Evolution of the Solar System Help

By — McGraw-Hill Professional
Updated on Apr 25, 2014

Introduction to the Evolution of the Solar System

On a clear night when the Moon is below the horizon, you get a feeling of great depth as you look at the heavens. Some ancient stargazers surely sensed this depth and decided that space must be a huge expanse and that Earth must be insignificant compared with the whole. For a long time, however, this idea was unacceptable. If anyone thought about such things, they kept their notions to themselves. Today’s astronomers theorize not only about what the Universe is like now but also about how it and our own Solar System came into being and evolved to its present state.

A Word About Probability

In science, there are certain things we do not know, but we develop beliefs according to what we can see and according to what we can obtain by using mathematics and logical reasoning. We might say “such and such is true” because we’ve seen it or because we’ve deduced it based on observations. If we think something is true but aren’t certain, it’s tempting to say that “such and such is likely.” But we’re still not sure.

Hypotheses And Theories

Most of the material in this book, up until now, has been based on observed facts (except, of course, for our “mind journeys”). The diameter of Earth can be measured, as can the temperature of the solar corona. It is taken as a fact nowadays that Earth revolves around the Sun. However, the way the Solar System was formed is not known with such certainty. No human ever saw nor has any machine ever recorded that sequence of events. The best we can do is propose a hypothesis , an idea of what we think took place. Then we can make arguments, based on logic, observation, and computer modeling, so that we can come up with a theory .

When people formulate a theory, it is tempting to say that something “probably” happened in the distant past or that there is a “good chance” that such and such exists in the Milky Way galaxy. This is a logical pitfall. It is so easy to make this thought-process error that I have probably committed it somewhere in this book. (Whoops! I did it in that very sentence!)

A Theory Is A Belief

An astronomer can say that he or she believes the Milky Way galaxy is moving away from all the other galaxies in the Universe; some will strengthen this into an opinionated statement of fact. If you say, “I think the Universe started with an explosion” or “I believe that the Universe started with an explosion,” you are within your rights. Even if you say, “The Universe began with an explosion!” your statement is logically sound, although it must be understood that this is a theory, not a proven fact. However, if you say, “The Universe probably started with an explosion,” you have committed the dreaded thought error, which, for lack of a better name, I call the probability fallacy . Whatever has been has been! Either the Universe started with an explosion, or else it did not. (There are some people who will argue that either statement can be true depending on how you define the various arrows of time, but I won’t get into that right now.)

The same holds true for other unknowns. A good example is the “probability that intelligent life exists elsewhere in the Universe.” Assuming that we have defined the meaning of the word intelligent , we can confidently say that such beings either exist or they don’t. If I say in this book that the probability of intelligent life existing elsewhere is “20 percent,” I am in effect saying something like this: “Out of 1,000 observed Universes, 200 of them have been found to have intelligent extraterrestrial life, but I don’t know which one of the 1,000 Universes I happen to live in.” This is nonsense!

When we think about how the Solar System was formed, we must keep in mind that there is a definite reality, a specific sequence of events, that took place to get us from that place where “all was dark and without form” to where we are now. Our task is to find out the truth and not to try to attach artificial “probabilities” to things that have already happened or to things that never took place at all.

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