Most things sound convincing when Morgan Freeman says them. The host of Through the Wormhole and the voice of God himself recently told told Craig Ferguson's Late Late Show that the Higgs Boson "explains everything - creation." "Oh oh", replies Ferguson, "that's not going to be popular."

The "science puts God out of a job" trope has been championed by a number of scientists in recent times. "We have discovered," says Lawrence Krauss, "that all signs suggest a universe that could and plausibly did arise from a deeper nothing. In this sense ... science makes it possible not to believe in God."

Krauss is in Sydney to debate the question "Why is there something rather than nothing?" - the traditional starting point for an ancient argument for the existence of God. Kraus, of course, is a cosmologist, known in the field for his work on the cosmological constant and dark matter, and to the wider public for books such as The Physics of Star Trek and A Universe from Nothing . Krauss's opponent is the Christian philosopher William Lane Craig. He has built a career around the philosophical defence of theism, and is best known outside academia for his many public debates with atheists.

I am, like Krauss, a professional cosmologist and astrophysicist. I've also interacted with a philosopher or two, and I've read a lot of Craig's work. So I thought it might be opportune to offer a guide to the uninitiated.

Science versus God

There is a temptation among the opponents of God to defend the following argument: "Science, science, science, science, science, science. Therefore the universe is all there is." The assumption is that science will automatically push God out of reality.

What is science? Here's what I try to do in my day job. Physics uses a rather peculiar approach to studying the universe. We can translate physical (measured) facts about the universe into mathematical facts about a "model" of the universe. Mountains of data are neatly summarised in a few equations. Having made the leap into mathematical space, we look for mathematical facts corresponding to measurements we haven't made yet - in other words, predictions. We can then, for example, build a 27 km long, multi-billion dollar machine under France to smash protons together at ludicrous speeds to see if we were right about a type of particle predicted on paper in 1964. This actually works.

Fundamental physics can be summarised by three statements:

A list of the fundamental constituents of physical reality and their properties.

A set of mathematical equations describing how these entities change, interact and rearrange.

A statement about how the universe began (or some other boundary condition, if the universe has no beginning point).

In short, what is there, what does it do, and in what state did it start?

Where does science fit into a theistic worldview? The story goes something like this. God can exist without the universe. He freely decides to create a world in which "the ordinary course of nature in the whole of creation [will have] certain natural laws ... determining for each thing what it can do or not do" (St. Augustine, circa AD 415). These laws will be chosen to allow for the development of moral beings. The universe is brought into being, and sustained according to certain regularities. The intelligent beings that the universe produces use their intellect to study the natural universe and, through empirical evidence and mathematical reasoning, discover the laws of nature. They call the enterprise "science." As Johannes Kepler said, "Those Laws are within the grasp of the human mind. God wanted us to recognize them by creating us after his own image so that we could share in his own thoughts."

Science in that universe looks an awful lot like science in ours. Thus, there is no obvious conflict between the methods and findings of science, and the idea that the laws of nature are the product of a supernatural mind. Science can fit neatly into a theistic worldview. This is exactly the worldview in which science was born, exactly the beliefs of the makers of the scientific revolution.

It follows that Krauss must do more than praise science. His atheism is built on philosophical naturalism, the claim that the ultimate laws of nature are the ultimate axioms of reality, that the ultimate stuff of physics is the only stuff. While its simplicity commends it, this philosophy does not win by default. In particular, it does leave a few questions unanswered.

Can science explain why there is something rather than nothing?

Krauss's latest book claims that advances in science have shown that we can answer the question "why is there something rather than nothing?" without invoking God. His argument can be summarised as follows:

The basic stuff of the universe, as we now understand it, consists of matter and energy, space and time, governed by laws of nature. Particles of matter correspond to certain configurations of quantum fields. There is a configuration that corresponds to no particles (the "vacuum"). A state with no particles can evolve into a state with particles. Thus, matter can appear from no-matter. The universe as a whole may have zero net energy. There are theories that suggest that that space and time themselves are not fundamental, but emerge from a state without space and time. The laws of nature may be stochastic and random, in which case there may be no ultimate laws of nature. Since we can imagine the universe coming from a state with no matter, no particles, no space, no time and no laws, something can come from nothing.

