A fundamental question in cosmology and philosophy, is whether our universe is finite or infinite. In other words, does the universe go on forever or is there an edge where it ends? Is it possible for us to detect the absolute boundary? If the universe does have a boundary, where is it and what happens at the boundary? This report will provide a simple and graphic approach to a complex problem.
Definition of a Universe Model
When an astronomer, cosmologist, philosopher, or physicist studies the origins of the universe, what are they referring to as the ‘universe’? In order to sub-organize what is being studied, the term “universe” is defined into three different types of universes; observable, entire, and physical.
Everything that we can see is the observable universe, including the stars, galaxies, and many other celestial objects that emit radiation in the form of visible light (Hodge, 1969). This is essentially the astronomer’s laboratory where all the primary data is collected. As will be explained in section four, the observable universe is constantly growing as the instruments that observe it get more powerful and improved.
The entire universe contains everything that is in an observable universe plus everything else (Hodge, 1969). This type of universe can be analyzed mathematically, metaphysically, or philosophically, because it deals with everything that we know of including consciousness, emotions, paranormal activities etc. Scientists and researches usually do not deal with entire universes; they’d rather just focus on the observable or on the physical as described below.
This is any part of the universe that can be treated in a scientific way (Hodge, 1969). It is really an extension of the observable universe but relies greatly on the laws of physics to explain what is being observed. For example, there are objects in the universe that are not directly detectable (as in an observable universe) but rather their existence is studied due to the effects it has on other objects. In this report, I will always be talking about the physical universe; all other references to the word will be explicitly stated.
Can a Cosmic Edge Be Discovered?
Before we can discuss what sort of boundary we may find and what theoretically happens there, we must first know if it is at all possible to detect such a thing. The following discusses three possible scenarios that may restrict our search for an answer.
Our Infinite Universe: Limits of Our Instruments
For thousands of years, the naked human eyes were the primary instruments for studying the observable universe. The boundary of the universe was what could be seen on a clear night. In 1611, Galileo built his own telescope and pointed it at the night sky, vastly pushing back the cosmic edge (Encyclopedia, 1993). In the next two centuries, the cosmic edge was pushed back exponentially as better and more powerful equipment was designed to look at the observable universe. Also, in the last hundred years, instruments that do not rely on visible light were invented to peer into the depths of the physical universe. (Hodge, 1969) These instruments focus on the whole spectrum of radiation celestial objects emit, including radio waves, x-rays, and gamma rays.
As of today, astronomers are still discovering new galaxies and other objects in the deepest parts of space. Is there any physical limit the universe can impose on our observations or will we continue pushing back the cosmic boundary until we hit an absolute cosmic edge?
There are two possible physical limits our universe may impose on our instruments that could restrict our search of ever finding a cosmic boundary. These limits are the amount of dust and gas in the universe, and how fast galaxies are traveling in space.
Dust and Gas boundary in Our Infinite Universe
There is a possible physical limit that may be imposed on our ever improving instruments that help us peer deeper into our universe. Astronomers may reach a point where remote dust and gases in space may begin to obscure our sight seeing (Hodge, 1969). This is easy to visualize: imagine you are looking up at the stars on a clear night somewhere in the country side where you may easily see thousands of stars with your naked eyes. Then, a light fog rolls in which slightly obscures your view and only the brightest two hundred stars remain visible. Later, there is cloud cover and your view is totally blacked out leaving a blank sky.
This is precisely the type of scenario astronomers might face one day, except that their view will be blocked by patches of dust and gas in deep space. In Fig 1, a simplified representation of a dust/gas boundary is visualized.
If this dust boundary is ever reached, it will mean we cannot directly witness a cosmic edge and our exploration of the observable universe will come to an end. Luckily, no such boundary is likely to be reached in the near future because even at vast distances, the amount of dust and gas obstruction in our view is actually very small and can be neglected.
