Image: Dansmuseet/Tobias Regell

It takes two to tango. We are interlocked in a dance with the world we see around us until death. If the universe is deterministic, the observed world leads the dance and the observing being follows. But, according to modern physics, each dancer can surprise the other with unexpected moves, taking the couple to parts of the dance floor that cannot be predicted.

If each dancer can surprise the other, and force a response, they are both indispensable to understand the ways of the world. Then the role of the subjective or the objective aspect of the world cannot be accounted for in terms of the other. The observer and the observed becomes equally fundamental.

This has been the take in my attempts to reconstruct physical law from underlying philosophical principles. I see the subjective and objective aspects of the world as two sides of a coin that can be distinguished but not meaningfully separated.

For example, to imagine an objective world that dances alone without any subjective partner in sight is a contradiction in terms, since the very word ‘imagine’ presupposes a subjective dance partner watching what goes on from the side lines.  

I have come to realise that this perspective resembles that of the renowned theoretical physicist John Archibald Wheeler in his later years. He coined the term participatory universe and came to believe that the relation between the observer and the observed is a crucial element in the world. Each one of us helps bring a collective world into being by our observations.

In a sense, this is the middle ground between a solipsistic idealism where the world is dreamed by a single subject, and metaphysical realism, where an objective world independent of any observers is all there is.

John Archibald Wheeler

Wheeler came to this view thinking about the conundrums of quantum mechanics. According to the original Copenhagen interpretation of the theory, it is meaningless to ask what moves the world makes on the floor when his observing dance partner loosens the grip and looks away.

This is so since all potential moves by the world in the time window before the observer grabs her partner again and fixes her gaze must be taken into account collectively in order to calculate correctly the probabilities what she will actually see at that point in time. The potential moves interfere with each other, and they all acquire a kind of quasi-reality.

Wheeler brought matters to a head by introducing the so-called delayed-choice experiment, devised in 1977. [1] In the tango metaphor it involves observing the tracks on the floor of the objective world, deducing its past moves. If the subjective dancer chooses to observe the tracks in a proper way, she can indeed deduce the past choreography.

But she can also choose to erase some tracks with a piece of clothing. And here comes the odd thing. To correctly calculate the pattern she will see on the floor after the sweeping of the cloth we again must take into account all potential tracks of the past.

Clearly, the subjective dancer has erased information about the past moves of the world. This is quite normal. A thief can hide her tracks. But not only that, she has denied the world any definite choreography at all at the passed point in time when it presumably should have been displayed. Further, by her choice of actions she can choose now whether to grant her dance partner any definite past choreography or not. This is quite a power.

Apparently, the history of the universe depends on how it is observed today. The obscure parts of the past seem to have no definitive reality until it is, perhaps, brought to light at some later time. If true, this highlights the essential role of the observer in the construction of the universe in the entire space-time domain.

Wheeler invented his own version of the game twenty questions to illustrate the state of affairs. Normally, a group of people agree upon a word, and another person asks yes-or-no questions to each one in the group. The interrogator wins if she converges on the agreed upon word before she has asked twenty questions.

In Wheeler’s version, each person in the group chooses her own word without telling the others. As the interrogator asks a question to one of the members and gets an answer, the others in the group may have to change their individually chosen words to be consistent with that answer. In the end, the word that the game converges on might not be any of the words chosen beforehand.

The word is clearly created in the interactive process of asking questions and selecting consistent answers, just like the moves of the objective world in the tango are not definite until his subjective partner checks them out. I let Wheeler describe the game and its interpretation in his own vivid words at the bottom of this blog post. The excerpt is taken from his essay Frontiers of Time. [2]

In Wheeler’s game, the group of people selecting words corresponds to the outside world, and the interrogator to the subject who poses questions about it, getting answers by observation or experiment. Both the word-selecting group and the interrogator have their freedom to make choices, and all these choices determine where the game ends up, at what final word.

In the same way, both dancers in the tango of the world can surprise their partner with their moves, taking the couple to unexpected parts of the dance floor.

Speaking less poetically and more physically, the observing subject has the freedom to choose what experiment to make, and the world has the freedom to select an outcome to that experiment, with probabilities given by the quantum mechanical formalism, as applied to the chosen experiment.

Both of these two kinds of choices change the state of the world and leads it into a new direction that could not have been predicted before the choices were made. And, according to present understanding of physics, the choice by the subject of the experiment to be made cannot be reduced to a probabilistic outcome of a meta-experiment, as discussed in another blog post.

