The Ruggiero de Ritis Biography
On the 8 of September 2000, Ruggiero de Ritis, professor of Physics at the University Federico II of Naples, founder and leader of the local group of gravitational physics, passed away at the age of 56, prematurely leaving friends, colleagues and students.
Ruggiero’s had very broad cultural and scientific interests. During his thesis work (on the foundations of Quantum Mechanics) he developed a deep interest for the philosophical foundations and implications of modern physics; an interest which has marked all his subsequent work, even the most technical part of it. Immedialy after graduation, at a time when the topic was still rather neglected from the scientific community, he started to work in the field of general relativity and, attracted by his strong scientific personality, many young researchers begun to collaborate with him, establishing the first nucleus of the future group of Gravitational Physics.
Over the years, the group grew involved in the fields of gravitational theory with torsion, inflationary cosmology, scalar-tensor theory, gravitational lensing, the nature of cosmological constants, the problem of the cosmic distance scale and, last but not least, Einstein’s epistemology.
In 1994, Ruggiero and his group begun to collaborate with the Capodimonte Observatory and started the SLOTT-AGAPE international project bringing to the Observatory a set of competencies and of international partnerships of which the Institute is still greatly benefiting.
To commemorate his activity, the Observatory decided to name after him a yearly series of lectures, The Ruggiero De Ritis Lectures, to be held every year by a leading authority in the fields of theoretical and observational cosmology, general relativity and epistemology.
Introduction
The lectures are presented as follows.
In the first part the experimental basis of modern cosmology is presented. Several decades ago the cosmology has only one basic experimental fact which form the experimental basis.
It was the expansion of our Universe. The main parameters of expansion were determined with huge uncertainty. For example, the Hubble parameter (H) which the main parameter determined the rate of expansion was measured as 50 < H < 150 (km/sec/Mpc). Only the last several years astronomers and cosmologists have instrument to measure this parameter with sufficient accuracy. The time begun when the 3K blackbody radiation was discovered.
Several years later cosmologists developed the theory of light elements production during the high temperature stage of the Universe evolution.
The conclusions of these calculations were cofirmed by observations. Later the theory of Large Scale Structure of our Universe was developed by Ya.B.Zeldovich and his collaborators. Next very important step in the Universe investigation was done by the observation of the anisotropy of the CMBR (3K blackbody radiation). The gravitational lenses though are not the subject of cosmological investigation can be considered as osmological objects. The last years the investigation of SuperNovae Ia stars reveale the accelarated expansion of our Universe. This very important fact of
the present day investigation is discussed in separate part of lectures.
The second part.
The correct cosmological model can be developed after the creation of the gravitational theory apllicapable to the strong gravitational field and to the large scales. This theory which is named now the General Relativity was created by Albert Einstein in 1916. The main ideas and differences of the relativistic theory of gravity are discussed in the second part of these lectures.
The third part of the lectures devoted to the analysis of the Friedmannien equations. The equations describe the evolution of our Universe were derived by Alexandr Friedmann in 1924. The conclusions of these equation were so unusual that even Albert Einstein did not belive in. But after the explanation of A.Friedmann transfered by A.Korotkov, Einstein agreed with the model developed. The Friedmannien equation predicted the expansion of our Universe. This expansion was discovered by Edwin Hubble in 1929 and the law of expansion has its name now.
The fouth part contains the newtonian description of the cosmological equations which reveal the physical sense of these equations and help to understand them. The fourth part contains the newtonian description of the cosmological equations.
The fifth part devoted to the determination (in mathematical sense) the observable quantities in the cosmology. The red shift, Hubble diagramms, distances, size of horizon are the subject of this part. At the end the solution of the Olberts paradox in Friedmannien cosmology is discussed.
The sixs part of the lectures are devoted to discussion of the small scale irregularities in cosmology and the equations for the evolution of these perturbations. The gravitational instability of different types of matter and on the different background is considered. The real matter in the early Universe is high temperature plasma. One has to consider the influence of high temperature plasma on the evolution of the irregularities during the expansion. The Silk effect (radiation drag) is one of the main effect which is considered here. The concept of dark matter is one of the most important concept in the astronomy as a whole. This concept is very important in cosmology.
The role of dark matter in the evolution of the small scale irregularities and different types of dark matter is discussed in this part of lectures.
