In answer to the question why does the Universe exist, the traditional theistic answer is to simply state that God did it1,2. The belief that "everything must have a cause, therefore God exists" is called a First Cause argument. But that merely results in new questions: (1) why did god create the Universe? and (2) why does God exist? If it is valid to say "everything has a cause except God", it is more likely that everything has a cause except the Universe. Both have one exception. If God doesn't need a cause because it is infinite, it is more likely that the natural Universe has existed forever and therefore doesn't need a cause. You therefore make fewer assumptions, and cause fewer puzzles, if you admit that you believe in one uncaused entity, and that that one uncaused entity is the Universe itself.
Aside from causal arguments, there are problems with the nature of god. If God can make plans and think logically, then, logic is an arch-power that encompasses God and gives reason for god's existence. I.e., God, without logic, could not do any creating nor planning. This appears to refute the idea that God could be the creator of logic. If logic was a precursor to God, then, God is not the sole Creator, but merely a side-effect of some logical process. If, in order to avoid this problem, you state that there is no logical reason why God exists, then it is more likely that there no logical reason why the Universe exists, and that instead of assuming that the organisational force is a 'god', it's simpler and more rational to assume that it is the universe itself. It appears that whether God exists for logical reasons or not a fundamental contradiction occurs. The only answer is that creator-gods cannot possibly exist. Atheism is more logical. This is also true if God is placed "beyond logic". Doing this puts God into the territory of irrational fantasy. To retreat into the corner where logic itself is denied, god-believers have admitted that there is no logical basis for their belief. And if it is said that Human logic is incapable of realizing such metaphysical truths, then this also undermines any argument that can be made by one human to another, for the existence of god.
“The single most common argument for the existence of a single creator-god is that things cannot "create themselves", therefore, there must be a Creator2. Everything must have a cause, therefore, god exists as the 'first mover'. But the argument means that god itself must have a cause, else, god cannot exist. So the true form of this argument is that "everything must have a cause, except one thing". The problem with this is that it gives no indication of what the first-cause must be. Monotheistic religions such as Judaism, Christianity and Islam say that 'god did it'1. Karmic religions such as Buddhism and Taoism conclude that a set of atheist mechanistic rules govern creation and destruction. Secular atheists conclude that the Universe itself is the first-cause. In all cases, the first-cause is not a pure or simple concept, but a collection of well-developed characteristics, drives and powers. "Everything must have a cause" arguments do not bring us any closer to working out why anything exists, nor to what the cause is, nor if the universe is a theistic, deist or atheistic one.”
An uncaused God is more complicated than an uncaused Big Bang. When it comes to comparing arguments where there is no hope of actually getting any physical evidence, there is a long-standing heuristic to help distinguish between theories, called Occam's Razor: after all evidence is accounted for, the theory with fewest assumptions is more likely to be true. God requires many properties and complexities such as consciousness, thought, personality, creative drive, love, an internal logic ordering its thoughts so that it can think coherently and rationally, memory, etc: All of these properties must have been derived from somewhere. It turns out that God is a vastly more complicated thing than the Big Bang and the fundamental laws of the Universe.
“The Universe exists. Both theists and atheists believe in one uncaused cause: atheists think that the Universe itself, with a few universal laws, intrinsic traits and properties, is responsible for everything including itself. However theists think that it is ridiculous that the Universe can exist without a cause, and, have come to the much more reasonable assumption: the Universe was created by God, who itself exists without a cause, complete with its range of intrinsic traits and values. Putting it like that, we can see that although theists believe in god(s) and atheists don't, both have some similar assumptions about how the universe came to exist.
Theists and atheists both believe in some universal laws of logic and/or nature which exist as the first cause. But the theist position adds on a list of personality traits to this first cause, and, calls the result "God". Whether these additional assumptions are warranted or not is hard to prove, hence why we say that the additional assumptions under theism are based on faith. These theistic assumptions include attributes about God: it is all-powerful, omniscient, benevolent, it has memory, it has rational and ordered thoughts running along logical lines, it is emotional, it wants to be worshipped and other particular assumptions of various religions. Even if it was found that the First Cause must be a conscious god, then, it is not reasonable to automatically assert that all those other assumptions are true too. There have been a great many variant concepts of god in history3 partially because it's not clear what properties and features God should have. In comparison to all that, atheists make far fewer ad hoc assumptions about reality, meaning, that their position is more likely to be correct.”
“The scientist, however, may wish to challenge the assumption that an infinite mind (God) is simpler than the universe. In our experience, mind only exists in physical systems that are above a certain threshold of complexity. [...] While it is possible to imagine a disembodied mind, there must be some means of expression of the pattern, and the pattern itself is complex. So it could be argued that an infinite mind is infinitely complex and hence far less likely than a universe. [...]
