June 25, 2005

If ONE was asked to name two geniuses who dominated physics in the previous millennium, most people will be quick to mention Newton and Einstein. I mean, after all, they did transform the way we perceive physics today. However, I beg to differ, for the overarching achievement of these intellectual giants in vastly different periods makes it unfair to at least one of them.

Sent home from Cambridge to avoid the plague, Newton within a year-and-a-half invented calculus, elucidated gravity, laid down the three laws of motion and developed a theory of optics. These years, 1665-1666, were Newton’s annis mirabilis (years of wonders). His fleeting discoveries completely revolutionized physics, accelerating the process of scientific discovery, initiated by Galileo. It became possible to explain most physical phenomena, largely based on Newton’s theories.

In the second half of the 19th century, a Scottish physicist, James Clerk Maxwell, provided a powerful mathematical basis for the electrical phenomena that had earlier been discovered by the Englishman Michael Faraday. Maxwell’s equations showed that all radiation, including light, propagated as electrical and magnetic waves at a constant velocity.

With mechanics and statistical mechanics taken care of, physicists became confident that all physical phenomena could be completely explained by using these basic concepts. But then, in a span of few years before 1900, this confidence began to unravel. A string of phenomena were discovered that could not be explained by classical Newtonian physics.

Come 1905 and Albert Einstein came to the rescue, bubbling with revolutionary ideas, which would transform physics. In three remarkable papers written in little more than eight months, he showed that atoms are real, laid out his special theory of relativity and breathed life into quantum mechanics. Einstein’s anni mirabiles (year of wonder) was no less startling than Newton’s. They were both in their mid-twenties when their intellectual prowess peaked. Where Newton had to invent calculus to describe mechanics, Einstein had to revise notions of space and time.

This was just the beginning — Einstein went on to publish his most revolutionary work on the general theory of relativity and to pioneer a new field of quantum mechanics. Both are remarkably accurate in their domain of the very large and the very small. Applying general relativity to the very small scales of atomic and nuclear phenomena, where quantum physics is the dominant mechanism, leads to inconsistencies, which despite 40 years of effort by Einstein, could not be removed satisfactorily. The quest goes on as string theorists for the last two decades have tried to formulate a quantum theory of gravitation that overcomes many technical problems that seemed insurmountable previously.

Quantum mechanics remained for Einstein an incomplete theory, whose philosophical foundations he was uncomfortable with. By poking holes in the theory and its implications, he invited its stronger proponents, such as Neils Bohr, to counter his reservations, thereby strengthening arguments in favour of the new theory. He did not, however, reject quantum mechanics, and his statement that “God does not play dice” is wrongly used to suggest otherwise. He, in fact, proposed the names of Schrödinger and Heisenberg, leaders in the younger pack that developed the new quantum mechanics, for a Nobel Prize.

The man’s power lay in thinking more clearly about the physical consequences of experimental results than any of his contemporaries, in fact, of anyone since then. With so many open questions in physics today, it would be pertinent to ask what Einstein would be working on now, were he still alive? What are the problems that young physicists ought to be looking at?

Much of the fundamental progress in physics to date, especially at the start of the 1900s, has occurred when experimental findings could not be explained by existing theories. The discrepancies forced a rethink of the theoretical foundations until a closer fit with experimental results was found.

The dynamic interaction of pure theory and experimental observations are essential for solid progress. Instruments and experiments of amazing precision are making it increasingly possible to test or constrain the predictions of theories, which in turn, are pushing experimentalists to develop more sensitive experiments.

Some of the significant questions in theoretical physics that experts feel have a good chance of being answered through experiments in the next 50 years are:

1. Is the current formulation of quantum mechanics true, or should it be modified to have a sensible physical interpretation?

2. What is the structure of space and time on the Planck scale, that is, are 12 orders of magnitude smaller than an atomic nucleus?

3. What explains the exact values of the parameters that determine the properties of elementary particles, including their masses and strengths of the forces by which they interact?

4. What explains the large ratios of scales we observe? Why is the gravitational force between two protons smaller than their electrical repulsion? Why is the universe so big? Why is it at least sixty powers of ten bigger than the fundamental Planck’s scale?

5. What was the Big Bang? What determined the properties of the universe that emerged from it? Was the Big Bang the origin of the universe? If not, what happened before it?

6. What constitutes dark matter and dark energy that make up between 80 and 95 per cent of the density of the universe?

7. How did the galaxies form? What do the patterns we observe in the distribution of the galaxies tell us about the early evolution of the universe?

The first four questions remain unanswered and add to the dilemma of unsolved riddles from fifty years ago. The other three are new. These questions, taken from an essay by a well-known theoretical physicist, Lee Smolin, could perhaps be supplemented by others, depending on the insight and interests of equally profound physicists. It is problems such as these, which, when attempted and solved, lead to the fundamental transformation in our understanding of the universe. Totally new theoretical insights by a new Einstein could speed up the resolution of some or all these issues.

