Bowerbirds use an optical illusion to trick their mates

Bowerbirds trick mates with optical illusions at Nature News. Male bowerbirds construct their bowers to create an optical illusion called forced perspective which makes them appear bigger than they really are.

The Problem of Time

The Problem of Time in Quantum Gravity

The problem of time in quantum gravity occurs because `time' is taken to have a different meaning in each of general relativity and ordinary quantum theory. This incompatibility creates serious problems with trying to replace these two branches of physics with a single framework in regimes in which neither quantum theory nor general relativity can be neglected, such as in black holes or in the very early universe.