#science #physics #ideas The Biggest Ideas in the Universe | 17. Matter

#science #physics #ideas The Biggest Ideas in the Universe | 17. Matter 79,242 viewsJul 14, 2020 Sean Carroll 154K subscribers 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 #17, "Matter." The matter of which we are made can be solid because electrons are fermions, meaning that they take up space. We talk about that and the closely related spin-statistics theorem. Complete with demonstrations using visual aids! My web page: http://www.preposterousuniverse.com/ My YouTube channel: https://www.youtube.com/c/seancarroll Mindscape podcast: http://www.preposterousuniverse.com/p... The Biggest Ideas playlist: https://www.youtube.com/playlist?list... Blog posts for the series: http://www.preposterousuniverse.com/b... Background image: https://www.publicdomainpictures.net/... #science #physics #ideas #universe #learning #cosmology #philosophy #matter #fermions #spin 223 Comments rongmaw lin Add a comment... Tickle Me and I'll Hurt You Tickle Me and I'll Hurt You 1 year ago Honestly I wish this would never end its kind of addicting 95 Rhonda Goodloe Rhonda Goodloe 1 year ago Sean, Thanks for your enthusiasm and patience in sharing your knowledge! 6 Jason Hord Jason Hord 1 year ago Best explanation for spin I have ever found. Thank-you! 9 annwwar annwwar 1 year ago Thank you for most interesting spin explanation I ever heard. I read before that matter is solid because of the EM repulsion forces between electrons. How does that fit in or compare to the Pauli pressure as the cause? 2 Marc Merlin Marc Merlin 1 year ago I have a question having to do with the Fermi pressure, specifically with the degeneracy pressure that keeps white dwarfs (or neutron stars) from collapsing any further. It would seem that the Pauli exclusion principle would, in some sense, be absolute: there's no forcing electrons (or neutrons) into the same quantum state. I assume that quantum mechanics doesn't break down, but somehow the Pauli exclusion barrier is circumvented for stars above a certain mass in both cases. How does gravity overcome this restriction? 9 Gilbert Anderson Gilbert Anderson 1 year ago (edited) I'm loving your relaxed presentation in this series. You've inspired a great many people; I'm sure wikipedia's servers have felt the burden. I've spent many hours in follow-up reading after GIitU videos, and since we, your viewership, matter, and this IS the matter GIitU: here are my questions. WOW, not only are Bosons bosons, but Fermions can be bosons too ! Cooper pairs of electrons are bosons. (What force do they mediate?) Mesons (composed of a quark and an antiquark, two Fermions) are also bosons. Pions mediate the transformation (decay) of quarks. Tritium and ⁴He are bosons. Who knew all these Fermion collectives could be bosons? 1) Why is hydrogen not a boson? Obviously it isn't or our sun would be a lot colder. 😡 But it is two spin ½ particles. ½+½≠1? This Wikipedia diagram https://en.m.wikipedia.org/wiki/File:Standard_Model_Of_Particle_Physics--Most_Complete_Diagram.png of the spin-0, spin-½ and spin-1 sectors before and after the spontaneous symmetry breaking of the Higgs condensation is quite fascinating. Is there REALLY an EM field, or is the overlap of (the crippled remaining half of) the weak hypercharge field and (the remaining crippled T³ component of) the weak isospin field what is reality. In describing the EM field are we in effect talking about the sun revolving around the earth (because obviously that is what we experience) ? 2) Would a super-advanced alien laugh at Maxwell's equations and rewrite them in terms of the underlying fields? (And what about strong hypercharge and strong isospin? And if isospin has nothing to do with spin, WHAT IS IT? You sometimes get a little casual in your wording ( the "electron field" ). Are the muon and tau separate fields, or is there a single lepton field with the muon and tau as extreme excitations ? (Recent muon results seem to call into question lepton universality.) Can you point us to a list of all the underlying fields of the SM? Come on Sean, give us ALL THE GOOD STUFF ! ) 1 Margarita Hernandez Margarita Hernandez 1 year ago I love his lectures. Physics has always amazed me. 1 Alex Tritt Alex Tritt 1 year ago “So the Universe does ultimately make sense, if not only for the reasons you might initially have guessed.” Amazing 11 Albert Feuerstein Albert Feuerstein 1 year ago Prof. Carroll, you are an extremely gifted teacher! Thank you so much for all your effort to put this series together. 1 Baris Sannan Baris Sannan 1 year ago (edited) its a great pleasure listening to all that complicated stuff so beautifully brought down to earth. Thanks a lot. 4 Steve Steve 1 year ago First, thank you for doing these videos, Sean. Your ability to clearly explain complex ideas so that they are understandable to those of us who are not career physicists is truly unparalleled. That being said, my brain is hung up on the fundamental relationship between matter and “space.” Why do physicists refer to space as if it were a container or substrate that matter is “in” as opposed to just an emergent property of the matter itself? In other words, why don’t we just think that the structure of matter IS space rather than space existing as something independent from matter? Bertrand Le Roy Bertrand Le Roy 1 year ago Sean, thank you for that explanation of spin