Without checking, ideas are just curiosities

There are many stories about Albert Einstein: some true, some not. In one of them he was a guest of honour at the opening of a major new telescope.

When his wife heard that the instrument was to be used to probe the depths of the universe, she is said to have commented, “My husband can measure the universe on the back of an envelope.”

Whether or not the story is true, her statement is very wrong. Making measurements and testing ideas requires instruments.Our efforts to better understand the universe around us involves a duet between ideas and observations or experiments. Without ideas, it is hard to know what we are looking for. Without checking out our ideas with Mother Nature, they are just curiosities.

In the 17th Century, when Galileo turned his telescope on the sky, it was widely believed that everything in the sky orbited the Earth and was perfect, as opposed to the imperfections of the Earth.

What he saw severely shook those beliefs. He saw that the Moon is not perfect; it is covered with lava flows, craters and mountains. Jupiter has moons orbiting it, whereas dogma dictated everything should have been orbiting the Earth.

By the 18th Century, it was clear that most of the objects in the sky are so distant they are too faint to see with the unaided eye, and the only way forward was to collect more light. This, rather than magnification, is the main function of astronomical telescopes.

William and Caroline Herschel built backyard telescopes with bigger and bigger mirrors. The largest had a diameter of 120 cm and collected around 60,000 times as much light as the human eye. In addition to identifying a large number of gaseous blobs produced by dying stars, they discovered a new planet, Uranus.

However, it was clear that to get a better view beyond our neighbourhood in the universe, even more light needed to be collected. The biggest backyard telescope of all was built by the Earl of Rosse. It had a 180-cm mirror and collected more than double the amount of light collected by the Herschels' 120 cm telescope mirror.

Some of the objects Rosse saw were spiral-shaped things. These were suggested to be new solar systems being formed.

The Herschels also tried to work out the shape of our galaxy, the Milky Way, by counting stars in various directions. They concluded our Solar System lies in the centre of a sort of irregular blob. To test these and other ideas required bigger telescopes, collecting even more light. These would definitely be out of the backyard league.

Since then, telescopes have been built by universities, foundations, nations, and through international partnerships. We now know from observations that those spirals are galaxies, and that we live in a spiral galaxy, but not at the centre.

One problem we have with ideas is that it is very hard to stop our beliefs and prejudices sneaking into them. Albert Einstein himself has given us an excellent example. When he was busy on the back of that envelope, his mathematical model for the structure of the universe kept predicting that the universe must be expanding or collapsing. He was so convinced this was not true that he added to his equation a fudge factor he called the cosmological constant, which made his model describe the steady-state universe he thought existed.

Soon after, new observations showed that the universe is expanding. Einstein afterwards said adding the constant was his biggest mistake.

This does not mean Einstein, Isaac Newton and their peers are not among the greatest scientists of all time. Their ideas give us a sense of direction for research, and indicate what sort of instruments we need.

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Saturn and Jupiter still lie close together, very low in the southwest just after dark. Mars is high in the southeast. Venus lies low in the dawn glow.

The Moon will reach Last Quarter on 6th January 2021.