It seems that one reason for the breakdown in communication between Christians and atheists is that each side is playing a different game in the same conversation. As a skeptic, the atheist's goal is to refute bad explanations, even if that means there is no explanation left to choose from. Conversely, the Christian's goal is to make an inference to the best explanation available, even if it is problematic. So when the atheist says "prove it" and the Christian can't, the atheist claims victory; and when the atheist says "I don't know" the Christian claims victory.
However, I'm convinced that the Christian position is so weak, particularly on the topic of creation and causality, that the atheist can play the Christian's game and still win.
While the skeptical atheist's actual position is "I don't know" when it comes to unresolved cosmic questions, let's nevertheless saddle the atheist with something so that they are playing the Christian version of the game. For simplicity, we will burden the atheist with the position that reality is as follows: The universe is a finitely large hypersphere of the smallest possible size that is consistent with the observation that the universe is strictly larger than the observable universe. Further, the bulk space, which is the space wherein the multiverse resides, does not exist. All that is, was, or ever will be is just our universe. So it is being said that something has come from nothing for no reason and with no cause.
The Christian position seems to be this: God created the universe (and also other realms beyond the universe) out of nothing by speaking such things into existence. I do not know of any explanation that is more specific than this.
So which is a better explanation?
As I understand it, this would be the typical Christian assessment of the atheist's position:
It is nonsensical to assert that the universe exists for no reason and with no cause. Something cannot come from nothing.
The problems with this assessment are, first, that the Christian tacitly asserts that God exists for no reason and with no cause, which is the special pleading fallacy. Identifying the fallacy is already sufficient grounds to ignore the rebuttal until it is amended, but it can also be said that the second objection is inadequate. We have not, and presumably cannot, observe nothingness, so there are no empirical grounds to say what can or cannot occur. Further, we know that nothingness entails a complete lack of rules or governing principles, so the governing principle "something cannot come from nothing" cannot apply to nothingness by definition. This point was made to Dr. William Lane Craig, and he responded with, "Then why aren't we seeing tricycles popping into existence randomly?" The answer, of course, is that empty space is not nothingness and so any expectation we might have about nothingness is irrelevant—in fact, Craig should be well aware of this because he has criticized Dr. Lawrence Krauss for equivocating empty space with nothingness. Let me clarify, though, that I'm not positively claiming that something definitely can come from nothingness, but rather that it cannot be ruled out.
The real reason that "nothing cannot come from something" is asserted presumably relates to the issue of causality. With regards to nothingness, there is nothing that can cause anything to occur; on the other hand, if a God exists, however inexplicable his existence may be, then there is at least an agent that can cause something to occur. This is, I believe, why Christians think that God is the best explanation for the existence of the universe.
However, this is not how causality works. An agent performing the causal influence is only half of what we would call an event that involves causality. There must also be a thing that is acted on; otherwise there is no effect. Billiard balls are often used as an example of causality, but a billiard ball flying through empty space devoid of interaction is not causing anything to occur. Another billiard ball is required for causality to have meaning because there is no cause without something that gets effected.
Absent creation, when the sum total of all existence was just the Christian God, what was available for God to act upon? Did God act on himself? Then we are all made of the stuff of God, and I don't think Christians take this position. Did God act on the universe before the universe even existed? How does that make sense? Did God act on nothingness? Nothingness is not a thing that can be acted on, and "acting on nothingness" is the same as acting on nothing, which is the same as doing nothing, which is the same as not causing anything to occur. God himself, nothing, and the universe itself seem to be the only conceivable choices of what we can even discuss as candidates for what God acted on, and none of them work.
Here are two definitions of causality that I know of:
PHYSICS
A system is a region of space.
A state is the arrangement of matter and energy in a system.
Causality is the process by which a system transitions from one state to another over a period of time.
ANTIQUITY
Aristotle proposed four causes, two of which are relevant here: efficient cause and material cause. For a marble statue, the material cause would be a marble slab, and the efficient cause would be the sculptor or the chisel. Causality requires both the efficient cause and the material cause. A causal event lacking one or the other is impossible to even describe.
You are free to come up with another definition of causality, so long as it models reality as we know it. The Christian's task is to think up a form of causality which is consistent with both what we observe in reality and also creation out of nothing. As far as I can see, this is impossible. It must be said that God's creation event did not involve causality, and that is extremely problematic to Christianity. Allow me to explain.
