Cosmology Cosmology is the study of the overall nature and behavior of the physical universe. Relativity as in Einstein’s General Theory of Relativity is well accepted by physicist and astronomers, it is the framework on which the prominent cosmologies of the day are built. This is primarily because General Relativity is capable of dealing simultaneously with the effects of gravitation and large velocities, where as Newton’s theories, though applicable to ‘everyday’ problems of force and small velocities, break down when applied to this segment of the universe. 1. What is the framework of today’s cosmologies? 2. What is one characteristic of galaxies that require the use of General Relativity instead of Newtonian theory? The cosmologist does not concern himself specifically with individual objects, such as stars or galaxies, but with the whole universe. Some observable facts must be taken into account by all cosmologists: 1. Galaxies are arranges isotropically (uniformly in all directions) on the celestial sphere. 2. There exists an isotropic background radiation. All parts of the Universe appear to be occupied by radiation whose spectrum is that of a black body at 3K (3° above Absolute Zero). 3. Fainter galaxies have greater red shifts (If red shifts are believed to be caused by recession from our own galaxy). 4. Within our own general neighborhood, velocity is proportional to the constant of proportionality (The Hubble Parameter) is 100 km l sec mpc (mega parsec) LINK: http://hyperphysics.phy-astr.gsu.edu/hbase/astro/hubble.html Recession Though, by Hubble’s Parameter the more distant galaxies recede faster from us then the nearer galaxies, making it seem we are at the center of the universe with everything receding from us, but we are in no special position. At any position in the universe observers will see all other galaxies receding at speeds proportional to their distance, this is only a fact of uniform expansion. 1. On average, are galaxies clumped in any specific direction or do they occur uniformly through out space? 2. Within our general neighborhood is the velocity of recession of galaxies proportional to distance? (Yes or No) LINK: http://en.wikipedia.org/wiki/Deceleration_parameter The Steady State Universe Major cosmologies have one axiom that they agree upon: 1. Axiom the universe of galaxies is statistically the same from where ever it is viewed. 2. All the galaxies look the same, their type, number, average density of matter, and speed of receding galaxies would not differ. LINK: http://en.wikipedia.org/wiki/Steady_state_universe The steady state theory adds a second fundamental axiom: Steady State Axiom: The universe of galaxies is the same whenever it is viewed. This axiom allows us the opportunity to disprove the theory by showing that changes do occur with time in the universe. However, the changes that the theory refers to would take place only after billions of years, this is of course longer then astronomers have been observing. The consequences of the steady state theory are: 1. The universe does not change with time; therefore it has existed for an eternity into the past and will continue for an eternity into the future. 2. If the red shifts of galaxies are interpreted as due recession then some galaxies have been receding for an infinite time. By consequence 1 the universe is either infinite in size or by Einstein’s theory as galaxies retreat from us and therefore increase in speed (in accordance with the Hubble Parameter) they contract in the direction of the motion. The universe we would see therefore has a bend since galaxies traveling at the speed of light would deliver no electro-magnetic relation to us. Those unseen galaxies at the rim would be infinitely thin so that an infinite number could be packed there and still the universe would be infinite in size. 3. A steady state also implies that the on going changes in the universe (recession of galaxies from each other and fusion of hydrogen into helium and other complicated atoms) must be neutralized. To accomplish this neutralization, the astronomers Bondi, Gold and Hoyle proposed in 1948 that Hydrogen is continually created out of nothing. Because of this, the Steady State Theory is also called the Continuous Creation Theory. This idea of course violate the conversion of Energy Law; but that law is only an assumption, based on the fact that no one has ever seen energy created from nothing. For this to occur you would need 3-4 atoms per cubic kilometer of space, and for this situation it would be to far for us to see. It is also in a position to combine with other hydrogen and form new galaxies to keep the universe in a steady state. The accumulation is slow, but so is the rate at which galaxies recede from each other compared to inter-galactic distances. Which of the following is the axiom upon which the major cosmologies agree? a. The universe of galaxies is the same whenever it is viewed. b. The universe of galaxies is the same wherever it is viewed. c. Both a and b. d. They agree on NO axioms. How long has the universe existed according to the Steady State Theory? How is it possible that the universe could have existed for an infinite amount of time in the same state if galaxies are continuously receding from each other? The Time Varying Theory The Time Varying Universe theory is less restrictive of the universe then the Steady State Theory, for it allows it to behave in several different ways. Although it agrees that the Hubble Parameter is constant in time. This appears to be true, for when distant galaxies are observed (seen many years in the past due to their distance) they are receding faster than they should be if Hubble’s Parameter is constant. The expansion of the universe seems to be slowing down. The mutual gravitation effect of the galaxies cannot be the complete cause of this slow-down, for the known density of matter is not great enough. Time Varying models of the universe come in 2 types: Oscillating Universe Dispersing Universe Both agree that the number density of galaxies is decreasing at the present time for there are no neutralization reactions to counter the lowering of density by expansion. If the universe is oscillating, even will follow the patter they are now for some time, then later due to the gravitational attraction or perhaps the “comical” force, the expansion will reverse and the universe will contract. All matter will condense into a super dense state and then some how explode and begin the universe again. The Dispersing universe begins the same way, but it never contracts, for it is believed here that the mutual gravitational attraction of the galaxies and even the ‘Comical’ force can never bring the universe together again. LINK: http://en.wikipedia.org/wiki/Oscillating_universe The Cosmic Egg The initial super dense state of the universe is often called the cosmic egg. In it all the matter of the universe is crushed to neutrons. This is an unstable state so the eggs explode and the universe is born! The expansion of the universe is therefore due to this initial ‘big bang’ theory and so the astrophysicist George Gamow dubbed it the Big Bang Theory. After the bang all the matter is thrown all over the universe creating a galaxy and forming the universe. LINK: http://en.wikipedia.org/wiki/George_Gamow Expanding Universe The Time Varying theory’s universe is not the continually statistically similar universe of the Steady State Theory no it is continually changing. Originally, the universe was quite densely packed, but the expansion due to the original explosion, thinned it out. We have just seen that the universe will continue to thin out until we see only our very nearest neighbors, but it may turn it’s self around and contract to a cosmic egg. Then explode to create a new universe and expand again, but even if it does the universe will continue to thin out for some time to come. What was the “cosmic egg”, the super dense matter conglomerate, composed of? Neutrons. What is the cause of the expansion of the Time Varying universe? Big Bang Is the Hubble Parameter constant through out time in the Time Varying universe? Most scientists believe the universe is Time Varying, instead of Steady State Theory. One reason is that with its big bang the Time Varying Theory can produce high enough temperature at the time of creation to convert hydrogen to helium. This is believed necessary to from stars and galaxies. Also the fact that distant galaxies appear to be receding faster then galaxies ‘now’ is a point in favor of the Time Varying Theory. Finally radio counts of the very distant galaxies show that at large distances (far in the past) galaxies are more densely spaced. This, as we have seen is what the Time Varying Theory believes true.
Pages to are hidden for
"Cosmology"Please download to view full document