Generally considered one of the most influential physicists in history, Albert Einstein’s (1879-1955) groundbreaking theories reshaped the scientific community’s view and understanding of the universe. He developed the special and general theories of relativity and won the Nobel Prize in Physics in 1921 for his explanation of the photoelectric effect.

Martin Rees is President of the Royal Society and also Master of Trinity College, and Professor of Cosmology and Astrophysics at the University of Cambridge. He is also a Visiting Professor at Leicester University and Imperial College London. He was appointed Astronomer Royal in 1995 and was nominated to the House of Lords in 2005 as a cross-bench peer. He was appointed a member of the Order of Merit in 2007. He has authored or co-authored about five hundred research papers and written widely on science and policy and is the author of seven books for a general readership.

Simply Charly: Generally speaking, 1905 is considered as Albert Einstein’s “annus mirabilis,” the miracle year during which he published five groundbreaking papers exploring some monumental ideas about time and space. Was his work during that year really of such colossal importance?

Martin Rees: Einstein’s greatest work was over well before he was 40. He was an amazing young scientist whose achievements have shaped our present view of the universe. Einstein’s 1905 papers were all classics. What’s astonishing is that they came, in a single year, from one unknown young man who worked in the Berne Patent Office. But it’s his theory of general relativity, completed ten years later, that elevates him to a status matched only by Newton. His vision of gravity—that “Space tells matter how to move; matter tells space how to curve” was revolutionary. But if Einstein hadn’t existed, the same insights would surely have emerged within a few years.

SC: Einstein was a theoretical physicist—one who used pencil and paper, along with sheer brainpower, to tease out the riddles of the universe. How right was he? Have all the tests that physicists devised to date yielded results consistent with his theory of general relativity?

MR: Einstein’s theories were not primarily motivated to explain particular observations. He was guided mainly by pure thought and deep intuition. His internal logic seemed so compelling he felt little need to defend it against criticism. For example, when asked what he’d have thought if the eclipse expeditions had got a discordant result, he said, “I’d be sorry for the good Lord—the theory is correct.” Indeed, general relativity was so far ahead of its time it remained for decades an austere intellectual monument sidelined from mainstream physics. Arthur Stanley Eddington, a British astrophysicist who wrote a number of articles to explain Einstein’s theory of general relativity, was once asked if it was true that only three people understood it. He’s rumored to have inquired who the third one was. That’s in glaring contrast to today. Cosmology and black holes, where the theory’s crucial, are among the liveliest research frontiers. And it’s been confirmed with high precision-indeed we prove it whenever you use the GPS system that would have serious cumulative errors if programmed assuming Newtonian gravity.

SC: Do you feel there is a lot more to physical reality than meets the eye (or telescope)? And if so, do you think we’ll ever come to a complete picture of reality? Or are our minds not capacious enough to wrap our heads around it?

MR: It is important to set our Earth in a broader cosmic context, and to understand the origins of planets, stars, and the atoms they’re made of. Modern technology has revealed to us a more varied and even vaster cosmos than Einstein envisaged. Probes to other planets have beamed back pictures of varied and distinctive worlds. The recent views from Titan, nearly a billion miles away, are the latest triumph of this quest. With our telescopes, we see places where stars form, and we see stars dying. We’ve recently learned something that’s made the night sky far more interesting: Stars aren’t mere twinkling “points of light.” They’re orbited by retinues of planets, just like the Sun is. Within 20 years, instruments will detect planets the same size as our Earth, orbiting other Sun-like stars. To envisage what we’ll learn, suppose you were viewing the Earth from (say) 30 light-years away—the distance of a nearby star. It would seem, in Carl Sagan’s phrase, a “pale blue dot,” very close to a star (our Sun) that outshines it by many billions: a firefly next to a searchlight. The shade of blue would be slightly different, depending on whether the Pacific ocean or the Eurasian landmass was facing us. Even though they won’t resolve surface detail with instruments at our disposal, we’ll infer the length of their “day,” their gross topography, even their climate. By analyzing a planet’s light, we could get clues to whether it had a biosphere. Let’s now enlarge our horizons further. If we could get two million light-years away and look back, we’d see something like this: Our Sun would be an ordinary star, out towards the edge. This is actually Andromeda—a galaxy, like the one we’re in, containing a hundred billion stars. But what about the still wider cosmos?

