When we think of the beginning, we think of it as the start of a series of chronological events. In the context of the Universe, the beginning refers to the origin of space and time. The beginning is dependent on time. Without time, we cannot have a beginning. Cosmology only started to make sense when people began to understand space-time as a living and evolving thing. Time is simply part of the Universe, and it must be considered when we analyze its existence.
In the early 1970s, English physicists Stephen Hawking and Roger Penrose postulated that the Universe did, in fact, have a beginning. Hawking and Penrose postulated that if the evolution of the Universe could be described by Einstein’s general theory of relativity, and it is composed of energy content that we are familiar with, then it had to have a beginning. Based on their observations, it is impossible to discern the actual beginning of space-time to a specific point. This theorem is known as the singularity theorem.
Wednesday, May 13, 2009
Chapter 17: Wrapped and Warped
Extra Dimensions of Space
When we perceive our Universe, we perceive it as being three-dimensional, however, we must consider that there are more than three dimensions. It is possible that certain dimensions are hiding. We can add another dimension to our Universe. We cannot interpret this extra dimension because from where we stand, we cannot see it. Every point in our three-dimensional space has an invisible dimension. This new idea was proposed by Theodor Kaluza and Oskar Klein and has been very influential in developing the current cosmological model. They proposed that the electromagnetic force arose like gravity, as a deformation of space-time. They postulated that the electromagnetic force resulted from the warping of the fourth-dimension. The third-dimension was warped by mass and energy, and Kaluza and Klein postulated that charge affected the fourth dimension.
When we perceive our Universe, we perceive it as being three-dimensional, however, we must consider that there are more than three dimensions. It is possible that certain dimensions are hiding. We can add another dimension to our Universe. We cannot interpret this extra dimension because from where we stand, we cannot see it. Every point in our three-dimensional space has an invisible dimension. This new idea was proposed by Theodor Kaluza and Oskar Klein and has been very influential in developing the current cosmological model. They proposed that the electromagnetic force arose like gravity, as a deformation of space-time. They postulated that the electromagnetic force resulted from the warping of the fourth-dimension. The third-dimension was warped by mass and energy, and Kaluza and Klein postulated that charge affected the fourth dimension.
Chapter 16: The Ecology Of Galaxies
There are many galaxies in the Universe. Our galaxy has two close neighbouring galaxies- the Large and Small Magellanic Clouds-which are a twentieth and a hundredth the size of the Milky Way. Also closely neighbouring our galaxy is the Andromeda Galaxy, and there are more galaxies that exist a little further out. Together, this group of galaxies form what is known as the Local Group. Throughout the Universe, there are many galaxies, embedded in larger agglomerations or cluster composed of thousands of individual galaxies. Closest to our Galaxy is the Virgo Cluster, which is situated about 50 million light years away. The Virgo Galaxy is so large that its gravitational force is sucking the Milky Way in towards it. Situated about 300 million light years away is the Coma Cluster, which is made up 10,000 galaxies.
Andromeda has a spiral shape and it is very similar to our Galaxy. Most of the galaxies that are observed have a spiral shape and extend to great lengths. They tend to be found in low-density regions of space, where there are few other galaxies.
Besides spiral galaxies, there are elliptical galaxies. Elliptical galaxies are large accumulations of stars with no obvious features. They do, as their name indicates, have an elliptical shape, and they are classified by their ellipticity. When naming elliptical galaxy, the convention is to indicate it with a E followed by a number. For example, if an elliptical galaxy is E0, it will not be elliptical, but it will be spherical. If it is classified as E1, the galaxy will be slightly elliptical. An E8 galaxy will be basically flat and look unlike a spiral.
Edwin Hubble developed a classification system for the galaxies. In his system, galaxies are ordered into a tuning fork structure. At the base of the tuning fork, are the E0s. As we move farther down the fork’s stem, the galaxies’ shapes become more elliptical, until the end of the tuning fork where they become essentially flat without spiral arms. This is where the two prongs of the fork begin. As you move down the prongs, the prongs become larger and larger, and the galaxies become larger with longer arms. On one prong, galaxies have spherical bulges, and on the other arm, galaxies have cores shaped as bars.
Most of the galaxies that are observed are classified under this classification scheme. Galaxies that are not classified are not because their shape is too irregular, or do not possess spiral arms. Galaxies that have an irregular shape are called irregulars, where all the other galaxies that cannot be classified are placed. Many irregular galaxies are a result of a collision between spiral and elliptical galaxies. Most irregular galaxies, such as the Magellanic Clouds, contain up to a third of their masses in gas, which is used to form stars.
Andromeda has a spiral shape and it is very similar to our Galaxy. Most of the galaxies that are observed have a spiral shape and extend to great lengths. They tend to be found in low-density regions of space, where there are few other galaxies.
