Einstein and Eddington


Einstein and Eddington is a 90 minute drama written by Peter Moffat, co-produced by BBC and HBO and first broadcast on BBC2 at . It was available on BBC iPlayer until .

The drama stars David Tennant as Arthur Stanley Eddington and Andy Serkis as Albert Einstein. It purports to cover the discovery by Einstein of the general theory of relativity, and the confirmation of the theory by Eddington’s observation of the gravitational deflection of starlight, while touching on the personal lives of the two scientists, both pacifists, during World War I.

The book I most recently reviewed (Incandescence by Greg Egan) was also concerned with general relativity, and it’s interesting to compare the approaches of the two works. Egan treats general relativity as a fact of the universe, unconnected to its human discovers, interesting for its own mathematical complexity, and discoverable by anyone able to make enough careful observations. Moffat treats general relativity as a McGuffin, uninteresting except for the opportunity it provides to look at the lives of the people who were involved in its discovery and confirmation.

Moffat’s lack of interest in the science made it a really frustrating programme to watch. The discovery and confirmation of general relativity ought to make a compelling story if told without distortion, or so it seems to me. But the script kept distorting facts, reordering events, getting distracted by other issues, reaching for the most sentimental effect, and often reaching too far and spoiling it.

Part of the problem is that the story tries to cover far too much ground. In addition to the main subject, Moffat tries to cover the split between Albert and Mileva Einstein, the romance between Albert and Elsa Einstein, Eddington’s repressed homosexuality, Quaker faith and pacifism, the treatment of Germans in the UK during World War I, scientific conduct during the war, the development of poison gas, the deaths of Raymond Lodge in 1915 (son of physicist Oliver Lodge) and Karl Planck (son of physicist Max Planck) in 1916, and so on. The wide range of subjects and the short time available results in some execrable infodumps, for example:

INT. Prussian Academy of Sciences, Berlin, 1914


Ah, Fritz Haber, you know of course.


Fritz Haber!


Einstein. Einstein and Haber shake hands.


You look a little, well, less Jewish than last time I saw you.


Well, a Christian now in a Christian country, I renounced my Jewish faith.


So what are you working on?








What about it?


Its conversion into nitrate.




What use is science if it has no practical application?


We should go, we’re late.

This is preparing us for Fritz Haber’s development of poison gases (notably chlorine) and his overseeing their use at Ypres in 1915. But the clumsiness is evidence of an overstretched plot. Indeed, Fritz Haber’s own tragic and horrible story probably deserves a dedicated drama of its own (Haber’s wife, the chemist Clara Immerwahr, killed herself in 1915, possibly in protest at his military work).

The second major problem is that the script several times reaches just a bit too far in search of an emotional effect, with the obvious fabrication ruining it. For example, in the drama the Cambridgeshire Regiment is wiped out in a chlorine gas attack at Ypres, thus making Eddington’s love interest William Marston a direct victim of Fritz Haber’s gas warfare. But in the real world, although the 1st battalion of the Cambridgeshire Regiment was present at Ypres in 1915, I’m pretty sure they weren’t wiped out by chlorine gas in the manner suggested by the drama (they were attached to the British 27th division, which was holding the southern flank of the Ypres salient, whereas the gas attacks were further north).

Similarly, in Moffat’s version of events, in about 1914 Eddington reads a paper by Einstein and has the insight that the anomalous precession of the perihelion of Mercury might be a problem that Einstein could work on. He writes to Einstein, who is inspired to complete his work on general relativity. In the real world, Einstein completed his general theory largely independently and published it in his 1915 paper “The field equations of gravity”; the problem of Mercury had been well-known since the mid-19th century and Einstein had no need of Eddington to bring it to his attention; in fact Einstein noted in his 1916 paper “The foundation of the general theory of relativity” that the problem would be a test of the theory. Because of the war, the English scientific community was unaware of these developments until Dutch physicist Willem de Sitter wrote to Eddington in 1917.

This distortion suggests to me that Moffat was not satisfied with the dramatic potential of the story he was telling: he has to put a cherry on top by giving Eddington a crucial link in the discovery of the general theory as well as in its confirmation.

The third problem is a persistent confusion over what general relativity actually is. Whenever anyone says something with some actual physical content, either it’s wordy nonsense (“Einstein says that time is not the same for all of us but different for each one of us.”), or it makes some sense but is clearly about special relativity (“[Einstein is] suggesting that time is at different speeds in the universe, depending on how fast you are moving. The faster you move, the more time slows down.”).

When the drama comes to the central issue of the gravitational deflection of light, it completely botches the science. Here’s Moffat’s Eddington:

If these stars on this photographic plate of the eclipse overlap with the comparison plate, Einstein’s theory is wrong and Newton’s theory holds. If there is a gap between the two images, then the sun’s gravitational field has shifted the stars’ position, and we have a new theory of gravity.

