Even Albert Einstein had to say “beats me” at one point in his brilliant career. One-hundred years ago, the great physicist had developed his general relativity theory. Like most scientists back then, he thought the universe was static. But if so, gravity would cause all matter to smash together. Einstein’s solution was what he called the “cosmological constant,” designated by the Greek letter lambda. Something, he reasoned, must be holding back gravity. Lambda was a placeholder for that something.
Less than a decade later, Edwin Hubble discovered that the universe wasn’t static but expanding. That explained the counterforce to gravity. Einstein shook Hubble’s hand for saving him from “the greatest blunder of my life.”
There’s a footnote. Scientists now believe the universe isn’t just expanding; it is accelerating. What’s driving that? Scientists can’t quite say. “Dark energy” is their placeholder term. Ongoing experiments at the Laser Interferometer Gravitational-Wave Observatory might soon determine what dark energy is. It might be Einstein’s lambda in one form or another. Until then, it is science’s latest “beats me.”
-- John Yemma (Someone posted that on Facebook, I have not been able to find the original).
In 1917, Albert Einstein inserted a term called the cosmological constant into his theory of general relativity to force the equations to predict a stationary universe in keeping with physicists' thinking at the time. When it became clear that the universe wasn't actually static, but was expanding instead, Einstein abandoned the constant, calling it the '"biggest blunder" of his life.
In cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: Λ) is the value of the energy density of the vacuum of space. It was originally introduced by Albert Einstein in 1917 as an addition to his theory of general relativity to "hold back gravity" and achieve a static universe, which was the accepted view at the time. Einstein abandoned the concept after Hubble's 1929 discovery that all galaxies outside the Local Group (the group that contains the Milky Way Galaxy) are moving away from each other, implying an overall expanding universe. From 1929 until the early 1990s, most cosmology researchers assumed the cosmological constant to be zero.
--Now consider Albert Einstein - not the wild-haired, elderly, absent-minded professor he became in his later years but a young, dashing scientist in his 30s. It's 1916, and he's just published his revolutionary general theory of relativity. It's not necessary to understand the theory (thank goodness). You just have to accept that it gave scientists the mathematical tools they needed to forge a better understanding of the cosmos than they'd ever had.
There was just one problem. Relativity told physicists that the universe was restless. It couldn't just sit there. It either had to be expanding or contracting. But astronomers looked, and as far as they could tell, it was doing neither. The lump of dough wasn't rising, and it wasn't shrinking.
The only way that was possible, Einstein realized, was if some mysterious force was propping up the universe, a sort of antigravity that pushed outward just hard enough to balance the gravity that was trying to pull it inward. Einstein hated this idea. An extra force meant he had to tinker with the equations of general relativity, but the equations seemed so perfect just as they were. Changing them in any way would tarnish their mathematical beauty.
Einstein did it anyway. The universe ought to behave according to the laws he had set out, but it simply wasn't cooperating. The "cosmological constant" - his name for the new antigravity force - became part of the theory.
Then, a decade or so later, the great astronomer Edwin Hubble went up to the Mount Wilson Observatory above Pasadena and used the world's most powerful telescope to peer deeper into the universe than anyone had before. Making excruciatingly careful measurements of the galaxies he could see beyond the Milky Way, Hubble was astonished to learn that they weren't stationary at all. The galaxies - the raisins in the bread dough - were in motion, each moving apart from the other. The dough was rising in all directions, and the raisins were going along for the ride.
This discovery ultimately lead to the Big Bang theory, which says that the cosmos was once tiny, with all matter packed tightly together, and that it's been expanding every since. When Hubble first announced his results, however, Einstein was more concerned with its consequences for general relativity. If the universe was expanding, the cosmological constant wasn't needed. His beautiful equations had been right to begin with. In 1931, Einstein came to Mount Wilson to shake Hubble's hand and thank him for saving relativity from the cosmological constant, whose invention Einstein denounced as "the greatest blunder of my life."
Read more at: https://phys.org/news/2011-10-einstein-wrong.html#jC