Dark energy a headache long before discovery

By Stuart Gary

December 10, 2012

A new review of century-old letters between two of the world’s leading physicists suggest dark energy was proving an headache well before it was discovered.

The study by Professor Alex Harvey of the City University of New York, examines comments made by Albert Einstein about a suggested change by Erwin Schrödinger to one of Einstein’s most famous equations.

In 1916, Einstein published his general theory of relativity to explan of how gravity is a consequence of the impact of mass on space-time.

Einstein like other scientists of his day believed the universe was unchanging and static.

However, general relativity predicts the universe would contract or expand depending on the strength of gravity, which depends on the amount of mass the universe contains.

So, in 1917, he introduced an additional factor that he called the ‘cosmological constant’ to counteract gravity and bring the universe back into equilibrium.

Several years later, George Lamaitre and Edwin Hubble discovered the universe was expanding. This caused Einstein to remove the constant, describing his failure to predict the expansion of the universe from his original equations as the biggest blunder of his life.

Published on the pre-press website ArXiv.org, Harvey, examined correspondence between 1918 and 1921 between Einstein and Schrodinger on the cosmological constant.

According to Harvey, Schrödinger suggested moving the cosmological constant to the other side of Einstein’s equation.

Harvey says Einstein’s reply asked whether Schrödinger was inferring the constant was something that changes with time.

“Moving the constant to the other side of the equation changed it to something which can vary,” says Harvey.

This change hinted at a force, rather than just a mathematical equation intended to counteract variability inferred by Einstein’s original theory.

‘Thicket of hypothesis

Einstein concluded saying, “The course taken by Herr Schrödinger does not appear possible to me because it leads too deeply into the thicket of hypotheses”.

Recent observations have found the universe is expanding at an accelerating rate, caused by a force known as dark energy, which hints that Einstein’s constant may change with time.

“Einstein’s concern about a thicket of hypotheses became real,” says Harvey.

According to Harvey, this shows Einstein describing both the central problem of the search for dark energy today and the headaches in formulating its structure.

Professor John Webb of the University of New South Wales says it’s a fascinating exchange of ideas.

“We really have no idea what dark energy is or even if it exists,” says Webb.

He says Einstein was describing quintessence, the possibility that negative energy density changes with time and isn’t constant throughout the universe.

“Schrodinger showed that Einstein’s cosmological constant allowed it to vary with time,” says Webb.

Why this occurs is a question that continues to confound scientists today.

“It’s absolutely astonishing that some 70 or 80 years ago these two scientists were holding a conversation about what is now the major problem facing astrophysicists today.”

Published by ABC.net.au