The Biggest Ideas in the Universe | 3. Force, Energy, and Action

The Biggest Ideas in the Universe is a series of videos where I talk informally about some of the fundamental concepts that help us understand our natural world. Exceedingly casual, not overly polished, and meant for absolutely everybody.
This is Idea #3, "Force, Energy, and Action." Already I have backslid on my idea that every idea would be encapsulated in just one word, but these three seemed to flow together.
My web page: www.preposterousuniverse.com/
My KZbin channel: / seancarroll
Mindscape podcast: www.preposterousuniverse.com/p...
The Biggest Ideas playlist: • The Biggest Ideas in t...
Blog posts for the series: www.preposterousuniverse.com/b...
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#science #physics #ideas #universe #learning #cosmology #philosophy #math #force #energy #action #classicalmechanics

[@colossalfart]

I work in railway engineering. "Jerk" is most definitely a used word and an important concept for passanger comfort and safety inside a moving train. Imagine if a train started moving from zero at a constant rate of acceleration (linear increase of velocity). A passenger inside the train would feel a sudden "jerk" from the instantaneously applied acceleration. This is obviously not only uncomfortable but dangerous, since it could cause one to lose his balance. It's exactly what happens when someone pulls the emergency brake. This is why in normal operation, not only the velocity needs to increase gradually, but the acceleration also, in order to keep the "jerk" below a certain value that is deemed safe (this value is dependent on the acceleration). Snap, crackle and pop, however, are concepts I've only come across at breakfast when I was a kid.

[@jonathansharir-smith6683]

That point is well taken - I certainly wouldn't want my coffee spilling all over me when the train starts going! But this could, to some extent, send us down an infinite regress. Were the jerk too high, then we would perceive that too. Some time derivative (at infinity?) of position needs to be a step or impulse function in order to move at all (in fact, I think this might be an interesting point for Professor Carroll in the follow up Q&A - this is another way of "showing" that movement is impossible, as was Zeno's paradox in an earlier video). I think Professor Carroll was just alluding to the fact that, for all intents and purposes, we need to choose to stop this infinite regress somewhere in order to move forward with analyzing a physical problem.

[@user-qf3lq4zj8g]

Thanks for sharing, one could say that the neck may _snap_ if the _jerk_ of the _acceleration_ is suddenly increased (that's why car seats have that head support).

[@colossalfart]

@@jonathansharir-smith6683 Of course you could take derivatives of higher order infinitely. For practical purposes, however, a roughly linear increase of acceleration (constant jerk below an empirically tested threshold value) is perceived as smooth enough. BTW, the same reasoning is applied to track transition curves in railways and highways for a smooth transition between a straight section and a fixed-radius curve.

[@jonathansharir-smith6683]

@@colossalfart Interesting and good to know (re: the empirical threshold value)!

[@r.murphy2311]

Also applies to rockets. The rocket engines apply a more or less constant force, yet the mass of the rocket decreases as the fuel gets burned so the rate of acceleration increases.

[@AlexPaven]

Don't force yourself to make these shorter, they're great as they are, and this includes the Q&A! Great stuff!

[@keithmccann6601]

so i'm really late to the party here - I've only just discovered this series - but I've said for a while now that these days it's possible to find out about anything you want to know - but you have 'want to know!!! - And now i'm 'blown away' that those of us who do 'want to know' can get taught by a Cal Tech PhD - the internet may be a double edged sword but when it's good it's brilliant!!!

[@samkratzer2549]

I think you underestimate the length of content that people are willing to pay attention to. This is great; the more the better as far as I’m concerned.

[@fallenangel8785]

4th year medical student here , I find your lectures and books in this series very enlightening and a way to improve a new way of thinking about everything in the world, waiting for your next books in the series. ❤

[@terrypussypower]

Sean is my favourite scientist. Even when I don't understand what he's on about, the tone of his voice makes me feel smarter.

[@Bill_Garthright]

TPP, I agree with the first part of that, but I guess I felt dumber, not smarter, when I watched this video. Heh, heh. Of course, it's been 50 years since I took my last - and only - calculus class. And my last physics class was before that, when I was still in high school. These things are fascinating, but... they don't want to stick in my mind. I don't think I retain the information even from one video to the next. :) I still watch the whole thing. I do find it fascinating.

