Elements in the Stars
Prisms and gratings disperse light into its characteristic colors. The dispersed light is called a spectrum. Scientists have heated samples of all the different elements until they became gases or plasmas and emitted light. Each element has a spectrum consisting of colored bright lines and dark spaces. The light of each bright line has a specific rate of vibration or frequency that is characteristic of the element. Astronomers have compared the spectra of elements heated in the laboratory with the spectra of sunlight, starlight, and the light of distant galaxies. Light from distant sources usually has the spectra of a number of elements all mixed together. The intensity of the lines for different elements varies with their relative abundance in the distant sources. With much patient work the astronomers have identified the elements and measured their abundances in distant stars. The same elements found on Earth are found throughout the universe. This shows the unity of the universe. A single process produced the entire universe, including the Earth.
All nuclei of the element technetium are radioactive, yet some stars have measurable quantities of it. Half of the most stable nuclei of technetium decay in a little over two million years. Its presence in some types of stars shows that they can make new technetium through natural processes.
Natural Radiation from Space
Victor Franz Hess (Austrian-American physicist, 1883–1964) found between 1911 and 1912 that natural radiation, energetic enough to include gamma rays, showers the Earth. We now refer to this radiation as “cosmic rays.” The term refers to the mixture of gamma rays and fast-moving particles that continuously strikes the Earth’s atmosphere. Some of the particles come from the Sun or other stars. Others are bits and pieces of atoms that happened to be in the way of gamma rays and broke up. Some of the rays are too energetic to have come from nearby stars.
There was a long debate about the source of the most energetic gamma rays. Every month or so some small region of the sky emits a burst of gamma rays. The energy of the new source fades quickly. Some astronomers thought that these burst sources must be far away, because light from them is extremely reddened like the light from the most distant galaxies. But if the burst sources are far away then while they flare up, they must briefly produce more energy than an entire galaxy. This led other astronomers to think that the burst sources are objects ejected at high speed from our own galaxy. If they are close to our own galaxy they don’t need to produce such great amounts of energy to achieve the brightness we see from the Earth. Still, there was no good explanation for what shoots them away so fast. The debate went on until new data resolved[i] it in 1997. Now we know that the burst sources are very far away and produce tremendous amounts of energy. They are truly cosmic, not local.
[i] Schwarzschild, Bertram, “High-Redshift Absorption Lines Show Convincingly that Gamma-Ray Bursters Are Very Far Away,” Physics Today, 50 (Number 7, July 1997), pp. 17–18.
The most energetic gamma rays come to the Earth from the most distant and oldest parts of the universe. Because they have traveled so far at the high but limited speed of light, these gamma rays are the oldest things in the universe. At the same time, we must conclude that they are not infinitely old. If the stars were uncreated and infinitely old, then all the ones that could flare up and emit bursts of gamma rays would have done so long before our time.
Stars Consume Their Fuel
The fact that the stars are still shining shows that they are not infinitely old. All stars including the Sun burn fuel. Their fuel supply must be limited. If they are infinitely old, it is hard to explain why they are still shining. Is it possible to renew the fuel of stars and make new radioactive materials?
The above arguments are valid, but some people have sought to get around them with a variety of complicated schemes. Most of them sought a continuous or renewable fuel supply so the universe could be uncreated, without beginning or end. Frankly this is a philosophical preference, without any scientific basis. To decide scientifically we first have to understand cosmology.
Cosmology and Relativity
By 1915 Einstein had generalized his theory of relativity and founded the science of cosmology. General relativity is really a set of complicated differential equations. There are many solutions because one may choose various parameters in the equations, and also postulate what are called the initial and boundary conditions.
At present we cannot observe either the beginning or the edge of the universe (if it has an edge). Therefore, the choice of initial and boundary conditions is arbitrary. Mathematicians start with initial and boundary conditions that seem good to them, solve the equations, and then see if the resulting model of the universe looks at all like the present universe. It would be more logical to write down present conditions in the present universe and then solve the general relativity equations backwards until we knew the conditions at the beginning. However, this procedure is much more difficult that solving the equations in the forward direction.
The values of the parameters and the conditions chosen may make the equations easy, difficult, or impossible to solve. Naturally Einstein and other physicists and mathematicians found most of the easy solutions first.
There is nothing wrong with solving the easy cases first. In doing so we may learn something that will make solving the harder cases easier or at least possible. The parameters and conditions that make for easy solution do not necessarily correspond to reality. The problem with solving only the easy cases is the temptation to jump to philosophical conclusions that don’t correspond to reality before doing the hard work necessary to solve a realistic case. Even great scientists are not immune to this temptation, as we shall see.
Willem de Sitter (Dutch astronomer, 1872–1934) found the first non-static solution in 1917. In his solution, the universe consists of empty space and time only. The solution is interesting to mathematicians, but it doesn’t correspond to reality. The solution describes a universe with zero matter density in it. Material objects (including us) exist in our universe. One may solve the equations for an empty universe, but such a universe could not have living, rational beings in it to find the solution.
