Cosmology and our View of the World
Everything out of Nothing? - Our sense of Place
Lead: Eberhard Möbius
1/27 & 2/3/2009
Summary by Nicholas Fawcett
Everything out of Nothing?
The first lecture of the semester was intended to introduce the contemporary model of the universe. The contemporary model is based upon well tested scientific observations of the observable universe. A solid grasp of the known universe and how it came to be is a fundamental first step in the discussion of cosmology and our view of the world because it grounds each participant to a reliable source of knowledge about existence.
The title of the first slide was “Everything out of Nothing”, the physical perspective of existence. The Dalai Lama was brought up who described the physical perspective as the ”-third person perspective,” meaning that this perspective was not from within the self. The physical perspective tells us a lot about existence, but it cannot tell us about how things are meaningful to the individual. Eberhard Moebius told the class that he frequently practices yoga, an aspect of his life which is self directed even though he is a physicist.
Professor Moebius brought up the question, what is the world? Is the world/universe like a room or a yard, such that is it finite, having an end with something beyond it? We Humans desire to stick our heads out from our own universe and view ourselves from without to understand ourselves and the universe. However, this is impossible and would be like looking at an M.C. Escher painting looping back upon itself.
“Cosmology: Science of the Universe” was the title of the next slide. Cosmology is a very tough topic for science to handle because the universe is unique: it is the only “item” of its kind that we can access, as far as we can tell. All of the objects and phenomena like planets and galaxies in the universe are changing and are impermanent, but the universe, though changing in the phenomena it contains and in its size, remains a constant for science. The Goal of cosmology is to create models that describe as many of the observed phenomena as possible with better and better accuracy. Human understanding of the universe is limited, so models will always only be the greatest approximation of how the universe operates that cosmologists can devise. No matter how good a model is or how much evidence is accumulated about a particular phenomenon, it is always better to have more and more evidence and more and more examples. One problem, however, is that there is only one thing to accumulate evidence about, and there is no capacity to perform tests on anything but the one universe we have.
Is the Universe a finite entity? Is it infinite? These are questions that need answers. . Moebius’s slide about the possibility of an infinite universe brought up Olbers’ Paradox “You can’t see the forest for the trees?” Why is the night sky dark? This relatively old cosmological question suggested that the universe was finite. This makes sense because if the universe were infinite and eternal and thus had an infinite number of stars in it, one would assume that light from the infinite number of stars would ultimately result in a completely bright universe. There seemed to be only three options which made sense. The first, that the universe is finite because an infinite number of stars would make it bright and it is not bright. The second, that there were an infinite number of stars but that they got so very small that there were still gaps, but this is not a possible answer because no matter how small they got and infinite number of them would still fill all the gaps. And the third possible answer was that it is impossible for humans to work with infinity, i.e. that it is beyond our capability. However, this final possible answer would be considered a copout to science.
This was a good way to introduce background information about distances in the universe. Moebius’s slide had various pieces of information about relative distances that would give the class an idea about scale with regard to the phenomena of the universe. The distance from the planet Earth to our star, the Sun, is described as one astronomical unit, 1AU, which is roughly equivalent to one hundred and fifty million kilometers. If one were to multiply this distance by a factor of ten, this is how far the planet Saturn is.
One of the methods astronomers use to know the distances between astronomical phenomena is called Parallax. Parallax is a geometric method of measuring distances by recording the disparate angles from two points of view given a known distance between the two points of reference. This is, in a sense, similar to human stereoscopic vision that allows us to have depth perception. Using trigonometry, the angles and known distances are used to calculate the distance to the planet or moon that is being observed.
In the past, observers were able to demonstrate that the earth was not the
center of the universe and that it was revolving around the sun, by describing
the paths of other celestial bodies and calculating their distances. This was
a revolutionary insight and was a paradigm shift in human understanding of the
universe and our place in it.
Moebius continued providing information regarding scale. The closest star, other than the sun, is Alpha Centauri, which is roughly twenty thousand times the distance from the Sun to Saturn. Twenty thousand times that distance is the approximate diameter of the Milky Way, about one hundred thousand light years. Twenty times that distance is about the distance between our galaxy and our neighboring galaxy Andromeda (two million light years), and ten times that distance is the diameter of the “Local Group” of galaxies. And finally this distance multiplied by one thousand five hundred is the diameter of the known universe. It is important to note that we are in the center of the observable universe, but that does not imply that our planet or even our solar system is at the actual center of the universe. Being at the center of the observable universe merely means that due to the speed of light, there is finite and definite limitation to our capacity to observe the universe. Hence every observing point of reference is at the center of the observable universe relative to itself.
