Was Max Planck a fundamentally decent man who actually confronted Hitler and tried his best to thwart the damage inflicted by the fascist regime, especially towards Jewish scientists?
Yes! Was Planck also complicit in the Nazi regime of terror by capitulating to Hitler’s demands and convincing others of the futility of protest? Yes! How can both be true? Let me explain.
Table of Contents
Planck’s Tragic Birthday Celebration
The Max Planck Award And The Rise of Hitler
Einstein, Erwin and Max Planck’s Resistance
The Discrimination Against Jews
How Hahn “Stole” From Meitner
Max Planck Versus The Nazis
In Planck’s Honor
Planck’s Tragic Birthday Celebration
I would like to begin in April of 1928, when Berlin University hosted a gala to celebrate Max Planck’s 70th birthday and it seemed like there was plenty to celebrate. It had been eight years since Planck formed a committee with the Chemist Fritz Haber to “Save German Science” and they could look around a say that German science was not only saved, but the center of Physics development in the world.
Planck and Haber were financially successful mainly because Fritz Haber had discovered nitrogen fertilizer just before the start of world war 1, and then chlorine gas to use in the war, so it seemed likely that Haber would produce something in peacetime that was profitable.
Planck then took his portion of the loot to fund theoretical Physics, something not particularly popular in other countries. Planck supported the delightful Max Born in Gottingen who then had a dizzying list of influential students and assistants: Wolfgang Pauli, Enrico Fermi, Edward Teller, Robert Openhiemer, and his star pupil: Werner Heisenberg.
In Berlin, Planck had just attracted Heisenberg’s rival Erwin Schrödinger which was great for Berlin’s reputation but Schrodinger wasn’t really part of Planck’s “physics family” which was primarily composed Max von Laue, Lise Meitner (shown here relaxing before the war with the chemist Otto Hahn and one of Planck’s daughters), and, most importantly, Albert Einstein.
Planck’s science family was especially important to Planck as they helped him through a series of personal tragedies. First, Planck’s first wife died of tuberculosis in 1909, his oldest son Karl was killed in action in 1916, and in 1917 when Planck’s daughter Grete died in childbirth and in 1919 when Grete’s twin sister Emma died in childbirth as well.
The death of the twins hit Planck and his physics family particularly hard. Many times, Einstein would visit Planck with his violin and Planck would play piano and Planck’s remaining son from his first wife, Erwin would play cello.
As a biographer wrote, “The trio of Einstein, Erwin and Max Planck mourned within their music.”In fact, Einstein started the tradition of a birthday celebration for Planck’s 60th birthday as a way to remind Planck of the love that so many felt for him during his times of personal tragedy.
The Max Planck Award And The Rise of Hitler
For Planck’s far happier 70th birthday, Einstein (along with Max Born, Max von Laue, Erwin Schrödinger, and Arnold Sommerfeld) gifted Planck the start of an annual gold medal named the “Max Planck Award”.
The next year, on June 28th, 1929, Max Planck was awarded the very first Max Planck award and he immediately turned around and gave Albert Einstein the second award. Then, everything fell apart as less than four months later, on October 24, 1929, the stock market crashed in America.
This started a global depression which was felt particularly hard in Germany, which had just barely managed to stabilize their economy after hyperinflation. Many Germans turned to a fringe group of racists led by a buffoonish moron named Adolf Hitler, and the National Socialists went from receiving 2.6% of the vote in 1928 to 18.3% in 1930!
Suddenly, Hitler led the second biggest party in power in Germany. Planck disliked Hitler intensely but agreed with Einstein that, “as soon as economic conditions improve, he will no longer be important.”
Of course, they were completely wrong, and the depression and Hitler’s popularity continued to ravage Germany. In July 1932, the Nazis won 37% of the vote, which made them the largest party in Germany, but without a majority. Terrified of the Communists, by January 1933, the parliament (and President Hindeburg) made Hitler the chancellor which previously was a weak and ceremonial position.
Einstein looked at this with horror and fear. He knew that the Nazis considered him a symbol of all they opposed (Jewish, pacifist, international) and his life was definitely in danger. In December 1932, Einstein went on a “vacation” and never returned.
Hitler was far from the weak chancellor that the German president was expecting especially after a communist burned down the Reichstag at the end of February and Hitler used it as an excuse to remove all communists from Parliament and German’s right to protest.
