#science #physics #ideas The Biggest Ideas in the Universe | 11. Renormalization

#science #physics #ideas The Biggest Ideas in the Universe | 11. Renormalization 107,724 viewsJun 2, 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 #11, "Renormalization." When you include particles in Feynman diagrams of all possible energies, you often run into infinite results, which are clearly wrong. The modern approach to this problem is to work with "Effective Field Theories," in which we admit that we only understand physics up to some cutoff energy scale. While enormously successful, this EFT paradigm also runs into issues with the Higgs mass and the cosmological constant. 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://art.alphacoders.com/arts/view... #science #physics #ideas #universe #learning #cosmology #philosophy #quantum #fields #effectivefieldtheory #renormalization 224 Comments rongmaw lin Add a comment... Zapp Brannigan Zapp Brannigan 1 year ago This is the best explanation i have ever seen on why infinities occur, why they aren't real, and how we correct for them without skewing results. Keep the great vids coming! 41 Steven H Steven H 1 year ago With all of the ugliness going on in the world right now, these videos remind me of how incredible humanity can be at our best. Thank you very much Prof Carroll. 24 Pamela Collins Pamela Collins 1 year ago Absolutely fascinating and enlightening. This is the first time I’ve heard the problematical infinities explained. Thank you!! 18 Shikhar Amar Shikhar Amar 1 year ago I am really enjoying how deep we are going here, keep doing Dr.Sean! 35 Picksalot Picksalot 1 year ago (edited) Renormalization has become my favorite topic in this series of lectures, and Ken Wilson is a hero. I'm so glad that he figured out how to get rid of all those "infinities." There is a point when concepts exceed available experiments, and it becomes a necessity to have a precise language to communicate coherently. Thanks 8 NoGary No NoGary No 1 year ago This has very quickly become my favourite series on youtube, thank you for the in-depth explanations Sean. 6 R C R C 1 year ago Dr. Sean Carroll, in the Q&A would you spend some time on the “quantum foam” of the vacuum? I understand that Feynman virtual particles are placeholders for the complicated back-reactions of the fundamental fields. But what about these foamy short-lived particles at the ground state? Thank you. 7 Axis Axis 1 year ago Hey Sean, thanks for these videos! One question that I still struggle with (and see contradictory answers) is whether Virtual Particles have any physical significance or if they are just mathematical "tricks" for doing calculations of complex field interactions. If they were the latter, there would be situations (like a free particle in a non-interacting field) where they should not matter. However, in this video, you indicated that they still cause vacuum polarization. Besides, as I understand it, Virtual Particles are directly responsible for static field forces (i.e. when a static electromagnetic field pushes/pulls on an electron). Is there a reason why they cannot be accepted as existing in reality, i.e. as another type of particle that cannot be directly observed and violates some principles, but is otherwise perfectly "real"? 1 59ratfink 59ratfink 1 year ago Thank you Sean for this amazing series. Wish i was younger and smarter to really grasp all these fantastic ideas but what i can grasp is so unbelievably satisfying. i can tell you truly love teaching physics and it shows. 1 Tommy Eden Tommy Eden 1 year ago I feel like I am getting a free education on my favorite side hustle. This is really awesome and noble of you Sean! Side note, seems computer programmers really like physics. Several I work with are studying the subject. I wonder why that is. Maybe the simulation is reality after all:) 1 Martin Miller Martin Miller 1 year ago Hi Sean, this is the first one I've caught so far, will definitely go back and watch the others. You've pitched this at the absolute perfect level for someone like me, who kind of gets what your talking about but doesn't have the maths to back it up! Thanks very much for all you do in promoting physics! 1 Mister Mxyzptlk Mister Mxyzptlk 1 year ago Amazingly clear and insightful, as always. Thanks a lot and I hope you will write a textbook on these thorny topics one day. Uzu Lim Uzu Lim 1 year ago thanks for this, it's a good complement to the more technical and localized introductions to this topic. 1 Lemon Party Lemon Party 1 year ago This is great stuff. You make it seem so simple. 1 calwz calwz 1 year ago Poor Sean, wanted to keep the episodes short, but they are just getting longer and longer. :) I'm not complaining tho. 78 Andrea Vecchione Andrea Vecchione 1 year ago Very very very beautiful lecture, I really appreciated it. Thanks professor Carroll and please don't stop making video-lectures like this one. unòrsominòre. unòrsominòre. 1 year ago Hi Sean, as always thank you so much for these wonderful videos. About the vacuum energy problem, what is your opinion about what Carlo Rovelli says, i.e. it is a false problem because quantum terms are "corrections" that do not affect the average "classical" terms? See here: https://youtu.be/fi3GZz4vWdo . Thanks! Dr10Jeeps Dr10Jeeps 1 year ago Wonderful presentation! Thank you. I really look forward to your YouTube videos. 