@savagemonk,
It's senseless to argue, "Since I cannot reason the beginning of time, every other achievement, realization, and mode of understanding is pointless". What's before and after isn't necessarily relevant, and I'm not quite sure why he's so obsessed with the time construct.
Clearly, he just doesn't have a passion for critical thinking. One must have a
passion for understanding if one's mind is to be truly open. You cannot
make someone have passion; all you can do is plant seeds of enlightenment and hope they decide to cultivate. Probe your father-in-law subtly, never force-feeding new thought processes or concepts -- just bring them up in normal speak, and let him make the connections. If he really has no interest, then he most likely won't pursue any of the matters further, and there's nothing else you can do. If he does have interest and decides to pursue the matters further, great, you've helped to enlighten someone.
Personally, one of the most exciting things in my life is probing others to consider. If I hear, "Wow, I've never thought of ... in such a way, thanks!", I feel absolutely amazing. There's nothing more fulfilling to me than to advocate critical thought and see another reap the benefits of further understanding. But, as I noted, I make a conscious effort not to force-feed, for that will drive the individual further away. Remember not to ridicule him for not critically thinking: don't place yourself on a pedestal. Speak to him as an equal, simply sharing new, different thoughts, and you will see better results.