Krauss's book was far from universally acclaimed. Fellow unbeliever and physicist-turned-philosopher David Albert wrote a scathing review for the New York Times . Krauss responded by calling Albert "moronic" and generally dismissing philosophy as a waste of time. I'd love to stick up for a fellow cosmologist, but I'm with Albert and my reasons mirror his.

Fundamental physics is, always has been and - unless it undergoes a major identity crisis - always will be about what the basic stuff of the universe is and how it interacts and rearranges. There is nothing deeper. Thus, there can be no answer within science as to where that stuff came from, why it is that type of stuff, why it obeys laws, why those laws, or why there is anything at all. All scientific explanations stop at the basic stuff.

This is why Krauss's argument fails. Particles can appear from no-particles, not from nothing. The underlying field is always there. A state with zero energy is not nothing. There must first be a thing before we can measure its energy, even if the number we get is zero. A physical state with no space or time, however strange, is still not thereby nothing. A universe with laws that vary from place to place and time to time is clearly not the same as one with no laws at all. It just makes the laws more complicated. Step 6 makes an unjustified leap from "something from not-these-five-things" to "something from nothing."

There must always be questions that science leaves unanswered. Naturalism posits that there is nothing but the stuff of science. Here, then, is the challenge for naturalism. To believe naturalism, one must believe that these questions are unanswerable. Not just unanswered, not just awaiting a breakthrough, not just an open research question. They must be non-questions, meaningless strings of words, nonsense cleverly disguised as the oldest and deepest questions mankind has asked about reality. Unfortunately for Krauss, to have any hope of doing that he's going to need to put on his philosopher's hat.

Can theism explain why there is something rather than nothing?

Sure, an atheist might say, there are some questions that science can't answer. But why think that religion will do any better? Why not simply say with Wittgenstein, "Whereof one cannot speak, one must be silent." For the theist, the question "why is there something rather than nothing?" motivates an argument for the existence of God that goes back at least to Plato and Aristotle, known as the cosmological argument.

Let me use an analogy. Most of the things around you, if you lifted them up and then dropped them, would fall to the floor. And yet most things around you are not falling. If everything is a "falling" kind of thing, then why is everything not falling? We have three options:

A. It's earth all the way down, each layer supporting the one above and supported by the one below. But this is no explanation at all, since all the layers could be falling together. So we still don't know why everything isn't falling.

B. A brute fact supporter, a magical floating layer. It is simply the case that one of the layers, which is made of the kind of stuff which would ordinarily fall, doesn't. For no reason at all. The question "why is the magic layer not falling?" has no answer.

C. A self-supporter. There is something down there that, somehow, supports itself. The question "why is this layer not falling?" is "because of the kind of thing that layer is."

In the case of Earth, as you hopefully know, C is correct. The core of the Earth is supported by its internal pressure and contains the Earth's centre of gravity. That kind of thing can hold itself up. In order to make sense of why all the things that could be falling are not falling, we need to posit a different kind of thing, an unsupported supporter. We need to take the series of supporters (I'm supported by my chair, supported by the floor, by the foundations, by the ground and so on) and find an appropriate, rather than arbitrary, stopping place.

Take that argument, replace "is supported" with "exists" and you've got a rough version of the cosmological argument. In order to make sense of why all the things that could have failed to exist ("contingent" things) do in fact exist, we must posit the existence of a different kind of thing, an uncaused cause, an uncreated creator, a necessary being. This is an attempt to tie off the loose ends of explanations. God is conceived of as the kind of being that must exist, whose existence is self-explained.