According to our best scientific understanding of the primeval universe it does indeed seem as though the universe began in the simplest state of all - thermodynamic equilibrium - and that the currently-observed complex structures and elaborate activity only appeared subsequently. It might then be argued that the primeval universe is, in fact, the simplest thing that we can imagine.”
The additional assumptions of theists are discussed on my page The Assumptions about God and Creation, of Both Theists and Atheists. Its list contains the following items - click on each for a discussion and some comments on the logical problems associated with them:
Some theists argue that God is eternal and was therefore never created. But I find this is an argument that can be used in conjunction with Big Bang theory to prove, again, that god is not likely to exist as a first cause. According to some Big Bang theories there has been an infinite number of cycles of Big Bang / Big Crunch (where the Universe ends in a big black hole after contracting, before exploding again) and that the Universe has existed forever. If it is possible for something to exist forever and not need a cause then it is likely to be the Universe, not God, and once again we can theorize that this is likely to be true because there would be no reason for god if it was true that something could exist with no cause6.
In order to create, to think, God's thoughts must be more than random. To create the universe and its laws, God must be able to think logically. If it can't think logically, then, the laws of the universe were simply random, and the Universe might as well have been self-created in an atheistic manner. In other words, for God to exist, God's thoughts must have always been ordered in a logical manner otherwise God could never have created order from chaos.
Kepler, one of the great minds in the history of science, came to similar conclusions about geometry, but didn't go as far as to say that it preceded God:
“Geometry existed before the Creation. It is co-eternal with the mind of God... Geometry provided God with a model for the Creation... Geometry is God Himself.”
Kepler was assumedly counting mathematics and the general rules of the universe as 'geometry'.
This means that logic is a precursor to God. Logic, with its simple relations and rules that lets thought itself be ordered, must have existed independently of God's creative power. God could not have created the logic because requires logical thoughts to do any meaningful creating.
This results in two conclusions:
In theology-speak, the first cause is the description given to the creator of the universe, time, the laws of physics, etc. But it seems that in order for the first cause to be a creator-god, then that god cannot have created logic, and cannot therefore be the first cause after all. In other words, the fact that God needs to think logically in order to create means that God itself cannot be the creator of everything, only of parts of reality. In other words, there cannot be any monotheistic creator god.
If God chose to create anything then it must have had reasons to do so. God's "will" is not random, meaningless, chaotic or thoughtless. This means that these "reasons" are dependent on pure logic and must have driven god to do its very first act of creation. These motivations, this initial logic, will have been dictating God's thoughts from the moment of God's inception. If there was no logic and no motivation, God did not create anything on purpose. In that case, you might as well admit that the Universe created itself randomly, and that no creator God was required.
If god created anything according to a thought-out logical plan, or, if God had a desire to create anything that wasn't pure random chaos, then, god's thoughts must have been framed around logic. This logic allowed god to think and create, and, gave motivation to God. Logic must have been the first cause; but if logic is a requirement for God and existed before God could create, then God cannot be the First Cause, and therefore, creator-god theism is false, and atheism is true.
Some theists will make assertions that god is "outside of outside", "beyond logic", "transcends logic", "not subject to logical limitations" or that "human logic is limited" and other similar argument-stoppers. Although this at first appears to throw all intellectualizing out the window, kick all theology out the front door and firmly garrison the houses of religion from debate, it actually opens up the theist to some further criticisms.
If "Human logic" is insufficient for metaphysics then debating for the existence of God is pointless. Because it is by Human logic, thought and mentality that we arrive at the concept of God in the first place.
If God behaves according to logic that we don't understand (i.e.: Human logic is limited) then God is still behaving according to logic, even if it is logic we don't understand.
To say that god doesn't obey logical rules, to say that God could create a round square, for example, is to say that the abilities of god are abilities that cannot logically exist, making God into fantasy.
"Beyond logic" is a synonym for "irrational", and admissions that beliefs are "beyond logic" is an admission that such beliefs are irrational and logically indefensible.
If God is beyond logic, is it not true that atheists are at least somewhat more rational and logical in their beliefs? It seems to be!
It is not enough to say that "God exists" as the explanation as to why the Universe exists. If a God created the Universe, then, why did it do so? God must have had thoughts - a creative impulse - to create the space-time continuum. Therefore it is the properties and thoughts of God that explain the Universe, not the mere fact that God exists. God could easily exist for all of its eternity, existing in perfection in a perfect world, without creating the Universe. So saying that God explains the existence of the Universe is not the whole story.
“If God has a plan for the universe, which is implemented as part of his will, why does he not simply create a deterministic universe in which the goal of the plan is inevitable? Or better still create it with the plan achieved?”
Unfortunately there have been no comprehensive or compelling arguments as to why God created the Universe. This is a problem that effects not only monotheistic religions like Judaism, Christianity and Islam, but also other religions such as Buddhism: Sages from all these religions have tried to explained why existence is the way it is, complete with suffering and death, but none have given a straight answer as to why any of it needed to exist at all.
