Shedding Light on Dark Energy
3:40 AM Edit This 0 Comments »What is the true nature of so-called ‘dark energy’, the mysterious force speculated to be accelerating the expansion of the universe? Is the amount of dark energy in any given space constant, or increasing with time? Or is there an even weirder solution to the accelerating universe problem that is being overlooked by cosmologists? The Dark Energy Survey (DES), a worldwide collaboration of institutions, including UCL, aims to uncover answers to these questions, and could reveal a little more on the final fate of the universe.
The phenomenal discovery in 1998 of the acceleration of the expanding universe by two independent teams of astronomers was revolutionary in that there was no element in modern physics that described such a process. Both teams discovered the light from a certain type of supernovae (an exploding star) in distant galaxies were stretched in such a way that could only be explained if the galaxies were accelerating away from us. The term dark energy was coined to explain the energy that provided this expansion, though many physicists believe that by modifying the theory of general relativity they can more aesthetically explain the acceleration. Others are rejecting the ‘cosmological principle’, which states that the universe is homogeneous (or the same in all directions) over incredibly large distances, to explain why our part of the universe seems to be running away with itself. Understanding if dark energy exists, and, if it does, in what manner, is perhaps the most fundamental problem of cosmology for this century.
The UCL Professor Ofer Lahav, an expert on the subject of dark energy, summed the ambiguity up perfectly when asked to explain the nature of dark energy: “The short answer is that we don’t know - there might not even be any dark energy, it could just be space curved in a funny way, mimicking dark energy.” The conventional theory of dark energy is to view it as the ‘cosmological constant’ in Einstein’s general theory of relativity - the solution to his equations that would enable a static (rather than expanding or contracting) universe. This solution turned out to be unworkable, and with the discovery of the expanding universe Einstein later called it the biggest blunder of his life. But in recent years the cosmological constant has come back, not least because it helps explain the reason for the accelerating universe.
The gravitational repulsiveness of dark energy is what’s thought to be causing the expansion of the universe to accelerate. If the concentration of dark energy in space is fixed, i.e. one litre of space always holds the same amount of dark energy, then as space keeps expanding the amount of dark energy keeps increasing. While the expansion of the universe is weakened by the gravitational influence of matter, due to the increased amount of space dark energy could eventually become dominant and thus accelerate the expansion of the universe.
All this depends on the repulsiveness of dark energy and how it changes with time: “And at the moment most of the observations are consistent with non-fluctuating dark energy”, according to Professor Lahav, “but not consistent enough. That is about to change.”
Professor Lahav and a group of physicists at University College London are one of the key players in the biggest ever survey of the universe, the Dark Energy Survey. The aim of the survey is to see whether the acceleration of the expansion of the universe changes with time and if it does, by how much. This would give scientists a better understanding regarding the nature of dark energy. The survey is unique in that is uses several different methods to measure the rate of expansion, such as determining the spatial distribution of galaxy clusters and looking at over 2000 supernovae. This could allow the survey to distinguish between other possibilities such as modified gravity, or large scale inhomogenity in the universe (in other words, saying that our local universe may be different from the ‘wider’ universe beyond our reaches).
The initial steps of the survey are underway and involve building a new generation of wide-field cameras, which will be able to take pictures of large areas of the sky simultaneously. The more supernovae that can be tracked down and measured the more consistently a value of the rate of expansion can be achieved. An incredible 500 million galaxies will be photographed during the survey. Currently Professor Lahav and the team at University College are working at the construction of the camera lens, which is scheduled to be operational in 2010. And Professor Lahav promises some provisional results on dark energy and its nature within two to three years after they’ve started, but the final results of the study are expected to be in 2015 – so dark energy will have to stay elusive from us for the time being.
The phenomenal discovery in 1998 of the acceleration of the expanding universe by two independent teams of astronomers was revolutionary in that there was no element in modern physics that described such a process. Both teams discovered the light from a certain type of supernovae (an exploding star) in distant galaxies were stretched in such a way that could only be explained if the galaxies were accelerating away from us. The term dark energy was coined to explain the energy that provided this expansion, though many physicists believe that by modifying the theory of general relativity they can more aesthetically explain the acceleration. Others are rejecting the ‘cosmological principle’, which states that the universe is homogeneous (or the same in all directions) over incredibly large distances, to explain why our part of the universe seems to be running away with itself. Understanding if dark energy exists, and, if it does, in what manner, is perhaps the most fundamental problem of cosmology for this century.
The UCL Professor Ofer Lahav, an expert on the subject of dark energy, summed the ambiguity up perfectly when asked to explain the nature of dark energy: “The short answer is that we don’t know - there might not even be any dark energy, it could just be space curved in a funny way, mimicking dark energy.” The conventional theory of dark energy is to view it as the ‘cosmological constant’ in Einstein’s general theory of relativity - the solution to his equations that would enable a static (rather than expanding or contracting) universe. This solution turned out to be unworkable, and with the discovery of the expanding universe Einstein later called it the biggest blunder of his life. But in recent years the cosmological constant has come back, not least because it helps explain the reason for the accelerating universe.
The gravitational repulsiveness of dark energy is what’s thought to be causing the expansion of the universe to accelerate. If the concentration of dark energy in space is fixed, i.e. one litre of space always holds the same amount of dark energy, then as space keeps expanding the amount of dark energy keeps increasing. While the expansion of the universe is weakened by the gravitational influence of matter, due to the increased amount of space dark energy could eventually become dominant and thus accelerate the expansion of the universe.
All this depends on the repulsiveness of dark energy and how it changes with time: “And at the moment most of the observations are consistent with non-fluctuating dark energy”, according to Professor Lahav, “but not consistent enough. That is about to change.”
Professor Lahav and a group of physicists at University College London are one of the key players in the biggest ever survey of the universe, the Dark Energy Survey. The aim of the survey is to see whether the acceleration of the expansion of the universe changes with time and if it does, by how much. This would give scientists a better understanding regarding the nature of dark energy. The survey is unique in that is uses several different methods to measure the rate of expansion, such as determining the spatial distribution of galaxy clusters and looking at over 2000 supernovae. This could allow the survey to distinguish between other possibilities such as modified gravity, or large scale inhomogenity in the universe (in other words, saying that our local universe may be different from the ‘wider’ universe beyond our reaches).
The initial steps of the survey are underway and involve building a new generation of wide-field cameras, which will be able to take pictures of large areas of the sky simultaneously. The more supernovae that can be tracked down and measured the more consistently a value of the rate of expansion can be achieved. An incredible 500 million galaxies will be photographed during the survey. Currently Professor Lahav and the team at University College are working at the construction of the camera lens, which is scheduled to be operational in 2010. And Professor Lahav promises some provisional results on dark energy and its nature within two to three years after they’ve started, but the final results of the study are expected to be in 2015 – so dark energy will have to stay elusive from us for the time being.
