When intellectual theists are asked to prove gods existence, one very common argument is the argument from complexity.
The argument is as follows:
Simple man made mechanises we encounter every day, a watch, a car, or a phone, have a certain level of complexity.
Obviously we already know they are man made, no matter where we are to encounter them.
So to begin the argument, we assume we don't know about the origin of these objects.
Due to their complexity, we could not imagine how would they form spontaneously or randomly in nature.
So we reach the conclusion that they had a creator, since we know intelligent life forms, such as ourselves have the capacity to invent and construct complex machinery.
From this premise, we extrapolate that since biological life, and its superset, the universe, are much more complex, it is obvious that it too needs a creator.
But first, what is complexity?
Using the standert definition from thefreedictionary.com :
'Consisting of interconnected or interwoven parts'
But this definition doesen't quite captures the intuition we have when using the word.
Why?
Think of a lump of coal, it is made of billions upon billions of carbon atoms, surely it can be considered as "consisting of interconnected parts", right?
But a lump of coal doesn’t strike us as complex, which means the definition isn’t precise enough to capture our intuitive understanding of the word.
I would try to come up with an improved definition, trying the capture the meaning behind the theists use of the words.
Complexity:
Consisting of interconnected parts which oparate together to form a greater purpose, function, or goal.
Using this definition, we can now understand why we think of a micro-organism as more complex then a lump of coal, although the coal may have a million times
more atoms (= parts).
Back to our universe.
The approach of argument is nonsensical, and here's why.
When talking about any physical property, i.e, mass, volume, length, time, energy,
Any sentence of the form "The universe is very *insert physical property here* " i.e:
"The universe is very massive"
"The universe contains a lot of energy"
"The univere is big"
is tautological.
Since by definition, our universe is the sum of all objects in existence, every property which increases as more objects are added will reach its maximum when including all objects.
Coming back to our complexity property.
For those sentences to have any meaning, we need to discover at least another universe, measure its complexity, and compare the two.
Then we will be able to say whether our universe is complex RELATIVELY to another universe.
Actually, to use this argument in the most confident way, we would need to observe many other universes, measure their relative complexity, see if they were created randomly or by intelligent design, and then reach the conclusion of the probable origin of our universe,
but this method is circular and thus impractical, if we could somehow find the creator or lack thereof in other universes, we would do so for ours.
