Video Transcript
Which of the following statements
is true? (A) The early universe underwent
expansion, but the universe is no longer expanding and now stays the same size. (B) The early universe underwent
expansion, but now the universe is contracting. Or (C) the early universe underwent
expansion, and the universe continues expanding to this day.
To begin, notice that all of the
answer choices say that the early universe underwent expansion. This is true. The rapid expansion of the universe
from an infinitely small point to a vast volume is known as the big bang. This initial expansion was the very
beginning of our universe. In the first moments after the big
bang, all of the energy in the universe was packed into a very small region,
resulting in an ultrahigh energy and high pressure environment. And as the universe continued to
expand, things cooled down and the rate of expansion gradually decreased.
But the expansion never
stopped. It just slowed down significantly
compared to the rapid expansion of the early universe. In fact, we can see evidence of the
expansion of the universe even today when we observe outer space, since all distant
galaxies appear to be moving away from our galaxy, the Milky Way.
But our vantage point isn’t special
because of this. If we were to look into deep space
from any point in the universe, we would still see galaxies in all directions moving
away from us. This is because the very space
between all galaxies is itself expanding. By observing how quickly certain
galaxies are moving away from us, scientists can even measure the rate of this
expansion. Thus, we know that the size of the
universe is not constant, so we should eliminate option (A).
We also know that space isn’t
contracting, because if that were the case, we’d see distant galaxies moving closer
together and closer to us. This isn’t what’s actually
observed, so let’s eliminate option (B).
That leaves us with option (C),
which is the correct answer. The early universe underwent
expansion, and the universe continues expanding to this day.
