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For decades cosmologists have wondered about the nature of dark energy, the proposed antigravitational force behind the accelerating expansion of the universe. Since the 1990s astronomers have observed that the universe is not only expanding, but also increasing its expansion rate. This is very strange, because the collective gravitational pull of all the “stuff” in the universe would be expected to eventually reverse cosmic expansion, or at least slow it down. Instead, just like a ball gently tossed overhead suddenly soaring off into the heavens, some mysterious force—the aforementioned “dark energy”—is pushing far-distant, galaxy-filled regions of space away from us at ever-greater speeds. No known physics has fully explained this phenomenon; it remains a cosmic enigma, and its true, as-yet-unknown nature will profoundly shape the ultimate fate of our universe.

Now, however, a new theoretical study, submitted for publication at the Journal for Cosmology and Astroparticle Physics, suggests dark energy’s apparent antigravitational properties may be the natural, inevitable consequence of how gravity works in the first place, at the universe’s most fundamental quantum scales. If eventually verified by further cosmological evidence, the idea would represent a major breakthrough in the long quest to mend the schism between physicists’ two most cherished theories: quantum mechanics, which describes the microscopic world of particles and fields, and general relativity, which describes the macroscopic cosmos of planets, stars and galaxies. General relativity posits that gravity is an emergent property of curves and warps in spacetime—the fabric of reality itself—but the theory loses its predictive power at quantum scales; conversely, quantum mechanics accurately incorporates all other known fundamental forces save for gravity, which fails to fit into the theory. Thus, many physicists suspect a quantum theory of gravity is the only way to unify these two opposing approaches..

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