PREFACE: Before a thing can change or be changed, act or be acted upon, it must exist. Those who would dissent must first confess their belief in things that don't exist. Fortunately there are now medications for that. Logically, this means change is a 'function of' existence and the phenomenon of existence is the source of cause and effect, not the result of it. To create is to cause to exist, so from Genesis to Big Bang, creation theories are fundamentally flawed.
Critical thinking applied to one basic principle of logic readily explains the enigma of existence without invoking undetectable extra dimensions, spontaneous singularities, multiverses or supernatural deities. Reconciling the phenomenon of being with the principles of logic requires nothing more than a simple, rational perspective. Citing empirical data and complex equations would be extraneous, but simplicity has no commercial value, so until the light of logic ultimately penetrates the hazy halls of academia, scholars will continue to engage in synaptic gymnastics, conjuring complicated calculations into esoteric hypotheses designed to justify 'Creation Ex Nihilo'.
Existence Ex Nihilo is justified by the simple and fundamental principle of 'Equilibrium'.
The Nature of the Cosmos
How was the cosmos created? When did it begin?
To be blunt, it wasn't and it didn't. Those age-old philosophical questions are falsely premised.
Like Newton, Einstein originally believed the cosmos was static, eternal, isotropic and homogeneous (not so sure about infinite), and he accounted for the misbehavior of observed phenomena with a reverse engineered factor, a cosmological constant. When Hubble's cosmological redshift implied an expanding Universe, Einstein initially contested the assertion because the effect of gravity on light was sufficient to explain the observation. Light passing through a gravitational field loses some energy, and since its velocity is constant, the loss has to come from a redshift of the wavelength.
Forget stars, moons, comets, astroids and planets, how many mass-laden ambient particles would a beam of light encounter in a multi-billion light year trek? We don't have the ability to study how the subtle nuances of nature might affect the properties of light traversing vast distances over billions of years. Empirically there are few research facilities of sufficient capacity and fewer scientists of sufficient longevity to engage in such a monumental endeavor. Gravitational redshift was ultimately confirmed by the Pound-Rebka experiment. Cosmological expansion was and still is hypothetical, invoking reverse engineered phantoms of dark energy and dark matter to bolster its questionable validity.
Unfortunately, Big Bang provided so much more fodder for publish-or-perish scholars Einstein ultimately relented and suddenly the cosmos became perceived as the finite creation of an ancient past event. His cosmological constant wasn't Einstein's biggest mistake, succumbing to cosmic expansion theory was.
Either the phenomenon of existence is the result of cause and effect or it is not.
"It is" implies Creation ex Nihilo
Conventional wisdom has concluded that the Universe must have come from somewhere, and the premise it was ushered into existence by some primordial nascent event appeals seductively to human intuition. Many secular models suggest it all began about fourteen billion years ago while most religious scholars depict a much more recent event. But both versions of 'creation' are demonstrably contrary to logic.
To create something is to cause it to exist, so creation is simply another term for the process of cause and effect. If we require everything that exists to be the result of creation and stipulate nothing existed prior to that process, then space, itself, must once have been absent until some ancient incipient event precipitated the manifestation of the cosmos and its sea of inhabitants. Any causative progenitor must be ruled out as it would either violate the second requisite of the premise or require such a creator to be a descendant of an even earlier predecessor similarly predated by an eternal procession of ancestry. This never ending chicken-and-the-egg redundancy which inevitably results from any causative approach to the enigma of existence either implies no logical beginning or the involvement of some inexplicably spontaneous source not derived from causation - a source which would not only violate the first requisite but would also render the entire premise of cosmic genesis totally moot, for if anything can exist without creation, why couldn't everything else?
Whenever the tenets of logic invalidate your argument, you should try to avoid them entirely, so there are those who would suggest whatever created the cosmos wasn't subject to logic or the laws of nature. Theologians profess an omnipotent deity created the heavens and the Earth in a miraculous act of divine inspiration. Many (but not all) contemporary cosmologists contend the progressive red-shift of light from distant galaxies is proof that a Big Bang Cosmos is still spewing from the bowels of some spontaneously spawned singularity in a process not governed by the canons of physics as we know them today. But even those relatively few reticent cosmologists who don't tout Big Bang as the absolute beginning of space and time don't actually refute the premise of creation, they simply avoid the issue entirely, declining any effort to reconcile the phenomenon of existence with the principles of logic.
All hypotheses of creation are equally specious. Once logic and the laws of nature are repealed anything is possible, even the absurd; and if we permit even one exception to those laws, why should we expect the rest of the Universe to abide by them? You may certainly choose to suspend rationality in favor of whichever belief system you might wish to embrace, but thereafter and forevermore don't try to profess your argument is derived from critical thinking.
So, why does something exist rather than nothing?
Basic principle of logic: Before a thing can change or be changed, act or be acted upon, it must exist.
It's a rather simple axiom, intrinsically self-evident since any who might dissent must confess they believe in things that don't exist (they now have medications for that). At first you might consider the premise to be rather obvious and inconsequential, but its deeper significance categorically refutes both the ancient mythology of Genesis and the contemporary mathology of those "Science Channel" cosmologists who tout Big Bang as the absolute beginning of all space and time.
Existence isn't a condition or a state of being, it is the very phenomenon of being, itself. Something must be in order to have a state of being and if being is necessary in order for change to occur, then cause and effect is derived from and thus subordinate to the more fundamental phenomenon of existence; and no phenomenon can be the product of its own subordinate derivative.
Existence is the source of cause and effect, not the result of it.
Change is a function of existence
It certainly doesn't take an Einstein or a Hawking to recognize the obvious, all it takes is an unbiased perspective; thinking neither outside the box nor inside the box, but eliminating the box entirely. This isn't exactly rocket science; it requires no esoteric equations, no orbiting telescopes or expensive particle accelerators; you don't need a degree in mathematics, physics or cosmology, or even a high school education to understand it, but in the publish-or-perish ivory tower of academia, hypotheses featuring multiverses, extra dimensions and cosmic expansion into entropy death are where the real money is (with some strings attached). Beautiful equations can describe fantasy as easily as fact, but without the capacity to parse differentials with any degree of integrity, no lowly layman would dare debate the sanity of such sophisticated scholarly branes.
Either the phenomenon of existence is the result of cause and effect or it is not.
"It is not" implies Existence ex Nihilo
All forms of change are governed by those fundamental laws of nature we call principles, so wouldn't it logically follow that the key which unlocks the enigma of existence must be a principle instead of a process? If we examine the nature of change, one simple prevailing dynamic emerges; a ubiquitous paradigm found at the heart of every equation, a familiar axiom universally known and accepted. Sadly, the significance of this principle has been ignored since the inception of scientific inquiry and, ironically, it remains concealed, hidden in plain sight.