New Model of the Universe Says Past Crystallizes out of the Future
What do you get when the past crystallizes out of the future? According to a new model of the universe that combines relativity and quantum mechanics, the answer is: the present.
What’s the difference between the past and the future? Not a great
deal, if you take a purely relativistic view of the universe, say
George Ellis from the University of Cape Town in South Africa and
Tony Rothman from Princeton University in New Jersey.
The standard spacetime diagrams used in relativity accord no
special status to the past, the present or the future. That’s because
they assume that everything evolves from time-reversible local
physics.
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In fact, it is possible represent such a universe using a kind of
spacetime diagram in which space and time merge into a single entity. “The universe just
is: a fixed spacetime block,”say Ellis and Rothman. In this view,
no instant has any special status: “All past and future times
are equally present, and the present “now” is just one of an
infinite number.”
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This kind of “block universe” has indeed been studied by various
physicists in recent decades with limited impact.
Today, Ellis and Rothman introduce a significant new type of block
universe. They say the character of the block changes
dramatically when quantum mechanics is thrown into the mix. All of a
sudden, the past and the future take on entirely different
characteristics. The future is dominated by the weird laws of quantum
mechanics in which objects can exist in two places at the same time
and particles can be so deeply linked that they share the same
existence. By contrast, the past is dominated by the unflinching
certainty of classical mechanics.
What’s interesting is that the transition between these states
takes place largely in the present. It’s almost as if the past
crystallizes out of the future, in the instant we call the present.
Ellis and Rothman call this model the “crystallizing block
universe” and go on to explore some of its properties.
They point out, for example, that this crystallization process
doesn’t take place entirely in the present. In quantum mechanics the
past can sometimes be delayed, for example in delayed choice
experiments. This means the structure of the transition from future
to past is more complex than a cursory thought might suggest.
Ellis and Rothman suggest that their model provides a straightforward
solution to the problem of the origin of the arrow of time. “The
arrow of time arises simply because the future does not yet exist,”
they say.
That’s a thought-provoking but ultimately unconvincing model in its current form. But it’ll
be interesting to see whether Ellis and Rothman can conjure a little
more substance from the idea.
What it needs, of course, are some
testable predictions, things that cosmologists usually spend little time worrying about. Don’t hold your breath.
