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| courses:ast100:1 [2024/10/13 14:32] – [2. Birth of Energy] asad | courses:ast100:1 [2024/10/14 15:21] (current) – [1. Spacetime from the Big Bang] asad | ||
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| SOCRATES: The Brahmaputra originates on the northern slopes of the Himalayas from some glaciers like Chemayungdung and Angsi, which are only 71 km east of Manas Sarovar. Many rivers emerge from these glaciers and merge into one stream to form the Tsangpo River. As difficult as it is to find the source of a river, it is at least 24 times more difficult to find the source of the universe. | SOCRATES: The Brahmaputra originates on the northern slopes of the Himalayas from some glaciers like Chemayungdung and Angsi, which are only 71 km east of Manas Sarovar. Many rivers emerge from these glaciers and merge into one stream to form the Tsangpo River. As difficult as it is to find the source of a river, it is at least 24 times more difficult to find the source of the universe. | ||
| - | Rabi: I understand that you want to focus only on Angsi to make things easier. But simplifying the description of the particle age of the universe will not be so straightforward. This cannot be understood without understanding the standard model of particle physics mathematically. | + | RABI: I understand that you want to focus only on Angsi to make things easier. But simplifying the description of the particle age of the universe will not be so straightforward. This cannot be understood without understanding the standard model of particle physics mathematically. |
| SOCRATES: The ancient Indians said that Brahma is the foundation of the universe, Manas Sarovar is created from the mind of Brahma, and Brahmaputra is the son of Brahma. Since Juno could not understand the mind of Brahma after so many visits to Manas Sarovar, I don't think we can understand the mathematical form of the Standard Model, no matter how much we talk to you. | SOCRATES: The ancient Indians said that Brahma is the foundation of the universe, Manas Sarovar is created from the mind of Brahma, and Brahmaputra is the son of Brahma. Since Juno could not understand the mind of Brahma after so many visits to Manas Sarovar, I don't think we can understand the mathematical form of the Standard Model, no matter how much we talk to you. | ||
| - | Juno: With that out of the way, everyone, let's go to the supposed source of the Brahmaputra. Sitting on the ice and talking will hopefully reduce Rabi's fire a bit. | + | JUNO: With that out of the way, everyone, let's go to the supposed source of the Brahmaputra. Sitting on the ice and talking will hopefully reduce Rabi's fire a bit. |
| - | Socrates: Where is this ' | + | SOCRATES: Where is this ' |
| - | Hermes: [[https:// | + | HERMES: [[https:// |
| [Everyone flies to the source of the Angsi River while listening to Hermes' | [Everyone flies to the source of the Angsi River while listening to Hermes' | ||
| - | ===== - Spacetime from the Big Bang ===== | + | ===== - Spacetime from Big Bang ===== |
| SOCRATES: The big bang theory, the standard model of cosmology, says that our universe, meaning all of us, came from an almost infinitely small point. Do you remember the comedy of Borges with two point-dwellers? | SOCRATES: The big bang theory, the standard model of cosmology, says that our universe, meaning all of us, came from an almost infinitely small point. Do you remember the comedy of Borges with two point-dwellers? | ||
| - | Rabi: If spacetime was born at the time of the Big Bang, then the question of what was before, or beyond, the Big Bang is meaningless. But the question is, can there really be no spacetime except our spacetime created from the Big Bang? Could it even be that nature is actually a multiverse with many or an infinite number of four-dimensional universes? Is there nothing beyond the four dimensions we are thinking of with three dimensions of space and one dimension of time? Could our four dimensions be born from another world of higher dimensions? We still don't know the answer to these, many mathematical theories have been made as an attempt to know, but which theory or model is correct has not yet been proven through observation. It is very common to use many dimensions in string theory. | + | RABI: If spacetime was born at the time of the Big Bang, then the question of what was before, or beyond, the Big Bang is meaningless. But the question is, can there really be no spacetime except our spacetime created from the Big Bang? Could it even be that nature is actually a multiverse with many or an infinite number of four-dimensional universes? Is there nothing beyond the four dimensions we are thinking of with three dimensions of space and one dimension of time? Could our four dimensions be born from another world of higher dimensions? We still don't know the answer to these, many mathematical theories have been made as an attempt to know, but which theory or model is correct has not yet been proven through observation. It is very common to use many dimensions in string theory. |
