From Genesis to Revelation

by Nicholas Mee on August 1, 2017

Modern cosmology is one hundred years old this year. Of course, poets, seers and sages have contemplated the origin of the universe for millennia and arrived at various conclusions. There aren’t really that many distinct possibilities, however. The universe is either finite, eternal or cyclic, and the third of these possibilities is like a combination of the previous two, an infinite sequence of finite cycles.

God the Architect, William Blake.

From Genesis to Revelation

The finite cosmos of the Judaeo-Christian tradition is an example of the first option. It opens with:

In the beginning God created
the heaven and the earth.

and ends with the Apocalypse. Writing in the 5th century, St Augustine claimed that the only logical conclusion was that time began with the Creation.

The Island Universe

The second option corresponds to the infinite cosmos of Aristotle, who believed the universe to be a sphere surrounded by the Void. Aristotle’s cosmos was enclosed by the sphere of the fixed stars whose distance was not much greater than that of Saturn. Aristotle held the view that although space is finite, it has always existed, so time is infinite.

The Ring Cycle

According to Hindu cosmology the universe is eternal and cyclic. There is an infinite sequence of universes that each emerge from chaos, to grow and flourish, then decay, die and dissolve into the chaos from which the subsequent universe is born. Each cycle takes an immense period of time, the kalpa, which lasts upwards of 4,320 million years.

Gotterdammerung Credit: Opera North.

There are parallels with Nordic cosmology where each world cycle ends with Ragnarok or, if you are an opera lover, Götterdammerung — The Twilight of the Gods.

Einstein’s Static Universe

Einstein completed his general theory of relativity in 1915. Formulating this new theory of gravity was possibly the greatest intellectual achievement ever made by a single individual. By 1917 he was ready to apply his new theory to the entire cosmos. But even Einstein had preconceived ideas about how the results should turn out. His initial calculations seemed to imply that the universe must either be expanding or contracting, which clashed with Einstein’s expectations that the universe was eternal. Einstein realised, however, that he could add an extra term to the equations — the cosmological term — that would only affect the results over cosmological distances. The inclusion of this term allowed a solution that was neither contracting nor expanding, but balanced on a knife-edge between the two. This was Einstein’s static universe. It was an island universe in some ways similar to Aristotle’s.

The Cosmic Egg

Georges  Lemaître, a priest from Belgium who became enchanted with general relativity while studying in Cambridge, took a different view. He published his results in 1927 and concluded that Einstein’s theory implies the universe is expanding and therefore must have begun at some point in the distant past. Lemaître dubbed this cosmic origin the primaeval atom or, even more poetically — the cosmic egg.

Einstein was not enthusiastic about Lemaître’s conclusions and pointed out that a Russian physicist Alexander Friedmann had derived similar results five years earlier. He told Lemaître: ‘Your calculations are correct, but your grasp of physics is abominable.’

In physics, however, authority counts for little. Ultimately there is one arbiter who decides the validity of a theory — the real world. Lemaître realised that there is a consequence of an expanding universe that could be tested. In an expanding universe the further away any light source the faster it will be receding, and the faster it is receding the greater the red shift of light in its spectrum.

The Cosmic Egg
Credit: Womb by Nicholas Mee and John Robinson.

Red Shift

Light from a hot body, such as a star, is generated by the random jostling of particles in its outer layers. This light is emitted at all wavelengths, so when dispersed with a prism it forms a continuous band or spectrum. Galaxies contain lots of stars and lots of clouds of hydrogen and other gases. The electrons in the gas atoms absorb light of specific wavelengths that promote them to higher energy levels in the atoms. This depletes the light we receive from a galaxy at precisely these wavelengths, forming dark absorption lines in the spectrum, as shown in the illustration below. (The electrons later emit light of exactly the same wavelength, but this is emitted in all directions, so only a tiny fraction is directed towards us.)

Centre: The spectrum shows absorption lines as they would appear in the laboratory. Top: Red shifted spectrum from a receding source. Bottom: Blue shifted spectrum from an approaching source.
Credit: Christopher S. Baird.

