The main argument:

The main argument:

The Universe cannot be the source of its own existence because it is
mutable. Therefore there must be a Supreme Being whose Essence is
Existence who causes the Universe to exist.

To understand why the Universe cannot be the source of its own
existence consider what would be the case if it were. For the Universe
to be the source of its own existence, Existence (the act which causes
things to exist) must be part of its Essence.

Since, by assumption, Existence is part of the Essence of the
Universe, then the Universe must always be the way it is now. After
all, Existence is part of the Essence of the Universe, therefore
Existence forces the Universe to Be what it is forever. IOW, because
the Universe has Existence as part of its Essence, it cannot be
something other than that which it is.

Therefore, by assumption, the Universe is immutable. But that is not
what we observe. Physicists observe a mutable Universe. Therefore the
Universe cannot have Existence as part of its Essence, and therefore
it cannot be the source of its own existence. Therefore there must be
a Supreme Being whose Essence is Existence and is the source of the
existence of the Universe.

===

One of the surest ways to start a big argument in philosophy is for
two people to adopt different Worldviews. According to Webster, the
Worldview (aka " Weltanschauung") is

Worldview: a comprehensive conception or apprehension of the world
especially from a specific standpoint

More specifically the Worldview is the epistemological basis, plus its
supporting ontology, for your rational system. It is the set of axioms
about how you view reality. It should be obvious that if your view of
reality is fundamentally different from my view of reality, we can
never argue our points to one another even though we may adhere to
rational arguments within the framework of our separate systems.

The two most promiment Worldview can be understood in terms of
"objectivity" and "subjectivity". We call the Worldview that claims
reality is objective by the name Realism. We call the Worldview that
claims reality is subjective by the name Idealism. I do not pretend to
know everything about Worldviews so I am not going to go any further
with this. But I do know enough to point out that certain rational
systems of thought are based on an objective Realist Worldview (eg,
Physics) and some are based on a subjective Idealist Worldview (eg,
Mathematics).

Physics is based on the Worldview of Objective Realism. There is no
doubt in the mind of the Physicst that electrons actually do exist in
objective reality. If you don't believe that - if you think electrons
are subjective constructs like the tooth fairy, then you will allow
yourself to be hooked up to a high voltage source. After about 1
millisecond you will decidethat electrons are very real.

Mathematics is based on the Worldview of Subjective Idealism. There
are no such things as "numbers" in objective reality. There is no such
thing as a circle in objective reality. If you don't agree, then I
will let you connect me to a number or to a circle. I guarantee that
nothing will happen, because numbers, circles and everything in
Mathematics are subjective constructs that reside completely in the
mind of the Mathematician.

One of the most fundamental axioms of Objective Realism (aka
"Existential Realism") is the Principle of Apprehension of Being. This
is also known as the Authority of the Senses. Something exists in
objective reality precisely because there is something out there that
can affect your senses - like the shock from a high voltage source.

The Apprehension of Being - the awareness of something out there - is
very primitive. A new born infant puts his hand on a hot stove burner
and immediately becomes aware of "something out there". He does not
know what it is, but he definitely knows it is there.

This Principle is not found in Mathematics. There is no "thing out
there" in Mathematics. Everything in Mathematics is contained in your
mind, subjectively. So the very first distinction between Objective
Realism and Subjective Idealism is that Realism adopts the Principle
of Apprehension of Being, and Subjective Idealism does not. This is
critical to deciding on which Worldview you must adopt for any
particular rational system.

Next there is the Principle of Consistency. This is Aristotle's
terminology for the notion of Non-Contradiction. This principle states
that there cannot be both "A" and "Not-A" in existence at the same
time. Either "A" exists or "Not-A" exists. Remember we are talking
about things out there - what we apprehend as Being. Something can
either Be or Not-Be. It cannot both exist and not exist at the same
time.

The third fundamental principle of Existential Realism is the
Principle of Causality. In Physics we realize that without Causality
there could be no Order. The reason is simple - for you to describe
the Order inherent in something, you must connect the ojects by
Causality. If you merely describe objects without connecting them
Causally, then you cannot describe the Order they exhibit because
there is no heirarchy to provide the disctinctions needed to describe
the Order.