| SOCRATES: I understand that we know what happened after the Big Bang, but the cause or mathematical basis of the Big Bang itself is still unknown. Are mathematical theorems part of the universe, or laws imposed on the universe from outside? | SOCRATES: I understand that we know what happened after the Big Bang, but the cause or mathematical basis of the Big Bang itself is still unknown. Are mathematical theorems part of the universe, or laws imposed on the universe from outside? | ||
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| - | Rabi: Good question. The debate started by your student Plato and his student Aristotle is still going on. This figure made by Roger Penrose can explain the matter. Three worlds can be imagined in nature or reality: mathematical, | + | RABI: Good question. The debate started by your student Plato and his student Aristotle is still going on. This figure made by Roger Penrose can explain the matter. Three worlds can be imagined in nature or reality: mathematical, |
| SOCRATES: That means Plato thought that all theories would exist even if there were no universe, because theories exist outside the universe in a separate mathematical world. | SOCRATES: That means Plato thought that all theories would exist even if there were no universe, because theories exist outside the universe in a separate mathematical world. | ||
| - | Rabi: Yes. And according to Aristotle, theory is a human-made model to explain various phenomena of the universe. If there is no universe, there will be no theory. | + | RABI: Yes. And according to Aristotle, theory is a human-made model to explain various phenomena of the universe. If there is no universe, there will be no theory. |
| SOCRATES: But Aristotle' | SOCRATES: But Aristotle' | ||
| - | Rabi: That is your own choice. I am a Platonist. One who understands the meaning of the beauty and theory of Math cannot think of anything other than Math as the source. | + | RABI: That is your own choice. I am a Platonist. One who understands the meaning of the beauty and theory of Math cannot think of anything other than Math as the source. |
| - | Socrates: Well, then these three worlds together what can be said to be the basic structural elements of reality? | + | SOCRATES: Well, then these three worlds together what can be said to be the basic structural elements of reality? |
| - | Rabi: Definitely STEMIC, meaning space, time, energy, matter, information, | + | RABI: Definitely STEMIC, meaning space, time, energy, matter, information, |
| - | Socrates: Where is your math? | + | SOCRATES: Where is your math? |
| - | Rabi: Everything in math is inside that information. | + | RABI: Everything in math is inside that information. |
| SOCRATES: What was the need to separate consciousness? | SOCRATES: What was the need to separate consciousness? | ||
| - | Rabi: Many cognitive scientists think that consciousness is another type of thing, not information. But that is another debate. We should first focus on just the ' | + | RABI: Many cognitive scientists think that consciousness is another type of thing, not information. But that is another debate. We should first focus on just the ' |
| SOCRATES: These four together can be explained by relativity, but only on a much larger scale. Relativity does not apply at very small atomic or subatomic scales, where energy and matter have to be explained by quantum theory. If a theory can be made combining general relativity with quantum theory, it is possible to explain STEM at all scales together. Many physicists are still trying to make a Theory of Everything (TOE), aren't you one of them? | SOCRATES: These four together can be explained by relativity, but only on a much larger scale. Relativity does not apply at very small atomic or subatomic scales, where energy and matter have to be explained by quantum theory. If a theory can be made combining general relativity with quantum theory, it is possible to explain STEM at all scales together. Many physicists are still trying to make a Theory of Everything (TOE), aren't you one of them? | ||
| - | Rabi: I still think some future version of string theory will unify everything. But surely you will not understand that. Rather, we should now see what it means to unify, and what is this ' | + | RABI: I still think some future version of string theory will unify everything. But surely you will not understand that. Rather, we should now see what it means to unify, and what is this ' |
| SOCRATES: Then tell us what is meant by Everything, and what is meant by unifying. | SOCRATES: Then tell us what is meant by Everything, and what is meant by unifying. | ||
| ===== - Birth of Energy ===== | ===== - Birth of Energy ===== | ||
| - | Rabi: Currently there are four types of energy in our universe. Each energy interacts differently. The interaction of energy is called a force. Then there are also four forces associated with the four energies: strong, electromagnetic, | + | RABI: Currently there are four types of energy in our universe. Each energy interacts differently. The interaction of energy is called a force. Then there are also four forces associated with the four energies: strong, electromagnetic, |
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| SOCRATES: Yes, it appears so in this figure of yours. But why do you start with energy, leaving space, time, matter of STEM? | SOCRATES: Yes, it appears so in this figure of yours. But why do you start with energy, leaving space, time, matter of STEM? | ||
