Cosmology

Our universe is truely a bizarre place. An inspirational place. A spiritual place even. At least to some people, the people who observe it, the people who measure it, the people who ponder it. To the people who don't, well that's really a terrible loss on their part.

Cosmology is the study of how our universe originated, evolved and how it will end up. It starts at the beginning of time and ends at the end of time. It looks at the contents of the universe, the geometry and structure of the universe, the history of the universe, the fate of the universe and our place in the universe. Much of our recent scientific past has been a struggle to come to terms with how the universe began, when and where (tough one!) it began and surely the greatest question of them all, why it began (tougher still!!).

If something has a beginning does it have a beginner? That's for another chapter.

The prevailing theory on the origin and evolution of the universe is the Big Bang theory a term ironically coined by Fred Hoyle who championed the rival 'Steady-State' theory. In the 1930's a combination of theory and observation came together in a remarkable fashion to point firmly in favour of the Big Bang theory. According to this theory the universe was born out of a mathematical point, called a singularity¹, which was infinitely dense. A cosmic explosion occurred at this singularity around 13.7 billion years ago. This was the moment of creation, the moment before that space and time didn't exist. All we know and all we see existed in this infinitesimal small entity we call a singualrity. What existed the moment before creation? God? Today we can see remnants of this explosion in the cosmic microwave background radiation (a uniform glow left over from the explosion itself) which pervades the universe. If we could see microwaves we would see the entire sky glowing with a uniform brightness in every direction. This is the solution to Olbers' paradox, which puzzled Astronomers for hundreds of years - Why is it dark at night? If the universe is static and infinite then no matter what direction you look at night you should see a galaxy in your line of sight. So the sky should be bright at nightime. However if the universe is expanding, then the wavelength of light from galaxies will be lengthened (red-shifted) to such an extent that it goes beyond the visible spectrum into the microwave region of the spectrum. So since evidence supports this conclusion we can deduce that the universe is expanding. We can also conclude that at some earlier stage of the universe the sky was indeed bright at night from planet Earth, at a time before the wavelength was red-shifted beyond the visible spectrum.

This background radiation along with Einstein's theory on general relativity and the Cosmological Principle (see below) strongly support the big bang theory. And a universe starting with a Big Bang would have been so hot that in its first minute theory predicts that Hydrogen and Helium would have been produced by nuclear fusion in amounts of about 80% and 20% respectively (along with a small amount of Lithium), whch is in accordance with current observations. And further, in 1929 Edwin Hubble made the landmark observation that wherever you look, galaxies are moving away from us and each other. In other words the universe is expanding, or at least 'space' is expanding. Implying that at some stage in the past everything in the universe was exactly in the same place. But will it expand indefinately or will it collapse back on itself in the so-called Big Crunch? Recent evidence from the late 1990s suggests that the universe has an increasing rate of expansion resulting from this mysterious and unseen 'dark energy' and will expand forever!

It could be argued that modern cosmology began in 1917. This was the year Einstein paved the way and many scientists followed. He had presented to the world his general theory on relativity in 1915. In it he built a complete new theory of gravity and the universe. And in 1917 he produced a paper regarding the cosmological considerations of his theory.

Albert Einstein

His theory implied the universe was expanding. However, though Einstein was never uneasy about moving into uncharted scientific territory (and perhaps even to ensure his theory stood a greater chance of being widely accepted), he mistakenly hung on to the belief that the universe was static. But he struggled to make his equations of relativity fit this belief. To stop the universe collapsing under the force of gravity he introduced a cosmological constant which was a force that opposed gravity. This 'anti-gravity' force was built into the very fabric of space-time according to Einstein.

In 1929 Hubble discovered a redshift-distance relationship with distant galaxies. He observed light being shifted to the red end of the spectrum corresponding to an increase in wavelength. This implied the distant objects emitting the light were receding from us and the universe was expanding. The red shift we observe in the expanding universe is not caused by the galaxies moving apart from one another. It's actually the space itself that's stretching between the galaxies. Space is expanding and carrying the galaxies along with it for the ride.

It was becoming increasingly clear what these observations and general relativity were saying. Galaxies are far apart today and are getting further apart. But this must mean they were closer together in the past. And if we can imagine going back far enough in the past we reach a time when there was no empty space between galaxies. Further still we reach a time when there was no empty space between stars, and earlier, a time when there was no empty space between atoms, and even earlier we reach a time when there was no empty space between the nuceli of atoms. We have reached the dare-I-say 'fabled' singularity.

The Cosmological Principle doesn't do our egos any good! It states that we (earthlings) are not privileged observers of the universe. It's misleading to think that because galaxies are receding from us, as we observe when we measure their red shift, that we are in some special place in the universe. Observers in other galaxies would record precisely the same effects. The entire fabric of space is expanding. If we can imagine a bubble marked with tiny spots of paint. As the bubble expands every spot moves farther away from every other spot. And the view from any particular spot will show all the other spots receding from it. So essentially we live in a typical ordinary region of the universe. And the view we get is just the same on average as the view anyone else would get anywhere else in the Universe. So when viewed on the macro scale, the universe is homogeneous and isotrophic. There are no special places or no special directions.

This is what Einsteins General theory on Relativity was telling us. The universe is either expanding or contracting, and not static. Unfortunately, as mentioned above, Einstein believed the universe had to be static, and he introduced the cosmological constant to make it so. Einstein eventually abandoned the cosmological constant in the 1930s after Hubble's red shift discovery. Introducing it into his equations in the first place he regarded as 'his greatest ever blunder'. But of course there is a twist to that tale also, i.e. that damn dark energy thing!

1. Of course according to quantum theory space and time are quantized which means this mathematical point is not really a point with zero dimensions, but had a defined length known as the Planck length of 10^-35 m. And the moment of creation did not start at zero time, rather it started at a time of 10^-43 sec, known as the Planck time. There is no length shorter than the Planck length and no time shorter than the Plank time.