Decades ago, Albert Einstein developed a theory that space not only bends, but also twists. It turns out that this idea - dubbed teleparallel gravity theory - abandoned by the scientific community in favor of general relativity and quantum theory, could solve several of the major problems of cosmology that arise today. /strong>
Midway through his career, Albert Einstein became convinced that his grand theory of general relativity — which describes gravity not as a force, but as the manifestation of the curvature of spacetime — had missed something. Yes, the space warped and bent, but not as he originally thought. By taking into account the true twist of space, it was possible, he thought, to arrive at a grand unified theory of physics, the hypothetical "theory of everything".
The physicist, however, did not dwell further on this idea and so it fell into oblivion. But today, nearly a century later, some intractable astrophysical problems (such as dark matter and dark energy, among others) are causing scientists to question all previously established and accepted theories; perhaps the key to all these unexplained problems lies in another understanding of space. They could thus be led to reconsider the forgotten theory of Einstein.
It now appears that if space undergoes a torsion in addition to a curvature, many of the most complex problems in physics could well disappear.
According to physicist John Wheeler, Einstein's theory of relativity, developed in 1915, can be summed up in a few words:“Spacetime tells matter how to move; matter tells spacetime how to bend ". One way to mentally visualize this theory of relativity is to represent three-dimensional spacetime as a taut trampoline canvas deforming under the weight of objects placed on it:if the canvas is taut, an object lightweight will cause almost no deformation and will roll in a straight line; on the other hand, if we add a heavier object in the center, it will "sink" into the canvas, and the lighter object will tend to deflect towards this heavy object.
In other words, the presence of matter (mass) changes the geometry of space-time and this deformation in turn tells matter how to move. Another key element of general relativity is the principle of equivalence, according to which the effects of a gravitational field are locally identical to the effects of an acceleration of the observer's frame of reference (gravity and acceleration are indistinguishable).
Then, in the 1920s, Einstein and other theoretical physicists laid the foundations of quantum theory, which made it possible to describe the behavior of atoms and subatomic particles, their interactions, as well as certain properties of electromagnetic radiation. It follows from this theory that for a given particle, it is impossible to simultaneously know its exact position and velocity (this is the uncertainty principle) — an uncertainty that Einstein could not accept.
This is how he began to work on an alternative theory of electromagnetism. In general relativity, Einstein had discovered that using a 4D version of curvature to describe spacetime worked perfectly. His idea was to develop a new version of his theory using torsion and test whether this could explain both gravity and electromagnetism (the latter being governed by Maxwell's equations).
According to this new hypothesis, massive objects and charged objects would cause the spacetime under them to twist in slightly different ways:one giving rise to electromagnetism and the other to gravity. This theory, known as "teleparallel gravity", was published in 1928. Nevertheless, it ultimately failed to explain electromagnetism convincingly.
With general relativity and quantum theory gaining the full attention of the scientific community, interest in teleparallel gravity — which was meant to unify all the forces of nature — quickly waned. If general relativity and quantum theory continue to be confirmed on many occasions today, they cannot however provide a complete description of reality because they are mutually incompatible and are powerless in the face of certain enigmas of the Universe.
While general relativity supports the existence of black holes, it completely falls apart when it attempts to describe their singular cores. Likewise, it is impossible to describe gravity on such a subatomic scale where quantum mechanics dominates:on this scale, when gravity becomes both strong and short-range, general relativity no longer holds.
Nor can these theories explain the accelerating rate of expansion of the Universe. Only a hypothetical substance, dark energy, could provide a reliable solution. Also, the expansion rate itself, the Hubble constant, is problematic:the two methods used to measure it — from the cosmic microwave background and from younger stars — provide different results. /P>
Eventually, either the Universe contains mysterious substances that can explain everything, or gravity just doesn't work the way we thought it would. These days, physicists don't think teleparallel gravity can unify physics, but it could be an interesting candidate for a new theory of gravity, even better than general relativity.
Recently, however, theorists have begun to link teleparallel gravity to string theory — one of the approaches to quantum gravity, which says that all forces and energy in the Universe come from the vibrations of invisible strings. In their work, they showed how teleparallel gravity could be a consequence of string theory. This is an important idea, because string theory should be able to explain all the laws of physics, and if teleparallel gravity is a better version of general relativity and ultimately proves correct, then it would be possible to derive teleparallelism from the mathematics of string theory.
However, the latter is not yet considered an established theory and certain points are still subject to debate among scientists. But if we can one day improve this approach so that it provides a flawless description of the real world, perhaps we will reach the theory of everything that Einstein dreamed of.
