Theoretical physics: The origins of space and time

Excerpt from nature.com
By

Zeeya Merali

Many researchers believe that physics will not be complete

until it can explain not just the behaviour of space and time, but where

these entities come from.

“Imagine waking up one day and realizing

that you actually live inside a computer game,” says Mark Van Raamsdonk,

describing what sounds like a pitch for a science-fiction film. But for

Van Raamsdonk, a physicist at the University of British Columbia in

Vancouver, Canada, this scenario is a way to think about reality. If it

is true, he says, “everything around us — the whole three-dimensional

physical world — is an illusion born from information encoded elsewhere,

on a two-dimensional chip”. That would make our Universe, with its

three spatial dimensions, a kind of hologram, projected from a substrate

that exists only in lower dimensions.

This

‘holographic principle’ is strange even by the usual standards of

theoretical physics. But Van Raamsdonk is one of a small band of

researchers who think that the usual ideas are not yet strange enough.

If nothing else, they say, neither of the two great pillars of modern

physics — general relativity, which describes gravity as a curvature of

space and time, and quantum mechanics, which governs the atomic realm —

gives any account for the existence of space and time. Neither does

string theory, which describes elementary threads of energy.

Van Raamsdonk and his colleagues are

convinced that physics will not be complete until it can explain how

space and time emerge from something more fundamental — a project that

will require concepts at least as audacious as holography. They argue

that such a radical reconceptualization of reality is the only way to

explain what happens when the infinitely dense ‘singularity’ at the core

of a black hole distorts the fabric of space-time beyond all

recognition, or how researchers can unify atomic-level quantum theory

and planet-level general relativity — a project that has resisted

theorists’ efforts for generations.

“All our

experiences tell us we shouldn’t have two dramatically different

conceptions of reality — there must be one huge overarching theory,”

says Abhay Ashtekar, a physicist at Pennsylvania State University in

University Park.

Finding that one huge theory is a daunting challenge. Here, Nature explores some promising lines of attack — as well as some of the emerging ideas about how to test these concepts…

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Theoretical physics: The origins of space and time