Hubble strengthens case for Dark Energy
Researchers using new data collected by the Hubble Space Telescope (HST) have refined our estimates of the rate at which the Universe is expanding to an uncertainty of only 3%. This new figure invalidates the idea that our region of space is situated in a vast unusually empty bubble, or void, which has up till now stood as an alternative to the Dark Energy hypothesis.
Albert Einstein recognised that the Universe could not be static, based on physics as he understood it, since there was nothing to hold it all up against its own gravity – eventually all the galaxies and stars should fall into each other. To try and explain why this had not happened, why we still in fact had a Universe, he added a term to his famous theory of relativity which he called the Universal Constant. The Universal Constant was a placeholder which would represent some as-yet undiscovered force that supports the Universe against its own weight. Shortly afterwards, astronomers like Edwin Hubble discovered something which would cause Einstein to discard his Universal Constant and describe at as his greatest blunder: They found that extremely distant objects were all uniformly moving away from us and that the further the object was, the faster it was receding. This could only be explained by an expanding Universe, and eventually led to the Big Bang theory.
In recent years, something astonishing was discovered: As astronomers worked to refine their measurements of the rate of expansion, they found that the rate was steadily increasing. Rather than slowing down, as both Newton and Einstein’s theories on gravity would suggest, the expansion is getting faster and faster. The term ‘Dark Energy’ was coined, as another placeholder to describe whatever force was pushing the Universe apart.
Scientists follow strict rules in their thinking, however, and one of these is Occam’s Razor. This rule requires a thinker to never waste time on the complicated difficult answers till the simpler ones have been tried and tested. In this case, scientists should not run around inventing entire new theories of physics when there could be a a quite ordinary explanation for this strange observation.
Of course, this does not mean that all solutions are simple, or that all complicated ideas are wrong, merely that simple ideas are easier to test and harder to get wrong. If the simple idea is wrong, you find out quickly, and if it’s correct then you haven’t wasted decades on a complex plan. In this case, the simple idea was that our region of space is situated in a vast bubble, unusually empty when compared to the rest of the Universe. Regions in the rest of the Universe would tend to be pulled slightly apart by the gravity of their neighbours, but ours would not. This would reduce the rate of expansion of our local space, and cause very distant regions to appear to be expanding faster than they should. Now as most people are aware, the speed of light travels at a fixed, limited speed, so that when we look very far away, we also look into the past. Distant objects appearing to expand more slowly than we expected would imply that the rate of expansion of the Universe was slower in the past. In other words, this idea suggests that the changing rate of expansion is simply an illusion, brought about by our assumption that the Universe is essentially the same (at a large scale) everywhere.
Albert Einstein recognised that the Universe could not be static, based on physics as he understood it, since there was nothing to hold it all up against its own gravity – eventually all the galaxies and stars should fall into each other. To try and explain why this had not happened, why we still in fact had a Universe, he added a term to his famous theory of relativity which he called the Universal Constant. The Universal Constant was a placeholder which would represent some as-yet undiscovered force that supports the Universe against its own weight. Shortly afterwards, astronomers like Edwin Hubble discovered something which would cause Einstein to discard his Universal Constant and describe at as his greatest blunder: They found that extremely distant objects were all uniformly moving away from us and that the further the object was, the faster it was receding. This could only be explained by an expanding Universe, and eventually led to the Big Bang theory.
In recent years, something astonishing was discovered: As astronomers worked to refine their measurements of the rate of expansion, they found that the rate was steadily increasing. Rather than slowing down, as both Newton and Einstein’s theories on gravity would suggest, the expansion is getting faster and faster. The term ‘Dark Energy’ was coined, as another placeholder to describe whatever force was pushing the Universe apart.
Scientists follow strict rules in their thinking, however, and one of these is Occam’s Razor. This rule requires a thinker to never waste time on the complicated difficult answers till the simpler ones have been tried and tested. In this case, scientists should not run around inventing entire new theories of physics when there could be a a quite ordinary explanation for this strange observation.
Of course, this does not mean that all solutions are simple, or that all complicated ideas are wrong, merely that simple ideas are easier to test and harder to get wrong. If the simple idea is wrong, you find out quickly, and if it’s correct then you haven’t wasted decades on a complex plan. In this case, the simple idea was that our region of space is situated in a vast bubble, unusually empty when compared to the rest of the Universe. Regions in the rest of the Universe would tend to be pulled slightly apart by the gravity of their neighbours, but ours would not. This would reduce the rate of expansion of our local space, and cause very distant regions to appear to be expanding faster than they should. Now as most people are aware, the speed of light travels at a fixed, limited speed, so that when we look very far away, we also look into the past. Distant objects appearing to expand more slowly than we expected would imply that the rate of expansion of the Universe was slower in the past. In other words, this idea suggests that the changing rate of expansion is simply an illusion, brought about by our assumption that the Universe is essentially the same (at a large scale) everywhere.
This relatively simple idea, when properly analysed, leads astronomers to specific rates of expansion that we should be able to observe. Previously, the error margins one our calculations were broad enough to include this idea. But the new work has narrowed the rate of expansion down to a much more precise figure. The predictions of the Void theory no longer match observations. As it stands, that theory is now proven wrong. Result: Dark Energy just took one step closer to being recognized as true. Which means that the Universe really is a very strange place that we still haven’t figured out yet.
For more information, read the official release here: http://hubblesite.org/newscenter/archive/releases/2011/08/full/