as the angular momentum of the quantum field and for the discussion of spin zero, integer and fractional in the context of Noether’s conserved quantities. It has never been explained so clearly to me before, despite having a PhD in theoretical physics. What I like the most about this series is how it never takes the shut up and calculate road that so many professors take, and instead takes the time to explain what it all means, and calls out common shortcuts as inaccurate. John P John P 1 year ago Thanks again for another great lecture. I'm wondering if we can use the field theories to explain how mater bends space-time, or the "bending" is just an approximation for graviton. Ofri Dagan Ofri Dagan 1 year ago This series is going to be one of the most meaningful treasures of the world-wide-web. I wish some day humanity reach a point where everyone have a basic grasp on reality. These videos will definitely help get there! Truly a gift. Thank you. 1 markweitzman's wannabe a theoretical physicist school markweitzman's wannabe a theoretical physicist school 1 year ago (edited) @Professor Carroll, Sean you are so productive - its makes the rest of us look so lame :-). 20 Steve Brown Steve Brown 1 year ago (edited) Hi Sean thanks for this riveting series of vids. You mentioned spin zero gravitons(which may not exist) , or more generally spin zero particles in a scalar field - exhibiting a 'breathing mode'. How does this square up with invariance under rotation of a scalar field please, Sean? (Does Higgs exhibit a breathing mode?) Barefoot Barefoot 1 year ago lol you just made my day, Sean! "Bosons vs. Fermions, that Classificashon..." XD Usually when you write and talk at the same time, it's the writing that dies a horrible death, but this time it was the talking, and I adore it! alexandeur alexandeur 1 year ago Amazing! Thank you so much, Sean! 1 Lạc Thường Lạc Thường 1 year ago Thank you Professor Carroll, Sean for the excellent lecture. how ever, keep in your mind that 10% is a part of true and the rest 90% is just a story. we are waitting for your next part of true physical lecture. 8:00 why one atom can not stack on top another one. 1. Because the atom want like that = thinking = a story =? 2. Because the matter have 2 forms: order energy mechanic and none order energy mechanic. After big bang all form of none order energy mechanic (FONOEM) transform into the particles. then all all form of order energy mechanic transform into the atom. 3. Matter have 2 mains state mechanic: state of lower order energy mechanic order energy mechanic and state of higher standard energy local reference mechanic. all atoms are usually standard energy local reference mechanic which called earth or solar space mechanic. Imagine if an atom outside of milky way or solar system enter into solar space. due on this atom motion creating a different energy vector and so on. We call anti-matter or none unique reference energy frame. Here the experiment: on the car running at constant speed as the car energy reference frame is the same. You must use force or energy to used the knife to cut the apple base on they are in the standard order energy mechanic and the same order energy mechanic. If the knife is being in the car running and the apple is being outside of the car. You can cut easy or can not cut the apple at all base on they are same form but in different state of vector energy. These explain clearly how chemical reaction and so on by physical term. May be no more rocket era enter into the space. Eric Svilpis Eric Svilpis 1 year ago Sean, these videos have been absolutely amazing. Exactly what I’ve wanted to know about the way these things work! Thanks so much! 2 Haydar Masud Haydar Masud 1 year ago Hello Dr, Carroll, thank you for breaking down such big ideas into the simplest form that even the dumbest people like me can understand. I hope you will make a lecture on tensor calculus and how to manipulate indices since it is at the heart of Relativity. R C R C 1 year ago This is the best video on spin I have ever seen, and it’s not even close. Amazingly, Sean Carroll is using earlier Biggest Ideas to teach us later Biggest Ideas. This is a lot of hard work given freely and I am equally excited and grateful to Sean Carroll. 1 Ernest G. Wilson II Ernest G. Wilson II 1 year ago First let me say thank you very much for making this video series and sharing it with all of us. I realize this series cannot go on forever, I hope you can find time to do another series after this series. A few thoughts, if our species goes to Mars for any reason, this series should come along for the ride and be part of the archive of things we would like to have saved (backed up) on a different planet. Additionally, it has been an extreme pleasure to have access to one of the greatest minds on Earth. It is particularly rewarding and enjoyable to have Sean Carroll reading comments, following up and doing Q&A videos as part of this series. I am grateful to be able to watch this series as it progresses. This series and or one like it hosted by Sean Carrol would be on national television picked up by a major network if I had my wish. The content is fantastic, the delivery is perfect, the interaction is excellent. I am of course subscribed to this YouTube channel with notifications turned on and thumbs up! 1 NOVA NOVA 1 year ago Thanks for the video! I just bought your book and I look forward to reading