[@ozkurede]

hahahahaajja :D

[@joshtargo6834]

did you ever watch the tv show Newton's Apple, or was that before your time? Sean sounds like Ira Flatow

[@daltsu3498]

@@joshtargo6834 I never made that connection but you are right! Ira flatow is spot on

[@carlmalone4011]

Sean, you really found the "sweet spot" for teaching physics. Nice work !

[@bz1222]

Trauma and critical care surgeon here. These videos have been a saving grace for me in the time between taking care of the COVID patients and ensuring my wife does not kill my 3 kids now being homeschooled. Please keep these coming. You obviously have limited time and many responsibilities so thank you for taking the time to reach the common folk!

[@ToriKo_]

What is it like 2 years later?

[@fallenangel8785]

4th year medical student here also

[@akumar7366]

Watching in UK England, how lucky we are to get to benefit from such a brilliant series.

[@javahaxxor]

Excellent video series, thank You! I'm starting to see how it all fits together

[@marwanelmobader7851]

I am so happy to know about this series of lectures

[@emrazum]

I really like this higher level approach to physics, digging into metaphysics more like. Way better than any of the science classes I've taken at Cal.

[@ASLUHLUHCE]

Great video! And I liked your closing sentence: "To improve our current understanding of the laws of physics, we have to be open to the possibility that we're gonna invent more words, more concepts, and more ways of looking at the same universe, that help us recast those laws, extend them, generalise them, and go beyond what we currently know, into the physics that we don't yet understand but hope someday to do."

[@jamesedward9306]

"Maybe you need to know the hopes and dreams of particles" .....made me laugh out loud. Sean is awesome.

[@xaviergamer5907]

We love these videos. Thank you. We specially loved where some cereal companies came out with “snap, crackle and pop” for their commercials.

All your technological improvements are good. Many thanks for these lectures and keep up the excellent work. Cheers.

[@Crazyeyes388]

Keep up the amazing content, have been a fan for years.

[@edwardcosio]

I am having so much fun with these. I’ve always wanted to get into and visit the ideas you present in these videos. The entirety of the natural world, to be honest. My interest was absorbed entirely into my undergraduate studies of music composition and, until recently, has reignited recently as of maybe this past year. Thank you again for your insight, I can’t get enough of it. 👍

[@MoyaErick]

Love the concept of this series Prof. Carroll!

[@sayedrahimrahimi3687]

Thank you so much for the precious content. It’s such a great luck and blessings to have access to such quality content put in such an eloquent way. Thank you so much dear Sean. You have been of the few best educators I have had in my life. Have been knowing you since quite a long time through your lecture in The Royal Institution. 🙏🙏😍

[@henrikwannheden7114]

I absolutely like the iterative process with how to do these videos. It shows that Sean is a man with teaching skills. By the time this series is done, he'll probably a full time KZbinr.

[@briancannard7335]

Took notes watching the previous video, raising questions about the concepts of "Force", "Energy", and "Potential", and here there are, the answers. Thanks so much Sean!

[@HowShouldIKnow6543]

Thank you Professor Carroll for creating this series, you have given us a tremendous gift

[@bryanroland8649]

Lucid and accessible to innumerate viewers like me. Long too. Love it! Thanks for making staying in more interesting.

[@llaauuddrruupp]

I really, really like these videos! I truly hope you keep making them.

[@alikarimi76]

I'm watching your videos and reading your book at the same time. Keep up the great job Sean. Thank you so much 🙏

[@sandrasandra7593]

Watching from Italy. I was expecting it! Great video, thank you so much

[@HawthorneHillNaturePreserve]

You are such a genius and wonderful teacher! It is so exciting to listen to you and you make it so accessible. No judgement or airs. I’m not made to feel dumb when you present such intricate theories and physical laws. You demand intelligence and critical thinking but deliver it in such a palatable way that I’m given the room to learn and think. Favorite professor I never had.

[@TheHalothane]

Love the lectures! Thank you for doing this. Love the Mindscape podcasts as well!

[@alexcherfan7762]

Loving these videos man. Thank you!

[@Shonucic]

Great video! The bit at end end was quite profound. Thank you for creating these.

