how constant are constants? 7/31/24

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Today's selection-- from The Science Delusion by Rupert Sheldrake. How constant are constants?:

“How constant are the 'fundamental constants'?

“Some constants are considered to be more fundamental than others, including the velocity of light, c, the Universal Gravitational Constant, known to physicists as Big G, and the fine-structure constant, a, which is a measure of the strength of interaction between charged particles, such as electrons, and photons of light. Unlike the constants of mathematics, such as n, the values of the constants of nature cannot be calculated by mathematics alone: they depend on laboratory measurements. As the name implies, the physical constants are supposed to be changeless. They are believed to reflect an underlying constancy of nature. The standard assumption is that the laws and constants of nature are fixed for ever.

“Are the constants really constant? The values given in handbooks of physics do in fact change from time to time. They are continually adjusted by international committees of experts known as metrologists. Old values are replaced by new 'best values' based on the latest data from laboratories around the world. Within their laboratories, metrologists strive for ever-greater precision. In so doing, they reject unexpected data on the grounds they must be errors. Then, after deviant measurements have been weeded out, they average the values obtained at different times, and the final value is then subjected to a series of corrections. Finally, in arriving at the latest 'best values’ international committees of experts then select, adjust and average data from laboratories around the world.

“Although the actual values change, most scientists take it for granted that the constants themselves are really constant; the variations in their values are simply a result of experimental errors. The latest values are the best, and previous values are forgotten. However, some physicists, notably Paul Dirac (1902-84), speculated that at least some of the fundamental constants might change with time. In particular, Dirac proposed that the Universal Gravitational Constant might decrease slightly as the universe expands. But Dirac was not challenging the idea of eternal mathematical laws: he was merely proposing that a mathematical law might govern the gradual variation of a constant.

“What about the data? All of the published values of constants vary with time, but here I will discuss only three of them: the Universal Gravitational Constant, the fine-structure constant and the speed of light.

“The oldest of the constants, Newton's Universal Gravitational Constant, Big G, is also the one that shows the largest variations. Towards the end of the twentieth century, as methods of measurement became more precise, the disparity in measurements of G by different laboratories increased, rather than decreased. Between 1973 and 2018, the lowest value of G was 6.6659, and the highest 6.734, a 1.0 per cent difference (Figure 3.1). These published values are given to at least three places of decimals, and sometimes to five, with estimated errors of a few parts per million. Either this appearance of precision is illusory, or G really does change. The difference between recent high and low values is more than forty times greater than the estimated errors (expressed as standard deviations).

Figure 3.1: Values of G (x 10-11m3kg-1s-2) at different times between 1973 and 2018.

“What if G really does change? Maybe it does so because measurements are affected by changes in the earth's astronomical environment, as the earth moves around the sun and as the solar system moves within the galaxy. Or maybe there are inherent fluctuations in G. Such changes would never be noticed as long as measurements are averaged over time and across laboratories.

“In 1998, the US National Institute of Standards and Technology published values of G taken on different days, rather than averaging them to iron out variations, revealing that there was a remarkable range: for example, on one day the value was 6.73, a few months later it was 6.64, 1.3 per cent lower.

“In 2002, a team led by Mikhail Gershteyn, of the Massachusetts Institute of Technology, published the first systematic attempt to study changes in. G at different times of day and night. G was measured around the clock for seven months, using two independent methods. They found a clear daily rhythm, with maximum values of G 23.93 hours apart, correlating with the length of the sidereal day, the period of the earth's rotation in relation to the stars.

“Gershteyn's team looked only for daily fluctuations, but G may well vary over longer time periods as well; there is already some evidence of an annual variation. And a team in California found that fluctuations in the value of G since 1962 were oscillatory, going up and down with a period of 5.9 years.

“By comparing measurements from different locations, it should be possible to find more evidence of underlying patterns. Such measurements already exist, buried in the files of metrological laboratories. The simplest and cheapest starting point for this enquiry would be to collect the measurements of G at different times from laboratories all over the world. Then these measurements could be compared to see if the fluctuations are correlated. And if they are around, we will discover something new.

“Another way of looking for real changes in nature is to compare astronomical observations of galaxies and quasars of different ages to see if there is any difference in the light they emit that implies long-term changes in constants. The Australian astronomer John Webb has applied this approach to the fine-structure constant, a. Around the turn of the millennium, his team found that a was slightly smaller in distant parts of the sky, suggesting that it had changed over billions of years. At first many physicists assumed that Webb's results must be due to errors, but by 2010 more data from different parts of the sky not only confirmed Webb's findings, but also gave new results that were quite unexpected. The variation in a depended on which way the telescopes were facing. The constant seemed to be larger on one side of the universe than the other. The variation of fundamental constants is now a matter of serious debate among physicists. As Webb and his colleague John Barrow pointed out, 'If a is susceptible to change, other constants should vary as well, making the inner workings of nature more fickle than scientists ever suspected.'

“Finally, what about the speed of light, c? According to Einstein's theory of relativity, the speed of light in a vacuum is an absolute constant, and modern physics is based on this assumption.

Not surprisingly, early measurements of the speed of light varied considerably but, by 1927, the measured values had converged to ~99,796 kilometres per second. At the time, the leading authority on the subject concluded, 'The present value of c is entirely satisfactory and can be considered more or less permanently established.’ However, all around the world from about 1928 to 1945, the speed of light dropped by about 20 kilometres per second. The 'best' values found by leading investigators were in impressively close agreement with each other. Some scientists suggested that the data pointed to cyclic variations in the velocity of light.

“In the late 1940s the speed of light went up again by about 20 kilometres per second and a new consensus developed around the higher value. In 1972, the embarrassing possibility of variations in c was eliminated when the speed of light was fixed by definition. In addition, in 1983 the unit of distance, the metre, was redefined in terms of light. Therefore if any further changes in the speed of light happen, we will be blind to them because the length of the metre will change with the speed of light. (The metre is now defined as the length of the path travelled by light in a vacuum in 1/299,792,458 of a second.) The second is also defined in terms of light: it is the duration of 9,192,631,770 periods of vibration of the light given off by caesium 133 atoms in a particular state of excitation (technically defined as the transition between the two hyperfine levels of the ground state).

“How can the drop in c between 1928 and 1945 be explained? This remarkable episode in the history of physics is now generally attributed to the psychology of metrologists. Brian Petley, a leading British metrologist, explained it thus:

The tendency for experiments in a given epoch to agree with one another has been described by the delicate phrase 'intellectual phase locking: Most metrologists are very conscious of the possible existence of such effects; indeed ever-helpful colleagues delight in pointing them out! Aside from the discovery of mistakes, the near completion of the experiment brings more frequent and stimulating discussion with interested colleagues and the preliminaries to writing up the work add a fresh perspective. All of these circumstances combine to prevent what was intended to be 'the final result' from being so in practice, and consequently the accusation that one is most likely to stop worrying about correction when the value is closest to other results is. easy to make and difficult to refute.

“Existing theories of varying constants, like Paul Dirac's, assume that the changes are small, slow and systematic. Another possibility is that the constants oscillate within fairly narrow limits, or even vary chaotically. We are used to fluctuations in the weather and in human activities: newspapers and websites routinely report changes in the weather, stock-market indices, currency exchange rates and the price of gold. Maybe the constants fluctuate too, and perhaps one day scientific periodicals will carry regular news reports on their latest values. 

“The implications of varying constants would be enormous. The course of nature would no longer seem blandly uniform; there would be fluctuations at the heart of physical reality. If different constants varied at different rates, these changes would create differing qualities of time.”