Astro 19N Exam 2
Give some examples of "back-formation" of an artificial memory that serves to justify subsequent action or emotion.
-when a victim of speaks out of their victimization, they reconstruct the past story slightly in order to emphasize the story. They aren't necessarily lying because they truly believe that is what happened based on what they are feeling now -Professor Hayot's example of his mother reconstructing the the truth of moving her food
What makes General Relativity "general"?
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Explain how our human experience of time is mediated by history in two distinct ways.
1) Human time is the result of the historical process of evolution, which results in certain biological and neurological affordances. 2) The affordances are also trained by the specific societies and families we live in.
What does an Eighties-era Reese's Peanut Butter Cup commercial have to do with the nature of spacetime?
3D space and 1D time, though separate dimensions, join together to form 4D spacetime. This relates to the Reese's commercial because two separate objects, chocolate and peanut butter, come together to form Reese's. The commercial says, "You got your chocolate in my peanut butter" and "You got your peanut butter in my chocolate." The same could be said if the words "peanut butter" and "chocolate" were replaced with "space" and "time." Space and time are mixed as a result of fast relative motion and strong gravitational fields.
Explain how a fast-moving train passing "moving" cars as well as "stationary" pedestrians illustrates the principle of inertia. Do the various parties agree on their relative velocities? Do they agree on their "absolute" velocities? Does it matter?
A fast-moving train passing "moving" cars and "stationary" pedestrians illustrates the principle of inertia because this would prove there is no absolute standard of rest. The people on the ground see the train moving by them, and the people on the train see the ground, or the people, moving relative to them. In the car, they can see the train moving past them, while they pass the people on the ground. Each case, the people on the train, in the car, or on the ground see motion relative to themselves, thus backing up there is no standard of rest. Each party can agree on the relative velocities, but they cannot agree on absolute velocities. It doesn't matter if they agree on absolute velocities because no physical experiment or observation is affected.
What is a geodesic? Give an example of a geodesic path on the surface of Earth.
A geodesic is the shortest distance path on a curved surface. An example on Earth is the flight path from California to Germany that goes over Greenland, which may appear out of the way on flat maps.
Give some examples of secular-historical teleologies.
A history that is described as teleological is history that is goal oriented and is continually improving. Examples of this in history is the extraordinary progresses made in technology and also progression towards evolutionary perfectionism.
What is the nature of reality (the metaphysics of time) according to the philosophical school of Presentism?
According to Presentism, only the present is real. The past was real, but it is not real anymore. As we can only experience the present, the future also does not exist.
What is the nature of reality (the metaphysics of time) according to the philosophical school of Eternalism?
All moments (past, present, and future) are equally real
List some contemporary examples of social activity that serve to maintain a society's reifications.
An example is getting a job/earning a living through being paid with cash, so an individual can obtain or maintain their financial goals: (this can be the reification of stability, luxury, getting out of poverty). Another reification can be the physical manifestation of the idea of being a "productive member of society" by working, contributing, and helping improve society as a whole.
List some contemporary examples of socially relevant abstract reifications. Are these reifications fixed or changing?
An example of abstract reifications is marriage. For example, in Medieval Europe marriages existed for political reasons - forging allies, acquiring land, and preserving power. Then, marriage evolved from that into a union out of love. This reification is always changing because as times have progressed there are new laws (legalization of interracial marriage in 1967 and same-sex marriage in 2015) and new attitudes (phenomena of Millenials marrying later).
What happens to the lengths of objects that are moving quickly with respect to an observer?
Another one of the Special Relativity consequences are that objects in motion are measured to be shorter along the direction of motion. This is called length contraction. For example, a stationary train is measured to be 1000 meters long. The same train now moves at a high speed; when moving, the train can now be measured to be 995 meters long. The train now comes to rest and is stationary again, it measured to be 1000 meters long again. This is the idea behind the consequence of length contraction.
Give some examples of irreversible physical systems.
Any heat engine is irreversible. For example, a steam engine transfers the chemical energy inside coal into heat and kinetic energy of the steam, through which entropy is increased. Afterwards, one cannot traceback all the heat and kinetic energy to store them back into coal again, as entropy cannot be reversed, unless through isolating specific spacetime and releasing even more entropy to some other spacetime outside its contour, which does not concern the original system. But if we see it from the perspective of the whole universe, the burned coal can never be restored again without changing some other conditions.
How are the past and future (almost universally) incorporated into the human experience of the present moment?
As we go through time in the present, our experiences are constantly being shaped by a memory of the past and the anticipation of the future. The past that we already experienced and the future that we are anticipating to experience both help to make sense of what we are experiencing now.
A passenger traveling on a spaceship at 50% the speed of light points a flashlight toward the front of the spaceship and turns it on. What speed does the passenger measure for the flashlight's light?
Because of velocity addition, most objects would move at their velocity plus half the speed of light. However, the speed of light is the upper bound. The light from the flashlight already moves at the speed of light, and it cannot be measured faster than that. So the flashlight's light moves at c (the speed of light). The passenger measures the flashlight's light to be moving at c, 3*10^8 m/s. As per Special Relativity, the speed of light is always measured by any observer with any relative velocity to be c.