Besides spiral galaxies, there are elliptical galaxies. Elliptical galaxies are large accumulations of stars with no obvious features. They do, as their name indicates, have an elliptical shape, and they are classified by their ellipticity. When naming elliptical galaxy, the convention is to indicate it with a E followed by a number. For example, if an elliptical galaxy is E0, it will not be elliptical, but it will be spherical. If it is classified as E1, the galaxy will be slightly elliptical. An E8 galaxy will be basically flat and look unlike a spiral.
Edwin Hubble developed a classification system for the galaxies. In his system, galaxies are ordered into a tuning fork structure. At the base of the tuning fork, are the E0s. As we move farther down the fork’s stem, the galaxies’ shapes become more elliptical, until the end of the tuning fork where they become essentially flat without spiral arms. This is where the two prongs of the fork begin. As you move down the prongs, the prongs become larger and larger, and the galaxies become larger with longer arms. On one prong, galaxies have spherical bulges, and on the other arm, galaxies have cores shaped as bars.
Most of the galaxies that are observed are classified under this classification scheme. Galaxies that are not classified are not because their shape is too irregular, or do not possess spiral arms. Galaxies that have an irregular shape are called irregulars, where all the other galaxies that cannot be classified are placed. Many irregular galaxies are a result of a collision between spiral and elliptical galaxies. Most irregular galaxies, such as the Magellanic Clouds, contain up to a third of their masses in gas, which is used to form stars.
Monday, May 11, 2009
Chapter 15: Primordial Sound
As we saw in the last chapter, in the 1970s, the Universe was believed to be homogeneous. The photons have been traveling since recombination; they have been affected by the roughness of the Universe on the scale of the cosmological horizon. Overall the level of inhomogeneity is very mild. If space-time were rough, it would be so warped that it would be populated by black holes. Rarely do we see black holes on small scales, which means that space-time cannot be too rough on small scales. When we look at galaxies on a scale, which correspond to sizes between thousands and millions of light years, it is clear that there is structure. This means that between the smoothness of large scales and the mild roughness of small scales, there is inhomogeneity on intermediate scales. Inhomogeneity has some randomness.
The existence of sound waves in the Universe was predicted in the 1970s and 1980s. The expedition of the COBE satellite revealed the discovery of inhomogeneities on large angular scales. A number of experiments were designed to detect sound waves from the primordial universe. To effectively measure sound, powerful telescopes were needed that could block out sound from contaminating sources. Contaminating sources, including the atmosphere, absorb and emit radiation. One way to get around the contamination from other sources, such as the atmosphere, is to send telescopes up in balloons to a height of about 40 kilometres. To accurately measure, it is essential to get high enough in the atmosphere to escape contaminating factors like variable weather conditions and other uncontrollable effects that might affect the interpretation of the relic sky.
The existence of sound waves in the Universe was predicted in the 1970s and 1980s. The expedition of the COBE satellite revealed the discovery of inhomogeneities on large angular scales. A number of experiments were designed to detect sound waves from the primordial universe. To effectively measure sound, powerful telescopes were needed that could block out sound from contaminating sources. Contaminating sources, including the atmosphere, absorb and emit radiation. One way to get around the contamination from other sources, such as the atmosphere, is to send telescopes up in balloons to a height of about 40 kilometres. To accurately measure, it is essential to get high enough in the atmosphere to escape contaminating factors like variable weather conditions and other uncontrollable effects that might affect the interpretation of the relic sky.
Chapter 14: From Order to Chaos
Although we believe otherwise, everything has texture- nothing is completely smooth. Even though it may feel smooth to the touch or look smooth to the eye, nothing is completely smooth. When we consider a wooden table for example. To the naked eye, it looks completely smooth, and to the touch it feels very smooth, however, if we could magnify the texture of the table with a superfine microscope at and extremely high magnification, we would realize that it is not smooth. Really, the table would look like a vast space of hills and valleys. The same can be said about the Universe. When we look at the night sky, it appears to be completely smooth and homogeneous, but on an extremely small scale, its constituents would not appear smooth. If we could see the Universe on such a scale, we would see the space between particles, and we could see that some areas are more dense or empty than others.
The Universe looks homogeneous from afar, but it in actuality, it is very structured. When we view the sky we can see some stars and maybe even a few planets depending on where we situated in relation to their positions. As we judge from a larger scale, we see that we are embedded in a galaxy, and that galaxy resides in and amongst a larger galaxy. From even further away, we see that cluster of galaxies is seen as many clusters composing a massive network of filaments, walls, and nodes of light. If we observe this from very far away, it appears as if all of these irregularities blend into one faint, smooth texture.
When we look at the surface of a table, a piece of material, or even the surface of the Earth, it appears that the farther away we move, the more indefinite textures become. When we view the Universe, we are confined to the Earth, so we can’t move further away, we can only move closer. The closer we get, the more irregularities that are present, and the more we realize that the Universe is simply not smooth.
