Abstract

I describe briefly the Cosmic Microwave Background (hereafter CMB) physics, which explains why high accuracy observations of its spatial structure are a unique observational tool to test our cosmological models, determine the global cosmological parameters, and constrain observationally the physics of the early Universe. I also briefly survey the many experiments that have measured the anisotropies of the CMB and led to crucial advances in observational cosmology. The somewhat frantic series of new results has culminated in the outcome of the WMAP satellite, which confirmed earlier results, set new standards of accuracy, and suggested that the Universe may have reionized earlier than anticipated. Many more CMB experiments are currently taking data or being planned, offering opportunities to challenge further the current concordance model. The large increase in accuracy promises the possibility of falsifying or consolidating even more strongly the current paradigm, which has already met with considerable predictive success.

Introduction

As we shall see, the analysis of the CMB temperature anisotropies indicates that the total energy density of the Universe is quite close to the so-called critical density, ρc, or equivalently Ω = ρ/ρc ≃ 1. We therefore live in a close-to-spatially-flat Universe. In agreement with the indications of other cosmological probes, the team of the CMB satellite WMAP [4] found that about 30% of that density appears to be contributed by matter (ΩM = 0.29 ± 0.07), most of which is dark – i.e., not interacting electromagnetically – and cold – i.e., its primordial velocity dispersion can be neglected.

Abstract

A reconstruction method for recovering the initial conditions of the Universe starting from the present galaxy distribution is presented, which guarantees uniqueness of solutions. We show how our method can be used to obtain the peculiar velocities of a large number of galaxies, hence trace galaxies' orbits back in time and obtain the entire past dynamical history of the Universe above scales where multi-streaming has not occurred. When tested against a 1283 ΔCDM simulation in a box of 200 h–1 Mpc length, we obtain 60% exact reconstruction on scales above 6 h–1Mpc. We apply our method to a real galaxy redshift catalog, the updated NBG (Nearby Galaxies), containing 1 483 groups, and clusters in a radius of 30 Mpc h–1, and reconstruct the peculiar velocity fields in the local neighborhood. Our reconstructed distances are well matched to the observed values outside the collapsed regions if Ωm(t) = 0.20 exp(–0.26(t – 13)), where t is the age of the Universe in Gyrs.

Introduction

Reconstruction of the initial condition of the Universe from the present distribution of the galaxies, brought to us by ever-more sophisticated redshift surveys, is an instance of the general class of inverse problems in physics. In cosmology this problem is frequently tackled in an empirical way by a forward approach. A statistical comparison between the outcome of an N-body simulation and the observational data is made, assuming that a suitable bias relation exists between the distribution of galaxies and that of dark matter.

Abstract

We are told that we are living in a Golden Age of Astronomy. Cosmological parameters are found with unprecedented accuracy. Yet, the known form of matter forms only a small fraction of the total energy density of the Universe. Also, a mysterious dark energy dominates the Universe and causes acceleration in the rate of expansion.

Introductory remarks

We live in an exciting age of astronomy. Some thirty years ago, cosmology was a science of only two parameters, the current expansion rate or the Hubble constant, H0, and its change over time or the deceleration parameter, q0. Questions such as the age of the Universe, its large- and small-scale structure, origin of galaxies, and the formation of stars were considered as speculative with no direct connection to precise measurements. The situation has changed drastically with the discoveries of giant walls of galaxies, voids, dark matter on the one hand, and on the other hand, the tiny variations in the cosmic background radiation and a “mysterious” uniformly distributed, diffuse dark energy causing acceleration of the expansion rate of the Universe. There are some sixteen cosmological parameters whose measured values exhibit unprecedented accuracy in the history of astronomy. Ten of these parameters are “global” in the sense that they pertain to the idealized standard model of a homogeneous isotropic universe governed by the Friedmann–Lemetre– Walker–Robertson metric within the framework of general relativity. The other six refer to more details of the model, to the deviations from homogeneity and their manifestations in the cosmic structure.

Abstract

An overview of the standard model of big bang nucleosynthesis (BBN) in the post-WMAP era is presented. In this context, the theoretical prediction for the abundances of D, 3He, 4He, and 7Li is discussed. The observational determination of the light nuclides is also discussed. While, the D and 4He observations are concordant with BBN predictions, 7Li remains discrepant with the CMB-preferred baryon density and possible explanations are reviewed.