Light as a Time Machine: Light has a finite speed, roughly three hundred thousand kilometers per second, and because of this when we view anything we see it as it was a certain time ago. Even the light hitting your eyes at this very moment is fractions of a second old. Light from the sun is about eight minutes old and light from Saturn is roughly eighty minutes old. The light from our neighboring star, Alpha Centauri, takes four point three years to reach us here on earth. Astronomers often refer to distance as a measure of the time. The distance light travels in one year is referred to as one light year. Thus, light from Alpha Centauri was emitted in 2005, and the light emitted from the Andromeda galaxy was emitted about two million years ago.
The first day concluded but resumed the following week with a continuation on the topic of distances and how we can know them.
Supernovas, which are massive collapsing stars, are the brightest beacons of light in the universe. They emit tremendous amounts of energy, quantities of energy (x-ray) that are very well known based on other observations and calculations. This quantity is referred to as luminosity and the equation to find distance, based on the known luminosity is: Relative luminosity = Actual luminosity / radius ^2, in which the radius is the distance to the object from the observer.
Astronomers that observed distant galaxies noticed that they appeared redder in color and hypothesized that this red coloration was due to the rate at which the stars were moving away from us. This is called Red-shift, and is a consequence of the Doppler Effect, which draws from the fact that light behaves a bit like sound, i.e. it propagates as a wave. The faster a galaxy moves away from us the stronger the red shift will become in its spectral lines. It has been observed that distant galaxies that make up some of our night sky are moving away from us. And the further away they are, the faster they are moving away from us. A galaxy in Virgo is moving away at eleven thousand kilometers per second. One in the Big dipper is moving away at fifteen thousand kilometers per second, in the Crown at twenty thousand five hundred kilometers per second, in Bootes at thirty six thousand five hundred kilometers per second, and in Hydra at fifty five thousand kilometers per second. Based on this observation, the equation of Hubble’s law is: Speed = H x Distance, in which H represents the Hubble constant.
As a consequence, the universe is expanding, i.e. each galaxy is moving away from each other galaxy. Moebius described the expansion of the universe as analogous to bread that has raisins in it as it cooks and rises in the oven. Each of the raisins moves away from each other raisin at a rate corresponding to its distance from the other raisins. The greater the distance between them, the faster they move away from one another. This fact is described by the cosmological principle, that no galaxy perceives its motion differently than any other galaxy relative to other galaxies. There is no center of the universe, the universe is the same everywhere. Space is expanding and the galaxies are along for the ride.
It is observed that the farthest galaxies from us, in the observable universe, approach the speed of light in their relative motion away from us. Over time, the universe expands, and as it accelerates in its expansion the galaxies at the very edge of the observable universe disappear. It can be asked if there are more galaxies beyond the observable universe. The likely answer is that there are a very great many galaxies in an expanse of space that is unconceivable by humans but this is only a likelihood, not an testable hypothesis. However, if the cosmological principle is correct, it is very likely that there are many galaxies.
We then came back to Olber’s paradox again in light of the knowledge about light and the cosmological principle. Based on the observed expansion, there are two solutions to the paradox. The first solution is that the observable universe is finite, in the sense that we cannot see those galaxies and stars that are receding away from us at the speed of light or faster. The second solution to the paradox is that we cannot observe galaxies if their light would need a longer period of time to reach us than the age of the universe. Although it seems likely that the universe is infinite and expanding, it is difficult to picture it.
Turning the Hubble equation around, the distance to a galaxy divided by the
speed that it recedes away from us is equal to the time that it took for the
universe to expand to its current state, the age of the universe. Distance /
speed = 1/H
Moebius posed the question, did the universe really start? Or is it just expanding, but stays the same forever? It is observed that there is an evolution in the arrangement of matter in the universe. Quasars are only found to exist in the early universe. They do not exist in areas of space that are near to us/ closer to us in age. Observation of the early universe suggests that it expands continuously, but this fact has consequences with relation to our understanding of what the conditions of the early universe were like. The matter of all the stars and all the galaxies and all gasses and dust of the universe were all together in an almost inconceivably dense and small volume. Was the universe hot or cold in the very beginning? Moebius demonstrated to the class, with a prop, what happens when density and pressure are very high. The conclusion is that the early universe was incredibly hot. The temperature of the universe was three thousand degrees Kelvin after three hundred thousand years. This is known because we can observe phenomena that existed at that space-time. Since then, the universe has expanded about one thousand times over, but we can detect the background radiation from this period of time.
