Physicist Brian Greene explains how the prevailing theories about the fabric of space changed dramatically in the last century — twice. The most recent shift in thinking came about from a strange mistake, and revealed hidden truths about the nature of our universe. Later in this episode, Greene talks more about why this discovery hints at the existence of other universes.
There's plenty of evidence that the climate has warmed up over the past century, and climate scientists know this has happened throughout the history of the planet. But they want to know more about how this warming is different.
Now a research team says it has some new answers. It has put together a record of global temperatures going back to the end of the last ice age — about 11,000 years ago — when mammoths and saber-tooth cats roamed the planet. The study confirms that what we're seeing now is unprecedented.