Is It Ever More Reasonable To Not Think For Yourself?

Just read a wonderfulpiece by John Hardwig called "Epistemic Dependence" in which he argues that for most of our beliefs, it is rational to not think for ourselves. He considers cases in which we are not capable of understanding, muchless evaluating, the evidence for a belief, but have a belief because someone we have good reason to be an expert believes it.

For example, in grad school at Johns Hopkins I took a course in general relativity from an astronomer who works with the Hubble Space Telecope Institute. The topic turned to contemporary views and when string theory came up, he told us that he had been on sabbatical the previous year at Princeton and his daughter just happened to be on the same soccer team as Ed Witten's daughter. Ed Witten is one of the BIG BIG BIG names in contemporary physics, a smart person of the highest order. He said that on the sidelines as they watched the game, he casually asked Witten about the prospects of string theory. The resulting animated response went completely over his head (astronomers are not physicists), but was unabashedly pro-string theory. He ended the story by saying that he had no idea exactly how strong the evidence for or against string theory was, but if it was good enough for Ed Witten, he'd believe it, too.

Now I believe it because he believed it because Ed Witten believes it. Surely, Ed Witten has a rational belief in the correctness of string theory, but do I? I believe it based upon an argument from authority, but I am incapable of assessing the evidence myself or even determining why this authority should be taken as one. I take it on authority that this authority is an authority. Is there an infinite regress here or is there good reason to believe? If I tried to gain the knowledge necessary, I would most likely screw it up because it is more complicated than I can make sense of. Is it then rational to necessarily farm out my beliefs or do I have to remain agnostic to avoid irrational belief?