Is that a good answer? "Necessary being" is a pretty baffling idea. Immanuel Kant argued that it is incomprehensible because existence cannot be a property of a thing. What a thing is, and whether it is, are always two separate questions. In more modern times, the eminent British philosopher and Christian Richard Swinburne has argued that the idea that God is a metaphysically necessary being doesn't make sense, substituting instead "factual necessity" - God's existence is independent of other beings. These issues are crucial to deciding whether theism's answer even makes sense. Given the specific focus of the debate, Craig needs to clearly explain and defend the theistic answer.

One thing is certain: this is philosophy. Nothing in methods and findings of science will help in the slightest. Krauss will need that philosophy hat, again. When Krauss first debated Craig in 2011, it was rather obvious that he hadn't done his philosophy homework. When Craig presented the argument from contingency, Krauss didn't know what "contingency" meant in this context (no, it's not just a property of snowflakes and earthquakes).

Is this universe morally good?

The modern atheist has a wide variety of rhetorical weapons at his disposal, many kindly provided by believers through the ages - just be sure to mention the crusades, inquisition, witch-burning, Galileo, paedophile priests, suicide cults, terrorism, Westboro Baptist Church, hell, the "dark ages," the wars of religion, and so on, and so on.

It would be easy for the Christian to blame fallen humanity for these terrible events. But there is a deeper reason why they could strike a blow against the case for God. When we analyse any hypothesis in light of some evidence, we must ask: Suppose I knew that the hypothesis were true; how likely is it that I would see the evidence that I have?

So, when it comes to God, we must ask: how likely is it that God would want to create a universe like this one? The key here is God's goodness. There are no limits on God's power, so a preference for one universe over another must be on moral grounds. The theist will argue that creatures with free will - who can recognise and appreciate good things, do good actions, interact with, influence and be responsible for each other, investigate their surroundings, learn the goodness of knowledge, beauty, love, and truth - are good things. A universe capable of producing and sustaining such creatures is a universe with moral worth, one that a God might consider creating. It helps if universes that can sustain the complexity required for intelligent life forms are rare in the set of possible universes - as seems to be true.

It makes perfect sense, then, for the atheist to point out features of our universe that are not morally desirable. Suffering, for example - the "tears of humanity with which the earth is soaked from its crust to its centre," in the words of Ivan Karamazov. This is known as the problem of evil. Theists have produced a wide range of responses, typically involving the claim that the evils in our universe are necessary to permit greater goods than would otherwise be possible. Free will is a dangerous gift, but necessary for love.

Krauss's favourite example seems to be the divine command in the Old Testament for the Israelites to exterminate the Canaanite men, women and children. This is particularly fruitful rhetorical ground, as Craig has argued that "God has the right to take the lives of the Canaanites when He sees fit. How long they live and when they die is up to Him. God does these children no wrong ... for they inherit eternal life." In the hands of Krauss, however, this case is largely used to attack Craig himself. The implication is that Craig's mind has been so corrupted by belief in God that he believes that genocide can be morally justified. It's not clear how this translates into an argument against the existence of God.

Many Christians would disagree with Craig's defence - or any such defence, for that matter. Given that the command was never carried out, if the Christian surrenders biblical inerrancy, then one is left with a rather nasty story was invented by persons unknown, which is hardly the worst thing that's ever happened. Krauss must keep focussed on the topic at hand, and put these rhetorical points to good use.

Who wins such a debate?

The only people who win or lose debates like this are the audience. They will win if the debate is civil, focused and thoughtful. If this debate inspires a chat between friends in a pub about the universe and the meaning of life, then it has done its job. On the other hand, everyone loses if either side is rude, condescending, resorts to personal attacks, wanders off on their favourite irrelevant rant, or fails to interact with what the other side has actually said. The audience may conclude that this topic causes more heat than light.

I'll be at the debate tonight. If it turns out to be uncivil, obfuscating and ego-driven, we can always show them how it's done in the comments ...

Luke Barnes is a postdoctoral researcher at the Sydney Institute for Astronomy, University of Sydney.