Here we go again, aspiring to the Star Trek universe. Scientists in Germany have created a cloaking device that masks objects perfectly...provided they're in a medium that diffuses light strongly, such as fog or... milk. It may not seem immediately applicable to daily life, but it means we're one step closer to invisibility cloaks, which is rather awesome.
The physics principles upon which the cloak is based are surprisingly simple: a cylindrical tube is coated in a chemical that scatters light much more strongly than the surrounding medium (e.g. fog). This sends light on a random path through the object's coating such that it is effectively impossible for the light to maintain enough directionality to cast a shadow. You could probably easily make one of these at home! Pretty nifty.
The 'optical invisibility cloak', they say, can be created by using diffused scattered light which allows the light source to penetrate without disclosing the source. And, they say, they've succeeded in testing an invisibility cloak that works in diffusive light-scattering media, such as fog or milk.