Mysteries of Modern Physics: Time

Course No. 1257
Professor Sean Carroll, Ph.D.
California Institute of Technology
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Course No. 1257
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Course Overview

Time rules our lives. From the rising and setting of the sun to the cycles of nature, the thought processes in our brains, and the biorhythms in our day, nothing so pervades our existence and yet is so difficult to explain. Time seems to be woven into the very fabric of the universe. But why?

Consider these contrasting views of time:

  • A movie of a person diving into a pool has an obvious arrow of time. When the movie is played backward, everyone recognizes that it shows an event that would never occur in the real world.
  • But zoom in on any part of this scene at the atomic scale and the movie can be run backward or forward and be indistinguishable. Either way, the particle interactions are consistent with the laws of physics.

Why does one movie have an arrow of time moving in only one direction and the other does not? Surprisingly, the search for an answer leads through some of the most pioneering fields of physics, including thermodynamics, relativity, quantum theory, and cosmology.

The key concept is called “entropy,” which is related to the second law of thermodynamics, considered by many scientists to be the most secure law in all of physics. The second law has even been compared to Shakespeare’s plays in its importance to the education of a culturally informed person.

But that’s only the beginning, since the quest for the ultimate theory of time draws on such exciting ideas as black holes, cosmic inflation, and dark energy, before closing in on a momentous question that until recently was considered unanswerable: What happened before the big bang?

In 24 riveting half-hour lectures, Mysteries of Modern Physics: Time takes you on a mind-expanding journey through the past, present, and future, guided by Professor Sean Carroll, noted author and Senior Research Associate in Physics at the California Institute of Technology.

Designed for nonscientists as well as those with a background in physics, Mysteries of Modern Physics: Time shows how a feature of the world that we all experience connects us to the instant of the formation of the universe—and possibly to a multiverse that is unimaginably larger and more varied than the known cosmos.

While focusing on physics, Professor Carroll also examines philosophical views on time, how we perceive and misperceive time, the workings of memory, and serious proposals for time travel, as well as imaginative ways that time has been disrupted in fiction.

Clues to the Origin of Time

Break an egg. Melt an ice cube. Mix coffee and cream. Each starts with an ordered state and ends with one that is much more disorderly. Each is an example of an increase in entropy, which is a measure of the degree of disorder in a closed system. The entropy of the universe was lower in the past; it will be higher in the future. Increasing entropy defines the arrow of time, implying that at the beginning of the universe entropy must have been extraordinarily low. This course seeks to understand why.

Professor Carroll begins like a detective by gathering the facts. What do we know about time, what characterizes it, and how do we measure it? Then he combs the universe for clues, from the contrasting views on time of Isaac Newton and Albert Einstein, to Rudolf Clausius’s invention of the concept of entropy and Ludwig Boltzmann’s brilliant insight about why entropy increases and therefore why time proceeds from past to future.

You explore Boltzmann’s statistical explanation for the nature of time, and you see how, carried to its logical conclusion, it leads to a bizarre scenario called Boltzmann brains. You look at another curious thought experiment, called Maxwell’s demon, which helps explain the presence of order and life in a universe of relentlessly increasing disorder.

In the course of these inquiries, you consider time from many perspectives, including these:

  • A dimension with a difference: Time is the fourth dimension. But unlike the three dimensions that constitute space, time can’t be explored randomly from point to point. You just experience it sequentially second after second. This continuous flow from past to future is the arrow of time.
  • The view from “nowhen”: The present moment seems real in a way that the past and future do not. But to better understand why time and the universe are the way they are, it’s useful to view all moments—past, present, and future—as equally real. This is the view from “nowhen.”
  • Quantum time: Some phenomena at the quantum scale are not reversible with respect to time—unlike all other processes in fundamental physics. Could these events be the origin of the arrow of time? Could they explain why we remember the past but not the future?

You also investigate the past hypothesis, which assumes that atomic theory and fundamental physics cannot account for the difference between the past and the future by themselves. Instead, the arrow of time can only be explained by the initial conditions that gave birth to the universe itself. Which brings you to the big bang, one of the major focuses of this course.

Time to Get This Course

Your time-traveling adventures also include excursions into fiction and film, which Professor Carroll engages with characteristic enthusiasm and wit. While storytellers are seldom concerned with getting the physics right, it’s instructive how they usually get it very wrong:

  • Stopping time: Stories that stop time as the hero moves through a stationary world fail to consider that no one could function in such an environment. Air would be as immovable as a brick wall. Light and sound would stop. No plot would be possible!
  • Time going backward: A character who experiences the arrow of time in reverse faces grave difficulties relating to another character going through time the normal way. They would be like travelers on the highway going in opposite directions.
  • Time travel: Fictional time travelers typically dematerialize and then rematerialize at a different point in time. But real time travel, if it were possible, could not skip over the intervening part of spacetime. Real time travel would be a journey through spacetime.

