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A New Explanation For Dark Energy: The Matter In Our Universe

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A New Explanation For Dark Energy: The Matter In Our Universe

Postby MrFredPFL » Fri Sep 01, 2017 9:29 pm

Story : https://www.forbes.com/sites/startswithabang/2017/09/01/dark-energy-may-arise-si





Since the expansion of the Universe was first found to accelerate nearly 20 years ago, scientists have yearned for a compelling, simple, and testable explanation. Yet as more and more data from experiments and observations has come in, the cause of this dark energy – the hypothesized cause of the acceleration – has been maddeningly elusive. While it's functionally equivalent to a "cosmological constant" (or the "energy inherent to space itself"), there's no good way to arrive at a prediction for its value. Yet if you consider that putting certain forms of matter in empty space changes the forces on that matter, perhaps dark energy arises from the simplest cause of all: the fact that our Universe contains matter at all.

Most of the forces and phenomena in the Universe have causes that can be easily uncovered. Two massive objects experience a gravitational force due to the fact that spacetime is curved by the presence of matter and energy. The Universe has expanded as it has over its history because of the changing energy density of the Universe and the initial expansion conditions. And all the particles in the Universe experience the interactions they do because of the known rules of quantum field theory and the exchange of vector bosons. From the smallest, subatomic particles to the largest scales of all, the same forces are at play, holding everything from protons to people to planets to galaxies together.

Even some of the more mysterious phenomena have underlying explanations that are well-understood. We don't know how there got to be more matter than antimatter in the Universe, but we know that the conditions we need for it – baryon number violation, out of equilibrium conditions and C and CP-violation – all exist. We don't know what the nature of dark matter is, but its generic properties, where it's located and how it clumps together is well-understood. And we don't know whether black holes preserve information or not, but we understand the final and initial states of these objects, as well as how they come to be and what happens to their event horizons over time.

But there's one thing we don't understand at all: dark energy. Sure, we can measure the acceleration of the Universe, and determine exactly what its magnitude is. But why do we have a Universe with a non-zero value for dark energy at all? Why should empty space, devoid of everything – no matter, no curvature, no radiation, no anything – have a positive, non-zero energy? Why should it cause the Universe itself to expand at an always-positive, never-reaching-towards-zero rate? And why should that amount of energy that it has be so unbelievably tiny, that it was completely unnoticeable for the first few billion years of the Universe's history, and only came to dominate the Universe around the time that Earth was being formed?







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