The Biggest Ideas in the Universe | Q&A 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 the third Q&A video, following the idea "Force, Energy, and Action" discussed here: • The Biggest Ideas in t...
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...
Background image: www.freeimages.co.uk/gallerie...
#science #physics #ideas #universe #learning #cosmology #philosophy #math #force #energy #action #classicalmechanics

[@rtheben]

This guy is a rock star, and lovely. I have his book Space-time and geometry, and it’s part of my physics bible- library. Many thanks

[@sebastianclarke2441]

Thanks once again for such a wonderful Q&A session. I'm truly humbled by your effort towards communicating these fascinating theory's in such a digestible manner. You truly are one of the worlds best teachers of physics, keep up the excellent work!

[@user-gj7vp6wk3e]

SPACETIME AND GEOMETRY IS EXCELLANT!❤

[@ToriKo_]

20:30 this is why so many people admire Sean’s ability to teach. Sean tells us the importance of labelling axis’s, as even if the teacher might know what they are, students may not. You have such a admirable ability to remember and empathise with what it’s like to learn something for the first time, which most people (myself) forget to do after they deeply grasp concepts Also I appreciated the BTS on how u make these videos

[@AvoidRunningAtAllTimes]

An unreal series. What luck we have to live with YT AND Sean

[@akumar7366]

Watching in England UK, I have only really started being interested in Sceince in the last few months, most particularly I find space / time /universe of interest. Really so recite the time and effort you are taking in preparing your presentations. I watched your discussion with Roger Penrose in relation to CCC theory, which I found fascinating, you are my favourite scienctists.

[@yeti9127]

Sean, you are quite an intellectual sharing all of these ideas so brilliantly and with simplicity. Selfless act of your generosity will pay off in the long run by making physics more accessible and exciting. It nurtures curiosity too. Many can write complex equations, (I do in my field), but those who can convey difficult theories through simple understandable examples, charts, and themes are the true teachers. Not many have that quality. With your videos, I finally understood the link between Newtonian physics and modern “interpretations,” and to some extent the work of Feynman that I had watched in a video series QED. I look forward to many more ideas. Thanks a bunch! I am a avid listener of your podcast. Keep up the great work you are doing.

[@gr500music6]

The RE 320 is a great choice for your voice, comes over perfectly.

[@michaelsmith935]

Outstanding video! And, I appreciate the description of your setup. Thank you.

[@Mike-jr7re]

If lockdown had brought anything positive, this is it. Man, what a great gift. Thanks for the lectures.

[@patrickmchargue7122]

"Thank you for watching." Sure! Thanks for exploring this here with us all.

[@DwainDwight]

Happy easter Sean. Thanks for this. Really interesting. Keep em coming.

[@edwardcosio]

The microphone really helps, don’t sell it short lol

[@joostvanrens]

I agree, if you have a good view of your iPad screen and good sound that is really all you need..... And a gaming chair of course.

[@jainalabdin4923]

Your passion for making these videos really shows, and is really appreciated.

[@lambda4931]

Thank you! Very interesting stuff. I’m so glad you’re doing this. You are becoming one of the great communicators of physics. Physics needed this.

[@chrihipp]

Thank you very much! This format is so useful and intersting! 👍

[@Saitama62181]

Thanks for the videos, Sean! They're helping to keep my brain alive during the lockdown! :-)

[@nvstvsi]

It's so interesting to see how you view and heuristically explain mathematics. Thanks for the great content!

[@emrazum]

Try recording in 1080p to keep the file sizes low. Great class as always

[@richardtarr5247]

What an amazingly brilliant teacher you are. After watching this video has made sense to so much. Thank you Sean ☺

[@MrRennybenny73]

This guy is a rock star, and lovely. I have his book Space-time and geometry, and its part of my physics bible- library. Many thanks

[@Cemselvi1988]

I am doing an astrophysics PhD and I enjoy this very much

[@lukelutio1246]

I'm watching from Switzerland and have been following this new series with great pleasure. I consider myself to be a youtube educated scientist aka taking the path of least action :-) and this sort of material has effects of mind blow and entertainment to me aside from it's educational value. I'm using this series to reconnect to all the unpleasant maths I've learned over the course of my life because using this sort of math (e.g. calculus) in the physics context is so much more satisfying than just memorizing formula over formula. To me it is still painful, but with all the added meaning and applications it makes wrapping my head around it much more efficient. Sean, with this segment, especially with your 'making of' section at the end, you've once more presented the passion you put into these productions and I enjoy that at least as much as the scientific content. Sincere thanks!

