2. Let Us Start from the Final Result, or Put the Horse in Front of the Cart

In the spring of 1979 I found myself in Dubna near Moscow, at the Joint Institute for Nuclear Research. I spent three months there writing my diploma thesis and for the first time entered the real whirl of big science: seminars, conferences, meetings, and anniversary sessions.

Of the many stories I heard then, two remained especially vivid. Much later both became unexpectedly connected, for me, with the problem of gravitational collapse.

The first was told at one of the anniversary meetings marking thirty years since the test of the first Soviet atomic bomb.

One of Kurchatov's close associates recalled a curious episode from the history of the atomic project.

After the successful test, the government instructed the project leaders to propose who should receive which ranks, awards, apartments, country houses, cars, bonuses, and other benefits.

One might think that after solving problems immeasurably more difficult, distributing rewards among the participants would be easy.

The opposite happened.

Several groups of scientists and engineers who had worked together for years on an extraordinarily difficult common task quickly fell into quarrels. Each considered its own contribution the most important and could explain why its work had been decisive.

When the heads of these groups met with Kurchatov, they admitted that they could not reach agreement and effectively asked him to decide.

Kurchatov then proposed an unexpectedly simple criterion.

He said, approximately:

— Let us start with the final result. Imagine that the bomb had failed to explode. Who among us would have answered for the failure first?

Everyone immediately stopped arguing.

The first few names were obvious. The project leader and those responsible for the key areas would have paid much more heavily than the rest — perhaps with freedom, position, property, and in that era possibly with still more severe consequences.

— Then they, — Kurchatov concluded, — should receive the highest rewards.

The next group would have borne somewhat less responsibility in case of failure, so their rewards should be one level lower.

Then another level.

And so on.

The dispute ended almost at once.

It turned out that people found it difficult to measure their own merit, but could assess much more objectively the measure of responsibility they would have carried in case of failure.

I remembered this story for the rest of my life.

Since then, when arguments arise about the importance of contributions, merits, and priority, I often recall this principle:

start with the final result.

What exactly would have been lost if that result had not been achieved?

Who was really responsible for what?

Sometimes this way of posing the question puts things in order better than a multitude of formal criteria.

A candidate is not yet a discovery

The second episode occurred at an anniversary meeting dedicated to Einstein's centenary in the large hall of the Physical Institute in Moscow.

World-famous physicists spoke there. Many were almost legendary figures to me; until then I had known them only from books and papers.

I especially remember a half-joking exchange between Yakov Zeldovich and Vitaly Ginzburg.

Zeldovich spoke enthusiastically about neutron stars and recently discovered compact objects which, he said, were most probably black holes.

At the beginning of the talk he was careful: black-hole candidates.

But soon, for brevity, he began simply saying this black hole, the mass of the black hole, the rotation of the black hole.

Ginzburg then stood up and reminded him that what was being observed were still only candidates.

Until direct confirmation of the principal distinguishing feature was obtained, it was premature to turn a hypothesis into an established fact.

Zeldovich laughed and explained that he was omitting the word “candidate” only so as not to repeat it in every sentence.

The hall laughed too.

The exchange was longer, but this is how its meaning remained in my memory.

It also revealed an important feature of the scientific culture of that generation: even committed supporters of a particular theoretical picture still clearly distinguished what theory assumed from what observations had actually established.

The distinction seems elementary.

Yet elementary things are sometimes forgotten with time.

How the word “candidate” disappeared

Decades passed.

The words “black-hole candidate” were used less and less often.

This did not happen because someone had gained a direct view into such an object or had unambiguously confirmed the entire proposed scenario of its formation.

The language simply changed gradually.

First for brevity.

Then from habit.

And eventually the habit itself began to be taken as evidence.

Compact massive objects were increasingly called black holes without qualification.

In scientific literature this can still be understood as terminology adopted within a particular model. But the same terminology then entered textbooks, popular literature, and the mass media, where it came to be perceived as a name for a directly observed fact.

For me this later became one of the clearest examples of how the logical status of a scientific statement can change almost unnoticed.

First:

if the theory is correct, such an object should be a black hole.

Then:

the observed object agrees well with some predictions of the black-hole model.

Finally:

a black hole is observed.

These are three different statements.

But in public perception the distinction between them disappeared.

When I too stopped doubting

Curiously, when I was young I went through the same path myself.

In 1983, while visiting Kyiv on dissertation business, I attended an international symposium on gravitation and astrophysics. Zeldovich chaired one of the main sessions.

I listened to the talks and was surprised by the speakers' complete confidence in the existence of black holes.

Yet the authority of the participants was so great, and the general atmosphere so unanimous, that I too soon stopped seeing any problem.

If all the specialists are sure, I thought, the issue must already be practically settled.

Only details remain.

At that time I was working on completely different problems and had not yet become seriously interested in gravitation.

A few years later, after developing the first version of ideas that would eventually lead to my diffusion interpretation of quantum mechanics, I was again in Moscow and decided to discuss them with Zeldovich.

But quantum mechanics itself was not my only concern.

There was a question I simply could not understand then: what happens when gravity is taken into account at extremely small, Planck-scale distances?

