Over on the Google+, Robin Hanson asks a leading question:
Explain why people shouldn’t try to form their own physics opinions, but instead accept the judgements of expert physicists, but they should try to form their own opinions on economic policy, and not just accept expert opinion there.
(I suspect the thing he wants me to explain is not something he thinks is actually true.)
I am a strong believer that good reasons, arguments, and evidence are what matter, not credentials. So the short answer to “when should we trust an expert simply because they are an expert?” is “never.” We should always ask for reasons before we place trust. Hannes Alfvén was a respected Nobel-prizewinning physicist; but his ideas about cosmology were completely loopy, and there was no reason for anyone to trust them. An interested outsider might verify that essentially no working cosmologists bought into his model.
But a “good reason” might reasonably take the form “look, this is very complicated and would take pages of math to make explicit, but you see that I’ve been doing this for a long time and have the respect of my peer group, which has a long track record of being right about these issues, so I’m asking you to go along this time.” In the real world we don’t have anything like the time and resources to become experts in every interesting field, so some degree of trust is simply necessary. When deciding where to place that trust, we rely on a number of factors, mostly involving the track record of the group to which the purported expert belongs, if not the individual experts themselves.
So my advice to economists who want more respect from the outside world would be: make it much more clear to the non-expert public that you have a reliable, agreed-upon set of non-obvious discoveries that your field has made about the world. People have tried to lay out such discoveries, of course — but upon closer inspection they don’t quite measure up to Newton’s Laws in terms of reliability and usefulness.
However, the recent talk by Sharachchandra Lele (and several discussions with another colleague about astronomical evidence for/against Aryan Invasion Theory) has convinced me that Natural scientists are equally unreliable if it comes to things in which value judgement is involved. So, anywhere, anything with even remote human interest is involved, one has to make one’s own decisions and not rely on expert opinions! It just so happens that in the case of things like Newton’s law, it is the engineering that is based on these laws that convince people to believe in them — at least for the majority!