Cosmology is an interesting science in many respects. A particularly fascinating thing is that Cosmology is a science for which, in the past, progress was sometimes driven by belief as well as by empirical facts. Today, the situation is completely different. Modern cosmological thinking is driven primarily by empirical data, the quality and quantity of which improves day-by-day. In Astronomy 123: Cosmology, we review the current state of our understanding of the Universe through consideration of theoretical models and the facts which underlie the modeling.
Despite the fact that, in the past, theoretical progress was sometimes driven by philosophical concepts, we do not say that theories were invented which were unfalsifiable (untestable) and therefore unscientific. We say that sometimes workers chose to explore and develop ideas about the Universe driven by philosophy, but that these notions were only considered as scientific if they led to hypotheses and predictions which were amenable to experiment and thus testable (falsifiable), within some reasonable timeframe.
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 about our Universe, and there is only one of our Universe, we use the capital. If we spoke of universes in general, then we would use the lower case "u." It is a little unfortunate that we only know of one universe because we are never sure if we are exceptional or if we are just one of the gang. However, this cannot be helped and we must play the hand we are dealt.
People view the Universe from different perspectives. So, what is the Universe?
In this class, we will discuss,
We do not discuss the true nature of things in a sense, rather, we construct models which can reproduce the actions and behavior of the Universe and, more importantly, which lead to predictions of phenomena not yet observed. This last point is crucial for this is what makes a model scientific (as it makes it falsifiable).
We do not know many things about the Universe, but there are some important things which we do know. We will expand greatly on each topic later in the quarter.
Today, we interpret these observations (and some further ones) within the context of what is known as the Big Bang Theory. We will say much more on the Big Bang later. However, note that the theory asserts only that the Universe in past was much smaller and denser and has been expanding since that time. These notions are amply supported by the current observations. Most of the current work improves on the details of the model, not its general validity. We will next investigate some ideas (principles) which have guide (orguided) how we view the Universe.
Scales of the Universe
Time line of the Universe