In the time that has passed since you started reading this, the entropy of the universe has increased. The future of a few moments ago is now the present. You are at a different point in spacetime, even if you haven’t moved from your chair. “What is time?” asked Saint Augustine 1,600 years ago. “If no one asks me, I know. But if I wish to explain it to someone who asks, I know not.” With Mysteries of Modern Physics: Time, you will be much closer to an answer.

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24 lectures
 |  Average 30 minutes each
  • 1
    Why Time Is a Mystery
    Begin your study of the physics of time with these questions: What is a clock? What does it mean to say that “time passes”? What is the “arrow of time”? Then look at the concept of entropy and how it holds the key to the one-way direction of time in our universe. x
  • 2
    What Is Time?
    Approach time from a philosophical perspective. “Presentism” holds that the past and future are not real; only the present moment is real. However, the laws of physics appear to support “eternalism”—the view that all of the moments in the history of the universe are equally real. x
  • 3
    Keeping Time
    How do we measure the passage of time? Discover that practical concerns have driven the search for more and more accurate clocks. In the 18th century, the problem of determining longitude was solved with a timepiece of unprecedented accuracy. Today’s GPS navigation units rely on clocks accurate to a billionth of a second. x
  • 4
    Time’s Arrow
    Embark on the quest that will occupy the rest of the course: Why is there an arrow of time? Explore how memory and aging orient us in time. Then look at irreversible processes, such as an egg breaking or ice melting. These capture the essence of the one-way direction of time. x
  • 5
    The Second Law of Thermodynamics
    Trace the history of the second law of thermodynamics, considered by many physicists to be the one law of physics most likely to survive unaltered for the next thousand years. The second law says that entropy—the degree of disorder in a closed system—only increases or stays the same. x
  • 6
    Reversibility and the Laws of Physics
    Isaac Newton’s laws of physics are fully reversible; particles can move forward or backward in time without any inconsistency. But this is not our experience in the world, where the arrow of time is fundamentally connected to irreversible processes and the increase in entropy. x
  • 7
    Time Reversal in Particle Physics
    Explore advances in physics since Newton’s time that reveal exceptions to the rule that interactions between moving particles are fully reversible. Could irreversible reactions between elementary particles explain the arrow of time? Weigh the evidence for and against this view. x
  • 8
    Time in Quantum Mechanics
    Quantum mechanics is the most precise theory ever invented, yet it leads to startling interpretations of the nature of reality. Probe a quantum state called the collapse of the wave function that may underlie the arrow of time. Are the indications that it shows irreversibility real or only illusory? x
  • 9
    Entropy and Counting
    After establishing in previous lectures that the arrow of time must be due to entropy, begin a deep exploration of this phenomenon. In the 1870s, physicist Ludwig Boltzmann proposed a definition of entropy that explains why it increases toward the future. Analyze this idea in detail. x
  • 10
    Playing with Entropy
    Sharpen your understanding of entropy by examining different macroscopic systems and asking, which has higher entropy and which has lower entropy? Also evaluate James Clerk Maxwell’s famous thought experiment about a demon who seemingly defies the principle that entropy always increases. x
  • 11
    The Past Hypothesis
    Boltzmann explains why entropy will be larger in the future, but he doesn’t show why it was smaller in the past. Learn that physics can’t account for this difference except by assuming that the universe started in a state of very low entropy. This assumption is called the past hypothesis. x
  • 12
