VIEWS: 6 PAGES: 22 POSTED ON: 8/14/2012
SPACE Introduction THE FIRST MOMENT At the birth of the universe all matter was compresses into a ‘fiery” mass of unimaginable density. The earliest moment that can be spoken of with certainty came after a period called the Planck time – the incredibly brief interval of 10-43 seconds. THE FIRST MOMENT The entire universe that is observable today – which may be only part of some unknown whole – occupied a space 10-20 times smaller than an atomic nucleus. And it is believed that an even earlier moment the four basic forces – gravitation, the strong and weak nuclear forces and electromagnetism – were unified into a single force. (We still do not know how this worked!!) THE FIRST MOMENT Present theories can be tentatively applied after the Planck time. But detailed information about the state of the universe at this time was irrevocably altered by the next major event in the history of the universe. When it was 10-35 seconds old the era of inflation began: a period of fantastically rapid increase in size, during which the universe swelled up to at least 1050 times its previous size. THE FIRST MOMENT Although the characteristics of inflation are incredible, theorists believe this idea – devised originally by Alan Guth in the US – must be correct, since it explains a number of puzzling features of today’s universe. THE FIRST MOMENT First it accounts for the fact that the closely packed infant universe expanded neither so slowly that gravitation could crush it back into nothingness, nor so fast that it could thin out before the galaxies and stars could form. Relativity tells us that space is in general curved, and that the amount of curvature depends on the amount of mass present in unit volume – the density. Too great a density and the universe would close round itself and collapse; too low a density and space would open out uncontrollably. THE FIRST MOMENT Mathematical analysis shows that to account for this fine balance the density of the universe must have had a particular, or critical, value, and no other, at a very early time. Indeed, at 10-33 seconds after the Big Bang, it could not have differed from the critical value by more than one part in 10-49. Such a precise agreement is predicted by the theory of inflation, and no other way of explaining it is known. THE FIRST MOMENT Inflation also solves the “horizon” problem. In our present universe we see galaxies moving away from each other into the depths of space. There is a horizon beyond which we cannot see, since galaxies at that distance are receding at the speed of light. The horizon is different for each galaxy. THE FIRST MOMENT Consider two galaxies, close to our horizon but lying in opposite directions from us: they will both be able to see us, lying at their respective horizons, but not each other. THE FIRST MOMENT The problem that arises is this: such galaxies, which cannot receive signals from each other, are very similar in what they contain, and in the density and distribution of their matter. The cosmic background radiation, too, is exactly the same temperature, from whichever part of the sky it comes (later!!). Why would the universe be so homogenous when each part of it sees only a small part of the whole? THE FIRST MOMENT Certainly, as we go back ever closer to the Big Bang itself, these widely separated parts of the universe were closer together than they are now. But the time that had elapsed from the beginning was shorter too. There still had not been time for radiation to travel between them, evening out any possible differences. On the basis of the galaxies’ present motions, there would never have been any contact between these regions. THE FIRST MOMENT But the theory of inflation solves the problem. Before inflation occurred the presently observable universe filled a tiny volume, far smaller than the horizon distance of that time. All parts of it reached temperature equilibrium, with any differences evened out. We see this equilibrium today, long after the most widely separated parts of the universe have ceased to influence each other. THE FIRST MOMENT The universe we now see is indeed very “smooth” on the large scale. Inflation shows how any initial irregularity in the density of matter and energy would be ironed out to a vanishingly low level. The problem now is to explain how sufficient irregularity survived inflation to make it possible for matter to clump into galaxies and stars. THE FIRST MOMENT Lastly, physicists have discovered that presently the universe contains between 100 million and a billion photons for each atom in the universe. Why it should be this number rather than any other is explained in the idea of inflation. THE FIRST MOMENT Inflation started when the strong force was beginning to separate from the electroweak force, but before their separation was complete. By the time this happened the temperature of the universe had dropped to a ten-thousandth of what it had been at the end of Planck time, although it was still at the enormous value of 1028K. Inflation was triggered by extreme supercooling of the infant universe. THE FIRST MOMENT Supercooling occurs when a system falls below a temperature at which it normally changes state, yet fails to undergo that change. At 10-35 seconds the universe was on the brink of a change in state marked by the separation of the strong and electroweak forces. But it continued to cool until it was about 10- 32 seconds old before this transition occurred. While it was in this supercooled condition, a false vacuum formed, the properties of which were very different from those of a true vacuum. THE FIRST MOMENT Usually the density of energy in any system – whether in the form of radiation or matter – decreases when the volume of the system increases and its particles become less densely packed. But the false volume state is one in which the energy density stays constant during expansion. Relativity theory shows that the existence of the false vacuum, with its constant energy density, would have caused a vast force of repulsion. Inflation occurred. THE FIRST MOMENT While the inflation period lasted the universe doubled in size every 10-35 seconds. It doubled hundreds of times, with the result that its volume grew at least 1050 times. The temperature plummeted from 1028 to 1023K. THE FIRST MOMENT Inflation ceased when the change of state had occurred and the strong force and electroweak forces had separated. The energy density of the false vacuum was released, rather as the latent heat stored in in steam is released when it changes state to become water. This burst of energy created a vast number of atomic particles, which reheated the universe to the temperature it had been when inflation began. THE FIRST MOMENT Inthis chaos of radiation and exotic particles began the building of matter as we know it today. THE FIRST MOMENT Matter, energy, space and time were created in an inferno of particles and forces unknown in the modern universe. Within a billionth of a second the initial force affecting all matter had frozen out into the forces known today. It took three minutes for the kaleidoscope of ephemeral particles to give way to stable atomic nuclei. Millennia were to pass before complete atoms were formed. THE FIRST MOMENT The colossal inflation of the universe was powered by the splitting of the GUT (grand unified theory) force into the strong and electroweak forces. The universe visible today is highly uniform because it lies in a “bubble” that was once within the horizon distance, throughout which physical conditions could be equalized.
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