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!
Does a black hole center have lower energy density, than a crust? In holography they renormalize the fields on the boundary towards lower energies. Going from the shell towards the center we encounter lower energies, no?
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.
As a person who studies Philosophy, and likes Science (especially Physics) I'm super happy to see a serious Scientist that takes Philosophy seriously and gives it the proper respect it deserves! Love your work! Keep it up!
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!
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!!
I am not sure your interpretation is correct though. In renormalizable theories (not EFTs), the renormalization scale is arbitrary and there is no need for new physics at some scale, unlike EFTs. In EFTs, you can still renormalize your theory order by order choosing your renormalization scale arbitrarily (hence the RG group flow just like renormalizable theories) but there is a cut-off. These are two different things. Renormalization itself does not necessitate any kind of physics beyond a renormalizable theory (e.g. QCD).
@@quantumgravity7704 The modern (majority) opinion in the field is that QFT is a framework for writing effective field theories. Given the symmetries (and broken symmetries) that we observe at the energy scales probed, no matter the form of the "True" theory that applies at higher energies (Strings, Loops, etc), the world will "effectively" appear to be composed of quantum fields.
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
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)!
This soothes my soul, thx. I don’t mean all that crap mixing pseudo spirituality with physics, just staying on the logical and technical ground of it it’s so rewarding
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 😊
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!
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 RUclips 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.
There is no question that the basic claims of religion are false. One has to wonder though why this meme managed to survive for so long. Is it the ferocity in fight it gives its bearers? Do groups need a strong common "banner" to tell friends from foes? Or is it the fact that a false positive in the wild is just safer than a false negative?
@@zwz.zdenek when you get right down to it, I have found, by asking many people, it is the fear of absolute death. It's one of the greatest challenges of being sentient, and, born in a time when death is an absolute certainty. Put it this way, imagine a time in the future where you could chose, to either age naturally, and die, or age naturally, and transfer your body to a younger one, or not age at all, or transfer to some synthetic body, I wonder how many would allow themselves to end, given that life in the future could be a total transformation from the crappy way we live today, chasing wealth accumulation just to live out our last days in some level of partial comfort, if life in the future, due to technology, was a utopian paradise, the need for a god, or religion, becomes less necessary to believe in, to be indoctrinated in. I don't think that religions are needed to teach people to be decent to each other, given a paradise, there's no need. If we can reach a state where technology can really save us, god , the notion of it, becomes meaningless.And it is my hope, that one day, gods and religions are just an ancient illogical curiosity, some are already.
Religion and science are able to exist together. If someone makes an excuse by claiming religion they are simply not smart enough to work out the science. Doesn’t make their religion wrong.
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!
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.
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.
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!
Thanks for these excellent videos! I especially appreciate how you point out the parts that still need work. Some physicists talk as if all is known, my guess is it will never be. We just add piece by piece as we learn more. The progress and the relentless effort are still amazing even if, as always, a new more comprehensive theory will likely arise in the future that will recast some of these things in different concepts that have more predictive power.
Some of the nuts /bolts/secondary concepts/mechanisms of physics are just a inspiring as more main stream bells & whistles! Really Fascinating lecture!
This is a pretty deep dive into physics right here I've learned a lot already. I'm kind of sick and tired of all the beginning level programs and videos that assume that you can't follow the math so they don't have any equations or anything and although I'm not a mathematicia and I can't really follow the math John Carroll does a good job of explaining what the numbers mean as he's writing them and I don't have to know how to do any of these equations myself just by listening to him I understand what they mean and that is the main point for me cuz I've always been mystified by how they convert things of the real world into the different number value so they do their equations and he does a good job of explaining that
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!
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.
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:)
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.
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.
They often make a popular phrase that the mind is what makes an observer. It doesn't work like that. For a particle to remain ambiguous, there needs to be very little energy exchange between it and the environment. Once there is such exchange, it already counts as an observer and the result is ruined. A computer recording the information is a much bigger "leak" than needed. On top of that, the retention of superposition is bounded by time. So even if your computer was processing very low energy, you would have to delete the information in femtoseconds, or the decision would have propagated to the electron ruining the interference once again.
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"?
