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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]

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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Our Universe Could Be An Expanding Bubble in an Extra Dimension

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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.

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As Peter Woit, a theoretical mathematician at Columbia University says, string theory "is not even wrong" because it is not falsifiable -a basic tenet of all science theory. Now, Uppsala University researchers have devised yet another "new model" for the universe based on string theory - one with the added bonus they propose may solve the enigma of dark energy.

Their new article, published in Physical Review Letters, proposes a new structural concept, including dark energy, for a universe that rides on an expanding bubble in an additional dimension.

We have known for the past 20 years that the universe is expanding at an ever accelerating rate. The explanation is the "dark energy" that permeates it throughout, pushing it to expand. Understanding the nature of this dark energy is one of the paramount enigmas of fundamental physics.

It has long been hoped that string theory will provide the answer. According to string theory, all matter consists of tiny, vibrating "stringlike" entities. The theory also requires there to be more spatial dimensions than the three that are already part of everyday knowledge.

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For 15 years, there have been models in string theory that have been thought to give rise to dark energy. However, these have come in for increasingly harsh criticism, and several researchers are now asserting that none of the models proposed to date are workable.

In their article, the scientists propose a new model with dark energy and our universe riding on an expanding bubble in an extra dimension. The whole Universe is accommodated on the edge of this expanding bubble. All existing matter in the universe corresponds to the ends of strings that extend out into the extra dimension. The researchers also show that expanding bubbles of this kind can come into existence within the framework of string theory. It is conceivable that there are more bubbles than ours, corresponding to other universes.

The Uppsala scientists' model provides a new, different picture of the creation and future fate of the universe, while it may also pave the way for methods of testing string theory.

The Daily Galaxy via Uppsala University

Image credit: Suvendu Giri

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"The Bubble Universe" --A New Model of the Cosmos | The Daily Galaxy

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As Peter Woit, a theoretical mathematician at Columbia University says, string theory "is not even wrong" because it is not falsifiable -a basic tenet of all science theory. Now, Uppsala University researchers have devised yet another "new model" for the universe based on string theory - one with the added bonus they propose [...]