Other researchers are working on related ideas, as more and more cosmologists are taking seriously the problem posed by the arrow of time. It is easy enough to observe the arrow—all you have to do is mix a little milk into your coffee. While sipping it, you can contemplate how that simple act can be traced all the way back to the beginning of our observable universe and perhaps beyond

clipped from www.sciam.com Does Time Run Backward in Other Universes? clipped from www.dailygalaxy.com clipped from www.sciam.com The basic laws of physics work equally well forward or backward in time, yet we perceive time to move in one direction only—toward the future Why? To account for it, we have to delve into the prehistory of the universe, to a time before the big bang.  Our universe may be part of a much larger multiverse, which as a whole is time-symmetric. Time may run backward in other universes clipped from www.sciam.com If the observable universe were all that existed, it would be nearly impossible to account for the arrow of time in a natural way But if the universe around us is a tiny piece of a much larger picture, new possibilities present themselves We can conceive of our bit of universe as just one piece of the puzzle, part of the tendency of the larger system to increase its entropy without limit in the very far past and the very far future the big bang is easier to understand if it is not the beginning of everything but just one of those things that happens from time to time