Redefining Reality - The Intellectual Implications of Modern Science

motion of the light source. If the light source is moving toward you,
you see more peaks per second, and the light shifts toward the blue
end of the spectrum. If it is moving away, then you see fewer peaks
per second, and the light shifts toward the red end. The amount
of redshift or blueshift tells us how fast something is moving and
whether it is moving toward or away from us.
In space, Hubble noticed that the farther away something is, the
more likely it is to be moving faster and moving away from us.
Very few objects are blueshifted, and they tend to be objects that
are among the closest. From this, he inferred that the universe
is expanding.
When we say that the universe is expanding, we mean that spacetime
itself is expanding, not that the things in it are moving away
island of mass taking up more space as time goes on. It is that the
universe itself, space-time itself, is expanding.
If the universe is expanding now, that must mean that it was more
compact previously. What is causing this expansion?
Two theories arose to explain the expansion of the universe, the
big bang theory. The central
idea here is that if the universe is expanding now, it must have been
compressed before. But if it is getting larger, something must be
causing the expansion.
There seem to be two possibilities: either a constant force that is
always at work repelling things or an initial event that caused the
expansion. Of course, the only force that can operate over long
distances is gravitation, which is an attractive force. Thus, we are
left with the second possibility. There was some singular event that
happened at the beginning, and we are still seeing the results of that
singular event everywhere.
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