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 ... ;-))
Though it, the explanation, seems to be very lucid and simple, but really it is not. A teacher knows the handwork behind it. It is your skill Sean. Great, fantastic ! Keep it up ! Thanks!....
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.
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.
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.
11:30 “maybe you shouldn’t have been so naive.” Classical vs Quantum. Real world etc. I should watch this part again 13:40 philosophy of counterterms 18:00 Effective Field Theory (below a certain cutoff) vs TOEs 23:00 philosophy of why we are allowed to ignore this aspect of our physical system 30:00 dimensional analysis 39:51 I think you meant to say ‘The actual Lagrangian is the intergral of the Lagrangian Density over [ *_time_* ]’. 50:00 relevant, marginal, and irrelevant interactions 55:00 is GR renormalizable? We is/isn’t that important? 58:40 the payoff. “You don’t need to know arbitrarily complicated things to do Effective Field Theory. Tell me what Fields you have and what symmetries they obey, I can go and use this theory, it will come with a small number of parameters that I can measure; I can figure out the Effective Field Theory at low energies really simply.” 1:05:00 Feynman Diagrams are story’s we tell to gain some intuition, what is the Field actually doing? 1:12:00 “when you really probe Quantum Fields, your probing them at some scale, and that scale matters. This is where renormalization matters, it is a physical effect.” What I don’t understand is that virtual particles don’t exist, so how non-physical virtual particles accounting for this physical effect? Also I don’t think I understand properly the link between virtual particles and renormalization. Sean goes on to talk about the Higgs Mass mystery after
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.
(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?
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
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
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?
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.
I feel like there's an echo in my house because every time I make a comment asking a question about something I Observer think about as he speaks the very next thing he speaks of there's something I just made a comment about. Maybe that means he's doing his job and explaining things properly maybe that means he's a good teacher.
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
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?
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?
There should be a msximum energy density within the universe because at some point the energy density would be sufficiently high to form a black hole, which would then promptly evaporate by emitting a load of particles and spreading the energy around.
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.
Wat. You had a fairly interesting question until you invoked Heisenberg, which... seems to have absolutely nothing to do with this, though it's possible I'm wrong. You certainly don't need ultra-high-energy physics to invoke the uncertainty principle; it's just a natural consequence of the introduction of wave mechanics into things. As for this highest limit you asked about... our best current guess is the Planck energy, though that's really just the answer to the question, "What if you set all the dimensionful constants of the universe equal to 1 and then do some dimensional analysis to figure out what 1 unit of that energy would be, converted back to SI units?" If that doesn't sound like a very promising guess... yeah. It probably shouldn't. Since, in fact, there are several other ways to derive very similar units, and there's nothing particularly special about the Planck units in comparison with those ones, and no particular reason I can think of why they should be treated as so significant as to define such lofty concepts as maximum possible energies, granularities to space and time, etc.
@@barefootalien I meant a limit of energy above which nothing can interact, which means talking about such a thing greater than this limit would be meaningless, like for a constant momentum, things become uncertain, a set of energy greater than that when needed to be observed would become uncertain like which is the energy you want? Any energy greater than that would have the same effect in our world.
Seems to me that the ebar going down in the Ibarra coming up with cancel each other out as you already said the same way that these counter operations are expressions or whatever you called them do. Kind of like how a negative integer and a positive integer of the same value would make 0
Is the numerical discrepancy in Higgs mass and the cosmological consented related to the relative difference of electrical and gradation always forces?
the effective field theory looks similar to the method of truncating an asymptotic (divergent) series that comes from a singular perturbation system. Truncate the series and take the limit of the epsilon to zero to get the leading order solution... Are the two related?
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.
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!
Does a black hole center have lower energy density, than a crust? In holography they renormalize the fields on the boundary towards lower energies. Going from the shell towards the center we encounter lower energies, no?
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.
What ugliness you are thinking about ? (Just want to know)
@@srghma everything was about covid 3 years ago
As a person who studies Philosophy, and likes Science (especially Physics) I'm super happy to see a serious Scientist that takes Philosophy seriously and gives it the proper respect it deserves!
Love your work! Keep it up!
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!
