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How big is everything? For a long time, the earth itself must have seemed vast enough. Imagine a Phoenician in about the year 1000 BCE standing on the shores of Spain and staring out across the void of the Atlantic. It must have seemed immeasurably vast and mysterious.
Ancient Greek astronomers such as Aristarchus and Hipparchus were the first to make scientific estimates of important distances, around the third century BCE. They were pretty good at it, considering that there were no telescopes. The Earth was about 39000 km in circumference (pretty accurate); the Moon about 383000 km(again pretty good); the Sun 16,210 000 km (out by a factor of ten). These distances were immense, inconceivable, by the standards of the time. The fastest ships would take weeks to make the passage from Alexandria to Rome. Trading expeditions to the East would need a year. To people of the time, reaching the moon was technologically impossible, it would be like us imagining a jaunt to the Andromeda Galaxy.
There matters remained for over a thousand years. But with the advent of modern science, things only got vaster. It was found that the earth rotated, and worse still, went round the Sun. Which discovery, as every schoolchild knows, was profoundly disturbing to most people. Cassini made the first accurate planetary measurements of Mars in 1672. With the use of telescopes and parallax, he was not far out. Once again the Universe had jumped in size. Once upon a time things had seemed very cosy, the world all on its own with God and the stars just above. Now what lay beyond Saturn, then the last known planet-and how far?
It was Bessel who in 1838 finally managed to squeeze enough out of parallax to finally give him a good distance for 61Cygni. For the record , it’s 11.398 light years. With the discovery of cepheid variables, astronomers such as Leavitt and Hubble were able to map out our local Milky Way Galaxy, then prove the existence of fractal numbers of other galaxies dotted around a universe which is currently estimated to be 46.5 billion light years across. Our current fastest spaceships, like the Voyagers and Pioneers have taken nearly fifty years to even get into interstellar space; they will take several tens of thousands to come near other stellar systems.
Is the Universe actually infinite? One problem is that people who know talk about these things in complicated mathematics. The use of words simplifies, but it also profoundly distorts. One man who tries to bridge the gap is the very intelligent Professor Brian Cox, In a you- tube video recommended to us by Mr Gary Herbert of Bedfordshire, Professor Cox gives his thoughts on the many exciting discoveries of modern astronomy-and their unsettling implications.
#briancox #sizeof universe #bigbang #relativity
Learning, Science and Society 