    Memory, Causality, and Action
    Can physics shed light on human aspects of the arrow of time such as memory, cause and effect, and free will? Learn that everyday features of experience that you take for granted trace back to the low entropy state of the universe at the big bang, 13.7 billion years ago. x
  • 13
    Boltzmann Brains
    One possible explanation for order in the universe is that it is a random fluctuation from a disordered state. Could the entire universe be one such fluctuation, now in the process of returning to disorder? Investigate a scenario called “Boltzmann brains” that suggests not. x
  • 14
    Complexity and Life
    Discover that Maxwell’s demon from lecture 10 provides the key to understanding how complexity and life can exist in a universe in which entropy is increasing. Consider how life is not only compatible with, but is an outgrowth of, the second law of thermodynamics and the arrow of time. x
  • 15
    The Perception of Time
    Turn to the way humans perceive time, which can vary greatly from clock time. In particular, focus on experiments that shed light on our time sense. For example, tests show that even though we think we perceive the present moment, we actually live 80 milliseconds in the past. x
  • 16
    Memory and Consciousness
    Remembering the past and projecting into the future are crucial for human consciousness, as shown by cases where these faculties are impaired. Investigate what happens in the brain when we remember, exploring different kinds of memory and the phenomena of false memories and false forgetting. x
  • 17
    Time and Relativity
    According to Einstein’s special theory of relativity, there is no such thing as a moment in time spread throughout the universe. Instead, time is one of four dimensions in spacetime. Learn how this “relative” view of time is usefully diagramed with light cones, representing the past and future. x
  • 18
    Curved Spacetime and Black Holes
    By developing a general theory of relativity incorporating gravity, Einstein launched a revolution in our understanding of the universe. Trace how his idea that gravity results from the warping of spacetime led to the discovery of black holes and the big bang. x
  • 19
    Time Travel
    Use a simple analogy to understand how a time machine might work. Unlike movie scenarios featuring dematerializing and rematerializing, a real time machine would be a spaceship that moves through all the intervening points between two locations in spacetime. Also explore paradoxes of time travel. x
  • 20
    Black Hole Entropy
    Stephen Hawking showed that black holes emit radiation and therefore have entropy. Since the entropy in the universe today is overwhelmingly in the form of black holes and there were no black holes in the early universe, entropy must have been much lower in the deep past. x
  • 21
    Evolution of the Universe
    Follow the history of the universe from just after the big bang to the far future, when the universe will consist of virtually empty space at maximum entropy. Learn what is well founded and what is less certain about this picture of a universe winding down. x
  • 22
    The Big Bang
    Explore three different ways of thinking about the big bang—as the actual beginning of the universe; as a “bounce” from a symmetric version of the universe on the other side of the big bang; and as a region that underwent inflationary expansion in a much larger multiverse. x
  • 23
    The Multiverse
    Dig deeper into the possibility that the big bang originated in a multiverse, which provides a plausible explanation for why entropy was low at the big bang, giving rise to the arrow of time. But is this theory and the related idea of an anthropic principle legitimate science or science fiction? x
  • 24
    Approaches to the Arrow of Time
    Use what you have learned in the course to investigate a range of different possibilities that explain the origin of time in the universe. Professor Carroll closes by presenting one of his favorite theories and noting how much remains to be done before conclusively solving the mystery of time. x

