“Copenhagen” - Another Round




by Mara Beller*


Michael Frayn’s fascinating and thought provoking play has captured audiences worldwide, and recently stirred a lively controversy.


While deliberately imitating the style of “Copenhagen,” I present a different perspective on the issues involved, both philosophical and political.


During my academic career, I have extensively studied dialogues among Bohr, Heisenberg and other quantum physicists.  The results of this research are described and analyzed in my book Quantum Dialogue – The Making of a Revolution, published by the University of Chicago Press, 1999.


Margrethe: But why? Why is he coming again tonight to discuss these matters?

Bohr: Such a good ending for Heisenberg. He had the last word in the play.

Margrethe: How prudent, how wise… Imagine, Heisenberg’s uncertainty appears to have saved humanity!

Bohr:  It is most interesting… Humanity saved by uncertainty… A new principle of complementarity – that between knowledge and salvation…

Heisenberg [enters]: I was not quite happy with my character. Certain about uncertainty, predicting unpredictability. Don’t you feel some contradiction, some deception? … I almost feel guilty about it.

Margrethe: So as not to feel guilty about more important things?

Bohr:  Let’s not start this again, my love.  [to Heisenberg] Heisenberg, there is absolutely no reason to question our revolutionary achievements. Uncertainty and complementarity are the final principles of science, no matter what progress the future will bring. Our version triumphed because it inevitably had to.

Heisenberg: Necessity of uncertainty? Is that not an oxymoron? What do we gain here, Niels, from having our version triumphed? Aren’t you bored to hear these old ideas again and again?

Margrethe [playfully]: It is not boring for me to hear Niels’ ideas repeated.

Heisenberg: I’d rather hear more about the new interpretations. Like many worlds, splitting into many others each moment…

Bohr: These “new” interpretations, Heisenberg, are either not new or too bizarre. Why do you think there can be so much novel under the sun? The ancient Chinese sages knew everything about complementarity.

Margrethe [to Bohr]: Because, as you taught, everything of importance can be said in plain language.

Heisenberg: Perhaps said, but not discovered. Quantum uncertainty could not have been discovered without mathematics no matter how much we misled the public on this point.

Margrethe: You misled, Heisenberg, not Niels. You made some very elementary mistakes in your thought experiment, and Niels called you to order. Everybody knows that Niels can sense nature directly, while lesser minds need calculations. Irving Berlin wrote great music without knowing notes…

Heisenberg [arrogantly]: This argument is complete nonsense. Irving Berlin also had a lever attached to his piano, to transpose from one key to another. He at least was aware of his limitations…

Margrethe [turning to Niels]: Now, when this polite German young man does not need your support anymore, he quite oversteps his limits!

Bohr: It is O.K., my dear, let him say what he pleases. Here he is bound to say what he has on his mind, sooner or later, so we better hear it sooner. [to Heisenberg] So what did you say about being bored with my ideas?

Heisenberg: Niels, please, do not be offended. I am also bored with my own ideas, when they are frozen as the final word. With all your corrections our thought-experiments are self-contradictory. Mixing of quantum and classical concepts to tailor them to a conclusion known in advance.

Bohr [irritated]: I can prove to you, in plain language…

Heisenberg: People who did exact mathematical calculations (what is the name of this chap in Cambridge?) showed all our thought-experiments are wrong, they only look convincing.

Bohr [angry]: This is very very interesting… I can prove to you, logically, without seeing what he has done, that this Englishman must be wrong.

Heisenberg: Niels, complementarity is good religion and bad physics. Already in 1928 we knew that waves and particles are not mutually exclusive, that a unified description is possible. The only small thing [crackles with laughter]… is to do it right… [after a pause] And perhaps old Einstein was right… Perhaps something completely new is needed.

Margrethe [to Bohr, affectionately]: Why look for something new, when something old works so well…

Bohr: That is certainly true for us, my dear.

Heisenberg [after a pause]: If we want to be honest we must admit that complementarity…

Margrethe: Look who wants to be honest!

Bohr: Margrethe!

Margrethe: Be honest, Heisenberg! Tell us why did you come to Copenhagen to see Niels in 1941?