I am really enjoying how deep we are going here, keep doing Dr.Sean!
Very cool comment
That’s what she said
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!!
I am not sure your interpretation is correct though. In renormalizable theories (not EFTs), the renormalization scale is arbitrary and there is no need for new physics at some scale, unlike EFTs. In EFTs, you can still renormalize your theory order by order choosing your renormalization scale arbitrarily (hence the RG group flow just like renormalizable theories) but there is a cut-off. These are two different things. Renormalization itself does not necessitate any kind of physics beyond a renormalizable theory (e.g. QCD).
@@quantumgravity7704 The modern (majority) opinion in the field is that QFT is a framework for writing effective field theories. Given the symmetries (and broken symmetries) that we observe at the energy scales probed, no matter the form of the "True" theory that applies at higher energies (Strings, Loops, etc), the world will "effectively" appear to be composed of quantum fields.
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
Like a lot of big discoveries, Ken Wilson wrapped up the ideas of his predecessors like Gel-mann.
Hundreds of thousands of people learning about renormalization in QFT. Astonishing! There is hope for mankind.
This has very quickly become my favourite series on youtube, thank you for the in-depth explanations Sean.
3:30 Sean Carroll is the Bob Ross of painting lush quantum fields with little trees with branches coming out.
Everytime a probability wave collapses, it's a happy accident
CoinStudio Crosstec I love that!
We need Sean Ross Happy Fields memes and Tshirts... NOW!
Denis Goddard Ha! Yes!
Haha exactly!🤣
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)!
I have an exam tomorrow, but who cares? Sean Carroll posted a new awesome video! :-)
This series is precious
Yep. Him and the Brian Greene ones are so good. The format is awesome and in particular the Q&A stuff.
Poor Sean, wanted to keep the episodes short, but they are just getting longer and longer. :) I'm not complaining tho.
Curiously, the opposite of his hair! :3
This soothes my soul, thx. I don’t mean all that crap mixing pseudo spirituality with physics, just staying on the logical and technical ground of it it’s so rewarding
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 😊
Absolutely fascinating and enlightening. This is the first time I’ve heard the problematical infinities explained. Thank you!!
A welcome break from everything going on right now. Thank you!!
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!
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 RUclips 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.
Totally agree and very elequently expressed.
There is no question that the basic claims of religion are false. One has to wonder though why this meme managed to survive for so long. Is it the ferocity in fight it gives its bearers? Do groups need a strong common "banner" to tell friends from foes? Or is it the fact that a false positive in the wild is just safer than a false negative?
@@zwz.zdenek when you get right down to it, I have found, by asking many people, it is the fear of absolute death. It's one of the greatest challenges of being sentient, and, born in a time when death is an absolute certainty. Put it this way, imagine a time in the future where you could chose, to either age naturally, and die, or age naturally, and transfer your body to a younger one, or not age at all, or transfer to some synthetic body, I wonder how many would allow themselves to end, given that life in the future could be a total transformation from the crappy way we live today, chasing wealth accumulation just to live out our last days in some level of partial comfort, if life in the future, due to technology, was a utopian paradise, the need for a god, or religion, becomes less necessary to believe in, to be indoctrinated in. I don't think that religions are needed to teach people to be decent to each other, given a paradise, there's no need. If we can reach a state where technology can really save us, god , the notion of it, becomes meaningless.And it is my hope, that one day, gods and religions are just an ancient illogical curiosity, some are already.
Religion and science are able to exist together. If someone makes an excuse by claiming religion they are simply not smart enough to work out the science. Doesn’t make their religion wrong.
@@zwz.zdenek interesting to know how you now this. Prove it.
Stopping everything and starting to watch, as usual! Thanks Sean!
Prof. Carroll, my gratitude field is in the Ultraviolet 🎇 Thank you for taking the time to share this knowledge
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!
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.
Sean Carroll is a legend! I love him.
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.
Awesome explanation!!! Fantastic Sean!!
Sean Carroll and Brian greene sir my role model sean sir lot's of love from india
thanks for this, it's a good complement to the more technical and localized introductions to this topic.
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!
