Is time real, or is it just an illusion? In our latest video, we meet Jim Al-Khalili, physicist and author of On Time, at the Royal Observatory Greenwich, the home of the Prime Meridian, to explore one of the deepest mysteries in science.

From space-time at the heart of Albert Einstein’s theory of relativity to the arrow of time, entropy and the origins of the universe, Al-Khalili explains why physicists remain divided over the true nature of time.

Could the past, present and future all exist at once? And is time travel really possible? Join us for a mind-bending journey through one of physics’ greatest puzzles.

Ghostly particles called neutrinos pose some of the biggest mysteries of modern physics, but researchers thought they could get a handle on them by corralling them into a laser beam. Two new analyses show that neutrinos are more slippery than that, making the proposed neutrino laser design impossible.

Researchers have been studying neutrinos since the 1940s. They are among the most abundant particles in the universe, but much about them remains unknown. Notably, they are extremely light, mere ghosts compared with more massive particles like neutrons, yet their exact mass is unclear.Ěý

In 2025,  at the University of Manchester in the UK and  at the Massachusetts Institute of Technology (MIT) suggested a novel and surprising way to gain clarity –  using thousands of extremely cold radioactive atoms to create a laser beam of neutrinos.

, also at MIT, heard a lecture about the idea and immediately worried about it being too good to be true. He and his colleagues have now confirmed that hunch with two rigorous mathematical investigations.

Neutrinos are produced when radioactive atoms undergo nuclear decay. Jones and Formaggio theorised that if many such decaying atoms were pushed into a quantum phase of matter called a “Bose-Einstein condensate” (BEC), where they all share a quantum state, then their respective neutrino emissions would be amplified, forming a laser-like beam. Creating such a BEC would require making thousands of radioactive atoms extremely cold so they could behave quantumly, which is a big technical challenge.Ěý

But Ketterle, who received the Nobel prize for creating some of the first ever BECs in the 1990s, and his team uncovered a more fundamental obstacle.

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The key to the neutrino laser proposal was a memory effect: when an atom in the BEC emitted a neutrino, it would be more likely to continue emitting more neutrinos in the same direction, thus pushing them into a beam, because the quantum state that all the ultracold atoms share would retain a trace of that first emission. Ketterle and his colleagues showed that this memory, although present, would be about 10,000 billion times too brief to affect the neutrinos as intended. Even more troublingly, the team uncovered that the memory would actually have the opposite effect from that intended, which Ketterle calls an anti-memory.Ěý

“If I am an atom and I have emitted a neutrino, I am not allowed to [immediately] emit a neutrino again,” he says. This effect’s origin is subtle, stemming from neutrinos being a type of particle called fermions, which fundamentally behave differently than particles of light that our ideas about lasers tend to be built upon.Ěý

We’ve spotted the strongest microwave laser in the known universe

Colliding galaxies can create a beam of focused microwave radiation known as a maser, and astronomers have discovered the brightest one ever seen

“I think these papers sharpen where the real difficulty lies,” says  at Queen’s University in Canada. “For nuclear-scale energies [pertaining to atoms’ decay], these requirements become extraordinarily demanding.” 

He says the new analysis does not categorically rule out every possible way to build a neutrino laser, but shows that the most conventional scenario where each atom emits one neutrino cannot work. If each atom emitted two neutrinos at a time, the analysis may be different, he says. “I think the interesting scientific question now becomes more precise rather than disappearing: what kinds of nuclear or neutrino processes, if any, avoid the limitations they have identified?” says Leach. In his view, this question is most likely to be definitively answered through experiments.Ěý

Formaggio and Jones didn’t respond Â鶹´«Ă˝â€™s request for comment.

For Ketterle, the lesson of the neutrino laser that couldn’t be is that science can correct itself even when doing so means abandoning inspiring and creative ideas. Getting clarity required hours of discussion, including with Jones and Formaggio. But that is ultimately how physics ought to work, he says.

If I could go back in time and tell my younger self something about life as a theoretical physicist, I might say: mind the gap between what’s exciting about physics and what the job actually is. My new book, , was born in part out of thinking about the physical questions that get pushed to the margins in professional physics. Big-picture questions like, what is the material nature of space? What is a quantum theory of time? It is very difficult to build a professional life working on these questions – even as books tout them as the most exciting ones in the universe.