Heisenberg: Intentions… The most elusive of all things… Don’t we always reconstruct them after the fact?

Margrethe: Evasive, like always. Did you come to ease your conscience, Heisenberg? Or were you on a spying mission? –to gain some knowledge to arm the Nazi government with atom bomb?

Heisenberg: Margrethe, I have nothing new to add to what I said many times. I was tortured by a moral dilemma.

Margrethe: Why was Niels so angry after you met? Why was he so devastated?

Bohr: And how did you feel, Heisenberg? Was it despair? Was it relief?

Heisenberg: I almost burst into tears.

Margrethe: Both relief and despair.

Bohr: Still another manifestation of complementarity. Though mutually exclusive, despair and relief…

Heisenberg: It was less complementarity and more uncertainty. Should scientists support their governments during a war? Which dangers are real and which are imagined? Are Allied scientists working on nuclear weapons?

Margrethe: The same Jewish scientists that were expelled from Germany, who fled from Hitler, for whom Niels – half Jewish – found positions in Britain and America.

Bohr: Heisenberg was also helpful. Writing recommendations…

Margrethe: And then – Jews threatening your beloved Germany with the atom bomb!

Heisenberg: You really dislike me, Margrethe. Nobody who knew me would suspect me of anti-Semitism. Did I not protest the expulsion of Jews? Did not Nazi physicists call me “an aberration of a Jewish mind”? I was in personal danger, Margrethe. Did not the Nazi newspaper print that I am a “white Jew” that should vanish…? I always defended Einstein and Bohr.

Margrethe: What did you defend, Heisenberg, the physics or the physicists?

Heisenberg: Both.

Margrethe: Did you not advise Sommerfeld to cross out Einstein’s name from his book on relativity?

Bohr: My dear, it was in 1943!

Heisenberg: Ten years earlier I was planning to resign in protest of the expulsion of Jewish people.

Bohr: And like an obedient child you went to consult the grand old spokesman of German science, Max Planck.

Margrethe: Whose advice you could have guessed in advance… One cannot do anything except to wait for the disaster to be over. And to dream of better times that will follow afterwards.

Bohr: And to plan one’s career after the war, no matter what its outcome.

Margrethe: In the meanwhile, you said, only a few Jews were affected by these laws – not Franck, Born, or Courant. So these laws are unlikely to harm German science.

Bohr: This was in 1933 – later you found otherwise.

Margrethe: Advice from Max Planck? The same Planck who tried to put in a good word to Hitler for a Jewish colleague Fritz Haber implying that there are two kinds of Jews – the valuable and the worthless. The valuable should be protected for the sake of Germany.

Bohr: Who cares about the fate of the worthless?

Margrethe: Hitler had no patience for such a duality. “A Jew is a Jew” he snapped back.

Heisenberg: I never liked duality. That was Planck’s argument, not mine.

Bohr: You are not a stranger to duality.

Margrethe: Did you not argue, Heisenberg, that there are two kinds of countries…

Bohr: Like two kinds of Jews.

Margrethe: Valuable and worthless. The worthless – like Poland, or Russia – cannot govern themselves. They need the strong German hand.

Bohr: So only a few days before our meeting you justified the occupation of East European countries by German troops.

Margrethe: No regret about Poland being destroyed. At least it is not France - you said.

Bohr: All this – on the territory of my country, Denmark, occupied by Nazis. Coming here as a commissar of German culture.

Heisenberg: It probably would have been good if physicists on both sides had made an agreement to withhold their efforts.

Bohr: But you later said you did not mean to suggest that.

Margrethe:  You were too clever to be that naive, Heisenberg. Even before Niels mentioned it would be unrealistic to expect physicists not to support their governments…

Bohr: Relief and despair, despair and relief.

Heisenberg: You forget I did let Niels know a top secret – that there is a German nuclear effort. I was risking my life…

Margrethe: Was there any other way for you to find out what the Allies were doing without disclosing this to Niels?

Heisenberg: Of course, Margrethe. In all honesty…

Margrethe: What do you mean by honesty, Heisenberg?

Bohr: How lucky for Heisenberg in 1943 to think that the building of an atom bomb cannot be realized in a short time.