[@colbynye5995]

Thank you for taking the make these videos! I appreciate learning from you

[@metalkokorea]

Thanks, Professor.

[@mandaglodon]

Well, this Background is Awesome!!!

[@laastchild]

I appreciate your efforts to improve these presentations, and thank you. You have been my favorite physicist to listen to. I have downloaded some of your work on TTC , The Great Courses. I, also, am an Everttian, and am anxiously waiting for some kind of collective decision on wtf are the fundamentals, the reason why, quantum mechanics works the way it does. I am glad that I am not the only one, by far, to appreciate your ability, Sean, as one of the very best communicators, and teachers, of the secrets, history, discoveries, and cutting edge research that is going on in all the various fields of science you work on, and expound on.

[@gildastigliano7936]

these classes are excellent! keep 'em comin' please!!!

[@veroosh]

I like the 1 hour sessions, keep going. Its a meditation.

[@veroosh]

Your design of today's session is on point.

[@Tony-Madisson]

Thank you for the effort and determination! Great video!

[@h.i.5280]

This is what the internet was made for. Pure intellectual gold. Keep them coming, Professor. With a Capital P. Thank you from Romania.

[@rc5989]

The quality of the presentation and the production value of the content is very well done! This is basically as if we are students in a classroom with Professor Sean Carroll. Personally, I am enjoying every minute.

[@JohnKallbrier]

Sean, I really enjoy your talks! There are however times in every lecture of yours I've seen that you get a sheepish, rye smile on you face, looking directly into the camera, that makes me feel like you're putting something over on us or maybe a inside joke. De-rails my thought process while I try to figure out what I missed. Keep up the good work 👌

[@WeeWeeJumbo]

Major improvements to the production! Fantastic, Doc

[@integza]

Long videos are fine Sean!

[@SicilianDefence]

Thanks you Sean! It's awesome videos, please keep them long, we have lots of free time in isolation to contemplate every minute of them :)

[@easterdeer]

These videos are fantastic. Thanks Sean!

[@edwardlee2794]

Certainly not the first one to draw me in, but definitely the one to keep me in. Making particle physics interesting, grace it in the splendor of humility and authority. Thanks for the efforts and keep up with the good work. From Hker worldwide

[@korosuchimu1479]

Thank you for all of these. The black screen is great. Considering I watch the before bed.

[@paulbrown6456]

Thank you Sean, your doing an immense public service here

[@jasonbeary5771]

I teach physics but I still love to hear Sean's explanations. They go very far back in the developement of the ideas. I think something from each "Biggest Ideas" will be used in lessons with my students.

[@thederivationchannel4243]

Also, this is only further validation that Dr. Carroll is the Feynman of our generation. The principle of least action is such a beautiful concept.

[@JoseRamirez-in5cn]

Keep up the good work, thanks for expanding my thirst for knowledge.

[@nicholaspiacsek5415]

I love what you share Mr. Carroll. Also a big fan of the "dark mode" format.

[@jcf20010]

I thought it was supposed to mimic a chalk board.

[@boilingluigi1824]

I really like him. He keeps away from trash tv. THANK YOU.

[@thederivationchannel4243]

Okay... so I may be here to plug my channel a little bit, but I am so pleased that Sean Carroll is digging in to the philosophy of physics. There are so many physicists unwilling to dive into the ramifications and meaning behind the equations. Besides the fact that equations have a "predictive" quality, there is a beauty in being able to explain the equations and therefore understand the universe. So glad that this content is reaching people. Thank you, Dr. Carroll.

[@peterparsons7141]

These videos are very satisfying, and enjoyable for me as an older man. A tremendous education platform and it permits me to continue my learning. The really big notion is; Somewhere in the world , there are brilliant young minds that are getting access to big ideas that matter. Just think about the potential of these lessons on the next generations. I applaud you, and thank you.

[@ankiesiii]

I really love these!