Without the communist to resist, on March 23 the parliament passed the “Law to Remedy the Distress of the People” which gave Hitler the ability to enact any law without parliamentary approval. With his new power, Hitler decided to have a holiday on April 1st, where all Jewish-owned stores would be boycotted, and as a cherry on top, they would publicly kick Einstein off of the Prussian Academy.
Einstein, Erwin and Max Planck’s Resistance
However, on March 29th Einstein pre-empted their PR attack by publicly resigning from the Prussian Academy and renouncing the Nazi regime. When the director of “educational and cultural matters” learned of this he was, according to contemporaries filled with “indescribable rage”.
However, Planck worried that Einstein’s public comments about Hitler would just make more trouble for what Planck called “your racial and religious brethren,” and when Planck was asked to sign a public declaration again Einstein he did. Only the Max von Laue objected.
Einstein wrote Fritz Haber that all Germans were “criminals” except for Planck and Max von Laue and Planck was only “60% noble”. The next year, in 1934, Einstein wrote a friend that even though he felt that Planck, “never compromised anything by his deeds or words,” Einstein would not have “remained president of the Academy and the Kaiser Wilhelm Society under such conditions. ”
In 1940, the scientist Paul Ewald was visiting Einstein before a trip to Germany and Einstein told him to, “Give my regards to Laue.” Ewald then asked if he should also give regards to Planck and Einstein just shook his head, “Give my regards to Laue,” he repeated sadly.
A few days after the boycott of Jewish stores, on April 7th, 1933, Hitler passed a law that non-Aryan Germans could not work in government or in law or as teachers in public universities with an exception for World War 1 veterans.
Although Fritz Haber who was born Jewish was personally exempt from the edict, Haber defied the order and wrote, “For more than forty years I have selected my collaborators on the basis of their intelligence and their character, and not on the basis of their grandmothers.”
Because of this, in June, 75-year-old Planck took the extraordinary step of seeing what he could do to help Jewish scientists (especially Haber) by talking directly to Hitler!
Supposedly, Hitler started freaking out and calling all Jews “communists” and “leaches” and declared that, “If the dismissal of Jewish scientists means the annihilation of contemporary German science, then we shall do without science for a few years.”
Then, according to Planck, Hitler started shouting about having “nerves of steel,” and according to Planck, “whipped himself into such a frenzy that I had no choice except to fall silent and leave.” A friend of a friend wrote how Planck felt in detail, “[Planck] returned home completely crushed… [Hitler was] more hopeless than anything the famous scientist and thinker had ever heard in his life.”
Planck wrote Haber, “I want to add a personal word of farewell to you. With what feeling you will leave the place of your long, fruitful, and glorious work, I do not even wish to imagine. Just the pure attempt makes my heart spasm.” And yes, you did hear that right, Planck did call Haber’s work “glorious”.
Now Haber’s work on making nitrogen fertilizer feeds billions of people to this very day and could easily be called “glorious” but his work on chemical warfare was repellent and the fact that Planck (and most other Germans aside from Einstein) didn’t see it is one of the worst views that Planck held.
Anyway, Planck never contemplated leaving Germany. As Einstein said in 1919, Planck is “rooted to his native land with ever fiber [of his being].” Planck also didn’t retire from any positions in protest.
Niels Bohr’s brother Harald was in Berlin at the time and said that, “Planck was … anxious to explain that his reason [for] staying in his position as director of the Kaiser Wilhelm Institute was to try to do all in his power to help in the situation, not only in this institute, but also in the different universities.”
At the end of May 1933, Schrödinger (who was not Jewish) left for England. Planck wrote Max von Laue, “I regard Schrödinger’s resignation as a new deep wound to our Berlin physics, which we must endure with all of the energy available to us.”
In November, Schrodinger won the 1933 Nobel Prize (with Paul Dirac) and he collected it with Heisenberg who won for the previous year. For that reason, Heisenberg became known as the pro-Nazi scientist for remaining in Germany and Schrodinger the anti-Nazi for leaving. If you have a positive view of Schrodinger from this action, let me ruin your day.
See, it turned out that in the 1930s it was very hard to be allowed into another country if you were Jewish unless you had a lot of money or a job. For that reason, the head of the Physics department at Oxford went to Berlin specifically to help Jewish scientists and asked Schrodinger’s help in recommending likely candidates.
Schrodinger thought it would be fun to go instead and was too famous to refuse. Schrodinger also insisted that they find a position for his non-Jewish assistant as the married Schrodinger was interested in starting an affair with his assistant’s wife which he did and then lived a polygamous life in England!