First, why is it that God's creation event did not involve causality? Well, let's consider the first model of causality. In that case, absent the universe, time does not exist and thus causality trivially does not exist by definition. If you want to posit the existence of some extra dimension of time that envelopes the universe, and that God performed an action of causality in that dimension of time, then that only pushes the problem back a step. At some point, if God is indeed creating everything out of nothing, there is a creation event where God creates time itself and this action is necessarily absent of causality under the first definition. Under the second model of causality, creation out of nothing is impossible by definition because there is no material cause.
Note that I am assuming God's omnipotence is limited to that which is logically possible, so I am talking about a God that cannot create a square circle or a one-ended stick. If you do believe that God can perform logically impossible tasks, then you must explain why God did not simply forgive us all as an act of will instead of sending his son to die, because God could have forgiven us all as an act of will even if it is impossible to do so. Right? Theologically, the only Christian God that makes sense is one that is unable to perform logically impossible tasks. I know that the "theory" of atonement is quite off topic, but it is a central issue of Christian theology and I cannot simply allow Christians to start a fire there just to put out a fire here.
Now, I did say above that I am not ruling out the possibility of something coming from nothing. Which is to say that I am not ruling out the possibility of things coming into existence by some means other than causality. So it then follows that God could have also used some means independent of causality to create the universe. The problem here, though, is that we have no way of explaining what that entails, and there are absolutely no grounds to say that God is necessary for the process. If the Big Bang was not caused, why is God needed? Even given unlimited power, it is impossible to describe how God could create something without invoking causality just like it is impossible to describe how God and his unlimited power could create a square circle.
So why did I say in the beginning that the atheist can play the Christian's game and win? It's because the Christian's explanation for the origin of the universe is necessarily worse. The Christian cannot account for God's existence (because God exists for no reason and with no cause), then insists that God is necessary for creation to occur, yet cannot explain, even given God's unlimited power, exactly why God is necessary for the process or what God did. While the atheist is saddled with the argument here that the universe exists for no reason and with no cause, the Christian—whether or not they know it themselves, and whether or not they want you to know it—asserts that God exists for no reason and with no cause, and that he, without the invocation of causality, spoke the universe into existence, which is to say that the universe exists for no reason and with no cause.
So the Christian has an extra assumption which explains nothing, and assumptions that explain nothing are supposed to be dropped. In logic, assumptions, while necessary, are a liability and should be limited to the best extent that is possible. So the Christian's argument can be improved by removing God from it, and doing so would make it effectively identical to the atheist's argument. The atheist's argument has no unnecessary components to it, and it does not make any assumptions that aren't already made by the Christian's argument. If the Christian's argument has to be improved just to be on par with the atheist's argument, then it follows that the Christian's argument is inferior to that of the atheist.
However, I'm convinced that the Christian position is so weak, particularly on the topic of creation and causality, that the atheist can play the Christian's game and still win.
While the skeptical atheist's actual position is "I don't know" when it comes to unresolved cosmic questions, let's nevertheless saddle the atheist with something so that they are playing the Christian version of the game. For simplicity, we will burden the atheist with the position that reality is as follows: The universe is a finitely large hypersphere of the smallest possible size that is consistent with the observation that the universe is strictly larger than the observable universe. Further, the bulk space, which is the space wherein the multiverse resides, does not exist. All that is, was, or ever will be is just our universe. So it is being said that something has come from nothing for no reason and with no cause.
The Christian position seems to be this: God created the universe (and also other realms beyond the universe) out of nothing by speaking such things into existence. I do not know of any explanation that is more specific than this.
So which is a better explanation?
As I understand it, this would be the typical Christian assessment of the atheist's position:
It is nonsensical to assert that the universe exists for no reason and with no cause. Something cannot come from nothing.
The problems with this assessment are, first, that the Christian tacitly asserts that God exists for no reason and with no cause, which is the special pleading fallacy. Identifying the fallacy is already sufficient grounds to ignore the rebuttal until it is amended, but it can also be said that the second objection is inadequate. We have not, and presumably cannot, observe nothingness, so there are no empirical grounds to say what can or cannot occur. Further, we know that nothingness entails a complete lack of rules or governing principles, so the governing principle "something cannot come from nothing" cannot apply to nothingness by definition. This point was made to Dr. William Lane Craig, and he responded with, "Then why aren't we seeing tricycles popping into existence randomly?" The answer, of course, is that empty space is not nothingness and so any expectation we might have about nothingness is irrelevant—in fact, Craig should be well aware of this because he has criticized Dr. Lawrence Krauss for equivocating empty space with nothingness. Let me clarify, though, that I'm not positively claiming that something definitely can come from nothingness, but rather that it cannot be ruled out.
