PHYSICS BY ALI SIDDIQUI
Introduction Albert Einstein revolutionized the world of physics with his theory of general relativity, but even he was not completely satisfied with its implications. In order to explain how the universe kept from contracting due to the effects of gravity, he introduced a fudge factor that he called the “cosmological constant” (1). After the discoveries of Hubble and other scientists, however, Einstein retracted this constant since the universe was evidently expanding. The “cosmological constant” was later called his “biggest blunder” (2). More recent findings, however, call for a cosmological constant to explain the presence of dark energy (1). Perhaps Einstein’s fudge factor was not that great of a mistake, but rather a prelude to one of the most enduring puzzles of our universe.
Einstein’s Blunder In 1917, Einstein wanted to derive a cosmological model of the universe using his theory of general relativity. Wanting his model to reflect the beliefs held by him and the majority of the scientific community at the time, Einstein assumed that the universe was homogenous, that the universe was closed, having a set volume, and that the universe remained static, meaning that its inherent properties did not change over time (3). Taking all these assumptions into consideration, Einstein determined that the universe was either expanding or contracting (4), a conclusion that did not seem intuitive to him. To keep the universe static, he added an extra term to the equations of general relativity. This term was called the cosmological constant. This constant represented the vacuum energy density of space (5), which can be attributed to the presence of particles and antiparticles that are constantly made and destroyed through collisions, thereby giving energy to empty space (6). The cosmological constant exerts a negative pressure, if one considers the pressure of typical matter and gravitational attraction to be positive. In and of itself, the constant could take a negative, positive, or zero value (7). Each value has a different implication: a positive value would add a repulsive force to the gravitational forces already present in the universe, a negative value would add another attractive force alongside gravity, and a value of zero would have no effect on the original
The Cosmological Constant:
Einstein’s Greatest Mistake or Universe’s Greatest Mystery? Figure 1: Hubble used the Hooker Telescope to make his discoveries on redshifts and the expanding universe.
Image courtesy of Wikimedia Commons. Available at http://commons.wikimedia.org/wiki/File:100inchHooker.jpg
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