Unlike Einstein, once safely in England, Schrodinger did not publicly say anything against Hitler and, after a few years he got bored with England and moved back to his homeland of Austria.
When Hitler took over Austria in 1938 Schrodinger was told his job was in jeopardy so he wrote a public “confession to the fuhrer” about how excited he was with Hitler and the “exultant joy which is pervading our country”. The “Confession” was not enough to make up for leaving Germany in 1933 and Schrodinger ended up being fired for “political unreliability”.
Scared, Schrodinger ran to Italy where the Vatican helped him to get back to Oxford and eventually Ireland. When Schrodinger was asked about his letter at a dinner party, he first said “what letter?” then he defiantly said, “What I have written, I have written. Nobody forced me to do anything.
This is supposed to be a land of freedom and what I do is nobody’s concern.” By 1939, Schrodinger backtracked and wrote Einstein a private letter that he only wrote the confession, “to remain free – and [I] could not do so without great duplicity.” Blegh.
When Fritz Haber left Germany, the Otto Hahn was placed as the new temporary director of Chemistry at the Kaiser Wilhelm Society. Hahn then suggested to Planck that the non-Jewish professors could stand up and protest the Nazi’s actions.
Planck thought all that would happen is that all the professors who objected would be fired and replaced with fascists, and Hahn recalled that because “Planck (and others) advised against it… [so] therefore [I] did not attempt anything.” Worse, Hahn completed the task that Haber refused to do, and fired a large swath of employees for their backgrounds or beliefs.
In late August, 1933 both Planck and Hahn tried to get an exception to the law for Lise Meitner. Planck wrote that, Meitner, “along with Otto Hahn, is the soul of the Kaiser Wilhelm Institute for Chemistry. That Institute owes those two its reputation and world renown.”
But it was no use, Meitner was no longer allowed to teach or attend lectures, and furtively did research under the wing of her friend Otto Hahn. Despite these setbacks, Meitner recalled that she didn’t want to leave her job and her life in Berlin and was, “only too willing to let myself be persuaded by Planck and Hahn.”
In October of 1933, a co-worker’s daughter named Lotte Warburg wrote in her diary: “Planck has become a stone-aged man, stooped, pitiful. I saw him shuffling through the park, untidy and unkempt…He said that no one asked him about things anymore, that science was no longer worth anything.”
Although Planck had saved some jobs, the capitulation to the Nazi state started to destroy his reputation and soul. In January of 1934, Fritz Haber died of a heart attack in Switzerland, possibly brought on by the stress of his removal, which Planck took very hard.
A few months later, Hitler required that all talks had to start with a Nazi salute, and a scientist named Paul Ewald recalled, “we were all staring at Planck, waiting to see what he would do… Planck stood on the rostrum and lifted his hand half high, and let it sink again. He did it a second time.
Then finally the hand came up and he said ‘Heil Hitler’” After the war, Ewald thought it was the correct move writing, “Looking back it was the only thing you could do if you didn’t want to jeopardize the whole [Keiser Wilhelm Society].”
But many others disagreed including Lotte Warburg who wrote in her diary in 1934: “Why does he not resign?… Why does he go about hunched over, moaning and complaining, instead of throwing back his head and damning them all?”
In January of 1935, on the urging of Max von Laue, Planck hosted a memorial for Fritz Haber. The Nazis were incensed and forbid any state employees to attend, writing, “a memorial celebration on the occasion of the one-year anniversary of Haber’s death must particularly be taken as a challenge to the National Socialist state.”
Planck told Otto Hahn, “I am going to be at this event, unless they have the police drag me away”. Because the international press had been notified, the Nazis did not cancel the memorial altogether but they made it illegal for any government employee to go.
Although Planck and Hahn fully expected to be beaten by Nazi thugs to keep them from entering the memorial, they entered unharmed. Planck gave the introduction address and Otto Hahn gave two speeches, one from himself, and one from a professor who was prohibited from attending.
The Discrimination Against Jews
On September 15, 1935, the Nazis created the Nuremberg Laws which specifically excluded German Jews from almost all employment and removing the limitation on World War 1 vets, and by the end of the year, one in four Physicists in Germany had been fired!
Planck managed to fenagle exemptions for several Jewish scientists especially in the Prussian Academy and the Kaiser Wilhelm Institute where Planck was president. However, by 1936, Planck was unable to get another term as President of the Institute, and the remaining Jewish employees were fired.