What was Boltzmann's insight into the nature of the thermodynamic (macroscopic) quantity known as entropy?
Boltzmann observed that low-entropy states were rare and special, having a low probability. He also observed that high entropy states were generic, possessing a high probability, with equilibrium (maximum entropy) states being the most generic and probable. This led to his development of Boltzmann's Law, which suggests that entropy is nothing more than counting equivalent states. In other words, it's extremely likely for entropy to increase, but it being "nothing more" than equivalent states means that it is still possible for entropy to decrease. The increase in entropy over time is not a guaranteed process, albeit an extremely probable one. The Arrow of Time is only temporarily present within systems that move from states of low-entropy to high-entropy.
What was Boltzmann's "Past Hypothesis," and does it hold for our universe or not?
Boltzmann posited that the visions of time as change and time as a dimension could be somewhat reconciled, so long as entropy was extremely low in the past. The cosmology behind Boltzmann's "Past Hypothesis" further suggests that we exist in a low-entropy bubble within a near equilibrium universe. The Arrow of Time may exist within the context of this "bubble," but it may not exist within the laws of physics. Cosmic microwave background radiation seems to imply that Boltzmann's hypothesis was correct, as this theory is consistent with our current understanding of the initially low-entropy state for our universe.
List some examples of proposed "historical laws."
Civilizations rise, peak, then fall Relationships undergo a "seven-year itch" Countries in financial crisis are more likely to have civil wars Civilizations organized along East/West axes are more likely to be successful than North/South ones
Approximately when do current calculations suggest our universe will achieve thermal equilibrium?
Current calculations suggest we will reach thermal equilibrium in 10^100 years.
Define daily (quotidian) time and distinguish it from historical time.
Daily quotidian time is the way individuals in a social context experience time. This can depend on their position as an observer or on the interface between physical time and biological/sensory affordances. Historical time is the general march forward in time that humans use to tell stories about the meaning of life. This can be the result of historical processes of evolution which can differ based on specific societies.
Explain how the nature of thermodynamic time (time as change) implies the time-embeddedness of all things.
Due to the Arrow of Time embodied by the 2nd Law of Thermodynamics, every facet of culture (e.g., a painted statue) is not a singular object to be examined in one context but rather the product of a process contingent upon time's "march forward" from order to disorder. German philosopher Peter Janich argued through his tenet of methodical culturalism that the humanities are indeed embedded in an ever-changing time (i.e., he would gravitate toward Boltzmann over Newton). Janich extended this way of thinking to encompass both the humanities and the sciences, or collectively the ontology of things.
How did Einstein anticipate the anomalous bending of starlight near limb of the Sun using General Relativity?
Einstein calculated that Mercury's orbit is 10km shorter than it should be and he predicted this was caused by the bending of light from the Sun's gravity, but it was not proven until light bending was verified by the 1919 solar eclipse expeditions organized by Sir Arthur Eddington. In General Relativity, light bends when it travels through spacetime that is significantly curved by a massive object, such as a large star or a black hole.
What was the key insight that allowed Einstein to see how he might incorporate gravity into relativity theory?
Einstein's happiest thought occurred after observing his neighbor fall off of a roof towards the ground. The man who fell told Einstein that he didn't perceive himself as falling, and it was the ground that moved closer to him. This idea was a revelation for Einstein and led him to incorporate gravity into his theory of relativity.
What key feature of the universe is left unaccounted for in Einstein's Special Relativity theory?
Einstein's theory of Special Relativity is an excellent model for transforming most of the established physics, such as conservation of energy, momentum, and Maxwell's equations (electricity and magnetism) between different reference frames, but it fails to adequately account for the effects of acceleration. Einstein later rectified this shortcoming and developed a relativistic model for gravitational fields in his much more mathematically intensive theory of General Relativity.
From an Eternalist perspective, what is probably the most pressing unresolved question about time?
Eternalism is the idea that all moments are real, often used in conjunction with concepts from Einstein's relativity. That is, the past and the future are just as real as the present. The most pressing question an eternalist would have might be something as follows. If the past and future are just as real and tangible as the present, why can't we control the flow of time rather than just being along for the ride? Why can't we walk to another point in time just like we walk across a room?
What do studies of eyewitness testimony tell us about the fidelity of memory?
Eyewitness testimony shows that memory is not always entirely reliable. Memories are influenced by social and environmental cues. A person's memory, and therefore their testimony, can change depending on their surroundings. A prompting question, such as, "Did the person you see have brown hair?" can cause a person's mind to latch onto certain details that may not actually have been true.
What was Francis Fukuyama's argument regarding "the end of history"?
Fukuyama believed that history was evolving towards the end goal of human freedom, which to him means capitalist democracy. Since this has been essentially realized with the collapse of the Soviet Union, he argued that history is over, and from now on, things just happen with no purpose. It should be noted that Fukuyama's prediction has not appeared to be accurate. The rise of nationalism, authoritarianism, and socialism in various fully developed capitalist democracies have shown that history has not stopped advancing, for now.