| - | Rabi: Because, Socrates, after the Big Bang there was only spacetime and energy in the beginning, matter was then created from energy; It can be explained by Einstein' | + | RABI: Because, Socrates, after the Big Bang there was only spacetime and energy in the beginning, matter was then created from energy; It can be explained by Einstein' |
| SOCRATES: Matter doesn' | SOCRATES: Matter doesn' | ||
| - | Rabi: We cannot explain something called zero time. At Planck time, all our theories fall apart. Planck time is 1 quattuordecillionth of a second (45 zeros before one), that is $10^{-45}$ seconds. Since Planck time, there has been spacetime, and with it only one unified energy and force. It's called the TOE force, because if a theory of everything is ever discovered, that theory can explain this force. | + | RABI: We cannot explain something called zero time. At Planck time, all our theories fall apart. Planck time is 1 quattuordecillionth of a second (45 zeros before one), that is $10^{-45}$ seconds. Since Planck time, there has been spacetime, and with it only one unified energy and force. It's called the TOE force, because if a theory of everything is ever discovered, that theory can explain this force. |
| - | Rhea: Wait, I don't understand the time and temperature thing in your figure. Accustomed to the cultural age, I have a hard time digesting such a small number. What was the age and temperature of the universe at the time of this tow force? | + | RHEA: Wait, I don't understand the time and temperature thing in your figure. Accustomed to the cultural age, I have a hard time digesting such a small number. What was the age and temperature of the universe at the time of this tow force? |
| - | Rabi: Remember, all forces are born in the first picosecond. The TOE force existed much earlier, when the universe was less than 10 trdecillionth of a second. If you go to the [[un: | + | RABI: Remember, all forces are born in the first picosecond. The TOE force existed much earlier, when the universe was less than 10 trdecillionth of a second. If you go to the [[un: |
| - | Rhea: From what I see in the list, 1 tredecillion means 42 zeros after one, then 10 tredecillion means 43 zeros after one. Just twelve zeros after one makes one trillion, and here we have to put 43. It is impossible for any human being to feel the terrible shortness of time when one second is divided by such a large number. And I don't even want to try to feel the temperature. | + | RHEA: From what I see in the list, 1 tredecillion means 42 zeros after one, then 10 tredecillion means 43 zeros after one. Just twelve zeros after one makes one trillion, and here we have to put 43. It is impossible for any human being to feel the terrible shortness of time when one second is divided by such a large number. And I don't even want to try to feel the temperature. |
| - | Rabi: It's cool to sit in this ice and wonder what the temperature of the universe was at that time. Think about it. The source of the Brahmaputra is very cold, the temperature increases as you go towards the estuary (Bay of Bengal). The opposite is true of the universe. The temperature was the highest during the Big Bang, and since then, as the universe has expanded, both its density and temperature have decreased, and are still decreasing. | + | RABI: It's cool to sit in this ice and wonder what the temperature of the universe was at that time. Think about it. The source of the Brahmaputra is very cold, the temperature increases as you go towards the estuary (Bay of Bengal). The opposite is true of the universe. The temperature was the highest during the Big Bang, and since then, as the universe has expanded, both its density and temperature have decreased, and are still decreasing. |
| - | Rhea: If we look at this figure and the list of numbers, we can say that when the age of the universe is 10 tredecillionths of a second ($10^{-43}$ seconds), and when the temperature is 100 nonillion Kelvin ($10^{32}$ K), then by breaking the TOE force, two separate forces were born, gravity and GUT force. What does ' | + | RHEA: If we look at this figure and the list of numbers, we can say that when the age of the universe is 10 tredecillionths of a second ($10^{-43}$ seconds), and when the temperature is 100 nonillion Kelvin ($10^{32}$ K), then by breaking the TOE force, two separate forces were born, gravity and GUT force. What does ' |
| - | Rabi: ' | + | RABI: ' |
| - | Rhea: On the left side of the name of the four forces, I see the names of some particles, and on the right side some numbers and pictures. What does this mean? | + | RHEA: On the left side of the name of the four forces, I see the names of some particles, and on the right side some numbers and pictures. What does this mean? |
| - | Rabi: This is a basic introduction to these four forces for the benefit of those who may not understand anything through math. Every force works by exchanging certain particles. The particles of the strong force or interaction are the gluons, the photons for the electromagnetic force, and the $W^+$, $W^-$ and $Z$ bosons | + | RABI: This is a basic introduction to these four forces for the benefit of those who may not understand anything through math. Every force works by exchanging certain particles. The particles of the strong force or interaction are the gluons, the photons for the electromagnetic force, and three types of bosons (for example, Z boson) |
