When people hear the word Cosmology, they fear the worst: relativity, dark matter, galaxy clusters. While these topics are a part of the study of cosmology, they are not the mysterious subjects some make them out to be.

Albert Einstein changed the way we look at our Universe. By realizing that time and space are one (space-time, the 4th dimension), we understand gravitational effects from objects like galaxies and dark matter that alter the paths of light. By determining these gravitational effects, we gain insight as to the mass distribution of our Universe and learn how it expands.

This section will introduce Einstein's Theory of Relativity and its effect on space-time. We will also take a look at the variety of galaxies in the Universe as well as their distribution in clusters. In addition, we will introduce dark matter - the unknown, highly massive material that is distributed through the halo of galaxies and galaxy clusters that make must almost 90% of all material in the Universe. We will also introduce the big bang and the Cosmic Background Radiation - the remnants of the big bang.

Most of what we know about cosmology is based on computer simulation and some observational data. What this means is that much of what we know is in flux - that is theoretical with only some observational evidence. However further observation, simulation, and theory refinement is helping to understand the nature of our Universe.

So what do we know so far about our Universe? This brief timeline is based from the big bang (T is time after the big bang).

• 13.6 billion years ago T=0, the Universe began with the big bang
• T = 300,000 years after the big bang, protons and neutrons form (combined from residual quarks)
• T = 300,000 to 10,000,000 years - recombination, that is hydrogen atoms form (this is what we see in the Cosmic Background Radiation)
• T = 10,000,000 to 1,000,000,000 years - clumps of matter combine to form proto-galaxies
• T = 1,000,000,000  to 3,000,000,000 years quasars form
• T = 3,000,000,000 to 8,000,000,000 years, galaxies form
• T = 8,000,000,000 to 12,000,000,000 years, our Solar System and planets
• The Universe is expanding, with the most distant galaxies (quasars) expanding faster than nearby galaxies

Between T = 0 and T = 300,000, many things occur and they will be introduced in the big bang section.

(Science Cartoons Plus)

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