Explain how a pickup truck can enable a baseball pitcher (who normally pitches at up to 90 mph) to pitch a 140 mph fastball.
Galilean relativity, and the principle of inertia, leads to a strict rule of velocity addition. Since the baseball player is already on the truck moving at a speed, however fast the baseball player can originally throw the ball from a stationary position is then added to the velocity of the truck. For example, since the final velocity of the ball mentioned in the question is 140 MPH, and the baseball player can throw a 90 MPH fastball, that means the truck is moving at 50 MPH, because 140 MPH - 90 MPH = 50 MPH. Or, 50 MPH + 90 MPH gives you a final ball speed of 140 MPH.
List some examples of socially relevant objects that can be seen as reifications of social activity, as per Garfinkel.
Garfinkel claims socially relevant objects are reifications of social activity and that social life involves the constant maintenance of reification because objects do not stay reified. An example would be reinforcing the idea that chairs are for sitting in by always using them that way rather than some other way, such as throwing them like a ball. Another example could be that plates are used for eating on because that's the socially accepted norm versus, say, tossing them like a frisbee.
How is gravity explained in the context of General Relativity?
Gravity is explained by the warping of spacetime. This warping dictates how matter moves through spacetime.
What was Hegel's view of the purpose of history?
Hegel believed in a secular version of history that was goal oriented. He said, "History is the process whereby the spirit discovers itself and its own concept." Along with other secular views, he believed that history was moving forward towards something better. He specifically thought that the realization of human freedom was this end goal.
Provide arguments for and against the claims of historical positivism.
Historical positivism is where an individual can confidently argue the validity of a belief they have and they believe it is 100% real and legitimate. This way of thinking can be justified such that their beliefs exist in their own personal reference frame. Their beliefs are their reality so, to them, their beliefs are what have structured their life that is very real itself so their beliefs that are connected to them are as real. On the contrary, one person's beliefs do not necessarily reflect the views of others who may have starkly different beliefs that they believe are legit. There are countless beliefs in our society that are believed to be legitimate that at the same time may debunk other's beliefs so we are left without an answer of who is right or wrong and what beliefs are real or not real. According to the theories of historical positivism, if each person's beliefs are real then this would mean there are multiple realities existing at once which. This is where there are flaws in historical positivism.
From what perspective is each moment in time unique? List some possible implications of this insight.
Historical time is unique in the sense that no moment repeats itself. You can repeat something, but you cannot perfectly mirror a moment because you cannot control minute details or what goes on in the world around you. This implies that we may experience time as repetitive, but it is always moving forward and no single moment can be replicated.
Explain the principle of inertia, and its relevance to our everyday lives on a rotating, revolving planet.
Inertia is the idea that objects in rest remain in rest and objects in motion remain in motion in a constant velocity unless acted on by an external force. Inertia relates us to our motion in the universe because the change in our motion is so slight that it is unrecognizable to us, ie. our acceleration is so minuscule that we don't feel our movement throughout the universe. If our planets motion was to be drastically disrupted we would likely be thrown about where ever we were because our change in acceleration would be so large.
Present an argument (with evidence) that the collapse of the Soviet Union in 1991 did not bring about "the end of history," even in the limited sense intended by Fukuyama in his 1989 essay.
It did not bring about the end of history because even though it was revealed that a capitalist democracy is the most effective way to govern (at least in our countries eyes) there are several countries today that do not follow this form of government. So even though the knowledge and facts are there that this system is a beautiful one that tends to work better than communism, the lack of application worldwide of it still leaves room for history to take its course. If there are still governments running in a way that is opposed to that of a capitalist democracy, the transition (or lack thereof) to something similar to what we have going on is still historical in nature.
Is the psychological past better treated as fixed or changing? How or why?
It is better treated as changing. The brain does not store memory like a computer. Our memories are always subject to change due to events that happen in the present. Such events can sometimes, by the one experiencing them, need a specific past to have happened even if that past never happened
Why was it important for 19th century physicists to reconcile the two competing visions of time?
It was important to reconcile these two competing visions because they opposed each other. According to vision 1, time is reversible and does not distinguish past from present. However, in the example of a steam engine, useful energy is transformed into unusable heat-this process is irreversible-which supports vision 2 that entropy is always increasing. Boltzmann reconciled these opposing visions through the approach of equilibrium, which connects the two visions as long as entropy was very low in the past.
Explain how a very low-entropy origin for our universe can be used with the Anthropic Principle to argue for the existence of the Multiverse.
It's extremely unlikely for a low-entropy universe to have been created. Thus, we can address this unlikelihood by referring to another universe that may have been in a state of high entropy or equilibrium (maximum entropy), which gave birth to our universe. This would be consistent with the anthropic principle, since there would seemingly have to be a reason why our universe possesses a proper amount of entropy to sustain human life. Given that this universe does sustain life, there would need to be an explanation for our universe's unlikely low-entropy origin that allowed for this life to develop.
