Did the universe have a beginning, or has it existed
from eternity past? If it did have a beginning, this raises a
question: did the universe have a creator? In part one, we
explored this question scientifically. Now let's look
at it philosophically. Aristotle believed the universe
was eternal in the past, but Al Ghazali disagreed. He pointed out
that if the universe did not have a beginning, then the number of
past events in the history of the universe is infinite, but
that's a problem, because the existence of an actually
infinite number of past events leads to absurdity. It's
metaphysically impossible. Why? The mathematician David Hilbert
illustrates the problem by imagining a hotel with an
infinite number of rooms, all of which are occupied. There's
not a single vacancy; every room in the infinite hotel is full.
Now suppose a new guest shows up and asks for a room. The
manager says sure no problem, then moves the guest who was in
room number one to room number two, and the guest who was in
room number two to room number three, and so on to infinity. As
a result of this shuffling, room number one becomes vacant, and
the new guest happily checks in, even though all the rooms were
already full, and nobody has checked out. And it gets even
more absurd. Suppose an infinity of new guests show up at the
front desk. No problem, says the manager. Then she moves each
person into a room with a number twice that of his own
room. So the person who was in room number one moves into room
number two, the person who was in two moves to four, the person
who was in three moves to six, and so on. Since any number
multiplied by two is always an even number, all the odd
numbered rooms become vacant, and the infinity of new guests
gratefully checked in. And yet before they arrived, all the
rooms were already full. It gets even crazier when the
guests start to check out. Suppose all the guests in the
odd numbered rooms check out. In that case, an infinite
number of people have left the hotel, and yet there are no
fewer people in the hotel. But suppose instead all the guests
in rooms numbered four and above check out. In that case
only three people are left, and yet exactly the same number of
people left the hotel this time as when all the odd numbered
guests checked out. Thus, we have a contradiction. We
subtract identical quantities from identical quantities, and
get different answers. These absurdities show that an actually
infinite number of things cannot exist in the real world.
Here is a second argument Ghazali offers against the past eternal
universe. Suppose that for every one orbit Saturn completes
around the Sun, Jupiter completes two. The longer they
orbit, the further Saturn falls behind. Now, what if these two
planets have always been orbiting the Sun, from eternity
past? Which has completed the most orbits? Strangely enough,
the number of the orbits is exactly the same. Infinity. But
that seems absurd, for the longer they orbit, the greater
the difference becomes. If the universe has always existed, then
an infinite series of past events has been formed by
adding one event after another. It's like a sequence of
dominoes falling one after another, until the last domino,
today, is reached. The problem is that the final domino could
never fall if an infinite number of dominoes had to fall
first. So today could never be reached, but obviously, here we
are. It's today. So the number of events leading to today could
not possibly be infinite. The infinite is nowhere to be found
in reality. It neither exists in nature, nor provides a
legitimate basis for rational thought. The role that remains
for the infinite to play is solely that of an idea. What
objections might be raised to these arguments? Some people
object that, unlike the rooms in Hilbert's hotel, the events of
the past don't all exist at the same time. But we can easily
tweak the story to get rid of this objection. Suppose the
hotel has been under construction from eternity past,
one room being added each year. How many rooms would there now
be in the hotel? An actual infinite number. So if the past
is infinite, that would imply that Hilbert's hotel could exist,
which is absurd. Others have objected that an actually
infinite number of things do exist, namely, numbers, and other
mathematical entities. However, this objection presupposes that
numbers really exist, but this is a highly disputed assumption
that most philosophers reject. So if Ghazali's two arguments are
right, then the universe is not eternal in the past; it
must have a beginning. And we know intuitively that whatever
begins to exist requires a cause of its existence. Thus we
are led to conclude that the universe has a cause of its
existence. So what caused the universe? Atheist Daniel Dennett
says the universe caused itself, but this is incoherent, because
in order to cause itself to come into existence, the
universe would have to exist before it existed. The cause of
the universe must therefore be outside of the universe,
spaceless, timeless, immaterial, and enormously
powerful, much like... God.