I've said before that both theists and atheists necessarily think that "something has always existed". So long as you accept the axiom that "something can not come from nothing", you're going to be faced with the above conclusion.
Theists think a god has always existed.
Atheists (generally) think that something material has always existed.
What I wanted to do is provide the philosophical and scientific evidence that we have for the atheists conclusion.
Both the theist and the atheist agree that "something material" currently exists, and certainly theism is compatible with the idea that something material has also "always existed". It is notable that the specific Christian dogma creation ex nihilo is not compatible, so they're going to have problems with the evidence I'm about to present.
So lets get to it.
This is the most intuitive form of evidence we have that "something material" has always existed, an argument from universal material causation.
Here I'm defining the universe hopefully uncontroversially as "all of material reality".
P1: All material things have material causes.
P2: The universe is a material thing.
C: Therefore, the universe has a material cause.
If the universe has a material cause, then it would follow that something material has always existed, unless we want to violate our concept of "something can not come from nothing", which Christians admittedly want to do at least in this specific way related to material causation.
The problem for Christians is that for anything we experience with material objects they come from preexisting material stuff, it's simply a rearrangement of whatever the fundamental material is.
This is where things get fun since we can start applying our substantial amount of scientific knowledge about material reality. Here I want to present two pieces of evidence based on what we know.
The Law of Conservation of Energy
"The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but cannot be created or destroyed."-Wikipedia (accessed 2/11/15)
If we define the universe as "all of material reality" then it seems to fit the bill of a physically isolated system.
If we agree that something must have always existed, and our best scientific investigation tells us that matter and energy can not be created or destroyed - then it seems pretty easy to think that the "always existent something" is matter/energy.
It's about here that I'd expect someone to object with a high school formulation of the second law of thermodynamics and how if the universe has always existed it should have a very high entropy condition and we shouldn't be here. I certainly would agree that question of why our universe has a low entropy condition in the past is an open one, but it is not one that has no possible scientific answers. Suffice it to say, once we start treating entropy the way it is currently treated in modern physics (ie. the field of Statistical Mechanics) we are able to deal with the questions raised by the second law.
None of this changes the fact about what the law of conservation of energy tells us about the material that makes up our physical universe.
The Quantum Eternity Theorem
We happen to know quite a bit about how matter and energy work. We know that all material things are made up of atoms, which are in turn made up of quantum fields. We don't know if quantum fields are in turn made up of something else, so at the moment our scientific inquiry puts it as the most "fundamental" constituent of material reality.
Quantum fields are so fundamental that they don't just make up "matter", but they make up space and time itself, at least as far as what our best science tells us.
So if we're going to learn as much as we can about what makes up material reality, we need to speak the language of quantum mechanics. There is certainly quite a lot we don't yet know about quantum mechanics, with quantum gravity being the biggest open question in modern physics.
This does not mean that what we do currently know about quantum mechanics is inherently wrong, or that what we do know carries no weight.
So what do we know about quantum mechanics and what does it tell us? Well to quote theoretical physicist Sean Carroll:
“Quantum Eternity Theorem” (QET) — under conventional quantum mechanics, any universe with a non-zero energy and a time-independent Hamiltonian will necessarily last forever toward both the past and the future."Astute observers will likely ask what about a universe with zero total energy? That's not really a problem for the naturalist since under the same laws of quantum mechanics (basically the Schrodinger equation) it would mean that time itself is emergent, not fundamental (like temperature). For those interested, the technical paper can be found here.
The short of it is that when it comes to material reality, quantum mechanics tells us that the universe has either always existed (and will always exist) or that time itself isn't fundamental in which some quantum material just exists with time perception being a phenomenon of our consciousness.
Is there a theistic response?
Suffice it to say, things don't look very good for our theistic opponents when one considers the current state of play, so to speak, of what physics is telling us about matter and energy.
What was telling is that in the proper debate between theoretical physicist Sean Carroll and philosopher/theologian William Lane Craig, Craig never addressed this explicit point about the Quantum Eternity Theorem (QET). Tellingly, he also never addressed the points about a well defined eternal universe model developed by Anthony Aguirre and Stephen Gratton during the debate either.
It wasn't until the second day during Jim Sinclair's talk that Carroll was able to get Craig to respond to the QET. Craig's response wasn't to deny what the science and equations tell us. It was to deny that the quantum level was more "fundamental" than the level of our conscious experience (contrary to everything we know about explanations for things like temperature, color, sound, etc). In his own words:
"if time does not appear on the fundamental quantum level, then so much the worse for the ontology of that level. Then that simply means that it doesn’t capture reality fully to speak of reality on that sort of a scale.”
-William Lane Craig, Responses during James Sinclair’s talk, “God and Cosmology” 2014Greer-Heard ForumNote that this holds on the only scenario available to the theist: that the total energy in the universe is zero. If the universe has a total energy level higher than that, it must "always exist". Tellingly, Craig still didn't address the Aguirre and Gratton model that was brought up, but fortunately Jim Sinclair was forced to admit at the end that it was a perfectly valid model that was eternal into the past.
The key take away point here is that theists can't really deny the QET, they simply have to say that they don't accept that science can fully explain material reality. It's simply a way of insisting that they can put "my metaphysics over your physics" in terms of what they want to believe.
Certainly, no one can stop them from believing what they want, but what the theist can't do is tell us that science somehow tells us that the universe was created ex nihilo.
There is quite a bit more that could be said here and about the quite varied possible states science has for what the universe might ultimately be like. There are models like the Hartle-Hawking model which effectively has it so the universe is a self-contained entity in which there is no proper beginning. Rather it's more like a four dimensional "block" (much like a 3D sphere) that just exists. Like a sphere has no beginning, so it could be with the universe. This "block" then just exists, with time being slices of spacetime within the block universe.
Theists could certainly embrace this model and then say that god just created the block, effectively embedding physical time into a larger metaphysical time in which the universe did not exist at some point (although that has it's own host of complex metaphysical issues). The key there though is that while such a scenario is logically possible, there is nothing we could infer from science to tell us that the universe was "created" in this way. There is also nothing in philosophy that can show that we can not just stop at "material reality" being the terminus point for reality, rather than a god.
There is one last thing I wanted to add as an addendum here. What I'm posting here in terms of the universe being eternal or that time is not fundamental is a concept that is actually endorsed by Evangelical Christian theoretical physicists like Don Page. You can listen to an interview with him done by Randal Rauser here where he admits that its quite plausible that time is not fundamental but emergent (roughly around the 5 minute mark). You can also hear him say that he also thinks that the cosmological argument is not a knock down proof, and he is personally very skeptical of the premises of the cosmological argument. He also admits that even if the universe had a beginning, it could simply just exist (roughly around the 9:27 mark) without a god, even though he thinks god exists.
The point is that theists can't really point to cosmology and try to use it as evidence for god. It's also not to say that theists can't come up with some kind of metaphysical framework with which to squeeze our understanding of material reality and then fit their god neatly in, even if the physical universe existed for an infinite amount of time. All one really must do is make a "metaphysical time" and just claim "physical time" is a completed infinite inside of the subset of metaphysical time.
So it's not that there is no conceptual space that theism can accommodate literally any view we have from science. The atheist is just left standing there asking why in the world the theist insists on adding so much superfluous metaphysical baggage to what we know about material reality!
The point of this post is to show that if we are going to take a neutral stance on our sweeping metaphysical assumptions about reality and examine what science tells us, the evidence is certainly pointing in the direction that something material has always existed.