One of the most mysterious components of the entire universe is dark energy, which – if we’re honest with ourselves – was not supposed to exist. We had assumed, reasonably enough, that the Universe was an act of equilibrium, with the expansion of the Universe and the gravitational effects of everything in it battling against each other. If gravity had won, the Universe would remember; if the expansion wins, all will be forgotten. Yet when we made the critical observations in the 1990s and beyond, we found that not only is expansion winning, but the distant galaxies we see are moving away from us at increasing rates. faster over time. But is it really a new idea, or is it simply the resurrection of what Einstein once called his biggest mistake: the cosmological constant? This is the question of Boris Petrov, who asks: “It is Einstein’s cosmological constant [the same] how dark energy? Why, over time, has the term “dark energy” replaced the original term “cosmological constant”? Are the two terms the same or not, and why? Ok, so there are a lot of questions. Let’s go back to Einstein’s original idea, the cosmological constant, for better or for worse. You must remember that at the time when Einstein was working on a theory of gravity to replace and supplant Newton’s law of universal gravity, we still didn’t know much about the Universe. Of course, the science of astronomy was thousands of years old, and the telescope itself had been around for nearly three centuries. We had measured stars, comets, asteroids and nebulae; we had witnessed novae and supernovae; we had discovered variable stars and knew the atoms; and we had revealed some intriguing structures in the sky, such as spirals and ellipticals. But we didn’t know that these spirals and ellipticals were galaxies by themselves. In fact, it was only the second most popular idea; the thrust of the time was that they were entities – possibly forming protostars – contained in the Milky Way, which in turn comprised the entire universe. Einstein was looking for a theory of gravity that could be applied to everything that existed and that included the known Universe as a whole. The problem became evident when Einstein succeeded in formulating his theoretical gem: general relativity. Instead of being based on masses exerting infinitely fast forces on each other over infinite distances, Einstein’s conception was very different. First, because space and time were relative to each observer and not absolute, the theory had to provide identical predictions for all observers: what physicists call “relativistically invariant.” This meant that instead of separate notions of space and time, they had to be woven together into a four-dimensional fabric: space-time. And instead of propagating at infinite speeds, which – in Einstein’s theory – is equal to the speed of light.
- According to Forbes “Ask Ethan: Is Einstein’s Cosmological Constant Equal to Dark Energy?”
- “It is Einstein’s cosmological constant [the same] how dark energy? Why, over time, has the term “dark energy” replaced the original term “cosmological constant”? Are the two terms the same or not, and why? “
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