The following is an extract from our Lost in Space-Time newsletter. Each month, we dive into fascinating ideas from around the universe. You can sign up for Lost in Space-Time here.

My first encounter with invisible light came in my early years, and I thought it was magic. Radios filled every room of my childhood home: the kitchen, bedrooms, even the hallway. I would slowly turn the dial on older sets, listening as music and voices emerged from the static before fading away again as I surfed the radio waves. Long before I understood I was tuning into part of the electromagnetic spectrum, I felt the wonder of sensing something my eyes couldn’t see.

Human eyes evolved to detect only a narrow band of light – enough to navigate landscapes and recognise danger – but the universe shines across a vast spectrum stretching from gamma rays to radio waves. Different wavelengths of light interact with matter in different ways, meaning each reveals a different side of the world, and universe, around us. We encounter these properties constantly in everyday life. Microwaves, for example, are just the right energy to excite water molecules, perfect for the noble application of reheating last night’s leftovers. X-rays, meanwhile, have just enough energy to pass through soft tissue, but are absorbed by bone, allowing doctors to image our skeletons.

Radio light is the longest wavelength and lowest energy light in the electromagnetic spectrum, able to travel enormous distances largely unimpeded, and pass relatively easily through Earth’s atmosphere. This makes radio waves a powerful medium for communication on Earth, as I experienced as a child, but they are also an ideal messenger from the distant reaches of space and time. Years later, as my interests turned towards cosmology, it felt fitting that I would end up using radio telescopes to study the universe’s first stars and galaxies.

The electromagnetic spectrum as we know it today follows centuries of scientific discovery, as researchers gradually discovered that the universe extended far beyond the limits of human vision. It started with a rainbow in 1665, when Isaac Newton used glass prisms to show that white light could be split into a spectrum of colours, from red to violet. By 1800, astronomer William Herschel had discovered infrared light, again with a prism, by measuring the temperature of different colours of light and noticing that his thermometer ticked higher just beyond the red end of the spectrum. By the end of the 19th century, advances in electromagnetism and laboratory technology had revealed radio waves, microwaves, X-rays, and gamma rays, completing our modern view of the spectrum.

Invisible made visible

Optical astronomy is as ancient as civilisation itself, born from the simple fact that we arrive into this world already equipped to see sunlight or starlight. Other regions of the spectrum require additional tools: antennas and dishes for radio waves and microwaves, and specialised detectors for X-rays and infrared light. We can think of each of these subcategories as languages where, to understand the universe, we need the ability to translate to the optical light our eyes more naturally comprehend or, in the case of household radios, sounds our ears can appreciate. Only then are we rewarded with a complete cosmos of unseen messages and hidden histories.

We need the entire spectrum to fully illuminate the cosmos. UV light, for example, traces water plumes erupting from the surface of the smallest of Jupiter’s Galilean moons, Europa. The strong magnetic fields enveloping the giant planet interact with the atmosphere of the orbiting moon, generating aurora that shine brightly in the ultraviolet wavelengths. As water vapour from the plumes rises into the atmosphere, it temporarily alters the brightness of the aurora. Observing this allows astronomers to infer the presence and composition of the material erupting from the potentially habitable ocean below Europa’s icy surface.

And for the infrared, we have the James Webb Space Telescope (JWST), which sits 1.5 million kilometres from Earth, shielded from the sun by a sunshade the size of a tennis court. With the clearest and coldest view of the universe ever achieved, JWST has been rewriting what we thought we knew about the how the first stars and galaxies formed.

As the universe expands, light from the early galaxies is shifted into longer, infrared wavelengths – it moves towards the red end of the spectrum, so we say it is redshifted – which goes on to be adeptly captured by JWST. With a simple translation, labelling infrared wavelengths with optical colours as if completing a paint-by-numbers, we see galaxies just as they were just a few hundred million years after the big bang. Fascinating for sure, but there is a problem. A lot of these galaxies look more middle-aged then youthful – they are simply too big to be explained by star formation and galaxy evolution as we thought we understood it. How did they grow so fast?

To answer that question, astronomers are gathering older light that has been shifted into even longer wavelengths: radio waves that have travelled further, for even longer. Headquartered at Jodrell Bank Observatory in the UK, the Square Kilometre Array (SKA) will consist in part of over 100,000 antennas spread across the Western Australian outback into one enormous radio observatory, able to hear the faintest whispers from only a few tens of millions of years after the big bang. By detecting faint signals from the hydrogen gas that swirled around the primordial universe, the SKA aims to translate messages from the very first civilisation of stars and baby black holes. This is only one scientific application for the SKA, however. It will observe a multitude of celestial phenomena, mapping the furthest arms of the Milky Way, for example, and listening for signs of extraterrestrial intelligence.

The search for extraterrestrial life (SETI) is a research area which particularly fascinates me, because it beautifully demonstrates the complementary nature of observations at different wavelengths. With optical telescopes such as the Transiting Exoplanet Survey Satellite (TESS), we are cataloguing thousands of planets outside our solar system, by measuring the infinitesimal drop in brightness we observe when a planet passes in front of the star it orbits. Then, with infrared telescopes such as JWST, we can measure the composition of the exoplanetary atmosphere, and flag it as potentially habitable. Finally, with radio telescopes, we can target the shortlist of planets promising for hosting life and listen for extraterrestrial messages, whether an intentional greeting, or the unintentional leakage of radio communications like television broadcasts. After all, the laws of physics apply as much on exoplanets as they do on Earth, making radio the most obvious medium for communication. Perhaps one day, as we surf the radio waves from other star systems, an altogether alien voice will emerge from the static.

We are born fluent in only a single language of light, yet the universe is profoundly multilingual. The electromagnetic spectrum is a Rosetta Stone, allowing our telescopes to translate unseen stories written in invisible scripts. When read together, these stories allow us to tune into a universe far richer than the one our eyes alone can see.

Emma Chapman is an astrophysicist at the University of Nottingham, UK, and author of Radio Universe: How to Explore Space Without Leaving Earth (John Murray, 2026).

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