If the galaxy is receding from us, the wavelength of the absorption lines shifts. This is analogous to the fall in pitch of sound waves from a siren when an ambulance or fire engine moves away from us. When applied to light, it is known as red shift, because red is the long wavelength end of the visible spectrum, even though the lines could be in any part of the spectrum, such as infra-red, ultra-violet or radio waves. Similarly, light from an approaching source is blue shifted.

Lemaître showed that in a steadily expanding universe the more distant a galaxy the faster it is receding from us, which implies that the red shift of a galaxy’s light is proportional to the distance to the galaxy. There was just one problem with using red shift to determine whether the universe is expanding. How do we measure the distance to each galaxy?

The Distance to the Stars

Henrietta Swan Leavitt (1868-1921)

Henrietta Leavitt was employed as a computer at Harvard College Observatory. She was given the task of studying and cataloguing variable stars. This topic was centuries old and probably seemed an unlikely subject for a major discovery. However, Leavitt found a remarkable pattern in a class of stars known as Cepheid variables. These are very bright giant stars that can be seen from immense distances. They go through regular cycles of brightening and dimming.

By studying a collection of Cepheids all lying at essentially the same distance in a dwarf galaxy orbiting the Milky Way — the Large Magellanic Cloud — Leavitt discovered that the brighter the Cepheid the longer its period. This means that by measuring the period of a Cepheid it is possible to determine how far away it is. Her original study was published in 1908 and this was followed by a more detailed account in 1912. Tragically, Leavitt died in 1921 before anyone realised the significance of her discovery.

Polaris and the Pointers. In the UK, the Big and Little Dippers are usually known as the Plough and the Little Bear. Credit: Astrobob.

Cepheid variables are named after the star Delta Cephei whose variability was discovered by John Goodricke in 1784. There is more about this remarkable astronomer here: The Gorgon’s Head.

You may have seen a Cepheid variable; the closest such star is very well known. It is the pole star, Polaris, whose position near the celestial pole has helped travellers navigate for several centuries. Although not one of the very brightest stars in the night sky, this is only because it lies 433 light years distant, fifty times further than Sirius (which is the brightest). Polaris is a yellow supergiant with over five times the mass of the Sun. Its brightness varies over a period of four days, but this is not easily noticeable to the naked eye.

Living in an Expanding Universe

Edwin Hubble tracked down Cepheid variables in a number of relatively nearby galaxies with the 100-inch Hooker Telescope at the Mount Wilson Observatory in California, and used them to calculate the distance to each galaxy. He compared this data to the spectra of these galaxies compiled by Vesto Slipher and Milton Humason. Hubble announced in 1929 that the more distant a galaxy the faster it is racing away and concluded that we live in an expanding universe.

Lemaître was proved correct, but he has been somewhat sidelined in the history of cosmology; perhaps because physicists were uncomfortable that their leading theory for the origin of the universe was proposed by a priest. Lemaître is remembered more for Einstein’s criticisms than his actual work, which is rather unfair, as in this case Einstein was wrong. Nevertheless, Einstein and Lemaître became firm friends.

Not everyone was convinced that the universe emerged from nothing in the distant past. The battle for the cosmos would continue for several decades. I will discuss how it played out in a future post.

 

Further Information

There is more about cosmology in my book: Gravity: Cracking the Cosmic Code.

The animation Womb, shown above, is one of a series of animations that I created with the sculptor John Robinson. You can see some of the others here: Symbolic Sculpture.

Click below if you like this post.

 

{ 5 comments… read them below or add one }

Dilip D James August 8, 2017 at 12:23 am

This is a wonderful take on Astronomy and the Cosmos and touches on almost all of the major points.

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Debra Nightingale August 10, 2017 at 9:33 am

A most enjoyable read.

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Roy August 28, 2017 at 9:39 am

Elegant description

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Carl Larsen August 29, 2017 at 11:48 am

The article has been presented in very clear and easy to read dialogue. I am so grateful for this pleasant read.

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L Pal September 3, 2017 at 5:10 pm

Good to read. It is easy to understand.

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