Andrew Robinson and Dipankar Home shed some light on the conversations between Einstein and Tagore on the nature of reality.

If the moon, in the act of completing its eternal way around the earth, were gifted with self-consciousness, it would feel thoroughly convinced that it was travelling its way of its own accord on the strength of a resolution taken once and for all", Albert Einstein wrote in 1930 in a little-known statement entitled About Free Will. "Man defends himself from being regarded as an impotent object in the course of the Universe. But should the lawfulness of events, such as unveils itself more or less clearly in inorganic nature, cease to function in front of the activities in our brain?"

Einstein was addressing Rabindranath Tagore, poet, philosopher and fellow Nobel laureate, in a contribution to a Festschrift for Tagore's 70th birthday. During 1930 the two men had a number of meetings in which they discussed the nature of reality and the relationship of determinism to free will, and they differed from each other profoundly. Publicised at the time - initially in the New York Times - the Einstein/Tagore talks continue to spark interest because they tackle some of the fundamental questions debated within science since the advent of quantum theory. The philosopher Sir Isaiah Berlin, who regards Tagore as a "highly gifted thinker", calls the talks "a complete non-meeting of minds". Brian Josephson, a Nobel laureate in physics, believes that "Tagore is saying that truth is a subtler concept than Einstein realises". Ilya Prigogine, a Nobel laureate in chemistry, goes so far as to say: "Curiously enough, the present evolution of science is running in the direction stated by the great Indian poet."

Instead of their minds meeting, the two men seem mostly to have talked past each other, where they did not openly disagree. A comparable mismatch occurred, famously, between Einstein and Niels Bohr, and lasted for 30 years right up to Einstein's death in 1955. A frustrated Bohr was never able to bring Einstein round to accepting the majority view of quantum theory. Although the philosophical views of Bohr and Tagore differ in crucial respects, there are important similarities too.

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Einstein, as he aged, adhered to a belief in realism - that the physical world has objectivity that transcends direct experience, and that propositions are true or false independent of our ability to discern which they are. Provoked by Tagore, Einstein expressed this belief in a remarkably clear-cut fashion:

E:"There are two different conceptions about the nature of the universe - the world as a unity dependent on humanity, and the world as reality independent of the human factor ."

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T: "This world is a human world - the scientific view of it is also that of the scientific man. Therefore, the world apart from us does not exist; it is a relative world, depending for its reality upon our consciousness."

A little later, Einstein took up the point again:

E:"Truth, then, or beauty, is not independent of man?"

T: "No."

E:"If there were no human beings any more, the Apollo Belvedere no longer would be beautiful?"

T: "No."

E:"I agree with regard to this conception of beauty, but not with regard to truth."

T: "Why not? Truth is realised through men."

Here, according to a later account by the note-taker, there was a long pause. Then Einstein spoke again very softly:

"I cannot prove my conception is right, but that is my religion."

After some further discussion - in which Einstein asserted, "I cannot prove, but I believe in the Pythagorean argument, that the truth is independent of human beings" - Einstein became concrete: "The mind acknowledges realities outside of it, independent of it. For instance, nobody may be in this house, yet that table remains where it is."

T: "Yes, it remains outside the individual mind, but not the universal mind. The table is that which is perceptible by some kind of consciousness we possess."

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E:"If nobody were in the house the table would exist all the same, but this is already illegitimate from your point of view, because we cannot explain what it means, that the table is there, independently of us. Our natural point of view in regard to the existence of truth apart from humanity cannot be explained or proved, but it is a belief which nobody can lack - not even primitive beings. We attribute to truth a superhuman objectivity. It is indispensable for us - this reality which is independent of our existence and our experience and our mind - though we cannot say what it means."

T: "In any case, if there be any truth absolutely unrelated to humanity, then for us it is absolutely non-existing."

E:"Then I am more religious than you are!"

(Here, said the note-taker, Einstein "exclaimed in triumph".)

The position of Einstein in this last extract is reminiscent of his well-known paradox: "The most incomprehensible fact about nature is that it is comprehensible." Nature, for Einstein, had to be independent of man and mind. He could not accept any idea that a universal mind might control nature. Tagore, by contrast, could accept this. As he said to Einstein: "What we call truth lies in the rational harmony between the subjective and objective aspects of reality, both of which belong to the super-personal man." In other words, Tagore did not adhere either to Einstein's realist, essentially objective position or to Bohr's quasi-positivist, essentially subjective view of nature, a position that, taken to its logical extreme, denies the existence of the physical world - or at least its dynamical properties - until they are measured. Tagore did not deny the existence of the table when nobody was in the house, but he argued that its existence becomes meaningful for us only when it is perceived by some conscious mind. And he said, further, that there is a universality in the nature of consciousness (contrary to our normal sense of consciousness as essentially private).