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Your professor

Sean Carroll

About Your Professor

Sean Carroll, Ph.D.
California Institute of Technology
Professor Sean Carroll is a Senior Research Associate in Physics at the California Institute of Technology. He earned his undergraduate degree from Villanova University and his Ph.D. in Astrophysics from Harvard in 1993. Before arriving at Caltech, Professor Carroll taught in the Physics Department and the Enrico Fermi Institute at the University of Chicago, and did postdoctoral research at the Massachusetts Institute of...
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Mysteries of Modern Physics: Time is rated 4.1 out of 5 by 118.
Rated 5 out of 5 by from Good title - encourages I'm still listening to this and am very pleased. I find the lecturer's voice pleasing & easy to understand. I have had other GC courses that were not so appealing. I will continue to study through the Great Courses, as I have been doing for about 10 years already.
Date published: 2017-04-20
Rated 5 out of 5 by from Engaging, Very interesting. The professor speaks quickly and very clearly. A lot of material gets covered. He presents a complicated subject in an easy to understand way.
Date published: 2017-04-20
Rated 4 out of 5 by from Its Strengths May Not Be Where You'd Like I watched this entire course and I've read a number of other reviews which raise various criticisms, some of which I'd also endorse. But I'll start by saying I am glad I bought the course and glad I spent the time viewing it. Let's start with the lecturer. Sean Carroll is one of the better lecturers I've watched in The Great Courses. Of course they try to select excellent lecturers for all their courses but as some people know, teaching well is really hard work. Being both an expert in your field AND a great teacher is even harder. Carroll is polished, professional, well-modulated, clear in enunciation, sometimes humorous, and well-paced. I've watched two other courses produced by him, both of which I liked better than this one. The problem perhaps is this subject matter. Yes, you could shorten the length without sacrificing anything important. I get the feeling some of these half-hours were added just to end up with 24, though whose agenda that was or why, I'm not sure. The first 3 in particular could be skipped over, and a few other later ones as well. What's good about the course is that it reviews a number of somewhat "interdisciplinary" topics, which for some may be their very first presentation and for others, perhaps the first time they see them as perhaps so connected: particle physics, quantum mechanics, relativity theory, cosmology and yes (sigh) complexity, information theory and thermodynamics. Ultimately it's this last part I found most disappointing. Spoiler: Carroll's final explanation is that it is entropy which drives the directionality of time. I ended the course still believing that this is somehow putting the cart in front of the horse and that it's the directionality of time which plays a causal role in entropy. I ended up believing that modern physics still does not have a proper understanding of the asymmetry or "directional arrow" of time, and perhaps this still awaits another fundamental revolution in our understanding. In the meantime it's a pretty nice if perhaps overly-long and sometimes meandering survey of ideas in modern physics.
Date published: 2017-03-11
Rated 5 out of 5 by from I listen every morning during a 30 minute exercise bike ride. Feel vastly informed on a usually difficult subject. Wonderful!
Date published: 2017-03-08
Rated 4 out of 5 by from Mysteries of Modern Physics - Time The subject matter is fascinating and the lecturer, Sean Carroll, is very good. His explanations are straightforward and comprehensible without talking down to the listener. It is a very enjoyable and worthwhile course. I have one issue, however, and that is the Teaching Company does not make much good use of the graphic possibilities of the DVD medium. Instead of helpful video clips or charts or graphs, you get static photos, whooshing boxes and a lot of hocus pocus. Which is a shame because physics in general, and time and cosmology in particular, could benefit from good graphic presentations.
Date published: 2017-01-22
Rated 4 out of 5 by from Does Anybody Know What Time It Is.... This is a topic I have been interested in; however this stretched my mental capacity. The professor talks about many topics that I never thought about and many that I didn't get. I am not sure the information will be appreciated by the AVERAGE participant but if you are up for the challenge than try it. I tell people about it but dont want to recommend it for fear they wouldnt enjoy it.
Date published: 2017-01-17
Rated 4 out of 5 by from Good Presentation of an Ambiguous Topic The problem with courses like this this is that they have to keep the mathematics at such a low level to get a wide audience, a lot of what is going on is left unexplored. This is not the fault of the instructor, but rather the constraints placed upon him. The second law of thermodynamics, which dominates the course, is really a mathematical idea. Not being able to use differential equations, probability theory, etc. to help explain it is a significant impediment. That having been said, this is a good example of a course on "popular" physics, For those wanting to get a brief introduction to some of the main ideas about time, this is a good course.
Date published: 2016-10-06