Quantum theory continuously involves virtual particles and energy fluctuations. At Planck scales, however, their energies should become so large, and the corresponding gravity so strong, that one might expect tiny regions of powerful gravitational collapse — a kind of mini black hole — to form.

If that really happens, what is space like on such scales?

If it does not happen, what prevents their formation?

And how are quantum processes and general relativity supposed to fit together there?

These questions seemed extremely important to me because I wanted precisely to understand physical processes at very small distances.

I went to Zeldovich's small office, briefly described my ideas about quantum mechanics, and then tried to turn to this problem.

He listened carefully and asked a few questions, but the discussion I had hoped for did not take place. My reasoning was still rather naive, and the problem itself proved much less clear than I had assumed.

Zeldovich said approximately what I later heard from Ginzburg: very few people truly understood such questions, while many different and often contradictory opinions existed.

He also did not go into a detailed discussion of my interpretation of quantum mechanics and advised me to speak with Ginzburg.

I called Ginzburg from a street telephone.

I briefly described both my idea and the same difficulty: what should happen at Planck distances, where quantum fluctuations can no longer be separated from extremely strong gravity?

He too listened and asked several questions, but the substance of the answer was similar: there was no clear generally accepted understanding, only many different and conflicting views.

As for my work on quantum mechanics, Ginzburg said that one of his students was working on that range of problems and that I should discuss it with him.

That was essentially the end of my attempts to continue the conversation at the time.

When one is young, such episodes are more painful than they seem later. One assumes that an important question must interest a famous scientist simply because it is important.

With time one understands that everyone has a circle of problems, limited time, and priorities. And some fundamental questions can remain so unclear for decades that even the greatest specialists prefer not to give a definite answer.

For me, however, the question of what happens to gravity at the smallest distances did not disappear.

On the contrary, the wish to understand it one day later forced me first to study classical general relativity much more deeply.

Quantum gravity was supposed to solve everything

In those years fundamental physics lived in expectation of a quantum theory of gravity.

It seemed that such a theory would solve all the deep problems: the structure of spacetime at short distances, singularities, and the interior of black holes.

For that reason many regarded Einstein's classical theory of gravitation as an almost completed chapter of physics.

I thought so too.

It seemed to me that the basic questions of classical gravity had long been settled and that the real mysteries began only where gravity had to be combined with quantum theory.

Only much later did I understand how premature that view was.

Before correcting Einstein's theory, one first had to establish with complete precision:

what does the theory itself actually predict?

Starting from the end

I returned seriously to the problem of gravitational collapse in the late 1990s.

Here the old story about Kurchatov unexpectedly became useful.

I began with the final result.

The black-hole picture led to a multitude of extremely difficult fundamental questions. In the standard account, collapse ends with the formation of a horizon and an inner region whose causal structure differs radically from the ordinary one. The singularity problem then arises, and attempts to include quantum processes produce further paradoxes.

John Wheeler, one of the founders of the black-hole hypothesis, called gravitational collapse one of the greatest crises in physics.

I therefore posed the question from the opposite end:

what must a theory of gravity be like so that a black hole cannot form at all?

Today that formulation seems unnecessarily complicated to me.

At the time it looked natural.

For several years I studied different ways of modifying gravitational theory, examined known alternatives, and devised variants of my own.

Some seemed very attractive.

One after another, however, they proved untenable.

The theory had to be made more complicated by adding assumptions, mechanisms, fields, or restrictions.

Yet the result remained unsatisfactory.

Einstein did not need to be changed

Then came the most unexpected development.

Gradually it became clear that general relativity did not need to be changed at all.

The problem was not Einstein's theory itself, but the way the collapse process had been interpreted.

When I began consistently to describe the motion of a collapsing star in world time and to compare the states of its different parts at the same moment of that time, the picture changed radically.

What had previously looked like the inevitable fall of matter through the gravitational radius turned into a process of ever stronger slowing.

As the critical region is approached, the rate of the matter's proper time relative to world time slows more and more.

Collapse does not end with the surface of the star passing through its own gravitational radius.

It freezes asymptotically.

The star becomes not a black hole but a gravitationally frozen object.

Later I called such an object a frozar, from frozen star.

This was an unexpected result.

For several years I had searched for a way to change Einstein's theory so as to prevent black-hole formation.

It turned out that this was unnecessary.

One only had to apply the theory itself consistently.

From the end back to the beginning

The picture finally took shape for me around 2004.

I then spent about two more years checking the calculations, studying the literature, and considering possible objections.

My first papers on the new interpretation of gravitational collapse appeared in 2006.

Since then its basic principles have not changed for me.

Details changed.

The range of systems considered expanded.

New consequences appeared.

But the initial idea remained the same:

when collapse is described consistently in general relativity, it produces not a black hole but a frozar — an object whose further contraction slows more and more with respect to world time.

Thus the old joke that it can sometimes be useful to begin with the final result unexpectedly became a working method of research for me.

I started with the question:

what must be changed in the laws of nature so that black holes do not exist?

And I arrived at a much simpler question:

what happens if nothing is changed at all and Einstein's theory is simply applied consistently?

Sometimes we search for something new where we should first have understood the old more carefully.

In this case that turned out to be the essential point.

I began with the end — and only then reached the beginning.