it. 1 Boris Petrov Boris Petrov 1 year ago (edited) An amazing lecture. Once again -- Sean Carroll's lecture made our day !! A question: In book reviews of Roger Penrose's "The Road to Reality" several reviewers, who apparently understand more than I, made surprising comments which I don't understand -- a la Penrose delivers the knock-out punch: --- Conservation of energy/momentum/angular momentum in General Relativity is non-local !!! What such comments really mean? What is their significance? Many thanks 4 Cooldrums777 Cooldrums777 1 year ago (edited) Very satisfying explanations of spin and wave function interchange. I have to admit that coffee cup example of 720 rotation was extremely satisfying. I definitely would not have grasped the concept without that example. Of course we are still missing an explanation as to exactly what object or abstract quantity the quantum wave function is rotating 720 degrees in relation to ( I presume it's not a Planck length version of Sean) but I accept your assertion that it's just too complicated to discuss here. The ribbon was excellent as well, and once you demonstrated the interchange and rotation it made sense immediately. This was an excellent lecture overall. A nice selection of big ideas were covered. Thank you Professor. Travis Travis 1 year ago You gave an amazing visual analogy for spin 1/2 particles with a coffee cup in your hand that has to be spun twice around to get back to the original state. Is there such an analogy for spin 3/2 or 5/2 particles and, if not, does that lack of a visual analogy say anything about the real possibility of such particles existing? 1 Gabriel Q. Gabriel Q. 1 year ago I realized that this serie of lectures will end eventually. We need more bigger ideas. 14 jan kåre Austinat jan kåre Austinat 1 year ago thank u carrol for beeing so consistent with us,this series will be like a sterter for a lot of peeps later on..thanks to corona too i guess I Z I Z 1 year ago Thank you your lectures (vlogs) are simply fascinating. Dan G Dan G 1 year ago How lucky we are to have these personal lectures by such a talent and gifted teacher delivered into our living rooms. John Długosz John Długosz 1 year ago Sean, you touched on complex dimensions in the episode on topology, and hinted at the fact that two complex dimensions is not quite the same as three real dimensions. But, you didn't come full circle (so to speak) when you got to spinnor fields. Also, after explaining that angle is defined via inner product in Hilbert space, you can show how rotating 360 degrees leaves the vector different from what you started with, mathematically. 1 Gabe E. Gabe E. 1 year ago That spin 1/2 practical example... got me on the edge of my seat. You can totally sense the Feynman of it. B T B T 1 year ago Hi Dr. Carroll, can you plesae do a video explaining about the myth of "warp speed" that we keep seeing in movie such as star trek and such? I am very curious what's the correlation between gravity and electrons? fsmv fsmv 1 year ago I hope we get to hear more about how the number of dimensions of spacetime affects the interchange operator. I can see how it would affect rotational symmetries and therefore angular momentum but I don't see how that argument about interchange causing us to have exactly two options could be modified. 1 Cronte Misto Cronte Misto 1 year ago Does the Pauli Exclusion Principle relate to a particular force that keeps particles away from each other? I.E., what happens physically, say in a neutron star, to keep particles from occupying the same location? g g 1 year ago Dear Sean, You are a GREAT communicator. Over the last few years, and throughout this series. I have learned SO MUCH from you. Things that I have been curious about for over forty years, you explain so clearly. If I were a president or king, I would appoint you as one of the important communicators of important subjects. How much better would this world be if only we had more real scientists, engineers, doctors, nad other well educated ETHICAL people in government? The answer is simple. The world would be a MUCH better place. Thank you for all you do! Boris Petrov Boris Petrov 1 year ago One more question -- to which book do you refer when you say "it is in my book"? I have all your books (as well as from biologist Sean Carroll ;-)) ) -- in Audible format -- only two of your books have illustrations in PDF formats (Higgs and Big Picture) 1 Twin Left Behind Twin Left Behind 1 year ago One small correction: the example of the electron going through the Stern-Gerlach experiment is not correct. As it is a charged particle is it subjected to the Lorentz force which will distort the clear separation in 2 discrete states. The experiment is usually done with charge neutral particles such as silver atoms. JohnE JohnE 1 year ago Planks constant is used as a measure of spin, as you have described. Planck's constant has units of angular momentum. If you fire a beam of up spin electrons at a target will that target gain classical angular momentum? (It might be too small to measure experimentally, but...) 1 EarlWallaceNYC EarlWallaceNYC 1 year ago (edited) So from where comes the exclusion pressure. The Exclusion Principle seems binary: How does it say anything about particles which are "close" to the same state? Another insightful lecture/video. Thanks. Aus Blob Aus Blob 1 year ago Dont get too focused on ended these discussions, i think i speak for everyone that watched these videos in saying we all love to hear you talk about the universe and would rather you just kept making videos about it if you can find the time haha Jonny See Jonny See 1 year ago You’re so awesome Sean!!! Love you buddy!!! 