Rated 5 out of 5 by from THERMODYNAMICS, COSMOLOGY, PHILOSOPHY, ETC. This is a course in Physics and Philosophy plus…small change (biology, medicine, psychology as well as the most up-to-date branches of these latter disciplines such as brain science and neural science). The physics is mainly thermodynamics and cosmology. My personal opinion is that one can absorb the course reasonably well (I couldn’t absorb it fully) and appreciate what is being said to some large degree (I couldn’t appreciate it in its entirety), i.e., one can understand the significance of the points being made, only if one has a good knowledge of, at the very least advanced high-school if not first year university, physics. For instance, one cannot appreciate how profound the message of lectures 7 and 8 is—however brilliant the lecturing might be—unless one is acquainted with the issues, i.e., topics in particle physics and quantum mechanics. Prior knowledge of philosophy (assuming there exists such a thing), better still, familiarity with the history of philosophical thought and with some of the philosophical debates would also make it easier in places to appreciate what the argument is about. Nevertheless, in my view, such prior knowledge is not essential unless one wants to assess how innovative or radical Carroll’s story is…or whether it is just a monstrous oversimplification. One’s first task should be, however, to understand Carroll’s story, to realize “what’s the big deal”, even as his excellent teaching skills make it relatively easy to follow the lectures. Carroll’s style represents the polar opposite to say Martin Heidegger’s writings which seem so impenetrable to the layman, to give an unrelated (though, come to think about it, Heidegger too is concerned with “time”!) and rather distant example which just came to mind... Prof. Carroll tries to fill-in the likely missing detail of required prior knowledge, and he is quite successful in relation to thermodynamics. It seems to me that, as far as thermodynamics is concerned, Carroll provides meaningful teaching: we can learn rather than (as elsewhere in this series of lectures) listen to, let’s call them, “unilateral announcements”, which we have , so to speak, to swallow without, however, really being able to munch. Having watched Prof. Grossmann’s “Thermodynamics” Great Course, some months ago, not to mention the fact that I have repeatedly watched Prof. Wolfson’s Great Courses on “Physics and our Universe” PLUS “Physics in our Life”, I found Prof. Carroll’s extensive elaboration of the concept of entropy quite illuminating. I still doubt, however, that somebody who has never been exposed to this concept before, stands a chance of reasonably comprehending the basic thesis of Carroll’s “Time”. In addition, I felt that more time and effort should have been devoted to explicating the significance of entropy in cosmology. Some explanation was given (mainly in connection with black holes) but my impression was that many logical steps that would normally occur in a fuller analysis had to be left out. They are probably too difficult, but the link between entropy and cosmology is central to Carroll’s argument. Finally, the brief exposition of relativity theory in these DVDs is, in my view, only suitable for viewers already acquainted with the concepts. It is not enough to constitute a primer. True, there are other Great Courses about relativity. By contrast, in my view, it is not impossible for somebody without any cosmology to follow “Time”: Prof. Carroll does provide a primer in cosmology in the course of these lectures. Given that the issues into which the lectures delve are absolutely profound and mind-boggling par excellence, as I was watching Carroll I realized what a great orator he is (for one thing he doesn’t read from, or even possess, notes!), how powerful and highly intelligent his speech is, and what great vitality and wit characterize his argumentation. It is a miracle (for which his science-popularizing supernatural abilities must take full credit) that Carroll manages to create a coherent account out of all this without creating a colossal muddle. The account is, I reckon, a la carte. Different viewers are likely to attain different levels of comprehension but provided one has some physics one would never drop-out. A feature of this Great Course, which may or may not appear convenient, is that “Time” can be viewed from beginning to end during a relatively brief…time period, e.g., over the course one week. This is because the additional information conveyed to someone who can already handle the physics, is not so much dense or rich (i.e., is not characterized by “complexity” according to the Kolmogorov definition Carroll cites!) as much as it is composed of numerous bits all of which, however, link comfortably together to build a single big argument about what “time” is. All in all, the course presents a challenge but is not overambitious or worse unrealistic. I think I managed to understand what Carroll’s message was 75% of the time in this course compared with a “personal absorption rate” close to 90% when viewing one of Carroll’s other courses, “Dark Matter, Dark Energy”. Even with only 75% of the total prize, I feel pretty pleased with myself and believe that my general knowledge and my understanding of physics have been significantly promoted—thank you Professor Carroll!
Date published: 2016-09-09
Rated 4 out of 5 by from Quickly went over my head. Especially went the started covering Quantum Physics and the Arrow of Time. Did find the English search for the timepiece that could be accurate anywhere in the world to be very interesting.
Date published: 2016-09-08
Rated 5 out of 5 by from Comprehensive Coverage of Time Wow! I never thought it would take 24 lectures to cover this topic - but I was wrong. Dr. Carroll's clear and comprehensive description of entropy gave me the clearest understanding of this topic. The arrow of time lectures spelled out this concept with clarity. Dr. Carroll often ventured into side stories which gave a human element to what could have otherwise been sterile facts. I have purchased other courses presented by Dr. Carroll in the past - he is a brilliant man who knows how to perfectly present complex topics in an understandable manner.
Date published: 2016-09-04
Rated 5 out of 5 by from Time I really enjoyed this course. Professor Carroll was very knowledgeable and I was able to understand the concepts he was trying to get across.
Date published: 2016-07-24
