Unifiers and diversifiers in physics, chemistry and biology

On my computer screen right now are two molecules. They are both large rings with about thirty atoms each, a motley mix of carbons, hydrogens, oxygens and nitrogens. In addition they have appendages of three or four atoms dangling off their periphery. There is only one, seemingly minor difference: The appendage in one of the rings has two more carbon atoms than that in the other. If you looked at the two molecules in flat 2D - in the representation most familiar to practicing chemists - you will sense little difference between them.

Yet when I look at the two molecules in 3D - if I look at their spatial representations or conformations - the differences between them are revealed in their full glory. The presence of two extra carbons in one of the compounds causes it to scrunch up, to slightly fold upon itself the way a driver edges close to the steering wheel. This slight difference causes many atoms which are otherwise far apart to come together and form hydrogen bonds, weak interactions that are nonetheless essential in holding biological molecules like DNA and proteins together. These hydrogen bonds can in turn modulate the shape of the molecule and allow it to get past cell membranes better than the other one. A difference of only two carbons - negligible on paper- can thus have profound consequences for the three-dimensional life of these molecules. And this difference in 3D can in turn translate to significant differences in their functions, whether those functions involve capturing solar energy or killing cancer cells.

Chemistry is full of hidden differences and similarities like these. Molecules exist on many different levels, and on each level they manifest unique properties. In one sense they are like human beings. On the surface they may appear similar, but probe deeper and each one is unique. And probing even deeper may then again reveal similarities. They are thus both similar and different all at once. But just like human beings molecules are shy; they won't open up unless you are patient and curious, they may literally fall apart if you are too harsh with them, and they may even turn the other cheek and allow you to study them better if you are gentle and beguiling enough. It is often only through detailed analysis that you can grasp their many-splendored qualities. It is this ever-changing landscape of multifaceted molecular personalities, slowly but surely rewarding the inquisitive and dogged mind, that makes chemistry so thrilling and open-ended. It is why I get a kick out of even mundane research.

When I study the hidden life of molecules I see diversity. And when I see diversity I am reminded of how important it is in all of science. Sadly, the history of science in the twentieth century has led both scientists and the general public to value unity over diversity. The main culprit in this regard has been physics whose quest for unity has become a victim of its own success. Beginning with the unification of mechanics with heat and electricity with magnetism in the nineteenth century, physics achieved a series of spectacular feats when it combined space with time, special relativity with quantum mechanics and the weak force with electromagnetism. One of the greatest unsolved problems in physics today is the combination of quantum mechanics with general relativity. These unification feats are both great intellectual achievements as well as noteworthy goals, but they have led many to believe that unification is the only thing that really matters in physics, and perhaps in all of science. They have also led to the belief that fundamental physics is all that is worth studying. The hype generated by the media in fields like cosmology and string theory and the spate of popular books written by scientist-celebrities in these fields have only made matters worse. All this is in spite of the fact that most of the world's physicists don't study fundamental physics in their daily work.

The obsession with unification has led to an ignorance of the diversity of discoveries in physics. In parallel with the age of the unifiers has existed the universe of diversifiers. While the unifiers have been busy proclaiming discoveries from the rooftops, the diversifiers have been quietly building new instruments and cataloging the reach of physics in less fundamental but equally fascinating fields like solid-state physics and biophysics. They have also gathered the important data which allowed the unifiers to ply their trade. Generally speaking, unifiers tend to be part of idea-driven revolutions while diversifiers tend to be part of tool-driven revolutions. The unifiers would never have seen their ideas validated if the diversifiers had not built tools like telescopes, charged coupled devices and, superconducting materials to test the great theories of physics. And yet, just like unification is idolized at the expense of diversification, ideas in physics have also been lionized at the expense of practical tools. We need to praise the tools of physics as much as the diversifiers who build them.

As a chemist I find it easier to appreciate diversity. Examples of molecules like the ones I cited above abound in chemistry. In addition chemistry is too complex to be reduced to a simple set of unifying principles, and most chemical discoveries are still made by scientists looking at special cases rather than those searching for general laws. It's also a great example of a tool-driven revolution, with new instrumental technologies like x-ray diffraction and nuclear magnetic resonance (NMR) completely revolutionizing the science during the twentieth century. There were of course unifiers in chemistry too - the chemists who discovered the general laws of chemical bonding are the most prominent example - but these unifiers have never been elevated to a status seen among physicists. Diversifiers who play in the mud of chemical phenomena and find chemical gems are still more important than ones who might proclaim general theories. There will always be the example of an unusual protein structure, a fleeting molecule whose existence defies our theories or or a new polymer with amazing ductility that will keep chemists occupied. And this will likely be the case for the foreseeable future.

Biology too has seen its share of unifiers and diversifiers. For most of its history biology was the ultimate diversifiers' delight, with intrepid explorers, taxonomists and microbiologists cataloging the wonderful diversity of life around us. When Charles Darwin appeared on the scene he unified this diversity in one stunning fell swoop through his theory of evolution by natural selection. The twentieth century modern synthesis of biology that married statistics, genetics and evolutionary biology was also a great feat of unification. And yet biology continues to be a haven for diversifier. There is always the odd protein, the odd sequence of gene or the odd insect with a particularly startling method of reproduction that catches the eye of biologists. These examples of unusual natural phenomena do not defy the unifying principles, but they do illustrate the sheer diversity in which the unifying principles can manifest themselves, especially on multiple emergent levels. They assure us that no matter how much we may unify biology, there will always be a place for diversifiers in it.

At the dawn of the twenty-first century there is again a need for diversifiers, especially in new fields like neuroscience and paleontology. We need to cast off the spell of fundamental physics and realize that diversifiers play on the same field as unifiers. Unifiers may come up with important ideas, but diversifiers are the ones who test them and who open up new corners of the universe for unifiers to ponder. Whether in chemistry or physics, evolutionary biology or psychology, we should continue to appreciate unity in diversity and diversity in unity. Together the two will advance science into new realms.