2 forbdonut0yt forbdonut0yt 1 year ago A welcome break from everything going on right now. Thank you!! 5 ADHD Asian ADHD Asian 1 year ago Interactions was a doozy, Normalization was no less! ty Sean for getting us through :) 4 Nicholas Rawhani Nicholas Rawhani 1 year ago Prof. Carroll, my gratitude field is in the Ultraviolet 🎇 Thank you for taking the time to share this knowledge 2 Sashwat Tanay Sashwat Tanay 1 year ago Sean Carroll is a legend! I love him. 1 KJ Runia KJ Runia 1 year ago 3:30 Sean Carroll is the Bob Ross of painting lush quantum fields with little trees with branches coming out. 46 Salah Sedarous Salah Sedarous 11 months ago Outstanding teacher, thank you 1 Mark Ragozzino Mark Ragozzino 1 year ago Thank you. Well done, great format, enormously appreciated. Isaac Ziskin Isaac Ziskin 1 year ago Definitely the best public explanation of renornalization that I have ever seen. AND he even justified it by citing the fact that when we renormalize we implicitly accept that we are just writing an EFFECTIVE field theory that approximates some deeper theory that describes interactions at energies above the cutoff (e.g. maybe String Theory, but probably not) Beautiful!! 2 Quantumpencil Quantumpencil 1 year ago Best Physics Series on youtube. Keep them coming Dr. Carroll! Gaus Edukativni centar Gaus Edukativni centar 7 months ago I am a theoretical physicist, working in the field of quantum gravitation, and I can say that this is the most straightforward explanation of the concept of renormalization compared to a lot of actual physicist books. You got yourself a new subscriber, Sean! 1 Andrew Andrew 1 year ago I found the dark energy pressure estimate under an Emergent gravity model. It would be interesting to compare with an order of magnitude to the cosmological constant at quantum scales. Gene Chen Gene Chen 1 year ago This is so neatly presented, thanks for making it public. Rory O Connor Rory O Connor 1 year ago Some of the nuts /bolts/secondary concepts/mechanisms of physics are just a inspiring as more main stream bells & whistles! Really Fascinating lecture! M Siemons M Siemons 1 year ago This was definitely one of the better lectures of this serie! I really enjoy the (relative) simple but still encapsulating math in order to show the important insights. 5 Pavlos Papageorgiou Pavlos Papageorgiou 1 year ago Is it one of the options for the universe to have some maximum energy density? It would make the field equations non linear at higher energies, but what if linearity is an approximation? 1 Tenzin Lundrup Tenzin Lundrup 1 year ago (edited) (1) It would be great to know where Lorentz invariance comes in. I remember reading that the Feynmann diagram approach maintains this invariance for each term. (2) Does a conformal field theory lack a cut-off? (3) It would help to know how the mass of the Higgs is measured. It is obtained as a peak in some curve. What does that curve mean? Miriam Hatira Miriam Hatira 1 year ago Hi the video is so good .. Can you maybe do more videos about renormalization group equation and fixed points ? I'm interested in fixed points of renormalization group equation of high partial waves of two nucleon-scattering it will be very helpful Adam Genesis Adam Genesis 1 year ago I love how down to earth this guy is!!!!! Great stuff. [GxQ=Universe] 1 M W M W 1 year ago Really appreciate these videos. Makes you wonder if we will ever wake up one day with no more mysteries to solve, and how depressing that day might be. But for now the rabbit hole is still deep! Apsteronaldo Apsteronaldo 7 months ago These are such amazing lectures. Especially these last two-three QFT lectures are so useful, gaining so much knowledge and finally understanding terms I heard about a lot but were a mystery to me, like the meaning of UV-cut off for instance. You're awesome Sean! Thank you! Lightning Lance Lightning Lance 1 year ago Sean! This has nothing to do with this video (maybe; I haven't watched it yet), but I was thinking about objects moving through higher or smaller dimensions... And somehow my mind combined that with dark energy and the arrow of time to come up with an interesting perspective on things. Imagine that instead of our universe being the 3d surface of a 4d object, it's actually a 3d object (matter) moving through a 4d object (spacetime). What would that look like? Maybe our universe exists out of 4 spacial dimensions, but matter is made up of 3 spacial dimensions. And while the matter moves according to its own pull on itself in the 3 dimensions familiar to us, it actually moves as one whole object through the 4th dimension, all at the same speed. Then if you imagine that the 4-dimensional object is a 4-ball (a hypersphere), you can imagine matter starting at the top (the big bang), and widening as it gets lower in the hypersphere. At some point, it will reach the middle, and then it will come back in a big crunch. In this hypothesis the 4th dimension isn't time, it's spacial, but the universe seems to change over time because we move through the 4th dimension over time. This also makes some sense of inflation, as it would make sense for the acceleration to increase through time until it reaches the middle, but that the increase would be the fastest at the top of the hypersphere. I know that higher-dimensional spheres are "pointy", so maybe that can explain the moment before inflation happens? If so, we could calculate the size of the 4d object from how long that delay was? You could even imagine dark matter as being matter displaced from us in the 4th dimension. In other words, it's ahead of us or behind us in moving through this 4th dimension. But it can still affect us because gravity is 4-dimensional. I imagine in this case some matter will actually seem to move faster or slower through time - in other words, dark energy can be slightly different in places with more dark matter? I imagine that the matter and dark matter together actually form a 4-dimensional disc-like object, similar