| - | Rhea: But the most important thing is to understand what the forces really are. | + | RHEA: But the most important thing is to understand what the forces really are. |
| - | Rabi: That is shown in the four pictures on the far right. Strong and weak forces act only inside the nucleus of an atom. The strong force binds three quarks together to form a proton. The weak force can convert an up quark of this proton into a down quark by converting the proton into a neutron, thus giving rise to radioactivity. Electromagnetic forces hold atoms together by creating an attraction between electrons and protons. And gravity bends the space around the earth and forces the moon to revolve around it. | + | RABI: That is shown in the four pictures on the far right. Strong and weak forces act only inside the nucleus of an atom. The strong force binds three quarks together to form a proton. The weak force can convert an up quark of this proton into a down quark by converting the proton into a neutron, thus giving rise to radioactivity. Electromagnetic forces hold atoms together by creating an attraction between electrons and protons. And gravity bends the space around the earth and forces the moon to revolve around it. |
| - | Rhea: But you didn't explain one thing. At one picosecond in the middle of your figure it says ' | + | RHEA: But you didn't explain one thing. At one picosecond in the middle of your figure it says ' |
| - | Rabi: That is the most important thing. I mentioned the sequence of birth of the four energies or forces, but did not explain why it broke from one into four in this way. The reason is called symmetry breaking in physics. A theory in physics that has symmetry means that the theory applies equally in all space and time. The theory of gravity is as true for the apple tree as it is for the Andromeda galaxy, and is as true today as it was yesterday. There is a more extreme form of this symmetry, where even the identity of the particles becomes symmetric, meaning that there is no theoretical difference between one particle and another. For example, there was no difference between photons and Z bosons before the electroweak theory' | + | RABI: That is the most important thing. I mentioned the sequence of birth of the four energies or forces, but did not explain why it broke from one into four in this way. The reason is called symmetry breaking in physics. A theory in physics that has symmetry means that the theory applies equally in all space and time. The theory of gravity is as true for the apple tree as it is for the Andromeda galaxy, and is as true today as it was yesterday, and will be as true tomorrow. There is a more extreme form of this symmetry, where even the identity of the particles becomes symmetric, meaning that there is no theoretical difference between one particle and another. For example, there was no difference between photons and Z bosons before the electroweak theory' |
| - | Rhea: I see, but don't you think, Socrates, that Rabi' | + | RHEA: I understand, but don't you think, Socrates, that Robbie' |
| SOCRATES: Right. | SOCRATES: Right. | ||
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| + | RABI: Time for a metaphor then. The reason for symmetry breaking at a certain point is actually phase change. For example, water is a gas at 200 degrees Celsius. Lowering the temperature won't do much until 100 degrees, but at 100 degrees the water will actually turn from a gas to a liquid. Not at any other temperature, | ||
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| + | RHEA: Now I understand better. But the inflation you wrote down at an octillion degree age needs a little explanation. | ||
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| + | RABI: Just as heat or energy is required to boil liquid water into steam, energy is released when steam is converted into liquid water. Similarly, every phase transition or symmetry breaking in the universe releases a lot of energy. At one octillion degrees, the energy release was so high that the universe suddenly became very large. This phenomenon is called inflation, but its definite proof is not yet available. | ||
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| + | RHEA: We need to get to know these phase-changing, | ||
| ===== - Birth of Matter ===== | ===== - Birth of Matter ===== | ||
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| + | RABI: That's why we have to keep an eye on the figure below. The seventeen particles that have so far held their place of honor in the Standard Model of particle physics are shown below in two ways: on the left is the mass, charge, and spin of each particle, and on the right are the same particles arranged differently to show the beauty of the model. | ||
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| {{: | {{: | ||
| - | ===== - Background | + | RHEA: Here we also see four particles known as carriers of the three forces: gluons, photons, Z bosons, and W bosons, each with spin 1. Strong and electromagnetic forces are similar in that their particles have no mass and no charge. Two particles of the Wick force are very heavy, one has a mass of 91 and the other has a mass of 80 GeV, but what is the meaning of this unit of mass? I understand that GeV stands for giga electron-volt, |