A popular theory about our universe is that it is expanding (Encyclopedia, 1993). Simply put, this means all galaxies are moving away and outward from each other. This was discovered in 1929 by Edwin Hubble, who noticed that light coming from a number of galaxies was displaced toward the red end of the light spectrum (Encyclopedia, 1993). By applying the principles of the Doppler Effect, he concluded that galaxies moving away from earth have give off light from the red end of the spectrum, while galaxies moving towards the earth will give off light from the blue end. He also found that the speed at which a galaxy is moving away form earth is proportional to its distance, leading him to conclude that the more distant a galaxy is, the faster its velocity (Encyclopedia, 1993). This is summarized in Hubble’s Law, which is
speed = H x distance where H = the Hubble constant
What this means is that galaxies are accelerating away from each other (Encyclopedia, 1993). This can be compared to marking dots on a balloon and filling it with air at an increasing rate. One notices that each dot is receding away from adjacent dots on the balloon surface (Hawking, 1988).
Relatively close galaxies have velocities of a few hundred miles per second, but in more distant clusters, speeds range in the 100,000 miles per second (Hodge, 1969). More distant galaxies were discovered with velocities that nearly reach the speed of light. If a galaxy were to travel at the speed of light or higher (which is impossible from Einstein’s theory of relativity), then the light from this galaxy would never reach the earth. This is called the velocity boundary and it is depicted in Fig 2. Like the dust boundary, this physical limitation would end the exploration of the observable universe since no light from super distant galaxies would ever reach us.
Models of the Cosmic Edge
It is conceivable that the universe has its own geometrical structure. This idea was first fully modeled in 1596 by Johannes Kepler, who proposed the structure of the universe as made up of geometric shapes.
Our infinite universe was composed of five regular or ‘cosmic’ solids (Ferguson, 1999). Namely, these solids were a cube, tetrahedron, dodecahedron, icosahedron, and octahedron. The outer sphere of the system was the cosmic edge of the universe, a physical solid shell where all the stars were fixed (Ferguson, 1999).
In February 2003, NASA released data gathered by the Wilkinson Microwave Anisotropy Probe (WMAP) which measured cosmic background radiation, thought to be the left over’s from the Big Bang theory (www.nationalgeographic.com, 10/08/03). A few months later on October 8th 2003, a team of scientists led by mathematician Jeffery Weeks (winner of the MacArthur Fellowship or “genius award”), proposed a new model of the shape of the universe. He announced that the shape of the universe could be a dodecahedron, a 12-sided shape made up of pentagons. What is interesting about the pentagon shape, is that its proportions are directly related to the numerical ratio called Phi (an irrational number, 1.618033…). This “golden ratio” is found virtually everywhere in nature, including the way spiral galaxies are structured (see Appendix for link). The middle solid on the top row of Fig 3 is a dodecahedron. Several other shapes like a torus or a flat plane were considered, but when compared to the data, calculations fit the dodecahedron (or the ‘soccer ball’) shape most accurately. The team admits this new model looks promising but there is still much more calculations to be done to confirm or refute the model. The highly technical and mathematical details of this theory are beyond the scope of this report. A simplified explanation of what could theoretically happen at the boundary of this model will be discussed in the next section.
Thought Experiments -What Happens at the Cosmic Edge?
This has been a long debated question among scientists and philosophers. It is known as the cosmic-edge riddle thought experiment: imagine a man who traveled to the cosmic edge, what happens when he throws a spear across it? (Harrison, 1981) I will state the three classical types of possible boundaries, and then explain the special boundary proposed by Jeffery Weeks in his soccer ball shaped universe.
Wall-like: The cosmic edge ends abruptly like a wall (Harrison, 1981). This is what Kepler supported in his five cosmic solids theory. The spear would hit the wall and bounce back, or break through the wall. This type of boundary is most easily refuted because according to modern physics, space cannot be terminated or bounded by anything. Also, if the spear broke through, it would mean there is no absolute cosmic edge.
