Recently my karma changed from negative to neutral, and then to positive.

A long time ago, someone had caused my karma to go negative. Since then, my comments have probably been largely invisible. But a kind soul gave me a boost recently. And then I managed to post something interesting enough to move into positive territory.

It's been a long time, but I'm grateful.

Not that I post very much, but it's been a bit depressing at some low level for a couple of years.

I was too slow to get my two cents together on the great solar sail debate earlier this month. The discussion has been archived, and so I can't post a comment there. I did, however, write up an analysis (HTML) that cleanly shows what's wrong with Gold's basic model. I even treat the relativistic case, all with just a simple collision model stolen from classical mechanics.