to how a galaxy forms a 3d disc-like object over time. Anyway, just a concept I thought of. I have no idea of it makes sense mathematically or when it comes to higher dimensions or quantum mechanics, but it seems to make sense conceptually... Boris Petrov Boris Petrov 1 year ago (edited) This is an absolutely outstanding lecture -- thank you soooo much !!! PS: Could you address the "cosmological constant" in more detail. Including your comment at the very end of this lecture.... about only two items that ... Many thanks in advance... PS: I keep re-watching episodes to better understand -- for example --- for decades I couldn't figure out just why (and how) eV unit is being created/used.... PS2: "..electron is, as we know, NOT a fundamental particle -- it is just an excitation in electric field " .... breaks my electronics engineer's heart ... ;-)) k quat k quat 1 year ago (edited) Brilliant series.Thank you. James L James L 2 months ago This lecture is awesome, except for one thing: The plot of the fine structure constant vs. energy should show that it’s asymptotically the true value. Unfortunately it appears as if the electric charge measured increases without bound. Guitarika Guitarika 1 month ago Hi, you said that the effective charge is dependent on the cutoff scale but I thought this was only true for bare charge ( couplings) and that renormalized charge (couplings) are dependent on energy at which one probes it but is independent of the cutoff Pedro 919 Pedro 919 1 year ago Awesome explanation!!! Fantastic Sean!! 1 Graham Lawton Graham Lawton 7 months ago I felt that this video was where the prep work started to crystallize. Sean is a star - love the style. Cannot help smiling when Sean pauses to clarify x, y and z and draws a little axis ……….. then rolls on to Fourier transforms, Hamiltonian, Lagrangian, Hilbert space and solving the Schroedinger equation in about 10 secs without skipping a beat. Definitely looking forward to the rest of the videos (not lectures)! Martin DS Martin DS 1 year ago Great video, thanks Sean. Shalkka Shalkka 1 year ago I was kept wondering whether effectiveness fo the field theory is somehow different than the domain of applicapbility of any theory. I would for example assume that with sound wave sonic theory at very high pressures for example air would ionize from gas to plasma or that the average kinetic energy of the individual molecyles would exceeed the speed of sound in the medium. A theory of sound probably doesn't predict at which points those happen. With water waves if you make a big enough splash you get water droplets flying all over the place. Those would be badly modeled as "height of water at each location" as in effect where there is droplet there is the water surface and then "two extra surfaces" in the droplet in the air. The mechanism is that if a wave is very narrow ("spikey") the surface tension elements wilil favour forming new volumes over pulling the water level. Droplets will often fall nearby where the rejoin the large body of water making a new wave source. Does the field approach come with assumtions whether there are "sideways" interactions that would be analogous to the droplet forming tension or is it all vertical plus derivates? If one has a large body of water the effect of surface tension to the shape of the water level will be neglible. However if one has a small droplet resting on a leaf or other platform the tension will make it take over only a finite surface area and the waves there are probably analogous to a finite length string. Could bending of space affect what vibrations are possible? Rahul Jain Rahul Jain 1 year ago The notation d^3x feels so strange to me... I've always either seen dx where the x has a vector arrow over it or dx dy dz JohnE JohnE 1 year ago (edited) Virtual particles / antiparticles that come and go. I have always assumed that these would be standard model particles ONLY, such as electron / positron, etc. Your discussion implies that they are not. That they have possibly a continuous range of mass. In other words these particles may have a mass much smaller than electron or much larger, and without limit. I'm confused. I've never heard anything mentioned about their mass. Never mind charge or other parameters. Only that they are antiparticles and the parameters cancel out to zero. I would love a brief answer: standard model only, or not. If not, what the hell are they? Thanks viewer viewer 1 year ago I hope there are some young Einsteins watching and learning from these and what Brian Greene is doing ! 22 Harry Georgakopoulos Harry Georgakopoulos 1 year ago (edited) Instead of working with continuous fields phi(x), psi(x), etc, are there discrete mathematical objects that can be used to formulate this theory? Maybe even throw in a postulate that infinities don't exist and see what comes out? I realize this throws calculus out the window. But there should be some kind of discrete analogue no? Martin Polonski Martin Polonski 1 year ago thank you for that great introductory video! AbsentMindedProf AbsentMindedProf 1 year ago "keeping some units around is good for the soul." hear hear! Leave pure numbers to those silly mathematicians. Javi Kroonenburg Javi Kroonenburg 1 year ago Does string theory give same predictions as these effective field theories do? I mean if we can't detect the effects of the string theory framework, can we just replace the current one with it to see if it gives the same predictions? Or is each of these frameworks bound to their specific energy region? Denis Nichita Denis Nichita 1 year ago I have an exam tomorrow, but who cares? Sean Carroll posted a new awesome video! :-) 11 MscBush MscBush 1 year