Does it seem likely that we can work to correct the ways in which we all (collectively) misremember the past? What might be an appropriate (achievable) goal in this regard?
It's hard to change individuals' perceptions and conclusions about past history. Sometimes we create our own 'echo chambers' and agree with like-minded people. We can use technology to help to come to a consensus.
What does Ray Kurzweil consider the ultimate goal of human evolution?
Kurzweil believes that the human species will evolve to become a sort of hybrid with technology as it advances, called Singularity. He thinks machine intelligence will surpass human intelligence and benefit the universe.
Give an argument that some particular division of historical time into a small number of large-scale units reflects an important feature of reality.
Many divisions are derived from legends, myths and historical record. These divisions also partially reflect reality, since myth, legend and history are derived from what has happened. For instance, even though many experts think reign of kings in Sumerian lists of kings has somewhat distortion, some kings do have connection with real Sumerian kings, even Gilgamesh could be one on lists of kings
What causes the "warping" (or curvature) of spacetime in General Relativity?
Matter causes spacetime to warp in General Relativity. In general relativity, gravity can lead space time to curve. Since any matter that has mass will create gravity, this will lead space time to curve under effect of gravity.
What sorts of memories are most likely to persist?
Memories and their strength are linked to psychology. We are more likely to remember something told as a story, including its details and the emotion involved in it, than something told more factually. Your memory of your most humiliating moments are more vivid than those of your happiest memories.
How did Einstein explain the anomalous precession of Mercury's orbit using General Relativity?
Mercury's anomalous precession is when the planet precedes more rapidly in it's elliptical orbit than what was originally predicted by Newton. As we learned in class, a planets precession is when the planets ecliptic shifts slightly over many years, and in the case of Earth, causes different stars to be viewable in the night sky. Einstein's General Relativity states that Gravity is not only spacetime curvature, but that mass and energy warps spacetime, so the greater the mass or energy of an object, the greater it warps spacetime. A planet like Mercury curves spacetime slightly, which needs to be taken into account when calculating its orbit and precession around the sun. Because of this curve to space, its orbit is very slightly shorter (10 km out of 360,000,000 km) which in turn causes its precession to be slightly faster than previously predicted.
List some examples of cultures dividing historical time into a small number of large-scale units (eras, eons, epochs, etc.).
Modern examples include how we split history into B.C. and A.D., or how many historians divide history into classic, medieval, and modern periods.
Will two observers in relative motion agree as to whether any two specified events are simultaneous or not?
No - two observers in relative motion will never agree about the simultaneity of any two events that occur at different distances along the axis defined by their relative motion. As velocities begin to increase, agreeing on the simultaneity of events becomes more difficult and relativity plays a larger role. Two observers in relative motion with speeds close to the speed of light would have major disagreements about whether two events are simultaneous or not. Suppose stationary Earth astronomers agree two supernovas A and B occur simultaneously, both on opposite sides of the celestial sphere. Observers on board a spaceship traveling towards towards A would find that supernova A occurs much earlier than B.
According to Maxwell's equations, does the speed of light depend on the observer's frame of reference or not?
No, in Maxwell's Equations the speed of light is a universal constant that is observed the same from no matter the perspective. This is because light is the fastest anything can travel, so you cannot add a speed to it and subtracting a relatively minuscule speed from it will not change it a noticeable amount.
According to Special Relativity, is it possible for any observer to measure a relative velocity greater than the speed of light for any object?
No, light is the universal "speed limit." Velocity between two objects can never be greater than the speed of light.
If you are swinging back and forth in the direction of the Andromeda galaxy, is it possible for your "simultaneous moment" in Andromeda to be constant throughout? If not, what will be the approximate amount by which your "simultaneous moment" in Andromeda changes between each forward and backward swing?
No, the event cannot occur simultaneously and the swinging forward and backward makes a difference of +2 and -2 days.
If an event happens in State College and another event happens on a plane flying towards or away from (and close to) San Francisco, is it possible for people on campus and on the plane to see the two events as simultaneous? If not, what will be the approximate amount by which the relative timing of the two events differs?
No, the event would be not be seen simultaneously and the time difference is around 10 nanoseconds
After it reaches thermal equilibrium, will the universe still have an arrow of time? Explain.
No. Because the only current condition that dictates the arrow of time is the increase of entropy. But in equilibrium, there can't be an increase in entropy anymore. Equilibrium is the highest state of entropy and you cannot go from a high state of entropy to a low state (cannot be reversible). Once you reach equilibrium, you don't move in entropy.
Regarding the system of balls in a box that was explored in class, explain how the recurrence times for the 20-ball and 50-ball systems can be so much longer than for the 5-ball system, which returns to its initial state roughly every 60 seconds.