Thanks for these excellent videos! I especially appreciate how you point out the parts that still need work. Some physicists talk as if all is known, my guess is it will never be. We just add piece by piece as we learn more. The progress and the relentless effort are still amazing even if, as always, a new more comprehensive theory will likely arise in the future that will recast some of these things in different concepts that have more predictive power.
Best Physics Series on youtube. Keep them coming Dr. Carroll!
Some of the nuts /bolts/secondary concepts/mechanisms of physics are just a inspiring as more main stream bells & whistles!
Really Fascinating lecture!
Wonderful presentation! Thank you. I really look forward to your RUclips videos.
Thank you Sean Carroll, this was a great lecture, one of the few lectures I watched at normal speed :D
Very very very beautiful lecture, I really appreciated it.
Thanks professor Carroll and please don't stop making video-lectures like this one.
Just. Wow. You made my Spring.
This is a pretty deep dive into physics right here I've learned a lot already. I'm kind of sick and tired of all the beginning level programs and videos that assume that you can't follow the math so they don't have any equations or anything and although I'm not a mathematicia and I can't really follow the math John Carroll does a good job of explaining what the numbers mean as he's writing them and I don't have to know how to do any of these equations myself just by listening to him I understand what they mean and that is the main point for me cuz I've always been mystified by how they convert things of the real world into the different number value so they do their equations and he does a good job of explaining that
This is a brilliant series, the best I have seen. Thank you for attempting to educate us.
Ooh here comes the big stuff
Interactions was a doozy, Normalization was no less! ty Sean for getting us through :)
Outstanding teacher, thank you
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!
This is great stuff. You make it seem so simple.
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.
This is so neatly presented, thanks for making it public.
Amazingly clear and insightful, as always. Thanks a lot and I hope you will write a textbook on these thorny topics one day.
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:)
Thank you. Well done, great format, enormously appreciated.
The series is great! Alway look forward to every video...
I hope there are some young Einsteins watching and learning from these and what Brian Greene is doing !
Present 🙋
I’m here too! However, I would rather pass all of this off to my 6 year old daughter!! So she can conquer space and I can have a mars hotel 🏨
It’s a golden age of self-learning
What is Brian Greene doing that I am missing out on?
And Sabine Hossenfelder
Brilliant series.Thank you.
Great video, thanks Sean.
at 11:34 i just now see, that the problem is that from E1 to E3 you have E_bar adding one way round the loop and minus E_bar going round the other way
Great Explanation 😍😍😍😍😍😍😍
I love how down to earth this guy is!!!!! Great stuff. [GxQ=Universe]
joyfully informal!!
best explanation ever
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.
16:24 - Groovy! ^.^
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.
They often make a popular phrase that the mind is what makes an observer. It doesn't work like that. For a particle to remain ambiguous, there needs to be very little energy exchange between it and the environment. Once there is such exchange, it already counts as an observer and the result is ruined. A computer recording the information is a much bigger "leak" than needed.
On top of that, the retention of superposition is bounded by time. So even if your computer was processing very low energy, you would have to delete the information in femtoseconds, or the decision would have propagated to the electron ruining the interference once again.
Good Idea. We know a rock can be an observer and destroy the interference pattern.
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"?
Masterpiece.
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.
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 ... ;-))
For many purposes the electron can be considered a particle.Many great physicists considered them as particles. Sean is in the other camp .
Though it, the explanation, seems to be very lucid and simple, but really it is not. A teacher knows the handwork behind it. It is your skill Sean. Great, fantastic ! Keep it up ! Thanks!....
Could you explain at 38:00 what the time derivatie of the Field is? As far as I understand it, it is not moving like a particle.
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.
What analysis of QFT!
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.
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.
The need for renormalization essentially points to the fact that we don’t as yet have a handle on the ultimate underlying theory.
Sean, you might want to turn off notifications on your iPad. We can hear you get a text message at 7:21! :)
Thank you
11:30 “maybe you shouldn’t have been so naive.” Classical vs Quantum. Real world etc. I should watch this part again
13:40 philosophy of counterterms
18:00 Effective Field Theory (below a certain cutoff) vs TOEs
23:00 philosophy of why we are allowed to ignore this aspect of our physical system
30:00 dimensional analysis
39:51 I think you meant to say ‘The actual Lagrangian is the intergral of the Lagrangian Density over [ *_time_* ]’.
