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The Mind-Bending Physics of String Theory

Take a wild ride with a noted expert through extra dimensions, black holes, inflating universes, and other marvels of string theory.
The Mind-Bending Physics of String Theory is rated 2.7 out of 5 by 26.
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Rated 2 out of 5 by from Well, it could have used a mediator The professor seems very knowledgeable and references many people and ideas throughout that seem to come out of nowhere. The graphics really make zero sense. The idea of making the area of a blackhole's event horizon account for the entropy is a bit strained. Information is lost going into a black hole and you can't write it on the event horizon or explain it away by holograms. String theory used to be about strings with different wavelengths functioning in space or as the fields in field theory. Now they are relegated to the dust bin in favor of branes and many dimensions. I think some people have really gone down a rabbit hole here. It's not useless as we need mind-thought experiments; but I'd really like some experiment to point the way somewhere. This is a sticky subject to me (Strings) as I was watching Brian Greene's video when I heard of my father's death in 2005. This is unrelatable to that presentation. This presentation needs some kind of mediator to explain where these ideas are coming from and where they are leading. This professor is not clearly doing his job in explaining this subject matter. Well, it's OK; I'm just running through these fast as I am just trying to gain some kind of picture in what is being presented and the current thought. It's still interesting and it goes off on tangents but that's OK. It's science (or mathematical philosophy).
Date published: 2024-05-31
Rated 1 out of 5 by from Incomprehensible Unless you are a student of particle physics or theoretical physics you will be totally lost by the third lecture.
Date published: 2024-02-18
Rated 2 out of 5 by from Hard to understand. I have bought several courses from greatcourses but this is not one of your best. The presentation is poor. The professor has a speaking problem. I will explain. He speaks very fast, like he is reading from a teleprompter. He starts out fast and full of energy and by the time he gets to the last two words of a sentence, he runs out of breath. I never get the whole sentence. I have asked others to listen and they felt the same way. A perfect example of course presentation, especially this course, should be like Ron Davis Jr., Don Lincoln and Sean Carroll. They are really good and I have several of their courses. It seems like GC has change their style and the professor is sitting and not standing.
Date published: 2024-02-14
Rated 1 out of 5 by from Incomprehensible This professor is a black hole. No information escapes him that I was able to snatch. An alternative possibility is that he is a mathematician, masquerading as a physicist. I did not learn anything new from him, what I knew before I still know, nothing new from listening dilligently to this entire course. My background is a Ph.D. in physics, as is the background of my spouse. Our background is not high energy physics. Still I expect to get something from listening to a physics course. Consider the first lecture. He threw some buzzwords around then ended with Planck’s scale. He gave no way to derive them, nor, any feel for their values. Totally frustrated, we went to youtube and found the video - The Planck scale: Is there a fundamental limit to space and time? This did a much much better job than this professor did. Someone with a passion for teaching, teaches step by step (without skipping too much) so that students can follow and get a gut feel for the subject. A good teacher does not drop buzz words merely to impress the audience and needs to know when the students are falling behind. I would not recommend this course for anyone at any level.
Date published: 2024-01-19
Rated 2 out of 5 by from Informative but a slog to get through Over the years I've watched several of these Great Courses physics courses. This one is probably the toughest, for a couple reasons. The professor's delivery style leaves no pauses for reflection. If you don't get what he says as he says it that's just the way it goes. And I lose track of his main points because I'm still trying to figure out what he was talking about a few minutes ago. I find I'm watching the lecture and then going back and watching it again. But I'm only doing it because the subject matter in the lecture descriptions is almost exactly what I'm looking for in a series on string theory. I can't help thinking that the course would have been more easily comprehensible and much more enjoyable if arranged and presented by Sean Carroll.
Date published: 2024-01-04
Rated 5 out of 5 by from Enjoyed the course Very much enjoyed this course. Enjoyed the presentation style and the graphics. Only problem is that I'll need to do the course again to get even a minimal grasp of the subject 😊
Date published: 2023-12-11
Rated 1 out of 5 by from Ok for a physics grad student I was hoping to learn just a little about string theory like what actually is the theory…why is it called “ string” theory. Unfortunately, after four lectures I was totally losses and unable to follow any of the lectures so that I actually asked to return the series. . Way too advanced for a non-physics grad student. The lecturer assumes an advanced knowledge of calculus, math and physics that you will most definitely need to appreciate this course.
Date published: 2023-11-25
Rated 3 out of 5 by from Swoosh... Swoosh... that is the sound of this presentation going completely over my head. I had a vague interest in this as my curated Google news feed occasionally has articles on string theory and quantum mechanics. I thought this might give me a bit of clue. My background is a Bachelors in Biology with a minor in Chemistry. I later went back later and picked up a Computer Science degree (more money in that field). Admittedly, my university education was almost 50 years ago. If they mentioned quarks and such in my chemistry or physics classes, I am not remembering it. Oh course, they had only been discovered a decade before. Nothing wrong with the presenter except he is operating at a level many degrees above where I am at in this field. I probably lacked the appropriate background to connect with what he was teaching. I picked up a few nuggets, but for the most part, I am where I started. Oh well.
Date published: 2023-11-15
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Taught by Professor Shamit Kachru of Stanford University, this course introduces the cutting-edge science of string theory, which holds that tiny strings are the bedrock of all matter and energy. You’ll explore the history of string theory, its promise as a theory of everything, its major thinkers, and objections and alternatives to string theory.


