In the dry, rarefied air of Chile’s Atacama Desert, nearly 17,000 feet above sea level, a remarkable machine opens windows into the deep past. The Atacama Cosmology Telescope (ACT), perched on the high plateau of Cerro Toco, has captured a breathtaking new image that reveals the universe as it was just 380,000 years after the Big Bang. This new portrait of cosmic infancy is not just a beautiful image; it is a scientific treasure trove, offering unprecedented insight into the birth, structure, and fate of the universe. In this article, we explore what makes this image special, how it was captured, and why it could reshape our understanding of cosmology.
Seeing the infant universe
The universe is about 13.8 billion years old, but for most of that vast timeline, direct observation has been limited. We can observe galaxies billions of light-years away, but truly seeing the early moments of cosmic history demands something more powerful than a regular optical telescope. Scientists turn instead to the cosmic microwave background (CMB), the oldest light in the universe, a faint afterglow from when the cosmos was just beginning to cool and form structures.
The CMB was first discovered in 1965, and successive generations of instruments, from COBE to WMAP to Planck, have mapped it with increasing precision. Yet ACT’s new image pushes the boundaries even further. It captures subtle variations in the temperature and polarization of the CMB, revealing the ripples and fluctuations that eventually grew into galaxies, stars, and planets, including our own.
Diagram by Lucy Reading Ikkanda, Simons Foundation
The power of the Atacama Cosmology Telescope
Why the Atacama Desert? The location is no accident. The desert’s extreme dryness and high altitude reduce atmospheric interference, allowing ACT’s sensitive instruments to detect the faintest microwave signals. The telescope itself is a six-meter dish, equipped with thousands of detectors cooled to just a fraction of a degree above absolute zero. This setup allows it to scan wide areas of the sky with incredible sensitivity.
Over the years of observation, ACT collected enormous amounts of data. Processing this information required sophisticated techniques, combining the efforts of an international collaboration of scientists. The result: the most detailed ground-based map of the CMB ever made. The new image released by the ACT team shows temperature differences of mere millionths of a degree. These tiny fluctuations are not random noise, they are the seeds of all cosmic structure.
Photo by Debra Kellner
What the image reveals
The ACT image doesn’t show stars or galaxies. Instead, it is a delicate patchwork of warmer and cooler spots, each representing slightly denser or thinner regions of the young universe. These differences were caused by quantum fluctuations during the earliest moments of the Big Bang, later stretched across the cosmos by cosmic inflation.
Crucially, the structure of the CMB encodes critical information about the universe’s fundamental properties:
- Age of the Universe: ACT’s measurements help confirm that the universe is about 13.8 billion years old, consistent with other observations.
- Shape of the Universe: The map shows that the universe is remarkably flat, supporting key predictions of inflation theory.
- Dark Matter and Dark Energy: The distribution of fluctuations gives scientists clues about the proportions of dark matter, dark energy, and ordinary matter.
- Expansion Rate: Interestingly, ACT’s data contribute to the ongoing debate over the Hubble constant, the rate at which the universe is expanding. Their measurements tend to align with the results from the Planck satellite, suggesting a slightly slower expansion rate than what other methods find by looking at nearby galaxies.
Image from ACT Collaboration
A triumph of technology and teamwork
Creating this map was no simple feat. For six years, ACT scanned nearly half the sky, capturing terabytes of raw data. The real challenge lay in separating the CMB from foreground noise: emissions from our galaxy, distant galaxies, and cosmic dust. Researchers employed sophisticated statistical techniques and machine learning algorithms to isolate the CMB’s signature. Each pixel in the final map represents painstaking effort, a balance of careful engineering, algorithmic wizardry, and sheer human perseverance.
The project is a collaboration among more than 160 scientists from 41 institutions across seven countries. Their work exemplifies the spirit of modern cosmology: it is a collective human endeavor, spanning continents and cultures, united by the desire to understand our cosmic origins.
What comes next?
Although the current ACT survey is complete, the story doesn’t end here. Scientists are continuing to analyze the data, looking for subtle patterns that might hint at new physics, such as primordial gravitational waves, signals from the earliest moments of cosmic inflation. Meanwhile, ACT’s successor is already in development. The Simons Observatory, currently under construction in the Atacama Desert, will feature even more powerful instruments and wider sky coverage. It promises to refine our picture of the CMB and delve deeper into the universe’s first few moments. And beyond that, the ambitious CMB-S4 project, an international collaboration aiming to deploy thousands of detectors across multiple sites, will push the boundaries even further, possibly reaching into physics realms we have only imagined.
Image from ACT Collaboration; ESA/Planck Collaboration
The Atacama Cosmology Telescope’s new image of the early universe is more than a scientific achievement, it’s a human triumph, born of curiosity, collaboration, and an insatiable desire to know our origins. By capturing this glimpse of cosmic infancy with unprecedented clarity, ACT has not only deepened our understanding of the cosmos but also opened new frontiers for future exploration. As we stand at the threshold of discoveries, guided by ancient light traveling billions of years to reach us, we are reminded of an essential truth: the universe’s past is not separate from our present. It is our story, written in the stars, and now, finally, within our grasp.
Clear skies!
