Clearly this was not the type of conversation I had in grad school, but in a lot of ways this guy was "my people." I recognized in him a lot of the same mental habits and personality quirks that you find in people who do science for a living. Geeks like me, in other words. But for various reasons he had never really studied much science and had instead read widely on intelligent design and creationism.
The interesting thing about our conversation is that he wasn't really opposed to the idea of evolution. He basically admitted that going forward into the future, species would slowly evolve in response to the environment and natural pressures. The sticking point really was that 6,000 year old universe, and the need to defend a "literal-factual" interpretation of the Bible. Disbelief in macro-evolution flowed directly from there simply not being enough time to get it done. And he's right! If the universe were only 6,000 years old there wouldn't have been time for humans to evolve from simpler life-forms.
Still, my friend had the whole ID/creationism talking points down pat, starting from the old parable about finding a watch on the beach and "knowing" that it must have been designed rather than evolved. Of course, relying on human intuition about how the world works is pretty much why we believed the Sun went around the Earth for millennia. (I mean, just look at it! It goes in a circle, right?) My mind naturally rushed to the astronomical objections to a young earth, i.e. the known distances of objects that we can see and observe. (Of course there are LOTS of good arguments against creationism, this was just what came to my mind). I mean, the vast majority of stars in our own galaxy are farther than 6,000 light-years away, to say nothing of distant galaxies or the CMB.
observed in A.D. 1006 and 1054 are located at a distance 7,200 and 6,500 light-years, respectively. Their observation by ancient astronomers, plus the light travel time from the object, already puts the age of the universe older than 6,000 years. The center of our Milky Way galaxy is at 27,000 light-years. Every time we observe objects orbiting the central black hole we are looking at the universe as it was 27,000 years ago.
Obtaining distances to even more distant objects is a little bit complicated and not necessarily intuitive to a layperson. Let's just say it involves a lot of calibration. (In fact, determining the rungs of the "distance ladder" is one of the great accomplishments of modern astronomy.) But in case you don't buy all that calibration stuff, we have direct, "intuitive," geometrical distance measurements (via parallax and the Hipparcos satellite) for most bright stars within 1,600 light-years of earth (and the recently launched Gaia mission will be able to measure accurate parallax distances out to 30,000 lyrs).
So unless you think scientists are lying about the speed of light, it's clear the universe is pretty big and pretty old -- far older than 6,000 years. But of course my friend knew all this and had an answer waiting. And it was pretty jaw-dropping (to me at least). The apparent answer to all these objections was that our enormous universe was created 6,000 years ago with the light from those distant galaxies already streaming en route towards us. Zoink.
In one respect it's a superficially clever response, as it it severs the link between distance and time and allows you to accept (more or less) most of modern astronomy. But in another respect it's a disaster. The universe in this tale is basically just an illusion, a film projected on a screen, a visual trick that God is playing on humanity. It's hard to reconcile this vision with a reasonable God, not to mention that it's completely extra-biblical (which we were presumably trying to avoid from the start). We started the conversation by appealing to human intuition and now find ourselves arguing something utterly non-intuitive.
However, apparently not all young earth creationists subscribe to this idea. And this is where it gets even weirder. The big creationist site Answers in Genesis comes down against the idea that God would be deceptive in this way, and instead rounds up a bunch of poorly understood ideas from relativity and cosmology in order to cast doubt on the basic idea that light travels at a constant velocity. For example, this:
Since time can flow at different rates from different points of view, events that would take a long time as measured by one person will take very little time as measured by another person. This also applies to distant starlight. Light that would take billions of years to reach earth (as measured by clocks in deep space) could reach earth in only thousands of years as measured by clocks on earth.Yeah, no. Relativistic time-dilation doesn't make the universe 6,000 years old. It just doesn't work like that. But there are words written on the page that sound like science, and if you hadn't studied physics it might even sound convincing.
Anyway, it was an interesting conversation and it helped me learn a little bit about where our teaching and public talk about science runs aground. More importantly I think it's good to get outside the bubble and have genuine conversations with people with radically different world views. I doubt I changed his mind during our chat (or he, mine), but I hope maybe I planted the seeds of the idea that you can in fact reconcile science and religion, you just have to read the Bible more metaphorically.