💪🏽👍🏽❤️ 1 Louis Cohen Louis Cohen 1 year ago When bosons gather in the same location, say the Physics lounge for the weekly wine and cheese, is the boson field value a superposition of all the bosons in that location? Is the field value ever ambiguous, ie, the same value could be a superposition of different bosons. Or will a Fourier transform always decompose the field vibrations into an unambiguous set of particles? Thanks, the series is great, 4 Rohit Pandey Rohit Pandey 1 year ago I kind of like having my own space. So definitely more of a Fermion. Nathan Okun Nathan Okun 1 year ago The "Spin" up or down at a fixed amount, no matter what increment of magnetic field is used gives a two-value-only "quantum" (stepped results) effect - how "Quantum Mechanics" gets its name - and not an incremental value, as :Classical" Physics would predict. I would assume that such a quantum effect also works with the double-slit experiment or all other quantum test results. The reason would be that to have different random results that all parties looking at each test agree to, no matter where or when they are (using Special Relativity to determine this), the values have to be stepped like in the smallest possible form of infinity, the countable or "Rational Numbers" infinite set (Cantor's Aleph-sub-zero infinity). Only this infinity has discrete, completely separate values with sharp boundaries separating them. The next higher known infinity (to my knowledge) is "c', the infinity for all the points on a line, which is the one used by Classical Physics (the "Real Numbers", I think), but these have no such discrete, separable values and the blurring of one result into the next would make different, slightly-offset (in the Special Relativity sense) observers IN THE SAME UNIVERSE (assuming Everett's Multi-World view of Quantum Mechanics is true) see SLIGHTLY DIFFERENT results. Thus, for Quantum Mechanics to be able to follow Everett's concept (which it can, though this may not be the only correct concept of how Quantum Mechanics works), ALL final results have to be stepped in the manner of Aleph-sub-zero discrete results and this can only happen when ALL quantum INPUTS (Spin and so forth) to the experiment are also stepped, not incremental. It looks like Quantum Mechanics is DESIGNED to create discrete results that allow the Everett-style "Multiverse" to exist... Josh Hickman Josh Hickman 1 year ago (edited) So, I'm imagining gravity as a vector field, and it doesn't seem like it would have spin-2, because up and down are different. Is the spin-2 from the idea that, in 4-d spacetime you'd swap up/down and future/past? I mean, it seems gravity is symmetric that way. [I'm thinking and reversing all components of the vector including time is the thing, yes? pi radians in all dimensions?] Brian Cannard Brian Cannard 1 year ago Thank you for the 360 degrees user friendliness. It adds a lot of charm to your way of explaining. I wish you to not talk and write at the same time more often. I'm curious how do you manage to keep your eyebrows calm when that happens? Have you trained to keep friendly facial expression so your student keep listening? :-) One of the greatest teachers in the world! For sure. Thank you for your Mission! Deez Nutz Deez Nutz 1 year ago Discussion of spin around minute 35 is one of the clearest I have heard! 7 Big Dee Big Dee 1 year ago We can't squish a table, but does the table eventually degrade or lose its energy or charge over time if it's protected by environmental factors? Stephen Bryant Stephen Bryant 1 year ago On the incompressibility of tables or wood: a nice illustration but if it were really true, I'd never be able to build anything with squared-off corners. WD Academia WD Academia 1 year ago To what extent is the non-squishyness attributed to Fermi-pressure rather than the electromagnetic force? I imagine that if the electromagnetic force was weaker, then Fermi-pressure would also be weaker. The "electron-wavefunction" around a nucleus would be larger and thus two atoms could overlap more before Fermi pressure really kicks in. Is that right? Elias Barrionuevo Tandel Elias Barrionuevo Tandel 1 year ago Something I always wondered: why not other fractional values or spin? Like 1/3 or e/pi? Why only multiples of 1/2? Sebastian Dierks Sebastian Dierks 1 year ago I still have a question on the last idea of gravity, it's probably too late but I'll ask anyway. You talked about gravitational time dilation and even derived a formula for the eigentime from the Schwarzschild metric. The eigentime goes to zero at the Schwarzschild radius. So from Earth's point of view that means that it would take an infinite amount of time to see something fall into a black hole. Or from the object's point of view, the universe far away would have aged infinitely when it finally falls into the black hole. How is it then possible that anything ever in the finite lifetime of the universe falls into a black hole? We seem to observe that black holes e.g. in the center of galaxies grow over time, at least they didn't start out that big at the big bang, so stuff must have fallen into them from Earth's point of view. Where is the mistake in my logic? 