On average, a ball switches sides once per second. With random motions we get one attempt every second with 2 sides the ball could be on. We have a 50% chance the ball will be on the left which gives us a 1 in 2^x chance to find all balls on the left. Therefore every additional ball doubles the reassurance time which will make the wait time much longer than 60 seconds. math: with regards to 60 seconds ... 5 to 20 balls: +15 so 2^15 ~ x30,000 20 to 50 balls: +30 so 20^30 ~x1 billion = 36 billion years For 5 balls, in order for them to all be on the same side of the box, each one has to be on a specific side, say left side. Since each ball has a 1/2 chance to be on the left, all five have a change of (1/2)^5 change to all be on the left. However, when we have 20 or 50 balls, the exponent changes from 5 to 20 and 50, which makes the chance exponentially smaller. And a much smaller chance means it takes a much longer time to happen or actualize.
What was Boltzmann's insight into the nature of the "arrow of time?" When is the arrow of time present for a system, and when is it not?
On the "physics-level" time is reversible as the time as dimension vision would suggest. In other words, the Arrow of Time doesn't exist on the "physics-level," since the distinction between moving forward or backward in time seems to be an arbitrary one at this level. On the large-scale, going back to the Big Bang, time is considered irreversible which is consistent with the time as change vision. The Arrow of Time does exist in terms of the Big Bang and development of our universe. There's no Arrow of Time for simple systems or for complex systems once they have reached equilibrium.
What happens to the "velocity addition" rule once the velocities being added or subtracted are a significant fraction of the speed of light?
Once the velocities are a significant fraction of speed of light, they don't follow the simple relative velocity addition i.e. v(ab)=v(a)-v(b) as the relative velocity of an object is given as (u-v)/sqrt(1-uv/c^2) in special relativity. On earth, we generally deal with speeds that are very very small than the speed of light (uv<<c) that is why we get velocity just as u-v. When we calculate the relative velocity when speeds are a significant fraction of speed of light we cannot neglect uv/c^2 term in the denominator and as a result, it changes the relative velocity equation.
What happens to the ticking of clocks that are moving quickly with respect to an observer?
One of the Special Relativity consequences are that clocks in motion are seen to tick slowly. This phenomenon is called time dilation.
Discuss common biases of the brain's "memory editing" process. Is the end result a more consistent or less consistent story? More flattering or less flattering to the self?
Our brain may edit what we remember based on difficult-to-control social and environmental cues that we experienced at the time (ex: we remember most embarrassing memories) Our brain is not a computer, therefore when asked to recall a story, our brain will edit the story so that we re-experience it, which often alters the exact story. Our brain may edit a past memory based on what is happening in the present to explain why we are feeling that way in the present moment.
How does our relativistic universe challenge Presentism?
Our realistic universe challenges Presentism because the relativity of simultaneity in our Universe, via special relativity. Instead, Eternalism is a more natural fit. Relativity postulates that there is no such thing as absolute time and that observers in different reference frames can disagree about which moment is the present moment. If there is no absolute present, then some observer's present moments would not be real, and Presentism breaks.
Is our universe evolving toward a low-entropy or high-entropy state? Explain.
Our universe is evolving towards a state of equilibrium, which entails maximum entropy. In accordance with the second law of thermodynamics, any closed system will increase in entropy over time. It is extremely unlike for entropy to decrease in a closed system. However, equilibrium won't occur for an exceedingly long time, meaning our universe is gradually reaching a state of higher entropy.
Why do we only refer to "spacetime" after Einstein, and not before?
Philosopher Zeno of Citium believed that space and time did not exist because they could not act or be acted upon by matter. He developed a relational view and an absolutist view of space and time. The relational view states that space can only exist as long as it can be related to matter. This would suggest that "empty space" does not exist. The absolutist view suggests that space is independent of matter, where a space has to exist in order for matter to move into it. These principles were manipulated and tweaked by other philosophers for centuries. Before Einstein published his work on special relativity, the universe was thought of as a 3-dimensional structure independent of time. Time is one-dimensional. When time is combined with the 3-dimensional spatial expressions, our universe is now considered 4-dimensional. This is known as space time.
Review the four chief varieties of Christian millenial teachings.
Post-tribulational Premillennialism: there will be a literal and physical reign of Jesus at the second coming. Pre-tribulational (dispensational) Premillennialism: the rapture will occur before the start of the seven-year tribulation period, and the second coming will occur at the end. Postmillenialism: views Christs second coming after the millennium. Amillennialism: rejects belief that Jesus has a physical and literal reign on earth.
Be familiar with Adams & Laughlin's concept of a "cosmological decade" (n).
Primordial Era n < 6 Stelliferous Era 6 < n < 14 Degenerate Era 14 < n < 39 Black Hole Era 39 < n < 100 Dark Era n > 100 nth cosmological decade: all times between 10^ n year and 10^ n+1 years after the Big Bang.
What do psychological studies tell us happens to stories that we tell and retell many times?
Psychological studies tell us that when we tell and retell stories a number of times that social and environmental cues profoundly affect this retelling and since our brain is not a computer and does not store information, it uses these feelings and cues to create an image and story in our mind that we tell in order to justify our need in the present.
What "interesting" events might occur before the nominal "end of time" for our universe? Would any of these events allow anyone or anything to survive?
