The Inherent Limitations Of Measurement In Science, Astrophysics In Particular

“And that inverted Bowl we call the Sky, Whereunder Crawling Coop’t we live and die, Lift not thy hands to it for help. . for It Rolls impotently on as Thou or I” — Fitzgerald in The Rubaiyat of Omar Khayyam

There are some people who feel that if scientists, particularly astrophysicists, continue to look at the cosmos the way they do now, they may never be able to really unravel its mysteries.

Each closer look at the sky with our increasingly sophisticated telescopes reveals something totally unexpected, upsetting our previous images of celestial objects. The details revealed by planetary probes have underscored the shocking paucity of precise information about the contents of the physical universe.

From a very close range, Mars proved to be far different from anything astrophysicists had imagined.

The Mars Rovers revealed details which earlier probes had not been able to. And how long we have come from the fantasies of Martian canals misidentified by the telescopic observation of Giovanni Schiaparelli in 1877 to the willing suspension of disbelief in seeing human face sculpture in Martian Cydonia from the Viking-I orbiter photograph of 1976 to be only disproved by later detailed photographs like Mars Global Surveyor and Mars Reconnaissance Orbiter almost two decades later.

The photographs of Saturn and Titan by the spacecraft Huygens gave extremely useful information which previous spacecraft like the Voyagers had been unable to obtain.

It would appear that whenever the ideas of some celestial object are based on what astrophysicists see, a closer look with more sophisticated equipment will reveal that they had been having erroneous notions about that object.

Yet a wrong scientific guess has always been more useful than the fancies of biased human imagination in furthering our knowledge.

And what is true of space seems to be true of specimens photographed in a laboratory under ever-increasing magnification and resolution.

Each closer look with a more sophisticated tool, reveals totally unexpected details that change previous beliefs. Thus, greater details of the physiological — the organs, muscles, bones, etc — gradually began to be revealed with the invention and use of increasingly sophisticated medical tools.

In June 1896, only six months after Roentgen announced his serendipitous discovery of X-rays, they were being used by surgeons in the battlefield to locate fractures in the bones in wounded soldiers. Prior to 1912, X-rays were used only to detect fractures in the realms of medicine and dentistry, underscoring the limitation in the capability of X-rays in revealing greater details of human physiology, though some X-ray pictures of metals were also taken.

Until 1950, it was the only tool in investigating fractures, and other abnormalities. No doubt they are proving useful even today, but their capacity to see detail in many regions of the human body is extremely limited.

Then occurred three major developments that revolutionised medical diagnosis — the invention of the large-scale human positron imaging, in the 1950s, the invention of the CAT Scanner in 1967, and the invention in 1967 of Magnetic Resonance Imaging (MRI), a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body in minute detail.

MRI is useful in the investigation of abnormalities like epilepsy, tiny tumours, and lesions — something inconceivable in the past.

It is, therefore, believed that even more sophisticated medical diagnostic machines will be developed in future. Doctors may have at their disposal devices that scan every organ of the body in much greater detail within seconds.

The most significant development in the treatment of heart patients occurred in 1960. The first coronary artery bypass surgery (a development nobody would have imagined possible in the first half of the twentieth century) was performed in the United States on 2 May 1960.

Today, bypass surgery is performed in district hospitals in India. All this goes to show that every new discovery or invention increases human capability in any branch of science, ranging from astrophysics to medicine, revealing at the same time the limitations in the capability of earlier diagnostic tools, and in some cases, making them obsolete technology.

Reverting to astrophysics, the dark patches between the stars had once been thought to be holes in the heavens; now astrophysicists are fairly sure they are dust clouds.

But suppose they are only as near to the truth about dust clouds as astronomers had been abut Saturn’s rings in the days when they had thought that there were only three of them?

Since most of what they believe about galaxies, supernovae, and nebulae are based on what they see in photographs, their opinions about them are way off base too.

Radio astronomy, which supplements what astrophysicists see, has its own limitations as the data is presented in the form of computer-enhanced maps made to resemble photographs.

Astronomers are aware that their vision is limited in this sense. Photographs and radiographs suffer from problems with resolution — the ability to distinguish detail. What they reveal is only the average of a large volume of space.

Astronomers use terminology like ‘a minute of arc’ or ’years of space’ to study astronomical distances, concepts which are outside the scope of this discussion, due to constraints of space.