It is up to young physicists joining the game at this exciting moment to dedicate their lives to such problems. This should, however, not exclude attention from other very interesting problems that do not necessarily lead to revolutionary insights. After all, Einstein too, first looked at some practical problems — those connected with mere particles in fluid undergoing Brownian motion and the designing of a refrigerator.

Einstein’s way of grappling with a physical problem, whether it was about cosmology or the design of a refrigerator, lay in focusing on the key features of the phenomena under study. This meant removal of all extraneous features that tend to cloud one’s understanding of the fundamental issue. Then, he would use insight and mathematics to solve it. It is this approach to problem solving that could lead us to understand and crack the physical problems that confront us. And, of course, to have a bit of fun.

The writer holds a doctorate in physics from Edinburgh University, Scotland, and is interested in the popularization of environmental issues, science and mathematics

The bomb that shook the world

The bomb had taken 43 seconds to fall from the B-29. There were small holes around its midpoint where wires had been tugged out of it as it dropped away, starting the clock switches of its first arming system.

More small holes had been drilled further back on its dark steel casing and those took in samples of air as the free fall continued. At 7,000 feet above the ground, a barometric switch primed the second arming system.

From the ground the B-29 was just visible, but the bomb — a bare 10ft long, 2.5ft wide — was too small to see. Weak radio signals were pumped down from the bomb to the Shina Hospital directly below. Some signals were absorbed in the hospital’s walls, but most bounced back skywards. Sticking out of the bomb’s back, near the spinning fins, were a number of whip-like radio antennae.

Nowhere on Earth had a ball of several dozen pounds of such purified uranium ever been accumulated. There were a number of stray neutrons loose inside it. Although the uranium atoms were densely protected by their outer flurries of electrons, the escaped neutrons — having no electrical charge —weren’t affected by the electrons. They flew through the outer electron barrier like a probe skimming past the planets down towards our sun. While many flew straight on out the other side, a few were on a collision course for the speck of a nucleus.

They overbalanced the nucleus, making it jostle and wobble. The uranium atoms mined on Earth were each more than 4.5bn years old. Only a very powerful force, before the Earth was formed, had been able to squeeze their electrically crackling protons together. Once that uranium had been formed, the strong nuclear force had held the protons in place over all that long span: while the Earth cooled, and continents formed; as America separated from Europe, and the North Atlantic Ocean slowly filled; as volcanic bursts widened on the other side of the globe, forming what would become Japan. A single extra neutron unbalanced that stability.

A single nucleus doesn’t weigh much. Its speeding impact into the other parts of the uranium didn’t heat it up much. But the density of uranium was enough that a chain reaction started, and soon there weren’t just two speeding fragments of uranium nuclei, there were four, then eight, then 16, and so on.

Mass was “disappearing” within the atoms, and coming out as the energy of speeding nuclei fragments. E=mc2 was under way. The bomb fell just a fraction of an inch in the time of most of the reaction. Only the first odd bucklings of its steel surface suggested what was going on inside. The chain reaction went through 80 generations of doubling before it ended. By the last few of those, the segments of broken uranium nuclei were so abundant that they started to heat the metal around them.

All the action of the E=mc2 reaction was over. No more mass was disappearing; no more fresh energy appeared. The energy in the movement of those nuclei was simply being transformed to heat — just as rubbing your hands together will make your palms warm up. But the uranium fragments rubbed against resting metal at immense speed, due to the multiplication by the immense value of C2 (the square of the speed of light).

The metals inside the bomb begin to warm. They had started at near body temperature — 98.6F or 37C — reached water’s boiling point — 100C — then that of lead — 560C. But the generations of chain reaction doubling had gone on, as yet more uranium atoms had been splitting.

An object resembling a giant sun fills several hundred times more of the sky than earth’s sun. It burns at full power for about half a second, then begins to fade, taking two or three seconds to empty itself, spraying heat energy outward. Fires begin, seemingly instantaneously; skin explodes off, hanging in great sheets from the bodies of everyone below. The first of the tens of thousands of deaths in Hiroshima begin.

The heat accelerates the air to speeds several times faster than any hurricane — so fast it outruns any sound its immense force might make. There is a second air pulse, a little slower; after that the atmosphere sloshes back, to fill up the gap. This briefly lowers the air density to virtually zero. Far enough from the blast, life forms that have survived will begin to explode outward, having been exposed to the vacuum of outer space.

A small amount of the heat remains, hovering quite close to where the fuses and antennae and cordite had been. In a few seconds it begins to rise. It swells as it goes, and at sufficient height it spreads out. As that great mushroom cloud appears, E=mc2’s first work on planet Earth is done. — Dawn/The Guardian News Service

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