There is a fundamental problem in physics: A single number, called the cosmological constant, bridges the microscopic world of quantum mechanics and the macroscopic world of Einstein’s theory of general relativity. But neither theory can agree on its value.

In fact, there’s such a huge discrepancy between the observed value of this constant and what theory predicts that it is widely considered the worst prediction in the history of physics. Resolving the discrepancy may be the most important goal of theoretical physics this century.

Lucas Lombriser, an assistant professor of theoretical physics at the University of Geneva in Switzerland, has introduced a new way of evaluating Albert Einstein’s equations of gravity to find a value for the cosmological constant that closely matches its observed value. He published his method online in the Oct. 10 issue of the journal Physics Letters B.

How Einstein’s biggest blunder became dark energy

The story of the cosmological constant began more than a century ago when Einstein presented a set of equations, now known as the Einstein field equations, that became the framework of his theory of general relativity. The equations explain how matter and energy warp the fabric of space and time to create the force of gravity. At the time, both Einstein and astronomers agreed that the universe was fixed in size and that the overall space between galaxies did not change. However, when Einstein applied general relativity to the universe as a whole, his theory predicted an unstable universe that would either expand or contract. To force the universe to be static, Einstein tacked on the cosmological constant.

Nearly a decade later, another physicist, Edwin Hubble, discovered that our universe is not static, but expanding. The light from distant galaxies showed they were all moving away from each other. This revelation persuaded Einstein to abandon the cosmological constant from his field equations as it was no longer necessary to explain an expanding universe. Physics lore has it that Einstein later confessed that his introduction of the cosmological constant was perhaps his greatest blunder.

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