It’s very rare that someone with such seemingly ineffable range and scope is combined with the ability to communicate so clearly and cogently. There’s nothing like this series available anywhere else - I look forward to each episode. I suspect people will be watching this series for decades to come and it might just inspire a new generation. Feynman and Sagan did this through their medium of the day. This is up there in my opinion.

Erratum: around 33:00 I misread "70" in my notes as "76." The mass of the Milky Way is about 10^70 times the mass of the proton.

My favorite thing about Sean Carrol is his objective viewpoints, and his understanding of philosophy that goes in tandem with his scientific knowledge

I have never followed a video series so passionately as this. Not even the Mindscape podcasts (the one on the meaning of life was awesome though). This is what I had been looking for years, sporadically finding pieces here and there, but never as comprehensively explained from the concepts point of view. Hopefully this will continue on for more episodes. Thank you to Prof Carroll so much for taking the time to do this.

Thank you Sean Carroll for your amazing series of videos. I grew up a child of the Apollo rockets and was 11 when "we" first stepped on the moon. I have been an avid watcher of science and rocketry since. You make these topics accessible and I find your dedication extremely admirable. Makes me feel like a slug! Thank you again. Your volume of quality output is extremely impressive as well!

I love this series. These videos are going to be staple for a long, long time

"You can smash airplanes together all you want." -Sean Carroll, 2020

I literally watch these videos 2 or 3 times before moving on to the Q&A and then watching those twice. Consequently I am still on interactions lol, this stuff is gold. Maybe my favorite series of anything ever.

29:25 'Chemists - bless their hearts - care about the real world (...)' That properly cracked me up.

My favorite floating half torso on the internet. Yee!

Professor Carroll, I really love what you're doing with this series and for physics education more generally. I ended up giving up on physics in undergrad (in favor of math) due to a combination of personal issues and poor preparedness (poor rural background, went to ivy league school, was arrogant and sabotaged myself basically) but ended up approaching physics again later in life and finding joy in it. These videos have been invaluable to me, and helped me clarify so much conceptual confusion I carried from undergrad/that common books on the relevant subjects often ignore in favor of mathematical formalism. You're an incredible teacher and your students are quite lucky. I for one am eagerly awaiting your upcoming Quantum Mechanics text, thankfully I have Spactime & Geometry's new printing to keep me occupied until then.

Request: would it be usefull to make a video "explaining" one of your physics research paper after this series is finished?!

Thanks for giving us a breather! I'll never stop watching these as long as you are making them.

This is the most mind-blowing edition yet in this series!

Awesome episode! One of my favorites so far!

A new video from this series! Thanks a lot! Stopping everything else and starting to watch! =)

Really enjoyed this change of pace in the series. I had no idea how much there is to learn about scaling. Thank you Sean Carroll!

Love the videos. Keep them coming 🥰

Hells yeah..keep these goin!!! Best series ever!!!!!!!!:)

Awesome series of videos. Love them, super juicy !! Thx for making them!!

Great Videos, please keep it going!

Absolutely excellent! Thanks

Thank you so much for all these great videos, I didn't miss one, although the math part is so hard to me! I loved everyone of them and, please, continue on with more big ideas!

Thank you so much Prof.Sean Carroll for such successful excellent video.Best of more videos.

Thank you Doctor Carroll.

Big fan! Please keep posting your inspirational views!! And I liked your book very much by the way.

Thanks Sean. Have watched most of the series - in a non-linear order. Hoping there is more.

I for one really enjoyed the deeper ideas of qft in the past few videos, I did sometimes have to pause or back up and think on what you had said to catch up (forgetting what the lagrangian was certainly made the last video harder to follow until I was able to put it back together in my head) but its been a great experience, you don't tend to see ideas of that depth and detail on youtube for any kind of general audience, certainly not in this much quantity! And I'll be honest, nothing so far has made me question my major as much as this. Thank you for making this series, I'll sure miss it when its over, hopefully not too soon though!

Great Video.

