Love is all you need
There's a moment in the film 'Contact' (no idea whether it's in the book) where, after listening to Jodie Foster defend the scientific worldview, Matthew McConaughey asks her if she loved her father. He then asks her to prove it.
She's left stumped.
The same question is wheeled out every so often by religious believers as what they seem to think is a trump card against the empirical view of the world.
Yet, as far as I can see, it's a pretty easy question.
The only real problem with it is our definition of love: If we believe it to be a “simple” physiological state then evidence isn't too difficult to come by – we can look at the person's behaviour (do they behave in a way consistent with people who claim to be in love), check their physical reaction (heart-rate, pupil dilation, etc.), maybe even bring in some neuroscience. If, as I suspect those asking the question do, we believe it to be a “spiritual” state, above and beyond the physical, then the onus is on us to provide a way of studying this state. Neither presents that much of a challenge to the empirical view.
Of course, the question could be seen as challenging the empiricist to prove that they have subjective experiences – but then such an extreme scepticism poses a challenge to all worldviews, including the religious.