The Expanding Universe Part 1: The Doppler Effect
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-The Expanding Universe Part 1: The Doppler Effect-
by
Phylis Johnson
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In modern scientific models of the universe it is believed that the universe is expanding and that at some point in the past the universe “began.” This is known as the “expanding universe theory” and the beginning of the universe is known as the “big bang.” But how did scientists come to the conclusion that the universe is expanding, and subsequently that it had a beginning of some description?
Until the early 1900s scientists had not questioned the notion that space was absolutely fixed - that it was a huge static container in which the material of the universe existed and moved. However, as John D. Barrow writes, “during the 1920s this simple picture was transformed,” primarily through “the results of observations of light from stars in distant galaxies by the American astronomer Edwin Hubble.” (The Origin of the Universe, p2)
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-The Doppler Effect-
To understand the importance of Hubble’s observations we first need to understand something about the property of waves. When the source of the wave is moving away from the observer the frequency of waves is less and when it is moving toward the observer the frequency of waves will increase. For instance - if you wiggle your finger in a fishtank waves will spread out from your finger. Now watch one point on the edge of the fishtank. When you move your finger toward this point while wiggling it the waves will get closer together in relation to that point. If you move your finger away from that point while wiggling it the waves will get further apart. As Barrow writes, “This property is shared by all waves. In the case of sound waves, it is responsible for the change in pitch of a train whistle or police siren as it passes you.” (p2) The relationship between the frequency and speed of waves is called the Doppler effect.
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-Edwin Hubble and the Expanding Universe-
It just so happens that light also has wave properties and therefore also exhibits a Doppler effect. With sound we hear the Doppler effect in the rising pitch. With light we see the effect as shifts in colour. When we look at a star or a distant galaxy light is traveling over millions of miles to reach our eyes. When the source of this light is moving away from us the light is tinted slightly “red” and when it is moving toward us it is tinted slightly “blue.” These shifts in light frequency are referred to as “redshifts” and “blueshifts.” What Hubble observed when studying the light of distant galaxy clusters is that they all “displayed a systematic redshifting,” meaning that they were all traveling away from us. He also discovered that “the farther away the light source, the faster it was moving away from us.” (Barrow, p2) This is now known as Hubble’s Law.
What this amounts to is that the universe is expanding and that it is not at all static as scientists had once believed. Albert Einstein’s “Theory of Relativity” had already suggested this outcome but Einstein was unable to accept the notion of a non-static universe. In order to create a workable theory of a static universe inside relativity Einstein introduced a “cosmological constant,” which he later called “the biggest blunder of my life.” As Barrow writes, “By introducing it into his equations, he had missed the opportunity to make the sensational prediction that the universe was expanding.” (p22)
There is an important question which arises from this conclusion that the universe is expanding. If everything is moving away from our galaxy cluster then does this mean that our galaxy is the centre of the universe? The answer is no. We are moving away from everything else as well. The most common way of explaining this effect is to think of a balloon being blown up. Imagine that there are a number of points drawn on the balloon’s surface. As the balloon expands every point gets further away from every other point and there is no center to the expansion. If we imagine that we are on one of the points looking out on the other points they would appear to get further away and we would appear to be staying still. But in actuality every point is getting further away from eachother. In this example we see that it is not the galaxy clusters which are expanding but space itself, carrying galaxy clusters with it.
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-The Big Bang-
The idea of the Big Bang, or the beginning of the universe, is a natural extension of the “expanding universe theory.” As Barrow writes, “If the universe is expanding, then when we reverse the direction of history and look into the past we should find evidence that it emerged from a smaller denser state - a state that appears to have once had zero size. It is this apparent beginning that has become known as the big bang.” (p4-5) Essentially, at one point in time - at the beginning of “time” in fact - everything in the universe was crushed into one tiny point. The moment when this point “exploded” and the potential material of the universe began to expand and evolve into what exists today is called the “Big Bang.” In modern physics the Big Bang theory was first proposed by Georges Lemaitre who called it the “hypothesis of the primeval atom.”
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The Big Bang is not only the beginning of the universe in terms of material contents, but also the beginning of space and time as we know it. Mark Midbon writes that “Lemaitre described the beginning of the universe as a burst of fireworks, comparing galaxies to the burning embers spreading out in a growing sphere from the center of the burst. He believed this burst of fireworks was the beginning of time, taking place on ‘a day without yesterday’.” (A Day Without Yesterday: Georges Lemaitre and the Big Bang) Lemaitre himself writes, “If the world has begun with a single quantum, the notions of space and time would altogether fail to have any meaning at the beginning; they would only begin to have a sensible meaning when the original quantum had been divided into a sufficient number of quanta. If this suggestion is correct, the beginning of the world happened a little before the beginning of space and time.” Einstein, who initially rejected Lemaitre’s theory, later said “This is the most beautiful and satisfactory explanation of creation to which I have ever listened.”
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Although the theory of the expanding universe and the Big Bang are relatively recent in terms of scientific thought, there have been many creation myths which suggest that the universe grew from a single point, from a “primeval atom” or “seed.” These mythologies often refer to the beginning of the universe as a “cosmic egg” which grows and grows until it cracks open to reveal the material universe. Lemaitre himself even referred to his theory as the explosion of the Cosmic Egg at the moment of creation. In the Vayu Purana for instance, a Hundu religious text, at the beginning of time everything was originally contained in the cosmic egg; “Inside the egg were all the worlds that would be created, in embryonic form. The earth was there, with its land, mountains, oceans and rivers. The moon, the sun, the stars and the planets were there.”
The further connections between mythology, metaphysics and twentieth-century physics will be examined in more detail in Expanding Universe Part 2 (to come). This short series of essays on the expanding universe is inspired by Dick Whyte’s series of art-works titled “White Circles.”
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-References-
John D. Barrow, The Origin of the Universe (Orion Books, 1994)
Stephen Hawking, A Brief History of Time (Bantam Books, 1989)
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-Online References-
John D. Barrow, Theories of Cosmology (originally published in The Astronomy and Astrophysics Encyclopedia, edited by Stephen P. Maran)
Mark Midbon, A Day Without Yesterday: Georges Lemaitre and the Big Bang (first published March 24, 2000)
Donald H. Menzel, Blast of Giant Atom Created Our Universe (amazing reprint of an article first published in 1933, just 3 years after Edwin Hubble observed the redshifts of distant galaxy clusters)
The Edwin Hubble Homepage (great page with amazing images of galaxies, like the one above, from the Hubble Telescope)
Albert Einstein Archives Online (an archive of Einstein’s manuscripts and writing)
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