Probably the biggest problem in cosmology is one that many people don't even think about or want to think about. It has to do with the nature of the redshifts of astronomical bodies.

Cosmic microwave and infrared background radiation (CMBR and CIBR) measurements in the near future have the potential to greatly advance our knowledge of the early universe. New instrument and space technology will soon enable much better measurements of both.

In traditional societies the remarks of seniors were prized, for their memories often spanned events rare enough to have remained unseen by most yet frequent enough to offer eventual challenges to all. Even here among friends who are self-styled cosmological “old radicals”, I think I am the senior.

These brief comments will reflect the point of view of an observer, rather than a theorist. They will also be quite informal, as were the remarks I made while at the symposium in The Hague. Finally, I will restrict myself to relatively low energy proton backgrounds-roughly speaking from 10−5–101eV. I fear that will slight the important work being done by our colleagues on the X-ray and gamma ray backgrounds, but those topics were nicely covered in the symposium itself.

In cosmology one faces the observational challenge that knowledge about distant regions of the universe is dependent on assumptions one makes about these regions which are themselves coupled to the observations. Within the framework of the Friedmann-Robertson-Walker big bang models the universe becomes opaque to its own radiation at z ≈ 1,000 and the earlier, and more distant, regions of the universe are not directly accessible through observations. Other challenges exist such as possible merging of extended distant sources and confusion of spectra from distant galaxies. One, therefore, encounters horizons in our understanding of the universe. Such horizons exist in any mode of description. To use the quantum analogy, the observer is always part of the system under study, the universe, and a description of the universe entails including the observer and observing apparatus. Since the early universe should be described in quantum terms, it follows that non-locality in the universe is not an a-priori requirement but the outcome of the observing process itself. As such, the flatness and horizon problems may not be preconditions on theoretical models.

We calculate the temperature fluctuations in the microwave background in open primeval isocurvature baryon models (Peebles, 1987) with cosmological densities in the range 0.05 ≤ ω ≤ 0.2 We assume that the power spectrum of fluctuations is a power law with the index varying between – 1 ≤ n ≤ 0, as indicated by observations of large scale structure in the Universe. The Universe is assumed to be always fully ionized. The South Pole 13 field point experiment (Schuster et al., 1993) is compared to our theoretical predictions, and we find that the models predict larger temperature fluctuations than are observed. The observed temperature fluctuations on intermediate scales of ≲ 1° thus seem difficult to reconcile with the isocurvature baryon model.

Most of the studies on the anisotropy expected in the temperature of the cosmic microwave background (CMB) have been based on linear density perturbations. The anisotropies at angular scales ≥ 1o (horizon at recombination) are preserved during the evolution of the universe, whereas for smaller scales new effects can appear, generated during the non-linear phase of matter clustering evolution: i) the Sunyaev-Zeldovich effect due to hot gas in clusters (Scaramella et al. 1993), ii) the Vishniac effect (Vishniac 1987) due to the coupling between density fluctuations and bulk motions of gas and iii) the integrated gravitational effect (Martínez–González et al. 1994) due to time-varyng gravitational potentials. A single potential φ(t, x), satisfying the Poisson equation, is enouph to describe weak gravitational fields associated to non-linear density fluctuations when one considers scales smaller than the horizon and non-relativistic peculiar velocities. The temperature anisotropies, in a flat universe, are given by the expression (Martínez–González et al. 1990)

A central problem in cosmology is the building and testing of a full and detailed theory for the formation of (large-scale) structures in the Universe. It is widely believed that the observed structures today grew by gravitational instability out of very small density perturbations. Such perturbations should have left imprints as small temperature anisotropies in the cosmic microwave background (CMB) radiation.

Temperature fluctuations in the CMB (Cosmic Microwave Background) are a key prediction of cosmological models of structure formation in the early Universe. Observations at the Teide Observatory, Tenerife using radiometers operating at 10, 15 and 33 GHz have revealed individual hot and cold features in the microwave sky at high Galactic latitudes. These well-defined features are not atmospheric or Galactic in origin; they represent the first detection of individual primordial fluctuations in the CMB. Their intensity is defined by an intrinsic rms amplitude of 54−10+14 μK for a model with a coherence angle of 4°. The expected quadrupole term for a Harrison-Zel'dovich spectrum is QRMS–PS = 26 ± 6 μK. When our data at Dec=+40° are compared with the COBE DMR two-year data, the presence of individual features is confirmed. New experiments to detect structure on smaller scales are described.

The aim of this brief report is to find a lower limit of the Hubble parameter using the COBE's detected fluctuations in the temperature of the CMBR.

It is generally believed that on very large scales the distribution of matter in the universe is homogeneous and effectively all the existing theoretical approaches are based on this assumption. However, recent re-analysis of galaxy-galaxy and cluster-cluster correlations by Coleman and Pietronero (1992, hereafter CP) and Luo and Schramm (1992, hereafter LS) indicates that the distribution of the visible matter in the universe is fractal or multifractal up to the present observed limits (~100 h−1 Mpc for H0 = 100 h km s−1 Mpc−1 and 0.5≤h≤1) without any evidence for homogenization on those scales. The fractal dimension obtained from these analyses is D ~ 1.2 - 1.3 (CP; LS).