| - | {{: | + | |
| + | RABI: I have already said that energy and matter (mass) are the same thing with Einstein' | ||
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| + | RHEA: Let's look at the left figure first. Here on the left are 12 particles of matter whose common name is fermion, named after Enrico Fermi of Italy, and on the right are 5 particles of energy whose common name is boson, named after Satyendranath Bose of Dhaka University. Energy particles have spin 1, matter particles have spin 1/2. Particles of energy are called carriers of interaction or force. The Higgs boson is called a scalar boson, and the other four are called gauge bosons, or vector bosons. Even if I understand scalar and vector, I don't need to understand the meaning of these names. The Higgs is the heaviest of the bosons, while the gluon and photon are massless. Matter particles are of two types: six quarks and six leptons. The six quark names are pretty cool: Up, Charm, Top, Down, Strange, Bottom. The charge of the first three is 2/3, the charge of the next three is -1/3. The names of the six leptons are electron, muon, tau, electron neutrino, muon neutrino, tau neutrino. The first three have a charge of -1, and the three neutrinos have a charge of 0, making them neutral. The heaviest quark is top, and the lightest is up. The heaviest lepton is the tau, and the lightest is the electron, our most beloved object. | ||
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| + | RABI: Great description, | ||
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| + | RHEA: But you told Socrates in the beginning that you would ' | ||
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| + | RABI: Good question. Since energy and matter are equivalent, one was created from the other after the Big Bang all the time. This phenomenon is called 'pair production' | ||
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| + | RHEA: So can matter and antimatter be created from energy even now? | ||
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| + | RABI: No. Because it takes a lot of energy to create matter through pair production, it requires temperatures much higher than today which does not exist even in the center of stars, but the Universe was hot enough just after the Big Bang. Antiparticle of electron is called positron. The temperature required to form an electron-positron pair is 10 billion Kelvin, the temperature required to form a proton-antiproton pair is 10 trillion Kelvin, and the various quark-antiquark pairs require about 1 quadrillion Kelvin. Since the temperature of the universe was one quadrillion kelvin at an age of 1 picosecond, quarks were first born between 1 picosecond and 1 nanosecond. Then at the age of 1 microsecond, | ||
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| + | RHEA: Interesting. But you only talked about particles of matter. In each of these cases, don't we also get antiparticles of antimatter? | ||
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| + | RABI: Yes, antimatter has always been created along with matter. But the interesting thing is that from the very beginning, for some unknown reason, there was a little more matter than antimatter in the universe. Now you see in the figure that just as matter-antimatter can be formed from energy, so also matter-antimatter can completely annihilate each other and return to energy. This destruction, | ||
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| + | RHEA: Where did the energy created from all these annihilations go? For example, where are the photons produced in all electron-positron annihilations? | ||
| + | ===== - Photon | ||
| + | RABI: Excellent question. These photons are called the Cosmic Microwave Background or CMB. It was with these photons that we were able to take the first pictures of the Universe, when it was three hundred thousand years old, and had a temperature of 3,000 kelvin. | ||
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| + | RHEA: But you jumped from the victory of the electrons in a battle with the positrons at the age of 1 second of the universe to the age of 300,000 years. What happened in the middle? | ||
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| + | RABI: Well let me go back a bit. In fact, sitting on this ice has frozen my head. Can't we take a little walk on the ice-molten water of the Angsi River? Jesus also walked on water. | ||
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| + | HERMES: Come on, everyone. Like Aristotle' | ||
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| + | RABI: The touch of ice-cold water on my feet opened my mind. The biggest event that happened when the universe was beteen 1 second and 10 minutes old was nucleosynthesis, | ||
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| + | RHEA: But why within the first ten minutes? | ||
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| + | RABI: The reason is again temperature. To create helium through fusion, the temperature must be at least 1 billion kelvin. By the age of ten minutes, the temperature of the expanding universe had dropped to 1 billion degrees, so this process only happened in the first ten minutes. At first, the chemical element in the universe was only hydrogen (meaning single protons), in the first ten minutes 24% of the hydrogen was converted into helium, and the remaining 76% remained hydrogen. The chemical composition of the universe is still the same. Astronomers' | ||
