Historical and Current Cosmology

It's interesting to determine what was the scientific view of the Universe that existed from classical Greece to the 19th Century. I'm not referring to the fictional universe as described in what was known to be works of fiction, such as the Bible. Unfortunately, for many centuries, there was a social taboo in Europe against publicly saying it was fiction, even though everyone knew it was. Therefore, it's difficult to determine what famous physicists and other scientists throughout history actually thought of cosmology. Nobody today would claim that Aristotle and the other ancient Greek scientists thought the gods from Greek Mythology were real. Similarly, the scientists alive during the Christian era didn't actually think the Christian god was real. They couldn't openly say this because it would have been considered a socially unacceptable statement in their society. Unfortunately, there is still a slight social taboo in our society against saying these words, even though everyone knows it's true, so people are still afraid to openly discuss this. I couldn't care less about this slight vestigial taboo, so I'm going to discuss it anyway. Let's determine what would have been a scientific view of the Universe based on what was observable from the ancient world to the 19th Century.

Obviously, Aristotle didn't think the version of the origin of the Universe, as described by Greek Mythology, such as in Hesiod's "Theogony", was true. What then, would he have thought of the origin of the Universe? By all accounts, he would have assumed that the Universe had existed forever without beginning. Indeed, there was no physical scientific evidence that the Universe had a beginning until the redshift of the galaxies was detected in the 1950's. That meant that the Universe was expanding so if you extrapolate backwards, it must have had a beginning, which they called the Big Bang. Prior to that, people ascribed to the Steady State model, which was that the Universe had existed forever without beginning. The Steady State model would have been the model of the Universe that had existed since the origin of science in the 6th century B. C. This might seem to contradict world mythology, including Hesiod's "Theogony", and Genesis, which include a "story of creation". However, if you look more closely at these stories of creation, they are actually analogous to Steady State models instead of Big Bang models. These stories of creation always assume that time and space extend infinitely backwards, and that some finite length of time ago, major events started happening that caused the Universe to take its present form. For instance, in Judaism, Jehovah sat around doing nothing for an infinite length of time before suddenly deciding to create the rest of the Universe. The Big Bang model states that there is a fundamental beginning of time itself, and there is no such thing as "before".

Throughout most of history, if there was some aspect of the Universe that they couldn't explain, they would just say "the gods did it" or "God did it". All they meant by that was that was something they hadn't yet invented an explanation for. That's simply how you would express your inability to explain whatever it was. You were not literally suggesting that an actual physical being consciously decided to make whatever it was the way it was. In the 17th Century, the great thinkers of the age of enlightenment claimed that they removed the need for God altogether except for the origin of the Universe itself. In other words, they claimed that they could explain every aspect of the Universe except for the origin of the Universe itself, which is something of an overstatement of their ability to explain the Universe. Rene Descartes claimed that God would only be needed to start the Universe in the first place, after which no divine intervention would be necessary. Other philosophers at this time promoted the idea of the Divine Watchmaker who turned on the Universe and then just let it go. Especially, when Newton's "Principia" was published, the Universe virtually seemed to run itself. The only thing unexplained was the supposed origin of the Universe, so that was the only thing for which they invoked the word "God". However, as I've said, there was no evidence that the Universe had a beginning at all. Therefore they could have just said the Universe had run forever without beginning. From their point of view, they could have gotten away with not using the word "God" at all. In fact, this probably is what they actually thought, but they couldn't say it because it would have been a socially unacceptable statement.

Ironically, when they used the word "God", they subtlety suggesting a Steady State model anyway. They could have invoked a true Big Bang in the modern sense, with a true beginning of time. Then the questions as to how or why the Universe began would be meaningless questions since the questions implicitly assume some sort of "before the Universe", and in a true Big Bang, there is no such thing as "before".

Let me step back, and describe the difference between a scientific way of describing the world, and a mythological way of describing the world, which is what we used prior to 500 B. C. In a scientific view of the Universe, there is a reason for everything. Even if we don't know what the reason is, even if we never know what the reason is, there exists an actual physical logical explanation for absolutely everything in the Universe. The actual reasons may be different than the explanations that we come up with. In physics, we try to think up possible explanations for what we observe. Science rests on the premise that there does exist actual reasons. In mythology, people frequently say, that's the way it is just because that's the way it is. Things exist without reasons. They just are. That is not a scientific view of the Universe. This sort of view lends itself well to personification. Often in daily life, you might do something, and you can't put your fingers all of the large number of small factors that combined in such a way to cause you to want to do whatever it. Therefore, if you were asked why you did it, you say "well, I just felt like it". Having witnessed this, primitive people thought, if there's something where you don't know why, maybe it's because some conscious being just felt like it. Why did it rain? If you can't think of an explanation, you would say, "the sky just felt like it", or "it rained because the sky wanted to rain". Viola! Instant deities.