In 1922 Alexander Friedmann (Russian mathematician, 1888–1925) found a solution that depends directly on the density of matter and energy in the universe. His was the accepted model until recently, when astronomers discovered that the expansion of the universe is accelerating. Now many physicists and mathematicians are working to extend and modify his solution, or to find another solution that includes accelerating expansion.
All nuclei of the element technetium are radioactive, yet some stars have measurable quantities of it. Half of the most stable nuclei of technetium decay in a little over two million years. Its presence in some types of stars shows that they can make new technetium through natural processes.
Natural Radiation from Space
Victor Franz Hess (Austrian-American physicist, 1883–1964) found between 1911 and 1912 that natural radiation, energetic enough to include gamma rays, showers the Earth. We now refer to this radiation as “cosmic rays.” The term refers to the mixture of gamma rays and fast-moving particles that continuously strikes the Earth’s atmosphere. Some of the particles come from the Sun or other stars. Others are bits and pieces of atoms that happened to be in the way of gamma rays and broke up. Some of the rays are too energetic to have come from nearby stars.
There was a long debate about the source of the most energetic gamma rays. Every month or so some small region of the sky emits a burst of gamma rays. The energy of the new source fades quickly. Some astronomers thought that these burst sources must be far away, because light from them is extremely reddened like the light from the most distant galaxies. But if the burst sources are far away then while they flare up, they must briefly produce more energy than an entire galaxy. This led other astronomers to think that the burst sources are objects ejected at high speed from our own galaxy. If they are close to our own galaxy they don’t need to produce such great amounts of energy to achieve the brightness we see from the Earth. Still, there was no good explanation for what shoots them away so fast. The debate went on until new data resolved[i] it in 1997. Now we know that the burst sources are very far away and produce tremendous amounts of energy. They are truly cosmic, not local.
[i] Schwarzschild, Bertram, “High-Redshift Absorption Lines Show Convincingly that Gamma-Ray Bursters Are Very Far Away,” Physics Today, 50 (Number 7, July 1997), pp. 17–18.
The most energetic gamma rays come to the Earth from the most distant and oldest parts of the universe. Because they have traveled so far at the high but limited speed of light, these gamma rays are the oldest things in the universe. At the same time, we must conclude that they are not infinitely old. If the stars were uncreated and infinitely old, then all the ones that could flare up and emit bursts of gamma rays would have done so long before our time.
Stars Consume Their Fuel
The fact that the stars are still shining shows that they are not infinitely old. All stars including the Sun burn fuel. Their fuel supply must be limited. If they are infinitely old, it is hard to explain why they are still shining. Is it possible to renew the fuel of stars and make new radioactive materials?
The above arguments are valid, but some people have sought to get around them with a variety of complicated schemes. Most of them sought a continuous or renewable fuel supply so the universe could be uncreated, without beginning or end. Frankly this is a philosophical preference, without any scientific basis. To decide scientifically we first have to understand cosmology.
Cosmology and Relativity
By 1915 Einstein had generalized his theory of relativity and founded the science of cosmology. General relativity is really a set of complicated differential equations. There are many solutions because one may choose various parameters in the equations, and also postulate what are called the initial and boundary conditions.
At present we cannot observe either the beginning or the edge of the universe (if it has an edge). Therefore, the choice of initial and boundary conditions is arbitrary. Mathematicians start with initial and boundary conditions that seem good to them, solve the equations, and then see if the resulting model of the universe looks at all like the present universe. It would be more logical to write down present conditions in the present universe and then solve the general relativity equations backwards until we knew the conditions at the beginning. However, this procedure is much more difficult that solving the equations in the forward direction.
The values of the parameters and the conditions chosen may make the equations easy, difficult, or impossible to solve. Naturally Einstein and other physicists and mathematicians found most of the easy solutions first.
There is nothing wrong with solving the easy cases first. In doing so we may learn something that will make solving the harder cases easier or at least possible. The parameters and conditions that make for easy solution do not necessarily correspond to reality. The problem with solving only the easy cases is the temptation to jump to philosophical conclusions that don’t correspond to reality before doing the hard work necessary to solve a realistic case. Even great scientists are not immune to this temptation, as we shall see.
Willem de Sitter (Dutch astronomer, 1872–1934) found the first non-static solution in 1917. In his solution, the universe consists of empty space and time only. The solution is interesting to mathematicians, but it doesn’t correspond to reality. The solution describes a universe with zero matter density in it. Material objects (including us) exist in our universe. One may solve the equations for an empty universe, but such a universe could not have living, rational beings in it to find the solution.
In 1922 Alexander Friedmann (Russian mathematician, 1888–1925) found a solution that depends directly on the density of matter and energy in the universe. His was the accepted model until recently, when astronomers discovered that the expansion of the universe is accelerating. Now many physicists and mathematicians are working to extend and modify his solution, or to find another solution that includes accelerating expansion.