The Big Bang was named on the radio by an astronomer who rejected it

Everything here earned its place by changing an outcome. Nothing about the naming of the Big Bang is included to round the number up.

The broadcast

In the late 1940s an astronomer giving a series of radio talks needed a vivid phrase for the model that begins with a hot dense state, and used the words big bang. He was at the time the most prominent defender of the steady-state alternative, in which matter is created continuously and the universe has no beginning at all.

It is often said that he coined the phrase as mockery, and he later denied this, insisting that he wanted a striking image for a general audience. Both readings are still repeated, and the honest position is that a broadcaster reaching for a memorable phrase is not obliged to have only one motive. What is not in doubt is that the name entered general use through a talk given by somebody who thought the theory was wrong.

What the words make you picture

A bang suggests a detonation happening at a particular place, with debris flying outwards into surrounding space that was already sitting there empty. Every part of that picture is misleading, because the model describes space itself expanding rather than material travelling outward through space. There is no centre to point at and no edge to stand outside, and the expansion looks much the same from any galaxy you care to sit on.

Tested properly, the early dense state was not localised somewhere far away, so it happened at the location of your kitchen exactly as much as anywhere else. A name that suggests a firework has to be undone in the first ten minutes of every introductory lecture on the subject.

What the theory actually claims

The model says the universe was once far hotter and denser than it is now, and that it has been expanding and cooling ever since. It does not claim to describe an origin from nothing, and the earliest instants sit outside what current physics can describe with any confidence.

Somewhere in the retelling, extrapolating the equations backwards eventually produces conditions where the theory itself breaks down, which is a statement about the theory rather than about the universe. Popular accounts that begin at a single mathematical point are describing where the equations stop working, not reporting an event that anyone observed. The scientifically interesting claim is the hot dense past, which is testable, rather than the moment of creation, which is not.

Why it was accepted

Light from distant galaxies is systematically shifted towards the red end of the spectrum, and the size of the shift increases with distance in a regular way. The relative abundances of the lightest elements match what a hot early phase would have produced, and are difficult to account for by any other route.

A faint radiation filling the sky in every direction was detected in the 1960s, and its properties fit the leftover glow of a hot early universe closely. That detection is generally treated as the point at which the steady-state model lost its remaining support, including from several of its own advocates. The case rests on a convergence of independent lines rather than any single decisive measurement, which is the usual shape of a well-supported theory.

The attempt to rename it

In the early 1990s an astronomy magazine ran a public competition to find a better name, drawing thousands of entries from many countries. The judges declined to select a winner, concluding that nothing submitted was an improvement on the phrase that everybody already used. This is a common outcome, because an established name does not have to be accurate in order to be useful, only unambiguous.

The same is true of terms like electric current and atomic weight, both of which carry pictures that stopped being correct a very long time ago. Once a word appears in every textbook index, replacing it costs considerably more than the confusion it was causing.

Why bad names survive

A term coined by an opponent becomes neutral through sheer use, and whatever sting it carried drains away within a generation. The picture a name suggests is stickiest for people meeting a subject for the first time, which is exactly when it does the most damage. Teachers compensate by spending time explaining what the name does not mean, a cost paid every year in every classroom that covers the topic.

The theory has never depended on the name, and would have identical support today if the phrase had never been broadcast at all. It remains a pleasing detail that the most famous term in cosmology was supplied, live on air, by the man arguing against it.

Everything above, in order of what to do first

1. The broadcast. In the late 1940s an astronomer giving a series of radio talks needed a vivid phrase for the model that begins with a hot dense state, and used the words big bang.
2. What the words make you picture. A bang suggests a detonation happening at a particular place, with debris flying outwards into surrounding space that was already sitting there empty.
3. What the theory actually claims. The model says the universe was once far hotter and denser than it is now, and that it has been expanding and cooling ever since.
4. Why it was accepted. Light from distant galaxies is systematically shifted towards the red end of the spectrum, and the size of the shift increases with distance in a regular way.
5. The attempt to rename it. In the early 1990s an astronomy magazine ran a public competition to find a better name, drawing thousands of entries from many countries.
6. Why bad names survive. A term coined by an opponent becomes neutral through sheer use, and whatever sting it carried drains away within a generation.

The takeaway

The best-known phrase in cosmology was supplied on air, for a general audience, by the man who thought the theory was wrong.

Believing it was ordinary. Continuing to is the avoidable part.