“Losing an illusion makes you wiser than finding a truth.” -Ludwig Borne

Every so often, an idea comes up in physics claiming that perhaps dark energy isn’t real. The ideas focus on one of two lines of thought: either they discount the observational evidence, or they attempt to show that all the calculations are fundamentally flawed.

Measuring back in time and distance (to the left of “today”) can inform how the Universe will evolve and accelerate/decelerate far into the future. We can learn that acceleration turned on about 7.8 billion years ago. Image credit: Saul Perlmutter / UC Berkeley.

The latter case often points to our Universe, and claim that our best models are based on a perfectly uniform Universe, while the actual Universe is very inhomogeneous. Yet these claims often forget one very, very important point: we know exactly how inhomogeneous the Universe is today, and those effects have been quantified. BY ME.

The contributions of inhomogeneity energy to cosmic expansion (top line), up to today (1 on the x-axis), and the fractional contribution to the expansion rate. Note that even into the far future, the contribution never approaches 1. The straight lines are linear approximations; the curves are the full calculation. Image credit: E.R. Siegel and J.N. Fry, 2005.

Dark energy is no illusion, and here’s the science to prove it!

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