[@alinab.4568]

Thank you for explaining all of this. Priceless knowledge and so interesting

[@helenwilliams3819]

Love these videos and follow your mindscape pod cast to. I'm not academic so these are a little bit difficult for me to completely understand. It's the same with all the Astro physics and partial physics I'm interested in. Lots and lots of it goes over my head but I'm so fascinated by the subjects I keep watching and listening until something goes in. Thanks for making my brain hurt. Stay safe, stay in and save lives. 💙NHS 🇬🇧 🌈

[@xcq1]

Isn't there a need to extend the principle of least action? Because if everything in the universe is evolving according to the least "expensive" action, wouldn't we expect the universe to quickly dissolve into a heat death scenario instead of producing complex structures of intelligent life? Oh and one more thing: Is there a way to support you exactly for this project? I know your wonderful podcast has a dedicated patreon, but this series is literally a dream come true.

[@barefootalien]

A useful illustration here is to consider the classic example of a cup of coffee and cream, carefully and lovingly layered by your favorite barista. At first, you have the two layers, which is both a low-complexity and low-entropy case; there are very few configurations of the coffee and cream that form those neat, tidy layers, so the entropy is low, and it's very simple to fully describe: "there is x amount of coffee and y amount of cream in the cup with a flat, crisp boundary layer in-between". At the end, you have a smoothly mixed latte, which is still very simple to describe ("There is x+y amount of homogenous coffee-cream mixture in the cup") and yet is now in a very high entropy state: almost any arrangement of particles in the cup results in this same description. Between those two times, though, is a period in which the entropy is increasing as the two mix, and as it does, the complexity rises to dazzling heights with all sorts of little swirls and whorls and fingers and curls along the complex boundary between the two, and fully describing the system would be nigh impossible. The universe is very similar to this; at The Big Bang, the entropy was extremely low, and it was also very simple, just a lot of basically homogenous "stuff" that was very hot and dense. At the end of time, we presume, the entropy will be extremely high... and yet it will still be very simple, just a lot of basically homogenous "nothing" with the occasional photon or particle zipping by with random momenta. It's in between, as the universe goes from low entropy to high entropy that complexity develops in the form of stars and galaxies and planets and people. Complexity is often sort of like a vehicle to get from low entropy to high entropy, and in some sense, life is a very efficient solution to the problem of what you might call "false vacuum states" along the way. Along this line of thinking, there are some postulates that life exists precisely in order to facilitate that efficient (and quick) movement toward thermodynamic equilibrium you were asking about. For example, there are chemical processes that take a highly ordered molecule present in the universe and rearrange it into a higher-entropy configuration, but that take multiple steps in which the first step costs energy, thus it would be highly unlikely to happen by coincidence. Life can willingly and repeatedly expend that initial activation energy in a way that random physical processes cannot. It can then reap the rewards of the further steps in the reaction giving off energy it can use, while in a sense, the universe reaps the benefits of moving a little bit closer toward its ultimate high-entropy state. This winds up in the slightly flippant quip that "The purpose of life is to hydrogenate carbon dioxide," and can even make life seem inevitable, and probably very common throughout the universe, facilitating the Second Law of Thermodynamics despite or perhaps because of its complexity. Another way to think of it is that yes, the universe is moving as quickly and efficiently as it can toward heat death, but it has no magic wand to wave in order to achieve this. It must do it piece-wise, step by infinitesimal, smoothly-evolving step, and that seems to necessitate complexity along the way. Hopefully Dr. Carroll will answer this question in the Q&A, as his explanation of all of this is likely to be much more eloquent than mine. :D

[@jean-francoisdorval5231]

Geez, it was touch and go there for a moment... My brain couldn't keep up with the "simple" math content, but you kept it on the road. Good job and thanks!

[@michu2345]

Watching from Poland. Thank you very much!

[@wiredrabbit5732]

I am so happy that a serious and respected scientist seriously mentioned snap crackle and pop. I don't care about Wikipedia, but i did learn that at Uni and rarely hear anyone use it.

[@moralboundaries1]

I honestly think studying things like the jerk, snap, crackle, and pop isn't silly, calculus teaches us that studying these "meta-changes" can give us a deeper insight into a system.

[@fastfitnessguru]

I’m becoming a bit of a groupie for Sean’s work at the moment. This is great and the podcast is the amazing. I know something about these subjects but I always come away refreshed. Sean’s Easy Pieces, like Feynman but with video.

[@Deanzoid]

Many thanks for the dark background! Now I can watch in a dark room without my eyes hurting.

