Unit 3:
How did our understanding of the Universe change
over time?
Synopsis:
Learn how scientists explored different answers to the question: ‘what happened at the
beginning of time?’ Learn how the main modern answer to that question emerged.
And learn about some of the most important evidence that supports the modern
answer. These are questions studied today in the disciplines of astronomy and
cosmology.
An impossible question! How did everything begin? Every society has asked the
question ‘what happened at the beginning of time?’ But this is an extremely difficult
question to answer. How can something come out of nothing? This unit focuses on the
answers developed by scientists over the last several hundred years.
The beginnings of a scientific account of the beginnings of everything: an infinite
universe? Modern science has its roots in the European “Scientific Revolution” of the
17th century. Before the ‘Scientific Revolution’, most European scholars believed that
God had created the world 6,000 years ago, and that the earth lay at the very centre of
the universe. But a number of remarkable thinkers, including Copernicus, Galileo and
Newton, began to reject that model, and a new idea emerged. Even if God had created
the universe, it began to seem that it was infinite, and had no beginning or end.
Mapping the position and movement of stars and galaxies: During the 19th century
astronomers attempted to construct accurate maps of the position and movement of
stars and galaxies.
Using parallax to measure distances: The ancient Greeks knew in principle how to
measure how far away stars were using trigonometry (a branch of mathematics that
studies the geometry of triangles) and parallax (the apparent change in position of some
stars as the earth moves). However, even the nearest stars were so far away that the
Greeks could not detect any changes in position. Not until the 19th century were
astronomical instruments precise enough to allow such measurements, and even then it
was possible to measure the distance only to the nearest stars. But during the 19 th
century other techniques emerged for estimating the distance to stars and galaxies,
improving scientific understanding of the ‘geography’ of the Universe.
Studying the spectra of star light: Meanwhile, development of the spectroscope (an
instrument used to study the properties of light from stars) combined with use of the
Doppler effect (the shift in wavelengths depending on whether an object is moving
towards or away from us) enabled astronomers to estimate whether distant galaxies
were moving away from us or towards us.
Hubble’s revolutionary discoveries: In the 1920s, by using these techniques,
astronomer Edwin Hubble made a discovery that would transform our understanding of
the universe. Hubble showed that all distant galaxies seemed to be moving away from
us (when studied through a spectroscope, their light was shifted to the ‘red’ end of the
spectrum; that is why astronomers call this a Red Shift). He also found that the further
away they were, the faster galaxies seemed to be moving away from us. Assuming our
part of the universe is typical, Hubble’s discovery suggested the surprising idea that the
universe was expanding. This implied that at some point in the very distant past the
Universe must have been tiny.
An expanding universe with a history? Belgian astronomer Georges Lemaitre called
this crushed, tiny, dense dot that would eventually form the universe, the ‘primordial
atom’. Hubble’s discovery showed that the universe was neither infinite nor eternal.
Instead, it had a beginning and therefore it also had a history. His discovery made
astronomy a historical science. It was also the basis for the modern, scientific account
of the origins of the universe.