From ‘Cosmic dawn: the search for the primordial hydrogen signal’, Physics World, November 18, 2025:
The EDGES instrument is a dipole antenna, which resembles a ping-pong table with a gap in the middle. It is mounted on a large metal groundsheet, which is about 30 × 30 m. Its ground-breaking observation was made at a remote site in western Australia, far from radio frequency interference.
The “observation”:
Hydrogen is the most abundant element in the universe. As neutral hydrogen atoms change states, they can emit or absorb photons. This spectral transition, which can be stimulated by radiation, produces an emission or absorption radio wave signal with a wavelength of 21 cm. To find out what happened during that early universe, astronomers are searching for these 21 cm photons that were emitted by primordial hydrogen atoms. … In 2018 the [EDGES collaboration] hit the headlines when it claimed to have detected the global 21 cm signal (Nature 555 67).
It will always be fascinating that a setup as deceptively simple as this one enables Earthlings to acquire information from distant reaches of the cosmos — the cosmos!— and from a time called the cosmic dawn. This is to me one of the great achievements of science, in particular scientists’ ability to link some information to specific sources in definitive ways. When you learn more, you realise where the lines between what you do and don’t know lie, at increasing resolution; about how you can and can’t interpret knowledge; and how to acquire more knowledge of increasing quality. That’s how a simple setup, one that can be transported on a small truck on a small planet in one galaxy in some part of the universe, allows us to learn about the universe as a whole.
I’ve been awed by certain advances in materials science and quantum technologies for the same reason. A good example is nitrogen vacancy centres. Take four carbon atoms, link them together in a tetrahedral shape, make millions of copies of this ‘unit cell’, and you get diamond. If in some of the tetrahedra you replace one carbon atom with a nitrogen atom and dislodge one of the neighbouring carbon atoms, you get a nitrogen vacancy centre. And in this centre, thanks to the relative arrangement of atoms around it, the electrons have a quantum spin that’s extremely sensitive to magnetic fields. For added measure the centre responds with red light if you shine green light on it when the quantum spin is excited by a field. Et voila: you have a powerful magnetic field detector that’s already miniaturised and with a convenient optical readout. But how did physicists get here?
They did by starting off studying why diamonds are different colours. They found that when they took a clear, transparent diamond and hit it with high-energy electrons or neutrons in a particle accelerator, the diamond would turn green or bluish. Then when they heated the irradiated diamonds to 600º C, the green colour shifted into a pinkish purple or deep red. Just as scientists could interpret data collected by the ping-pong-table-sized antenna to possibly be radio waves from the early universe, scientists understood these tests to mean the carbon atoms in the diamond lattice could be knocked off and replaced with nitrogen atoms. In 1965, a South African researcher named L. du Preez found that when his team irradiated a diamond with nitrogen in it and heated it, the material seemed to emit radiation of 637 nm wavelength. In the 1970s, Gordon Davies and M.F. Hamer in the UK found that when they squeezed this diamond, the light it emitted split and shifted, proving the defect had a specific axis. Finally, in the 1990s, Jörg Wrachtrup and others found that these ‘defects’ had a magnetic property that could be controlled with microwaves and ‘read’ using laser light.
You learn something, you learn how to apply it to make a tool, use the tool to develop a technique, use the technique to detect something that you couldn’t before, use what you learn to hone the next tool, develop new techniques, and discover even more. Computer scientist Étienne Fortier-Dubois’s ‘Historical Tech Tree’ visualisation offers a captivating view of this knowledge loop through history. However, what it doesn’t depict, and what most histories of science and technology focused on the technic don’t depict, is crucial: the value of the knowledge loop is determined almost entirely by how it interacts with societies and vice versa.
As technologies mature, some discoveries seem to become almost inevitable but which ones do see the light of day depends on power. In a 1922 article in Political Science Quarterly, the sociologists William Ogburn and Dorothy Thomas described 148 major inventions and discoveries that two or more people had made independently, arguing that culture and technology actually co-evolve. Some famous examples from history include calculus (Isaac Newton and Gottfried Wilhelm Leibniz), evolution by natural selection (Charles Darwin and Alfred Russel Wallace), the discovery of oxygen (Carl Wilhelm Scheele, Joseph Priestley, and Antoine Lavoisier), and the telephone (Elisha Gray and Alexander Graham Bell). On the other hand, scientists worked out public-key cryptography inside Britain’s signals intelligence establishment in the early 1970s but remained officially unacknowledged for that until the government declassified it in 1997. Similarly and effective antiretroviral therapy for HIV existed by the mid-1990s but for years remained concentrated among richer countries and elites in practice because patent, pricing, and political pressure choked off generic competition and access.
Some of the most consequential technical systems were also incubated in secrecy and under pressure, showing that states and firms can concentrate talent and money in ways that a ‘republic of letters’ can’t — exemplified by the military-industrial complex in the post-war US — and still have the same outcomes. These settings have the same knowledge loop but the state has fenced it off from society at large, whether by classifying it or, as is often the case in India, by structurally weakening the means to access it. To use a different example: the American writer Charles Fort famously said, “A steam engine comes when it is steam engine time”. The more important question however is how “steam engine time” itself arises: when the corresponding supply chains, capital, geopolitical competition, profit, surveillance, and labour regulations, among other things, are in place.
(Aside: Fort’s comment also reveals a well-known problem with world-building in the sci-fi and fantasy genres of literature. The British writer M. John Harrison called it the “great clomping foot of nerdism”, an expression with which I’ve taken offence more than once, but over time I’ve come to discern a particular problem — one that this post allows me to articulate clearerly: if you world-build a world in which steam engines appear without the requisite social and cultural conditions, you’re not doing it right. That, for all its focus on the technic, would indeed be a great clomping foot.)
In order to facilitate such scientific and technological progress, then, a human society needs to get itself on and then stay on the path of learning, investing, researching, and maturing knowledge and technologies. It needs to facilitate that combination of availing scientists the freedom to ask questions and the resources to answer them, over and over — and it needs to develop the social, economic, and political conditions to apply the outcomes of that loop efficiently for the better of society, without entrenching existing inequities or creating new ones. The latter is very important because societies generally don’t stay on that path by consensus but by so using coercive instruments like budgets, patents, labour policing, and bargaining with other countries.
In the end a potent technique can be born in a cramped corner of human society — whether a lab or a monopoly — but culture matters most for whether it spreads, who controls it, who gets to benefit from it, and, eventually, what kind of change it leads to in turn. It’s difficult not to return to what now seems like the absurdity of the ping-pong-table-sized antenna bolted to a groundsheet in a quiet patch of Earth, a modest platform from which humans are trying piece back together a time when there were no planets, no eyes, no archives, just hydrogen and the universe’s first pinpricks of light. The achievement isn’t only that we can sense something so ancient but that we can justify that we’re hearing it, step by step, against noise as much as self-deception.
