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Source: The Hindu

(http://www.hinduonnet.com/br/2002/02/12/stories/2002021200110600.htm)

 

 

Story of the universe

 

 

 

 

 

THE BIRTH OF TIME How We Measured the Age of the Universe: John Gribbin,

Universities Press (India) Ltd. Distributed by Orient Longman Ltd., 160, Anna

Salai, Chennai-600002. Rs. 200.

 

ONE COULD say this book is a sequel to an earlier one with the title, by the

same author, where the focus was to present evidence that the Big Bang really

happened. The author had rather grandly concluded that book with the remark: "It

is now possible to give a good scientific answer to the question `where do we

come from' without invoking either God or special boundary conditions for the

universe at the moment of creation."

 

In the present book he has chosen to deal with the cosmological mystery, namely

the age of the universe and proceeds to walk the reader through events that

finally led to finding a solution to that mystery. The key to this lay in

arriving at an accurate estimate for the value of the Hubble's constant as well

as the distances to various galaxies and globular clusters. The author himself

joined a team of astrophysicists to try and work out the value of Hubble's

constant, which has a direct bearing on the age of the universe. The story of

the universe, how it was created, how it evolved to be what it is today and what

kind of future it faces, is a fascinating one. And Gribbin is a master

storyteller who has to his credit several books on cosmology. Another of his pet

subject is quantum physics and both this and Einstein's general theory of

relativity are needed to describe the events, which led to the creation of the

universe and eventually us.

 

Before attempting to determine the age of the universe, scientists had to

determine the age of the solar system itself to get a handle on the cosmological

scale involved. After several false starts spread over centuries the discovery

of radioactivity (the credit for which goes to pioneers like Rutherford, the

Curies and Becquerel among others) was to give a most conclusive evidence for

the age of the Earth and, hence, the age of the solar system. We now know this

to be about 4.6 billion years, a figure which could at once satisfy geologists

and geochemists alike. Radioactivity provided a timescale and an energy source

in one package leading to the concept of half-life and providing a clock for

measuring the age of the Earth and putting an absolute date into the fossil

records. It also explained the nagging puzzle: from where is the Sun drawing its

seemingly inexhaustible supply of energy?

 

Coming to the question of the age of the universe, it is pretty evident that the

figure has to logically match the age of the oldest star. In an expanding

universe it makes sense to say that measuring cosmological distances is a

prerequisite to working out the age of the universe. The earliest approach to

measuring cosmic distances was the well-known triangulation method, which

determines distances by parallax.

 

Huygens, the Dutch astronomer, arrived at a value of 28 astronomical units for

the distance of Sirius from the Earth (one A.U. is the distance of the Sun from

the Earth). This of course had to be increased several times over in later years

as more accurate methods became available. In the early 1920s the known universe

was less than 200,000 light years in diameter and consisted of our galaxy and

the two neighbours, the Megallanic Clouds. The U.S. astronomer, Shapley, had

already provided a picture of the size and shape of our galaxy using Henrietta

Leavitt's Cepheid variable method. His figures too had to be revised later on.

 

Einstein published his general theory of relativity in 1917 and his equations

pointed to an expanding universe: an idea somewhat repugnant to him. He

introduced a constant in his equations to knock this out and make a steady state

universe. De Sitter came up with a model of the universe with no matter in it

and did away with the constant. In 1927 LeMaitre and Friedman found a further

possible solution, an expanding universe containing matter.

 

Soon Edwin Hubble published his paper and the astronomical community sat up to

take note of the idea that the universe was expanding and must have been born at

a definite moment in time. However, the red shift-distance relationship found by

Hubble would not match up with either the Einstein or the de Sitter model of the

universe. The Doppler effect does not cause the red shifts mentioned here

because they do not involve velocities in the everyday sense but the stretching

of space itself. By 1932 Einstein abandoned his cosmological constant and came

round to accepting the concept of an expanding universe.

 

There is a lot more in this book. The author then goes on to discuss the

Einstein-de Sitter model, the basic concept of which rests on astronomical

observations giving a very simple relationship for calculating the age of the

universe. By the 1970s a controversy erupted with one set of astronomers opting

for a lower value for Hubble's constant and another for a much higher value.

That gave rise to a split, one school favouring less than 10 billion years and

the other about 13 billion years for the age of the universe. About a decade

later this ran into serious problems because by then the age of the oldest star

was estimated to be around 18 billion years a peculiar case of the

daughter being older than the mother. Around this time the author and his team

working on the size of the Milky Way and the age of the universe sent out their

work for publication.

 

A few years earlier, in 1989, the European Space Agency had launched the

Hippocras satellite, which failed to reach the desired geostationary orbit, and

ended up in a highly elliptical orbit. Everything was not lost though. This

satellite was used to measure cosmological parallaxes with a high degree of

accuracy and the processed results were available in 1997.

>From the results it was conclusively proved that the age of the oldest among

stars was about 11 billion years and not 16-18 billion years as believed

earlier.

 

By now the author's team had settled for a value of 50-60 for the Hubble's

constant based on Cepheid distances and geometrical techniques.

 

To make a long story short it all boils down to this: in the simplest

Einstein-de Sitter model the universe is about 13 billion years old and nearly

flat.

 

If we accept a universe that is nearly open, its age would work out to about 16

billion years, giving us a possible range of 13-16 billion years which does not

clash with the age of the oldest among stars a comforting thought for

everyone.

 

The author concludes his book in a rather emphatic fashion: "We really do

understand the way stars behave," says he, adding "the universe really did begin

at a definite moment in time. If anything in science is really a Deep Truth, it

is the match between stellar astrophysics and the discovery of the birth of

time." He has given us yet one more fascinating book on cosmology.

 

 

 

 

 

C. V. SUBRAMANIAM

 

 

 

 

 

 

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