We're Running Down the Clock (The universe can't be infinitely old)It makes sense that the universe cannot be infinitely old. You see, what Russell did without knowing it is he substituted his own line of turtles for the old lady's. If the universe is infinitely old, then we'd have a never-ending chain of events going back, back, back without a beginning. Now think about that for a minute. If the universe is infinitely old, that means that it had to start an infinite amount of time ago, right? But if the universe started an infinite amount of time ago, that means that it would take an infinite amount of time to get to where we are today. But we're here, so how did we cross infinity and get to its end if infinity has no end? Since we're here, we know that the universe had to have started less than an infinite amount of time ago. Otherwise, it's like turtles all the way back, as opposed to turtles all the way down because it uses an infinite regress of time. Since the universe is experienced inside of time, then it must have a starting point, a beginning some finite amount of time ago.
We're Running out of Steam (The universe is losing functional energy)There's another interesting thing that we notice about the universe. It's like a wound-up clock that is continually running down. We see this all the time in our lives. If I pour myself a hot cup of coffee, I would want to drink it within a reasonable amount of time from when I poured it. Why do I say that? Because my coffee's going to get cold. How can I tell whether a coffee cup has been sitting for five minutes or over an hour? I simply touch it and see if it's still hot. Coffee can't stay hot on its own, since it loses its heat energy to its surroundings. This is called entropy, which states that all things in our universe are radiating away their energy. Every battery you have will eventually run out of juice whether you use it or not. Every coffee cup will eventually run out of steam. Even our sun and our earth, anything that holds heat, will eventually turn cold and dark to a point where everything in the universe is equal. There will be no functional motion at all. So if everything is running down, it follows that everything was wound up to some point in the beginning, and the clock's moving forward in a certain direction.
We're Running Away from Everything Else (The effects of the Big Bang are still seen)There are more reasons, however, than just the winding-down of the universe for knowing that it had a beginning. Scientific discoveries made in the 20th century have been so astounding, they have pretty much put Russell's assertion of "no reason to assert the world has a beginning" to rest. The first was when famed astronomer Edwin Hubble calculated the speeds at which all of the galaxies in the universe are moving. He found that they are moving away from each other, and they separate faster the farther apart they are from each other. This was just the kind of motion one would see in the aftermath of an explosion; everything that exploded would be moving away from each other to greater distances. Since all the galaxies were acting this way (and it didn't matter where in the universe you looked), Hubble came to the conclusion that they were all together at one point and there was some kind of an explosion, and that's what's causing everything to separate as it does. It validates the Big Bang.
One of the most definitive discoveries happened in 1965, when two scientists who were listening to the sounds of space heard a distinct type of noise found throughout the universe. What they heard was background radiation which is a kind of the noise that would accompany the Big Bang. It was the confirmation everyone was looking for to prove that the universe did indeed originate with a bang. After their discovery was published, even scientists who still held out against the concept were forced to accept the Big Bang as the origin of the universe. This is a huge development because it means that scientists were in all in agreement in that the universe began to exist at some point in the past. NASA astronomer Robert Jastrow put it this way:
Jastrow, Robert. God and the Astronomers (Toronto: George J. McLeod, 2000)107.