Seeking Out the Error
(appeared on 16th Oct 2013)

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Getting it right is no good. It is when we go wrong that we learn, says S.Ananthanarayanan.

The trouble with the current theories of physics is that they work so well. And yet, the different theories tell only part of the story. Alternate, comprehensive, proposed explanations of nature bring in a new element, which can be tested, to say whether there is something missing in the current view.

The current theories of physics are the quantum theory and the General Theory of Relativity. Quantum theory starts from the discovery that at the very fine scale, changes of energy are not smooth changes but always in minute steps, like a staircase as opposed to the banister railing. The theory then deals with the forces between very small objects, like atomic particles or small groups of atoms, at very small distances, like between nearby atoms or within the atom. At this limit of matter, quantum physics has got it right to incredible accuracy – expressed as ‘one part in 100 billion’, which translates into being right to a hair’s breadth over 3000 miles! But quantum mechanics deals with minute particles that interact through forces that exist only at very small distances, or through the electric force. As the particles are small, there is no reference to the force of gravity.

Einstein’s Theory of Relativity takes a new look at the nature of space and time. The theory shows that both these measures depend on the way the observer is moving. Time and distance hence appear to be slower and shorter to a moving observer, only providing, fortunately, that the difference is noticeable only when the motion is near that of the speed of light. And out of this comes the proof that that mass and energy are forms of the same thing, related by the speed of light, the legendary e=mc2 relation. Refinement of the theory then leads to considering the quality of mass to be the same as curve in the dimensions of space and time - again an intuitively incomprehensible idea but one which has been verified, by sighting stars, during an eclipse, that should have been hidden behind the sun – which shows that the mass of the sun has bent the path of light round to reach the earth! The gravitational effects predicted by the theory have again been verified in stellar and planetary dynamics and there is no reason to think that it is anything but exact.

And yet, the two theories have no meeting ground, one reigns supreme at the limit of the very small, the other is unquestioned at the scale of the cosmos. Yet neither is good to explain the domain of the other. Scientists have hence striven to develop a ‘unified theory’, which would take into account the forces at the atom scale and also the force of gravity. All these theories, however, need to reduce, at the very small and the very large limits, to the existing theories, which are seen to work. A common feature of most of these theories fortunately provides a test, albeit difficult, by which we could tell if quantum mechanics is actually not the whole truth even at the atomic level.

The assumption

All matter is found to consist of fundamental particles, containing at least the negatively charged electron and the positively charged proton. With estimates of the masses of these particles and the value of the charge they carry, a comprehensive model of ‘elementary’ particles has been developed, which, with the help of a discipline called quantum electrodynamics, has given us the marvels of the modern world. Another observed feature of nature is that when energy is converted to light or vice versa, there is a proportionality, which is constant, expressed as ‘h’ or Planck’s constant, after Max Planck, who first proposed it.

Now, while working out interactions of atomic particles and exchanges of energy, there are two factors, connected with the masses of the particles and the energy and frequency of light, which recur in the calculations – the fine structure constant denoted as ‘a’, which relates the charge on the electron, Planck’s constant and the speed of light - and the ratio of the masses of the electron and the proton, denoted as ‘µ’. The value of these relationships is thus central to the structure of fundamental particles as created by the theory, and the values, being derived from observation, are assumed to be constant.

But the alternate theories, which seek to bring gravitation and also discoveries like the expansion of the universe and the existence of dark matter, and quantum electrodynamics into a single theory, generally relate the value of the fine structure constant and the electron-proton mass ratio to the time, position or the density of matter at the place. If any of these theories are the correct explanation of nature, then the values of a and µ would not be constant and the currently accepted model of the particle physics may not be valid in the ancient past or at point deep within space. Scientists have thus gone to great lengths to verify if a and µ remain unchanged in the remotest places – in the hope of finding a difference, which would be a lead out of the impasse – of nature being explained so well, but in part only, by a pair of theoretical systems.

Put to test

S. Truppe, R.J. Hendricks, S.K. Tokunaga, H.J. Lewandowski, M.G. Kozlov, Christian Henkel, E.A. Hinds and M.R. Tarbutt, of London, Colorado, Gatchina in Leningrad, Bonn and Jeddah report in the journal, Nature, their latest assessment of the values of a and µ in distant places om space, which shows that any variability is less than the order of one and a half to three parts in ten million.

A natural way of testing the value of the constants is to measure the energy levels within atoms and molecules, as these levels arise from the values of the constants. a, the fine structure constant is so named because its value is involved in the splitting of energy levels in atoms, or in molecules, which also depend on the value of µ. Study of the spectral lines, which arise from transitions between energy levels in atoms and molecules, could hence detect variation in the values of a or µ. The work done so far had detected no variation, but only to the extent of the accuracy of the experiments, which are of the order of a few parts in a million, and there is tentative support for changes at a finer scale. Hence the need for more sensitive measurement and better astronomical observations.

The authors of the present study note that the transitions of a normally short lived molecule, CH or an atom of carbon and an atom of hydrogen, which is found in low pressure environment in distant places in space, has a pair of transitions, with emission in the microwave region, which is notably sensitive to the values of a or µ. The team has developed a device to generate and excite these molecules with a reference microwave signal, yielding accuracy down to the units in frequency of the order of 10 million. The frequencies have been compared with emissions from sources in parts of the Milky Way, where the density of matter is a tenth of a billionth twice over (10 -19) of what it is on earth. But as there is inherent uncertainty in the estimates of the radiation from the distant sources, any variation is taken as limited to 1.4 to 3 in ten million.

What has been done is to overcome the existing limits of the comparison frequencies, and pushing the accuracy of the assessment to the quality of the signal from the distant source of emission. With dedicated astronomical measurements, using facilities we already have, even higher precision could be reached, the authors say.

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