Aristotelian: The outer edge is not abrupt but gradual (Harrison, 1981). This was widely believed by the Greeks and Europeans during medieval times Harrison, 1981). As the spear travels further from earth and nears the “heavens” or cosmic edge, it will have to return to earth because it is made from ‘Earth based’ elements. Otherwise, its physical properties would have to transform into etheric or spiritual elements to pass the boundary. This explanation is clearly not scientific in any way, and is heavily based on human beliefs rather than any sort of logical “proof”. Though there is a point to be made here; the laws of physics as we know them may or may not hold at the cosmic edge.
Stoic Cliff-like edge: There is an inner cosmos (the universe) and the outer void which is completely empty. This transition is abrupt like a cliff edge. A spear flying across this boundary will simply extend the inner cosmos, thereby extending the cosmic edge. Since our universe is known to be expanding, this type of boundary is plausible.
The Boundless edge: This is where things start to get a little more mind bending. A spear traveling through one of the sides (pentagons) of the dodecahedron, would reappear on the other side of the universe in a pentagon directly opposite of where it entered. Jeffrey Weeks explains “Hypothetically speaking, if you head off into space you can travel in a straight line and [eventually] come back to the starting point, but it would take a long time” (Weeks, Oct 8th, 2003). It’s a similar idea to traveling in a straight line across the surface of the earth, you would eventually return to your starting point because the seemingly flat earth is actually round and leads you back around.
Examination of the Universal Boundary
For thousands of years, humans have gazed at the night sky and wondered how it began, where it comes from, and where it ends. I cannot pretend to know the answers to these age old questions about the structure of the universe, but we can ask more questions that probe deeper into the mystery:
- If our infinite universe is expanding, how can there be a boundary?
- Can the cosmic edge be expanding? Can it shrink?
- What lies behind the boundary? Another universe? Another dimension? God?
- Are there multiple universes like soap bubbles in a bath tub, where each bubble is its own universe?
- Is Man capable of understanding the truth?
A Concluding Look at Our Infinite Universe
The new “Soccer Ball” model universe presents many fascinating and ingenious solutions to the cosmic edge problem. It supports the “finite” side of the argument but with a boundary that is a “boundless edge”. This is unconventionally but as Weeks and his team suggest, it seems to fit measured scientific data very nicely. This model (which is presently being further developed and tested) is another step toward discovering the origin of the universe, that may prove to be one of the most important discoveries in human history. 54
Appendix – Definitions
(all taken from www.dictionary.com)
galaxy – Numerous large-scale aggregates of stars, gas, and dust that constitute the universe.
Doppler Effect – A change in the observed frequency of a wave, as of sound or light, occurring when the source and observer are in motion relative to each other, with the frequency increasing when the source and observer approach each other and decreasing when they move apart. The motion of the source causes a real shift in frequency of the wave, while the motion of the observer produces only an apparent shift in frequency. Also called Doppler shift.
The Big Bang Theory – A cosmological theory holding that the universe originated approximately 20 billion years ago from the violent explosion of a very small agglomeration of matter of extremely high density and temperature.
clusters – A grouping of many galaxies in some volume of space.
light spectrum – The distribution of energy emitted by a radiant source, as by an incandescent body, arranged in order of wavelengths.
Britt, R. “Space seen as finite, shaped like a soccer ball”.
Phi, Golden Ratio number, http://goldennumber.net/universe.htm.
Crofton, I. (1993). The Guinness concise encyclopedia. Enfield: Guinness Publishing.
Ferguson, K. (1999). Measuring the universe. New York: Walker and Company.
Harrison, E. (1981). Cosmology: The science of the universe. New York: Cambridge University Press.
Hawking, S. (1988). A brief history in time: From the big bang to black holes. Toronto: Bantam Books.
Hodge, P. (1969). Concepts of the universe. Toronto: McGraw Hill.
Markey, S. “Universe is finite, “soccer ball”-shaped, study hints”. National Geographic News, 10/08/2003.
About The Author
Maciej Stec holds an Aerospace Engineering degree from Ryerson University in Toronto and has been studying astronomy, science, philosophy, and history for over a decade. Maciej has also worked as an aircraft engineering analyst at Bombardier Aerospace and is not one to pass up looking at the night sky while camping or through a telescope.