In 1978, a Nobel Prize was awarded to individuals who had first observed the existence of the background radiation from the early universe, which had been predicted earlier. This theory was tested by many people and there was agreement that the background radiation existed. In 2006, there was another Nobel Prize given when a satellite observed the background radiation in detail and took images of it. This background radiation is the reason why space is not completely cold. The temperature of the background is 2.7 degrees Kelvin. From the satellite image it is thought that the composition of the early universe was just twenty five percent helium and seventy five percent hydrogen. Two percent heavier elements formed only later from super novas.
The Big Bang model is our current best cosmological model because several independent observations support the principles behind it. Hubble observed that there is expansion throughout the universe, which put in reverse temporally suggests a single origin/event. Background radiation from the incredibly hot early universe is observed at the predicted value. And the predicted composition of the universe is the same as what is observed in the universe.
It is important to understand that cosmologists, astronomers and physicists create models, or theories about the universe. The theories that are developed are always only approximations of what is actually occurring based upon observations. Because these theories are only approximations, highly accurate though they may be, there are often problems with them. The Big Bang Model has the problem called “Flatness,” or fine tuning.
Our universe is ”Just on the edge to expand forever or collapse.” The amount of matter that exists is just right for balancing out the expansion of the universe. More matter, and thus more gravity, would have resulted in the collapse of the universe long before now, and less matter would have made the formation of galaxies an impossibility. Currently, the difference between too much gravity or too little could be either way by about one order of magnitude. However, in the young universe, back to the time when the universe was only a few minutes old, these values had to be “accurate to 10^-15” for our universe to continue to form as it did.
Another problem is called the Horizon problem. The universe is the same in
all directions, but no communication between two opposite locations in the sky
was possible over 300,000 years from the Big Bang to that time when the background
radiation formed. Given the uniformity of what is observed, there is an expectation
that there is a cause for the observed uniformity, and this cause could only
be transmitted between two locations at the speed of light.
And a third problem with the Big Bang Model is called the Matter Problem. There is an equation that for every two pounds of light that exists, there must have first existed one pound of matter and one pound of anti matter, but if there were symmetry, then it would seem impossible that there would be any matter left over at all. In the Big Bang, matter and anti-matter were created in equal amounts. Furthermore, when matter and anti-matter meet, the result is total destruction of both, yet the universe we know is almost all matter, very little anti-matter, How could that be?
The Inflation model, which says that the universe expanded extremely rapidly during the first small fractions of a second, overcomes these three problems of the big bang model. The flatness problem is overcome with an analogy to the surface of a balloon, that when a balloon is inflated to extreme size its surface appears to be flat even though when it started off it was far from flat. Moebius reminded the class that humanity thought that the earth was flat for quite a long time in the past. The Horizon problem is also overcome by the inflation model because rapid inflation in the beginning has caused the observable universe to be similar everywhere. And the Matter problem is overcome because the complete symmetry in the interaction between matter and anti-matter is destroyed during the rapid cooling in the expansion. (This is analogous to freezing nicely smooth and thus ”symmetric” water into asymmetric chunks of ice.) Thus asymmetry is completely commensurate with the inflation model.
One issue that is puzzling to cosmology is that the observable universe is accelerating in the rate of its expansion. This fact suggests that the common understanding of the big bang as being some sort of initial and definite rate of expansion is incorrect. We are used to thinking that gravity would slow the rate of expansion but observation is contrary to this intuition. This fact was an opener to the topic about the Fate and Structure of the universe. Astronomers have observed that galaxies and other macro scale phenomena like galaxy clusters do not behave as they ought to behave according to the observable quantity of matter that composes them. In light of this, it is thought that there is a massive amount of matter and energy that we cannot observe, called dark matter and dark energy. It is thought that the observable matter is only about three percent of the total matter and energy. The rest is composed of twenty seven percent dark matter and seventy percent dark energy.
Moebius then switched gears and brought up the Anthropic principle. Why is it that our universe appears to be just suited for intelligent life to arise? There is no certain answer to this question, perhaps because it is a question that is unanswerable. The best answer to the question so far is that the universe began with the right condition. There are two forms of the Anthropic principle, The strong and the weak. The Strong Anthropic principle suggests that the universe was set up to provide for the existence/development of life. The weak Anthropic principle suggests that we live in one of the few universes in which the conditions are possible for life to develop. These two principles are not explanatory about anything, they only refer to conditions that are fundamental to a universe if that universe is to be capable of supporting life. There is no way to test the Anthropic principle with science.
On a final note at the end of the lecture, Moebius brought up a man by the name of John Archibald Wheeler. Wheeler held the view that our universe was self reflecting, that our universe looks back at its own origins of the big bang and also looks at itself as it is now through our eyes. This final idea is tied to the idea of consciousness as a phenomenon of the universe, in which our consciousness takes on a meaning that is much greater than the limited scope which we commonly think of our experience as being.