The Hubble Deep Field shows a small patch of sky, less than a hundredth of the area covered by a full moon. It’s the deepest exposure ever taken. Each faint smudge of light is actually an entire galaxy, which appears so small and faint because of its huge distance. The light from these remote galaxies set out up to 10 billion years ago. They’re being viewed when they have only recently formed. Some consist mainly of glowing diffuse gas that hasn’t yet condensed into stars. When we look at Andromeda, we might wonder whether there are aliens looking back at us, … perhaps there are. But the light we see from these remote galaxies set out before there’d been time for stars to forge the silicon, carbon, and oxygen needed even to make planets, so there’s scant chance of life.

SC: What other insight can you offer us into the mysteries of the cosmos and Einstein’s contributions to our knowledge of it?

MR: The great astrophysicist Subrahmanyan Chandrasekhar wrote: “In my entire scientific life, the most shattering experience has been the realization that an exact solution of Einstein’s equations provides the absolutely exact description of untold numbers of massive black holes that populate the universe.” A theory like Einstein’s is also essential for a consistent picture of the entire expanding universe. Cosmologists are sometimes berated for being “often in error, but never in doubt.” But even the more cautious among us are confident that our universe is the expanding aftermath of a “big bang” nearly 14 billion years ago.

The most compelling evidence is that all space is pervaded by weak thermal microwaves-the diluted and cooled afterglow of the hot, dense beginning. After the first microsecond, conditions are as confidently established by the “fossil” evidence as most of what we know about the early history of the Earth. Ancient cartographers wrote “here be dragons” beyond the boundaries of the then-known world. These “dragons” have now been driven back into the first microsecond when conditions are so extreme that experiments offer no guide to the relevant physics.

Our present complex cosmos manifests a huge range of temperature and density. People sometimes worry about how this intricate complexity emerged from an amorphous fireball. It might seem to violate a hallowed physical principle—the second law of thermodynamics—which describes an inexorable tendency for patterns and structure to decay or disperse.

The answer to this seeming paradox lies the force of gravity, which amplifies small initial density contrasts in an expanding universe. Any patch that starts off slightly denser than average would decelerate more, because it feels extra gravity; its expansion lags further and further behind, until it eventually stops expanding and separates out.

SC: Einstein spent his remaining years seeking a unified theory of everything—one that would link together all known physical phenomena. Based on what we know today, is such “unification” feasible?

MR: Our everyday world is determined by atoms and chemistry. Stars are powered by nuclear fusion—all the atoms we’re made of are nuclear waste from long-dead stars. Galaxies are seemingly held together by swarms of subnuclear particles that make up the “dark matter.” General relativity and quantum theory are the twin pillars of 20th-century physics. But at the deepest level, they contradict each other—they haven’t yet been meshed together into a single unified theory. In most contexts, this doesn’t impede us because their domains of relevance don’t overlap. Astronomers can ignore the quantum fuzziness in the orbits of planets.

Conversely, chemists can safely ignore gravitational forces between individual atoms in a molecule: they’re nearly 40 powers of ten feebler than electrical forces, But at the very beginning, when everything was squeezed smaller than a single atom, quantum fluctuations could shake the entire universe. To confront the overwhelming mystery of what banged and why it banged, we need a unified theory of cosmos and microworld. Einstein spent the last half of his life searching in vain for such a theory. In retrospect, his efforts were doomed, because he didn’t know about the nuclear force, and because he famously wouldn’t accept quantum mechanics. But there’s now intense effort on these theories. Just as all material has an atomic structure, theorists believe space and time are themselves structured on some tiny scale—a trillion trillion times smaller than atoms. According to superstring theory, what we think of as a point in our ordinary space may actually be a complex origami in six further dimensions, so tightly wrapped that it’s very hard to detect it. (It’s rather baffling. It could be due to “lambda”—a term Einstein added to his equations, back in 1917. He added it because he wanted a static universe. He abandoned it when the expansion was discovered. But it looks as though what he called his “biggest blunder” might be vindicated. If my research group had a logo, it would be this.

