Features
Precision measurement shakes world of science
By Prof. Kirthi Tennakone
ktenna@yahoo.co.uk
National Institute of Fundamental Studies
Precision measurements have transformed science, influenced our way of thinking and impacted technology. A recent experiment conducted at the Fermi National Accelerator Laboratory, in the United States, poses questions regarding how nature operates at the deepest level. The experiment measured the magnet-like property of the elementary particle named muon, giving a numerical value to a quantity termed the g-factor. According to the most successful theory humans have devised, known as the Standard Model, this factor should be 2.0023318362. The experiment planned for decades has found that the measured value is 2.0023318412.
Why is a discrepancy in the eighth decimal place of a measurement, regarded a tantalising issue to agitate the world of science?
Before going into details of this experiment, it is interesting to recollect landmark examples of previous measurements that revolutionised the world and how definitive unvarying units have been adopted to do measurements.
Precision measurements: A few examples
One of the greatest precision measurements in the ancient world was invoked in planning the construction of Yoda Ela to carry water from Kalawewa to tanks in Anuradhapura. The slope of the 87 km channel measures less than 10 cm per kilometer!
Today, non-contact infrared thermometers instantly assess our body temperature, when we enter a supermarket. The first precise temperature measuring device, the so-called mercury-in-glass thermometer was invented by the Dutchman Daniel Fahrenheit in 1709 and the medical version by Thomas Allbut after a century. Later on, much more accurate temperature recording instruments were introduced, permitting determination of the temperature of ovens, planets, stars and the universe itself. The increased precision of temperature measurement unrivalled fundamental knowledge and elevated the quality of life. The thermometer has saved many lives, and cosmic background temperature measurement convinced us of Big Bang origin of the universe.
In mid-1800s astronomers measured minute deviations in the orbit of Uranus. The French mathematician Joseph LeVerrier, performed an unbelievably precise calculation and pointed out that the anomaly was due to the existence of another planet. He predicted that if astronomers point their telescopes to a certain point in the sky at a time he had calculated, the planet could be seen. This is how Neptune was discovered – confirming the preciseness of LeVerrier’s calculation! The ability to deploy exploratory robots to chosen locations on Moon or Mars rely on accuracy of such calculations, performed today with computers. LeVerrier did his laborious calculation manually!
Verification by observation and measurement is the ultimate test of any scientific theory. Unlike in other human affairs, individual opinions and politics entail no relevance. When Albert Einstein formulated his famous theory of general relativity, test he proposed was to measure the bending of light by gravity of the sun, seen as a minute change in the apparent position of a star during the time of a total solar eclipse. A measurement conducted during 1918 solar eclipse, visible to the island of Principe on African coast, agreed with his prediction, but he had to await further confirmation during the next solar eclipse that occurred in 1920.
Modern fundamental science stands firm and progress on basis of ever increasing accuracy of measurements.
Units of measurement
Reliable and unambiguous measurements require fixed unvarying standards to be used as units. In the 12th century, the Royal Court of England, pleaded with King Henry I to tell what the length of the yard was. The King stretched his arms horizontally and said, “It is the distance between my nose and the thumb – a convenient length to match the size of the human body but not an accurate unvarying standard. After the French revolution, the Academy of Sciences in Paris decided to adopt a decimal metric system of units to ease measures in business and engineering. The metric unit of length ‘meter’ was originally determined as one ten- millionth of the shortest distance between North Pole and the Equator. As the extent of this length is hard to determine repeatedly, in 1779 meter was redefined as the length of a metal bar secured at the International Bureau of Weights and Measures in Paris. Likewise, the unit of mass, the kilogramme was fixed as that of a cylinder of metal kept in the Bureau. The definition of the unit of time, the second, relied on the period of rotation of the earth (one day) divided into hours, minutes and seconds in the usual way.
The units of length, mass and time defined as above are not guaranteed to remain unchanged. The standard of length, the metal bar kept in Paris could slightly warp and cylinder defining the kilogramme may lose weight owing to evaporation of the metal or gain weight by deposition of dust. Earthquakes and falling meteors alter the rate of rotation of the earth.
It is amazing that nature has provided a method of permanently fixing the units of time, length and mass so that standards remain unvarying and same everywhere whether it is on earth, mars or any other remote corner of the universe. There are unchanging constants in nature and the standards of time length and mass can be fixed in terms these quantities.
The modern international standard unit of time is defined as a 9.1926331770 billion periods of a specific oscillation of the cesium atom. Nearly 9 million odd number is chosen to adjust approximate agreement with the previous definition of the unit of time based on earth’s period of rotation.
The velocity of light in vacuum is constant and independent of the motion of the light source, according to Einstein’s theory of relativity. Once a velocity and time are fixed, a length can be fixed. Thus the international standard of length is now defined as the distance traversed by light in vacuum in 1/299 792 458 of a second. Here again this odd fraction is adopted to ensure good agreement with previous definition of the unit of time – the second.
New International Standard of Kilogram – Effective from 20th May 2019
Although the units of time and length have been redefined in terms of fundamental constants, until 20th May 2019, the standard of mass (weight) continued to be the chunk of metal kept in Paris. The definition of mass based on this standard is unsatisfactory because the metal chunk could lose or gain mass owing to natural causes. Mass can also be defined in terms of another constant of nature termed the Planck constant. The German Physicist Max Planck and Albert Einstein derived this constant to formulate the quantum theory. The Planck constant has dimensions of an energy multiplied by time. Einstein’s famous equation––Energy = mass x square of the velocity of light––allows unit of mass to be defined in terms of energy. Alternatively fixing the standard of mass is equivalent to fixing the value of the Planck constant.
