“But evidently there is a first principle, and the causes of things are neither an infinite series nor infinitely various in kind. For neither can one thing proceed from another, as from matter, ad infinitum…, nor can the sources of movement form an endless series.” 
Aristotle, Metaphysics, Bk II, Ch 2
How did the physical world come into existence? It would be very easy to take the existence of the physical world for granted, to let the Ordinary World take control and simply not think about it. But as ordinary as the existence of the physical world may seem, the fact that the physical world does exist, the fact that anything exists is spectacularly extraordinary. One foolproof method of holding the Ordinary World at bay is to think about this question, and to think about it regularly.
It is a common misconception to believe that this is a question for science; it is not. In fact, bringing modern cosmology into the discussion is more likely to lead the discussion astray than to illuminate. Aristotle wrote his Metaphysics two thousand years before modern science was born, and yet his handling of this question is as valid today as it was when he lived. My point is that there are few prerequisites to thinking about this question. So if you have not already done so, it is time you gave this question some serious thought. The answer you find could change your life.
Of course Aristotle was not the first to attempt to answer this question and many have done so since. While there are many variations, all of the possible answers can be boiled down to one of the four below:
- The physical world did not come into existence; it has always existed and thus depends on nothing else for existence. In other words, the physical world is self-existent.
- The physical world came into existence spontaneously from literally nothing.
- It is impossible to know the answer to this question, so it is pointless to ask.
- There is something else, self-existent and fundamentally different from the physical world, that brought the physical world into existence.
The first thing to notice about these answers is that each one of them is in some respect, unbelievable. And yet the physical world does exist, so one of them has to be correct. Let’s examine them one by one.
Before I start it is important that I clearly define what I mean by the “physical world.” By “physical world” I mean the world of matter and energy which exits in space and time. It is important to understand that I use the term “physical world” very broadly. While I do not find the highly speculative idea of multiple physical universes even slightly compelling, I use “physical world” so broadly here that it would include not only our universe, but the entire system of universes were such a system to exist.
1. The Physical World is Self-Existent
If all that exists is the physical world, then it must follow that the whole of reality consists of the state of the entire physical world at this one instant in time. I cannot overstate the importance of this statement. It is not good enough that you merely understand the words, you must think on it until you grok it and only then will you fully comprehend the implication of asserting that the physical world is self-existent.
Before I expand on this thought I am going to digress for a paragraph to state that I think the physical world had a beginning in time. Modern investigations of quantum entanglement and other hard to explain phenomena notwithstanding, time moves forward, not backward. I think this asymmetric nature of time along with the not unrelated nature of causation, eliminate the possibility that our time-bound causally connected physical world has always existed. However, this is a more difficult argument to make and I do not think it is necessary for my purposes here, so I will not attempt to prove that the physical world had a beginning in time. The argument I present against the idea of a self-existent physical world is therefore even more compelling because it is true regardless of whether or not the physical world has always existed.
I return again to the thought worth repeating; if all that exists is the physical world, then it must follow that the whole of reality consists of the state of the physical world at this one instant in time. As soon as time moves forward by even a nanosecond, the state of the physical world changes and thus the state of a moment ago no longer exists. Thus, only one state of the physical world exists at a time. To be self-existent means to be independent of anything else for existence. Now the state of the physical world at this instant in time is clearly not of this type, because it is very much dependent on the state of the physical world at the instant prior to it. Indeed, this instant of time, this reality, would not exist if the previous instant in time did not precede it. This instant in time is therefore most definitely not self-existent. If the physical world is not self-existent at this instant, then it was not self-existent a minute ago, or a minute before that, or... Even if time were to extend backwards infinitely, this would not lead to the conclusion that the physical world is self-existent. Indeed, if the physical world is not self-existent at this very instant, then an infinite succession of previous instants in no way weakens the conclusion that the world is not self-existent. This is essentially the argument that Aristotle articulated thousands of years ago, that countless others have made since then, and that modern science does not, and in fact could not, affect in the least because it is more fundamental than anything modern science studies.
One fallback position could be to say that while no instant of the physical world is self-existent, the physical world looked at as a whole, including all of time, is self-existent. In other words, one might say that while no single instant is self-existent, the system as a whole (i.e. the entire history of the physical world looked at as a single entity) is self-existent. But if all that exists is the physical world, then such a conception as “the entire history of the physical world as a single entity” is a fiction. If all that exists is the physical world, there is nothing but now, this instant, this current state of matter and energy. The very idea of “all of time” would be merely the arrangement of atoms in the brain of the person with such a thought at the very instant the thought occurred. If all that exists is the physical world, then the only thing with objective reality is the state or arrangement of stuff in the physical world at this very instant in time. Everything else is a fiction, and any thoughts or conceptions human beings might have about the physical world are nothing more than the arrangement of atoms in the thinker’s brain which is itself just a physical state. Once more, if all that exists is the physical world, then the thought and the brain state are one and the same, and the transcendence we attribute to our thoughts is a fiction. Thus “the entire history of the physical world as a single entity” is not only not self-existent, it is nothing more than the arrangement of atoms in a human brain.
Another related fallback position would be to say that while the physical world itself is not self-existent, the laws that govern the physical world are self-existent and it is from these that the physical world arose. But again, trouble ensues for the materialist (i.e. for the person who believes that all that exists is the physical world) as soon as we start asking questions about the nature of these laws. What type of thing are the laws of the physical world? Do these laws have objective existence apart from the physical stuff that they govern? Indeed, do the laws of the physical world really govern at all? To govern implies the power to force another to act in a certain way, but the “laws” of the physical world do not govern in this way. The laws of the physical world merely describe the way the stuff of the physical world behaves. They describe the properties of the physical world, but they do not have any objective existence apart from the physical world. Certainly the stuff of the physical world interacts with other stuff in regular ways, but this is merely a characteristic of the stuff and this regularity of interaction does not possess any objective existence apart from the stuff. In other words, these characteristics or laws cannot be abstracted from the stuff to possess their own objective existence; the characteristics are intrinsic to the stuff. Only the human mind can abstract laws from observing the behavior of the stuff, and if we are nothing more than machines made of physical stuff ourselves, then these abstractions are merely the arrangement of physical stuff and again have no objective reality and are nothing more than the arrangement of atoms in the brain of the scientist who is thinking about them. If all that exists is the physical world, then there are no laws of the physical world that possess objective existence, there is just the stuff of the physical world. Lacking objective existence, the laws of the physical world can hardly be the self-existent base upon which the physical world owes its existence.
For the reasons articulated above, the idea that the physical world is self-existent—that only the physical world exists and that it has always existed—seems so manifestly false to me that it surprises me that anyone actually believes this. But it is my experience that this is in fact exactly what most people believe who believe that only the physical world exists. I think the primary reason for this is that the idea of infinite time is so beyond our ability to comprehend, that thinking of history extending backwards infinitely makes anything seem plausible. “Sure,” their thinking goes, “the very ordinary physical world of today isn’t self-existent, but who could say anything is impossible given an infinite amount of time?” First, please notice that this is not an argument; it is an impression, a feeling. Second, if all that exists is the physical world, then the only thing that has objective reality is the state of the physical world at this very instant, and the state at this instant is no different in kind, albeit radically different in the particulars, than the state of the physical world at any time in history no matter how far back history extends. Infinity changes nothing. Do not let the incomprehensible notion of infinite time deceive you into thinking that anything is possible.
I therefore conclude that if the physical world is not self-existent at this very instant, then it never was self-existent and thus Answer #1 is false.