The seventh part of the lectures is devoted to the nonlinear regime of evolution of density perturbations. The main feature of this stage is formation of the 2D structures which were named pankecks. Now is known as Zeldovich approximation. This type of structure was discovered and called now the Large Scale Structure of the Universe.
Introduction
In this subdirectory the first part of this lecture is presented. The first part devoted mainly to the experimental basis of the modern cosmology. The main experiments and observational facts are discussed. There are several observational facts which form the experimental basis of the modern cosmology. They are:
1. Expansion of our Universe.
2. Discovery of the CMBR.
3. Discovery of Large-Scale Structure of our Universe.
4. Light element abundance.
5. Discovery of anisotropy of the CMBR.
6. SuperNovae cosmology Project???
7. Gravitational Lenses?????
Main ideas of General Relativity
In this subdirectory the brief introduction to Special and General Relativity is presented. Here I describe the main ideas of Special and General Relativity with simple physical explanation. Let list the main ideas of General Relativity and the main difference of Newtonian gravity from the General Relativity (GR below).
The space – time in GR is curved.
The main object in GR is metric.
The metric coefficient determine the property of space – time and the property of gravitational field.
The gravitational field in Newtonian physics is determined by the one scalar value which is gravitational potential.
In GR the gravitational field is 10 function which are metric coefficients. The metric of space -time determines both
geometry of space and time and properties of gravitational field.
The law of motion in cosmology (for instance, the light ray law) is the motion laws on the curved nonstationary background.
The source of gravitational field in Newtonian gravity is mass. This is no longer valid in GR. The source of gravitational field in GR is stress – energy tensor which has 10 independent component. It provides more complex behaviour of gravitational field in GR.
In particular conditions gravitational attraction can trasforms into gravitational repulsion. In the modern cosmology these conditions are called the negative pressure or false vacuum conditions.
Equations which describe the evolution of the expanding Universe
Here the Friedmannien equations are presented and analized. These equations are described the physics and evolution of our Universe.
Newtonian description of the Universe’s expansion
The Friedmannien equation can be represented in newtonian form. Moreover the evolution of our Universe can be described in newtonian form. This approach reveal the physical sense of the cosmological equations and help to understand them. The main difference between the exact (Friedmannien) equations and newtonian form is that one can
account that the source of gravitational field is both the density of matter and pressure of matter. It changes the numerical value of gravitational field and in the case of negative pressure it can change the attraction into repulsion. The newtonian description of the Universe’s expansion is presented as comparison with the motion of a rocket which leaves the Earth.
Observable quantities in cosmology
The observable quantities of the expanding Universe differ from the same ones in nonexpanding space.
In this subdirectory are slides which devoted to discussion of cosmological red shift, the Hubble law, the Hubble
diagrammes toghether with definition of distances in cosmology.
Small-scale irregularities
The homogeneous and isotropic model is first approximation to the real Universe. In our Universe are large scale structure, cluster of galaxies and galaxies. They are the result of gravitational instability originated from the small scale density perturbations. In this section I discuss the newtonian equation for gravitational instabilty, Silk effect (radiation drag) which dampts the instabilty in radiation dominated era. The concept of dark matter in cosmology primevally arose when the structure formation was discussed. Dark matter along with its types are discussed in here.
Nonlinear regime of structure formation
Here the nonlinear regime of structure formation is discussed.
The main difference between the formation of Lrge Scale Structure in cosmology and gravitational instability in star formation is in the pressureless regime of formation of the Large Scale Structure.
The abcense of pressure leads to the 2D object to be formed. These object were predicted by Ya.B.Zeldovich and his followers:Andrey Doroshkevich and Sergei Shandarin. The moder approach to the structure formation is mainly numerical as far as it requires the solution of N body problems. The analitical theory (Zeldovich approximation) is discussed here, followed by the discussion of the numerical methids in the simulation of the Large Scale Structure of our Universe.
Gravitational lenses
Though the gravitational lenses are not the object for cosmology, they are very close to cosmological investigation. To determine the distance to a lens one has to use cosmological distances. The gravitational lens testes play very importrant role in the cosmological investigations. Moreover gravitational lenses were the Rujero de Ritis favorite topic of investigation during the last years.
Its are why I add the section devoted to gravitational lens investigation to this coource of lectures. In this part the effect of gravitational lens is discussed including the pedagogical simple case up to the real cases.
Several examples of extragalactic gravitational lenses are discussed in this part.