SC: If Einstein were alive today, what knowledge we have gained since his death would surprise him the most?

MR: That we’re in an accelerating universe, probably dominated by the cosmological constant “lambda.” And that the elaborate geometry of ten dimensions may lead to the unified theory he vainly sought. I say “may,” because there’s no guarantee that even a “new Einstein” would succeed-but the quest is no longer premature. There’s one fascinating possibility that these new ideas raise. But it’s so speculative that it should be prefaced by a “health warning”: It’s that there may be far more to physical reality than what we’ve traditionally called “our universe”—the aftermath of our bang. Just as we’ve learned that our solar system is one planetary system among zillions, so we may discover that our big bang was not the only one. Another idea is that there could be another universe only a millimeter away. But if that millimeter is measured in a fourth dimension and we’re imprisoned in our three, we’ll be unaware of it. However, we shouldn’t take such ideas seriously until there’s a unified theory that’s been experimentally vindicated—but it’s speculative physics, not metaphysics.

Achieving such a theory would be the culmination of an intellectual quest that started with Faraday and Maxwell’s unification of electric and magnetic forces. It would exemplify what the great physicist Eugene Wigner called “the unreasonable effectiveness of mathematics in the physical sciences.” But I hope it’s not curmudgeonly to point out that such a theory would offer absolutely zero help to 99 percent of scientists. Calling it a “theory of everything,” as some popular books do, is hubristic and misleading. It would indeed unify two great scientific frontiers, the very big and the very small.

SC: What do you think are the most complex entities in the universe?

MR: The most complex entities we know of-we ourselves-are midway between atoms and stars. It would take about as many human bodies to make up a star as there are atoms in each of us. Indeed, our everyday world presents intellectual challenges just as daunting as those of the cosmos and the quantum. Insects are harder to understand than stars-their structures far more intricate; and the weather’s harder to predict than celestial orbits are.

The sciences are sometimes likened to different levels of a tall building-mathematics on the ground floor, then physics, then chemistry, and so forth—all the way up to psychology—and the economists in the penthouse. There is indeed a hierarchy of complexity—atoms, molecules, cells, organisms, and so forth. But the analogy with a building is poor. The “higher level” sciences dealing with complex systems have their own autonomous concepts, and aren’t imperiled by an insecure base, as a building is. To understand why flows go turbulent or chaotic, or why waves break, we treat the fluid as a continuum—its subatomic details are irrelevant. An albatross returns predictably to its nest after wandering ten thousand miles in the southern oceans. But this isn’t the same kind of prediction as astronomers make of celestial orbits and eclipses. Problems in biology and in environmental and human sciences remain unsolved because scientists haven’t elucidated the patterns, structures, and interconnections.

SC: Why has Einstein’s fame so disproportionately eclipsed other 20th century scientists—Planck and Bohr, Dirac, and Schrodinger?

MR: It’s partly because he engaged more overtly with themes that fascinate all thinking people—time, space, origins, and the cosmos. It was fortunate for science that its pre-eminent practitioner purveyed such an engaging and idealistic image. But there’s one downside of his pre-eminence. It unduly exalts “arm-chair theory.” Pure thought by itself wouldn’t have gotten us far. The cumulative advance of science requires new technology and new instruments—in symbiosis, of course, with theory and insight. The cosmic discoveries I mentioned earlier depended on space technology, sensors for faint radiation, powerful computers, and so forth.

We could do with some higher-profile role models in more practical fields. Most people can readily name great 19th-century engineers—Brunel, for instance. Those who’ve given us today’s amazing technologies deserve as much acclaim. (Indeed, engineers have been even worse at PR than physicists-this seems to be one reason why their leading practitioners shouldn’t have the same glamorous profile as our more celebrated architects). In a recent study, groups of primary school children were asked to draw a scientist. In their portrayals, he (and it’s always a he) generally has thick spectacles and Einstein’s hair.

Einstein’s fame extends far wider than science. He’s as much an icon of creative genius as Beethoven (who also looks good on T-shirts). By the way, it seems that the advancing years take a heavier toll on scientists than on artists.