What a fantastic lecture. Learned so much about the impact scale has on the 'real world' and on quantum considerations all the way to the Planck scale.

Loving the uploads sean. yea it takes some thinking , but thats a good thing. i have understood everything you have said so far. i put that down to your careful way of teaching which is great.

Thank you sir! Very eloquent teaching! On top of your scientific knowledge, you are naturally born teacher! Rare combination and because of it, every university would like to have you as their professor...

Thanks for this, really interesting stuff

Thank you professor Carroll

I like this video the best out of the whole series XD It's the most fun and relatable one :)

These videos gems💎

prettay, prettay, prettay...good stuff Sean.

Big Brain Sean!

I am sorry to say Prof. Carroll - but YES, they ARE intrinsically hard !! I still enjoy every minute though, so many thanks again, for this amazing series.

Sean, thank you! The depiction of the energy used in a clap versus the LHC, a surprise, the impact energy of a loaded train, lures me towards the processes smaler then the Planck scale.. At the end I'm wondering about the energies needed for concentration, fantasy and unanswered thoughts. This was, although not a breather to me, a delight.

feel like this should be #1 episode in the series

After these covid lockdowns, we are going to have a lot more people coming out the other end with their curiosity switched on due to vids like these, I love it.

According to this scaling, the speed of light is constant and equal to one, because roughly one second is equal to 10^15 ev ^-1, and the distance of 300,000,000 meter that it covers in one second is roughly equal to 10^15 ev^-1, therefore c=1 and constant, since c=distance/seconds. this means, in terms of their ev value, the time unit and distance unit(if we think of 300,000,000 as one unit of distance) change simultaniously for the light and therefore light does not feel passage of time!(light is stuck in time because it moves exactly with time’s speed and time’s speed is one second per second!

A masterpiece -- by a Grand Master ;-))

This video is awesome! My two cents is that this video should be reordered to the beginning of the series.

Christof Wetterich's describes a Scale Relativity as "Only dimensionless ratios as the distance between galaxies divided by the atom radius are observable." An expanding universe would be equivilant to a static universe with shrinking all rulers. Leading to a simplification: "Is the universe expanding or are we shrinking?"

You have given me the Title of my BOOK, I have been trying to write a simple book that may help someone/anyone to question. The scale of "life the universe and everything"is both amazing and disturbing. As soon as a child starts to read, scale and measurements are needed to form an accurate internal frame of reference. Thank You for the Help.

Cool lecture❗ Thanks³³

Thanks for that.

Great overview - I'm going to teach this to my A-level students :-)

Ty Sean

No need to look it up to see if the Milky Way is 10^70 or 10^76 proton masses. If the observable universe is 10^82, then at 10^76 per galaxy, you'd only have 100 million galaxies. There are something like 1 trillion galaxies, but while we may not remember that number exactly, most of us probably know that there are at least billions, so Milky Way should be 10^70. This is one of my favorite videos in the series, by the way. Thanks a lot for doing this Sean!

Thank goodness it’s returning back to something understandable in our realm of experience. Next time I am in an airplane I am going to fixedly observe the propeller, lest it become just some weird compound vorticity in the wave function of the universe, instead of an actual solid body made up of molecules of stuff. 😇😇

Super nice.!!!👍🏻👍🏽🌞🌿

You could measure energy in foot-stone. It’s approximately the energy you need to break a toe.

Sean, here's what I tell my students.: a cheeseburger weighs about 1 Newton. So 1 Joule is amount of work done lifting the burger by 1 meter. Hopefully it helps students gain a feel for what a Joule is. So I tell them a Joule isn't really a whole lot of energy. Then I tell them that if we ground the burger up and spread the cheeseburger powder evenly over 1 square meter that would be a pressure of 1 Pascal to let them know a Pascal isn't much pressure.

Always dig you

Sean: writes Avogadro's number to *one* significant figure, rounds to 1e24 Me: dies internally Sean: "Chemists, bless their hearts" Me: dies externally 😅

Thanks for explaining this to us. You certainly have your work cut out for you.

