Why Does E=mc2? (And Why Should We Care?), by Brian Cox and Jeff Forshaw, Da Capo Press, 262 pp., $24
The speed of light is constant. It travels through the lenses of your eyes at a nice and even 299,792,458 meters per second. Albert Einstein has gained so much traction in the culture that many of us know this as a factoid from his theories of relativity, even though it has little relevance in our day-to-day lives. As far as we’re concerned, light appears instantly and bathes everything, illuminating the way. But what does it mean exactly to say that the speed of light is constant?
In the everyday world, I might see the bus I need to catch just as it rounds the corner and disappears. I run after it while it accelerates to about 50 kilometers per hour; I frantically pick up my pace, peaking well short of the speed I need to catch up. I lose ground, lose hope, drop my bag, and trudge back to the stop. If I were a world-class runner, perhaps there would be a version of this story where I do catch up to the bus and maybe even overtake it. If I run parallel to the bus and match its speed, from my perspective the bus and I might as well be standing still.
Now, imagine a beam of tight red light emitted from a professor’s laser pointer. I’d have to be much more than a sprinter (a miracle worker, actually), but endow me for the moment with the power to catch the tip of this beam of light. In principle, if I could accelerate to 299,792,458 meters per second, I should be able to pace the laser beam. It’s just like the bus. If I have the legs, I can match the beam. Except this time, even if I somehow achieve the speed of light, the laser beam will always be traveling exactly 299,792,458 meters per second faster than I am. I can never hope to catch it. In this way, the speed of light is the same for me, speeding along, and for the professor pointing at some equation, standing still behind a podium.
Think about that for a moment. It is a bizarre assault on our common sense. Even more bewildering is that light’s universal speed requires that time, our best and most constant friend, be as relative as space. But this result has been in the works for hundreds of years. Galileo’s celestial observations seeded the notion of relativity: an object in motion only makes sense relative to some other object. Michael Faraday’s experiments, showing that electrical current generates a magnetic field and that magnets in motion generate current, hinted at some deep connection between magnetism and electricity. James Clerk Maxwell formalized Faraday’s ideas into a physical description of light: electrical and magnetic fields oscillating around one another at exact right angles, always at a fixed speed regardless of motion in the observer. And Einstein was smart enough to take them all seriously. Relativity was the next natural step in this scientific progression. Four physicists armed with simple instruments, pen and paper, imagination, and the courage to defy common sense, redefined Newtonian physics and relegated it to a mere approximation of reality.
We live in an era of Big Science. Galileo observed the skies using only a 20X telescope. Michael Faraday ushered in an understanding of electromagnetism from his lab bench with a few wires and some basic magnets. In contrast, the Large Hadron Collider at CERN (European Organization for Nuclear Research) is a 27-kilometer track through which subatomic particles accelerate almost to light speeds. Thousands of people engineered both the machines capable of the tremendous magnetic fields required and the high-resolution detectors necessary to detect the faintest subatomic particles. Today this is how bleeding-edge physics gets done. Large-scale projects in biology, including model organism genomics, require armies of technicians, engineers, scientists, and the computational horsepower to make sense of the data flood. Big Science broadens our view of nature, but it also deadens the romance of discovery.
Brian Cox and Jeff Forshaw’s Why Does E=mc2? (And Why Should We Care?) chronicles the unique but experimentally simple contributions of the physicists that inspired Einstein’s crowning equation. But Cox and Forshaw also spend time dissecting the challenges involved in discovering the essential nature of matter, studies that require the Big Science embodied in the Large Hadron Collider. The more engaging portion of the book is historical. Cox and Forshaw skillfully combine biography with a narrative of discovery, employing some of Einstein’s own thought experiments in conceptual derivations of his most famous results. They are careful to omit the math almost entirely, but consistently revisit something they call its “unreasonable effectiveness.” Often mathematics alone leads us to “laws that describe physical reality . . . and it is truly one of the wonderful mysteries of our universe that it should be so.” Sparing us the math and then expounding on its prowess leaves the reader in a state of limbo. We’re proud to have followed along but know that we’ve come up a bit short.
I expected Cox and Forshaw to lament the current gaps in physics: the fact that gravity (general relativity) does not jive with quantum theory; that string theory is a mere fragment until it is grounded in experiment; that we are probably more than a 27-kilometer loop away from a theory of everything. But they are optimists tempered by hard doses of reality. “Science is at its heart a modest pursuit, and this modesty is the key to its success.” Rather than pining for something in an unknown future, they are preparing themselves for a break with the past. “Einstein’s theories are respected because they are correct as far as we can tell, but they are no sacred tomes.” Science stands until new science makes the old stuff fall, a self-correcting mechanism that leaves no room for ego.
Perhaps it is good then that we’ve entered a scientific era where accolades and failures spread thin across all the minions manning Big Science projects. Once the Large Hadron Collider comes online, the energies of particle collisions will be such that the experiments will reveal something new. This kind of guaranteed result is unheard of. But it is unlikely that any result will ever bring an end to physical inquiry. Cox and Forshaw affirm this: “The perception that we somehow know enough, or even all there is to know, about the workings of nature has been and will probably always be damaging to the human spirit.” Let’s hope that the elusive theory of everything is like light: forever running away from you.