Margrethe: Otherwise – he might have faced the possibility of deceiving his superiors! Imagine – to lie to Nazi officials! Not Heisenberg!

Heisenberg: Yes, I did explain after the war that I did not think the project was practical. So, in all good conscience, I could give an honest advice. What’s wrong about that?

Bohr: A brilliant solution – no wrongdoing towards humanity and still faithful to his country.

Margrethe: No matter what the deeds of the country are?

Bohr: No moral dilemmas. How clever - Heisenberg could not have committed any wrong – in principle, so to say! And what would have been your advice if you thought there was this practical possibility?

Heisenberg: Fortunately, I did not have to face this question.

Bohr: “Would you betray your brother because he stole a silver spoon”, you once asked.

Margrethe: Stealing a silver spoon? What a comparison!

Bohr:  Remember that in 1944 you,  Heisenberg,  said “would it not be grand if Germany won the war”.

Margrethe: With the atom bomb? Or without it?

Heisenberg: Please stop, both of you. You don’t let me say a word. I can explain…

Margrethe: I have no doubt.

Bohr: Heisenberg’s own private uncertainty principle. One cannot predict the future, but one can control it.

Margrethe: Defeat or victory for Germany – Heisenberg was certain to be the spokesman of German science.

Bohr: Whom nobody could ignore after the war.

Margrethe: Not even you, Niels.

Bohr: Ever so brilliant. A perfect sense of timing.  When Germany was losing the war in 1943, you were happy that the prospects for the German nuclear project were very dim.

Margrethe: But how did you feel when you came to Niels in 1941, confident of German victory, happy that Germany was closing in on the Russian army?

Bohr: These are good developments, you said.

Heisenberg: I was always terrified thinking of an atom bomb in Hitler’s hands. Actually, in any hands!

Margrethe: Why should we believe your words, Heisenberg. Don’t you carefully plan them in advance?

Heisenberg: It is not as simple as that, Margrethe. We often do not know what we will say or do before it happens. And even after it did, we can never be sure what our motives were.

Bohr: Not to criticize… but some things are clear even if imprecise.

Heisenberg: Aren’t we always trapped in contradictions? In superposition of different states, not knowing which will actualize – as in an act of measurement…?

Margrethe: We do make our choices. We do and say definite things even if we are ambivalent about them.

Heisenberg: Are you ambivalent about what you just said, Margrethe?

Bohr: Trying to set a logical trap for Margrethe, Heisenberg?

Margrethe: Do not worry, my dear, I can take care of myself.

Heisenberg: Niels, how can anybody be certain what exactly happens after it is gone? Competing version of past, present and future, all existing simultaneously.

Bohr: Wait, Heisenberg, wait. Not so fast. This is not skiing, you see.  The future is open, yes, but not the past. At least part of the past. Even in quantum physics, while we cannot predict the result of measurement, we sometimes can say exactly what the state of the system was at the time the measurement was made.

Margrethe: I do not follow all these quantum details, and anyhow, ethics does not follow from physics. Are we not – all of us – scientists, this audience, we ourselves – a little too tolerant? Too understanding? A trendy sophisticated stand – no villains, no saints, no black, no white, no victims and no murderers. How easily the ultimate uncertainty can lead to comfortable complacency. And then - to ultimate irresponsibility.

Heisenberg: You often sound so self-righteous, Margrethe. Sometimes there are simply no good choices, only bad ones. Would it have been better if I had accepted the offer in Ann Arbor before the war and was recruited to work on the bomb to be dropped on my own country?

Bohr [in deep thought]: Interesting… Complementarity between complacency and self-righteousness. Though mutually exclusive…

Heisenberg [irritated]: They are not mutually exclusive Niels! One can be both complacent and self-righteous.

Margrethe: One of those deep truths the opposite of which, as Niels taught, is not a falsity but another deep truth.

Heisenberg: Margrethe, is Niels’ statement of the existence of such deep truths also a deep truth?

Margrethe: Of course.

Heisenberg: In that case – the opposite statement – there simply are no such deep truths – is also true!!

Margrethe: Here you go again?!

Bohr: Heisenberg, you are not thinking, you are simply being logical… In any case, if you never liked complementarity, why did you support it?

