Constraining dark energy

One of the difficulties in understanding the origin of dark energy is that any one technique for probing the universe returns an answer that combines different pieces of information. Fortunately, certain techniques can be combined to give much more powerful answers. By plotting the equation-of-state parameter for dark energy, w, which measures the amount of "antigravity" pull that it has, against the amount of matter present today, Ω_M, which makes up the rest of the universe, we can see that current data from supernova surveys (blue band), the cosmic microwave background radiation (orange), and baryon acoustic oscillations (green) all give different angles on the nature of dark energy (the darker shades of each colour represent 68% confidence intervals and the lighter shades 95% and 99% confidence). By combining the results from all three probes together, we can focus in dramatically on the nature of the dark energy. This is shown by the small central dark region, which shows that dark energy is consistent with Einstein's cosmological constant given by w = –1.
Source: M Kowalski et al. 2007 Astrophys. J. submitted

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