1 qclod qclod 1 year ago These videos matter a lot to me! 3 Alex Doll Alex Doll 1 year ago (edited) New video! Popcorn time. Question, valence electrons must be separate "shapes" to have different psi, but the quantity of valence states increases with atomic number. What is actually changing? 1 Pavlos Papageorgiou Pavlos Papageorgiou 1 year ago In the Stern Gerlach experiment, if the electron was a classical spinning particle with negligible moment of inertia wouldn't that explain the quantized results? First the particle gets aligned with the field, then it gets deflected. Is that explanation obviously true or obviously stupid? Barefoot Barefoot 1 year ago (edited) So a question for the Q&A if it's not too late... in the Stern-Gerlach experiment you drew the possible quantized values for measurements of particles for particles of spin-0 having 1 possible result; spin-1/2 having 2 possible results, and spin-1 having 3 possible results. But how does that pattern continue? Would a Gravitino with spin 3/2 have 4 results, and a Graviton with spin 2 have 5? Or does it just alternate back and forth with the results getting further and further apart, so a Gravitino would have 2 results at 3/2 and -3/2 while a Graviton would have 3 at 2, 0, and -2? Could this point to any insights we might get about the graviton through other kinds of tests, despite not having detected them? Renaud Kener Renaud Kener 1 year ago I believe this serie of videos will reach the same status as "The Feynman Lectures on Physics" for the next generation of undergraduate students. Lucky guys :-) 7 Doug G Doug G 1 year ago “ fieldness makes up nature “ that should smoke everybody’s minds 16 valrossen valrossen 1 year ago What is the cause and what is the effect in the Pauli Exclusion Principle? Is the spin causing the minus-sign? Or is the minus-sign causing the spin? Or do the different underlying behavior of the fields cause both? Or are they all independently just different things that happen to correlate? The Screaming Ellens The Screaming Ellens 1 year ago Is the fact that W/Z Bosons and Photons all have Spin 1 a result of the fact that EM and Weak Force are really the same force at higher energy levels? Or is it just an unreleated coincidence? ROBOT UNIC0RN ROBOT UNIC0RN 1 year ago 25:00 Fermions are described by spinor field, while bosons by tensor field you tou you tou 1 year ago Absolutely brilliant Adam S Adam S 1 year ago "...this will be on youtube for a million years so I might as well make it pretty..." I love you Sean Carroll. Roy Sablosky Roy Sablosky 1 year ago You talked about the Stern-Gerlach experiment, where instead being deflected through a range of angles, half of the silver atoms went one way, and half the other way. So, spin is quantized. But why??? Intuitively, I accept that electrons are constrained to discrete orbits because only a whole number of standing waves can persist within a fixed boundary. Is there an analogous consideration for spin? One website told me, “Half-integer spins are consequence of group theory.… The spin operators and associated Hilbert space of spin states are governed by Lie SO(3) algebra, with resultant eigenvalues of ±½.” But I object to the word “consequence” here. Properties of the real world can’t be a consequence of group theory; it’s the other way round! (Isn't it?) Can you explain in English why spin is quantized? 1 Liam McCarty Liam McCarty 1 year ago What’s the simplest argument that atoms exist? How would you convince a non-physicist if they were skeptical and didn’t have much background knowledge? Paul C. Paul C. 1 year ago Just got home and found a new BIitU video waiting. Ditto to Joao below - stop everything else. Get comfortable with a drink & a smoke - click on "Like" and starting watching for first time. Then watch again tomorrow, Brilliant. Thanks again Prof. Carroll. 2 Chirality452 Chirality452 1 year ago One this issue of spin in a fermion such as the electron. The electron is a quantum field not a literal point particle. A classical field can have an angular momentum so does the quantum field have an angular momentum in a similar sense? That was what I understood from your comments about the paper you published with a student. Thales Fontanetti Thales Fontanetti 1 year ago "of course it's the quantum state; what else could it be?" 8 David Hand David Hand 1 year ago In what sense are we exchanging these two fermions if the whole picture is different after they swap? Valdagast Valdagast 1 year ago So how would a gravitino behave in a Stern-Gerlach experiment? thePhuntastics thePhuntastics 1 year ago What about the psychedelic synthesis ? So far i havent heard anything that could explain the psychedelic experience. Its a mindverse. Once you saw reality unfold and reconstruct around you and you experience being the observer and fall into other realities , lived episodes of other lifes ... well ... And then you see grown men and women like toddlers in a sandbox playing with toys pretending to have any clues about the universe , while you sit on the bench next to them , exhaling your dmt and a cosmic giggle is heard in the background ... Mark Stump Mark Stump 1 year ago So the table is solid-ish in the electron field, and certainly seems solid to other electrons, but I have plenty of disinterested little friends that assure me the table is most certainly NOT