Video Transcript
When the universe began, was it at
a higher temperature, a lower temperature, or the same temperature as it is
today?
To think about this, let’s first
recall that the universe includes everything that exists, all of the galaxies,
planets, stars, space, and time. We should also recall that as time
goes on, the universe is expanding. Now, the universe is about 14
billion years old. And throughout its entire
existence, the universe has always included the same amount of matter and
energy.
In this question, we want to think
about the universe when it began 14 billion years ago and compare its temperature
then to its temperature now. To do this, let’s think about
traveling backward in time to the beginning of the universe.
If we were to somehow travel back
in time over billions of years, the expansion of the universe would be reversed. And so space itself would be
shrinking or contracting. This means that the further back in
time we look, all matter is closer together, and so the universe back then was
denser than it is today. As we continue to look further back
in time, we would go back to when the universe was so energetic, so hot and dense
that atoms could not even form. We can describe the universe at
this state as an ultrapressurized soupy mixture of particles and energy.
As we go all the way back in time
to the very beginning of the universe, all energy and matter is tightly packed into
a single point. This was the point of origin of the
universe, which is known as the Big Bang. The early universe was very small,
very dense, and very, very hot. Then, as time passed, the universe
expanded and was able to cool down significantly. Therefore, when the universe began,
it was at a higher temperature than it is today.