Lise Meitner managed to hang on but was even more handicapped by the regime so that Hahn noted, “one constantly hears essentially only my name for an investigation in which Lise Meitner has participated at least as much as I have.” In March of 1938, Hitler annexed Austria, and Meitner finally realized she was in mortal danger.
Luckily, Niels Bohr helped her escape in secret to Sweden and Otto Hahn gave her his mother’s diamond ring to bribe guards. Just after Meitner reached Sweden, Hahn was shocked to find that their four-year-long project of hitting uranium with neutrons resulted in some material with about half the atomic number and sent a note to Meitner asking for her advice.
Meitner and her nephew Otto Frisch then became the first to realize that the atom had split (Frisch named this process “fission” after the biological effect where cells split). Meitner then predicted this effect would reduce the mass by a tiny bit and produce a lot of excess energy from (E=mc^2).
Hahn published without mentioning Meitner or Frisch as he wasn’t allowed to include Jewish names in a German journal and in 1944, Otto Hahn won the Nobel Prize without any mention of Meitner. (Planck had nominated both Meitner and Hahn for Nobel Prizes in Chemistry multiple times in the 1930s, and for Lise Meitner alone for Physics after the war but to no avail).
Max Planck Versus The Nazis
Meanwhile, things became even more dire in Berlin, especially for the Jewish people still living there. Six months after annexing Austria, in late October of 1938, Hitler expelled all Polish Jews living in Germany but Poland won’t let them in, so the poor deportees end up stuck in no-man’s-land between the two countries.
A few weeks later, on November 7th, a teenager living in Paris whose parents were trapped in that terrible situation, shot and killed a Nazi diplomat in revenge. The Nazis then claimed it is a grand Jewish plot and for two days burn synagogues, trash houses, and businesses, and kill dozens of people in what was known as the night of the broken glass (Kristallnacht).
After that, they made a law forbidding Jewish children from attending school and sent 30,000 Jewish men to concentration (labor) camps. Unable to defend anyone in science anymore in December of 1938,80-year-old Planck resigned his secretary-ship of the Prussian Academy (after 26 years), and was fully retired from science work.
On September 1, 1939, Hitler broke a treaty with England and France and attacked Poland and two days later France and the UK, and its allies declared war with Germany. By May 1940, Germany had overrun Belgium, the Netherlands, and Luxenberg and by June, France signed an armistice leaving only Great Britain fighting the Nazis.
Now the fascists had millions more Jewish people and other “undesirables” to deal with and the systematic oppression of Jewish people ramped up to more organized methods, for example, in November of 1940, they forced over 400,000 Polish Jews to live in a square 1.3 mile fenced enclosure called the Warsaw Ghetto where they attempted to kill all the residents by starvation.
In June of 1941, Hitler started “Operation Barbarossa” which was an attempt to overrun all of Russia, and kill all the people and replace them with Germans.
It wasn’t as easy as western Europe and 5 months later they were deadlocked on the eastern front and Stalin was now allied with the UK. Meanwhile, the Germans were rounding up and shooting all the Jewish people they could find and following the “hunger plan” to enslave Ukrainians and Russians farmers and steal all their food so that Germans would have plenty and the city dwellers would starve to death.
Then, on December 7, 1941, this happened. The next day the US declared war on Japan and three days later, Italy and Germany declared war on the US in retaliation. Hitler was very upset and he decided that Pearl Harbor was a Jewish conspiracy! (OF COURSE).
Hitler also became “concerned” that he might not have enough time to kill every Jewish person in Europe with bullets and starvation and started the “final solution” where all Jewish people and other undesirables were taken by train to remote camps where they were either worked to death or systematically poisoned often using Zyclon-B, a poison that was a derivative of Zyklon-A created by Fritz Haber at the Kaiser Wilhelm Institute in the 1920s as a pesticide.
Planck must have known about some of what was going on with the abuse of his countrymen, as according to the Holocaust Museum documents found that there were 3,000 camps and mini-camps in Berlin alone, and as Planck saw bombing in both Berlin and Kassel, he would have also seen camp victims clearing rubble afterwards.
Planck fought against this in the most Planck manner possible: he started giving speeches about the history of science and “Religion and Science”. In theory, his talk was how science is compatible with religious beliefs. But in his proof, he stated that, “we must never forget that even the most sacred symbol is of human origin.