The standard model [1] of big bang nucleosynthesis (BBN) is based on an extended nuclear network in a homogeneous and isotropic cosmology. Apart from the input nuclear cross sections, the theory contains only a single parameter, namely the baryon-to-photon ratio, η ≡ nB/nγ. The theory then allows one to make predictions (with specified uncertainties) of the abundances of the light elements, D, 3He, 4He, and 7Li.

There have been many improvements over the last few years in the state of the theory, particularly in the treatment of the nuclear cross-sections. However, perhaps the most important new input is the WMAP determination of the baryon density [2], ΩBh2, or equivalently η. Thus one is now able to make very precise predictions of the light element isotopes, which can be individually compared with observation [3]. The predictions span some nine orders of magnitude in abundance. The major uncertainties in BBN calculations come from the thermonuclear reaction rates. There are 11 key strong rates (as well as the neutron lifetime) that dominate the uncertainty budget [4, 5].

Recently the input nuclear data have been carefully reassessed [4–7], leading to improved precision in the abundance predictions. The NACRE collaboration presented a larger focus nuclear compilation [6].

We had a good discussion of various issues relating to cosmology and there has been a clear division of perceptions of what is considered important evidence. On the one side, the conventional one, we have heard the very detailed evidence of CMBR and high redshift supernovae, evidence that is popularized in the phrase “concordance cosmology.” The Universe according to this view went through an inflationary phase, had an era of nucleosynthesis and then had the surface of last scattering when the radiation background became decoupled from matter. The package comes with a large part of the matter energy (around 75%) being dark and hitherto unknown, a substantial part of strange kind of matter (21%) and only around 4% of ordinary matter that we are familiar with. Once you believe all of these ideas, you feel convinced that the cosmological problem is all but solved.

On the other side, some of us have been increasingly worried at what appears to be anomalous evidence, evidence that does not fit into the standard picture just mentioned. Even the very basic Hubble law applied to QSO redshifts seems to be threatened if one takes the evidence on anomalous redshifts seriously. In the 1970s when Chip Arp first started finding such examples, he was told that these were exceptions and that he should find more. He has been doing just that and his cases now include not just optical sources but also radio and X-ray sources. Then there is the evidence of periodicities of redshifts that has not gone away with larger samples. As I discussed, even the gamma ray burst sources appear to show the effect.

The redshifts of normal galaxies

For more than 70 years observational evidence has been steadily accumulated that shows that the original observations of Hubble, which led directly to the view that the Universe is expanding, apply to normal galaxies made up of stars. Hubble's original redshift-apparent magnitude relation of 1929 was steadily extended to fainter galaxies, so that by the 1950s it covered a range from about cz≃ 1000 km s−1 to values of z close to 0.2 (Humason, Mayall, and Sandage 1956). By about 1960, following the discovery of the radio galaxies, Minkowski (1960) had reached a redshift record with the galaxy associated with 3C 295, which has z= 0.46. In the 1960s it was very difficult to go beyond that. The limits were set by sizes of the telescopes, the efficiency of the detectors, the faintness of the galaxies, and ways of finding suitable distant clusters. These barriers were all eventually overcome, and for galaxies we can now confidently extend the Hubble law out to galaxies with z≃3.

However, while this redshift-apparent magnitude relation taken in the large is apparently a smooth function of z, Tifft showed in the early 1960s, first by studying the redshifts in the Coma cluster of galaxies, that the differential redshifts z among the different galaxies in a cluster appeared to be quantized, so that the redshift differences are of the form nΔz, with cΔz, ≃72 kms−1 and n is an integer.

The idea of a Colloquium on “Cosmology: Facts and Problems” was mooted when one of us (JVN) was to visit Collège de France as Professor (Chaire Internationale) during 2003–04. Both of us felt that the subject of cosmology has seen considerable advancement on both observational and theoretical fronts but that there are many issues of observational nature that will remain to be understood. With this point of view the Colloquium was arranged during June 8–11, 2004, at Collège de France.

The Colloquium attracted leading workers in the field. They could be divided into three categories: 1. Observers 2. Theoreticians who liked to explain all the observed data in terms of the standard big-bang paradigm 3. Theoreticians who felt that there were some observations that did not allow a standard interpretation. Sometimes the observers also fell under categories 2 and 3. We were happy that the Colloquium attracted good participation from several countries and there was amiable and frank discussion on various issues. We had allowed plenty of time for discussion after each presentation including a panel discussion at the end. The proceedings presented here reflect this openness of the debate. Several participants who had not given a formal presentation also took part in the discussion.

We would like to express our grateful thanks to all those who helped us in various ways towards making this Colloquium such a success. In particular, we would like to thank Professor Jacques Glowinski, Administrateur du Collège de France, for his kindness in hosting the Colloquium at the Collège de France.