[@shaunlanighan813]

These videos are so helpful.

[@abdessadaksallam626]

i really appreciate the idea of presenting and explainning physics concepts and laws with a philosophical and historical views, respect from Morocco

[@lautarokinalczyk838]

Im loving the math in this videos! Keep it up!

[@user-qf3lq4zj8g]

9:15 Is a particle with "daddy issues" a Big Bang denier? 😂

[@anvillal.7787]

Haha! Please answer this question in Q&A.

[@666LonesomeSailor]

Yes please! Mister Sean Caroll, please do so and explain to us, what a particle with "daddy issues" is!

[@dinhnguyen2110]

@@666LonesomeSailor Virtual particle. It's parent was never there.

[@rostamr4096]

I love your lectures. Thank you.

[@simonconvey9645]

Wonderful ! Jerk and snap are used in engineering. Think of a camshaft in a combustion engine which rotates at half the rotaional speed of the crankshaft. The lobes on the camshaft open the inlet / exhaust valves. Engineers would like to control these events very accurately, and they do consider the acceleration of the valve opening and closing. ( They are masses acting against springs ). They also consider jerk, and to a lesser extent "sanp". ( Snap is called "quirk" in camshaft engineering. ) The noise, vibrations, harshness, power and ecconomy of an engine all rely on these calculations.

[@canopus127]

I was feeling quite boring, and I saw this video. Trust me, this video just inspired me to look again into classical mechanics in details. Newtonian mechanics is beautiful and full of beautiful concepts, and enough to describe the macro-world we experience in daily life.

[@parthadeka5871]

I keep waiting for your lecture everyday during lockdown.. All the love from India Sir.. Namaste🙏

[@cordatusscire344]

Thank you for the video!

[@singularonaut]

Newton rules 💪 Greetings from Kyrgyzstan 🔥

[@CallMeChato]

I like that the writing doesn’t seem to lag any more.

[@autonomesinklusionsreferat1251]

Most enjoyable Videos!

[@alonescool]

I love your videos!

[@dougporter2356]

Dr. Carroll - there's little that I can add to your praises that isn't already proclaimed in the Comments Section so I will just say that I really like your videos. Back in high school, I wish now, after listening to these videos, that I had spent less energy calculating how to sneak a cigarette in the Boys Room, and more energy paying attention in Algebra class. Dang it...

[@AJBtheSuede]

"Jerk" and "Snap" are two perfectly valid and often used parameters or talking points when you tune s suspension system for cars.... They define the variations in the road condition that you tune the handling and comfort parameters of a suspension to.

[@sztaba100]

Thank you - I learnt a lot. It was a bit of a slog but philosophically very significant. What has a name doesn't confer existence on it - that's a biggie especially for Force. Gravity as being due to geometry is another. You have an amazing mind - I love your work!

[@RandyH524]

This is great.

[@elenteny]

Thank you for what you do. I decided to go back to school for physics largely due to a series of lectures I heard from you from the Great Courses series. That and your books, so thank you for all you do and keep up the great work. Also, I believe that "Phase Space" comes from trig. Phase shifting is shifting the origin of the functions graphical representation, so "Phase Space" seems as though it should be roughly understood as the total space in which we may shift the origin to any given starting point.........maybe.

[@un4given868]

The ball wants to live up to its maximum potential, as fast as possible. A ball to be admired!

[@qingyangzhang887]

In the end when you talk about reality, you say "the universe is real", which I agree with. I think that statement is true by definition. Your definition of "real" will be based on some physical stuff in the universe, so the statement is kind of analytic (as opposed to synthetic). Maybe that's exactly what you meant when you said the sentence, and I am just rambling on. Thank you for making this series.

[@henryD9363]

Thank you for explaining action. I got a BS in physics in early 60s and it was not really taught. Actually it was defined with some examples examples and then we almost never heard about it again.

[@tripp8833]

Bro it’s probably the most important concept in classical mechanics! Least action! Euler-Lagrange !!!

[@henryD9363]

@@tripp8833 yes indeed. I was stating it as a complaint about the textbooks and quality of teaching at State U.

[@SicilianDefence]

You are awesome!

[@richardrodfar1]

What's the name of blackboard app on your screen??