A fractal universe model has been proposed elsewhere (Driessen, 1991, 1994), based on the assumption of perfect self-similarity between some definite scales, and in particular between particles and galaxies. Its motivation rested essentially on two ideas: first, if striving for unification is justified, then the fractal idea makes sense, for in this case one single theory of particles could encompass all self-similar structures at once. Secondly, it could be demonstrated that, provided some reasonable hypothesis were made about the structure of spiral galaxy cores, they came back to the same topological state after two complete revolutions (Driessen, 1991). These ideas combined suggested that spiral galaxies might correspond to electrons on the cosmic scale. The main test of the coherence of the fractal picture was then to discover if other galaxy types and quasars do find a place in this model. Now, a small group of dissident has sustained for years that QSOs (or at least a certain class of QSOs) are local objects emitted by galaxies. This class would contain very small (d ≈ 0.3 kpc), faint (Mv ≈ −12), and most often radio-quiet objects with large (non cosmological) excess redshift. The analogy between the two statements “electrons emit photons” and “galaxies emit QSOs” hinted that QSOs embody cosmic scale photons, and entails that galaxies experience quasar exchange interactions. It was claimed further that galaxy clusters reproduce atomic and molecular-like systems with one or a few central giant ellipticals (the cosmic scale nuclei) interacting via quasar exchange with their satellite spirals (the cosmic scale electrons). The flock of dwarf galaxies around large ellipticals and spirals would result from condensation of dusty gas clouds entrained by ejected QSOs.

The radio properties of powerful extended radio sources may be used to study the environments of the sources, the source energetics, a characteristic length-scale that can be used as a cosmological tool, and the relation between radio galaxies and radio loud quasars. Thus, these sources offer a rich variety of diagnostics, both direct and indirect, of the cosmological model that describes our universe. They, indeed, are a goldmine for cosmology.

Perhaps the most significant result of the investigations mentioned here is the use of the radio properties of the sources to estimate the ambient gas density in the vicinity of the radio lobe. As discussed below, the ambient gas densities estimated using the strong shock jump conditions across the radio lobe indicate that these sources lie in relatively dense gaseous environments, similar to the intracluster medium found in clusters of galaxies at low redshift. Thus, the observations suggest that at least some clusters with their intracluster medium in place exist at high redshift.

The well- grounded polemics about the fractal structure of the Universe and a new cosmological picture which appears in connection with this, in first instance the absence of any evidence for homogenization up to present observational limits 200h−1 Mpc, have been detailed at the work by Coleman, Pietronero (1992). Two versions on nature of fractal pattern of the galaxy distribution in the observed universe also are now: it behaves like a simple homogeneous fractal (Pietronero 1987; Coleman et al. 1988) and as a multifractal - fractal having more than one scaling index (Jones et al. 1988; Martinez, Jones 1990; Martinez et al. 1990; Borgani et al. 1993 (with the good review for matter of above)).

This work does not play decisively into hands of these versions so the fractal concepts, exactly a selfsimilarity and multifractal, were applied here for the analysis of two - dimensional distribution of the bright galaxies and dwarf galaxies of the low surface brightness (LSBD) belonging to the Local Supercluster (LS). But if the observed universe holds the fractal structure, so it is useful to trace over the lower fractal pattern on the small scales of clustering of galaxies within the framework of the known superclusters and, in the first instance, within the local overdensity of galaxies. This work is a preliminary before preparing one with the same analysis of three- dimensional distribution of galaxies of LS.

Recent achievements in Very Long Baseline Interferometry (VLBI) allow the reconsideration of milliarcsecond radio structure of Active Galactic Nuclei (AGN) as a “standard object”. The basic concept of this approach is described and illustrated.

In regions away from the Galactic plane, formal tests indicate an isotropic, random and independent distribution of radio sources on the sky (e.g. [1], although there are strong indications of large-scale anomalies (e.g. [2], [3]). An accommodation of these results was suggested by Shaver and Pierre [4] and by Shaver [5] who showed that the large-scale deviations could be due to the supergalaxy, a possibility which had been noted by Pauliny-Toth et al. in 1978 [6]. As to the influence of other superclusters, or indeed the cellular structure of the universe in which galaxies cluster on scales up to at least 100 h−1 Mpc (e.g. [7]), at what flux-density level does this large-scale structure become apparent? Conversely, what can be learnt about structure on the largest scales through the sky distribution of radio sources? Here we describe three investigations in various stages of completion which consider these issues.

The recently completed Rhodes/HartRAO 2300 MHz radio continuum survey is the highest resolution and highest frequency survey of the entire southern sky. This makes it useful for those wishing to model the Galactic foreground in order to study cosmic background emission. Unfortunately there are low-amplitude, large-scale gradients in the survey data which make it difficult to interpret the very high latitude Galactic emission. We describe a small, low-cost horn telescope which we hope to use to correct the gradients in the survey data.

We have considered two compilations of angular-size/redshift data for ultra-compact radio sources, due to Kellerman (1993) and Gurvits (1994) respectively, and a family of homogeneous isotropic universes with two degrees of freedom, represented by pressure-free matter and vacuum-energy. Kellerman's results seem to support the canonical model q0 = 1/2, ω0 = 1; the question posed here is: can we produce significant deceleration without dark matter?

This paper presents our investigations of statistical behavior of the small-scale jet orientations and the intrinsic polarization position angles. We found that the distribution of the milliarcsecond-scale jet orientations and intrinsic polarization position angles of extragalatic radio sources appears anisotropic with high significance levels in most cases.