what is Cool?

How can cool make up our social hierarchy, as being popular or un popular when part of the definition of cool means emotionally unaffected and/or lack of interest. It used to be that cool meant engaged and loud, being part of a movement against society. To rebel you need to be able too, scream out loud, say your point and stand up against all or most authority. How does the definition of cool fit now, because 40-50 years ago cool meant to be a rebel. Now cool is uninvolved and following mainstream. So I find cool has not changed but lost its definition.