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| + | RHEA: I understand how the nucleus, the center, of hydrogen and helium was formed. But why could not electrons combine with them to make neutral atoms? Is that because of the temperature? | ||
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| + | RABI: Yes. The higher the temperature, | ||
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| + | RHEA: And if we come toward the present, we see that the temperature and density are decreasing day by day due to the expansion of the universe. | ||
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| + | RABI: Yes. And the density of energy decreased more rapidly with temperature than the density of matter. This is why when the universe was 50,000 years old, the density of energy was less than that of matter. The first fifty thousand years were the reign of energy, after which the reign of matter began. | ||
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| + | RHEA: And exactly what happened at the age of three hundred thousand years? | ||
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| + | RABI: Then the temperature dropped to about 3000 kelvin and the electron could no longer remain free. The proton binds the electron with its potential energy, creating a neutral hydrogen atom. After that the helium atom was also born. And since there are no more free electrons, the photon starts its free journey in a straight path. The event didn't happen exactly at three hundred thousand years, it happened over a period of three hundred thousand to one million years, but I'm using three hundred thousand for poetic reasons. | ||
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| + | RHEA: Well, I understand what the CMB of your figure is. It's understandable why it's called a background, because it's the first picture we've taken of the universe, meaning the very back, the background of everything. The figure shows a colorbar from -300 to +300 microkelvin. White-green means 0, the more you go towards the blue, the more negative the temperature, | ||
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| + | RABI: Here zero means the average temperature of the universe at the age of 300,000 years. The temperature difference of the entire universe with respect to this average is shown in this map. It is a map of the entire universe. The universe was then a single gas of hydrogen-helium, | ||
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| + | RHEA: Ok I understand. But what does this ' | ||
| + | ===== - Light and Color ===== | ||
| + | RABI: When the CMB radiation occurred, the temperature of the universe was 3000 degrees, so the wavelength of the CMB was in the infrared range, a few micrometers, | ||
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| + | RHEA: Yeah, so it turns out that microwave light from space doesn' | ||
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| + | RABI: That picture was taken by a space-telescope called ' | ||
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| + | SOCRATES: I think we should take this opportunity to discuss light. What is light? What is the wavelength and frequency of light? | ||
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| + | RABI: Light is electromagnetic (EM) energy. Light is made of photons. Light can also be thought of as a wave. We are now walking over the Angsi River. If I kick the water with my foot, a wave will be created on the surface of the water. Light is also a wave that is created only within the EM field. I can make waves in the water with my feet. But the EM field requires charged particles, such as electrons, to create waves. When an electron is accelerated, | ||
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| + | RHEA: Socrates, you yourself know everything very well, but you pretend to know nothing. | ||
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| + | SOCRATES: My daemon does not think so. Anyway, tell me if you're going to make waves or not. | ||
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| + | RHEA: Ok, instead of making waves in the air with words, I am directly making waves in the water. We are very close to the Tsangpo River. Look there, an empty boat tied to the shore. I will make waves in the middle of the river with this boat, you all stand on the bank with your feet in the water so that you can actually feel the waves. Now I'm pedaling too hard. Socrates, put aside your irony, tell me how the waves seem. | ||
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| + | SOCRATES: It seems to come more frequently, meaning that the distance from one crest of the wave to the next is shorter. | ||
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| + | RHEA: You have understood both wavelength and frequency. The distance between two adjacent peaks is the wavelength. And frequency is how often one wave (peak) comes after another. I changed pedal speed many times. Did you get a change in the wave? | ||
