
Originally Posted by
simoncpu
Reflective surfaces can be used as a mirror, so I guess I can't answer water or something. We can construct a lensless camera (yepp they exist), and view the back of our heads with a glassless e-ink, but it's a boring answer.
I propose that we observe the back of our head by using immense gravity field to bend light that has reflected from the back of our heads into the front of our heads. Of course, our atoms would be ripped off in the process, but who cares?
Another method is to find a traversible wormhole and accelerate one end to the speed of light and bend it back to its point of origin. Effects on time dilation means that the accelerated end of the wormhole has aged more than the stationary end, so if you enter the accelerated end, you can see the back of the head of your past self. You can even sleep with your past self! Hahahaha...
I love typing BS on the Internet. Hehehe...

2nd and 3rd answer is correct
the name for this place where light bends so that it cannot escape is "event horizon". sa blackhole ni makita