When primitive people spoke in this way, they intended it literally. However, this sort of personification is such a natural way to phrase things, that people say it when they are not intending it literally. There was an expression, "Nature abhors a vacuum". Obviously, no one is suggesting that there is a conscious being called Nature that dislikes vacuum. In "Fundamentals of Physics" by Halliday and Resnick, they says, "Since particles prefer to be in states of lowest energy, bosons tend to cluster together in the lowest possible states". Obviously, they not suggesting that particles are conscious beings that choose to be in the lowest energy states. What they mean is that particles go to the lowest energy states. No one would misinterpret their meaning. A typical paper in advanced physics is "Supersymmetry at Large Distance Scales" (hep-th/0004003) by Herman Verlinde. At one point, he says, "A different version of the same objection is that the AdS/CFT dictionary tells us that the normal variations of the local supergravity fields near the Planck brane in fact know about low energy quantities of the dual field theory, such as vacuum expectation values, etc." He is not suggesting that local supergravity fields near the Planck brane are sentient beings that consciously know about low energy quantities of the dual theory. He is not suggesting that something called the AdS/CFT dictionary deliberately tells us things. Nobody reading his paper would misinterpret that to be his meaning. For most of history, people would use the word "God" in this same sense. When Einstein said "God does not play dice", what he meant was that he didn't think there was randomness in the Universe. No one would have misunderstood his meaning.

In the 1950's, they discovered the redshift of the galaxies. Then they realized that the Universe had a beginning. Before that, they thought the Universe had existed forever. However, they knew that the Solar System had not existed forever because of radioactive dating. They knew the Earth was about 4.6 billion years old. They would have assumed that stars were born, existed for a time, and then died, and that this process had been going on indefinitely. The first indication that the Solar System had not existed forever came in the 19th Century. There was the question as to what powered the Sun. At first people thought the Sun was a ball of fire, like little kids do today. However, if the Sun was powered by a chemical reaction, it would run out of reactant in a very short time. Hermann von Helmholtz and Lord Kelvin theorized that the source of the Sun’s heat was the gravitational collapse of its mass. They calculated the age of the Solar System to be 20 to 40 million years old. However, before the 19th Century, no one even addressed the question as to what caused the Sun to shine since no one could even begin to guess. Therefore, they had no indication that the Solar System or the Earth had had a beginning.

If you say that the Earth existed forever, what does that mean exactly? Does that mean that all life on Earth, all existing species, had also existed for an infinite length of time? Modern cosmology has zero connection with biology. A modern cosmologist would have zero interest in biology, in less they happen to be interested in it as a totally unrelated subject in the same way they might also be interested in medieval architecture. The subject of biology does not come into play in cosmology because cosmology is the study of the entire Universe. The life that happens to exist on this one insignificant planet orbiting a normal star in an insignificant normal galaxy is less than of negligible infinitesimal importance on the scale of the entire Universe. However, for someone alive in the Renaissance, or any time before that, this planet, and the life on this planet, would have seemed like the main thing in the entire Universe. In fact, humans would have seemed an extremely important thing in the Universe, which led Renaissance thinkers to attach such extreme importance to Mankind. Therefore the subject of biology, trivial as it seems to us, would have been of central interest for someone studying the entire Universe.

When you look at the natural world, you are struck by how well species are adapted to their environment. Why is this? A modern reader would assume this is a rhetorical question, since we know the answer. Species evolved to be well adapted to their environment. Completely random mutations and sexual reproduction causes genetic diversity in a population. Those possessing characteristics that increase their likelihood of surviving and having offspring will be more likely to, and will pass those characteristics onto their offspring. Evolution completely explains why species are well adapted to their environment. Charles Darwin published "On the Origin of Species" in 1859. The idea of evolution had been kicked around for a long time before that. It's just people couldn't figure how exactly how it worked. In the 18th Century, Lamarck discussed species changing into other species. Let's say you're in the 17th Century, before anyone thought of evolution. How would you explain why species seem so well adapted to their environment?