Compare this with Eddington’s actual words, from the very clear introduction to his 1920 paper with Frank Dyson and C. R. Davidson “A determination of the deflection of light by the sun’s gravitational field, from observations made at the total eclipse of May 29, 1919”:

The purpose of the expeditions was to determine what effect, if any, is produced by a gravitational field on the path of a ray of light traversing it. Apart from possible surprises, there appeared to be three alternatives, which it was especially desired to discriminate between—

  1. The path is uninfluenced by gravitation.

  2. The energy or mass of light is subject to gravitation in the same way as ordinary matter. If the law of gravitation is strictly the Newtonian law, this leads to an apparent displacement of a star close to the sun’s limb amounting to 0″.87 outwards.

  3. The course of a ray of light is in accordance with Einstein’s generalised relativity theory. This leads to an apparent displacement of a star at the limb amounting to 1″.75 outwards.

In either of the last two cases the displacement is inversely proportional to the distance of the star from the sun’s centre, the displacement under (3) being just double the displacement under (2).

In other words, the programme has completely obscured the crucial point that the question wasn’t just about whether there is a deflection, but exactly how big the deflection is. How many people will come away from the drama with the idea that according to the Newtonian theory of gravity, light is not deflected?

In real life, the question of the deflection of light was settled by the 1920 paper by Eddington, Dyson, and Davidson. On television, publishing a paper is not dramatic enough, so Moffat has Eddington resolve to make the definitive comparison in front of an audience, on the stage of the Royal Society. He aligns the eclipse plate and the comparison plate, places his eye to a microscope, and adjusts the focus. As the two plates come into simultaneous focus it is clear that the stars on the eclipse plate are displaced outwards. “A gap,” intones Eddington. “Einstein!”

This raises so many awkward questions that the scene is absurd rather than dramatic. If this is the first time they have looked at the plates, how come they line up so accurately? Since the stars we can see are all on one side of the sun how do we know that the displacement isn’t due to a simple translation? How do we know that the displacement is not a systematic error due to the different scale of the two plates, or to variation in instrument performance, perhaps due to the different temperature and humidity conditions of Principe in May and Oxford in January, not to mention that one photo was taken in the daytime and the other at night.

Reading Eddington’s paper shows a complete contrast: not a dramatic flash of light, but the taking of considerable pains over many months to ensure the most accurate measurement, and the elimination of all possible systematic sources of error in what were very difficult conditions (due to cloud, of the 16 plates taken at Principe during totality, only two have clear images of enough stars to be usable). The issue of alignment of the eclipse and comparison plates takes up the majority of the computation:

The sign of the results shows that the scale of the photographs is larger at Principe than at Oxford; in fact the focus must have been set about 1.2 mm further out (apart from any change of length compensated by expansion of the photographic plates). As the error in focussing was probably not more than 0.5 mm, the greater part of this shift must be due to the focal length of the lens combination increasing with temperature more rapidly than the linear expansion of the glass.

The problem of systematic error due to the instruments is handled by making a series of check plates:

In addition to the eclipse field, a check field was photographed both at Oxford and at Principe. The field chosen included Arcturus, so that it was easily found with the coelostat. Its declination was nearly the same as that of the eclipse field, and it was photographed at the same altitude at Principe in order that any systematic error, due to imperfections of the coelostat mirror or other causes, might affect both sets of plates equally. … [The check plates] show that photographs of a check field of stars taken at Oxford and Principe show none of the displacements which are exhibited by the photographs of the eclipse field taken under precisely similar instrumental conditions. The inference is that the displacements in the latter case can only be attributed to presence of the eclipsed sun in the field.

It is only by takings these kinds of pains that Eddington and his collaborators were able to get the errors in the comparison down to the small fractions of an arc-second needed to distinguish between Newton and Einstein.

I know that simplification and compression are necessary in order to make history into drama. But is simplification to the point of falsehood really necessary? Couldn’t Eddington’s mastery of accurate astronomical measurement make just as compelling a television scene, or even more so, because of its essential truth? Who could be inspired to be a scientist when science is presented as a matter of sudden inspiration for geniuses that is not worth trying to explain?

It’s disappointing to be so critical because the acting was very good, especially David Tennant who was compelling to watch, and the locations, sets, costumes and cinematography were of the BBC’s usual high standard. But they struggled with the scattergun plotting and the clumsy dialogue.

Summary figure from Eddington, Dyson and Davidson (1920)

Here’s part of the concluding speech from Einstein and Eddington:

None of us can know what the world is in the way that we used to know it. Einstein says that time is not the same for all of us but different for each one of us. It’s very hard to conceive of such separate views, of such relative way of seeing. Today is the first day of a new world that is much harder to live in: less certain, more lonely.

The concluding figure from Eddington, Dyson and Davidson (1920) requires no woolly nonsense for its impact.

The figure plots the angular distance from the limb of the sun against the radial displacement for seven stars photographed at Sobral in Brazil. The uppermost thin line shows the line of best fit for the data; the solid line is the displacement predicted by Einstein; the dashed line is the displacement predicted by Newton.