After many discussions on fixing the value of the kilogramme, lasting for more than a decade, the Meeting of the International Bureau of Weights and Measures held in Versailles, in November 2018, unanimously voted to fix the value of the Planck constant as 6.62607015 kg square meters per second. As in the cases of the units of time and length, this particular value of Planck constant was chosen so that the value of the kilogramme agree with previous definition. A procedure was also established to calibrate the kilogramme using a device known as the Kibble Balance. The new definition of the kilogramme was declared to be effective from 20th May 2019.
The modern units of time, length and mass have the same meaning to us as well as aliens wherever they exist;they can decipher our units!
Fermi lab Experiment: Possibility of something hidden deepest in nature
The Fermi Lab particle accelerator, near, Chicago in the United States, and the more powerful sister machine, the Large Hadron Collider in Geneva are the world’s leading particle accelerators, built at an exorbitant cost to understand the ultimate constitution of matter and forces governing their interactions. Accelerators energise protons or electrons and impinge them on each other and the products of the crash, yield a wealth of information.
Based on such experiments carried out at accelerator laboratories since early 1960s, we know that all matter around us is constituted of three particles–– up-quark, down quark and the electron, carrying electric charges 2/3, -1/3 and -1 in units of charge of the electron. Though not found in ordinary matter, experiments indicate occurrence of other brands quarks and electron like objects. Up-quark, down quark and the electron, have two other heavier companions each. Nobody knows why quarks and electron like objects, known as leptons, belong to families with three members. However, a theory known as the Standard Model accounts for forces between these particles mediated by another set of quantum objects known as bosons. The theory of the Standard Model is so general; in principle, it encompasses,large portion of physics, the whole of chemistry and therefore biology as well. Nevertheless, it has several discrepancies. The major one is that the model cannot accommodate gravity and the theory of gravity stands separate unmarried to the Standard Model as Einstein’s General Theory of Relativity. Experiments conclusively demonstrate that quarks and electron like particles of opposite charge also exist as demanded by the theory, but bulk matter made out these of these entities (antimatter) is not seen in the universe. Another anomaly is the existence of a triad of particles without electric charge known as neutrinos. The standard model could accommodate neutrinos if they have zero mass, but now they are known to be endowed with miniscule masses. Again observed faster expansion of the universe imply that the space is filled other forms of matter and energy not accounted by the Standard Model.
Science has furthered longer leaps, not by finding more and more evidence to support a favourite theory but by focusing greater attention on things refuting it.
Finding a disagreement with a theory is more important than dozens of supportive evidence.
Last week, the scientific world was shaken by an announcement of the Fermi Lab that the result of an experiment, suggested another glaring contradiction of the Standard Model.
Anomaly challenging established science
Electron and its 206 times heavier companion particle muon in the lepton family behave as miniature magnets and their magnetic properties are measured by a parameter referred to as the g-factor. As a result of magnetism these particles wobble in a strong magnetic field, similar to the motion of a spinning top just before it falls. Fermi lab experiment studied this motion using gigantic magnet, enabling evaluation of the g-factor of the muon to an utmost precision. The value they determined experimentally, deviate from the number predicted by the celebrated Standard Model by one part per one hundred million. Result confirms a previous measurement and therefore points to an anomaly. Scientific world is excited, because it may be a clue to disclose a deeper secret of nature, bearing profound implications. Possibly a crack in the Standard Model – a gift to amend the Standard Model and go beyond.
Why we should engage in advanced studies to learn secrets of nature?
One might ask what’s the use of this brain-teasing science, which seems to be of no relevance to the majority of the people, is. This query, in some sense, is equivalent to the question; what is the use of Totagomuwe Sri Ruhula Thera’s Salalihini Sandesaya or Shakespeare’s A Mid-Summer Nights Dream to people’s economic aspirations? The answer to both the questions is that these may not have immediate practical benefit to the average man or woman, but their value to humanity has been enormous. An average human being is benefitted most by overall advancement of the civilization.
In an era of telemedia which display everything hastily on two dimensional screens, society tends to seek quick answers to most issues and end-up with marginal solutions, refraining from deep contemplation
Every nation needs to encourage curiosity and imagination motivating advanced fundamental science, arts and literature. In reality those nations who have successfully earned economic returns from technology are the ones who excelled in the former themes.
Years ago, only Europe and the United States of America engaged in advanced precision experimentation and theoretical calculations to understand hard unresolved puzzles. Now, the developing countries have also realised the importance of such endeavors.
In fact, Sri Lanka was one of the first countries in Asia to recognise the importance of theoretical and mathematical studies and establish an Institute for the purpose; the proposal to set-up the Institute of Fundamental Studies was drafted by a Committee, headed by the late Prof. M.W. Mailvagnam, in 1969, on instructions of the Minister of Scientific Affairs M.D. H. Jayewardhana.
Sri Lanka possess talented young minds to tap and we need to provide them with opportunities to comprehend and pursue advanced frontier studies of the level that agitated the scientific world the past week; it is the duty and mandate of the institutions established for the cause to do so.