Rated 5 out of 5 by from Fabulous Lecture Series I'm a bit biased because I thought Sean Carroll was one of the best explicators of modern physics prior to purchasing this course. He does a wonderful job of explaining some of the essential ideas - entropy, the 2nd law, reversibility - underlying the notion of the arrow of time while also tackling much more esoteric topics like Boltzmann brains and Kolmogorov complexity. Professor Carroll's explanations are clear and thorough. He finds the right balance between sophistication and approachability. It's a challenging but worthwhile journey into one of the most fascinating puzzles of physics. Highly recommended.
Date published: 2016-07-13
Rated 5 out of 5 by from Enthusiasm Meets Expertise Prof. Ressler is a very close second-best of your lecturers I have encountered. His blend of enthusiasm, light humor and his ability to make technical material clear to the layman all work together to make his courses interesting, and to make one happy to be learning.
Date published: 2016-07-06
Rated 5 out of 5 by from great course Really fantastic course, especially worth listening to his theory on the the 2d law of thermodynamics and the origin of life on earth. Blink and you'll miss it. It's a little repetitive but complicated ideas so nice to have the reinforcement.
Date published: 2015-09-26
Rated 3 out of 5 by from The Arrow of Time Not Well Spent This is a case of an inherently interesting subject delivered in a mind numbingly monotonous and uninteresting manner. Professor Carroll is highly qualified and fully engaged but he seems to have missed his target audience. Perhaps if I were smarter I would have been carried away, but in the event I was just anesthetized into a comfortable sleep, which was not without value. I made my way through 15 of the lectures but couldn't hang in there any longer.
Date published: 2015-07-29
Rated 4 out of 5 by from Wow ! Food for the brain. The key word in the title is "Mysteries". If you are looking for a simple explanation of "time" this course will not give it to you. What it will give you is a lot of intriguing hypotheses, theories, and concepts. I can see some validity in some of the lower ratings given to this course. However, Professor Carroll provides a through discussion of time from the history of calendars (including leap seconds , leap months, leap years), to the thoughts of ancient philosophers, to concepts presented by the deepest thinkers of the modern world. I think that completeness, even though some of it is rather simple, enhances the course. You do not have to be told the Earth rotates around the Sun about every 365 days; however, those comments lead into something else to help make a point. If you have no background in college physics/math/thermodynamics this course may be a challenge. However, I still recommend the course because Professor Carroll makes every attempt to put advanced physics into terms none physicists can understand. My one complaint is the Guidebook does not have a glossary of important terms and no biographical sketches of the people mentioned in the lectures.
Date published: 2015-07-03
Rated 3 out of 5 by from Unanswered questions I gave the course a higher value because it got me interested and fascinated by cosmology. I gave the course lower marks because I found that Professor Carroll made many conclusions unsupported by the information he presented. He talked about the universe being created from nothing and then went on to explain what that meant in effect claiming what amounted to gibberish. Early on when he first discussed the meaning of entropy, he pointed out that it increased as the number of particles in a given volume increase. In a much later lesson he claims that an empty universe would have maximum entropy. He claims that most of the entropy of the universe is in black holes. My question unanswered in the course is, if the matter in a black whole is being attracted towards a singularity why wouldn't the entropy be decreasing? I would not recommend the course because the questions raised for me were unanswered by the presentation.
Date published: 2015-06-14
Rated 5 out of 5 by from Entropy was lower in the past A really good course where you will learn a lot. easy to understand. Sean is always engaging and enjoyable to listen to. does a great job educating on a fascinating topic. if you learn nothing else you Will know by the end of the course that entropy was lower in the past and increases towards the future (because he says so over 8 million times). for a course about time im very very surprised he had nothing to say about time theories A and B. there was one lecture more about neuroscience and psychology which didnt need to be there. overall it was grt and i would recommend people watch it.
Date published: 2015-02-12
Rated 5 out of 5 by from Well worth the Time I would recommend video format but not essential. It takes a historical approach. Each lecture building on the prior lecture. Some people were tired of hearing about entropy but then this was the key to the arrow of time- question that is raised was why is entropy lower in the past. I appreciated that he was clear when he was speculating on these issues. This is not an easy course, however. One's background is important. It does not have that much math. If you wonder how I can rate each part at 4 stars but give it a five star overall, it is because the sum is greater than the parts. If you have an interest in this topic, it is well worth the time.
Date published: 2015-01-10
