Cosmology

Just as gravity is the inequable flow of time from place to place, it is also the change in spatial distances from time to time. Since time is just another form of space in the spacetime, if time can depend on space, it should also be true that space can depend on time.

When Einstein proposed his theory, he certainly expected the relation between time and gravity. It was really the very basis of his development of the theory. But he absolutely did not expect that gravity could also affect space. A Russian Metrologist from Leningrad, A Friedmann, found a solution of the equation which stated that distances in space could also change. His solution was one in which all spatial distances increased by the same fractional amount in time. The solution was not one in a vacuum, but had matter uniformly distributed, and the frame in which the matter was at rest defined a frame of simultinaity. In that frame, the distances between objects increased. It did not increase because the matter was moving. Every piece of matter had no acceleration. It was travelling in straight lines, which you could regard as at rest, in spacetime. Despite that the distance between two adjacent pieces of matter grew with time.

Einstein was firmly of the opinion that the universe was not dynamic. To him he felt that it remained the same in time. And he tried to change the theory to get rid of those solutions. He introduced what is called the cosmological constant. Unfortunately it was almost immediately shown by A Eddington, and by the Dutch physicist W. de Sitter, that the solution was unstable. Ie, a tiny change in the universe would result in one that either rapidly expanded exponentially, of it would collapse.

In addition E Huble in the USA showed that the distance to remote galaxies was increasing, with the distance growing fractionally just as Einstein's original theory had predicted as shown by Friemann (Ie, the rate at which distance increased was directly proportional to how far away those galaxies were located.)

This is often called the expanding universe with the idea being that the galaxies are moving away from each other. A better way of thinking about it however, is that new space is being created between the galaxies. Ie, the increasing space between the galaxies is not due to the motion of the galaxies, but rather because new space in inserted. It is as if the universe is rebuilding its home to make room for all the kids, but doing it like Dr Who's Tardis-- just sticking in more space.

Since the universe is getting bigger, if we go into the past it gets smaller. Given the measurements of how fast it is now getting bigger, one can predict that about 13 billion years ago, it was so small that the average density is far larger than the density of the atmosphere of the earth (right now the average density of the universe is a few atoms per cubic meter, so it has got to be a lot lot smaller to up the average density by that much. Our atmosphere has about 10^(25) (a one followed by 25 zeros) atoms per cubic meter). Shortly before that, the density was as high as in the middle of a neutron star-- it was the nuclei of the atoms which were in contact with each other. Before that it was even smaller.

In the late 1940's and early 1950's there was a debate. In this early instances, was everything hot, so it gradually cooled as the universe expands, or was it cold? In Princton in the early 60s, a group around R. Dicke decided to try to measure that temperature. Since they could not go back in time, they relied on the fact that a hot universe would emit radition, and the radiation would, after the matter cooled, keep travelling through the universe. Because of the expansion of the universe that radiation would also cool (but less quickly than the matter). But before they could get their experiment going in '64, Arno Penzias and Robert Wilson, at Bell labs just north of Princeton, had been trying to figure out why the microwave receiver for the Echo sattelite was showing more noise than expected (the Echo sattelite was one of the very first sattelites launched. It was a huge inflated mylar ballon, and its purpose was to reflect back microwaves to earth, in the hope of using it for long distance communications). Because the signals were very weak, one wanted to make sure that the noise in the receiver was a small as possible. It was too large. They tried everything they could to reduce the nose, including scaping out pigeon shit from the antenna because it might reflect radio waves emitted by the hot ( 20 degrees C, while the noise in the receiver was supposed to be less than that emitted by 1 degree above absolute zero, 292 degrees below the earth's temperature )earth up into the receiver before it was smaller and smaller. They finally came to the conclusion that the noise was coming from outside the receiver and the earth. Due to a conversation with another physicist on a flight, they phoned Dicke at Princeton, who explained that what they could be seeing was the radiation which could have been emitted from the very early universe, when the universe was far far smaller, and temperature of everything was of the order of 10,000 degrees C. and was emitting radiation at that temperature. (They got a Nobel prize.) This radiation, now with a temperature around 3 degrees above absolute zero (in the microwave region).

All of the evidence is that the prediction of the both the expansion and the birth of the universe from Einstein's theory was correct.

The evidence is that when the universe was born, it was incredibly small ( the whole universe we now see being smaller than a cm in size) and that distribution of matter in the universe was extremely uniformly spread throughout space. As it expanded, some extremely small fluctions in the density (probably caused by quantum flucuations and with a about one part in 100,000) were such that areas of slightly greater density would gravitationally attract matter from areas of lesser density, growing the density contrast, resulting eventually in all of the contrast (eg between the earth and the a thousand kilometers outside the earth) that we see around us.

This is the fluctuations in the microwave light that escaped from those initial stages. The colours represent difference of 1/100000 of a degree differences (a thousandth of a percent difference) in the radiation from various directions coming from the earliest stages of the universe. These are now extremely large scale fluctuation (each of the "pixels" are of the order of the size of the clusters of galaxies now). The hottr regions indicate slightly overdense matter. (1/100000 more) which by "gravitational attraction" collected more and more matter and eventually created the clusters of galaxies, the galaxies, and the stars in those galaxies and the planets like earth.

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