Shamit Kachru

How did the universe begin and what's matter made of? These types of questions first led me to study string theory, which to physicists is the theory of everything.


Stanford University

Shamit Kachru is a Professor of Physics at Stanford University, where he has also served as the chair of the Physics Department. Additionally, he is the director of the Stanford Institute for Theoretical Physics. He earned a PhD in Physics from Princeton University, and he coedited the book Strings, Branes and Gravity. His research focuses on string theory and quantum field theory as well as their application to particle physics, cosmology, and condensed matter physics.

By This Professor

The Mind-Bending Physics of String Theory
The Mind-Bending Physics of String Theory


What Led to String Theory?

01: What Led to String Theory?

After a quick review of 20th-century physics, Professor Kachru introduces the concept of unimaginably minute strings. These appear to solve longstanding problems in quantum mechanics and achieve Einstein’s dream of a quantum theory of gravity. Learn why string theory predicts extra dimensions of space—10 in total, according to some models. Then explore the startling implications.

25 min
The Hidden Dimensions of the Universe

02: The Hidden Dimensions of the Universe

Delve deeper into string theory by probing the geometries of the extra dimensions. In the simplest cases, these could be curled into tiny circles. Also explore branes, analogous to two-dimensional membranes. See how elementary particles are a reflection of underlying string states, and learn what “spherical cows” have to do with the unifying principle of supersymmetry.

22 min
Strings, Branes, and the Standard Model

03: Strings, Branes, and the Standard Model

The Standard Model of particle physics accounts for the fundamental particles and forces of the universe, apart from gravity. Use the framework developed so far in the course to construct a streamlined version of the Standard Model. Key concepts include D-branes (which connect open strings), scalar fields (generated by D-branes), and superpartners (a byproduct of supersymmetry).

24 min
Oscillating Strings and Supersymmetry

04: Oscillating Strings and Supersymmetry

In the Standard Model oscillating strings are still a dream since they create particles beyond the reach of current particle accelerators. But what would happen if scientists could dial up the energy to produce highly excited strings? Draw on the work of Indian mathematician Srinivasa Ramanujan to count the almost limitless string states for a given energy level. Then see something bizarre happen.

21 min
How String Theory Explains Black Holes

05: How String Theory Explains Black Holes

Investigate the physics of black holes, focusing on their entropy, a measure of disorder that is proportional to the black hole’s event horizon—or its “point of no return.” Find that string theory can explain this property, providing a tool to study one of the most puzzling objects in the universe. As in Lecture 2, utilize a spherical cow model and supersymmetry.

20 min
How Strings Imply a Holographic Universe

06: How Strings Imply a Holographic Universe

Dive into the mystery of a black hole’s event horizon through the medium of hyperbolic art. Utilize the concept of anti-de Sitter space in conjunction with the holographic principle to probe the peculiar properties of this region. Discover how Argentine theorist Juan Maldacena harnessed these concepts, along with string theory, to enhance our understanding of quantum gravity.

18 min
The Origin of the Universe

07: The Origin of the Universe

Shift from the study of black holes to the problem of the Big Bang. Both phenomena involve singularities, where matter is infinitely dense, and the known laws of physics break down. How did the universe get from a point-like singularity to a vast, geometrically “flat” realm, filled with the particles and fields of the Standard Model? See how a theory called cosmic inflation accounts for this fact.

18 min
Strings and Inflation

08: Strings and Inflation

Continue your investigation of the aftermath of the Big Bang. Analyze the evidence for a mysterious “dark” energy that is causing the expansion of the universe to accelerate. Then apply string theory to this phenomenon as well as to cosmic inflation. Although the answers are not yet definitive, string theory provides a powerful theoretical tool for understanding the earliest instant of the universe.

24 min
The Many Avatars of String Theory

09: The Many Avatars of String Theory

Step back to inspect the simplest features of string theory. Professor Kachru has already shown that string theories are well suited to 10 space-time dimensions. But why is this, and how many separate string theories are possible in 10 dimensions? To address these questions, appeal to the spherical cow approach introduced earlier. Also, see how supergravity theories fit into this framework.

19 min
Duality: Which String Theory Is Fundamental?

10: Duality: Which String Theory Is Fundamental?

Explore a key feature of modern theoretical physics: the equivalence between apparently dissimilar theories, a property known as duality. Probe a pair of examples in string theory: type IIA and heterotic theories. Markedly different, they can nonetheless be shown to be mathematically equivalent under certain conditions, suggesting that a more fundamental theory underlies them.

19 min
Finding Evidence for String Theory

11: Finding Evidence for String Theory

The energies needed to prove the existence of strings are far beyond today’s research tools. Is it even possible to test the theory? Learn how resourceful physicists have come up with several indirect methods of inferring the reality of strings. Hunt for the extra dimensions required by the theory, and search for the hypothesized cosmic strings left over from the era of cosmological inflation.

20 min
Emergence: Can We Test String Theory?

12: Emergence: Can We Test String Theory?

Why has it been so hard to verify or disprove string theory? Close the course by looking at other cases in physics where what researchers saw in an experiment and what they got as an underlying theory were vastly different. String theory has already been enormously productive in particle physics, cosmology, and mathematics. The theory is beautiful and powerful—and it may even be right!

24 min