solid! And by "plenty," I mean trillions; By "disinterested," I mean "Objective,"...by which I mean "Neutral"; And by little I mean Neutrino sized! Alex Tritt Alex Tritt 1 year ago Once again. Me: I’m going to bed now. Sean Carroll: Uploaded 3 minutes ago Me: new plan 67 David Hand David Hand 1 year ago Is there an actual energy gradient to Fermi pressure? Sebastian Dierks Sebastian Dierks 1 year ago At 40:26 you say that "spin-1 really means spin of 1 hbar". I've heard this so often online and even in lectures and I'm still confused about this. A particle in the state |s,m> satisfies the eigenvalue equations S^2 |s,m> = s(s+1) hbar^2 |s,m> S_z |s,m> = m hbar |s,m> where S is spin operator (I'm not able to draw the vector arrow on top) and S_z is its z-component. s takes values of 0, 1/2, 1,... and for given s, m takes values from s, s-1,...-s+1,-s. That said, taking the first eigenvalue equation, shouldn't the absolute value of the spin vector of a spin-1 particle be the square root of the eigenvalue of the operator S^2? That would be square root of 1*(1+1) hbar^2 = sqrt(2)*hbar. Not 1*hbar. Similarly, the spin of a spin-1/2 particle would be sqrt(1/2*3/2) hbar=sqrt(3)/2*hbar. Of course, the second eigenvalue equation shows that a spin-1 particle can have a z-component of its spin vector of 1, 0 or -1 hbar. Or a spin-1/2 particle with spin up would have a z-component of hbar/2. But I think at this moment in the video you're talking about the absolute value of the spin, not the z-component. Jas Choudhury Jas Choudhury 1 year ago "Why aren't atoms squishy?"...ahhh...that exam question we all dread!! Sebastian Dierks Sebastian Dierks 1 year ago At 24:07 you mention that "whether bosons and fermions are the only possibilities depends on the dimension of spacetime". Could you elaborate? I'm a physics master's student and in my QM II lecture we basically exactly followed your line of argument (of course more mathy and more detailed but still). So it's not clear to me how the argument that the square of the interchange operator is 1, i.e. having eigenvalues of 1 and -1 such that psi(X2,X1)=+ or - psi(X1,X2) but excluding the possibility of arbitrary e^(i*theta) phases, depends on the dimension of space. Daubechies wavelets Daubechies wavelets 1 year ago 23:40 Can someone give a reference or explain what's different in a (2+1)-spacetime? TheyCallMeNewb TheyCallMeNewb 1 year ago A visual demonstration.. And then a second? This proved a different peregrination today! swOOp swOOp 1 year ago 28:22 that bit of Jamaican Patois had me giggling ^_^ thank you for the teachings! Mark Callaghan Mark Callaghan 1 year ago Given fermions take up space , I presume they didn’t exist at the instant of the Big Bang J.F. G.H. J.F. G.H. 1 year ago Sean: it is something confusing the notation you used when discussing the particle exchange symmetry in your notes. You should have written \Psi(x_1,x_2)=+\Psi(x_2,x_1) for bosons [you wrote \Psi(x_1,x_2)=+\Psi(x_1,x_2)] AND \Psi(x_1,x_2)=-\Psi(x_2,x_1) for fermions [you wrote \Psi(x_1,x_2)=-\Psi(x_1,x_2)] . Otherwise, the particle argument is a bit nasty and unconventional. elck3 elck3 1 year ago @Dr. Carroll, inside a black hole, right at the boundary that is infinitesimally close to the actual singularity, does matter take up any space? Mad Science Workshoppe Mad Science Workshoppe 8 months ago I'm going through some health things right now and the drugs give me weird and intense dreams. When I listen to these lectures at night somehow that fades away and I have mathy dreams instead, sleep longer, and don't wake up as often. menecross menecross 1 year ago I finaly understand the property Spin. Thank you! 1 Sekeriya Sharif Sekeriya Sharif 1 year ago Is antimatter and dark matter linked with each other since they both something we don't know that much about 1 Kyle Baker Kyle Baker 1 year ago (edited) Sean Carrol: “Here are the secrets of the Universe.” Me: “Ahhh, pretty cool pretty cool.. 💁🏻‍♂️” Sean Carrol: *Holds empty mug and rotates it with his arm* Me: ....... 🤯🤯🤯....... Colby Nye Colby Nye 1 year ago Sooo sad to hear we are nearing the end! But thank you so much for doing these videos! 3 Partha Banerjee Partha Banerjee 1 year ago I agree that Satyendranath Bose's departed soul would not be very happy but then why not just call them pileon instead of boson? Étienne Parcollet Étienne Parcollet 1 year ago Would have liked a word on anyons. Moreover given recent experimental evidence. Hulkster Hulkster 1 year ago Ahhh matter, something I can get a grip of. 24 deth deth 1 year ago It's a rare narcissism to presume that a human any human would have any inkling of the beginning of the idea of what could possibly constitute the biggest ideas of the universe. It harkens back to pre Copernican world views. Tizza96 Tizza96 1 year ago Amazing thank you so much Mason Temiquel Mason Temiquel 1 year ago Thank geometry for Sean! Robert Shirley Robert Shirley 1 year ago I need one of those schrodinger’s cup so bad :)) 4 Piyush Verma Piyush Verma 1 year ago 7:09 Prof.Carroll; hope this helps - "Sat"-"Yen"-"Dre"-"Nath" (Sat as in Sat, Yen as in Yen, Dre as in Dr.Dre, Nath as in Nathaniel) 1 Cooldrums777 Cooldrums777 1 year ago (edited) Is a monochromatic and coherent LASER beam composed of Bosons that are all in the same quantum state? Chris Lecky Chris Lecky 1 year ago Do atoms produce a standing wave? Cally Craig Cally Craig 1 year ago