You could just say that they've always been like that for an infinite length of time. The question as to why they are like that is meaningless since they've always been like that. However, notice you are saying that's the way it is just because that's the way it is. That is not a scientific view of the Universe. Another way to say that's the way it just because that's the way it is, and there is no why, is to use the word "God". It's just an expression to mean there's no reason, which is not a scientific view of the world. What would be the scientific answer given by someone asked to explain the biological world, living in a time prior to the discovery of evolution?

If they really wanted to give the correct answer, they would say that there exists a reason where we don't know what it is. If they were honest, they would swallow their pride, and concede that this was an issue on which Humanity was currently ignorant, but that there did exist a logical rational scientific reason for what we observe, and that we would do everything in our power to find out what it is. They essentially did admit this, using the language of the time. It was traditional that when you didn't know the reason for some naturally occurring phenomena, you would toss out the phrase "God did it", which means simply that you don't currently know the reason. It was a code expression that anyone at the time would have correctly interpreted to mean such. Actually, I don't think it would have been that difficult to think up some sort of explanation that partially explained. You could have said that there originally existed a large number of species, and those that were best adapted to the environment out competed the others and survived while the others did not. That would not technically involve evolution since it would not involve the development of new species.

This gets to a question that is relevant to modern cosmology. From the point of view of someone alive before Darwin, if all the life on Earth just happened to be beautifully adapted to its environment, and fit perfectly together in ecosystems, that would seem to be a very lucky unlikely occurrence. However, in order for it to be unlikely for the Universe to have the form it does, it would have to have been possible for the Universe to have a different form that it does. You can't say it is unlikely that the Universe would have the form it does, if there is no way it could have had a different form. Many modern physicists point to aspects of the Universe that they claim are lucky or unlikely. The paper "Supersymmetry at Large Distance Scales" that I mentioned earlier, as well as many other papers, speak of something called "fine-tuning". This is when you have to assume the Universe had to have what they consider unlikely characteristics in order for their theories to fit what we observe, or in order for the Universe to have a form that would allow us to exist. Therefore people try to reduce the fine-tuning required by their theories. Again, this assumes its possible for the Universe to have had a different form than it does. Is this true? Another way of phrasing the question is, is there true randomness in the Universe? When Einstein said, "God does not play dice" what he meant is that there is not true randomness in the Universe. He said that as part of a debate with Niels Bohr who developed quantum mechanics which assumes there is true randomness in the Universe. Quantum mechanics is now accepted as true, so most physicists believe there is true randomness in the Universe.

If you flip a coin, the result is not truly random. The result is determined by the way the coin is flipped, its trajectory, etc. Is there true randomness in the Universe? According to quantum mechanics, there is. There’s the famous thought experiment of Schrodinger’s Cat. If a uranium atom decays in a specific time interval, the cat dies. If not, it lives. According to the Copenhagen Interpretation, it is truly random whether the cat lives or dies. If an electron is fired at a double slit, and you check to see which slit it goes through, it’s truly random, which slit it is. This is fundamentally different than flipping a coin, and other things we call random but aren’t really random. This is currently the majority view. The downside of this view is that if you actually sit down and think about it, it is fundamentally unscientific. According to a scientific view of the world, there is a reason for everything, even if we don’t know what it is. Here you are saying there are things for which, there is no reason.

Another view is that the result of the double slit experiment or the Schrodinger’s Cat experiment is not random but is actually determined by things that we don’t know about, analogous to flipping a coin. This is called pilot wave theory. Here, you maintain the assumption of physics which is that there is a reason for everything, even if we don’t know what it is. It might make some people uncomfortable however, since if there’s no randomness, then everything is predetermined. That means George Bush had to become president, etc. Another view is the Everett Many World’s Principle. According to this, if you conducted the Schrodinger’s Cat experiment, the universe would divide into two universes, one in which the cat lived, the other in which it died. Here you have a reason for everything without predestination, but many people would be uncomfortable with the idea of our universe continually dividing into an infinite number of universes.

Anyway, in order to say that it would be unlikely for the Universe to have the form it does, it would have to be possible for the Universe to have a different form than it does, in other words, there would have to be randomness in the Universe. If there is no randomness, then its not unlikely since its the only form it could have had. If you had something analogous to the Everett Many World Principle, with an infinite number of universes, then its not unlikely, since all possibilities are realized in the greater multiverse, and we just happen to be in a universe with the so-called unlikely characteristics.