Margrethe: You know why, my dear, do not agonize over it again. Heisenberg himself said that he supported complementarity because it did not contradict uncertainty, but that he never believed in it.

Heisenberg: I never said I did not believe in it. I only said it was not necessary…

Margrethe: What’s the difference?

Bohr:  But it is necessary, Heisenberg.  Otherwise, we are trapped in contradictions between…

Heisenberg: The contradictions are not resolved by complementarity, only evaded. Besides, how can one live or create without them? If one waits to resolve contradictions, one cannot move forward.

Margrethe: At least not with your speed, Heisenberg.

Bohr: And after the war? Why did you support my principle of complementarity after the war?

Margrethe: Especially after the war – all the more reasons to be on Bohr’s better side.

Heisenberg: Margrethe, why this suspicion, all the time. Even here? Even now? Why can’t you trust, just a little bit, what I say?

Margrethe: Trust… Is it not the crux of the matter, Heisenberg? If there was one thing that was painfully clear at the time of your visit to Copenhagen, it was just that – that you could not be trusted.

Bohr: Neither your words nor your actions.

Margrethe: The German nuclear effort – having a person of Heisenberg’s brainpower working on it. How terrifying!

Bohr: It is not so much the brainpower. It is to have no inkling where Heisenberg’s heart was that was so shattering.

Heisenberg: Despite our years of friendship, Niels?

Margrethe: No friend could have suggested to Niels to collaborate with the German authorities in occupied Denmark.

Heisenberg: It was only to help to protect you, Niels.

Margrethe: And to think that the fate of our children, our country, the whole world, might have depended on Heisenberg…

Heisenberg: May I remind you,  both of you, that it was not Germany that dropped an atom bomb, killing innocent people. Hiroshima … Nagasaki…

Margrethe and Bohr [together]: An undescribable disaster!

Heisenberg: Niels worked on it!

Margrethe: Thanks to you, Heisenberg, to that visit of yours.

Heisenberg: What about responsibility versus complacency, Margrethe?

Margrethe: Niels had no idea it is going to be used that way!

Heisenberg: One does not build something in confidence it will be never used!

Bohr: Heisenberg, your favorite symmetry principle does not apply here. There is no symmetry between the one who attacks and the one who defends.

Heisenberg: At least my hands are clean. Germany did not build an atom bomb. I did not kill anybody.

Bohr: One’s hands are as clean as the cause one supports.

Margrethe: You do not mean to suggest, Heisenberg, that you knew how to build the bomb, but deliberately, secretly, kept this knowledge to yourself?

Heisenberg: I never said anything of the kind, Margrethe. Others came up with this idea.

Margrethe: So where was your heart Heisenberg? Or perhaps you consider this question meaningless? As in your philosophy – what cannot be directly observed – does not exist.

Heisenberg: Not my philosophy – both mine and Niels’. The central Copenhagen tenet.

Bohr: Not to criticize, but again you are not quite right. This is only true at the atomic scale. Did I not tell you, time and again, that there is this fundamental dividing line – cut we call it – between the realm of atoms and that of the big things.

Heisenberg: Another superfluous duality!

Bohr: And on the scale of big things – in our everyday world – things are different.

Margrethe: Very different!

Bohr: So tell me, Heisenberg, what was your purpose when you came to see me on that visit?

Margrethe: Niels, that wartime visit was a hostile visit, no matter what people say or write about it.

Bohr: Yes, my dear, that’s what you said to Viktor Weisskopf at my funeral.

Heisenberg: We all had our funerals a long time ago. But look at that world – it is still there, and as beautiful as ever. Mountains, trees, flowers. The lakes and rivers of my Germany. The Faelled park near your home that we walked in and talked so many times. Our children, our children’s children… living their lives…

Bohr: Except those who perished in those years.

Margrethe: Or did not even get the chance to be born.

Bohr: How can we say that “now no one can be hurt, no one can be betrayed”?

Margrethe: How can we afford not to take a stand?

Bohr: Even if there is this ultimate uncertainty at the core of things…

* Barbara Druss Dibner Professor in History and Philosophy of Science
  Philosophy Department, The Hebrew University of Jerusalem