Had mankind taken this truth to heart at all times, it would have been spared an infinity of woe and suffering [from] the terrible religious wars [and] the horrible persecutions of heretics.”
If that doesn’t sound brave or profound, remember that some of the people in the audience were the ones systematically slaughtering millions of innocent people for which sacred symbol they prayed to while others cheered or looked away. Planck was so popular that he was allowed to travel all over even in neutral Switzerland and Sweden.
At first, he was very careful with his words, as you can see from this amazing 1942 video where he mentions his love of relativity without mentioning Einstein’s name. But soon he had enough and in 1943, a Swedish reporter noted that Planck, who was talking to Nazi Foreign officer’s club mentioned Einstein by name, “as a leader and way-shower in the world of thought, [Planck] looked beyond raw prejudices and fanatics, entirely regardless [of where he was].”
But Planck was aware of where he was and his part in it. While in Sweden, Planck visited Lise Meitner, and according to Lise, Planck told her that, “terrible things ought to happen to us, we have done the most horrible things.” Meitner thought Planck was being too hard on himself and, after the war, wrote to a friend that, Planck, “used the words ‘we’ and ‘us’.
And yet this 85-year-old man was more courageous in his resistance than all the others” Lise Meitner wasn’t as forgiving of her best friend Otto Hahn, writing him just after the war, “[although] you occasionally helped an oppressed person; still, you let millions of innocent people be murdered [and]…you bear responsibility for the occurrences as a result of your passiveness…
Perhaps you remember that when I was still in Germany (and I know today that it was not only stupid, but a great injustice that I didn’t leave immediately), I often said to you ‘As long as we [the Jewish people] and not you have sleepless nights, it won’t get any better in Germany.’ But you never had any sleepless nights: you didn’t want to see – it was too disturbing.”
Things got more tragic for Planck. In February of 1944, Planck’s home was bombed and he lost all of his possessions. Then he learned his granddaughter Emma (daughter of his daughter Emma) had tried to commit suicide and had to be hospitalized but Planck was too ill to travel to her himself.
Then in July, 1944 a group of high-level Nazis attempted to assassinate Hitler and failed. Hitler arrested more then 7,000 people including Planck’s youngest son from his first wife, Erwin.
By October, Erwin was sentenced to death. Max Planck put “heaven and hell in motion” to save his son and even wrote Hitler directly, “as the gratitude of the German people for my life’s work, which has become an everlasting intellectual wealth of Germany, I am pleading for my son’s life.”
Planck never heard back from Hitler but three months later, Planck heard that Hitler’s right-hand man Heinrich Himmler was personally intervening on the issue and his son would get a pardon soon. Five days later, Erwin was executed. Planck was destroyed, writing his niece that, “no words can describe what I have lost.”
Planck’s body started destroying himself and his vertebrae fused while the home they were staying in was under fire, and Planck and his wife ended up hiding in the woods and sleeping in haystacks.
Marga Planck wrote to Planck’s nephew Hans Hartmann: “The very worst was the frightful suffering that Uncle Max had to bear. He often screamed from the pain.” Finally, the American officers who just liberated Gottingen were alerted to his situation and personally interfered to get him medical care.
After a few months in a hospital, he could shuffle about and went back to traveling and giving his talks. A few months before he died, he explained why he continued talking: “At eighty-nine I cannot be productive scientifically, what remains to me is the possibility of [helping]… people struggling for truth and knowledge.”
In Planck’s Honor
When the war ended, Max Planck’s reputation seemed to have escaped his time under Hitler pretty much unscathed. For example, in 1946, Planck was the only German citizen invited to England for the belated 300th birthday party for Isaac Newton.
When Planck was introduced, the page announced him as “Professor Max Planck of no country,” to deep applause, and they then corrected it to “Professor Max Planck from the world of science.”
At around the same time, there was talk of dissolving Planck’s beloved Kaiser Wilhelm Institute as it was connected to the poison gas of World War 1 and the gasses used in concentration camps to kill millions as well as munitions and biological human experiments.
In England, the president of the Royal Society, Sir Henry Hallett Dale thought that the institution was worth saving but the name was too toxic to survive. Dale suggested to Otto Hahn (who was the new president of the Kaiser Wilhelm Institute) to rename the Kaiser Wilhelm Institute the Max Planck Institute and he happily agreed (it was easy for Dale to talk to Hahn as Hahn was being held by the British at the time).
