1. God Throws Dice.
Einstein was one of the founders of quantum mechanics. His explanation of the photoelectric effect showed that light itself is quantized, and it was this work that won him his Nobel in 1921 (He didn't get it for relativity, which was more controversial.) Yet as quantum mechanics developed, he refused to believe what became a central tenet: that all events could be described only in terms of probability. Einstein summarized this by his famous statement, "God does not throw dice." According to quantum mechanics, two absolutely identical radioactive atoms will probably decay at different times. Einstein believed that there must be something hidden inside the nucleus, a hidden variable that was different for the two. Very sensitive statistical tests performed by experimentalists have shown that he was wrong. There aren't any hidden variables, at least not the simple kind.
2. Hubble Trouble
When Einstein developed his theory of gravitation, usually called general relativity, he found a problem. The universe, which he thought was static, could not be static according to his equations. Instead of predicting that the universe was changing, he modified his equations to introduce a cosmological constant that would support his theory. When physicist Edwin Hubble discovered that the universe was not static but was expanding, Einstein called his cosmological constant "the greatest mistake of my life".
3. Constant Hassles
Einstein effectively abandoned his cosmological constant when he learned of Hubble's discoveries. Ironically, calling this a mistake made for the second greatest mistake of his life! In the late 1990s Saul Perlmutter and his group at Berkeley discovered that the cosmological constant was not zero but was causing the universe to accelerate. Their result was soon confirmed by another group. So, had Einstein stuck to his guns, he could have been given credit for predicting one of the great scientific findings of the last 10 years - the accelerating universe.
4. A Field Day with Field Theory
Einstein spent the latter decades of his life trying to find a unified field theory that would illuminate a connection between gravity and electricity. In 1920, when he was in his forties, he decided to devote his career to unifying the theories of gravity and electromagnetism. He was so far ahead of his time that his major effort in this problem was doomed to failure. Although his work is full of mathematical insights, Einstein passed away before realizing his error. In the late 1960s and early 1970s, physicists Steven Weinberg, Abdus Salam, and Sheldon Glashow (and others) finally succeeded where Einstein couldn't - in unifying electromagnetism with the weak force - not the gravitational force that Einstein had worked on. The weak force is the force that makes for most radioactivity. It wasn't even known at the time Einstein began his work, so he couldn't have guessed that he was unifying the wrong forces.
From mental_floss' book Condensed Knowledge: A deliciously Irreverent Guide to Feeling Smart Again, published in Neatorama with permission.
[Update 3/15/07: Original article written by Richard A. Muller, professor of physics at the University of California at Berkeley.]
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