Our tango with the world indeed seems to be an interactive improvisation. Sometimes the subjective observer leads, and maybe more often the objective observed world does. It feels like most of the time we must follow its merciless moves, dictated by the laws of physics. But sometimes the world has to follow us. Then it must produce an improvised response consistent with the same laws of physics.

To allow for the multitude of observers, we may see the world as a movie set, and ourselves as actors, rather than as a dancing couple. Here is a charming story about the mutual improvisations in the setting and among the actors that led to The Godfather – which in hindsight seems like an inevitable classic.

The following is an excerpt from the essay Frontiers of Time by John Wheeler

The universe can’t be Laplacean. It may be higgledy-piggledy. But have hope. Surely someday we will see the necessity of the quantum in its construction. Would you like a little story along this line?

Of course! About what?

About the game of twenty questions. You recall how it goes – one of the after-dinner party sent out of the living room, the others agreeing on a word, the one fated to be questioner returning and starting his questions. “Is it a living object?” “No.” “Is it here on earth?” “Yes.” So the questions go from respondent to respondent around the room until at length the word emerges: victory if in twenty tries or less; otherwise, defeat.

Then comes the moment when we are fourth to be sent from the room. We are locked out unbelievably long. On finally being readmitted, we find a smile on everyone’s face, sign of a joke or a plot. We innocently start our questions. At first the answers come quickly. Then each question begins to take longer in the answering – strange, when the answer itself is only a simple “yes” or “no.” At length, feeling hot on the trail, we ask, “Is the word ‘cloud’?” “Yes,” comes the reply, and everyone bursts out laughing. When we were out of the room, they explain, they had agreed not to agree in advance on any word at all. Each one around the circle could respond “yes” or “no” as he pleased to whatever question we put to him. But however he replied he had to have a word in mind compatible with his own reply – and with all the replies that went before. No wonder some of those decisions between “yes” and “no” proved so hard!

And the point of your story?

Compare the game in its two versions with physics in its two formulations, classical and quantum. First, we thought the word already existed “out there” as physics once thought that the position and momentum of the electron existed “out there,” independent of any act of observation. Second, in actuality the information about the word was brought into being step by step through the questions we raised, as the information about the electron is brought into being, step by step, by the experiments that the observer chooses to make. Third, if we had chosen to ask different questions we would have ended up with a different word – as the experimenter would have ended up with a different story for the doings of the electron if he had measured different quantities or the same quantities in a different order. Fourth, whatever power we had in bringing the particular word “cloud” into being was partial only. A major part of the selection – unknowing selection – lay in the “yes” or “no” replies of the colleagues around the room. Similarly, the experimenter has some substantial influence on what will happen to the electron by the choice of experiments he will do on it; but he knows there is much impredictability about what any given one of his measurements will disclose. Fifth, there was a “rule of the game” that required of every participant that his choice of yes or no should be compatible with some word. Similarly, there is a consistency about the observations made in physics. One person must be able to tell another in plain language what he finds and the second person must be able to verify the observation.

Go on!

That is difficult! Interesting though our comparison is between the world of physics and the world of the game, there is an important point of difference. The game has few participants and terminates after a few steps. In contrast, the making of observations is a continuing process. Moreover, it is extraordinarily difficult to state sharply and clearly where the community of observer-participants begins and where it ends.

This comparison between the world of quantum observations and the game of twenty questions misses much, but it makes the vital central point. In the real world of quantum physics, no elementary phenomenon is a phenomenon until it is an observed phenomenon. In the surprise version of the game no word is a word until that word is promoted to reality by the choice of questions asked and answers given. “Cloud” sitting there waiting to be found as we entered the room? Pure delusion! Momentum, px = 1,4 × 10-19 gcm/s, or position, x = 0,31 × 10-8 cm, of the electron waiting to be found as we start to probe the atom? Pure fantasy!

Mann may be going too far when he suggests [3] that “. . .we are actually bringing about what seems to be happening to us.” However, it is undeniable that each of us, as observer, is also one of the participants in bringing “reality” into being.


[1] John Archibald Wheeler, The “Past” and the “Delayed-Choice” Double-Slit Experiment. In: Mathematical Foundations of Quantum Theory, pp. 9–48, Ed. A. R. Marlow (Academic Press, 1978)

[2] John Archibald Wheeler, Frontiers of Time. In: Problems in the Foundations of Physics, pp. 395-497, Ed. G. Toraldo Di Francia (Elsevier, Amsterdam, 1979)

[3] Thomas Mann, Freud, Goethe, Wagner (New York, 1937), p. 20; translated by H. T. Lowe-Porter from Freud und die Zukunft (Vienna, 1936); the cited words were included in the lecture given at the 80th birthday celebration for Sigmund Freud, 8 May 1936.