A new method may or may not solve the puzzle of what is accelerating the expansion of the universe
Amit Oren
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Cosmologists from Princeton University have announced a new method to understand why the universe is accelerating its expansion. The proposed technique will be able to determine whether the source of cosmic acceleration is a form of dark energy in the universe that is not yet known or is a sign of the collapse of Einstein's theory of general relativity on the vast scale of the universe. The result is presented today by the lead researcher, Dr. Mustafa Ishak-Boushaki, a research associate at Princeton University in New Jersey, before the meeting of the Canadian Astronomical Society in Montreal, Quebec.
"The increasing expansion of the universe relies on one of the most challenging and intriguing problems in astrophysics. Furthermore, it is linked to problems in many other subjects in physics. Our research work is focused on constraining different and possible reasons for this acceleration." says Dr. Ishak-Bushki.
Over the past eight years, several independent astronomical observations have demonstrated that the expansion of the universe has entered a phase of acceleration. The discovery of the acceleration came as a surprise to astrophysicists, who expected to measure a slowdown in expansion, caused by gravitational pull between matter in the universe."
In order to explain the cosmic acceleration, theoretical cosmologists presented the idea of the new energy component that would establish two-thirds of the total energy density in the universe and is gravitationally repulsive, not attractive. This component is called "dark energy."
Is dark energy real? "We don't know," comments Professor David Spergel of Princeton. "It could be a completely new form of energy or an observational stamp of a failure of Einstein's theory of general relativity. In any case, its existence will have a strong impact on our understanding of space and time. Our goal is to be able to differentiate between the two things."
The simplest argument for dark energy is the cosmological constant that Einstein introduced eighty years ago in order to complete his general theory of relativity with his preconceived notion that the universe is static. He was forced to retract the theory of the cosmological constant several years later, when the expansion of the universe was discovered. The discovery of cosmic acceleration revived the discussion about the cosmological constant in a new framework.
Another fundamentally different possibility is that the cosmic acceleration is a hallmark of a new gravitational theory that enters the very large scales of the universe, rather than a product of dark energy. Some of the recently proposed adapted gravitational models are influenced by superstring theory and multidimensional physics.
Can we differentiate between these two options? The proposed procedure shows that the answer is - yes. The general information is as follows: If the acceleration is due to dark energy, then the expansion history of the universe should be consistent with the rate at which galaxy clusters grow. These tracking deviations will mark the collapse of general relativity on very large scales of the universe. The proposed procedure implements this idea by comparing dark energy data from different cosmological research satellites and makes it possible to clearly identify any inconsistencies.
For example, a universe described by an adapted five-dimensional gravitational theory was taken into account in this study and it could be seen that the procedure could identify the signature of this theory. Importantly, it could be seen that future astronomical experiments could distinguish between adjusted gravitational theories and dark energy models.
The research work on the results presented was led by Dr. Mustafa Ishq Bushki in collaboration with Professor David Spergel, both from the Department of Astrophysical Sciences at Princeton University, and Amul Upadhye, a final year student in the Department of Physics at Princeton University.
Astrophysics connoisseur - the universe
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