Sean Carroll - Welcome Time Travelers

Image: Geoff Oliver Bugbee

Beginning with a story set slightly after the beginning of time, theoretical physicist Sean Carroll tells the audience at the 2010 IdeaFestival that Galileo was bored, perhaps unhappy, in church. Observing the chandelier in the Cathedral of Pisa, Galileo wondered why it appeared to sway in rhythmic time, and by checking the movement against a variable - his pulse - he could clock its movement.

Sean Carroll is a theoretical physicist at the California Institute of Technology and the author the book, "From Eternity to Here."

Time has a regularity. But unlike space, time has also a direction referred to as the "Arrow of Time." We experience a past and will have a future. But why?

To the average person it's hard to explain why that's a problem, Carroll jokes. "What's next, an explanation of alphabetical order?"

But the reason the question is interesting is that in physical theory, time should run both ways. Eggs break but don't spontaneously reassemble, a rack of billiard balls can be broken, but don't fall back into order. "You don't have to go into your house and messy-up your room because the house has been cleaning itself while you were away."

One way of understanding this direction is through "entropy," the embodiment of the second law of thermodynamics. Applied universe-wide, it means that from a highly ordered start to a cool, dark, lifeless end - oddly to the human ear, "equilibrium," in some distant future all the energy of the universe will have been expended. We experience a past that was infinitesimally more energetic to us than today. Energy is continually falling into a universe that is also, we know, rushing away from us.

If the past and future are equally real, then what about our free will? Using a physical explanation, there are many different possible futures, or many more opportunities, available to us. Entropy (remember, a measure of disorder) increases.

With one hundred billion galaxies and a hundred billion stars in each galaxy, the universe is a big place. And unfolding at colossal speed since the Big Bang 13.7 billion years ago the question naturally arises: why did the history of the universe began in a highly ordered state.

There are emerging theories the fit that data - such as it is - but physicists are unsure.

Scientists have considered and rejected and are now reconsidering theories that might explain the initial order. Perhaps in an endless universe and with endless possibilities, spontaneous instances of you or me or some flickr of consciousness that hung around just along enough to see equilibrium, might combust. All the oxygen molecules in the room you are in now could move to one side, leaving you in a vacuum. It's possible, and vanishingly unlikely.

New evidence that the universe is not endless, helps with explanations of the energetic release known as the Big Bang.

Thanks to a little matter-energy energy called dark energy, we now understand that galaxies, including our own, are rushing toward a far horizon, and that, thanks to a contribution from Steven Hawking, even in the least dense areas of the universe, minute scaps of matter can pop into and out of existence, which means energy.

Thanks to those speculative physics, perhaps in an as yet unknown way, those highly disordered, cool expanses near equilibrium pinched off other universes. Perhaps we inhabit one vast realm of an unimaginable, and so far, unknowable, multi-verse.

Back to what we know. According to Carroll:

Entropy is responsible of the arrow of time.

Entropy increases (become more disordered) because it started out low (colossally energetic).

We still don't know the why of the physics that precipitated the Big Bang.

Tomorrow, however, you will travel to the future.