As showing how far under favourable conditions the reflection of light from a cloudy sky is visible, I may perhaps be allowed to mention that last night at nine o'clock the reflection of the London ...

Can we turn back time? Ask a savvy physicist, and the answer will be “it depends.” Schemes for retrograde time travel abound but usually involve irreconcilable paradoxes and rely on outlandish ...

Introduction Can you imagine a bouncy ball that could bounce back and forth between two walls, infinitely—that is, forever? Wouldn't that be amazing? What if, instead of a ball, light was bouncing ...