ago Love viewing the point where qft disintegrates into the abstract. Or cuts off as u stated. Music Video Vault Music Video Vault 10 months ago (edited) Pushing the effective field theory to high E's and then concluding you need new physics (i.e. postulating more particles or forces to be added to the zoo) because the results contradict experimentation implies that the theory is already presumed to be perfect but just needs some adjustments from new experimental information. Science becomes fine-tuning without new paradigms, something that would eventually collapse in absurdities. Alex Alex 1 year ago The need for renormalization essentially points to the fact that we don’t as yet have a handle on the ultimate underlying theory. eefaaf eefaaf 1 year ago You do exactly in handwriting what I do ever since I could write... my hand is slower than my thinking, so I skip letters, start writing what I am thinking of next. dr1971bz dr1971bz 1 year ago A couple of questions. 1. Can you think of the original UV catastrophe or the Plank theory of Black body radiation in terms of EFT? 2. A little more prosaic, what hardware & software are you using to produce your videos? Jainal Abdin Jainal Abdin 1 year ago All the Quantum fields, known and undiscovered, at their lowest ground state energy levels, should contribute to the vacuum energy. And there should be some interactions between some/ all fields being in superposition to give the observable vacuum energy. Getting current discrepancies of order 120 sounds like a system of out-of-phase waves providing constructive interference when there should be more destructive interference. Charles Durrett Charles Durrett 1 year ago At 30:00 shouldn't the dimensionality of h-bar be [h-bar] = [M][D]^2 ? h is an amount of work needs to be done to create a photon. How quickly that work is done is the energy needed as per Planck's E=fh. Dimensionality of f-frequency would be [f] = 1 / [T] so that [E] = [M][D]^2/[T] but [h] is only [M][D]^2. Really like your series. Cozy. John Ky John Ky 1 year ago At 10:00, you say that energy (E bar) can be any number from minus infinity to plus infinity and you add them up and what you get is an infinitely big contribution. Can that statement be clarified further because my intuition tells me that adding everything from -∞ to +∞ is zero. Ghan04 Ghan04 1 year ago When we talk about something like the electron field with a configuration that looks like a particle at some location in space, what implication does this have (if any) on the field's configuration in the rest of space? If we set an E* cutoff at some value near the Planck scale, it would seem that that would place an effective maximum energy on the field across all of space. It seems clear that the different modes of the field don't have an infinite contribution to the vacuum energy based on our observations, so is it possible instead that any given field has some constant energy across all of space that is instead required to be conserved? (I.E. the distribution isn't uniform, but the total energy is constant) David Kierans David Kierans 1 year ago I love these series. It’s few and far between that we can put on a playlist and get lost in it. Very cool. Since getting into these it’s weird that many people say they fall asleep to it. Me too. You would think that would be insulting to the creator but it’s totally the opposite. I must have re listened a million times. Anyway, fascinating speakers and playlists are always great. Here is another one: https://www.youtube.com/playlist?list=PL848F2368C90DDC3D Erik Dahlgren Erik Dahlgren 1 year ago (edited) Question: what if we did the double slit experiment, recorded on a harddrive which slit the electron went through. Then we deleted the harddrive directly or after 5 minutes. Then we can rule out or confirm if the experiment is dependent on a (subjective) observer. Owing to if there is a interfenerce pattern or not. But I assume this already is done. The result would be that there is no interference pattern, I belive, but then we can rule out that the wave collpase when we are looking at it. 2 Cooldrums777 Cooldrums777 1 year ago So this is my takeaway from considering a combination of dimensional analysis and QFT; Is my description below a true statement??? With the possible exception of Quantum Gravity and black holes, one should be able to completely describe the universe with just a few key concepts. 1)The Four natural fundamental quantities of nature (mass, distance, time and charge) 2) The abstract platonic object of mathematical structures 3) The equation of QFT (I guess this really is just an element in the set of number 2 above) 4) A sprinkling of a handful of the constants of nature The above should be all that one requires to describe the entire functionality of the universe. Yoda Jimmy Yoda Jimmy 1 year ago Just a insight question. What would be the mass of a 75 kg man in terms of GeV? Do I weigh more than 10^18 GeV? pia thus pia thus 1 year ago Question about the loop-feynman diagram? What about using a harmonic oscillator on the loop? Could this solve the infinity of this loop ,an oscillator has an infinity momentum? Jeff Spaulding Jeff Spaulding 1 year ago I do not have the education to understand this. I'm just a guy with a bit of math (nothing above diff eq) and almost no physics outside the occasional Wikipedia binge and memories of a basic physics class fifteen years ago. While I certainly couldn't follow much of this subject matter, I do feel like I got something out of this, even if it's only a small intuition of how physics theories work. The fact that I got anything at all out of the video is a testament to your presentation skills. Excellent video! 