50:00 relevant, marginal, and irrelevant interactions
55:00 is GR renormalizable? We is/isn’t that important?
58:40 the payoff. “You don’t need to know arbitrarily complicated things to do Effective Field Theory. Tell me what Fields you have and what symmetries they obey, I can go and use this theory, it will come with a small number of parameters that I can measure; I can figure out the Effective Field Theory at low energies really simply.”
1:05:00 Feynman Diagrams are story’s we tell to gain some intuition, what is the Field actually doing?
1:12:00 “when you really probe Quantum Fields, your probing them at some scale, and that scale matters. This is where renormalization matters, it is a physical effect.” What I don’t understand is that virtual particles don’t exist, so how non-physical virtual particles accounting for this physical effect? Also I don’t think I understand properly the link between virtual particles and renormalization.
Sean goes on to talk about the Higgs Mass mystery after
Would fields be mere fictitious instruments to avoid the idea of unmediated action from a distance?
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.
(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?
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
Hahah “it works very effectively - as it were”
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
no those variables are in a diferent category
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?
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.
[E] = [M][D]^2/[T]^2, not [E] = [M][D]^2/[T]. you get one [T] from [f] and the other from [h]
I feel like there's an echo in my house because every time I make a comment asking a question about something I Observer think about as he speaks the very next thing he speaks of there's something I just made a comment about. Maybe that means he's doing his job and explaining things properly maybe that means he's a good teacher.
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
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?
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?
There should be a msximum energy density within the universe because at some point the energy density would be sufficiently high to form a black hole, which would then promptly evaporate by emitting a load of particles and spreading the energy around.
Can someone provide the link to Dr. Carroll's lecture notes?
The cut-off idea came out with Debye's Specific heat theory, only wavelengths of interatomic distances were included, circa 1905. More rip-off!!
So if I understood correctly: quantum gravity is not renormalizable essentially because it couples to too many other fields?
How do you calculate Phi without getting infinities? Is there a cutoff?
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.
Wat.
You had a fairly interesting question until you invoked Heisenberg, which... seems to have absolutely nothing to do with this, though it's possible I'm wrong. You certainly don't need ultra-high-energy physics to invoke the uncertainty principle; it's just a natural consequence of the introduction of wave mechanics into things.
As for this highest limit you asked about... our best current guess is the Planck energy, though that's really just the answer to the question, "What if you set all the dimensionful constants of the universe equal to 1 and then do some dimensional analysis to figure out what 1 unit of that energy would be, converted back to SI units?" If that doesn't sound like a very promising guess... yeah. It probably shouldn't. Since, in fact, there are several other ways to derive very similar units, and there's nothing particularly special about the Planck units in comparison with those ones, and no particular reason I can think of why they should be treated as so significant as to define such lofty concepts as maximum possible energies, granularities to space and time, etc.
@@barefootalien I meant a limit of energy above which nothing can interact, which means talking about such a thing greater than this limit would be meaningless, like for a constant momentum, things become uncertain, a set of energy greater than that when needed to be observed would become uncertain like which is the energy you want?
Any energy greater than that would have the same effect in our world.
1:22:30 how would a multiverse explain this? What is even meant by multiverse?
Awesome! Thank you :D
hey, are these in a podcast format somewhere? i would love to listen to them while driving but its hard with youtube.
How possibly can you listen only and understand?
Seems to me that the ebar going down in the Ibarra coming up with cancel each other out as you already said the same way that these counter operations are expressions or whatever you called them do. Kind of like how a negative integer and a positive integer of the same value would make 0
Is the numerical discrepancy in Higgs mass and the cosmological consented related to the relative difference of electrical and gradation always forces?
Is the hierarchy problem actually a physical problem? It could be simply a "coincidence" that the Higgs Mass is not at the order of the Planck scale.
Love keeping the hair growing...
the effective field theory looks similar to the method of truncating an asymptotic (divergent) series that comes from a singular perturbation system. Truncate the series and take the limit of the epsilon to zero to get the leading order solution... Are the two related?
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.