Is the Universe Expanding? from David A

Nature Vol. 289 26 February 1981 74S Last supper of two Indian Triassic reptiles? from Barry Cox DURING the winter of 1965-66, Indian palaeontologists found a pair of skeletons of the crocodile-like phytosaurian reptiles in the late Triassic rocks of the Maleri Formation in the Pranhita-Godavari Valley, Andhra Pradesh, central India. They were found so closely associated that they soon became known as 'the loving couple'. During the removal of the soft, clay-like matrix from their skeletons, it soon became clear that they had also eaten a similar last meal, for within the rib cage of each there appeared the skeleton of a smaller reptile. Life restorations of two specimens of Malerisaurus, showing quadrupedal and bipedal gaits. These two skeletons have now been described by Chatterjee (Phil. Trans. R. Soc. B291, 163; 1980) as a new genus, trunk. Proportions of this kind are found was probably very similar to that found Malerisaurus. It belongs to a group of still today in a number of facultatively bipedal there today, with a subtropical monsoon poorly known and poorly understood lizards, such as the frilled lizard climate. Malerisaurus therefore probably Permo-Triassic lizard-like reptiles that Chlamydosaurus, and the life lived in a densely forested, lowland includes the ancestors of the lizards restorations of the two specimens that environment with lakes or flood-plains. themselves. Malerisaurus was of illustrate Chatterjee's paper show them in The Maleri fauna also contains a considerable size, some !.3m long, and it two alternative poses. The dentition of variety of other reptiles, as well as the is notable for its rather large hind-limbs. Malerisaurus suggests that it fed on the large aquatic amphibian Metoposaurus. The length of the fore-limb is only 59 per general range of invertebrates that is All of these belong to groups that are cent of the length of the hind-limb, and described as an 'insectivorous diet'. widely known throughout the Triassic the latter is 74 per cent of the length of the The sedimentology of the Maleri world, and attest to the ease of dispersal Barry Cox is Professor of Zoology at Kings' deposits suggests that the environment of through that ancient Pangaea world College, London. this part of India during the late Triassic continent. Is the Universe expanding? from David A. Hanes THE DISCOVERY by Edwin Hubble1 that the variance with the predictions of homogeneous and isotropic on sufficiently Universe is not static, but an evolving Einsteinian General Relativity. At the very large scale~. There are other reasons for entity, is surely the most important finding least, these statistical demonstrations the faith of astronomers in the expansion in extragalactic astronomy this century. demand explanations in terms of unsus hypothesis: the expansion is associated Few astronomers would contest the view pected selection effects, subtly biased with a characteristic time (which may that the Universe is in a state of general samples, or local anisotropies or inhomo naively be thought of as the time since the smooth expansion. However, recent geneities; and, should convincing explana Universe was in a state of infinite density) provocative statistical studies by J. F. tions be lacking, they may suggest that the which is closely comparable with the ages Nicoll, D. Johnson, I. E. Segal and W. usual cosmological descriptions of the of the oldest known stars; and the Segal2 of the relationship between the Universe are inadequate. discoverys of the predicted6 cosmic redshifts of moderately nearby galaxies Edwin Hubble's original data suggested microwave background strongly suggests and their apparent brightnesses have a linear relationship between velocity that the Universe has evolved from a hotter brought this simple yet profound picture (inferred from redshifts) and distance dense state. Moreover, the Hubble under attack. (inferred from apparent luminosities) for expansion finds a natural theoretical In a general expansion, the recession galaxies. This relationship has an appealing framework - that of Einsteinian General velocity of a galaxy (or empirically its simplicity, for in a universe in which we are Relativity - which in fact predates7 the Doppler redshift) should be directly in no preferred position and where there discovery of the expansion and which has proportional to the distance of that galaxy. are no preferred directions - that is, in a been amply confirmed in the limited tests Nicoll et a/. claim they can reject such a universe where the 'cosmological principle' possible to date8 • relationship; rather, their findings imply a holds- it can be shown that such uniform For all these reasons astronomers will be quadratic relationship between redshift expansion (or contraction) is the only unmoved, except by unequivocal tests, to and distance for a moderately nearby permitted large-scale motion. The adopt alternative cosmological descrip sample of galaxies (those with recession cosmological principle is justified both tions of the Universe. Segal's chronometric velocities less than 5,000 km s-1). Such a philosophically and empirically: the cosmology is one such description. It has discovery is consistent with the predictions former in the neo-Copernican sense that we been characterizecfl as a 'gravitational tired of I.E. Segal's3 alternative world model, must assume that we are in no way singled light' theory; that is, one in which observed the chronometric cosmology, and at out as special observers of the cosmos; and redshifts for remote galaxies arise through the latter in that galaxy counts and the the loss of energy by photons during their David A. Hanes is at the Anglo-Australian isotropy of the cosmic background radia propagation rather than because of any Observatory in New South Wales, Australia. tion suggest that the Universe is indeed systematic motions. In Segal's 0028-0836/ 81 1090745·02$01.00 © Jl}8J Mac.:millan JC'Iurnals ltd .

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