I was recruited into the world of physics by the Errol Morris documentary about Stephen Hawking, A Brief History of Time. Eventually, I read Hawking’s book of the same name and my impression of a working life in physics was that, for the most part, physicists think big thoughts about wonders of the universe every day.

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Today, I’m a tenured professor of physics at a major research institution, and a lot of my job is sending emails about bureaucratic things, like asking whether anyone can tell me the policy that is governing changes that the university is making to my grant. On a good day, I get to have conversations about science with the postdoctoral fellows I employ in my research group – but that’s not every day. And in either case, the kind of research that we can get grant funding to do is quite limited. The sort of work Hawking did on the nature of time is financially out of reach for most physicists, a situation that is getting worse as the UK and the US both slash and burn basic science budgets.

The Edge of Space-Time was born in this gap between what we say science is and the reality of living it. I began it at a moment of transition. I had just been awarded tenure, which, in the US, historically has meant my position is permanent, and I am free to research whatever interests me without worrying about being fired. At the moment my tenure became official, I was thinking about what I had given up to get there, the strategic choices I had made.

I gave up working on quantum gravity, for example, both because of racism I experienced as a PhD student and because the job prospects weren’t good. I never took a class where we were asked to think deeply about time, space and the fundamental nature of space-time. Mostly, I learned to calculate and pursue questions that were broadly agreeable to the physics community, like understanding the nature of dark matter. And while I think these questions are important and interesting, they live at a kind of margin that physicists are pushed to by economic and social forces that determine which questions we can be paid to pursue and which we won’t be.

When I began working on the book in 2023, I was in the midst of a five-year stint working in US science policy, alongside colleagues from around the world (mostly the UK, Europe and Canada). As I learned more about the politics of science at the government level, it became clear to me that particle physics and cosmology were in trouble. Politicians were no longer sold on the fundamental importance of our research and didn’t see how it was beneficial to the capitalist economy or the military, which historically is how that support has been rationalised. The cultural arguments – that a well-cultured civilisation does things like try to understand the universe – didn’t seem impactful at all. And the general public, struggling with climate change and economies that don’t serve the 99 per cent, couldn’t see how we had anything to add.

I could see that we were about to be on the margins in a new way. And so The Edge of Space-Time became not just a return to my roots and the big-picture questions that once drove me, it also became a plea: don’t let me be the last of my kind. The cuts that are being made to science in the UK and the US right now seem like a political problem that is easily remedied, but it is more complicated than that. Even one year where there is a gap in funding means we haemorrhage workers who may never return. As those researchers leave, they take with them knowledge. Because the sciences work through apprenticeship, if there is no senior instructor to pass on knowledge, it doesn’t matter if there is money and an apprentice waiting in the wings.

With The Edge of Space-Time, I take readers on a journey through huge questions, like why does my favourite physics experiment foist the structures of quantum physics on us? And will we ever know what space-time really is, or is it always just going to be a useful mathematical construct that allows us to calculate motion in environments where gravity plays a significant role, like near black holes?

While thinking through the physics, I also try to make the case for why any healthy democracy needs people who live at the edge of what is known and what is unknown – the keepers of these cosmic stories that have fascinated humans for millennia. I make the case that, like poetry, physics gives us a viewpoint on the universe that we need because it is our ancestral inheritance. I also argue that spending time with what feels strange about physics can help prepare us to better reckon with difficult political questions.

Given the crises we face – genocides, climate change, attacks on transgender people – we need our critical faculties now more than ever. Thinking a bit about the various edges of space-time, like black holes and cosmic event horizons, can help us build the better world we need.

by Chanda Prescod-Weinstein (Canongate Books) is the September read for the Â鶹´«Ă˝ Book Club. Sign up for the club here, and join the discussion on Discord .

When you make a purchase via the links on this page, we receive a commission.

sε wo werε fi na wosan kɔfa a, yεnkyi

it is not incorrect to go back and get what you forgot

—Akan proverb

We are called to go back and get the history of space-time. And who am I to argue with the ancestors?

