One
of the more modern fictional depictions of parallel universes is the
notion that multiple, split-off copies of each of us exists in
these countless other universes. How does this happen? At each moment, we
are presented with multiple choices; the road branches again and
again. We choose one path, but other copies of us (in other
universes) make other choices, each time creating endless copies of
ourselves that do their own thing in their own universe. These
replicas of us carry on in their lives pretty much as we do, but
pursue an infinite number of alternative possibilities.
After
each moment's decision that we make, we sometimes wonder: What if I were
to have chosen another path? (The fun part of the fiction is that
another “me” did so, in another parallel universe.) What
would my life be like today? If only I could peer into one of those
alternative worlds. These fanciful questions often occur to us, and
we can get into daydreams about another path that we might have
taken. Another playground for science fiction.
Once
the sole realm of science fiction, the possibility of the existence
of parallel universes has entered mainstream science in recent years.
Parallel universes pop up in physics and cosmology in several ways.
One of the ways is via the field of quantum mechanics. Its
predecessor, classical mechanics (the result of Isaac Newton's
insights), described an exact, unique universe—in which the laws of
physics allowed us to make precise predictions of the future behavior
of things such as planets and billiard balls. Given enough
information, one could describe precisely where that planet would be
in a hundred million years, or in which pocket a billiard ball would
eventually drop. Classical mechanics offered a certainty that we humans like to
have.
But
then quantum mechanics entered the picture and introduced the fact
that chance, instead, may rule our beloved universe. Physics was
transformed from an exact science to a probabilistic one. (This irked the hell out of some scientists... Einstein was one of them.) Quantum
mechanics tells us that an event, rather than being unique, may have
any number of outcomes—each with a given probability of happening.
We won't know what outcome actually will occur, until we run the
experiment. Afterwards, we may wonder why that particular result
occurred. Another outcome theoretically could have happened.
This probabilistic nature of the quantum world posits the possibility
of multiply-different outcomes in multiply-different universes—each
outcome equally likely to have occurred in its own universe. Weird!
More
on alternative universes next time...
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