Originally, the fact that life was so well-adapted to the environment and each other would have seemed an unlikely lucky coincidence. We explained this using the idea of evolution, that originally there were many possibilities, and the best ones were selected for. Ironically, we use a similar method to explain supposed unlikely lucky coincidences in the Universe. We say that somehow, there are an infinite or very large number of universes, or parts of the universe, and only a few have characteristics that would make it possible for us to be here. Therefore, the fact we are here asking the question, means that we are therefore in one of the preferred universes or parts of the universes. In other words, the universe possessing these rare characteristics was selected for. This is called the anthropic principle. It could be a specific point in time in the age of the universe that makes it more likely for us to here. There are many ideas as to how there could be an infinite number of universes. You have the Everett Many World’s Principle which I mentioned. In the past, people theorized that we could live in an oscillating universe, where each Big Bang follows a Big Crunch, and each Big Crunch precedes a Big Bang. In that view, there are an infinite number of universes like beads on a necklace. Another view, is that we have a branching universe, where spacetime pinches off via general relativity, and you have a bunch of different universes. Probably the least drastic version is simply that the fundamental constants aren’t set until after different parts of the Universe are no longer casually connected. These parts end up having different values for different fundamental constants.

Let me illustrate this with an example. Currently, the vacuum energy density p[lambda] appears to be about equal to the present matter density pMo. It is difficult to understand why we happen to live in an epoch when pM ~ p[lambda]. In other words to ~ t[lambda], where to is the present time and t[lambda] is the time when the cosmological constant starts to dominate. Observers living at t < t[lambda] would find pM > p[lambda], while observers living at t > t[lambda] would find pM < p[lambda]. One explanation is to invoke anthropic selection effects. In this approach, the cosmological constant is assumed to be a free parameter that can take different values in different parts of the Universe, or perhaps in different disconnected universes. Weinberg was the first to point out that not all values of [lambda] are consistent with the existence of observers. The density or likelihood of observers is proportional to the density of galaxies. Therefore the most observers will be at the values that correspond to the highest density of galaxies. Observers come into existence shortly after galaxies, and galaxy formation takes place around t[lambda]. If you work out the calculations, you discover the coincidence is actually what you would expect.

If you were to say the Universe has the characteristics it does just because that’s the way it is, and that they are not coincidental or lucky because it wasn’t possible for them to be different, you are still saying that there is a reason for everything. For instance, the speed of light has the value it does for reasons we don’t know about, and haven’t even tried to guess at, and those reasons are the way they are for even deeper reasons, ad infinitum. This is analogous to pilot wave theory, where you say that in a double slit experiment, the electron goes through the slit it does for reasons we don’t know about. An alternative view is that there is true randomness in the Universe. This currently the favored view in quantum mechanics. However, we don’t use this randomness to explain the characteristics of Universe that appear coincidental or lucky because if they were the result of true randomness, then they really would be truly coincidental or lucky, and in physics we assume that we don’t occupy any sort of favored place in the Universe. Also, you have the idea of things for which there exists no reason, even a reason we don’t know about, and in physics you assume there is a reason for everything. Anyway, if you were to assume these characteristics of the Universe are the result of true randomness in the Universe, that’s analogous to the Copenhagen Interpretation.

Then you have all the variations on the idea that there are a large number of universes, parts of the Universe, or points in time in the history of the Universe, and all of these have different characteristics. We are in the one that has the characteristics that would maximize the likelihood of the existence of observers capable of asking the question. That way you can explain why we observe characteristics of the Universe that appear coincidental or lucky. This is analogous to the Everett Many World Principle in quantum mechanics. Actually the Everett Many World Principle is included as one of the many possible forms this idea can take.

Let’s take this back to the world view that existed centuries ago. Saying the Universe has these lucky coincidences just because it does, and also the Copenhagen Interpretation of quantum mechanics that the electron goes through a given slit just because it does, is analogous to someone in the 17th Century saying the biological world fits together and works so well just because it does. You are saying that there are things for which there are no reasons, which is contrary to the premise of physics. If you were to say the Universe has these characteristics for reasons we don’t know about, and also pilot wave theory which states that the electron goes through a given slit for reasons we don’t know about, that’s analogous to someone in the 17th Century saying that organisms are so well adapted to the environment and each other for reasons we don’t know about. If you explain the cosmic coincidences using the anthropic principle, or use the Everett Many World’s Principle to explain quantum mechanics, that’s analogous to using evolution to explain the biological world.

