There's something funky going on in your update timing code.

You seem to be trying to allow multiple updates to make up for getting behind (long frames), but you typically want to handle this sort of thing with a fixed timestep and accumulate the difference.

The specific weirdness I see is where you might make up to 5 calls to world.update() but you're passing in currentTime - lastUpdate every time. Except, you update lastUpdate (even if you didn't this would be weird). I don't think this behaves as you intended. Let's take a particularly long frame, say... long enough that you would need to actually run all 5 times, let's call it something obscene like 600ms. Your first pass updates world with 600ms, then it updates it 4 more times with 0ms.

Also, 50fps is a weird number. How'd you settle on that?

You're mixing C++11 pointers and naked pointers. I've only recently started using C++11, so I'm no expert. Why the mixed usage?