Right before this point, the universe may experience a "Big Rip" if Dark Energy increases, a "Big Crunch" if Dark Energy weakens, or vacuum decay which would sweep across the universe and obliterate everything, creating new laws of physics. Also, although extremely rarely, a new universe could form.
Give some examples of reversible physical systems.
Simple physical system 5 balls in a box. Takes 60 seconds for all balls to go back to the same side. Less simple physical system 20 balls in a box. Takes 12 day for all balls to go back to the same side. Even less simple physical system 50 balls in a box. Takes 36 million years for all balls to go back to the same side. 5 to 20 balls: +15 so 2^15 ~ x 30,000 20 to 50 balls: +30 so 2^30 ~ x 1 billion
Explain the relevance of the "Presentism vs. Eternalism" debate to the feasibility of time travel.
Since presentism means that only the present moment is real, time travel is impossible given the presentist perspective. It would be impossible to travel to something that doesn't exist/isn't real. Since eternalism means that every moment of time is equally real and existing at the same time, it is at least philosophically possible for time travel given the eternalist perspective. Though possible, we would still need a means of getting to the equally real moment of the past or future, which as of now, remains our biggest unsolved problem.
Explain how curvature of spacetime can explain why planets orbit, instead of "flying off" into space.
Spacetime is warped from single massive objects, like a planet. If another planet is flying in a straight line and it enters the warped spacetime caused by the first massive planet, it will no longer move straight and instead follow the curvature of the massive plane. This creates an orbit rather than the planet just "flying off" into space.
If the experience of time is observer-dependent (as we learn from Special Relativity) then in what sense is the observer-independence of scientific observations preserved?
Special relativity showcases how time is observer-dependent. However, observer-independence of scientific observations is preserved because the idea that "time is observer-dependent" is observer-independent. The idea is observer-independent because because it affects everyone everywhere equally under the laws general relativity.
List some examples of cultures dividing historical time into exactly two units. For each such case, specify whether the earlier epoch is utopian (perfect), superior, or inferior to the present epoch.
Sumerian List of Kinds: divides the world into Pre-Flood and Post-Flood periods The Garden of Eden: divides world into Golden Age and the Fall; the earlier each is superior to the present epoch The bible: the new testament and old testament
Distinguish the synchronic and diachronic visions of an object or person from each other.
Synchronic visions of an object or person are time-frozen, whereas, the diachronic visions are moving-time.
Since "clock time" is subject to effects of relative motion and gravity in relativity theory, what does it mean to say that "all clocks can be synchronized"?
Synchronizing the clocks means that we can manually change the clock times so that the times that each clock shows when an event happens, in all the time frames of each clock, match each other. In other words, we can deliberately turn the clocks faster/slower in order to take into consideration all the things that may affect time (motion, gravity, etc.), so that we can have simultaneity of the same event.
Use an Anthropic Selection argument to explain why we find ourselves living in the "Stelliferous Era," even though only a tiny fraction of the universe's lifetime (from birth to thermal equilibrium) is occupied by this era.
The Anthropic principle is the notion that the observations and theories we form of the universe must be in accordance with the ability to harbor sentient life. An even narrower statement can be made specializing the era of the universe will live in. That is, the properties of the universe must be such to allow for our existence in the Stelliferous Era, where some matter is arranged in stars and planets, and energy is given off by stars. Although the universe has been around and will continue to be around for quite a long time, most of the life of the universe appears to be inhospitable for life. It seems impossible to imagine life could exist at another era in the universe, like shortly after the Big Bang or during the Dark Era. Thus our cosmology must be fit with observations that are made in the Setlliferous Era, since it appears to be the only era that selects for life.
What are the defining beginning and ending times for Adams & Laughlin's "Black Hole Era?" What interesting cosmic events occur during this era?
The Black Hole Era is from cosmological decade 10^39 until 10^100. During this time all matter will be gone from the universe and only black holes will be left. First the small black holes will start to disappear then the larger one will follow until there is no mass remaining anywhere in the universe.
List some examples of ways in which a changing cultural context can lead to alteration of individuals' memories.
The British starving the Irish off their land and later finding out about the prison ships that sent the men elsewhere, sometimes Australia. The orphanages that we thought took care of children and many corpses found buried in Florida. The abuse of kids in foster care in Philadelphia and the overhaul of DHS. In all three, people thought one thing was happening, primarily that they were being cared for, and when the truth came out, it altered the public's mind of our institutions and public service.
What are the defining beginning and ending times for Adams & Laughlin's "Dark Era?" What interesting cosmic events occur during this era?
The Dark Era is all cosmological decades greater than or equal to 10^100. During this time not much happens, there are only elementary particles existing, thermodynamic time has come to an end and space is just an endlessly fluctuating vacuum.
What are the defining beginning and ending times for Adams & Laughlin's "Degenerate Era?" What interesting cosmic events occur during this era?
The Degenerate Era is from cosmological decades 10^14 until 10^39. During this time period high mass stars stars start to explode when the run out of hydrogen and low mass stars expel their outer layer when they run out of hydrogen. The high mass stars may make black holes or neutron stars, and the small mass stars may make white dwarfs.