Since the 1970s, it has been possible to measure angular positions of galaxies in the sky. These observations relay that galaxies tend to be evenly distributed throughout the sky. There aren’t any preferred directions in the sky, which is expected if the Universe is homogeneous. It is not only possible to measure the angular positions in the sky, but also the distances to galaxies. As we can recall from a previous chapter, we know that a red shift is a measure of how fast a galaxy is moving away from us; Hubble’s law tells us that the more distant a galaxy is, the faster it moving away from us. Therefore, we can use the angular positions and the red shift to construct a three-dimensional model of the galaxies.
The most compelling evidence for homogeneity is relic radiation. Homogeneity implies that the Universe cooled at exactly the same rate at all points in space. Basically, the rate at which hydrogen and helium captured electrons was the same at all points in space. The left over radiation must have had exactly the same temperature everywhere. The smooth collection of radiation is an indication that the Universe was smooth in the past. This is the strongest evidence for a homogeneous Universe. A rough Universe on small scales appears smoother and smoother the farther away we move from it.
The Universe looks homogeneous from afar, but it in actuality, it is very structured. When we view the sky we can see some stars and maybe even a few planets depending on where we situated in relation to their positions. As we judge from a larger scale, we see that we are embedded in a galaxy, and that galaxy resides in and amongst a larger galaxy. From even further away, we see that cluster of galaxies is seen as many clusters composing a massive network of filaments, walls, and nodes of light. If we observe this from very far away, it appears as if all of these irregularities blend into one faint, smooth texture.
When we look at the surface of a table, a piece of material, or even the surface of the Earth, it appears that the farther away we move, the more indefinite textures become. When we view the Universe, we are confined to the Earth, so we can’t move further away, we can only move closer. The closer we get, the more irregularities that are present, and the more we realize that the Universe is simply not smooth.
Since the 1970s, it has been possible to measure angular positions of galaxies in the sky. These observations relay that galaxies tend to be evenly distributed throughout the sky. There aren’t any preferred directions in the sky, which is expected if the Universe is homogeneous. It is not only possible to measure the angular positions in the sky, but also the distances to galaxies. As we can recall from a previous chapter, we know that a red shift is a measure of how fast a galaxy is moving away from us; Hubble’s law tells us that the more distant a galaxy is, the faster it moving away from us. Therefore, we can use the angular positions and the red shift to construct a three-dimensional model of the galaxies.
The most compelling evidence for homogeneity is relic radiation. Homogeneity implies that the Universe cooled at exactly the same rate at all points in space. Basically, the rate at which hydrogen and helium captured electrons was the same at all points in space. The left over radiation must have had exactly the same temperature everywhere. The smooth collection of radiation is an indication that the Universe was smooth in the past. This is the strongest evidence for a homogeneous Universe. A rough Universe on small scales appears smoother and smoother the farther away we move from it.
Chapter 13: Dark Energy is the Fifth Element
Max Planck, a German Physicist, postulated that energy existed in discrete chunks or quanta, to explain how we view radiation. Einstein proved that this, in fact, was a reality, and it was acceptable to think of radiation as a collection of individual photons. This led to the duality of light as a wave and as a particle. French Physicist Louis de Broglie recognized that this principle explained energy levels in all particles, like electrons and protons. What he discovered was that everything in nature has quantized energy levels. All objects have well-defined and discrete energy spectra.
Many people ask, “What is the lowest possible energy state?” Logically, most people would assume that it is zero, but the truth is that an energy state can never be zero. The Uncertainty Principle can be stated in terms of energy and time. Basically, it is impossible to measure, at the same time, to measure the time elapsed and the energy involved in any given process. If we consider a particle, which has a finite lifetime, we can conclude that there is an uncertainty in its lifetime, meaning that it cannot have a zero energy level. Two important observations come from this observation. First, the minimum energy level cannot be zero because it has a value, which is fixed by the uncertainty principle. Secondly, we can no longer think of parts of the Universe as “empty space”. We can pick any region of the Universe and consider it for a fixed amount of time, there is an uncertainty placed on the energy in that region- it cannot equal zero because of the Uncertainty Principle. Therefore, from these speculations, we can conclude that empty space is not simply empty- it actually has energy.
In conjunction with the Uncertainty Principle, we can assume that at any given moment, there is an uncertainty in the amount of energy present. It is possible that certain areas of space will have more energy than others. This energy can give rise to particles, which collide and disappear very rapidly. The energy continually presents itself in the form of various particles swaying in and out of existence.
