Heavy as they hurtle

The Coca Cola logo, I read somewhere once, is the most widely recognized symbol in the world. (Considering I once found Coke in remote villages in Madagascar reachable only by a three day hike from the nearest town, I'm willing to believe that). Question: is there a scientific statement that might run Coke close, recognition-wise?

I don't know about "close", but one does come to mind, and I suspect it is at least known, if not understood, by hundreds of millions. I'm sure it came to your mind too: Albert Einstein's famous E = mc² .

In a time when every high school student is taught this as a routine part of a physics curriculum, it's hard to believe that when Einstein first propounded it, it was a revolution that turned the scientific world on its head. His theories shook those hoary pillars of physics, Newton's laws, mightily. Not that they were wrong, or at least, not wholly. But there were small, but troubling and significant, errors in how they explained certain phenomena. Only when Einstein came along were they satisfactorily explained.

Energy (E), Einstein tells us, equals mass (m) multiplied by the square of the speed of light (c). But what does that mean?

In essence, the equation says mass and energy are equivalent. If Celeste the elephant is moving, she has energy from that motion. That energy, being equivalent to mass, adds to Celeste's mass; that is, she becomes heavier. Not just that. Because she is heavier, it's harder to increase her speed -- it needs more energy to make her move even faster. Think of the effort you would put into pushing a SUV, and compare that to the gentle nudge a toy car needs to get moving (well, before my son gets at it). I'll take the toy, thank you.

Before you rush off to weigh yourself while running around at different speeds, hold on. A qualification is in order. The increase in mass is only noticeable at speeds close to the speed of light, a small matter of 300,000 km per second. Not even Carl Lewis runs that fast, so don't bother trying. This must remain a thought experiment.

Lumbering along at a tenth the speed of light, or 30,000 km/sec, Celeste becomes only 0.5 per cent heavier; if she weighed 1000 kg, she would now be up to 1005. But suppose she managed to ramp up to 90 per cent of the speed of light, to 270,000 km/sec? She'd be over twice her stationary mass.

That is, as Celeste nears the speed of light, her mass increases more and more rapidly. Which makes it more and more difficult for her to go faster -- she needs more and more energy to do so. And in turn, that adds ever more speedily to her mass. That's the energy-mass equivalence.

Will Celeste ever reach the speed of light? No, because getting there will need an infinite amount of energy, and there simply isn't quite that much around.

So Einstein's equation leads to this interesting conclusion: the only things that can zip around at the speed of light are those that have no mass to begin with. About the only such thing we know about is ... well, light. Einstein showed that other everyday objects -- your Carl Lewises, your suburban trains, your Celestes, your letters through the post -- are always restricted to speeds well below the speed of light.

And this is Einstein's central idea. The speed of light, said Einstein, is an absolute (about the only one around). Whoever you are, whatever you are doing, however fast you are moving, you will see light moving at the same speed. (And nothing can move faster).

A rather counter-intuitive idea, actually. Suppose you are in a car, rattling down the highway at 100 kmph. Going just slightly faster than you, let's say at 105 kmph, I overtake you in my car. As you wave frantically to me, it might strike you that I'm going rather slowly -- relative to you. At a mere 5 kmph, as a matter of fact.

But our mutual friend Shabnam, standing on the side of the road trying to thumb a lift, sees me going at a pretty fair clip. Relative to her, I'm doing that 105 kmph. Not the 5 kmph that you see. That is, you and Shabnam observe me travelling at different speeds.

However -- and this is the fun part -- if a massless Celeste trundled past at the speed of light, both you and Shabnam would see her moving at that speed. There would be no difference in her speed relative to Shabnam, and relative to you.

In other words, whoever measures the speed of light, however fast they themselves are moving, will produce the same figure. Now you know why Einstein called it the theory of relativity. Whether relative to a stationary Shabnam or relative to a speeding you, light moves at one speed.

Such a simple idea. But touched by genius, because of its revolutionary consequences. One of those is Einstein's energy-mass equivalence, as his equation spells out. There are others.

Einstein changed forever the way we look at gravity, at space, at time, even at our very place in the universe. Which is why, if there are other forms of life somewhere in the universe, it's a good bet they'd know about E = mc² before they know about Coke. So for now, Coke can rest on the laurels from remote Madagascar villages. When the aliens come calling, heavy as they hurtle through space, Coke might have to reconsider.

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Postscript: I'm usually not inclined to take newspapers' internet polls too seriously. But yesterday's Times of India has the results for this poll they conducted: "Do you think planetary influences determine the outcome of people's lives?"

"Yes" beat "No", 61 per cent to 39.

Those numbers alarmed me. The occasional science column, like this one, is a small response to that alarm.