The world in 2050... will be vastly different from the world of today, no doubt. America will not longer be a hyperpower.
The world economy will be in the shitter with the drying up of oil resources and a lack of replacement. America will nearly, if not totally, crumble because of said complications because of how reliant we are on oil to do everything. Nothing gets anywhere without oil. We might make up somewhat by reintroducing rail systems and bio fuels but we're really screwed.
China will probably have another revolution by this time, for better or for worse, and with the problems in the U.S. economy they'll also have serious economic problems. Brazil and India will be major powers, possibly superpowers. If France can get over themselves between now and then, Europe may be unified and will likely also be a major power, if not a super power, assuming it includes key countries such as the UK, Germany, France, Spain, Sweden, Norway, Italy, the Low Countries, Poland, Greece, etc. Japan will probably have some problems and will wane in economic power as their population stagnates. Russia will continue to be Russia - unstable both economically and politically - until they're either destroyed or they re-create the Soviet Union.
Alternatively, we'll all be dead by 2015 because of a nuclear war. I prefer this ending because it's far simpler.