Moderni fysiikka Soveltava kurssi Seija Valtonen Hello everybody

Moderni fysiikka Soveltava kurssi Seija Valtonen Hello everybody!!

What do Physicists mean by “We understand”? “The Particle Garden” by Gordon Kane Mothofela Levels of Understanding I Descriptive Understanding II Input and mechanism Understanding III Why Understanding Feb-21 Hello everybody!!

Videocassette recorder I We can do everything that it is capable of, by experimentation, no documents came with it II Can repair it without outside help and parts III Can make it from raw materials without outside help Feb-21 Hello everybody!!

I. Descriptive Understanding Newton • Motion and gravitation • Took some inputs and described the motion of the objects Feb-21 Hello everybody!! Particle physics Standard theory 1. Constituents 2. Forces 3. Rules

3. The rules • Einstein’s special relativity • The quantum theory • The modern form of the rules Since the 1920 s the rules for calculating have not changed in principle, tremendous improvement in understanding how to use them. Feb-21 Hello everybody!!

II. Input and Mechanism Understanding Requires that • To recognize the mechanism how things work • Knowing the solution of the equations • No masses, constants or parameters be inputs, they must be derivable from theory Feb-21 Hello everybody!!

Newton’s law of gravitation What causes the attraction? The notion of a field • Faraday • Maxwell • Einstein Feb-21 • A field is established by every massive body • The field configuration propagates out from the body at the speed of light • Any other body feels the field and is attracted Hello everybody!!

Atomic physics and quantum theory We are taught that atoms are understood, but • Why the force that bounds the atom is what it is? • Why the proton and electron has the same magnitude of electric charge? • Why the masses are what they are? • Etc. Feb-21 Hello everybody!!

Standard Theory • The mathematical form of each force can be derived from the rules once it’s guessed that the force exists. • The existance of a new kind of force is required if a new type of charge is discovered. • No progress in deriving the values of the masses until this. Feb-21 Hello everybody!!

The Standard Theory • 6 quark masses: u, d, c, s, t, b • 6 lepton masses: Electron, muon, tau and the neutrinos • 3 kinds of charge Electric, color, weak • Newton’s gravitational constant G • Planck’s quantum unit h • Speed of light c Nearly 20 quantities in all Feb-21 Hello everybody!!

h and c • Quantum theory • The energy levels of atoms are quantized. The spacing between the levels is determined by Planck’s constant, h. 1. The basic laws of nature are the same in any nonaccelerating coordinates 2. The speed of light has the same value under all conditions, c Feb-21 Special relativity Hello everybody!!

Mechanism understanding is braking the symmetry of the equations • The standard theory equations are symmetric in many ways. • The world is described by a solution that is not symmetric. Spontaneous symmetrybreaking - why? Feb-21 Hello everybody!!

III Why Understanding in Particle Physics • A derivation of the existence of e. g. electron, muon and tau leptons? • The values of their masses? • Why 3 leptons, that differ only in mass? • What is electric charge? • Why the forces are the ones we know? • Much more Feb-21 Hello everybody!!

The mere existence of a problem is no proof of the existence of a solution Why Understanding in particle physics is a major research activity today. “Theory of everything” The glimpses so far of how nature works have shown an austere beauty. Made by God, who has the keys of life and death We can’t do even the least, to continue our life – or the life Hello of everybody!! our beloved ones