Rated 5 out of 5 by from Time is Common to Us All. Understanding is Not. This is the second of Professor Carroll's lecture series I have enjoyed. Luckily, it happened that I didn't read the reviews before I viewed the course. Had I done so, I might have missed a remarkably valuable experience. I believe the simplicity of the title and the sophistication of the concept could combine to mislead a naïve learner, and could lead to the misunderstandings I see reflected in the reviews. His use of thermodynamics is masterful. I'm not a thermodynamicist, but I have taken a few courses at various undergraduate and graduate levels in that field many moons ago. The parts that he presented with which I was familiar were spot on. Those parts that were unfamiliar to me check out with other lecturers and readings. There may be some misunderstandings due to the fact that the Great Courses company does not require prerequisites of its students and strives to make the topics approachable by every level of learner. I believe that they succeeded with this course, but it did press the boundaries. To those reviewers who believed that the topic introduced philosophical irrelevancies, I ask you to consider his defintion of “now” as the bright, dividing line between 13 Billion years of the past and an unguessable duration of our future. That line divides what is changeable and yet to be determined from what is done and locked into the books forever. This alone brings in epistemology, causality, and tests the limits of your belief in free will. And to those reviewers who believe he spent too much or too little time on entropy, and the time implications of the second law, I would humbly disagree. These concepts are sophisticated, with subtleties that can bemuse those new to the ideas. As one who has tried to explain entropy to others, I am envious of his skills. In short, I loved this course. It occupies a valuable space on my shelves, and I will view it again in the future.
Date published: 2014-12-30
Rated 4 out of 5 by from The Mysterious 4th Dimension This course provides a deep conceptual explanation of the nature of Time. The student who tackles this course should not expect a simple answer that explains what time is. Furthermore, be prepared for the fact that the passage of time is not invariant as at relativistic velocities time dilates. Dr. Carroll demonstrates that the "arrow of time" is a result of the tendency to move toward states of higher entropy according to the Second Law of Thermodynamics. He devotes a considerable amount of lecture time showing how the universe started from a very low entropy state with entropy increasing, and hence time moving forward, ever since. How and why the universe had such low entropy to begin with largely remains a mystery even as the course concludes. Along the way of this intellectual journey, Dr. Carroll delves into things like memory, origins of life, aging and the perception of time. These are interesting but are also a bit meandering off the path of explaining the physics of time. He also introduces theoretical concepts like the multiverse and "bubble" origins for the universe which are topical in cosmology but not particularly relevant to the topic of time. (Though wormholes and time travel do fit within the course context.) If these excursions are understood to be such in following the course, one will be satisfied later as Dr. Carroll returns to the physics in the last several lectures. All in all, I found the course fascinating. But I do have a Ph.D. in physics, albeit from 35+yrs ago, not in cosmology, and without having worked as a research physicist for the bulk of the intervening time. Nevertheless, with an educational background in physics I found Dr. Carroll's lectures easy to follow as they were non-mathematical, conceptual and, at times, philosophical in nature. Without a basic understanding of concepts of physics (e.g. classical mechanics, quantum physics, relativity, and thermodynamics) I can imagine that this course will be harder to follow. Note: an in-depth math background is not needed. The production quality of this course is excellent with many animated graphics used to illustrate concepts. For this reason, I would definitely recommend the video version. Dr. Carroll is an articulate speaker who maintains a steady pace, uses good inflection and body language, and never uses non-words (e.g. "aah"). He clearly can explain things at multiple levels of abstraction and is comfortable speaking to a lay audience. Comparing his style to other outreach speakers in cosmology/astrophysics, such as Noel DeGrasse Tyson or Brian Greene, I would characterize Dr. Carroll as less theatrical, equally as articulate, and deeper conceptually. The accompanying course guidebook is OK, but not great. The lecture summaries are fine and contain a slightly above average number of illustrations. A bibliography is included. A glaring omission is a glossary which every technical course should include. For those of us who have a science background, an appendix with the appropriate mathematics for the physics would have been a nice addition (see M. Whittle's course recommended below for a good example of this). I would definitely recommend this to anyone who is interested in the physics and philosophy of time.
Date published: 2014-12-28
Rated 5 out of 5 by from Superb Carroll is an excellent speaker and this is a deeply fascinating topic. Additionally, Carroll's brief digressions into philosophy and psychology are nice touches. This course is essentially and audio version of his book, "From Eternity to Here", which is also excellent. I thoroughly enjoyed both.
Date published: 2014-12-22
Rated 5 out of 5 by from A transformative course. Although non-mathematical, this course operates at a very high level of abstraction. It is physics and cosmology at the border of philosophy. What I found so impressive is that Dr. Carroll was able to unify a vast body of physics and cosmology through his central theme of the arrow of time. For the first time, I was able to gain an inkling, as a non-scientist, of how the main strands of modern physics (general relativity, quantum theory, thermodynamics) interrelate. Through his fairly brief discussion of brain chemistry and the psychology of perception, Dr. Carroll was able to show the connections between this fundamental physics and our daily lives. Our memories, our thoughts, our perceptions of ourselves depend on the arrow of time. And the arrow of time results from the Second Law of Thermodynamics. The central question Dr. Carroll tries to answer is why time always moves forward when, under the symmetries of the laws of physics, it can equally well run backward. His speculation is that this is the result of an eternal increase in entropy caused by cosmic inflation. He builds his argument painstakingly over the course of the lectures. Only