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Cosmology’s Biggest Conundrum Is A Clue, Not A Controversy

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The expanding Universe, full of galaxies and the complex structure we observe today, arose from a smaller, hotter, denser, more uniform state. It took thousands of scientists working for hundreds of years for us to arrive at this picture, and yet the lack of a consensus on what the expansion rate actually is tells us that either something is dreadfully wrong, we have an unidentified error somewhere, or there’s a new scientific revolution just on the horizon. (C. FAUCHER-GIGUÈRE, A. LIDZ, AND L. HERNQUIST, SCIENCE 319, 5859 (47))

How fast is the Universe expanding? The results might be pointing to something incredible.

Ethan Siegel  May 10, 2019

If you want to know how something in the Universe works, all you need to do is figure out how some measurable quantity will give you the necessary information, go out and measure it, and draw your conclusions. Sure, there will be biases and errors, along with other confounding factors, and they might lead you astray if you’re not careful. The antidote for that? Make as many independent measurements as you can, using as many different techniques as you can, to determine those natural properties as robustly as possible.
If you’re doing everything right, every one of your methods will converge on the same answer, and there will be no ambiguity. If one measurement or technique is off, the others will point you in the right direction. But when we try to apply this technique to the expanding Universe, a puzzle arises: we get one of two answers, and they’re not compatible with each other. It’s cosmology’s biggest conundrum, and it might be just the clue we need to unlock the biggest mysteries about our existence.

 

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Dark energy survey finds eight more galactic neighbours

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The Dark Energy Survey has now mapped one-eighth of the full sky (red shaded region) using the Dark Energy Camera on the Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile (foreground). This map has led to the discovery of 17 dwarf galaxy candidates in the past six months (red dots), including eight new candidates just announced. Several of the candidates are in close proximity to the two largest dwarf galaxies orbiting the Milky Way, the Large and Small Magellanic Clouds, both of which are visible to the unaided eye. By comparison, the new stellar systems are so faint that they are difficult to “see” even in the deep DES images and can be more easily visualised using maps of the stellar density (inset). Fourteen of the dwarf galaxy candidates found in DES data are visible in this particular image. Illustration credit: Dark Energy Survey Collaboration.

 

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