Explain how adopting an Eternalist perspective might affect one's views of mortality.
The Eternalist perspective includes the nature of time and the viewpoint that all existing time in nature is equal or equally real no matter when it happened. This perspective might affect one's view of mortality because if one thinks that his/her time on Earth is all equally real, they view their future as "already there." This means that they essentially already know their future as being equal to their past and present, which affects how they view their future. There would be no point in planning the future because they already know that it will be equally real.
What are the defining beginning and ending times for Adams & Laughlin's "Primordial Era?" What interesting cosmic events occur during this era?
The Primordial Era is defined as anytime before the the 10^6 cosmological decade. During this time there was the Big Bang and it ended just after the emission of the cosmic microwave background. During this era, plasma fills the universe and fusion reactions form light elements. Plasma cools and transforms into neutral gas and the cosmic microwave background. Cosmic inflation also occurs in this era. The primordial era ends just after the microwave background is emitted.
What are the defining beginning and ending times for Adams & Laughlin's "Stelliferous Era?" What interesting cosmic events occur during this era?
The Stelliferous Era is from cosmological decades 10^6 up until 10^14. During this time period gravity starts to form structures like stars and galaxies throughout the universe. We are also currently living in this era
What is the "arrow of time?"
The arrow of time is the one-way passing of time from the beginning of time, the beginning of our universe when entropy was low, till the end of time, the end of our universe when entropy will be very high. The arrow of time is defined by the second law of thermodynamics stating that entropy increases with time in a closed system. The arrow of time also confirms that it can only be present in complex systems that haven't already reached equilibrium. It cannot be present in a simple system because it tends to be reversible (which the arrow of time cannot be since it is the one-way passing of time). An example of a simple system would be 5 balls in a chamber that has an opening. The 5 balls would easily come back to the side they started on in 60 seconds, which shows reversibility. The arrow of time also could not work with a complex system that has already reached equilibrium because equilibrium is the highest state of entropy, meaning that it cannot get any more disordered. You would need to start at a low entropy state and gain more disorder in order for there to be an arrow of time because you need to move in one direction.
As a spaceship passes by an astronaut at 50% the speed of light, a passenger on the spaceship points a flashlight toward the front of the spaceship and turns it on. What speed does the astronaut outside the spaceship measure for the flashlight's light, relative to the astronaut? What speed does the astronaut measure for the flashlight's light, relative to the passenger on the spaceship?
The astronaut will measure the speed of the light to be c relative to himself and 0.5c relative to the spaceship since he sees the speed of the light to be c and the speed of the spaceship to be 0.5c in the same direction, so the relative velocity of the light would be c-0.5c=0.5c.
What equation defines the equivalence of (and "conversion rate" between) mass and energy?
The equation that relates mass to energy is E = mc^2 This is called mass-energy equivalence and is a consequence of special relativity.
What single observation established the validity of General Relativity and "made Einstein Einstein"?
The first empirical evidence corroborating general relativity came thanks to to observations of Arthur Eddington during a total solar eclipse in 1919. Einstein's relativity predicted that the warping of spacetime by the Sun would cause light from distant stars to deviate slightly and make the stars appear to be in different positions than in the night sky. After photographing the same set of stars during the eclipse and at night, Eddington and his team superimposed the two images and discovered there were indeed discrepancies in the stars' positions, proving the the Sun bends distant starlight as Einstein had predicted.
Present an argument as to why the realization of superhuman machine intelligence might not mean the end of history, even in a human-centered sense.
The interaction between how humans adapt to these new technologies and the transforming society around is historical in nature. This is because it begs the question of will there be a divide between superhumans and "regular humans?" Will there be a split of the two such as one side of half supers and half regulars vs another side made up of the same construct going against each other? The way this scenario will play out will be historical because the timeline of the events, from developing this technology, to living with it, to the possible end of it will be very historical.
Name some challenges with the application of historical laws.
The main problem with applying historical laws is that there are so many variables that influence the context of historical events that their context might be different enough to the point where it may not be valid to apply the laws. In summary: the two events might not be comparable due to the context of each event being too different.
What happens to the measured masses of objects that are moving quickly with respect to an observer?
The measured mass of objects that are moving quickly with respect to an observed will increase with its velocity and will approach infinite mass as relative velocity approaches the speed of light. This is called relativistic mass increase, and it is a consequence of special relativity.
What sorts of memories are most likely to be forgotten?
The memories that are the most likely to be forgotten are those that may seem subjectively mundane in the moment. For instance, if you often have fun and get along with your friends, it is unlikely that you will remember every good time you have had with them. However, if you had a big fight with those friends, it is more likely that you would remember that time because it diverges from what you normally expect out of an interaction with those friends.
After Einstein, why do we often choose to speak of 4D spacetime instead of 3D space + 1D time?
The new image of 4D spacetime was led to by the effects of relativity of simultaneity, length contraction and time dilation. We choose to speak about the 4D spacetime picture instead of the 3D space + 1D time picture because the 4D image provides an essential starting point for Einstein's theory of gravity as spacetime curvature, general relativity.