For many composers and painters, their greatest creations were among their last. That’s seldom true of scientists: even the ones who don’t become administrators tend at best to stay on a plateau. As we get older, it’s harder to absorb new ideas and techniques, as scientists must. But an artist’s style can deepen through internal development alone.

Even Newton became an administrator in his 50s, but Einstein worked on his unified theory until his dying day. Cynics have said that he might as well have gone fishing from 1920 onwards. But there’s something rather noble about the way he persevered and “raised his game”—reaching beyond his grasp. (Likewise, Francis Crick, the driving intellect behind molecular biology, shifted, when he reached 60, to the “Everest” problems of consciousness and the brain even though he knew he’d never get near the summit).

SC: What, if any, impact beyond physics did Einstein have, either during his lifetime or since his death?

MR: It’s been pervasive, but ambivalent. It’s a pity, in retrospect, that he called his theory “relativity.” Its essence is that the local laws are just the same in all inertial frames. “Theory of invariance” might have been an apter choice, and would have staunched the misleading analogies with relativism in other contexts. But in its humanistic “spin-off” relativity has fared no worse than other pivotal scientific concepts. Heisenberg’s uncertainty principle—a mathematically precise concept—became encumbered with oriental mysticism. And Darwin has likewise suffered tendentious distortions, especially in applications to human psychology.

But in one very important respect, Einstein had an exceedingly positive global influence, which still resonates today. When the nuclear threat first loomed over us, he was an inspiration and moral compass to other scientists. Back in 1955, just a week before he died, he co-signed, with Bertrand Russell, a manifesto that launched the Pugwash Conferences, an international forum for scientific discussions on disarmament and world affairs.

It was Joseph Rotblat who organized the Einstein/Russell manifesto, and became the driving force behind Pugwash. He remained active until aged 96, but died in 2005. Rotblat was among those who worked at Los Alamos on the project that led to the atomic bomb. The last of the survivors was the great physicist Hans Bethe, who died recently at 98. These people belonged to the “golden generation” of physicists who established our modern view of atoms and nuclei. After World War II, Rotblat, Bethe, and many others set an admirable precedent for researchers in any branch of science that has grave societal impact. They didn’t say that they were “just scientists” and not politicians. They deemed it their duty to alert the public to the implications of their work, and to campaign for arms control.

SC: What scientific breakthroughs do you envisage in this century and beyond?

MR: 21st-century science is changing the world faster than ever. It may change human beings themselves—that’s something qualitatively new in our history. Humanity’s impact on the biosphere and climate is unprecedented. Science offers exhilarating promise, but it will confront us with new ethical challenges—and perhaps with new global threats as grave as the bomb. These threats could come from bio, cyber, and environmental science, as well as from physics. In all these fields society will need latter-day counterparts of Joseph Rotblat and Hans Bethe. University scientists and independent entrepreneurs have a special obligation because they’ve more freedom than civil servants, or company employees subject to commercial pressure. Such individuals can sensitize our consciences. They can catalyze dialogue with the wider public. And they can put a spotlight on long-term issues. At the Royal Society-and in similar academies-we often scan the horizon a century ahead—in assessing energy, climate, and so forth. And those discussing the disposal of nuclear waste talk with a straight face about what might happen in thousands of years. But the political planning-horizon is seldom longer than the 20 years of the economic discount rate-often just the next election. Even a millennium, however, is a mere “instant” in our planet’s history.

When Einstein died in 1955, a memorable tribute to his global status came from an American cartoonist called Herblock. He depicted the Earth viewed from afar. It had a plaque reading “Einstein lived here.” Ever since Darwin, we’ve been familiar with the stupendous time spans of the evolutionary past. But most people aren’t yet mindful that the vistas stretching ahead are even longer—they could be infinite. There’s time for further evolution as dramatic as what’s led from the very first life to humans. But It won’t be humans who witness the Sun’s demise 6 billion years hence: it will be entities as different from us as we are from bacteria.

The future of our “pale blue dot” in the cosmos will depend on how we choose to apply our expanding scientific knowledge-to share its benefits, and minimize the risks. If we choose wisely, Einstein’s legacy will resonate through this century, and indeed far beyond.

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