1 David Hand David Hand 1 year ago In a loop diagram, doesn't the total energy around the loop need to be zero? Going around the loop arrives at the same spacetime coordinate as it started, it would be really surprising if it was two different values. Tim Seguine Tim Seguine 1 year ago So if I understood correctly: quantum gravity is not renormalizable essentially because it couples to too many other fields? Anand Hiremath Anand Hiremath 1 month ago I am not a physicist but have a genuine interest in it. So glad Dr. Carroll explains it so beautifully and includes math to explain concepts that are understandable for a non-mathematician like myself. Can’t wait for more like these on other topics from Dr. Carroll. Thanks again 😊 Aravind H Aravind H 1 year ago This series is precious 28 Mark Holm Mark Holm 1 year ago Those of us who eat oatmeal and raisins for breakfast are concerned about the attractive force between protons and electrons. Without this force, there would be neither oatmeal nor raisins. Every physicist I have read or heard is happy to explain and draw Feynman diagrams of electron-electron scattering, where we know the effect is repulsive, but despite the vast importance of oatmeal and raisins in the universe, I have yet to come across a physicist trying to explain their existence with Feynman diagrams. What gives? Why won’t anyone explain both repulsive and attractive electromagnetic interactions on the same blackboard? 2 Graham Wykes Graham Wykes 1 year ago How does the vacuum energy calculated by this method compare with the vacuum energy during the inflationary period? Could the vacuum energy be responsible for the rapid inflation? Perhaps a working theory of quantum gravity would tell us that gravity almost cancels the vacuum energy somehow. Syrax Syrax 1 year ago hey, are these in a podcast format somewhere? i would love to listen to them while driving but its hard with youtube. Yoda Jimmy Yoda Jimmy 1 year ago I want to know what would be the true cut off, a limit where everything interacts, above which nothing can be measured, nothing can be affected. Some value for which E* would give a theory like Heisenberg's uncertainity principle. Dr10Jeeps Dr10Jeeps 1 year ago As a (semi-retired) Canadian professor of psychology, apart from my own field of social psychology, one of my passions is physics. During this pandemic lock down I am thrilled to be able to watch YouTube videos from some of my favourite physicists including Sean Carroll, Brian Greene, and Lawrence Krauss. What a shame it will be when these videos come to an end. The promotion of the physical, biological, and social sciences in society is a must when certain populations, especially in the United States, appear to be turning away from science and filling their knowledge void with religion and superstition. Humanity needs a greater knowledge and understanding of science, not superstitious nonsense. 34 Marc Merlin Marc Merlin 1 year ago Sean, would the use of thermodynamic variable like pressure, volume, and temperature be considered a kind of renormalization? Admittedly, thermodynamics isn't a field theory, but it does seem to be an "effective" theory for describing physical systems that uses a cutoff distance instead of a cutoff energy. Or is this thermodynamic thinking not a faithful analogy? It seems to me that this kind of "effectiveness" is reminiscent of your discussion of appropriate levels of description in The Big Picture. Is Wilson's renormalization group an extension of this approach to encapsulating detailed mechanisms where our knowledge is limited or does it represent something entirely new and different. Thanks for these great videos! - Marc The Ahmads The Ahmads 1 year ago Can someone provide the link to Dr. Carroll's lecture notes? Jagdeep Jagdeep 1 year ago He should make a book on qft as well Parveen Farook Parveen Farook 1 year ago Sean Carroll and Brian greene sir my role model sean sir lot's of love from india 2 Valdagast Valdagast 1 year ago (edited) And gas mileage (miles per gallon) has the dimension length^-2. So gas mileage is the inverse of an area. ManWhoUsesComputer ManWhoUsesComputer 1 year ago Awesome! Thank you :D Larry Borsinger Larry Borsinger 1 year ago Is the numerical discrepancy in Higgs mass and the cosmological consented related to the relative difference of electrical and gradation always forces? Mike D Mike D 1 year ago (edited) Dr. Caroll , can we say that the cutoff Energy , E* can be view as the Energy that defines our reality , because of the emergence phenomena ? I mean , if we define our reality as emergent , then the E* should be the Energy that its first ''born'' into our reality , because everything greater that E* dont matter for us ? Like the fact that Newtons equations are good enough for our day to day life , but at relativistic speeds you find it has limits . The difference its that , we will never get more that E* ....because..well ....reality breaks down ( like a black hole for example ) . By the way , what its the E* max ? I understand that you can have many cutoff E*, but just one should be the E* that Im talking? I think its the E* max , where a black hole should form . Thank you ! Mark Compton Mark Compton 1 year ago Vacuum Polarization causes my mind to imagine Sacred Geometry. :D Yoda Jimmy Yoda Jimmy 1 year ago 43:00 You're not simplifying anything here. It'd be better if you've showed us the equations. Why this happened? Because for the people who don't know L density (energy over time), scalar field (scalar function) to the power something, it can't exist in L density. What does that 'in' means there? Seif Haridi Seif Haridi 1 year ago how do measure/observe