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The Wall Street mantra “greed is good” could soon be adopted by cosmologists to explain the origins of dark energy, the mysterious entity that is speeding up the expansion of the Universe.

At a cosmology meeting last week in Cambridge, UK, attendants debated a controversial class of theories in which gravity is carried by a hypothetical ‘graviton’ particle that has a small, but still non-vanishing, mass. Such a particle would tend to gobble up vast amounts of energy from the fabric of space, enabling the Universe to expand at an accelerated, although not destructive, pace.

Since astronomers discovered in the late 1990s that the Universe's expansion is accelerating, researchers have struggled to explain not only the nature of the hypothetical entity — dubbed dark energy — that's causing the acceleration but also why the acceleration is so weak.

One of their best guesses is that dark energy is an inherent property of the vacuum of space. Particle physics predicts the existence of such vacuum energy, but also that it should be a whopping 10120 times larger than what is needed to explain the acceleration observed by astronomers. If dark energy were that large, the Universe would have been ripped apart long before stars and galaxies ever formed.

In 2010, Claudia de Rham, a cosmologist at Case Western Reserve University in Cleveland, Ohio, and her colleagues came up with the surprising suggestion that dark energy could be the vacuum energy if most of it were swallowed up by the hypothetical ‘graviton’ particle1, 2. Physicists generally believe that there should be elementary particles, called gravitons, that carry the force of gravity, just as similar particles are known to carry the other three fundamental forces of nature: electromagnetism; the weak nuclear force, which governs radioactivity; and the strong nuclear force, which glues subatomic particles together within nuclei.

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