What did Tagore mean by this concept of a universal human mind? He once wrote: "The Universe is like a cobweb and minds are the spiders; for mind is one as well as many." He tried to amplify his meaning in his conversation with Einstein. Pursuing the example of the table, Tagore said: "Science has proved that the table as a solid object is an appearance and therefore that which the human mind perceives as a table would not exist if that mind were naught. At the same time it must be admitted that the fact that the ultimate physical reality of the table is nothing but a multitude of separate revolving centres of electric force, also belongs to the human mind. In the apprehension of truth there is an eternal conflict between the universal human mind and the same mind confined in the individual. The perpetual process of reconciliation is being carried on in our science, philosophy, (and) in our ethics".

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If mind/consciousness, the first-person perspective, is somehow to be incorporated into physics, as certain physicists believe it should be, this must inevitably entail consequences as dramatic as those involved in the introduction of relativity by Einstein. For it would mean an acceptance of evolution and complexity - time's "arrow" - as integral to the physical world, and an abandonment of the long-cherished hope, shared by Einstein, of one day finding fundamental, reversible laws, of beautiful simplicity, that will by themselves explain the workings of the universe. According to Prigogine: "We have to face the fact that we live in a dual universe, whose description involves both laws and events, certitudes and probabilities."

But God does not play dice, said Einstein. He was committed to the realism, determinism and strict causality of classical physics, as he made plain to Tagore in their second, more free-ranging conversation :

T: "I was discussing with Dr Mendel (a friend of Einstein) today the new mathematical discoveries which tell us that in the realm of infinitesimal atoms chance has its play; the drama of existence is not absolutely predestined in character."

E:"The facts that make science tend towards this view do not say goodbye to causality."

T: "Maybe not; but it appears that the idea of causality is not in the elements, that some other force builds up with them an organised universe."

E:"One tries to understand how the order is the higher plane. The order is there, where the big elements combine and guide existence; but in the minute elements this order is not perceptible."

T: "This duality is in the depths of existence - the contradiction of free impulse and directive will which works upon it and evolves an orderly scheme of things."

E:"Modern physics would not say they are contradictory. Clouds look one from a distance, but if you see them near, they show themselves in disorderly drops of water."

Tagore continued: "Are the elements rebellious, dynamic with individual impulse? And is there a principle in the physical world which dominates them and puts them into an orderly organisation?"

E:"Even the elements are not without statistical order; elements of radium will always maintain their specific order, now and ever onwards, just as they have done all along. There is, then, a statistical order in the elements."

T: "Otherwise the drama of existence would be too desultory. It is the constant harmony of chance and determination which makes it eternally new and living."

E:"I believe that whatever we do or live for has its causality; it is good, however, that we cannot look through it."

To summarise, then, we can discern three philosophical attitudes towards the relationship between man and nature arising from the Einstein-Tagore conversations. The first, held by Einstein, is that nature exists, objectively, whether we know it or not. Hence Einstein thought it was essential to describe "what nature does" instead of merely "speaking of what we know about nature". The second, held by Bohr, is that the objective existence of nature has no meaning independent of the measurement process. The third position, held by Tagore, is more complex. Tagore says, centrally, that nature can be conceived only in terms of our mental constructions based on what we think we perceive: to reiterate his earlier comment, "This world is a human world - the scientific view of it is also that of the scientific man." Tagore says further - and it is a separate though dependent point - that there exists a universal mind.

Obviously these are extremely difficult problems with an ancient philosophical and scientific pedigree. In 1611, Galileo noted that "it would seem ridiculous to me to believe that things in nature begin to exist when we begin to discover and understand them." Einstein went on worrying at the "reality question" until the day he died; so, less conspicuously, did Tagore. Neither came to a definite conclusion. All three viewpoints have adherents throughout science today, with Bohr's predominating among quantum physicists and Tagore's the least accepted of the three. It will be interesting to see how the balance alters as science changes: will Prigogine's prediction - that science is evolving according to Tagore - come true during the next century? For now, perhaps we must be content with the view of a ruminant Richard Feynman, talking shortly before his death in 1988: "The problem of existence is a very interesting and difficult one . . . . When you discover things in mathematics you get the idea that somehow they existed somewhere, but there's nowhere for such things . . . . Well, in the case of physics we have double trouble. We come upon these mathematical interrelationships but they apply to the universe, so the problem of where they are is doubly confusing . . . . Those are philosophical questions that I don't know how to answer."

Andrew Robinson is literary editor of The THES and the author, with Krishna Dutta, of Rabindranath Tagore: The Myriad-Minded Man, published by Bloomsbury. Physicist Dipankar Home is a Homi Bhabha fellow at the Bose Institute, Calcutta, who is writing a book on quantum theory.

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