Meet the CHIME Telescope
Nestled in the hills of British Columbia, Canada, the Canadian Hydrogen Intensity Mapping Experiment, or CHIME, looks more like a set of massive skateboard ramps than a typical telescope. It has no moving parts, no giant dish. Instead, its four 100-metre-long
metal half-pipes lie still, using the Earth's rotation to scan the entire northern sky each day. While CHIME has become famous for detecting hundreds of 'Fast Radio Bursts' (FRBs), its primary mission was always even more ambitious: to map the history of the universe's expansion. This latest discovery shows it can now do what it was built for, using a novel and cost-effective technique.
A Signal from the Universe's Youth
The signal CHIME detected is the collective glow of neutral hydrogen gas from a time when the universe was about five billion years old. This isn't a picture of a single galaxy but something much broader. The technique, known as 'intensity mapping', measures the combined radio emissions from vast regions of space. Think of it not as seeing individual trees, but as measuring the density of the forest. By capturing this faint radio light, which has a specific wavelength of 21 centimetres, scientists can create a three-dimensional map of how matter was distributed across the cosmos billions of years ago.
Why Is This Hydrogen Signal So Important?
Hydrogen is the most abundant element in the cosmos and the raw material for stars and galaxies. Its faint radio signal acts as a cosmic tracer, revealing the large-scale structure of the universe — the web of filaments and voids where matter has gathered over aeons. By mapping this structure at different points in cosmic history, scientists can measure how the universe has evolved. The key breakthrough here is that CHIME achieved this detection on its own, without having to cross-reference its findings with data from other, more expensive optical telescopes. This 'auto-correlation' proves the technique works and makes CHIME a powerful, independent tool for cosmology.
Connecting the Dots to Dark Energy
The ultimate goal is to understand dark energy, the mysterious force that makes up about 68% of the universe and is causing its expansion to accelerate. By creating a detailed history of cosmic expansion, scientists can test their theories about what dark energy is and how it behaves. For example, has its strength been constant, or has it changed over time? A changing strength could lead to vastly different futures for our universe, from a 'Big Rip' that tears everything apart to a 'Big Crunch' where gravity reasserts control. CHIME’s maps provide crucial data points in this history, helping to constrain the possibilities and home in on the nature of this enigmatic force.
A New, Cost-Effective Era for Cosmology
This achievement is a major milestone, proving that innovative, relatively low-cost instruments can tackle the biggest questions in physics. Traditional galaxy surveys that also probe dark energy can cost millions more and focus on smaller, denser regions of space. CHIME's intensity mapping approach allows it to survey much larger volumes of the universe, further back in time, at a fraction of the cost. The data used for this initial detection came from just 94 nights of observation in 2019. With years of data already archived and more being collected daily, the CHIME team is now poised to create even more detailed maps of the universe’s history, pushing further back to when the cosmos was only about three billion years old.