Hipparchus of Rhodes (190 B. C. – 120 B. C.) was one of the most important astronomers of the ancient world. He discovered the procession of the equinoxes, and was one of the inventors of trigonometry. Unfortunately, the only one of his works to have come down to us is “Commentary on Aratus and Eudoxus”, an obscure commentary on three other writings. However, Ptolemy relied heavily on his work, and you can learn much about Hipparchus by studying Ptolemy. Most of the information which we have about the work of Hipparchus comes from Ptolemy's “Almagest” written in 140 A. D., where he advanced a model of geocentric motion which remained the prevailing view until the 16th Century.

Hipparchus developed a system of measuring the brightness of stars which we still use today. He placed all stars into six categories of brightness. The brightest stars were given the designation 1. Dimmer stars were given the designation 2, and so on. The dimmest stars you can see were given the designation 6. In this system, a star with magnitude 1 is 2.5119 times brighter than a star with magnitude 2. This is still the system we use today. In 1856, Norman Pogson established a precise numerical relationship between one magnitude and the next. It was realized that there were stars brighter than those that had been given the designation of first magnitude. The scale was therefore extended below 1. The magnitude scale therefore goes to 0 for stars 2.5119 times brighter than magnitude 1, and -1 for stars 2.5119 times brighter than magnitude 0. The star Spica is magnitude 1, Vega is magnitude 0, Sirius is -1.4, the full Moon is -12.5, and the Sun is -26.7.

Originally, it was believed that the stars were fixed on the interior surface of a giant celestial sphere that surrounded the Solar System, and in fact defined the entire Universe. Then in the 1570’s, this was replaced by the view of an infinite Universe. This was a major change in our view of the Universe, and it’s hard to say exactly why it happened. There was, of course the debate between the Ptolemic geocentric model, and the Copernican heliocentric model, with Tycho Brahe’s model being sort of a hybrid. However, all of these models retain the same assumption that had always existed, namely that our Solar System WAS the Universe, and that the stars were printed on the interior surface of the celestial sphere.

Thomas Digges (1546 - 1595) was an English astronomer and military scholar, who was a champion of the Copernican system. In 1576, he wrote “A perfit description of the caelestiall orbes” where he describes his own model of the Universe. Digges saw an infinite universe of stars each like the Sun. His revolutionary leap shattered the appearance of an outermost sphere of stars and replaced it by space of limitless extent filled with stars. Digges was the first Renaissance writer to advance the idea of a physically infinite universe. Eight years after Digges' proposal, the Italian philosopher Giordano Bruno published similar ideas. For this and other impieties, Bruno was burned at the stake in 1600.

If all the stars were printed on the celestial sphere, then the differences in their brightness had to be intrinsic to the stars. However, if they were of various distances to Earth, then their differences in apparent brightness was due partly to differences in apparent brightness, and partly due to differences in distance. Measuring the distances to the stars became an important, although very difficult study. Surveyors had long used the system of triangulation to determine the distances to inaccessible points. You have a triangle where you can access two corners, and the third corner is the most distance object. You look at the object from each corner, and it’s apparently different position against the background, you can measure that angle of the other corner. With that angle, and the length of the baseline, you can determine the distance to the distant point.

When measuring the distance to stars, you determine the stars position against the background stars at either side of Earth’s orbit around the Sun. The difficulty is that the star is so distant that the angle you trying to measure is extremely tiny. In 1839, Fredrick Bessel found the distance to 61 Cygni, but the angle he had to measure was only 0.35 arc seconds. One arc second is 1/60 of one arc minute, and one arc minute is 1/60 of a degree, so Bessel’s angle was only one ten thousandth of a degree. Even so, this method could only be used for the nearby stars.

For more distant stars, you need to determine the intrinsic brightness of the star. If you have the intrinsic brightness and the apparent brightness, you can determine the distance. A Cepheid variable is a young star of several solar masses and roughly 104 solar luminosities whose luminosity changes periodically. As radiation streams out, some He+ in the atmosphere of the star is ionized to He+2, making the atmosphere more opaque. The decreased transparency of the stellar material blocks the energy flux and heats the gas, and the increased pressure pushes the envelope out, thus increasing the star's size and luminosity. As the star expands, it cools and He+2, gains an electron, converting back to He+. The enhanced transparency causes the atmosphere to shrink again. The period of a Cepheid variable is related to its intrinsic luminosity. Hence, measuring the period of light fluctuations allows the object's absolute luminosity to be determined, and its distance then follows through comparison with the observed brightness. Therefore, the Cepheids play an important role as a standard candle in assessing the distance scale in the Universe. The luminosity relation was found by a woman named Henrietta Leavitt in 1912.