Does our universe sit on a bubble
expanding into a higher dimension. A new physics theory says yes.
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Like a bit of froth on
the crest of an ocean wave, our observable universe may be nothing more than a
sliver sitting within the edge of a bubble that's constantly expanding into a
higher dimension.
While this mind-boggling
idea might sound like something out of a physicist's fever dream, it is in fact
a new endeavor to reconcile the mathematics of string theory with the reality
of dark energy,
a mysterious, all-pervading cosmic force that acts in opposition to gravity.
String theory is an
attempt to unite the two pillars of 20th century physics — quantum
mechanics and gravity — by positing that all particles are
one-dimensional strings whose vibrations determine properties such as mass and
charge. The theory has been described as mathematically beautiful, and for a
long time has been one of the leading contenders for what scientists call a
Theory of Everything, meaning a framework to explain all physics, popularized
in books like Brian Greene's
The Elegant Universe (Norton, 1999). [Big Bang to
Civilization: 10 Amazing Origin Events]
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But string theorists
have lately been lost in a warren of their own speculations. Many versions of
string theory require that reality consist of 10 or more
dimensions — the three of space and one of time we normally experience, plus
many others that are rolled up into an extremely tight point. Exactly how those
extra dimensions are configured determines the characteristics of the universe
we perceive.
In the early 2000s,
researchers realized that string theory allowed for as many as 10^500 (that's
the number 1 followed by 500 zeroes) unique universes to exist, creating a
multiverse landscape in which our particular universe was just a tiny
subsection, as Live Science
previously reported. But string theory equations also mostly
produced hypothetical universes lacking in dark energy, which astronomers
discovered in the 1990s and which is currently accelerating the expansion of
the cosmos.
Earlier this year,
researchers dealt a blow to string theory by suggesting that not a single one of
the nearly countless universes it describes actually contains dark energy as
we know it . "It is increasingly clear that the models proposed so far in
string theory to describe dark energy suffers from mathematical problems,"
Ulf Danielsson, co-author of a new paper published Dec. 27 in the journal Physical Review
Letters and a theoretical physicist at Uppsala University in
Sweden, told Live Science.
The basic problem,
Danielsson said, is that the equations governing string theory say that any
universe with our version of dark energy in it should quickly decay away and
vanish. "Our idea is to turn this problem into a virtue," he said.
Along with his
colleagues, he constructed a model in which the process causing these
dark-energy-permeated universes to decay actually drives the inflation of
bubbles made from many dimensions. We live within the boundary of one of these
expanding bubbles and "dark energy is … induced in a subtle way through
the interplay between the bubble walls on which we are living and the higher
dimensions," Danielsson wrote in a blog
post describing the new theory.
The Big Bang, when our
cosmos was born, then becomes the moment when this bubble began expanding, according to
Danielsson. Particles in our universe are simply the end points of
strings extending out into extra dimensions. Danielsson and his colleagues are
interested in checking if their model is compatible with other known aspects of
physics. And the hypothesis might serve to help physicists make observable
predictions about the early universe and black holes, Danielsson said. [Stephen
Hawking's Most Far-Out Ideas About Black Holes]
But other researchers
aren't buying it.
"This is a
math-fiction that has zero experimental evidence speaking for it," Sabine
Hossenfelder, a physicist at the Frankfurt Institute for Advanced Studies in
Germany, told Live Science.
Hossenfelder has been
critical of much of the latest pontificating in fundamental physics, and
published a book last year called Lost in Math: How Beauty Leads Physics Astray
(Basic Books, 2018). "String theorists propose a seemingly endless amount
of mathematical constructions that have no known relationship to
observation," she said.
But Danielsson does not
think that string theory will be forever untestable, and that the current
debates surrounding it are already providing some checks on the theory.
"If it turns out that string theory cannot yield dark energy of the kind
we observe, then string theory is not only tested, it is proven wrong," he
said.
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