[@SonaliSenguptasengupso41]

Bravo ! Professor Carroll. In-depth and nuanced explanations. "Principle of Least Action " explains it. Thank You.

[@charl160]

Thanks for sharing your knowledge. Excellent videos!

[@jamesschinner5388]

Awesome Mr. Carroll, this is great and enjoyed seeing the setup!

[@cazymike87]

Thank you Dr. Sean Caroll ! This is Amazing !! Thanks !

[@tonybowen455]

So good. Thanks for doing these!

[@xaviergamer5907]

Love the videos. Thank you Sean.

[@SimonsAdventureStories]

Thank you for taking the time to explain how you put it all together. I've been producing science based audio's for kids for a few years now and am always fascinated to find out how much time and effort goes into what other people do. It's also very humanizing to hear about little details like your trip to the camera store. Just started on your podcast and will be slowly working my way through the episodes, trying to keep up! Thanks again for all the efforts you make to spread this knowledge and your excellent way of being able to explain concepts.

[@prawnmikus]

Thanks Sean! Really great stuff, as are all of your talks.

[@johnphamlore8073]

Professor Carroll: Calculus of Variations by IM Gelfand and SV Fomin, translated by Richard Silverman, is an incredible introduction at the level of someone who can understand college calculus. In particular, in Chapter 3, General Variation of a Functional, Gelfand and Fomin show an incredibly simple calculation that explains everything. There is a somewhat local feature of an action integral -- it's a sum of sub-integrals if one breaks up the say time integral. Now if we fix the end points of how one makes a variation and figure out an extremum, one gets the system of differential equations known as the Euler equations. But if one calculates what happens if endpoints are not fixed, the variation along the time direction turns out to be, plus or minus, a quantity H called the Hamiltonian. The variation along the curve direction turns out to be a generalization of the concept of momentum variables p.

[@gdenyer]

Fantastic info, Sean! Modern day national treasure!

[@FurryArmMaths]

Thankyou so much for your time, effort and patience in producing these series of lectures and follow up Q&A. It is very much appreciated. They are so entertaining, informative and thought provoking. Use of technical terms such as, "chug" and "stuff" makes explanations so very palatable. Also, I had a fleeting thought that perhaps you have secretly figured out how to slow time locally in your office for you develop these lectures. Please share if you have. Thanks once again.

[@KieranGarland]

Am really, really enjoying these videos. Answers an awful lot of questions (in my mind, poorly formed) that I've had about many areas of physics. Despite some attempts, I don't think I'll ever study physics formally, but these videos and Q&A follow-ups are improving my intuition and enjoyment of physics no end. Thank you.

[@hodgymac]

Privileged to see Sean in London at the RI last January - feels like a lifetime ago, but thats time for you!!! Anyway fantastic as usual, keep it up Sean, science is truly a candle in the dark

[@johnwaite6387]

Many thanks for aiding my understanding of the conceptual foundations underlying both classical and quantum mechanics. While I'm far from being either a physics or a math guy, I can at least get a sense of the history behind these two approaches and descriptions of the physical world. You have been so very generous with your time to help introduce these topics to the non-scientific community. In a world where specialized knowledge and expertise is often walled-off and guarded, it is especially gratifying to be given a chance to learn from an authoritative source whose prime interest in this setting is teaching.

[@_Messiii]

Sean thank you for telling us how you make these videos!

[@alikarimi76]

I'm enjoying watching your Q&A videos as well. I'm currently stuck with reading your book, Something Deeply Hidden. I'll sure come up with questions to ask you 🙌

[@ComisPeritus]

Thank you for all you do !

[@alexwilson8034]

Thank you for working hard for us! No one else does what you do

[@ToriKo_]

So we are left with the issues of teleological language from last episode, where people learning have an impulse to ask ‘how does nature know to pick the laziest path of least action?”. I think Sean tells us that this is a bad question formulation, as what the principle of least action is actually telling us is; given you know 2 coordinates of a particle’s position in space and time, then you know something about the Action. If the Action was higher or lower, the particle would have taken a different path, but as it isn’t, we can find out a set of solutions that the particle could’ve taken, and we do this by finding the integral ([of Kinetic - Potential Energy] * the Time interval). The disadvantage is that we do not have a unique solution (like the Laplacian framework does), but the advantage is that we have a set of possible solutions, which may be useful to us in different ways.