Try describing an atom without invoking Causality. You will not be
able to talk about the Order inherent in an atom, in which case you
are forced to describe as a glob of amorphous matter. But we know
better than that because we know that an atom is a highly ordered
entity capable of doing very ordered things, like emitting a photon of
very precise wavelength. That can happen only if an atom is Ordered,
and it can be Ordered only if there is Causality with which to create
the Order based on the heirarchy of cause and effect.

From here we move on to Metaphysics, which is the Science that
explains Being. That is what Aristotle meant by it - the Science of
Existence. But whatever it is, it is critical to realize that it is
based on Physics ("Meta-Physics", after Physics, about Physics) - and
that Physics is based on the Worldview of Existential Realism.

Assuming that you adopt the Worldview of Existential Realism, we can
now present the argument that the Supreme Being exists. In fact we
will also show that the Supreme Being *must* exist or reality would
not exist.

This argument was first given by Thomas Aquinas in his book on
Metaphysics entitled "On Being and Essence". This argument is not
taken from his religious book entitled "Summa Theologica". The famous
"five-fold ways" from the Summa are religious arguments. The arguments
we give below are based on Existential Metaphysics and not on faith.

The Universe is mutable. Not only is that intuitively obvious but it
is codified in Physics. Physics is the science which explains how
physical objects can exist at one moment and can cease to exist at
another. That's what is meant by "mutable" in Existential Metaphysics.

Mutable objects cannot be the cause of their own existence. The reason
requires some thinking, so either put away whatever is distracting you
and pay close attention - or this will go completely over your head.

There are several kinds of causes in Aristotle's Metaphysics. Here we
are talking about the "Efficient Cause", the one which is responsible
for an object to exist in an essential way. If I hit a baseball with a
bat, the bat is the efficient cause of the baseball flying thru the
air.

The baseball cannot spontaneously fly - it does not possess "Flying
Thru The Air" as part of its Essence (its Nature, its Design, its
Internal Construction, its Intrinsic Behavior, etc.). If it did
possess Flying Thru The Air as part of its Essence, then it would
always be Flying Thru The Air - it could never stop Flying Thru The
Air because that is its Nature.

Therefore in order for the baseball to Fly Thru The Air, some separate
object which possesses the Efficient Cause to make the ball Fly Thru
The Air must act on the ball - like a bat. This relationship between
the bat (Cause) and the ball Flying Thru The Air (Effect) is what we
call Causality.

The critical point here is to understand that mutable objects cannot
be the source of their own Existence, because if they were, they would
be forced for all time to be the same thing they were when they were
created.

---
Consider what it means "To Be". Don't get bogged down in what it means
to be a particular kind of being, just focus on the "Act of Being",
the "Act of Existence".

One way to do that is to consider what it means not To Be. You as a
person were once non-existent. What was it like? Of course if you did
not exist you did not have an essence therefore you can't consider
what kind of being you were not. You were not any kind of being when
you did not exist.

OK, now that you have had time to consider Being and NonBeing, do you
get the idea that there must be some kind of entity that has always
existed in order to explain how you and the whole Universe can exist?

You cannot possibly be the cause of your own existence because before
you existed, you did not exist. It would be absurd to claim that a
nonexistent could cause itself to exist.

But even if you existed for all eternity, you still cannot be the
source of your own existence or else you would always be the same kind
of being that you were for all eternity. You could not die, for
example. You could not grow, for example. But that is not how it works
- you will die one day, you did grow from an embryo to an adult.
Therefore you cannot be the source of your own existence.

The same kind of reasoning applies to the Universe as a whole. Whether
the Universe came into being at a moment in time or whether it has
always existed, it is a mutable entity and therefore cannot be the
source of its own existence. If it makes a transition to a new state,
which according to Physics it does constantly, how is this new state
going to be if it was not before? How can this new state come into
existence if it had no existence prior to its coming into existence?

Mutable objects cannot have Existence as part of their Essence. Their
Existence must come from a separate entity, one which is the cause of
their existence. This entity causes mutable objects to exist since
mutable objects cannot be the cause of their own existence - or else
they would not be mutable.