The real reason that "nothing cannot come from something" is asserted presumably relates to the issue of causality. With regards to nothingness, there is nothing that can cause anything to occur; on the other hand, if a God exists, however inexplicable his existence may be, then there is at least an agent that can cause something to occur. This is, I believe, why Christians think that God is the best explanation for the existence of the universe.
However, this is not how causality works. An agent performing the causal influence is only half of what we would call an event that involves causality. There must also be a thing that is acted on; otherwise there is no effect. Billiard balls are often used as an example of causality, but a billiard ball flying through empty space devoid of interaction is not causing anything to occur. Another billiard ball is required for causality to have meaning because there is no cause without something that gets effected.
Absent creation, when the sum total of all existence was just the Christian God, what was available for God to act upon? Did God act on himself? Then we are all made of the stuff of God, and I don't think Christians take this position. Did God act on the universe before the universe even existed? How does that make sense? Did God act on nothingness? Nothingness is not a thing that can be acted on, and "acting on nothingness" is the same as acting on nothing, which is the same as doing nothing, which is the same as not causing anything to occur. God himself, nothing, and the universe itself seem to be the only conceivable choices of what we can even discuss as candidates for what God acted on, and none of them work.
Here are two definitions of causality that I know of:
PHYSICS
A system is a region of space.
A state is the arrangement of matter and energy in a system.
Causality is the process by which a system transitions from one state to another over a period of time.
ANTIQUITY
Aristotle proposed four causes, two of which are relevant here: efficient cause and material cause. For a marble statue, the material cause would be a marble slab, and the efficient cause would be the sculptor or the chisel. Causality requires both the efficient cause and the material cause. A causal event lacking one or the other is impossible to even describe.
You are free to come up with another definition of causality, so long as it models reality as we know it. The Christian's task is to think up a form of causality which is consistent with both what we observe in reality and also creation out of nothing. As far as I can see, this is impossible. It must be said that God's creation event did not involve causality, and that is extremely problematic to Christianity. Allow me to explain.
First, why is it that God's creation event did not involve causality? Well, let's consider the first model of causality. In that case, absent the universe, time does not exist and thus causality trivially does not exist by definition. If you want to posit the existence of some extra dimension of time that envelopes the universe, and that God performed an action of causality in that dimension of time, then that only pushes the problem back a step. At some point, if God is indeed creating everything out of nothing, there is a creation event where God creates time itself and this action is necessarily absent of causality under the first definition. Under the second model of causality, creation out of nothing is impossible by definition because there is no material cause.
Note that I am assuming God's omnipotence is limited to that which is logically possible, so I am talking about a God that cannot create a square circle or a one-ended stick. If you do believe that God can perform logically impossible tasks, then you must explain why God did not simply forgive us all as an act of will instead of sending his son to die, because God could have forgiven us all as an act of will even if it is impossible to do so. Right? Theologically, the only Christian God that makes sense is one that is unable to perform logically impossible tasks. I know that the "theory" of atonement is quite off topic, but it is a central issue of Christian theology and I cannot simply allow Christians to start a fire there just to put out a fire here.
Now, I did say above that I am not ruling out the possibility of something coming from nothing. Which is to say that I am not ruling out the possibility of things coming into existence by some means other than causality. So it then follows that God could have also used some means independent of causality to create the universe. The problem here, though, is that we have no way of explaining what that entails, and there are absolutely no grounds to say that God is necessary for the process. If the Big Bang was not caused, why is God needed? Even given unlimited power, it is impossible to describe how God could create something without invoking causality just like it is impossible to describe how God and his unlimited power could create a square circle.
So why did I say in the beginning that the atheist can play the Christian's game and win? It's because the Christian's explanation for the origin of the universe is necessarily worse. The Christian cannot account for God's existence (because God exists for no reason and with no cause), then insists that God is necessary for creation to occur, yet cannot explain, even given God's unlimited power, exactly why God is necessary for the process or what God did. While the atheist is saddled with the argument here that the universe exists for no reason and with no cause, the Christian—whether or not they know it themselves, and whether or not they want you to know it—asserts that God exists for no reason and with no cause, and that he, without the invocation of causality, spoke the universe into existence, which is to say that the universe exists for no reason and with no cause.
So the Christian has an extra assumption which explains nothing, and assumptions that explain nothing are supposed to be dropped. In logic, assumptions, while necessary, are a liability and should be limited to the best extent that is possible. So the Christian's argument can be improved by removing God from it, and doing so would make it effectively identical to the atheist's argument. The atheist's argument has no unnecessary components to it, and it does not make any assumptions that aren't already made by the Christian's argument. If the Christian's argument has to be improved just to be on par with the atheist's argument, then it follows that the Christian's argument is inferior to that of the atheist.