If and when is this series going to come out on a set of dvds? 1 Too Crash Too Crash 1 year ago (edited) Vectors don't change under Bro°😅 - tis information is applicable to so much, it's distracting. Sean thank you! venustus100 #science #physics #ideas The Biggest Ideas in the Universe | Q&A 17 - Matter 29,336 viewsJul 19, 2020 669 DISLIKE SHARE DOWNLOAD CLIP SAVE Sean Carroll 154K subscribers 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 Q&A video for Idea #17, "Matter." We talk about what "matter" means (including in contexts such as cosmology), why you get discrete results when you measure spins, and related issues. My web page: http://www.preposterousuniverse.com/ My YouTube channel: https://www.youtube.com/c/seancarroll Mindscape podcast: http://www.preposterousuniverse.com/p... The Biggest Ideas playlist: https://www.youtube.com/playlist?list... Blog posts for the series: http://www.preposterousuniverse.com/b... Background image: https://www.publicdomainpictures.net/... #science #physics #ideas #universe #learning #cosmology #philosophy #matter #fermions #spin 56 Comments rongmaw lin Add a comment... Dr10Jeeps Dr10Jeeps 1 year ago I'm certainly going to miss these sessions with Dr. Carroll when he stops. The internet needs much more of this type of content. Personally, I would love to see the internet filled with podcasts dealing with the social, biological, and physical sciences. People need to be educated. 13 Kobev3li Kobev3li 1 year ago As soon as my brain registered that you were talking about why gauge bosons, and fermions have their respective spins, I had to immediately drop everything I was doing. As always, an extremely elegant characterisation to these complex topics. I am so thankful for this wonderful series, keep up the great work Dr. Carroll !!! 3 Goat boy Goat boy 1 year ago So many questions I had answered in this video. Great work! 2 Quahntasy - Animating Universe Quahntasy - Animating Universe 1 year ago So many great questions and such nice answers. Thanks for making our weekends 3 protoword protoword 1 year ago (edited) Doctor Carroll, one of major reasons I wanted come back from hiking vacation sooner is your lectures. Than you! One question remain to puzzles me: Is it possible to measure movement and density of dark matter with help of gravitational lensing? 1 Paul C. Paul C. 1 year ago Thanks again Prof. Carroll, for these superb lectures. Sorry - I mean videos. gisteron gisteron 1 year ago Regarding 26:10 The Stern-Gerlach experiment was made with electrically neutral silver atoms. The entire point was that these were not charged particles deflected by a magnetic field, but neutral ones, deflected only because of an internal magnetic moment - which at first they interpreted as orbital angular momentum, not knowing that the total orbital angular momentum of the electron shell of silver is in fact zero in its ground state - coupling to an inhomogeneous external field. A Kumar A Kumar 1 year ago Weekend treat, thank you Sir. 17 R C R C 1 year ago (edited) I particularly enjoyed Sean Carroll explaining how cosmologists and quantum physicists sometimes use the same or similar terminology to mean different things. These distinctions are probably elementary to trained physicists, but not to the average viewer. Almost as a throw away, Dr. Carroll explains how understanding what scientists mean by the word ‘matter’ turns out to be important. I am comfortable with the broad strokes of familiarity enough that “It’s all fields, all the time.” However, it never dawned on me until this video that the forces in nature can therefor be considered matter just as much as so called particles. I know he repeated this several times previously, but I get it now finally. It is really really really all fields. All the so called forces, all the so called particles, these are all excitations in fundamental fields of nature. Period. The end. That’s it. Which is actually the beginning, because so many supposed paradoxes or mysterious features of quantum mechanics are actually not mysterious at all (or much less so) because we don’t have to tell ourselves the “particles & forces” stories which are only crude visualization tools compared to what is really going on. 3 Beau Beau 1 year ago So, being that A.I and quantum computing can now transfer information more efficiently through light. Do you think it would be possible to look to the stars and universal light for out reaching contact of other life? Though using radio waves in the lower spectrums of light could we swim through the information at higher energy density, maybe checking directed light towards obvious bodies of energy and solar systems? andybob andybob 1 year ago These talks are great, but one observation about Sean’s descriptions. Sometimes the math is used to describe why nature is a certain way. For example, the graviton is a spin2 particle because it has two spacetime indices. This feels like putting the cart before the horse. Gravitons don’t have little indices attached to them. We might say instead that our model of the graviton has two spacetime indices and that description is consistent with observing a spin2 particle. So we are confident that we will observe the graviton to be spin2 and if it isn’t then we will need to revisit our model and perhaps change the indices in some way. I don’t expect this is contentious, and I can understand physicists omitting to mention it all the time because it is simply a given. But it can contribute to a prejudice that maths is unreasonably effective at describing the universe. The alternative view is that maths is simply a very effective abstract language that could describe any universe. Stepan Anokhin Stepan Anokhin 1 year ago I just wonder.... 