The Early Universe

It is a great honor to have been invited to deliver the Fourth B.M. Birla Memorial Lecture following in the footsteps of Fred Hoyle, Philip Morrison and Abdus Salam. I must express my gratitude to Dr. B.G. Sidharth, Director of the Birla Science Centre, for all he has done to make the arrangements for the travel here and the stay here of my wife and myself so pleasant and so comfortable. Finally we are most grateful to Mr. and Mrs. G.P. Birla for their gracious hospitality at their home and its beautiful gardens here in Hyderabad.

Now I will turn to my subject for today. In this talk I will take you back eleven billion years ago to the first few thousand seconds after the origin of our universe of which we and the earth and the sun and our galaxy, the Milky Way, are but a very small part. Many cosmologists think my age of eleven billion years is too short and many prefer a number more like fifteen billion. We need not worry about this detail today. The title of my talk should have been OUR EARLY UNIVERSE not THE EARLY UNIVERSE. Many cosmologists, and I am one of them, believe that our universe is just an expanding bubble in an otherwise infinite universe both in space and time. This infinite universe consists of strange stuff about which we know very little except that it has exceedingly high density. From the basic equations which Einstein gave us we also know that this stuff exerts negative pressure. It is equivalent to Einstein's cosmological constant. In the Friedmann/Elinstein equation for pressure in the universe the cosmological constant term is preceded by a minus sign. Thus instead of compressing our expanding bubble it actually maintains the expansion. Eleven billion years ago a phase transition took place which changed this strange stuff into ordinary matter like you and me which has been expanding ever since. There may be other expanding bubbles but we will never be able to observe them through the dense intervening stuff.