at the close of the last lecture do you fully see where he has been leading. I felt vastly rewarded that I could actually understand a good part of such a complex speculation. I have two criticisms of the course. First, Dr. Carroll speaks too quickly. Maybe this is because he has so many difficult and subtle ideas to present. I found it necessary to listen to many of his more difficult points several times before I could even begin to grasp them. Second, I disagree with his concept of what consciousness is. He says that consciousness depends on self-recognition, awareness of alternative futures, and symbolic thought. This is true of higher human thought, but there is a more basic level of consciousness probably shared by all forms of life and maybe even inanimate particles, which involves only sensation. But these are quibbles. If you are perplexed by the passage of time and your place in the vast and evolving universe, this course is indispensable.
Date published: 2014-12-05
Rated 5 out of 5 by from Must have Outstanding course. You will not be disappointed!!
Date published: 2014-11-01
Rated 2 out of 5 by from Interesting topic but . . . didn't know much more about it than I did before taking the course. I had high expectations upon seeing this course offered but learned less than any other course taken.
Date published: 2014-09-22
Rated 1 out of 5 by from Mysteries of modern physics:Time This course was advertised in Time Magazine On DVD for $69.95. Whats up?
Date published: 2014-07-03
Rated 1 out of 5 by from Mysteries of modern physics This course could be described as someone talking a lot but not saying anything particularly relevant to the subject matter. The professor spends a lot of time jumping from subject to subject without connecting the dots. Mercifully, the course is only 24 lectures long. Of the 75 or so courses I have listened to, this is the first I found to be completely worthless. Future physicists will no doubt have a good laugh listening to this course and professor. So, save your CD’s; they might be worth something next century.
Date published: 2014-06-13
Rated 5 out of 5 by from Superb treatment of very deep material I found Prof. Carroll's course excellent, though it may be a bit too deep for listeners without some college-level physics or general science. He covers thoroughly, clearly and quite engagingly the idea of time, which is, as the course points out, quite hard to define. The course covers time, thermodynamics, entropy, special and general relativity, cosmology, the Big Bang, black holes and more, all in the quest to explain the arrow of time and the nature of time. I enjoyed every lecture and found the overall course very satisfying. I have enjoyed many TC science courses on DVD but generally listen when I'm driving to I bought the CD version of this course. I was a little concerned that the audio version might not work well for this deep and complex material, but it was great. I find Prof. Carroll quite engaging and easy to listen to as a lecturer. His enjoyment of the material comes across in every sentence.
Date published: 2014-06-03
Rated 4 out of 5 by from Maybe It's me. This was a challenging and fascinating course. Dr. Carroll is obviously extraordinarily bright and articulate. I like his conversational and somewhat informal style. That being said, I have a sense of frustration at the completion of the course that I did not understand much of what he was getting at, and don’t have a satisfying or deep grasp of time that is much different from before i sat the course. there are several possibilities for this i’d like to enumerate: 1. He talks too fast, and often does not adequately define a term or concept. for example why time is reversible at a subatomic level. if there is a collision in an accelerator and a particle is split into two particle and energy is released, can you really conceive of playing the movie backwards and having it look perfectly “natural?” I don’t think he explained adequately how it can be said that time is reversible—or did i miss it? 2. my physics education pretty much stopped at newtonian mechanics. maybe bright young people today are better grounded in quantum mechanics and relativity, and i just haven’t caught up with new physics. I have, however, taken courses from The Great Courses in relativity, cosmology, sub-atomic particles, and chaos theory, so i have some background. I do not recall feeling quite this lost in those courses. 3. similarly, maybe i am too old, at 65, to really grasp or envision things outside of the realm of my human experience as so often seemed necessary during this course. i have a real hard time conceiving of dimensions beyond 4—and I am not even sure i have a good feel for space-time (especially insofar as its being curved or flat). i have a hard time conceiving of any number larger than Avogadro’s or smaller than pico- or femto- stuff. 4. maybe the stuff gets clearer when one is, upon repetition, more facile with the terminologies. I remember feeling this way in the first year of medical school. I may re-sit the course in a year or so. 5. maybe my IQ is just 10-15 points shy of grasping all this. 6. maybe he has not tried hard enough to make this understandable to people outside his field. 7. And...he said this a time or two, and i think it’s important: “maybe that is just the way it is.” Don’t we ultimately have to stop asking “why" at some point? (or is that anti-intellectual? ) “time goes on.” “entropy always increases” ("there are more configurations possible in high entropy than there are in low entropy,” “matter exists” “we remember the past, and not the future"—maybe it is just counterproductive or impossible to ask why things like these are true. some of them seem true by definition—particularly that we recall the past.
Date published: 2014-06-01
Rated 5 out of 5 by from Only for science freaks like me This course given be master prof is a must for science freaks. But not for beginners. It will scare to death any beginner in science knowledge.
Date published: 2014-03-13
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