1. As we know Einstein's equation says that distribution of masses, momentum and energy determine geometry of space-time. 2. According to quantum mechanics matter could be in a superposition of states. Do 1 and 2 imply that geometry of space-time (space-time itself) could be in a superposition of multiple states? 1 nosirrbro nosirrbro 1 year ago (edited) I believe there is at least some reason to think that strange matter can be formed at sufficient pressures, and it could grow to contain an arbitrarily large number of quarks not confined into any sort of specific particle, which may even be more stable than regular matter at any pressure. However, what that reason is, or how compelling of an argument it makes, I couldn't tell you. The wikipedia article isn't much help either https://en.wikipedia.org/wiki/Strange_matter Tova Tova 1 year ago (edited) I'm sure you've heard but like a week or so ago news hit of a gravity wave detection of iirc 23 M[sun] black hole and something between the masses of the largest neutron stars known and under the masses of the smallest black holes known at 2.6 M[sun]. A lot of popularizers have cautiously leaned in on it maybe being a quark star - I think Matt O'Dowd with PBS's space time got into it. David Hand David Hand 1 year ago Let's say I have two electrons and I'm going to throw one at the other. You're telling us that the Pauli exclusion principle will stop them from overlapping, presumably causing them to bounce off or something. However, the PEP only prevents electrons from sharing the exact same state; if they are moving toward each other, they have different momenta and therefore are unaffected by the PEP. What, then, stops them from passing through each other? It seems like the principle is so exact that it ought to be of no consequence at all to two systems interacting such as two atoms as there are so many degrees of freedom and energy gradients. Yeah, I still don't get it. 1 Bernard McGarvey Bernard McGarvey 1 year ago At about 9:00 you talk about particles with some speed - but what is that speed measured relative to? I am sitting at my table at rest but there are some particles somewhere that relative to my speed is close to c. Rick Harold Rick Harold 1 year ago Awesome. Love these 1 Pamela Collins Pamela Collins 1 year ago Does the creation of the neutron star have anything to do with the uncertainty principle? kindlin kindlin 1 year ago I like to imagine the NS turning into a BH is throwing the neutron-ness out the window. If anything like a singularity exists (which theoretically is infinitely dense, but in 'reality' could be on the order of the planck scale) the quarks must be so packed they are basically on top of each other, and maybe reach some quark degeneracy pressure, or if string theory is correct, a string degeneracy pressure where you just cannot pack the individual quark strings any closer. I like to imagine the 1D strings (I'm a fan of string theory) are turning into something like your headphone cables, just getting all warped around each other in a Kaluza–Klein manifold. Being 1D, you could say they infinitely warp themselves, ever approaching a true singularity, but that would also take infinite time, so no 'true' singularity will ever exist in our universe. Rhonda Goodloe Rhonda Goodloe 1 year ago Sean, Thanks for doing this series. Sorry to hear it's not infinite. I'm hoping the version of me lands in the branch of the world where the series continues. 5 Johnathan _ Johnathan _ 1 year ago At ~41:00 Sean says "No, Pauli's Exclusion principle is not being violated when a white dwarf becomes a black hole." Then proceeds to tell us he is unclear how that happens and quantum mechanics has nothing to do with attempting to explain it. Bro, love ya but just say: "Yea, black holes destroy quantum mechanics. Pauli's Exclusion principle and black holes are mutually exclusive." Wanttofanta Wanttofanta 1 year ago "What do you mean by 'matter'?" "I think....I forget exactly." Sean Carroll quotes out of context :P I2yantheGreat I2yantheGreat 1 year ago Thank you Simpson's-style disembodied head of Sean Carroll! 4 David Davies David Davies 1 year ago Black holes evaporate so when they reach a low enough mass do they revert to neutron stars ? Johnny Rocketfingers Johnny Rocketfingers 1 year ago Very interesting Justin time Justin time 1 year ago (edited) You certainly are a treasure and a joy to listen to I must say and I really enjoy everything you have to offer I was just curious and wondering if you could perhaps please change that awful background of the bricks please? Isaac Anderson Isaac Anderson 1 year ago Can’t wait to watch 2 anthony devito anthony devito 1 year ago why don't we have print of the lectures for us hard of hearing....reading is better than merely listening Patrick McHargue Patrick McHargue 1 year ago What is the force that enforces (*cough*) the Pauli exclusion? Gus Tziavelis Gus Tziavelis 1 year ago Matter matters. 1 Joshua A Martin Joshua A Martin 1 year ago so can * be used with n! FABRIZIOZPH FABRIZIOZPH 1 year ago first like :) 3 venustus100 1 year ago