[@Petrov3434]

PS: An amazing effort in production of these masterpieces...

[@danielm8482]

Thank you, awesome content

[@woody7652]

Thanks, Sean!

[@akashmalhotra4787]

Regarding the apparent information difference between the least action, and the newtonian way, the information is the same because momentum has two numbers: magnitude and direction. So, in Both paradigms we total four numbers: In Newtonian: x0, t0, p_mag, p_dir. In least action: x0, x1, t0, t1.

[@lucofparis4819]

What I find fascinating is that nowadays, when we examine scientific fields across the board, a continuum becomes apparent: from human actions as explained by sociology and psychology, then generalized by evolutionary psychology, then generalized by the modern evolutionary synthesis, then recontextualized in the origin of life research - to chemical evolution, as part of a broader generalization in thermodynamical terms (with biology and abiogenesis basically steming from the second law of thermodynamics). The interesting part here is that the second law of thermodynamics can be described in two forms: • the evolutionary principle by natural selection • the principle of least action In turn, both can be connected via the fitness criterion when described in thermodynamical terms. At this point, nothing really stops us in principle from conducting an inter-theoretic reduction on human behavior, all the way down to molecular dynamics and nuclear physics even. The question remains whether this can be done all the way down to quantum mechanics however.

[@robertmolldius8643]

Thank You for explaining about video making! 🙂🙂🙂👍👍

[@redgemon]

Great show Doc! 😃

[@Bestape]

37:47 to 44:40 is really good. I was imagining electrons in chemistry and Feynman's "QED: The Strange Theory of Light and Matter" p. 104 during it. When I read Frank Wilczek's "A Beautiful Question: Finding Nature's Deep Design," I got a lot out of it but I didn't realize my mass comes from QCD. Gives me a think about how to reconcile that with the feeling I have hauling myself up the climbing wall. Thank you!

[@quantumjet253]

As if being a scientist isn't cool enough, being a theoretical physicist, and a charming one at that, is almost going over the top, but to finish the video with "...I could just play video games all day" is just cheating. Love these videos. Barely understand anything in them, but I live in a foreign country and don't speak the language so maybe that's my destiny as it clearly wasn't to be smart enough to understand everything I find fascinating and interesting. Oh, and Mr C's a cat lover too!

[@barefootalien]

Neat! I also use Camtasia when I make videos. Your setup looks pretty good. The only thing I'd suggest adding from my experience would be a backlight for yourself. That would get rid of the little green halo at the edges of your hair. It doesn't need to be anything like as powerful as those big studio lights with the umbrella diffusers; just a desk lamp on the floor or a small box or chair or something would be fine. I personally have found warm light to look best for that one, so a "warm white" or "soft white" maybe, around 2700 or 3000k.

[@MeissnerEffect]

Sean you are a handsome man, please don’t disappear anymore behind the green screen than you have 😄. We don’t need discombobulation of our favourite minds and their physical telepresence at this time! OK, that’s just a little humour on my part (Australian spelling). Love how you, Brian Greene and other great thinkers of our time are finding ways into our lives right now. Thank You 😊🎋🌿🦋

[@MrPythonnn]

thanks for your effort

[@abdennourabdennour2755]

Thanks once again

[@johnp1]

The tutorial about your recording studio is very useful.

[@SandipChitale]

Sean, thanks for these excellent videos followed by Q&A episode. The Q&A episode allows us to ask the questions in the context of the subject of the video. Also, thanks for clarifying where to ask the questions i.e. on you blog entry for the video. Thanks for clarifying the issue around the imprecision around the statement that "all we only need to know is the position and momentum of every particle in the universe to predict how the system evolves" - by making it clear that there are some assumed initial conditions - not only such as mass but also electric charge or color charge in context of quarks (say!). To me mass is to gravitational field as the charge is to electric field with a difference that there is a notion of positive and negative charge. Is there a notion of negative and positive mass. Is the dark energy equivalent of the negative mass via E=mc2? Just like when a lot of mass is concentrated at one point a black hole forms, is there a notion of black hole formed because of the concentration of electric charge? Or because positive charge repels and thus cannot be concentrated and thus cannot form a black hole. It is interesting to note that the formula for the force produced by electric charges does not involve mass of the charge holder thus the acceleration produced by the force of electric charges can produce different acceleration. Whereas the gravitation force depends on the involved masses and hence the acceleration is proportional to the masses.

