15 September 2010

Scientific ideas sometimes come full circle

By Dr Manas Kumar Haldar

(Published in’Campus & Beyond’, a weekly column written by Swinburne academics in the Borneo Post newspaper)

In mathematics, we prove or falsify ideas and that is the end of it. Not so in science; ideas once discarded can return in a new form. I illustrate this with two stories.

The first story concerns the nature of light. There were two competing theories – light consists of particles, and, light is a wave. The first theory was propounded by none other than Sir Issac Newton. Light travels in a straight line just as a particle not subjected to force would. A wave would spread out. Light as particles does not require a medium to travel, whereas light as a wave was thought to require an elusive medium called ether. On the other hand, wave theory explained phenomena which particle theory could not. But such was the authority of Newton that the particle description continued to hold its ground until bang came its death – how?

When a light ray travels from one medium into another, say from air into water, it is bent at the common boundary. A quantity called refractive index can be determined from this bending. It was found to be greater than one for water. Following Newton’s particle analysis, the refractive index of water is the ratio of the velocity of light in water to the velocity of light in air. This together with a refractive index greater than one implies that the velocity of light in water is greater than the velocity of light in air. In Newton’s days, the velocity of light in water could not be measured. But in 1850, Foucault’s experiments showed that the velocity of light in water is less than its velocity in air, contradicting Newton’s result but supporting the result obtained from wave theory. So the particle theory was abandoned.
Then something happened. Planck showed that experimental results of blackbody radiation could only be explained if light is considered to be made of particles of energy equal to the product of Planck’s constant and the frequency of light. Einstein further showed that the experimental results of photoelectric effect (generation of electric current by light) could only be explained by Planck’s particle hypothesis. Particle idea returned, but in a different form.

So who was the winner – particle or wave? It is a win-win situation. Light is now considered to have both particle and wave like nature. The quantum theory of light incorporates both ideas.
The second story is concerned with finding our position on earth. Consider travelling to some place on land, say in Kuching. We find our way by observing features called landmarks. But what happens in the high seas where there are no discernible features? We can locate our position by determining the latitude and the longitude. Latitudes are imaginary circles on spherical earth running parallel to the equator and measure distances in the north and south directions. Longitudes are imaginary circles intersecting at the north and south poles and measure distances in the east and west directions. Sailors could determine the latitude by determining the position of the Sun or the North Star. But inability to determine longitude accurately, and hence position, resulted in many shipwrecks. The British Government in 1714 offered a prize of ?20,000 to anyone who could solve the problem.

There were two competing ideas. Professors and astronomers looked to the heavens. Among many proposals, a 1699 proposal, relevant to this story, was to mark longitudes in the sky using twenty four rows of stars rising from the horizon. The other idea was to determine the time at the home station while sailing in a ship. Then, knowing the local time, the longitude could be determined. The ease of this method compared to the astronomers’ methods is like the ease of using a mouse as compared to writing a computer program. Determination of time requires a clock, while the astronomers’ methods required precise observations and complicated calculations. The problem with the time method was the inaccuracy of available clocks. It was solved by John Harrison who first made clocks accurate enough for the purpose. Harrison, a self taught scientist and watch maker, won the prize against challenges from Oxbridge scientists. The help from the “heavens” was rejected in favour of the clock.

But the “heavens” are back in business with the advent of GPS (Global Positioning System). GPS consists of 24 orbiting satellites. Observe the resemblance to the 1699 proposal. The position on earth can be accurately determined from the timing signals transmitted by the satellites. The complicated calculations are done by a computer. So it is as easy to use as a clock, but the determination of position is far more accurate.

So, once again, who was the winner – the “heavens” or the clock? It is a win-win situation again. Although positions of the satellites in the “heavens” have to be known accurately, accurate clocks (atomic rather than conventional) are required for timing signals.

There are other resurrected ideas in science. But space in these columns does not permit any more “story telling”.

Dr Manas Kumar Haldar is an Associate Professor with the School of Engineering, Computing and Science, at Swinburne University of Technology Sarawak Campus. He can be contacted at mhaldar@swinburne.edu.my