective degrees of freedom

can emerge at new lengths scales. Physics is DIFFERENT at different

lenght scales.