For instance, astronomers studying the nearby Magellan clouds 180,000 light years away, assume on the basis of practical experience that one minute of arc represents three years of space. A 'minute of arc' is a unit of angular measurement equal to 160th of one degree.

At sea level, one minute of arc along the equator equals exactly one geographical mile along the Earth's equator or approximately 1.151 nautical miles.

A second of arc, one sixtieth of this amount, is roughly 30 metres (98 feet). A light year, as most know, is the distance travelled by light at 18,600 miles per second for a whole year.

Put briefly, few telescopes can see one minute of arc very clearly; the pictures they get convey virtually nothing about structures smaller than three light years across.

This kind of astronomical shortsightedness can be compared to mapping the continental United States from space with a resolution of three miles. The Rockies and the Sierra Nevada would appear as ridges interrupting a plain sloping to the west.

It would not be possible for them to extrapolate the existence of the mighty mountain range from the gently undulating ridge; they would also miss such details as fault planes, erosion, glaciers, or any valley smaller than five miles across.

Their picture itself would be not only very crude but also wrong, though it may work for some time, just as epicycles had explained planetary motions for a while.

Then astronomers argue that in spite of resolution problems, they can be at least certain that they are seeing motions produced by Doppler shifts of distant objects in the universe. Many astrophysicists believe that the universe is expanding because everything shows a redshift. But some physicists rather jocularly observe that one can also get a redshift effect in an accelerating, contracting universe.

Particles that accelerate emit radiation, and so, if the universe is accelerating locally as part of an oscillation, they would see all sorts of radiation from them.

If they, therefore, conclude that it is the background radiation left over from the 'Big Bang’, astrophysicists belonging to another school of thought would perhaps feel that they are wrong again.

The question now arises whether there is any hope of finding out the ultimate truth about the universe, considering that everything astrophysicists know today by observation with their measuring instruments might or will be found to be wrong tomorrow at some level.

So is the case of medical diagnostic tools. Will the pictures of the world be eternally under revision, new truths superseding old? When are astrophysicists and physiologists ever going to decide that they know enough?

They can continue to get better and better pictures, at an ever-accelerating pace and yet, they may never get any closer to the “ultimate” perfect image. However, it is very unlikely that scientists will ever admit that their work should be terminated.

They are having too much intellectual excitement. They will justifiably argue that no one can predict what exciting discovery is around the next celestial or nanometric corner.

Astrophysicists have been taken by surprise at various times in the history of science by fantastic discoveries — the unanticipated existence of all kinds of fundamental particles, gigantic galaxies, peculiar properties of matter, and the atmosphere in the various planets and their moons.

Each discovery meant unsettling revision of our earlier views of the universe. But to have discontinued at any one of these points, to have thrown up their hands on a “why should we go on” attitude would have been to miss the potential for exploitation of these discoveries.

They would do well to keep in mind Clough's famous lines, about not giving up hope.

Clough was right. If scientists had given up hope at some stage, they would have missed, for example, the semiconductor industry, nuclear power, space technology, genetic engineering, and organ or tissue transplantation.

When viewed from the point of view of a pragmatic technological society, astronomy would be regarded as the greatest luxury in science. It is not immediately obvious that there have been many exploitable discoveries made in the depths of space.

Yet, for example, high-resolution quasars are, in fact, now being exploited to measure the movement of continental drift and monitor activity along earthquake fault lines — practical uses, entirely unpredicted as recently as about three decades ago.

Astrophysicists will continue to look closely at the universe and will continue to believe what they see — even though all their experience shows them that what is here today is gone tomorrow, that what they thought they saw in their photographs yesterday is forever changed by today’s clearer view.

Astrophysicists will continue happily revising the pictures for ever, driven by the joy of exploration.

Hence astrophysicists should continue to design increasingly powerful telescopes to obtain pictures of greater accuracy and clarity while studying the observable universe.

There is also another philosophical consideration.

To the true astrophysicist or any other scientist, the journey itself is more important than reaching the destination. One is reminded of Churchill’s famous lines about Richard I, King of England — "He loved war, not for the sake of glory or political ends, but as other men love science or poetry, for the excitement of the struggle and the glow of victory”.

This is the same spirit that provides the motivation for basic research in science.