Max Planck

Max Planck

1858–1947

Planck, engraved after the antique manner, about the time of the Nobel Prize. It was given in 1918 for the discovery he had spent the previous eighteen years attempting to explain away, and he is looking, here as elsewhere, somewhere off to the side of it.

Born	23 April 1858, Kiel
Died	4 October 1947, Göttingen[1]
Advised as a student	Not to bother; physics was finished[2]
The quantum	14 December 1900
His own word for it	Despair[3]
Years spent trying to undo it	Five, then a decade doubting Einstein
Nobel Prize	1918
Succeeded at Berlin by	Schrödinger, 1927
Children outliving him	One

Max Planck (23 April 1858 – 4 October 1947) was a German theoretical physicist who, in attempting to account for the light given off by a hot body, was driven to suppose that energy is emitted only in fixed indivisible amounts. The supposition was correct, it founded quantum theory, and he did not want it.

He is the encyclopedia's clearest instance of a proposition it meets constantly from the other side: that the person least persuaded by a discovery is frequently the person who made it. Planck introduced the quantum as a device, described it afterwards as an act of despair, and spent years attempting to derive the same result without it. He also wrote the best-known statement of why such resistance is normal, and he was writing about himself.^[3]

Advised against

Planck was told as a young man not to go into physics: the subject was essentially finished, and what remained was the filling-in of decimal places.

The advice was widely given at the time and was not stupid. Mechanics, thermodynamics and electromagnetism between them appeared to cover the ground, and what stood out were a few small unexplained residues of the sort that usually turn out to be experimental error. One of those residues was the spectrum of a hot body. Another was the failure to detect the Earth's motion through the aether, which Kelvin would shortly file under the first of his two clouds. Both clouds ate the century.^[2]

The act of despair

The problem was the distribution of light from a heated cavity, which no existing theory could reproduce across the whole spectrum. Planck found a formula that fitted, and then spent some weeks trying to justify it.

The justification required supposing that the energy came in packets of size $E = h\nu$: proportional to frequency, and indivisible. He presented it on 14 December 1900, and he did not believe it described anything real. His own account, given long afterwards, is exact and is worth having entire:

…an act of despair. I was ready to sacrifice any of my previous convictions about physics.
– Max Planck

For years afterwards he worked at recovering his result within classical physics, which cannot be done, and which he was not to know cannot be done. It was Einstein, in 1905, who took the packets literally and applied them to light itself, and Planck thought that a step too far for some considerable time.^[4]

Planck's principle

The observation for which he is quoted outside physics is this one, from the autobiography published after his death:

A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it.
– Max Planck, Scientific Autobiography

It is usually deployed as a sneer at the obstinacy of established scientists, generally by people whose own position has not been established at all. Two things are worth noticing before it is used that way.

The first is that Planck was describing himself. He had been the obstinate one, about his own result, in the face of his own evidence, and the sentence has the weight it has because it is a confession rather than an accusation.^[5]

The second is that the principle is not a licence. It says that acceptance lags evidence; it does not say that anything unaccepted is therefore true. A great many positions are resisted for the excellent reason that they are wrong, and their holders take considerable comfort from this sentence.^[6]

The last years

Planck stayed in Germany after 1933 and the record of those years is not a comfortable one to summarise.

He was by then the most senior figure in German science, he intervened for individual Jewish colleagues and failed, he met Hitler once to argue that expelling Jewish scientists would destroy German physics and was shouted at, and he did not resign. He has been defended as a man preserving what could be preserved, and criticised as a man lending his name to an institution that was being hollowed out. Both readings are available and the encyclopedia does not adjudicate.

His son Erwin was arrested after the July plot of 1944, condemned, and executed in January 1945. Planck's eldest son had been killed at Verdun and both his daughters had died in childbirth. His house and his papers were destroyed by bombing. He died at Göttingen on 4 October 1947, aged eighty-nine.^[1]

See also

• Wave–particle duality – what became of his packets
• The double-slit experiment – where the consequences are on display
• Albert Einstein – who took the quantum literally first
• Schrödinger's cat – devised by his successor at Berlin, against the theory he founded
• Luminiferous aether – the other of Kelvin's two clouds
• Grimble's razor – on the setting aside of unwelcome consequences, which he did not do

References

1. ^ Erwin Planck was executed on 23 January 1945. The encyclopedia records it without embellishment; it is the one fact in this article that admits of no observation.
2. ^ The advice that physics was complete is often told as a joke against the nineteenth century. It was a reasonable reading of the evidence and it was wrong in exactly two places, both of which were known at the time and neither of which looked important.
3. ^ The phrase is his, recalled in later correspondence. "Act of despair" is the usual English rendering; "act of desperation" is also given.
4. ^ Planck's own reservations about the light quantum persisted for something like a decade after Einstein's paper, and he said so in writing while nominating Einstein for membership of the Prussian Academy, which is a form of scientific manners now largely lost.
5. ^ Which is why the sentence is worth more than the use commonly made of it. A man describing his own obstinacy has better standing than a man describing everybody else's.
6. ^ See Grimble's razor, whose users find this sentence extremely congenial and rarely quote the surrounding paragraphs.

External links

• Max Planck – Nobel Prize in Physics 1918 – the official record
• Max Planck – general reference