the vacuum energy? Bohan Xu Bohan Xu 1 year ago Your explanation of the origin of infinity (in say 3+1dimension phi-4 theory) is that it is some kind of difference between classical theory and quantum theory. It doesn't make sense to me (and I don't really understand what you meant). If you are talking about non-measurable quantity like absolute energy. Then it's a fine argument. But scattering amplitude is measurable. I don't even know if {phi-4 in 3+1D is a well-defined quantum theory} or not...or it's only well-defined as a low energy effective theory after renormalization? is there a known definitive answer to this question? Bruce Sinclair Bruce Sinclair 1 year ago I thought I had read that the LHC search for the Higgs boson "expected" a mass in the 120 Gev range. How does this jibe with your discussion of the hierarchy problem? TetonGemWorks TetonGemWorks 1 year ago "You're more sophisticated than a few video ago..." Thanks for believing in me Professor, but not that much... Paul Michael Freedman Paul Michael Freedman 1 year ago Has anybody noticed Sean's hair is looking more and more like that of Rick Feynman in his later years? Jeffery WYSS Jeffery WYSS 1 year ago Masterpiece. Naimul Haq Naimul Haq 1 year ago Why doesn't Sean discuss 'amplituhedron' in interaction or renormalization? Does it show that there is nothing called 'a theory of everything'. Yoda Jimmy Yoda Jimmy 1 year ago (edited) Sean Carroll please answer my one question even if it's not from the topics. I'm indeed very needy for the answer. Do we observe dark matter in voids? I can't find a source of observations. If it only does near matter particles, it really can be the dark gravity indeed. Or a fake gravity from a fake velocity due to closeness of matter. Which is indeed big in numbers. Can we observe dark matter around small localities than a galaxy? I just need a yes or no for both the questions. Тимофей TIENTI Глухих Тимофей TIENTI Глухих 1 year ago best explanation ever Michael J Morrison Michael J Morrison 1 year ago Dear Professor Carroll, I really enjoy your videos…. We are so lucky to have your expertise. I do my best to follow the math and concepts but one area really inspires me: If Gravity is emergent (as Erik Verlinde suggests), theoretically can gravity be manipulated?? Can the entropy of a space be changed and used to make gravity cause a repulsive force?? Brian Cannard Brian Cannard 1 year ago Just. Wow. You made my Spring. 1 sleepy314 sleepy314 1 year ago Good news is that there is still something for my grandchildren to figure out. 4 Sergey Simon Sergey Simon 1 year ago Sean why are you so against infinity? The only thing holding us back to explain everything, is your own capability to accept the word "infinity" in its full glory. Please expand your imagination to things what full infinity may produce. For example, in a full infinity there is room for ALL time travel related paradoxes. Meaning you can produce all kinds of time travel loops, infinite times, in an infinite loop. Producing infinite universes at the same time in those loops, which producing infinite splitting universes on its own. There is no time travel paradox at all if we allowed infinity to produce those paradoxes infinite amount of times for as long as the eternity goes. There is no limit for infinities in an eternity. What a learned from Jesus lately is that kind of infinity is the basic level of reality in "gods dimension". Our own world was produced as a result of condensed versions of all previous countless infinities of eternities together. Don Dovahkiin Don Dovahkiin 1 year ago I finally get why astrophysics is important. We simply cannot creat tests here on earth to test tgese ideas. We have to look in nature fro answers. DrDress DrDress 1 year ago 29:07 you mention [cgs] first? OMG he's an astronomer! Teddy Brow Teddy Brow 1 year ago (edited) 15:13 - One might say it felt like there was "Something Deeply Hidden" ;) apper cumstock apper cumstock 1 year ago Enlightning. MC Squared MC Squared 1 year ago The Higgs mass is not a constant. It is a constant for proton-proton collisions. What is the Higgs in electron-positron annihilation? Maybe a pair of photons with a total spin of 0... in the reference frame of the electron-positron couple... It would be nice if you could comment on the path from QFT to QCD. Ryan Kray Ryan Kray 1 year ago Sean, would you consider becoming a Brave Verified Publisher? I know you have a Patreon account, but you could also get BAT (Basic Attention Token) for these excellent videos as well Joshua A Martin Joshua A Martin 1 year ago entropy is the inability of the electrical field to maintain bonding when interacting with the weak(muonic) and strong(tauonic) fields, an interaction that exceeds these electrical bonds part of my idea for the Yang–Mills existence and mass gap for the Millennium Prize, would you like to have a share in the 1mill US?? Yoda Jimmy Yoda Jimmy 1 year ago 1:21:00 Then we need a way too heavy mass which account for the observations. I mean literally wayyyy toooo biiiig. And gravity is weak. So it's even wayyyyyyyyy toooooooooo biiiiiiiiiiiig. Joao Joao 1 year ago Stopping everything and starting to watch, as usual! Thanks Sean! #science #physics #ideas The Biggest Ideas in the Universe | Q&A 11 - Renormalization 36,916 viewsJun 6, 2020 716 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 associated with Idea #11, "Renormalization." Mostly it is me trying to say in slightly better ways what I tried to say in the original video. But we also talk a bit about whether virtual particles are real, and whether an effective field theory of gravity can really explain all the data. 