magz wrote:
The black physicists I met came from Africa and Carribean but none from the US. Why? It's not the genes.
I suppose being black in the US carries some social load that being black in Africa does not.
This probably does not explain your experience. The US is a very comfortable place to live for those of us with enough income (typically a physicist would fall in that category although exactly how much they earn depends on whom they work for). And has provided this level of comfort to the more fortunate among us for many decades. It is relatively unusual for a physicist or other person with a similar career path to engage in much foreign travel. Possibly academicians, but then most of them are probably immigrants (other Americans can confirm this). A good physicist who is also a US citizen probably has a job that pays much better than academia. A large number probably work for the US government as employees or contractors, which requires them to have a top-secret clearance that a foreign national can't get.
All sub-Saharan African countries are basically poor to varying degrees. Sorry, I have to say that — blame colonialism. A physicist having been born in Africa more or less has no choice but to travel to more affluent countries where they can be well compensated for their talents. You may not think Poland is a wealthy country, but purchasing power parity per capita is still about 5x that of Ghana.
To recapitulate my earlier point, international travel is something Americans tend to be rather bad at except for pure recreational purposes, and even then we tend to be timid about where we go. I suggest you visit any place where an international endeavor of some sort is taking place, for example a Greenpeace ship. You usually won't find many Americans.