I recently read your autobiographical talk “Escape from Nihilism,” and was a little shocked by the improbable course of events that have shaped your adult intellectual life. Your path of seems to have followed a reverse course to mine, and for that matter to that of most thinking adults.
You say that there are holes in the arguments for the denial of free will. One hole, you say, is that “in order to deny free will I assumed that I understood causality. That is foolish because I didn't know what causality really is any more than I understand what free will really is. They are equally wonderful and mysterious." Why don't you understand causality? Are causality and freedom really "wonderful and mysterious"?
You express amazement that I find causality mysterious. Since to you causality is an open book, perhaps you might enjoy thinking about some of the questions which have riddled lesser thinkers down the ages. Why are the patterns of causality what they are and not otherwise? Why is there such a thing as causality at all? Why is there something, and not rather nothing? May you fare well.
What would you say is the most powerful evidence for the existence of God?
Where to begin? There are so many. However, I would say two of most powerful arguments for the reality of God are the following.
1. The fact that we are here thinking about it. Unless you are willing to tolerate an infinite regress – and you shouldn’t be -- contingent being can be explained only by necessary being.
2. All of the things about human beings which have no adaptive value. A few of these conscience, the sense of beauty, and the desire for meaning, none of which can be explained in terms of natural selection unless you employ smoke and mirrors. I discuss the argument here.
Many of my atheist friends say the reason they are atheists is that there is no physical, tangible evidence of God. They want God to come down and say “Hi, I'm God,” or something like that. How would you respond?
If by physical and tangible evidence you mean something we can reach out and touch, like my computer keyboard, then it’s true that there is no physical and tangible evidence of God, but we can’t reach out and touch electrons or historical figures either, and atheists believe in those.
On the other hand, if by physical and tangible evidence you mean the sort of evidence we do accept for the existence of electrons or historical figures, then certainly there is physical, tangible evidence of God. First there is evidence from the sciences, for example the fact that the cosmological constants appear to have been “fine tuned” to allow life as we know it to exist. Second there is evidence from empirical history, for example the miracles of Christ, whose life is better attested by eyewitnesses than the life of any other ancient figure, such as Julius Caesar.
I realize that atheists don’t accept these sorts of evidence, but in rejecting them out of hand, they are being inconsistent. When we point to things like fine tuning, they say that a physical explanation for it will eventually be found -- which is merely blind faith. But when we point to things like miracles, they dismiss them on grounds that they are contrary to the laws of nature -- which is to assume what they ought to be proving. Neither response takes the evidence seriously.
Try presenting your atheist friends with the classical arguments for the reality of God’s existence, for example the cosmological argument. The cosmological argument relies on the principle of causality, which is part of metaphysics, but part of ordinary science too.
The argument begins with a logical distinction between contingent beings and necessary beings. Necessary beings – if there are any, which is not assumed -- have to exist. By contrast, contingent beings do not have to exist, so if they do, there must be some explanation, some cause, of their existence. For example, you are a contingent being. You might never have existed, and the reason you do exist is that your parents conceived you. Now consider the whole universe. So far as we know, it didn’t have to exist; so it is a contingent being and requires a cause. Someone might say, “Yes, but the cause isn’t God; it’s just another thing that doesn’t have to exist. There might even be a whole series of contingent beings, so that the universe is caused by cause one, cause one is caused by cause two, cause two is caused by cause three, and so on.” Very well, but could such a chain of causes or explanations be infinite? The answer is no. Why? One reason is that to say that the chain of causes or explanations is infinite amounts to saying that there is no ultimate cause or explanation, because every contingent being requires a cause. Another reason is that there is no such thing as what philosophers call an "actual" infinite series. For both reasons, the chain must stop somewhere; there must be a first cause. Call this first cause cause N. But the chain couldn’t stop with cause N unless cause N were a necessary being. This necessary being is what we call God.