By Don Lincoln
Updated 1504 GMT (2304 HKT) May 14, 2017

(CNN)A recent astronomical observation of a "cold spot" in the universe is stirring the interest of scientists who are intrigued with an exciting and highly speculative theory that there may be more than one universe.

Now before you get incredibly excited about that prospect, I should caution that this particular explanation is a huge long shot and there are more prosaic possible explanations. The idea of multiple universes, or multiverses, is a highly speculative and contentious one, and many experts view it with a very jaundiced eye. (This includes me.)

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Ethan Siegel, Contributor

MAY 11, 2017

All scientific ideas, no matter how accepted or widespread they are, are susceptible to being overturned. For all the successes any idea may have, it only takes one experiment or observation to falsify it, invalidate it, or necessitate that it be revised. Beyond that, every scientific idea or model has a limitation to its range of validity: Newtonian mechanics breaks down close to the speed of light; General Relativity breaks down at singularities; evolution breaks down when you reach the origin of life. Even the Big Bang has its limitations, as there's only so far back we can extrapolate the hot, dense, expanding state that gave rise to what we see today. Since 1980, the leading idea for describing what came before it has been cosmic inflation, for many compelling reasons. But recently, a spate of public statements has shown a deeper controversy:

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Professor Andrei Linde is among the physicists responding to a recent media story taking aim at inflationary theory. Credit: L.A. Cicero

May 11, 2017 by Amy Adams

From the earliest human civilizations, people have looked to the heavens and pondered the origins of the stars and constellations above. Once, those stories involved gods and magical beings. Now, there's science, and a large research enterprise focused on understanding how the universe came to be.

Squarely in the center of this research enterprise is what's known as inflationary theory. It argues that the universe was born out of an unstable, energetic vacuum-like state then expanded dramatically, spinning off entire galaxies produced by quantum fluctuations. This theory was proposed in 1980 by Alan Guth, presently at MIT. A year later, this theory was improved and extended by Andrei Linde, Stanford professor of physics, who has spent a lifetime modifying and updating it as new data emerged.

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Figure 1: Both the LUX and PandaX-II experiments look for dark matter particles (𝜒) by sensing their interaction with xenon atoms. The detector in each experiment consists of a large tank of ultrapure liquid xenon (dark purple) topped with xenon gas (light purple). An interaction produces two light signals, one from photons, S1, and another, S2, from electrons when they drift into the gas. The signals are detected by photomultiplier tubes at the top and bottom of the tank (yellow cylinders). 

Jodi A. Cooley, Department of Physics, Southern Methodist University, 3215 Daniel Ave., Dallas, TX 75205, USA

January 11, 2017• Physics 10, 3

No dark matter particles have been observed by two of the world’s most sensitive direct-detection experiments, casting doubt on a favored dark matter model.

Over 80 years ago astronomers and astrophysicists began to inventory the amount of matter in the Universe. In doing so, they stumbled into an incredible discovery: the motion of stars within galaxies, and of galaxies within galaxy clusters, could not be explained by the gravitational tug of visible matter alone [1]. So to rectify the situation, they suggested the presence of a large amount of invisible, or “dark,” matter. We now know that dark matter makes up 84% of the matter in the Universe [2], but its composition—the type of particle or particles it’s made from—remains a mystery. Researchers have pursued a myriad of theoretical candidates, but none of these “suspects” have been apprehended. The lack of detection has helped better define the parameters, such as masses and interaction strengths, that could characterize the particles. For the most compelling dark matter candidate, WIMPs, the viable parameter space has recently become smaller with the announcement in September 2016 by the PandaX-II Collaboration [3] and now by the Large Underground Xenon (LUX) Collaboration [4] that a search for the particles has come up empty.

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New research confirms the role Type Ia supernovae, like G299, play in measuring universe expansion. Credit: NASA

New research by cosmologists at the University of Chicago and Wayne State University confirms the accuracy of Type Ia supernovae in measuring the pace at which the universe expands. The findings support a widely held theory that the expansion of the universe is accelerating and such acceleration is attributable to a mysterious force known as dark energy. The findings counter recent headlines that Type Ia supernova cannot be relied upon to measure the expansion of the universe.

