Caveats, before we go on:
1) I am an atheist, and have been a hard atheist for over two decades.
2) I run a board for non-theists, which translates out to mostly atheists with some agnostics.
3) I realise Tai Chi has a certain reputation here, which leads to skepticism regarding his motives for the OP etc.. However, I only want to address certain very concrete points here, I do not want to be seen as backing Tai Chi up or anything like that.
4)PZ, the author of Pharyngula, is a remarkably unpleasant person with regard to the atheist broad community; he's flounced off two seperate, unconnected atheist boards because he simply could not bear people being allowed to disagree with him.
5) PZ makes a most stunning garbage statement in that blog entry, which I will get to below.
And Tai, since the author doesn't seem to want to answer this, maybe you can:
Why can't we approach the possibility of God's existence (or lack thereof) scientifically?
We can certainly approach all the "Natural Theology" side of things scientifically; and Catholicism for example depends a good deal on Natural Theology, while the more extreme Protestantism prevalent in the USA depends on a kind of "miracle theology", which is also adddressable scientifically
to a large degree.
However, not all aspects of theology nor of belief can be addressed "scientifically". To see what and why, let's examine a statement PZ makes in his Pharyngula blog entry:
PZ, the author of Pharyngula, is a remarkably unpleasant person with regard to the atheist broad community; he's flounced off two seperate atheist boards because he simply could not bear people being allowed to disagree with him.
PZ on Pharyngula said:
Also, I'd like to know what he means by this category of "scientific objects". Everything is a scientific object, from distant stars to grains of dirt, from the first picoseconds of the Big Bang to pillow talk between lovers. If we can ask a question about it, it can be science.
This, bluntly, is garbage, and shows PZ's rather willful deep ignorance concerning science.
Science concerns itself with intersubjectively verifiable phenomena; that makes it already hazy, when you consider that purely abstract concepts can also be likewise treated, and therefore theoretical mathematics is a part of science, and theoretical mathematical models with no apparent connection to the real world can also be and are addressed "scientifically".
That gives us a huge leeway in defining what science is, and what science can address;
but even with that huge leeway, PZ's statement is simply false.
For example, ethics.
Now, the only way you can at all address ethics scientifically is to study what ethics obtain, who holds them, when they are held, and possible biological bases for ethics.
But science
cannot tell you what ethic to hold. That is because
science cannot make value judgments for you.
And among all the reasons for that, the most pertinent reason is one Hume described hundreds of years ago, to wit:
There is no
logical way to make a prescriptive statement using descriptive premises;
which can be said otherwise, to wit:
You cannot in any logical way derive a "should" from an "is".
This means science can never tell you what your ethics should be. That means the essence of ethics is not a scientific question.
That takes us onto other examples, such as aesthetics:
No way on Earth can science tell you if The Ninth Symphony is any good or not. You must decide that for yourself, and it's not a question to be addressed scientifically.
No way on Earth can science tell you if you should prefer strawberries or bananas.
And PZ knows this all already (after all, the subject comes up with monotonous regularity), yet he still evades it; not at all inspiring, and rather ironic when he accuses McGrath of evasion.
Going on, the subject of subjectiveness and subjective perception is also a question that in the end can only be addressed philosophically, not scientifically, which means some aspects of overall theology can only be addressed philosophically --- that is, atheism utilises and must utilise philosophy just as much as science.