The phrase 'anthropic coincidences' refers to the theory that the Universe is so delicately fine-tuned for life that it must have been designed with that purpose in mind, by an intelligent creator-god11. The main argument is that if you fiddle with the universal constants of physics (such as the strengths of the weak and strong nuclear forces) and change their values even by a little bit, then the Universe would be completely unsuitable for life as we know it. Therefore, God created the Universe for life, and in particular, created it for mankind here on Earth. Some scientists subscribe to this idea, and use it to justify (and promote) belief in God12. But there are a number of convincing logical and evidential arguments against this idea. Mainly: the unimaginably vast Universe is almost everywhere completely unsuitable for life, and even here on planet Earth we can exist only on in a thin crust of a planet that is two-thirds made of water (yet we have no gills). Also, it took nine billion years to make the Earth, and then another four billion before Humankind appeared13. The timetable makes no sense: If the Universe was designed for life, it ought to have simply started with life. When it comes to the sun, which religionists are sure was created to warm us, "of all the energy [it emits], only two photos in a billion are used to warm Earth, the rest radiating uselessly into space"13. The theory that God done it this way on purpose simply doesn't make sense. Evolution does a much better job of explaining why and how life evolved, and is a theory based on evidence, unlike the "God designed life" theory, which is based on pure speculation. Not only that, but it simply reeks of egotistical and prideful wishful-thinking to imagine that the creator of a billion galaxies made all of it with our particular species in mind. If we did change the Universal constants, then, for all we know, even more intelligent life could have evolved in even more different ways. In other words we have no knowledge at all to indicate that the current set-up is optimal for life. For these reasons, the anthropic coincidences argument has been abandoned philosophically and even used to argue against the idea of a God, although in its simpler forms it is still vocalized by many laypeople as being a reason for their belief in God14.
For a full discussion, see: "The Anthropic Coincidences: Is the Universe Fine-Tuned for Life?" by Vexen Crabtree (2015).
The "law of conservation of energy" holds that energy cannot be created nor destroyed, only changed in form. This means that although everything in the Universe may be destroyed, the total energy stays the same. This fundamental law of thermodynamics is one of the most important laws in physics, and is applicable at all scales, from the quantum, to the large scale sciences of engineering and chemistry. It is so important that most physics think that this law can simply never be broken.
Many theists have argued that the scientific laws of thermodynamics, in particular the conservation of energy, imply that there must be a God. If energy cannot be created nor destroyed, they say, then this is proof that the entire spectacle of reality has to be the exercise of a creator God. I.e., a God that creates all of the energy, and then, who creates the laws of thermodynamics. On the face of it, it is certainly one way to explain away the existence of all energy.
But it turns out that the explanation isn't necessary, because the current evidence shows that there is no contradiction to the law of conservation of energy, and it all comes down to gravity16. You expend energy to climb out of an energy well, and, if you add up all the energy of objects and masses and take into account gravity and balance this against the gravitational power of black holes and galaxies, we find that the net value of the energy involved is zero. In other words, if all of the energy in the universe can be accounted for as being matched equally by gravity, it appears that there is actually no created energy.
“Astronomers can measure the masses of galaxies, their average separation, and their speeds of recession. Putting these numbers into a formula yields a quantity which some physicists have interpreted as the total energy of the universe. The answer does indeed come out to be zero within the observational accuracy. [...] The cosmos can [come] into existence without requiring any energy input at all.”
“Physicist Frank Wilczek, who was one of the first theorists to explore these possibilities, has reminded me that he utilized precisely the same language I have used previously in this chapter, in the 1980 Scientific American article he wrote on the matter-antimatter asymmetry of the universe. After describing how a matter-antimatter asymmetry might plausibly be generated in the early universe based on our new understanding of particle physics, he added a note that this provided one way of thinking about the answer to the question of why there is something rather than nothing: nothing is unstable. [...]
[We see that] the total energy of a closed universe is zero, and if the sum-over-paths formalism of quantum gravity is appropriate, then quantum mechanically such universes could appear spontaneously with impunity, carrying no net energy. I want to emphasize that these universes would be completely self-contained space-times, disconnected from our own. There is a hitch, however. A closed expanding universe filled with matter will in general expand to a maximum size and then recollapse just as quickly, ending up in a space-time singularity where the no-man's land of quantum gravity at present cannot tell us what its ultimate fate will be. The characteristic lifetime of tiny closed universes will therefore be microscopic, perhaps on the order of the Planck time, the characteristic scale over which quantum gravitational processes should operate, about 1044 seconds or so. [...]
The very creative cosmologist I mentioned earlier, Alex Vilenkin, who has since become a friend, had actually just written a paper that described in exactly this fashion how quantum gravity indeed might create an inflating universe directly from nothing.”