GLORY OF THE STARS

New Zealand Herald, Volume LXXI, Issue 21764, 2 April 1934, Page 6

GLORY OF THE STARS

HEAVENS IN APRIL A SPACE-TI ME: UNIVERSE CONCEPTIONS OF RELATIVITY BY CRUX AUBTRALIS The theory of relativity" is such an unusual blend of purely imaginative concepts and actual laboratory facts dealing with a type of universe which it is difficult, even impossible, for the mind to visualise, that only a few of the world's leading mathematicians can truly be said to understand the theory Certain mathematical results of the theory are very difficult to translate into words conveying meaning to the average mind, and although popular books have been written on the subject and prize essays published, it remains a most difficult subject of study. Relativity has been acclaimed as destroying Newton's conception of gravitation and Euclid's geometry, but really it presents the same immutable laws viewed in a universe of four dimensions, instead of in one of three dimensions. A Russian mathematician, Lobatschevsby, accepting all Euclid's postulates except the one which states that only one line can be drawn through a given point parallel to another line, substituting that many such lines could bo drawn, formed a new geometry. Although the Russian's postulate seems wrong, his geometry is equally logical and leads to equally sensible truths. In fact there are situations where Lobatschevsky's geometry is natural and Euclid's inconceivable. An equally true and logical geometry was evolved last century by a German, Riemann, postulating that no lines can be draw through a point parallel to a given line. If we are to interpret our own space then geometry provides us with three main patterns which we may use. We feel;, however, from our everyday experience that Euclid's system is the one which best describes our universe. Experiments With Light Rays The famous Michelson-Morley experiment was performed by" physicists to measure the absolute motion of the earth through the ether. By sending two light rays in directions at right angles to each other, the one flowing against and then with the ether stream and the other across it, it was hoped to find a retardation of the former as compared with the latter. But no difference could be found. Both rays returned to their source in exactly the same time. Einstein swept away established conventions by saying that Nature is such that it is impossible to determine absolute motion, all motions being relative to something else. Beginning at this point Einstein constructed his special theory of relativity. Lorentz had assumed a physical contraction of space to explain the failure of the Michelson-Morley experiment. Einstein showed that the contraction i;s an appearance only, due to the relative motion of the two objects or observers. In this new world there were no permanent relationships, time, length and order varying. The only permanent things are the laws of its behaviour. In the space-time continuum of four dimensions, states F. J. Brand, in the Journal of the Royal Astronomical Society of Canada, all the electromagnetic laws conform beautifully to the principle of relativity. Newton's laws of gravitation failed to do so, however, and in 1915 Einstein published his general theory, postulating a universe based on Riemann's

geometry. In many ways the theory of relativity has already been borne out by observation. The rate of advance iu the perihelia of the planets is exactly that predicted from Einstein's theory. The deflection of a light ray passing through a strong gravitational field was proved in the solar eclipses of 1919 and 1923. '"'There are other tests which have not been satisfactorily applied because of their difficulty," says Sir. Brand. " But. up to the present the experimental evidence is in the theory's favour. There are blemishes in its form which will have to be corrected, but even as it stands it is the most comprehensive and unified body oir principles. in the entire range of scientific thought." Phenomena in April The Sun will be in the constellation Pisces until April 18, when it will pass into Aries. Its noon altitude at Auckland declines from 49 degrees to 39 degrees during the month. The Moon will be in conjunction with the naked-eye planets as follows: — Saturn, 10th, 8 a.m.; Venus, 10th, 9 p.m.; Mercury, 12th, 4 p.m.; Mars, 14th, 4 p.m.; Jupiter, 28th, 2 .p.m. 1 Mercury :is to-day at its greatest elongation west of the Sun in the morning sky and is favourably placed for observation shortly before dawn. The other inferior planet, Venus, reaches its greatest elongation on the 16th. It is a splendidly brilliant object after 3 a.m. in the eastern sky. Mars is in conjunction with the Sun on the 14th, and is therefore riot observable. Jupiter is a splendid object in the evening sky, being directly opposite to the Sun on the Bth, and therefore above the horizon practically all night. Saturn lies in the morning sky near Venus, but is not at present a striking object on account of its low altitude.