Assumptions about our place in the cosmos could be skewing our view of it, says ChrisClarkson

Read more: "Crunch time for physics: What's next?"

In all the directions we look, we see a cosmos that appears broadly the same. Since we arenowhere special, the same is probably true of everywhere else.

This is the sensible assumption known as the Copernican principle. But it is hard to confirm whataliens in faraway galaxies see. What if it is not true? Observations of supernovae at differentdistances convinced us that the universe's expansion is accelerating, and that dark energy mustexist. But thanks to light's finite speed, the further we look in space, the further back we look intime. Variation in space can be surprisingly easily confused with evolution over time. Darkenergy might conceivably be an illusion.

Imagine a spherical universe a bit like an onion, made of layers of different density. Gravity'scohesive force will hold back expansion in denser areas. If we are sitting in a central void with alow density and high expansion rate, and looking outwards in all directions to regions of higherdensity and slower expansion, this would look to us very like a universe whose expansion hasbeen accelerating in recent times.

Such a universe could be produced with a change in the inflationary conditions during the firstsplit second to produce areas of such colossal under-density. But it would violate the sacredCopernican principle: others less advantageously situated in the onion would see a distinctlyinhomogeneous cosmos.

The chance of 1 in a few million that we are at the centre of a void isn't that unlikely to anyonewho plays the lottery. But studying variations in the temperature of the cosmic microwavebackground around distant galaxy clusters allows us to "see" the universe from distant locationsand tell whether it is homogeneous or not – and the latest observations suggest it is.

A model that abandons the Copernican principle will need a lot of fine-tuning to fit reality, if itworks at all.

This article appeared in print under the headline "What's Next Ditch Copernicus"

Chris Clarkson is a cosmologist at the University of Cape Town, South Africa

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Physics crunch: Time to ditch Copernicus?

27 February 2013 by Chris ClarksonMagazine issue 2906. Subscribe and saveFor similar stories, visit the Cosmology Topic Guide

From issue 2906 of New Scientist magazine,page 43.

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