The solution to one of the most profound and intractable mysteries of modern physics could be found in one of Albert Einstein's forgotten theories that the famous physicist abandoned almost a century ago.
Dark energy and dark matter are invisible theoretical substances that are thought to constitute 95 percent of the universe, but their existence is theorized only on the basis of the effects they seem to have on the normal matter we all know. Some of the most sophisticated and sensitive tools ever created by human beings have failed to detect any sign of this after almost 50 years of research.
As detailed in an article published this week a Astronomy and Astrophysics , a theory developed by Albert Einstein in 1918 and then abandoned may have held forever the key to the mystery of dark matter and dark energy. The Oxford astrophysicist James Farnes drew on this theory to elaborate a new theory that unifies dark matter and dark energy as a single "dark fluid" that permeates the universe.
This dark fluid, if any, has negative mass. Unlike normal matter, which has a positive gravitational charge or mass (which means it attracts other matter), negative mass could reject matter. In short, if you pushed an object that had a negative mass away from you, the object actually moved towards you rather than moving in the direction of the applied force, as in the case of ordinary matter. According to Farnes, the negative masses would be spread throughout the universe as a single substance in the form of dark fluid.
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"The result looks pretty good," Farnes said in an article about his theory in The Conversation. "Dark energy and dark matter can be unified into a single substance, with both effects simply being explained as a matter of positive mass that sails on a sea of negative masses."
The new theory of Farnes is at the same time elegant and intuitive. After all, as Farnes points out in his article, polarization – simply, things that exist in positive and negative forms – is a common property in the universe. There are positive and negative electrical charges, and even the information itself seems to be polarized as if it were one and zero. It would be strange, says Farnes, if such a fundamental property as the mass monopolized the positive charges.
The Farnes theory has its roots in a small note that Einstein did to himself in 1918 as he struggled to explain the cosmological constant – that Einstein used for the first time to describe the dynamics of the universe – in his equations for general relativity.
Einstein invoked the cosmological constant to explain how the universe could be static, which was widely accepted at the time, also taking into account the effects of gravity. Without this cosmological constant, Einstein realized, the gravitational force of the universe would have collapsed on itself. Basically, the cosmological constant was a term that functioned as a sort of anti-gravity. The problem for Einstein was to explain what consisted of this cosmological constant.
In the 1918 memo, Einstein described a modification of his general theory of relativity in which "empty space" assumes the role of gravitational negative masses that are distributed throughout the interstellar space, "the key phrase here is" negative mass ".
However, the following year, Einstein had adopted a different interpretation of the cosmological constant and this little note was lost in history. In 1931 Einstein removed the cosmological constant from his theory of general relativity entirely after Edward Hubble discovered that the universe was not static, but expanding.
This overwhelming observation led Einstein to describe his invocation of the cosmological constant as his "biggest mistake". Today, however, Einstein's cosmological constant is hardly considered a mistake by most physicists.
In fact, the cosmological constant is an integral part of the lambda-CDM model, the most accepted cosmological model of the universe. In this model of the universe the cosmological constant represents the dark energy, which is invoked to explain the accelerated expansion of the universe.
The lambda-CDM model also incorporates dark matter as a way to explain the observed galactic rotation. The gravitational influence on stars at the periphery of a galaxy is less than the gravitational influence on stars at the center of the galaxy, which suggests that stars on the periphery of the galaxy should rotate faster than internal stars. In fact, galaxies should fly away because of their own rotational force. Dark matter is theorized as the substance that keeps the galaxies intact and explains the observed rotational speed of the stars.
Yet in the last half century, dozens of experiments made to detect dark matter have come away empty handed.
In the case of dark matter, much of the problem is that physicists are not exactly sure what they are looking for as there are many prime candidates for dark matter particles. As for the dark energy, which is thought to be a property of the space itself, there are also several theories ranging from virtual particles that enter and leave existence to a type of field known as "quintessence". In both cases, physicists have no idea how to detect dark energy and can only place its existence based on the expansion of the universe.
There is, of course, the possibility that Einstein completely wronged gravity and that we have to completely abandon the concept of dark matter and dark energy. While some physicists have created alternative gravity theories that eliminate the need for dark matter, these are generally considered marginal in the scientific community. This is mainly due to the fact that they usually require an alteration of Einstein's general theory of relativity, which has been proven correct in every test launched in the last century.
Read more: Scientists observed a stellar orbit in a black hole and confirmed Einstein's theory of relativity
The new theory of Farnes is a radical departure, but if it is correct it would radically change our understanding of the universe.
So far, the first rudimentary models created by Farnes on the basis of his theory have been able to explain a handful of observed properties of the galactic rotation and the expansion of the universe that are normally attributed to dark matter and the dark energy. This is a promising start, but Farnes said more observational data will be needed from tools like the Square Kilometer Array to push his theory into the mainstream.
"Self [my model is] Really, it would suggest that the 95% missing of the cosmos had an aesthetic solution: we had forgotten to include a simple sign less ", concluded Farnes in the Conversation.