[@venil82]

First! Loving this series

[@theechoholic]

Sean, i love that the videos run on. Right now, where I can't be in Uni, listening to you, PBS Spacetimme etc. is quite relaxing. A standalone series on QFT would also be delightful.

[@kc-cn8zy]

Initially skipped #3, big mistake, wonderful presentation. TY.

[@greencoder1594]

[54:00] *Words are tools,* becoming *real only by being particularly useful* for talking about the universe, grasping and interpreting it, as well as anticipating one's future experience to be able to decide what to do.

[@jkinkamo]

Thanks for this great lecture! There was a question of lecture length. I'd prefer one hour or even longer ones as it seems to be more or less "industry standard" in online open university lectures. In my opinion combination of the main lecture and the following QA-video is rather nice lecture package for one day while forced to stay at home. Also one can rewind and replay the points of interest while studying the topic further with additional web material from other websites. Of course, thanks to the Internet and KZbin one can divide one longer lecture or multiplex shorter ones in order to achieve optimum length for himself.

[@shuozhang7048]

Thank you so much!!!!!!

[@mus3equal]

I have been diving deep into what I can teach myself regarding quantum mechanics and physics. I arrived at this point of my journey interestingly through linguistics and phonetic phase shifts as it relates to evolution of language and cultural dynamics. I continue to find abstractions that align with quantum mechanics, mathematics, chemistry and so forth. Language feels tied to time and our conceptions in many regards. I often wonder why we seem to have lost these connections, as I haven't yet come across applied research in this regard despite the huge aggregation of available data. It has however served a logical key of sorts to be able to decipher the "language" of mathematics. This required some very deep digging into Latin, Greek, Arabic and Chinese texts and historical codices, leveraging AI to assist in translation. I always reinforced the idea that I was terrible at math until I broke the traditional mold of learning and applied a new approach. While I still struggle with many technical aspects my learning curve feels exponential. Much of my approach is rooted in my own linguistics. German was my first language at an early age, I found that one of the "reinforced issues" with my mathematical approach was in the functional dynamics of how numbers are spoken and the translation over to English. A few months of historical research and diving into etymology and phonetics turned on the light bulb. I have been essentially thinking in terms of the functions rather than the input and output values. Still piecing together a lot but I can not split the passage of time and the evolution of language and how it intertwines with consciousness and perception of the cosmos. Thank you for this series, lacking mentorship has been difficult but videos like yours keep me plowing through the unknown. Hopefully I can pull a proof of some kind together to share my journey, even if my approach is wrong it might help someone flip their own light switch as well!

[@GiorgosTsiledakis]

The Principle of Least Action seems to be one of the deepest 'laws' of our universe. But why is this the case? Are there any insights about that? I guess a 'Principle of Random Action' could actually be kind of more 'natural'. By following the Principle of Least Action, the universe seems to know in advance the value of all possible actions and then always choose the one with the lowest value. Isn't that strange and wonderful at the same time? Thanks for the amazing content by the way!

[@rv706]

Actually, the correct paradigm is not the principle of least action, but the principle of *stationary* action.

[@waynelast1685]

@@rv706 true but it just wording here , and the significance of the question is still valid. The action in some situations needs to be minimized , and in other different situations maximized, both cases being called “principle of least action” but technically speaking it is the “principle of stationary action”. ( stationary just means a minima or maxima) .However the question is referring to the significance that the laws of the universe know when to minimize , or when to maximize, depending on the particular situation involved.

[@rv706]

@@waynelast1685: I forgot to write I was just nitpicking. But yeah, a stationary point need not be a minimum nor a maximum (think of a saddle). I think there are physical systems like that, though I can't write down one off the top of my head.

[@renaudkener4082]

Superb videos. Now, I have time to open my old books of physics and re-learn maths :)

[@ronanmehigan5044]

Hi Sean - great video. Can you discuss how the Lagrangian relates to the Conservation Laws in Physics ?

[@shantanu275]

50:59 also explains light bending under gravity (General Relativity)

[@feynman_3224]

Not exactly. Light follows geodesics on spacetime caused by a gravitational field. In light point of view, it travels on a straight line.

[@timwakeford8471]

Like the new, improved 'blackboard'