Passion for Science 2

11) How old is the sun and what will happen when it runs out of energy? The sun and its family of planets, including the earth, formed about four and a half billion years ago from a huge cloud of gas and dust called a nebula. As the cloud condensed under the force of gravity, it began to heat up. Further contraction caused more heat until finally the immense pressure and incredibly high temperature triggered the fusion process and the sun began to shine. The planets were formed from the residue orbiting the sun, with the rocky planets in close orbits and the gas giants like Jupiter and Saturn further out. Our life-giving star is middle-aged and when it has burned most of its hydrogen fuel, it will begin to swell because its internal pressure will become greater than the gravitational force holding it together. It will grow into a Red Giant and swallow the planets Mercury and Venus. All life on earth, animal and vegetable, will be killed; the oceans will be boiled away and the earth will be a searing, volcano-ravaged desert bathed in the red glow of our swollen star. Following the expansion stage, the sun will collapse becoming a cold White Dwarf star, a fraction of its former size! Not to worry, however, because this won’t happen for billions of years to come.
12) What is relativity? This would need an entire book to explain properly, but I will try to give you an insight into it. In 1905, Albert Einstein formulated his theory of ‘Special Relativity’, which was hailed as the most remarkable insight into the workings of nature. It was ‘special’ because it dealt only with bodies at constant velocity. Einstein’s other great discovery, the General Theory of Relativity, was even more groundbreaking when he published it in 1915 because this dealt with accelerating and rotational velocities as well. Up to that time Sir Isaac Newton’s theory of gravity had worked perfectly well for over 200 years and still does for most applications. Newton had said that any two bodies in space attract each other with a force that is dependent on the masses of those bodies and the distance between them. His formula worked well for falling apples, flying cannonballs and orbiting planets, but he did not know what caused this attraction. Einstein’s theory identified this illusive cause. Again it was so radical and revolutionary that physicists either rejected it out of hand or failed to even understand it, because the maths involved was so daunting. In one instance physicist Ludwig Silberstein suggested to British astronomer Arthur Eddington (who had written a book on Einstein’s theory) that probably only three people in the world understood relativity. Eddington replied, ‘Well there’s Einstein and there’s me, but who’s the third’?
The essence of Einstein’s General theory is that matter warps space. Strictly speaking matter warps space and time, which Einstein called ‘space-time’. He correctly stated that one cannot travel through space without travelling through time as well. The best way to try to visualise how this warping of space-time works is to imagine a large rubber sheet stretched taut like a trampoline and this becomes our two-dimensional representation of space-time. Now if we place a heavy bowling ball in the middle of the sheet it will deform it into a deep hollow. The bowling ball represents a massive body in space like our sun. Now imagine rolling a golf ball (the earth) past the bowling ball, it will be deflected from its straight-line path into a curved path around the bowling ball (sun). This is gravity. Matter distorting space-time. In reality because the rubber sheet would impart some friction to the golf ball it would slow down and eventually roll into the hollow. But in space there is no friction so the earth rolls around the sun virtually for ever, as do all the planets. Einstein needed to prove his theory by the time-honoured method of making a prediction that could be tested. Nowhere on earth was there anything with enough mass, but in space there was the sun. Einstein suggested that it should be possible to test his theory during a total eclipse of the sun. By photographing the true position of a star relative to the other stars, (when the sun was in a different part of the sky), it should be possible to detect any bending of the light from that star, months later when it would be just hidden by the rim of the sun. If relativity were to be judged true, the hidden star should become visible because its light would be bent around the sun and picked up by the telescopes! Naturally the brightness of the sun would swamp the faint glow of the star, so the only time such an experiment could be performed would have to be during a total solar eclipse. The upshot was that Arthur Eddington himself organised and carried out the experiment by accurately measuring the bending effects of the sun’s gravity from photographs taken during the eclipse in Brazil. The figures exactly matched Einstein’s predictions. Mass does indeed distort space!


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