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://art.alphacoders.com/arts/view... #science #physics #ideas #universe #learning #cosmology #philosophy #quantum #fields #effectivefieldtheory #renormalization 81 Comments rongmaw lin Add a comment... Wayne B Wayne B 1 year ago "There will be black holes" - a happy addition to my growing list of Carrollisms! "But that's OK." "We can do better." "Sorry about that." Thanks for the great videos - and the new drinking game! 14 doobs doobs 1 year ago Loving this series. I've learned a lot. I have wondered for a long time how it is that a field of virtual photons can mediate both repulsion between two electrons and attraction between an electron and positron. What are the photons doing differently? Thanks 1 Commander Shepard Commander Shepard 1 year ago I’m taking my formal course in quantum mechanics this fall, your videos on the subject were a great overview of what I learned in modern physics this past semester. Thanks for the review Dr. Carroll! barry wilmot barry wilmot 1 year ago Great series of videos. This one kind of answers a nagging question I've always had about why physicists refer to gravity sometimes as a field and sometimes in terms of a distortion of spacetime. Catching up after doing a degree in Physics nearly 40 years ago :-) Michael W Michael W 1 year ago This is so stimulating, my brain freaking loves it. Thanks!! NoWhereMan NoWhereMan 1 year ago Thank you Dr. Carroll, I always had my intuition about how virtual particles could explain the proton/electron interaction of an atom, but making it a clear distinction (not necessarily better) from the quantum wave function help me in my understanding. D L D L 1 year ago It's always good day when Sean Carroll uploads a new video 👍 29 DreamDesk Design DreamDesk Design 1 year ago Hi Sean! Love all your videos! Ive just got one question in regards to entanglement...is it possible for entangled particles to be in different time periods (one in the past and one in the future) since the distance between them can be eg: between 2 galaxies or further , and time dilation comes into play. Thanks! David David 1 year ago I love you Sean Carroll! In a way, it is a testament to the power of field theory to be applicable in effective ways to so many things, more than it is a testament to the unity of nature. And yet this applicability is the reason why Eugene Wigner spoke of the unreasonable effectiveness of mathematics. Joao Joao 1 year ago Hi doctor Sean! I'm speechless about how grateful I am for your videos! I am a psychologist and I study quantum mechanics as a hobbie and I never hoped to understand as deeply as I am understanding this topics! It's simply amazing! Do you think in the future we will have "flat spacetime" society, like we have the flat earth society? Hehehehehehe! Just kidding! Again, really, really thanks a lot! 1 R C R C 1 year ago Another great Q&A video. Thank you Dr. Sean Carroll! Robert Shirley Robert Shirley 1 year ago I wouldn’t name it ‘virtual particles!’ Maybe ‘transitional wave state!’ But if they named it that way, we have a bigger problem! Namely, what is wave and who is particle? What is the line between them to be described? More importantly, wave on what? All these questions would be irrelevant if we thought of matter as only a distortion of space itself! 1 Too Crash Too Crash 1 year ago Thank you, for guidance through those dualities. Barefoot Barefoot 1 year ago Wow, very nice lecture! Mind is a bit blown. This is why I watch things like this. Most of the time, most of the things are things I know... but every so often someone phrases something just a little bit different and creates an epiphany, and this video did that for me, specifically with regard to EFTs being able to describe different sets of fields. I'd never heard anyone state that quite so explicitly. Thank you! Redai Ron Redai Ron 1 year ago If the sun's gravity increased or decreased, what effect would be on the earth's velocity? Andrew Campbell Andrew Campbell 1 year ago There seems a clear cut difference between forms and processes. Forms are static representations that may or may not be accurate representations of underlying reality and reality we might say is process more than form. Us human beings are designed to see forms rather than processes - processes are usually inferred by 'stacking' forms. 1 MadderHat MadderHat 1 year ago 14:50 It would be cool if we could have a 'prism' to do this in reality. ManWhoUsesComputer ManWhoUsesComputer 1 year ago Great explanation around minute 10 to 11:00 Soggy Gamer Soggy Gamer 11 months ago I look for an hour video from you every night. No matter the topic I enjoy your knowledge! Bill Holland Bill Holland 1 year ago I guess we can say that the fields interact, terms like e-(x)e+(x)gamma(x) appear in the Lagrangian for the field interactions, and we can experimentally measure the magnitudes for each of the terms, so that’s how we describe the field interactions. But I think what we lack is a way to derive the magnitudes from first principles. We don’t know why the magnitudes are what they are. It’s as if there are a bunch of knobs that set the interaction strengths for sets of fields that interact in our universe, and we don’t know why the knobs are set to those values. This situation is a bit unsatisfying. Things are the way they are because that’s the way they are. It would be more satisfying if the knobs could be shown to have only one unique set of values. Yoda Jimmy Yoda Jimmy 1 year ago Can virtual particle be of any different configuration than any known or would be known particle in standard model? glynnec2008 glynnec2008 1 year ago Question: Since the positron is the anti-particle of the electron, is