Even so, I do. Science in this society is often done for the wrong rea­sons, I find myself telling them. And they remind me that because it’s my job to study the origin and evolution of the universe and every­thing inside it, I know there is a location in space-time where the uni­verse became transparent to light: the first place where light could fly free. The ancestors insist: This is a story that I have learned so I could tell it to others. To do cosmology—to study the beginning and evolu­tion of space, time, and matter—is to be a griot, a keeper of stories and history. To do cosmology is to go back and get the beginning, to map out the future.

So: Quite nearly at the beginning, the universe said let there be light. And particles of light—photons—all of them traveling at the speed of light, the fastest in the universe, couldn’t get very far. They were stuck in a plasma stew where they constantly bumped into par­ticles, especially electrons, which swallowed their energy and spat it out in the form of new photons and other particles.

Humanity has only been aware of this cosmic light for eighty-two years. It has been there almost since the beginning of everything and has been traveling for nearly 14 billion years. It was there when the universe was cool enough for atoms to form. It was with the sun when it was just a cloud of gas, and it was there when the sun’s hydrogen ignited with fusion, turning the sun into a star. It was there when the leftovers from the gas cloud condensed into planet Earth. And it was there when carbon-based life forms evolved into apes.

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This light is a cosmic edge: We cannot look past it because at any time earlier than that, the photons were trapped, unable to get out. And this edge is a reminder that physics is a way of gaining deep insight into the universe, one we can add to the variety of overlapping forms of knowing that we have long used. To understand this bound­ary, and how we have come to know about it, is to deepen our rela­tionship with ourselves and the universe around us in a very specific and beautiful way. We should embrace it, for ourselves, and for future generations, because it is our history—and who are we to argue with the ancestors?

…

The book you are reading is about the queer, poetic wonder that is our universe and what we gain when we look at it from the margins. It is my version of what historian Aimé Dafon Sègla calls cosmovi­sions, a response to the question of why we should bother trying to get beyond the edges of human knowledge about the physical universe. The Edge of Space-Time is part of a larger tradition that includes not just scientists but also artists. People like jazz percussionist, artist, and technologist Milford Graves, who used percussion, sound, and observations of praying mantises and plant growth to understand a phenomenon he termed “cosmic energy.” Graves, a maker working in a long tradition of Black artists, was not formally trained as a scien­tist, and “cosmic energy” sounds a little like mystic talk. But when I listened to him describe his ideas in the documentary Milford Graves Full Mantis, I heard a familiar sensibility about how matter is linked with and through space-time, a relationship that takes center stage in this book.

As a set of knowledges and techniques, physics provides a path­way toward answering the same questions Graves asked about the fundamental nature of our cosmos and the relationship between matter, energy, and space-time. It allows us to specify in great detail the relationship between photons and the plants in Graves’s garden which transformed the photons into living particles. It is another entry point to what plant biologist and Black feminist theorist of intersectionality in science Beronda L. Montgomery calls lessons from plants.

When it’s at its best, physics is a kind of poetry, a story about the cosmos that is made from metaphors—and a producer of metaphors in its own right. We often analyze the world through metaphor, and I believe that seeing the universe through the perspective offered by physics strengthens our ability to understand what work metaphors are doing on us and how we might wield them. It is in this sense that physics works on us like poetry: a perspective on the world that provides insights not available to us elsewhere. This helps us under­stand why we should bother with it. We should bother with physics because it is, in part, how we as a species learn to use our minds. We should learn and teach poetry, physics, algebra, and other abstract ideas because they train us to think in symbolic and figurative terms. The same goes for calculus and quantum mechanics. And if we can­not learn to think in and through the abstract and the symbolic, then we are pliable. We are sitting ducks for the fascists and authoritarians who will use us for their ends, and their ends are ultimately catastro­phe for the rest of us. That’s always been true, and it always will be.

In a world where genocides (plural) can be live-streamed and still continue unabated, it is hard to imagine that society could be oth­erwise when what is broken about it feels so total and, in the case of the families shattered and lives lost, so final. I don’t think cosmology by itself can save the world. Even so, I believe in the ways that people experience a connection to the cosmos as nourishing. And I believe in preparing for the better world that is coming.

This is an extract from by Chanda Prescod-Weinstein (Canongate Books), the September read for the Â鶹´«Ă˝ Book Club. Sign up for the club here, and join the discussion on Discord .

When you make a purchase via the links on this page, we receive a commission.