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Cosmology is an interesting science in many respects. A particularly fascinating thing is that Cosmology is a science which, in the past, was sometimes driven by belief because of the presence of weak empirical data or the absence of empirical data. Today, the situation is completely different. Modern cosmological thinking is driven by empirical data, the quality and quantity of which improves day-by-day. In Astronomy 123, we review the current state of our understanding of the Universe and our place in the Universe through consideration of theoretical models and the observational facts that underlie and drive the modeling.
On occasion, theoretical progress has been driven by philosophical concepts. However, even in these cases, the theories that were invented were scientific in that the theories were falsifiable (testable) by data. What happened is that sometimes workers chose to explore and develop ideas about the Universe driven by philosophy, but that the proposed notions had to be able to lead to predictions amenable to experimental and thus to be testable (falsifiable) within some reasonable time frame.
Before we go on, let's make an observation about Universe versus universe. Why do I use a capital "U" rather than a lower case "u"? Well, because we are speaking of our Universe, and there is only one of our Universe. Consequetly, we use the capital U. If we spoke of universes in general we would then use lower case "u" in our descriptions. It is unfortunate that we know of only one universe because we are never sure if our Universe is exceptional or if it is just one of the gang. This, however, cannot be helped and we simply play the hand we have been dealt.
 Videos: The Known Universe and Powers of TenComment: We use two different length scales in astronomy when dealing with cosmology. The scales are the light year, the distance a beam of light travels in 1 year or |
Sagan's Cosmic Calendar |
We do not know a ton of things about the Universe (such as we do about the Solar System, for example), but there are several important things which we do know. We will expand greatly on each bit of information in the next few weeks. The following observations are the three underpinnings of the hot Big Bang model:
We interpret observations within the context of the Big Bang Theory. The Big Bang Theory asserts only that in the past, the Universe was much smaller, denser, and hotter than currently, and that it has been expanding since. These notions are amply supported by past and current observations:
Most current work improves on the details and what can be learned from the Big Bang model, and not on its general validity. We next investigate some ideas (principles) which guide (or have guided) how we view and think about the Universe.
