Don't pity those in the past – in their own way, they might have a lot to look forward to. From our perspective, events in some universes may seem to unfold backwards. That implies there could be alternate worlds whose future is actually even further in our distant past.
This trippy idea has been suggested before, often with very specific caveats. In 2004, Sean Carroll, now at the California Institute of Technology in Pasadena, showed it could apply, but only if complex and unlikely physics was involved.
Now Carroll and cosmologist Alan Guth of the Massachusetts Institute of Technology have shown how time itself can arise organically from simpler principles, then flow in opposite directions in adjacent universes.
Guth and Carroll’s work is motivated by a problem vexing physicists and philosophers: why it is that time’s arrow points in just one direction. It’s true we can only remember the past (see “Why the future keeps slipping your mind“), but the laws of physics don’t much care which way time flows: any physical process run backwards still makes sense according to those laws.
“There’s no such thing, at a very deep level, that causes [must] precede effects,” says Carroll.
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