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Celebrating a bit of smart physics

100 years ago, Albert Einstein formulated the equation E=MCSquared, that expresses Einstein’s theory that as one accelerates an object, it not only gets faster, but gets heavier. I must admit it is not very often that I come across the anniversary of a theory like this. We normally mark dates of births, deaths, battles, elections or great reforms. Theories don’t quite have the same resonance. I don’t imagine that there will be grand parades marking Einstein’s achievement.

I have read a bit about this incredible man and his life, and to this day I’ll frankly admit to finding it pretty hard to get my head around some of the ideas of relativity. (Physics was never one of my stronger subjects, something I intend to fix at nightschool. Never too late to learn). But there can be no doubt at all about the impact this man has had on the subsequent 100 years, in terms of our understanding of the universe and of course in fields such as nuclear power, both in its benign and not-so-benign forms.

And Einstein of course is incredibly famous not least for personifying the “eccentric genius” with his mass of scruffy hair, wild-eyed expressions and casual manner. How often are scientists in the movies, television and theatre portrayed in this way (assuming that scientists are portrayed at all). More recently, the late great Richard Feynman continued the tradition for iconoclastic irreverence, famously deflating science establishment in a marvellous collection of books about science and public policy.

For those interested in Einstein’s contemporaries in the science community in America, I can strongly recommend this book by Ed Regis.

20 comments to Celebrating a bit of smart physics

  • John Steele

    One of my favorite Einstein stories is about the letter to President Roosevelt. Leo Szilard went to meet with Einstein at his vacation home on Long Island to talk about sending the letter to FDR. But Szilard, one of the brightest physicists in the world, didn’t drive. The simple solution was to have Edward Teller serve as his chauffeur!

  • Reid of America

    Johnathan quotes the BBC: “that expresses Einstein’s theory that as one accelerates an object, it not only gets faster, but gets heavier”.

    This is not correct. The Newtonian equation F=ma is what the BBC is refering to.

    E=mc(squared) basicly states that all matter is highly condensed energy. Hence, transforming a small amount of matter into energy can yield a nuclear blast.

  • Noel Cooper

    This is not correct.

    Jonathan and the BBC have got it right, they are referring to this

  • Russell

    Actually, speaking as a physicist, so far nobody has quite gotten it right.

    Jonathon is wrong on the meaning of E=mc2 – Reid is correct that the implication of the equation is that mass and energy are interchangeable and that mass equates to a lot of energy.

    Noel is, sort of, correct to note that the concept that mass increases as speed increases (which is only noticable as v/c approaches 1) is an element of special relativity, but that element is not related to the e=mc2 equation.

    So scoring Jonathon got no element correct, Reid was half right (apart from the appallingly incorrect reference to Newton) and Noel has made a fool of himself.

  • Robin Goodfellow

    E=mc^2 is more fundamental than relativistic mass, it is, in fact, the expression of the shockingly bizarre idea that mass and energy are equivalent and closely related. At the time this was nothing less than revolutionary.

    Also, I should point out that relativistic mass is somewhat of a tricky subject, and the term is not much used nowadays. Typically, real physicists tend to talk about either energy or momentum and reserve the term “mass” to refer only to “rest mass”. This is because energy and momentum are both reference frame dependent measurements, so they don’t want them to be confused with frame invariant values like rest mass.

  • Jake


    I heard a physicist say that it is possible that no one would have come up with E=mc^2 even after 100 years if it had not been for Einstein. It was that revolutionary of an idea.

    What do you think?

  • Russell

    G’day Jake,

    I have heard the view expressed but I do not find it very convincing – a re-think of physics was required and Einstein was the first to get there. But there were elements of the new physics that never made sense to Einstein (trying looking up the Einstein-Podolsky-Rosen paradox and/or Bell’s inequality).

    The world of ideas just doesn’t work like that. Exceedingly odd ideas occur to multiple people in different ways eg. Schrödinger and Dirac both separately came up with equations that express the same thing (though it only ever gets called Schrödinger’s equation). Part of the problem is that you need a very good understanding to see that the equations (that look nothing alike) mean the same thing – I suppose it is because Schrödinger had the cat.

  • Chris Harper


    Contrary to what you said, my understanding is that the mass gain as v/c tends to 1 is directly related to e=mc^2. That part of the energy of acceleration which is not expressed as delta v is expressed as delta m, in the relationship of m = e/c^2.

  • Chris Harper

    “I suppose it is because Schrödinger had the cat.”

    Are you certain?

  • timmah!

    From A. Einstein, “Does the Inertia of a Body Depend Upon Its Energy-Content?”, a lovely 3 page add on to the main paper on special relativity, as translated in __The Principle of Relativity__ (Dover):

    “If a body gives off the energy L in the form of radiation, its mass diminishes by L/c^2…The mass of a body is a measure of its energy-content….If the theory corresponds to the facts, radiation conveys inertia between the emitting and absorbing bodies.”

    So mass and energy are one and the same. To better understand this, we need the general theory of relativity. Maybe I’ll understand something of that by the time its centennial comes up in 2016.

  • guy herbert

    As Russell says, rethinking was happening all over. It always is. The story of science is only a succession of pellucid individual triumphs in retrospect.

    As far as relativistic kinematics are concerned, Poincaré and Minkowski were on much the same track as Einstein, and Minkowski subsequently made Special Relativity much easier to follow for those of us having difficulties.

