Science Seen Time One author Colin Gillespie helps you understand the physics of your world.

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A New Reality Check for Relativity

This week we take a look at a new telescope. It is called CHIME. Its design is unconventional, using cylinder-shaped antennae rather than dishes. There are five of them. Each has a parabolic shape to focus the signal. Construction of the 10,000 sq. m. array is now underway. First operation is set for next year.CHIME image from Dunlap

CHIME is being built for a special mission. It will give us a new way to test the theory of relativity at very large scales. How far can we rely on relativity? In the case of special relativity (SR) we know that the answer is: Not very far. SR is just a local theory of motion in not too much space over short times, nowhere near masses that give rise to gravity. What of general relativity (GR)? It launched the modern (and still young) science of cosmology. It is now widely used to calculate events across the whole universe and back to times a fraction of a second after the Big Bang, almost fourteen billion years ago. But are GR calculations accurate at such scales or not—or could they maybe even be misleading?

Here’s how CHIME’s technology can give answers to such far-flung questions. It ‘sees’ radio waves emitted by the wisps of hydrogen gas that permeate deep space in distant galaxies. Though this gas is thinner than the best vacuum we can make on Earth, it amounts to almost nine-tenths of the visible matter in the universe. In other words, the gas has much more mass than do all the objects tracked by ordinary telescopes. And hydrogen emits a signature radio-wave signal. As the universe expands, the signal’s frequency becomes lower (it gets red-shifted as astronomers say). So by scanning for this signal over a range of frequencies CHIME can map the hydrogen gas across a significant percentage of the visible universe. Its map will have three dimensions where the distance dimension also corresponds to time. We know the gas has a vast pattern (called the baryon acoustic oscillation) imprinted on it. It’s as if it bears a map grid and scale bar. So the map of hydrogen gas density should show us how the expansion rate changed as the universe grew.

Unlike many astronomical surveys, which look either at nearby galaxies as they were in recent times or at very distant galaxies in the first few billion years of the universe’s lifetime, this survey is designed to scan the universe’s middle age. These are the years—from two and a half billion to seven billion years after the beginning—during which the universe’s expansion must have switched from slowing down (due to its own gravity) to speeding up (due to a mysterious antigravity effect known as Dark Energy). This speeding-up is a recent discovery; it was the subject of the 2011 Nobel Prize. CHIME’s central question is: Is the expansion and its speeding-up consistent with the rules of relativity? It’s our best shot yet at asking: Is GR real?

This question and CHIME’s answer have special relevance for me. In Time One I suggest that on the universe’s scale space does not conform to GR; and the speeding-up results from the creation of new space quanta in the highly-curved space found in big black holes. As American space physicist David Miller has observed, there is no need for mysterious Dark Energy in this universe.


[Unfortunately, it has not been kept not up to date] “CHIME: The Canadian Hydrogen Intensity Experiment”;

Image credit: Dunlap Institute for Astronomy and Astrophysics,

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