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December 7, 2016

This map of dark matter in the Universe was obtained from data from the KiDS survey, using the VLT Survey Telescope at ESO’s Paranal Observatory in Chile. It reveals an expansive web of dense (light) and empty (dark) regions. This image is one out of five patches of the sky observed by KiDS. Here the invisible dark matter is seen rendered in pink, covering an area of sky around 420 times the size of the full moon. This image reconstruction was made by analysing the light collected from over three million distant galaxies more than 6 billion light-years away. The observed galaxy images were warped by the gravitational pull of dark matter as the light travelled through the Universe. Some small dark regions, with sharp boundaries, appear in this image. They are the locations of bright stars and other nearby objects that get in the way of the observations of more distant galaxies and are hence masked out in these maps as no weak-lensing signal can be measured in these areas. Credit: Kilo-Degree Survey Collaboration/H. Hildebrandt & B. Giblin/ESO

Analysis of a giant new galaxy survey, made with ESO's VLT Survey Telescope in Chile, suggests that dark matter may be less dense and more smoothly distributed throughout space than previously thought. An international team used data from the Kilo Degree Survey (KiDS) to study how the light from about 15 million distant galaxies was affected by the gravitational influence of matter on the largest scales in the Universe. The results appear to be in disagreement with earlier results from the Planck satellite.

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The newborn universe may have glowed with light beams moving much faster than they do today, according to a theory that overturns Einstein’s century-old claim that the speed of light is a constant.

João Magueijo, of Imperial College London, and Niayesh Afshordi, of the University of Waterloo in Canada, propose that light tore along at infinite speed at the birth of the universe when the temperature of the cosmos was a staggering ten thousand trillion trillion celsius.

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A new theory of gravity might explain the curious motions of stars in galaxies. Emergent gravity, as the new theory is called, predicts the exact same deviation of motions that is usually explained by invoking dark matter. Prof. Erik Verlinde, renowned expert in string theory at the University of Amsterdam and the Delta Institute for Theoretical Physics, published a new research paper today in which he expands his groundbreaking views on the nature of gravity.

In 2010, Erik Verlinde surprised the world with a completely new theory of gravity. According to Verlinde, gravity is not a fundamental force of nature, but an emergent phenomenon. In the same way that temperature arises from the movement of microscopic particles, gravity emerges from the changes of fundamental bits of information, stored in the very structure of spacetime.

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Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA)

The observable Universe contains about two trillion galaxies—more than ten times as many as previously estimated, according to the first significant revision of the count in two decades.

Since the mid-1990s, the working estimate for the number of galaxies in the Universe has been around 120 billion. That number was based largely on a 1996 study called Hubble Deep Field. Researchers pointed the Hubble Space Telescope at a small region of space for a total of ten days so that the long exposures would reveal extremely faint objects.

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X-ray: NASA/CXC/SAO; Optical: Detlef Hartmann; Infrared: NASA/JPL-Caltech
Data from galaxies such as M101, seen here, allow scientists to gauge the speed at which the universe is expanding.

Davide Castelvecchi
11 April 2016

The most precise measurement ever made of the current rate of expansion of the Universe has produced a value that appears incompatible with measurements of radiation left over from the Big Bang1. If the findings are confirmed by independent techniques, the laws of cosmology might have to be rewritten.

This might even mean that dark energy — the unknown force that is thought to be responsible for the observed acceleration of the expansion of the Universe — has increased in strength since the dawn of time.

“I think that there is something in the standard cosmological model that we don't understand,” says astrophysicist Adam Riess, a physicist at Johns Hopkins University in Baltimore, Maryland, who co-discovered dark energy in 1998 and led the latest study.

Kevork Abazajian, a cosmologist at the University of California, Irvine, who was not involved in the study, says that the results have the potential of “becoming transformational in cosmology”.

Uncertainty limits
In the accepted model of cosmology, the Universe evolves mostly through the competing action of dark matter and dark energy. Dark matter’s gravity tends to slow cosmic expansion, while dark energy pushes in the opposite direction and makes it accelerate. Earlier observations made by Riess and others suggest that dark energy’s strength has been constant throughout the history of the Universe.

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