Chapter 2: This chapter explains the basics of Einstein's theory of relativity, and uses his model of the universe to explain why there may be parallel worlds. For those unfamiliar with the theory of relativity, it was proposed by Einstein to explain the pull of gravity.
Because Isaac Newton's model of gravity explained only that objects that have mass attract other objects, but not HOW they pull the objects towards them, Einstein proposed the theory of relativity to explain this. Essentially the theory of relativity tells us that this "pull" of gravity is actually time and space being warped by objects that have enough mass to have gravity of their own.
The author uses an analogy of rolling a marble across a table, if the table is level and flat the marble will roll straight, but if the table is warped, the marble will be influenced by the warps in the table. On the scale of our planet orbiting the sun, Earth's gravitational force warps space and time around the planet, and the sun warps space and time around itself. This is what causes the earth to continually orbit and to do so in a much smaller orbit than, say, Haley's comet.
In this chapter the author also examines the different currently accepted models of the shape of the universe as well as it's expanse. (Finite vs. Infinite). Relatively recent evidence suggests that the universe is ever expanding, and therefore slowly becoming less dense. This goes hand in hand with the currently accepted theory of the creation of the universe that we all know as "The Big Bang". If the universe began as an incredibly dense speck, and exploded outwards, it stands to reason that given the right conditions (which scientists now believe exist currently) that it would continue to expand outwards, forever.
This was not the most interesting part of this theory to me though. I have often wondered, if the universe is infinite, what would happen if you got beyond the point that matter had expanded to in the finite amount of time since its creation? Would there just be a whole bunch of nothing? The author explains 2 theories that suggest an answer. One is that the universe is constantly expanding outward in all directions, and that if you left Earth and travelled at one heading that you would just go on forever and see infinite galaxies and infinite parallel worlds. Another theory is that the universe is like playing pac-man, you go out one side, you come in the other, so if you left earth and travelled for millions or billions of years, in the same direction, you would eventually end up back at earth.
Now I don't claim to be an expert in physics so I'm not 100% on my explanation of this but this is my interpretation of the author's writing.
-Onward and Upward!
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