The Oskar Klein Memorial Lectures

The following sections are included:

• CONTENTS

• PREFACE

The following sections are included:

• Introduction

• Detection of Solar Neutrinos

• What Is Wrong?

• Neutrino Conversion

• A New Experiment

• A Proposed Solution

• Final Comments

• References

Supernovae are very spectacular phenomena. In a short time, a supernova produces as much energy as the sun in its entire lifetime of about 10¹⁰ years, namely about 10⁵¹ ergs (1 foe for fifty-one ergs). It is generally agreed that all elements heavier than helium came into the world from supernova explosions. There are two types of supernovae: type I originates from white dwarfs, type II from massive stars (≥ 8M_⊙, where M_⊙ is the mass of the sun) at the end of their life. Only type II will concern us here…

A summary is given of the key developments of cosmology in the 20th century from the work of Albert Einstein to the emergence of the generally accepted hot big bang model. The successes of this model are reviewed, but emphasis is placed on the questions that the model leaves unanswered. The remainder of the paper describes the inflationary universe model, which provides plausible answers to a number of these questions. It also offers a possible explanation for the origin of essentially all the matter and energy in the observed universe.

Essentially all modern particle theories suggest the possible existence of a false vacuum state—a metastable state with an energy density that cannot be lowered except by means of a very slow phase transition. Inflationary cosmology makes use of such a state to drive the expansion of the big bang, allowing the entire observed universe to evolve from a very small initial mass. A sphere of false vacuum in our present universe, if larger than a certain critical mass, could inflate to form a new universe which would rapidly detach from its parent. A false vacuum bubble of this size, however, cannot be produced classically unless an initial singularity is present from the outset. E. Farhi, J. Guven, and I have therefore explored the possibility that a bubble of subcritical size, which classically would evolve to a maximum size and collapse, might instead tunnel through a barrier to produce a new universe. We estimated the tunneling rate using semiclassical quantum gravity, and discovered some interesting ambiguities in the formalism.

During the 1920's the Compton effect was very much at the centre of interest among physicists due to its demonstration of the inadequacy of the classical theory for light when trying to account for the scattering of X-rays. The angular intensity distribution of scattered X-rays had not been successfully described by theory until Oskar Klein and Yoshio Nishina in 1928 solved the problem using the then new Dirac theory for the electron. The present paper gives an account of the collaboration in the summer of 1928 between the two physicists — one a theorist, the other an experimentalist — when both were visitors at the Niels Bohr Institute in Copenhagen.

The intensity of Compton scattering radiation is calculated on the basis of the new relativistic quantum dynamics developed by Dirac. The result shows deviations from the corresponding Dirac—Gordon formulae of second order with respect to the ratio of the energy of the primary light quantum to the rest energy of the electron.

The reflection of electrons at a potential jump is investigated according to the new dynamical theory of Dirac. At very large values of the potential jump, electrons may according to the theory penetrate against the electric force acting on them through the surface of the jump and arrive at the other side with a negative kinetic energy. This could be regarded as a particularly sharp example of the difficulty emphasized by Dirac of the relativistic dynamics.

Not until the summer of 1935 did I make new attempts concerning the five-dimensional theory, in connection with a conversation with Pauli, who had in the meantime himself published two articles containing a modified form thereof, which had been proposed by Veblen. However, it was not until 1937 that I once again took hold of it — this time in connection with Yukawa's idea concerning the interaction of the nucleons through an intermediate particle, which gradually appeared to be essentially correct and utterly fertile for all of nuclear physics…