Wow! I wasn't expecting it but I think this was the best episode yet. So many ideas all coming together. If there is this "minimum size" for particles, then why do people talk about elementary particles as point particles? Also, what is the relationship between Compton wavelength and de Broglie wavelength?

I really enjoy this series. I just thought I should mention around 9:30 you say "one second of time corresponds to a much tinier amount of energy than 1 cm does" when I think you meant the exact opposite.

OK. Since the fine structure constant is obviously a critical component of many "Biggest Ideas", I think it's time Prof. Carroll gives us at least an arm waving back of the envelope explanation as to how Alpha was discovered and or calculated.

10:00 eV scale 27:00 reminder of what we mean by proton mass. And 32:00 most of the Earth is neutrons not protons 33:00 Why are there hierarchies of scale at all? Why is not everything on the scale of 1-10 proton masses. Well, we also have electrons, and things like gravity, which is important. 34:30 Compton Wavelength, and our intuitions on why more energetic/massive things are bigger. And 1:05:20 Bigger special scales, bigger temporal scales, equal lower energy scales. 1:04:00 “the set of sin waves you can add together in a Fourier Transform, to get any wave at all is what we call a mode”

super!

44:36 Haha. My childhood fantasy magical power was to make things smaller or bigger, but I was clear it was by magically adding or removing atoms close to similar atoms. That wouldn't work for biology etc. but the magical power was only supposed to make things like toys and model cars bigger or smaller. It's important to be scientifically precise about your imaginary magical powers.

What creates the underlying reason that heavier a particle is, the shorter is the wavelength? What is the cause that 1/M works out (Compton wavelength to be the limit of smallest size possible) as it seems that heavier an object is, the slower (longer wavelength) it is. This assumes an uniform speed of force for each particle.

So we can define 1 Caliban to be 10^36 eV? Minor Point: In _The Fantastic Voyage_ they alter Planck's Constant as they shrink (and alter the speed of light as well; the two are said to be inversely correlated).

Am really enjoying this series. Some elemnts of it I already know and understand, others I'm learning and picking up and yet others that I'm not currently or may ever grasp, but still; interesting. Plus the informations within the grey matter now, so you never know! I sort of have a question/idea with regards to dark matter and its gravitational effects. When thinking about gravity I often think of the demonstration of balls/marbles rolled around a weighted trampoline simulating orbits etc. I often wonder if, that instead of or as well as dark matter, the motion and gravitation could be effected by something else. If you thought of the fabric of space-time as an actual fabric. The passage of something massively dense over it could cause folds or valleys which other matter, planets, marbles galaxies may encounter and run along. Even if this process was not a permanaent one, any following interactions with it would obviously affect everything around it within it's gravitational field, causing a sort of domino effect which in turn gives the appearance of missing matter!?? I know its probably been considered before and/or its utterly wrong or implausible. But I'd properly kick my self if I'd not posed it and it later on became right or relevant!! If you ask the average person who Alfred Wallace is, they likely won't know, because Darwin beat him to the punch on the idea of natural selection. Saying I thought of that after the fact's never going to get you anywhere or anything! Obviosuly there's matter-energy equivalence. I take it there's no dark matter energy equivalence!! It's dark so maybe just E=m? ;) jk, unless again it strangely led to something! I do have other thoughts/ideas (some outside the box thinking, at least to me anyway), but I don't want to overburden the comments section; unless interested. Either way, thanks for the video series! - Ewan edit: you answered one of them in this video. Re: existence at atomic scales. Can also infer another answer from that. i.e the universe is definitely expanding, not just us shrinking

How do i get the same results for scale when my energy cutoff gave me a different value for alpha? Is my compton wavelength also different?

