Does Dark Energy Have Quantum Vacuum Roots?

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The mysterious dark energy that's driving the universe's accelerated expansion may have its roots in the background "vacuum energy" that pervades all of the cosmos, a new study suggests.

"What we think is happening is a dynamic effect of the quantum vacuum, a parameter that we can calculate," co-author Joan Sola, of the University of Barcelona in Spain, said in a statement. "Nothing is more 'full' than the quantum vacuum since it is full of fluctuations that contribute fundamentally to the values that we observe and measure."

New findings bolster the argument that dark energy is the reason our universe is expanding.
NASA/JPL/Hubble

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Though dark energy constitutes about 75 percent of the universe, scientists don't know exactly what it is. They've developed several different ideas, including the theory of "quintessence," which proposes a sort of anti-gravitating agent that repels rather than attracts. [The History & Structure of the Universe (Infographic)]

Another concept posits the existence of a "phantom field" whose density continues to increase with time. This theory predicts an accelerating expansion so powerful that it will eventually break apart the bonds that hold atoms together, tearing the universe apart in a "Big Rip" about 20 billion years from now.

The quintessence and phantom field hypotheses are based partly on data gathered by NASA's Wilkinson Microwave Anisotropy Probe (WMAP) and the European Space Agency's Planck satellite— spacecraft that have studied the cosmic microwave background, the ancient light that began saturating the universe 380,000 years after the Big Bang.

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In the new study, Sola and lead author Spyros Basilakos of the Academy of Athens in Greece analyze the same spacecraft observations and find less support for either quintessence or the phantom field idea.

"Our theoretical study demonstrates that the equation of the state of dark energy can simulate a quintessence field, or even a phantom field, without being one in reality," Sola said. "Thus, when we see these effects in the observations from WMAP, Planck and other instruments, what we are seeing is a mirage."

Basilakos and Sola instead suggest that dark energy is a type of dynamic quantum vacuum energy — something different than Einstein's cosmological constant, which describes a static vacuum energy density and is another possible explanation of dark energy's nature.

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Basilakos and Sola acknowledge there are some issues with the quantum vacuum energy theory but say it's a promising idea.

"However, quintessence and phantom fields are still more problematic; therefore the explanation based on the dynamic quantum vacuum could be the more simple and natural one," Sola said.

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