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| + | SOCRATES: Yes. The faster the velocity changes, the shorter the wavelength of the wave, and the higher the frequency. Shorter the wavelength the higher the frequency, lower the frequency the longer the wavelength. | ||
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| + | RABI: Let's all get on the boat and finish the rest. | ||
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| + | [//All eight in a boat, on the Tsangpo River.//] | ||
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| + | RHEA: I have another question about the figure of the EM spectrum. In order of wavelength, radio light is the longest, followed by microwaves, infrared, visible, ultraviolet, | ||
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| + | RABI: Until the 19th century, people did not know any light except visible light. Two German scientists were the first to discover light other than visible light. Heinrich Hertz discovered radio light in 1888, and Wilhelm Röntgen discovered X-rays in 1895. Then all light from radio to gamma-rays gradually became available to humans. The name of the device that captures light is telescope. Since Mars was the only astronomer among us, he should lead the telescope discussion. | ||
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| + | MARS: I have a small portable smart telescope with me. The behavior of all telescopes at all frequencies can be explained with this small telescope. It is a visible light telescope, operating at a wavelength of 400 to 700 nanometers, i.e. at a frequency of approximately 400 to 700 terahertz. The unit of frequency Hertz is named after Heinrich Hertz. We see light of different frequencies as different colors. If the wavelength of light is 450 nanometers, its color is blue, if it is 550 nanometers, it is green, and if it is 700 nanometers, it is red. There are actually not seven colors between red and blue, but an infinite number. | ||
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| + | RABI: So why did people think of exactly seven colors in the rainbow? | ||
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| + | MARS: Isaac Newton attributed seven colors to the rainbow for the same reason that we divide the history of the universe or the river Brahmaputra into seven parts, i.e. for poetic reasons. Many colors are also visible in the images of this telescope. We can use frequency and color as synonyms. | ||
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| + | ===== - Telescope ===== | ||
| + | RABI: Since the night is here, give us a demonstration of this telescope. | ||
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| + | MARS: The main parts of any modern telescope are three: collector, detector, processor. The figure shows all three that you can match with the telescope. The vertical slab mounted on the tripod is an altitude-azimuth mount, with an optical tube attached. At the lower end of the tube is the collector, in this case an 11-cm diameter mirror, and at the upper end is the detector, in this case a CCD sensor. The sensor is placed where all the light falling on the curved mirror of parabolic shape meet after reflection. If you follow the arrow you will understand. The sensor converts all photons of light into electrons and sends them through wires to the processor, which is housed inside the vertical mount. In this case, the processor is a Raspberry Pi mini-computer with 64 GB of storage, and a WiFi modem. The computer power switch is on the surface of the vertical mount. And here's where the power comes from—the battery housed inside the horizontal part of the mount, just above the tripod. When switched on, the telescope itself will create a WiFi network to which we can connect with the phone' | ||
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| + | RABI: What is the meaning of the specifications of the telescope in the picture? | ||
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| + | MARS: The efficiency of any telescope is determined mainly by two parameters: resolution and sensitivity. A telescope' | ||
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| + | RABI: And what is sensitivity? | ||
| - | ===== - Light, Color, Telescope ===== | + | MARS: Sensitivity refers to how dim objects a telescope can see. In this case, the sensitivity is defined by the limiting magnitude, which here has a value of 18. I am explaining. Following the ancient Greeks, astronomers developed a logarithmic system to express the apparent brightness of any celestial object. In this system, the higher the brightness of the object, the lower its magnitude. The Sun has an apparent magnitude of -26, the Moon -13, bright stars 0, and humans can see a maximum of magnitude 6 with the naked eye. Our telescope' |
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| - | {{https:// | + | RABI: So we end the particle age discussion by taking a picture of an object in the sky? |
| - | < | + | MARS: We cannot take a very good picture from the boat. Today, let us see the sky with our naked eyes. Going further along the Tsangpo River, we will take pictures from the shore another day. |
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courses/ast100/1.1728851531.txt.gz · Last modified: 2024/10/13 14:32 by asad