    It is the astonishing fertility of 1905 and the mind-boggling follow-up provided by General Relativity that gets Einstein top billing. Einstein is the most cited scientist counting papers published before 1930–but it is his Brownian Motion paper that wins, not E=mc^2. The Nobel Prize was nominally for the explaining the photoelectric effect by the quantization of light.

    My own suspicion is that he might yet have been an important but little-known scientist–like Maxwell, say. He became a popular hero because of two political contingencies. The fervid rejection of relativity as “Jewish science” by the Nazis, made the transparently genial, unthreatening Einstein a representative emigré: a good man as contrast to unmistakeable evil. And E=mc^2 got a universal currency from awe of The Bomb.

  • Chris Harper

    “If a body gives off the energy L in the form of radiation, its mass diminishes by L/c^2…The mass of a body is a measure of its energy-content….If the theory corresponds to the facts, radiation conveys inertia between the emitting and absorbing bodies.”

    If e truly does equal mc^2 then the above is simply an indesputable statement of fact.

    Of course, if Einstein is wrong and e only aproximately equals mc^2 and we simply can’t yet measure the discrepancy yet, then the statement is a load of complete bollocks.

  • The Wobbly Guy

    I had always wondered why scientists didn’t come up with E=mc^2 sooner, given the SI units for mass, energy, and velocity… Remarkably elegant equation.

    One of those counter-intuitive things, I guess.

  • guy herbert

    That’s a joke TWG? Just checking.

  • doug

    For those interested , I recommend this book:

    Einstein’s Clocks, Poincaré’s Maps

    By Peter L. Galison


    True time would never be revealed by mere clocks–of this Newton was sure. Even a master clockmaker’s finest work would offer only pale reflections of the higher, absolute time that belonged not to our human world, but to the “sensorium of God”. Tides, planets, moons–everything in the Universe that moved or changed–did so, Newton believed, against the universal background of a single, constantly flowing river of time. In Einstein’s electrotechnical world, there was no place for such a “universally audible tick-tock that we can call time, no way to define time meaningfully except in reference to a definite system of linked clocks. Time flows at different rates for one clock-system in motion with respect to another: two events simultaneous for a clock observer at rest are not simultaneous for one in motion. “Times” replace “time”. With that shock, the sure foundation of Newtonian physics cracked; Einstein knew it. Late in life, he interrupted his autobiographical notes to apostrophize Sir Isaac with intense intimacy, as if the intervening centuries had vanished; reflecting on the absolutes of space and time that his theory of relativity had shattered, Einstein wrote: “Newton, forgive me ['Newton, verzeih' mir']; you found the only way which, in your age, was just about possible for a man of highest thought–and creative power.”

    At the heart of this radical upheaval in the conception of time lay an extraordinary yet easily stated idea that has remained dead-center in physics, philosophy, and technology ever since: To talk about time, about simultaneity at a distance, you have to synchronize your clocks. And if you want to synchronize two clocks, you have to start with one, flash a signal to the other, and adjust for the time that the flash takes to arrive. What could be simpler? Yet with this procedural definition of time, the last piece of the relativity puzzle fell into place, changing physics forever.

    This book is about that clock-coordinating procedure. Simple as it seems, our subject, the coordination of clocks, is at once lofty abstraction and industrial concreteness. The materialization of simultaneity suffused a turn-of-the-century world very different from ours. It was a world where the highest reaches of theoretical physics stood hard by a fierce modern ambition to lay time-bearing cables over the whole of the planet to choreograph trains and complete maps. It was a world where engineers, philosophers, and physicists rubbed shoulders; where the mayor of New York City discoursed on the conventionality of time, where the Emperor of Brazil waited by the ocean’s edge for the telegraphic arrival of European time; and where two of the century’s leading scientists, Albert Einstein and Henri Poincaré, put simultaneity at the crossroads of physics, philosophy, and technology.


  • pommygranate

    Further to a prior thread on the pre-eminence of physics, there is a delightful if slightly condescending quote from Ernest Rutherford.

    “In Science, there is Physics. Everything else is gardening”

  • “In Science, there is Physics. Everything else is gardening”

    I believe the correct quote is “All science is either physics or stamp collecting”.

    To which one of my lecturers allegedly added “Much of physics is stamp collecting too”.

  • The Wobbly Guy

    Guy-It’s not a joke. Many physical properties are indeed related to one another. Eg. charge, current, energy, and force, for example. It’s interesting how the units for certain properties offer tantalising hints of their origins and how they are related to other properties.

    The unit for energy is the joule, but in base SI units it’s kg(m^2)(s^-2). On the other side of the equation, when you look at the product of the units for mass and the square of the speed of light, you get kg(m^2)(s^-2). When I showed it to students, they were all awed.

    As if it’s that difficult to figure out!

  • The unit for energy is the joule, but in base SI units it’s kg(m^2)(s^-2). On the other side of the equation, when you look at the product of the units for mass and the square of the speed of light, you get kg(m^2)(s^-2).

    But this would still be true in a universe where Einstein’s postulates were false, and E=mc^2 therefore meaningless.

    The equivalence of the joule and kg m2/s2 follows from the definition of work, and is already apparent in the non-relativistic equation E = 1/2 mv^2.

    You need Maxwell’s equations, or some other relativistic phenomenon, before the significance of the speed of light becomes apparent. Without that, then why pick the speed of light for E=mc^2, rather than some other speed?

  • Kim du Toit

    What saddens me about Einstein was that despite his brilliance as a scientist and mathematician, he was a total boob politically. Essentially, he was a statist, almost a socialist.