How long does light last?

Aug 15, 2025

Pascale Hibon, a staff astronomer at the European Southern Observatory in Chile, shares her expertise in studying distant celestial objects using the Very Large Telescope. The conversation reveals how light from these objects often journeys for billions of years, making Hibon a kind of time traveler. They discuss the nature of light, its dual wave-particle characteristics, and breakthroughs in telescope technology. The podcast also raises intriguing questions about the longevity of photons and their transformative journey across the universe.

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INSIGHT

Astronomy Is Time Travel

When we observe distant objects, we see them as they were when their light left them, not as they are now.
Pascale Hibon emphasises that looking further is equivalent to looking back in time.

INSIGHT

Oldest Light: The Cosmic Microwave Background

The oldest light we can observe is the cosmic microwave background from when the universe became transparent about 300,000 years after the Big Bang.
That radiation has travelled across the universe for ~13.8 billion years and is observable everywhere.

ANECDOTE

A Night Shift At The Very Large Telescope

Pascale Hibon describes working at the Very Large Telescope on Paranal, Chile, operating huge mirrors and observing distant galaxies and exoplanets.
She highlights the site's clear skies and the technical scale of nightly operations.

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When listener Rob from Devon, UK, heard of a newly detected planet light years away, he was struck by the sheer scale the light must travel to reach us here on Earth. It got him wondering: How long does light last? What’s the oldest light we’ve ever observed? And does light ever die?

To find out, presenter Anand Jagatia calls on some of the brightest minds in astronomy and physics.

Astronomer Matthew Middleton from the University of Southampton describes himself as “a kid in a sweet shop” when it comes to physics, and that enthusiasm comes in handy, because scientists still struggle to define exactly what light is. What we do know is that light comes in many forms, and choosing the right kind can peel back the cosmic curtain, revealing the universe’s deepest and darkest secrets. That knowledge will prove vital in Anand’s search for the oldest light ever observed.

At the European Southern Observatory in Chile, staff astronomer Pascale Hibon gives Anand a behind-the-scenes look at the Very Large Telescope, one of the most advanced optical instruments on Earth, perfectly placed under some of the clearest skies on the planet. Light from the objects Pascale studies has often travelled for billions of years, making her images snapshots of the distant past. In a sense, she’s pretty much a time traveller.

If light has crossed the vastness of the universe to reach us, it must be unimaginably ancient. But what will become of it in the far future? Could we trap it and preserve it forever?

“If we knew what light is, that might be an easier question to answer,” says Miles Padgett at the University of Glasgow, who has spent his career trying to pin it down. As Anand discovers, physics can be more philosophical than you might expect.

From redshifted galaxies at the edge of the observable universe to exotic materials that can slow light to walking pace, CrowdScience explores whether we can catch light, how it changes over time, and why truly understanding it remains one of physics’ most stubborn challenges.

Presenter: Anand Jagatia Producer: Harrison Lewis Editor: Ilan Goodman

(Image: An area of deep space with thousands of galaxies in various shapes and sizes on a black background. Most are circles or ovals, with a few spirals. More distant galaxies are smaller, down to being mere dots, while closer galaxies are larger and some appear to be glowing. Red and orange galaxies contain more dust or more stellar activity Credit:ESA/Webb, NASA & CSA, G. Östlin, P. G. Perez-Gonzalez, J. Melinder, the JADES Collaboration, M. Zamani (ESA/Webb))