there a corresponding property in their quantum fields? The positron field and electron field overlap in spacetime, do non-particle vibrations in these fields somehow synchronize and/or annihilate each other? bryan stephens bryan stephens 1 year ago This may be off topic but it is a question :/ .. anyways what do you think of the ideas in "Lost in Math" by Sabine Hossenfelder 17 James L James L 2 months ago This is the most infuriating answer to the question “Are virtual particles real?” Because there’s a real question here. If I said there is an angel pushing around the virtual particles, you might ask: Is the angel real? The answer “well it’s a superposition over many states of the angel” dodges the question. Angels have angel-like properties. Can those be observed? Also: This is dynamical but the wave function is not dynamical. This is also silliness. That’s like taking a block model of space-time and saying “if you zoom out, there’s no dynamics.” If I am given a superposition over quantum states, then I can imagine a physical system being in each of those states. Here it’s not the case. So what’s really be asked is: Why is there a superposition over non-physical things and how does one make sense of that? (Non-physical because mass-energy is not conserved by the virtual particles.) Álvaro Rodríguez Álvaro Rodríguez 1 year ago I was one of the maybe many who asked how it was possible that fields interacted. I did not phrase it properly, but with a bit of time to introspect I find that my confusion came from what I learned about the Maxwell Equations. It was more or less let to believe by my teacher that, as the electric and magnetic fields influence one another's strength, they were the same field. The reason for the electric and magnetic fields being one might be more related to observer's independence issues, but now I get how fields interact. If everything is represented by a field,...yeah ok, you'll have somewhat translated equations to this new paradigm. (an electron [[field]] will influence the electic field. And I guess that does not have to mean that all fields are the same underlying one. Great videos. Thanks again. Tubluer Tubluer 1 year ago We really need a better term than electron-ness. Any ideas? David Hand David Hand 1 year ago Regarding "how do fields interact?", isn't it more intuitive to say that they are coupled in various ways such that their values pull on each other as if physically connected, e.g. by a spring or something? That's a much better answer, but I don't know that it's true =/ Ross E. Forp Ross E. Forp 1 year ago (edited) Dr. Carroll, if I understand it correctly, when a photon is redshifted (blueshifted) it loses (gains) energy ([EDITED]: proportionally to its wavelength change, since E = hν). Where this energy is transferred to/from ([EDITED]: and how)? Yigal S Yigal S 1 year ago If you could only write QFT book at some introductory level like your GR "Spacetime and Geometry" book... IMO there is still lacking a good clear introduction to the QFT accessible to amateurs and B.Sc. level students. M S M S 1 year ago Great content. Titles should start with the subject. MyOther Soul MyOther Soul 1 year ago One thing that sets humans apart from all other animals is we tell stories. Stories are powerful, the words on the page and the symbols in the equations are meaningful things. The more they correspond with reality the more powerful they are. Still they are not what is real, the wave function of the universe isn't what is real, the universe is, the wave function is powerful because of it's correspondence with reality. It is a mistake to confuse the story with what it is about. Wrong Time Weeder Wrong Time Weeder 7 months ago I love your videos. Gogo Gogo 1 year ago I don’t know anything about this, but I’m here because your voice is so soothing to me!! :) found you from Joe Rogan! ❤️ hope all is well!!! 1 Yoda Jimmy Yoda Jimmy 1 year ago What's that private video just added in this playlist? Sean, you should tease the next idea at the end of each video so that we can come prepared and excited with dreams and hopes. 1 Chris C Chris C 1 year ago Do virtual particles sleep and dream (at night)? Rob Ross Rob Ross 1 year ago Well I used to think I understood virtual particles. I don’t anymore. 1 Valdagast Valdagast 1 year ago When are physicists going to own up to the fact that the letters in the Latin and Greek alphabet are used up and introduce runes, Japanese hiragana and katakana, etc. to new stuff? 5 Jay Davids Jay Davids 1 year ago Tell it Sean!!! 1 Praetor2000 Praetor2000 1 year ago SC: "They are not arrows of movement!" Also, SC: "Think of the positron as going backwards in time." viewer viewer 1 year ago Is Time and Entropy connected / the same thing ? Jon Charlat Jon Charlat 1 year ago May our Almighty God continue to bless you and your beautiful family in Jesus mighty name i pray 🙏🙏🙏🙏🙏🙏🙏🙏😘💕✌ No Bell No Bell 1 year ago Virtual particles = fatal attraction.. 1 Yoda Jimmy Yoda Jimmy 1 year ago Why fields vibrate? Eliézer José da Silva Rios Eliézer José da Silva Rios 1 year ago So, fields is a mathematical abstraction, correct ? they are not real!!!! Gülşen Gülşen 1 year ago You speak too fast, please speak more slowly, thank you so much 🙏 T S T S 1 year ago make the background even darker Peggy Beverley Peggy Beverley 1 month ago No black holes ...now Yoda Jimmy Yoda Jimmy 1 year ago Is ontology english? Mark Heller Mark Heller 1 year ago try to realize the truth there is no spoon 1 Ben Cancio Ben Cancio 1 year ago I'm sorry it's 2am and I don't understand all of this at the moment...maybe that's why I didn't finish college haha 😅 Dave Wilson Dave Wilson 1 year ago Damn. 399 😣