One thing that I found very interesting was the author’s explanation of water. It had never occurred to me how the cracks in water form when water freezes. When water freezes and there are no cracks or fissures present, water is said to be symmetrical, however, this symmetry can be broken. The orientation of each water molecule is completely random, meaning that they have no preferred direction. Water molecules are weakly bound through each other by electrostatic forces, but are still able to freely move around. As water cools, its molecules slow down, and its electrostatic forced help to lock it into place in an order where they can all fit together. As a result of this random arrangement, each molecule chooses its own direction in space and water starts to solidify.
Each section of water begins to solidify independently. One location begins to freeze and then another begins to freeze. Each of the molecules at that site pick out a preferred direction at that site, and there is no guarantee that the preferred direction will be the same at all of the sites- most will be misaligned. When the different sections are misaligned, we are left with cracks and fissures. The cracks represent the separation between the different zones that have frozen and to tolerate the tension created by the misaligned water molecules.
Many people ask, “What is the lowest possible energy state?” Logically, most people would assume that it is zero, but the truth is that an energy state can never be zero. The Uncertainty Principle can be stated in terms of energy and time. Basically, it is impossible to measure, at the same time, to measure the time elapsed and the energy involved in any given process. If we consider a particle, which has a finite lifetime, we can conclude that there is an uncertainty in its lifetime, meaning that it cannot have a zero energy level. Two important observations come from this observation. First, the minimum energy level cannot be zero because it has a value, which is fixed by the uncertainty principle. Secondly, we can no longer think of parts of the Universe as “empty space”. We can pick any region of the Universe and consider it for a fixed amount of time, there is an uncertainty placed on the energy in that region- it cannot equal zero because of the Uncertainty Principle. Therefore, from these speculations, we can conclude that empty space is not simply empty- it actually has energy.
In conjunction with the Uncertainty Principle, we can assume that at any given moment, there is an uncertainty in the amount of energy present. It is possible that certain areas of space will have more energy than others. This energy can give rise to particles, which collide and disappear very rapidly. The energy continually presents itself in the form of various particles swaying in and out of existence.
One thing that I found very interesting was the author’s explanation of water. It had never occurred to me how the cracks in water form when water freezes. When water freezes and there are no cracks or fissures present, water is said to be symmetrical, however, this symmetry can be broken. The orientation of each water molecule is completely random, meaning that they have no preferred direction. Water molecules are weakly bound through each other by electrostatic forces, but are still able to freely move around. As water cools, its molecules slow down, and its electrostatic forced help to lock it into place in an order where they can all fit together. As a result of this random arrangement, each molecule chooses its own direction in space and water starts to solidify.
Each section of water begins to solidify independently. One location begins to freeze and then another begins to freeze. Each of the molecules at that site pick out a preferred direction at that site, and there is no guarantee that the preferred direction will be the same at all of the sites- most will be misaligned. When the different sections are misaligned, we are left with cracks and fissures. The cracks represent the separation between the different zones that have frozen and to tolerate the tension created by the misaligned water molecules.
Chapter 12: An Accelerating Universe
Using Supernovae to Measure Distances
Supernovae are some of the brightest objects in the sky, characterized as the explosions of massive stars. Interestingly enough, supernovae shine as brightly as billions of stars put together, emitting as much light as the` galaxy of its residence. It is likely to find supernovae on a given night. They have been observed and recorded for many hundreds of years. The last reported supernova in the Milky Way was in 1572, and it was visible by the naked eye.
A supernova finalizes the life cycle of a star- a star that is heavier than the Sun. The supernova is dependent on the mass of the star. Nuclear forces cause the collapse of the lighter stars, where as heavier stars ignite because of such strong gravitational attractions present at their core. Therefore, there are two types of supernova.
Supernovae Ia have very distinctive features, making them very identifiable. Supernovae Ia correspond to light stars and Supernovae Ib, correspond to heavier stars. When the supernovae Ia detonates, its spectra is easily identifiable because hydrogen is absent, allowing them to be distinguishable compared to other types of supernovae.
Supernovae are some of the brightest objects in the sky, characterized as the explosions of massive stars. Interestingly enough, supernovae shine as brightly as billions of stars put together, emitting as much light as the` galaxy of its residence. It is likely to find supernovae on a given night. They have been observed and recorded for many hundreds of years. The last reported supernova in the Milky Way was in 1572, and it was visible by the naked eye.
A supernova finalizes the life cycle of a star- a star that is heavier than the Sun. The supernova is dependent on the mass of the star. Nuclear forces cause the collapse of the lighter stars, where as heavier stars ignite because of such strong gravitational attractions present at their core. Therefore, there are two types of supernova.
Supernovae Ia have very distinctive features, making them very identifiable. Supernovae Ia correspond to light stars and Supernovae Ib, correspond to heavier stars. When the supernovae Ia detonates, its spectra is easily identifiable because hydrogen is absent, allowing them to be distinguishable compared to other types of supernovae.
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