Abstract

Reasons are given as to why the standard cosmology does not give an entirely satisfactory description of the Universe and why one needs to look for alternative cosmology. An alternative cosmology is presented in which matter creation takes place in mini-creation events at regular intervals and in response the Universe oscillates on a short-term period of ∼50 Gyr while it also has a steady (exponential) long-term expansion at a characteristic time scale of ∼1000 Gyr. The explanation of the major observed features of the Universe in terms of this cosmology is given and new observations distinguishing it from standard cosmology are proposed.

Introduction

Any proposal to describe the Universe in terms different from the so-called standard cosmology is met with the criticism that, “If the standard model is working so well and now it is possible to quantify that model with great precision, why look for an alternative?.” Before describing the quasi-steady-state cosmology (QSSC in brief) I will therefore spend some time in pointing out the weaknesses of standard cosmology, weaknesses that rob it of many of its merits as a scientific theory. First let me talk of the three claimed successes of standard cosmology.

The big-bang cosmology began with the advantage that the models predicting expansion of the Universe by Friedmann (1922, 1924) and Lemaitre (1927) came before the discovery of the phenomenon of recession of galaxies and Hubble's law (1929). Thus one can say that as a scientific theory the big-bang cosmology made a prediction (namely, that the Universe is expanding) that was successfully verified.

Abstract

A brief explanation of the meaning of the anthropic principle – as a prescription for the attribution of a priori probability weighting – is illustrated by various cosmological and local applications, in which the relevant conclusions are contrasted with those that could be obtained from (less plausible) alternative prescriptions such as the vaguer and less restrictive ubiquity principle, or the more sterile and restrictive autocentric principle.

Introduction

Having been asked to contribute a discussion of the anthropic principle for a colloquium on cosmology, Iwould start by recalling that although its original formulation [1] was motivated by a problem of cosmology (Dirac's) and although many of its most interesting subsequent applications (such as the recent evaluation [2] of the dark energy density in the Universe) have also been concerned with large scale global effects, the principle for which I introduced the term “anthropic” is not intrinsically cosmological, but just as relevant on small, local scales as at a global level. In retrospect I am not sure that my choice of terminology was the most appropriate, but as it has now been widely adopted [3] it is too late to change. Indeed the term “anthropic principle” has become so popular that it has been borrowed to describe ideas (e.g., that the Universe was teleologically designed for our kind of life, which is what I would call a “finality principle”) that are quite different from, and even contradictory with, what I intended. This presentation will not attempt to deal with the confusion that has arisen from such dissident interpretations, but will be concerned only with developments of my originally intended meaning, which I shall attempt to explain in the next section.

In introducing the general topic of this meeting I am going to give a personal view. Only late in my professional career (∼1990) did I begin to work seriously in cosmology, though I had always followed with interest the various claims that progress was being made, and I even wrote a review of the state of affairs for Nature in 1971 entitled, “Was There Really a Big Bang?” (Burbidge 1971).

Introduction

For some years this period, starting in the 1990s, has been said to be the golden age of cosmology. Compared with the situation earlier, this is a fair judgement, since in the last decade or more there has been a tremendous increase in the number of people working in the field, and large sums of money have been invested in new methods of observation of the background radiation and of large numbers of galaxies and other discrete objects, often those with high redshifts. Another important ingredient is the renewed interest in cosmology taken by many theoretical physicists and experimental particle physicists.

With this expansion has come a great deal of new information, and a model for the Universe that almost everyone believes in. This in turn means that while there are many conferences on cosmology, the theme is almost always the same. This meeting will be different because some of its organizers have for a variety of reasons not followed the main stream. At the same time I hope that there will be a fair discussion of the conventional cosmological model.

Introduction

In this chapter, we should like to address the following question: can we invoke gravitational lensing as a possible explanation for anomalous redshifts? In the rest of the chapter, anomalous redshifts refer to redshifts observed for two distinct objects with an angular separation less than 5′ and whose difference is larger than 0.1.

Multiply imaged quasars

Unlike most astrophysical discoveries made during the last century, the physics of gravitational lensing (GL) was understood well before the first example of a multiply imaged object was found (see Einstein 1912 quoted in Renn et al. 1997). The existence of multiply imaged, distant sources had been predicted by Zwicky (1937)… although the first case of a doubly imaged quasar was only reported in 1979 (Walsh et al. 1979).We refer the reader to Surdej and Claeskens (2001) for a recent account on the history of gravitational lensing.