Using the arguments from the "balls in a box" discussion in class, estimate the recurrence time for a gas box containing 1023 molecules, where at room temperature each molecule loses memory of its position every 1 millisecond or so (10-3 seconds)
The number of gas particles dictates that there are 2^(10^23) possible states for the box. Every 10^-3 seconds, there is a 1/[2^(10^23)] chance that state matches the original low-entropy state. Assuming a Gaussian distribution, it is most likely that such a state will be achieved after all other states have been exhibited exactly once. Thus the recurrence time is 0.001 * 2^(10^23) seconds, 3.17e-11 * 2^(10^23) years, or 2.3e-21 * 2^(10^23) times the current age of the universe. The expression 2^(10^23) cannot be readily expanded by a calculator, as it is 2 multiplied by itself 100 sextillion times (barring a supercomputer's abilities, even if a person were capable of performing one multiplication each second, he/she would not finish until the Degenerate Era).
What does it mean to say that "clock time is reversible"?
The reversibility of clock time suggests that moving forward or backward through time is a relative concept, akin to moving left and right or up and down. The universe does not distinguish between these physical directions, so the reversibility of clock time would similarly imply that movement through clock time is something that the universe doesn't distinguish. In other words, if clock time is reversible, it would mean that our process of going forward through time is not a universal process, but merely a direction we are moving in. Clock time is reversible under the vision of time as a dimension, which is consistent with Newtonian physics.
Is the Second Law of Thermodynamics (entropy of closed systems is always increasing) an absolute law of physics, or not?
The second law of thermodynamics, which suggests that entropy cannot decrease in a closed system over time, is not an absolute physical law. It is a probabilistic law, implying that the decrease of entropy in a closed system over time is extremely unlikely, but not necessarily an impossibility.
According to experimental physicists of the late 19th century, does the speed of light depend on the observer's frame of reference or direction of motion, or not?
The speed of light does not depend on these factors, instead, it is different and does not apply to the velocity rules. The speed of light is a universal constant, and because it is measured the same at all times, all observers will view it the same way as well.
How might the transformation over time of a statue from brightly painted to marble-white be used to argue for the importance of adopting a diachronic perspective even for long-lived objects?
The transformation over time of a statue from brightly painted to marble-white can be used to argue the importance of adopting a diachronic perspective for long-lived objects. For example, the ancient Greek statues were once said to be painted and since these colors have faded, they take away from the purpose that these colors presented. Adopting the diachronic perspective is important because it allows you to understand that even-long lived objects (like statues) have a moving history. The statues history will forever be affected by time, and how humans perceive them based on which time they perceive them (the ancient Greeks viewed the statues differently than we do). Culturally speaking, these statues have been treated (almost unconsciously) as unchanging, which caused people to think of them very differently than their creators intended
What are the two postulates of Einstein's Special Relativity?
The two postulates of Special Relativity are as follows. 1) The laws of physics remain the same in all inertial reference frames moving in uniform motion with respect to each other. 2) The speed of light must be measured to be c with respect to all inertial observers, regardless of the motion of the source. The first postulate should be "only relativity speed, not absolute speed, can be measured. "(Lu Yin)
Explain how tidal forces appear as a feature of warped spacetime.
Tidal forces are an effect of spacetime curvatures that we can actually feel. It deals with the difference in gravity from one side to the other. Because of general relativity, the gravitational effect on the tides is different. Oceans aligned with the moon bulge out whereas oceans at 90 degree angles to the moon are squeezed inward. This makes the ocean rise and fall twice a day, which causes the tides.
What are the two visions of time? Distinguish "time as a dimension" (clock time) from "time as change."
Time is viewed as either a dimension or as change. Time as a dimension was developed under Newtonian physics and suggests that time can be reversible. Similar to how the universe does not distinguish between "left" and "right" or "up" and "down," the universe would also not distinguish between "forward" in time or "backward" in time. Time as change, developed under thermodynamics, suggests that "The Arrow of Time" is not merely subjective, meaning there are objective, meaningful distinctions between going forward or backward in time. Under the vision of time as change, entropy and disorder are always increasing in any complex system.
Did our universe originate in a low-entropy or high-entropy state? Explain.
We definitely know that our universe started out in a very low entropy state, because we see this in the cosmic microwave background., but this is highly unlikely. Thus, many suggest that a multiverse picture may help reconcile this issue. A "parent" universe that may have been in a state of high entropy or equilibrium could have given birth to our universe, potentially solving the issue of how a low entropy universe could have been created.
Is it true that "Every time you scramble an egg, you're doing cosmology"? Why or why not?
Yes. Because each time one scrambles an egg, one is essentially breaking the egg and stirring it so that it becomes more chaotic and random, which resembles the increasing entropy of the universe.
List some ways in which the experience of boredom has evolved over time.
used to be thought of as laziness and a sin due to its social/religious significance now, boredom is trained by society from different types of media fast paced society lead us to need faster paced experiences in order to not get bored this explains the decline in average shot length time over the years