Currently, the Max Planck Institute is one of the most influential and important science research institutes in the world. Max Planck died of a stroke on October 4, 1947 at the age of 89 just a year after his beloved Institute was renamed in his honor.
[My personal opinion] Planck was a decent and brilliant man. It was completely reasonable for him to conclude in 1933 that Hitler was an anomaly and would be removed soon and to try to sustain physics in Germany in the interim. It was reasonable, but it was a catastrophic and moral mistake with repercussions that will reverberate for all of human history.
It is arguable what influence Planck could have had on the atrocities committed by the Nazis, but there is another facet of this time where Planck’s actions had tragic repercussions.
For Werner Heisenberg tried to emulate Planck in “saving German science” and in doing so ended up being responsible more than any other scientist in the world for the creation of the nuclear bomb! And I’ll prove it next time on the lightning tamers.
Whew! So, that is my third part of my biography of Planck. If you haven’t watched part 1 and 2, please check them out, way more science, way less Nazis. I also have videos with more details on how Planck wrote his 1900 paper and why Planck wrote Boltzmann’s equation and how it ended up on Boltzmann’s grave and more about Einstein. Check them out and stay safe.
 Brown, B Planck: Driven by Vision, Broken by War (2015) p. 94
 According to Hoffmann, D and Walker, M The German Physical Society in the Third Reich (2012) p. 169
 According to Holocaust Encyclopedia “The Nazi Rise to Power” https://encyclopedia.ushmm.org/content/en/article/the-nazi-rise-to-power
 Albert Einstein quoted in Levenson, T “The Scientist and the Fascist: How Einstein reacted to Hitler’s rise” The Atlantic (June 9, 2017)
 Albert Einstein to Haber (1933) found in Grundmann, S The Einstein Dossiers (2006) p. 286
 “Politics and the state” Biography of Max Planck from the Max Planck Society Website, max-planck.mpg.de
 Found in Moore, W Schrodinger: Life and Thought (1992) p. 266
 Translated and quoted in Edmondson, N Some Aspects of the Politicization of Science in the National Socialist Germany (1956) p. 42
 Max Planck translated and found in Haberer, J Politics and the community of science (1969) p. 132
 Max Planck to Fritz Haber (1933) found in Stolzenberg, D Fritz Haber (2004) p. 283
 Albert Einstein to Heinrich Zangger (June 1, 1919) The Correspondence of Albert Einstein: Volume 9 p. 44
 Harald Bohr to R.G.D. Richardson (May 30, 1933) Found in Heibron, J The Dilemmas of an Upright Man (2000) p. 182
 Max Planck to Von Laue (1933) Cassidy, D Beyond Uncertainty (2010)
 Arthur March’s wife Hilde became Schrodinger’s defacto polygomous second wife. Halpern, P Einstein’s Dice and Schrodinger’s Cat p. 130
 According to Simon, F Nuclear Dawn (2014) p. 50
 Otto Hahn found in Sime, R Lise Meitner: A Life in Physics (1996) p. 145
 Sime, R Lise Meitner: A Life in Physics (1996) p. 145
 Lotte Warburg (October, 1933) found in Brown, B Planck: Driven by Vision, Broken by War (2015) p. 186
 Paul Ewald translated and found in Ball, P Serving the Reich (2014) p.80-1
 Lotte Warburg (1944) found in Heibron, J The Dilemmas of an Upright Man (2000) p. 236
 Ministry of Education, January 15, 1935 found in Beyerchen, A Scientists under Hitler (2018) p. 110
 Max Planck (1934) found in http://www.max-planck.mpg.de/frameset_e.html
 Found in Ball, F Serving the Reich (2014) P. 72
 Found in Sime, R Lise Meitner: A Life in Physics (1996) p. 150
 Found in Brown, B Planck: Driven by Vision, Broken by War (2015) p.25
 Max Planck “Religion and Natural Science” (1937) found in Planck, M Scientific Autobiography, and Other Papers (1947) p. 113
 Gunner Pihl as found in Heibron, J The Dilemmas of an Upright Man (2000) p. 220
 Lise Meitner to Martha Krause (Jan 15, 1948) found in Rife, P Lise Meitner and the Dawn of the Nuclear Age (2019)
 Lise Meitner to Otto Hahn (1945) found in Rife, P Lise Meitner and the Dawn of the Nuclear Age (2019)
 Marga Planck to Hans Hartmann in Heilbron, J The Dilemmas of an Upright Man (2000) p. 227