Gravitational lensing coupled with redshift-distance relations has enabled one to make the prediction that cases of multiple images of a distant source with redshift zs should be detected around a foreground lens with redshift zl ≪ zs.

Following the discovery of the first multiply imaged quasar candidates, some doubt had been cast on the interpretation of gravitational lensing as the possible origin of these systems (see Arp and Crane 1992 for the case of 2237 + 0305). Today (see the URLs http://cfa-www.harvard.edu/castles/ and http://vela.astro.ulg.ac.be/grav lens) some 92 cases of multiply imaged extragalactic sources have been reported. Among these, the sources and lens redshifts have been successfully measured for 53 of them. All these show so-called anomalous redshifts (zld zs). Note, however, that not a single case with zld zs has been identified.

Abstract

Observations of “abnormal” (non-Dopplerian) redshifts in the spectrum of nearby sources (the Sun, binary stars, close-by galaxies in groups), and of “abnormal light deflection in the vicinity of the Sun,” are presented. Emphasis is given on the need of reconsidering the observations, which have not been seriously considered since the 1970.

During the early 1970s, Chip Arp started discovering several cases of “abnormal” (i.e., non-Dopplerian) redshifts in the spectra of extragalactic objects. It is one of the most important observational discoveries of our times, in my opinion. At about the same time, I became interested in the abnormal redshifts found in the spectrum of the Sun. J.-P. Vigier, at the same time, was involved in understanding the nature of the photon, along the lines defined by Louis de Broglie, and he did not accept the idea of a zero rest-mass of the photon. We put our efforts together, and we tried to link the abnormal redshifts observed in the local, nearby, universe as consequences of some “tired-light” mechanism, closely linked with the rest-mass of the photon, which we assumed to be a “non-zero restmass,” without actually knowing anything else but an upper value of this rest-mass.

I feel it is a need today to remind the audience of these local, solar and others, abnormal redshifts, although they were mentioned extensively several years ago, but they were neither properly confirmed nor really accounted for. Almost all relevant references can be found in our review paper (Pecker 1977).

Q : M. MOLES :

There is a theoretical possibility to differentiate between stationary and evolutionary models: To look for cosmic evolution, in particular to verify TCMBR = To(1 + z).

A : G. BURBIDGE :

You are correct, and attempts are being made to verify that TCMBR = To(1 + z).

A : A. BLANCHARD :

Yes, this is a way to test expansion. It has already been attempted and results are consistent with the standard picture. The time dilatation of the apparent duration of SNIa light curves is another interesting test whose results also agree with the standard picture.

Q : M. MOLES :

It has been said that we cannot ask a theory to integrate all the observational facts at once. What we would need, if the aim is to build an alternative cosmology, is a change in perspective.

Both the standard and quasi-static cosmology accept expansion as the primary mechanism to understand the z-phenomenon. Whereas it is perfectly acceptable, it rests on the hypothesis that the general behavior of the space-time is the cause for the observed z-distance relation. A completely different view can be put forward, trying to look for a different explanation for the z-phenomenon. This could then be, in principle, tested at the laboratory level, as stated by Zwicky in 1929. In those views, started by Pecker, Vigier, Molés, and others, the CMBR could be understood as a phenomenon related to the z-phenomenon.

Abstract

The full recognition of the genuine expansion of the Universe and all its consequences is what led to the construction of the “hot big-bang” scenario. The reasons why it is now widely accepted as the standard model of cosmology are reviewed. They are all related to the fact that, if matter and energy are to be conserved in an expanding Universe, its content gets diluted over cosmological time implying that it has experienced a thermal history. Many physical phenomena associated with this evolution have been identified, the signatures of which have been actively looked for and indeed been found in a series of crucial observations, from big-bang nucleosynthesis to the patterns expected from the gravitational growth of structure of the Universe.

What is well established, what is speculative, and the questions that are left totally unanswered in the standard cosmology scenario are succinctly presented.

Introduction

Most modern cosmologists would certainly agree that the rapid and recent progress in observational cosmology has put the standard model of cosmology, what is often referred to as the hot-big-bang scenario, on increasingly solid ground. Since the discovery by Hubble in 1929 of the apparent expansion of the Universe from the observed tendency of the faint galaxies to be redshifted, the idea that the Universe is expanding has attracted the attention of many astrophysicists. It led to the idea that the Universe, rather than being in some sense immutable, was born from a primordial explosion, a “Big Bang.” As will be discussed in the conclusions, the issue of the “birth” of the Universe is actually beyond the standard cosmology theory.