[@peterbarabas9358]

Thanks for the extra (studio setup). :)

[@donbasparklane]

Thank you 🙏

[@Chayonray]

Great Q&A session. Enjoyed the discussion of QCD contributing most of the mass of the proton and neutron. I'm assuming you are discussing the Strong Nuclear force. Please correct me if I'm mistaken. Also, really appreciated the discussion of your studio setup. It was very useful sir!

[@wgcar]

Kudos!

[@zamurahanay9067]

Sir, I'm one of ur student who haz been influenced a lot by Carroll's work.... But keeping physics aside for a moment, this video is so good n helpful for ppl who wana help others by making videos az muxh possible az uh did.... Thanks sir a lottttt.... Luv from Kashmir, IOJK....

[@r2roberts]

So glad you added the video production info at end. Also Sum Over Histories.

[@karitakoi]

Subscribed !!!

[@expchrist]

amen to "enormously more rewarding"

[@peterphil9686]

Very good

[@anirudhadhote]

❤ Very good 👍🏼

[@HypnoticSuggestion]

I gotta hand it to you peeps who use laptops, in particular Macbooks for things like video work. You have the patience of a saint and then some.

[@randcontrols]

Thanks very much for the excellent series Sean. I want to comment on "how does the particle 'know' how to get to another point with given coordinates in given time"? I'd like to offer my thinking on it and ask whether I'm wrong. Of course the particle does not 'know' that, but neither does the particle 'know' that you want it to get there in the given time. Every different initial velocity will result in a different time for the particle to get to the second point. The particle only "knows" how to get to the next infinitesimally small instant and proceeds like this. If you want to know the initial velocity for the particle to get to the destination in a specific time, you can use the minimum action principle, instead of Newtonian mechanics, to get the answer. What I'm saying is: horses for courses. Depending on the problem, it's sometimes easier to use minimum action and calculus of variations and for other problems it's easier to use Newtonian mechanics to get the answer. Is my explanation valid?

[@surfingmoose]

As Peanut would say, VROOOOOM. I enjoy listening to these vids. Some ideas stick (but there is some teflon involved), while most VROOOOOM.

[@enkiorenlil]

Sean Carrol thanks for your effort. I have started watching your videos but still neglecting a little bit. But I will overcome that. I have a question about dark matter and dark energy. Should I wait for your video about the subject ?

[@josemariodelapiedra611]

Excelent

[@ssshurley]

60 gigs wow!!!! That’s huge, well thank you for doing that! Sounds difficult......

[@qingyangzhang887]

15:00, in your box example, is the straight path the global minimum of the action, while there are infinitely many local minima (as the particle can bounce infinitely many times back and forth between two walls)?

[@Petrov3434]

Thank you -- outstanding as always. A question on actions, energy, forces epizode: -- Is there any explanation for the "inflation" hypothesis in the first infinitezimal nanoseconds after "Big Bang" -- besides the universal microwave background? Why exactly has that, somebody could say lunatic, hypothesis been universally accepted? Many thanks in advance, Boris PS: Have all your books and videos...

[@chromabotia]

Thank you Dr. Carrol for doing these videos. In explaining physics from first principles, could you inject some humor into the process and in general loosen up a bit. I know you have his chair and desk but maybe you could learn to play the bongos. It's like you are grinding out some 101 physics for freshman class and a bit of that is coming through. I remember Feynman doing a lecture for the general public on QED and I got a real sense of the meaning. Thank you ~ appreciate your work expanding Everett's many worlds!

[@markchadwick77]

Sean you are so wrong! (tougue in cheek) Good audio DOES matter for KZbin, and green screen is much better than your office when we are watching you for an hour at a time. Thanks for this great series.

[@theodorei.4278]

Please do a related episode about tensors

[@flymypg]

Would it be useful to discuss path integrals vs. surface and volume integrals? It seems implicit in the discussion, but perhaps a moment should be taken for it to be made explicit.

[@DaKoopaKing]

60 gigs sounds accurate. A lot of the file size is probably due to having 40-50 minutes of audio since the video doesn't change frames too often. If you can, export audio as FLAC - it compresses the audio but still keeps it lossless. You might save like 5 gigs of space with that.

