well, english is of course indeed used in a lot of branches as a common language. but not as much as english speaking people often think ... when there are no native english speakers around, often there is another language used. also in politics or in science or whatever, there are a lot of other languages used. if english would be the lingua franca, than here in Brussels we wouldn't have the need for so many translators in the offices of the UN and Europe.
in science, well I can only speak for my branch, there I know you have to understand (and speak) french and german as well, preferably also some other language (italian is often used, or spanish, or more and more even arabic or turkish, for my branch that is).
it is however true that when you contact some one from another country, you start in english ...
but go to italy or france and try to come by with only english. it's very difficult there. same for japan or china. but I guess the reason that english speakers often think that it is a common second language all over the world, is because mostly people adjust towards english speakers, because we all know that you guys don't really know other languages
this is a result from the domination for over a century by english speakers.
but of course, this will change eventually ... it will be gradually, don't worry
so yeah, in a way you might think of lingua franca, although I wouldn't agree with it. just realize that 90% of the people in the world don't use english, aren't fluent in it or often don't even know the basics, and that in a lot of branches english is only used when english speakers are present. isn't that friendly