[@tomingrassiaimages8776]

Audio is perfect

[@richardalan8867]

Thank you for the info on your studio setup. Just wanted to mention: for me audio is as more important than the video. I have stopped watching videos with poor sound. Good picture quality helps. Most important is what is said and how it is presented. Last, I can close my eyes and enjoy your presentation. Again, thank you.

[@_John_Sean_Walker]

The Higgs Boson is the only particle in the Standard Model with a first name. 😂

[@schlengbryzl]

In my simple mind I would think that a field would require space in order to exist but has there been any talk about space requiring fields? Are space and fields codependent? What came first the space or the field?

[@rainerwahnsinn3262]

24:55 typo for the derivatives of the η field

[@ZeedijkMike]

What you are doing is admirable. The content is very good, though quite a bit of it doesn't stick with me. (Endless re-watching helps 🤔) The quality is brilliant. I do love the black board look.

[@stevemonkey6666]

This was extremely interesting. The explanation about how a particle seems to take the best path overtime was something that I had never heard before.

[@iruleandyoudont9]

hi Sean. I know you're always getting wacky questions but I suppose we all have some, and I know you don't have all the answers, but you know how Penrose has his conformal boundaries in CCC but then no two events can be said to be simultaneous in relativity? is it possible his infinite universes could also conformally map onto your many worlds? the photons are always at that infinity... so even though we can think of the universes as cyclical or chained, we could also think of them as stacked and simultaneous right? also I think those people asked about "static time" are referring to B-theory. thanks for all the great content!

[@afifakimih8823]

I'm waiting for the topic about "symmetry in physical laws" and "noethers theorem"

[@commonsense1103]

The path of an object is set by the energy acted upon it, the particle, in this case, taking from that energy a set direction and speed that does not change unless forces act upon it, a new trajectory and speed, thus, occurring. The fact you think a particle knows the best path to take is foolish in my book unless you think particles have consciences.

[@paulc96]

Reminder - at 23:00 Lagrangian & Lagrange Density explained.

[@MyWissam]

Is special relativity derivable from a least action principle? (a reference)

[@KieranGarland]

This was waaaay more productive than Mario Kart 8.

[@onepieceatatime]

Is QCD the "strong force"?

[@604Nighthawk]

in wiki it says - Names for the number 0 in English include zero, nought (UK), naught (US)

[@604Nighthawk]

I would spell it not since I'm a Computer Engineer

[@ManWhoUsesComputer]

Great production Sean Carroll! Impressive. I have an amendment to my question, and an addition: Questions: * If I assume SpaceTime is emergent from entanglement, is it reasonable to ask if dark matter could also be a form/effect of entanglement? Or blackholes...for that matter * How would Dick describe/explain entanglement? I've looked here [www.feynmanlectures.caltech.edu/], but no chapter title contains "entanglement". PS: the videos are great at a time like this. :) keep it up!

[@somecreeep]

What video games would you be playing all day were you not making these videos?

[@rushyscoper1651]

am CS major finish two year ago but still love physics couldn't take it because of were i lived CS was just way safer path. anyway i decide that am gonna learn high level physics on my own as a hobby, is their any tips to what field in math i need to learn first before jumping to high level physics? if u can list a math courses/field in order it would be great.

[@djbabbotstown]

Sean! You’re a top fucking bloke. Hello from Ireland. I’m gargled.

[@florh]

Professor Carroll, theories aside, no bias, when do you think the universe got hot and dense? At the same moment gravity broke symmetry, or in mathematics at T=1x10^-44 seconds (or is it 43), planck time will sound familiar as well, or during inflation? My postulation about gravity is , that it broke symmetry one dimension at a time, and inflation was like the total area it already covered in a 2 dimensional state, to a 3 dimensional state, and that might look as if it were faster than light, and then.... my best guess so far is, because of interactions of the higgs field with itself, bosonic fields like the strong-nuclear-force and/or decay of gravitons into glueballs, which all together caused a hot and dense state for a brief moment, first glueballs, then quark-gluon plasma, electroweak symmetry breaking, non-zero potential for the higgs, etc... I have no clue how the universe could have started hot and dense, none what so ever, but that's physics... but hey, if I'm on to something, then black holes just become symmetric again at the core into a 2 dimensional spacetime instead of a singularity? The bigger they get, the colder the core becomes right, maybe that's just it? The closer to 0°kelvin, the more gravity becomes symmetric?