@38:00 delta p in the uncertainty principle is change in momentum, not “position” ; that was delta x ;)

This has been the hardest one so far to pay attention to. It's not because I'm not interested, but I just can't seem to concentrate on it. I think because it's kindof largely "background knowledge" that you need to have, with a few "big ideas" sprinkled here and there. I just keep getting distracted :(

So...I'm 24 videos into this series. I'm with you 100% until "Antman isn't real"

Before Prof Caroll physics for a non-physicist looked like "well, that's a spherical Schrodinger cat on a moving train - whoosh - and now solve these ten PDEs with weirdest boundary conditions just because". Now it all finally starts to make sense, thank you so much! And yet I have a question for Q&A: isn't "the size" of a nucleus (and nuclons) determined by nuclear forces constants the same way as Bohr's radius is determined by fine structure constant? Or are there complicating factors?

λ*m=1. This is the right and exact response for the mystery of dark mass and energy! Basically the equation implies “If the whole mass of the universe were to put in some box, therefore one over the wavelength for the mass of that universe would be some number equal to the mass( if we take the whole mass of the universe as 1). I am having hard time to gather my thoughts to explain it but nevertheless what I mean is that the observable universe has certain amount of mass in it but the wavelength goes beyond that because if the universe is literally infinite but the mass is in certain huge number therefore the wavelength literally goes to infinity in order for lambda to become 1 for the mass of 1. So what about the rest of wave for the observable mass of the universe? Let me clarify it by an example; if the mass of observable universe is 5 kg, therefore it’s wavelength in an infinity beyond that observe would be 1/5, but what we normally do is that we calculate the wave for that observable universe which whiteout a doubt the universe is greater than the observable part of it. Therefore when we say the mass of universe is 5 kg, the lambda of universe that we normally calculate as 1/5 , is not for observable universe and it is for an infinite space much greater than observable part of it. For the sake of argument let’s say The mass of observable universe is 5kg for some finite distance we observe the universe, the lambda of that mass would be 1/5 but for a much greater space than the observed one. Now, if we get the 1/lambda for that observable universe, it should be much lesser than the one for literally infinite universe, let’s say something like lambda=2 and 1/lambda=.5 And therefore, our mass for that equation would be m=1/ λ, 5kg=!1/2 since we assumed m=5 and λ is any number considerably less than 5 for example λ=2. Well, m= 1/2= .5 kg, where does the rest of 5 kg go? That 4.5 kg is the dark mass! The reason is that wave is much far distributed than mass for the mass we talk about! What I mean is that dark matter does not come from some unseen matter but it is because what we measure as mass for any single particle is not actually its true mass! Because the absolute mass of a particle is distributed all over the infinite space although the greatest amount of mass is in the closest perimeter of the particle and we measure its mass only in its vicinity! Dark mass= absolute mass of a given particle(absolute mass of a wave for particle) - detectable mass of that particle at its vicinity(detectable wave by quantum equations) . Here we go, there is the lost mass called dark mass. The same goes for dark energy! I believe! Believe me I am right but I have hard time to explain it. I know this sounds crazy but indeed what is crazy is that to consider mass and energy as fundamental things in the universe.what is fundamental is space itself, the distortions and stretch of it plus the distance. What ever exist in physics as mass, energy, time,... are simply depiction of them to us! Kind of personification of space with and without distortion makes the reality we know of but indeed the reality has to be the space itself and its distortions! Eventhough I screwed up by Things explanation :)

I think emergent phenomenon would be a great topic. I was looking at comments on the recent Mindscape episode about the meaning of life, and noticing a lot of people wanting to reduce the meaning of life down to simple thinks like entropy or a chemical process as the goal. But its useful to see emergent patterns that reveal themselves at a higher level as real phenomenon. People act like its not real just because its not the lowest level possible. Even with humans, real statistically significant patterns emerge at higher levels when you consider how entire groups behave together as one. Big Data wouldnt be "Big Data" if there wasnt real value in all the patterns that emerge at higher levels we just dont see. It always makes me wonder about galactic superclusters and what emergent patterns exist on scales that large (and time scales that long)... we just can't see it from down here. Even though we're right in the middle of it.

How would you define a space-time density? And from them getting number of particles in a 4-volume.

Is there a scale of measurement used where the basic energy level isn't eV (which relies on what a Volt is), but instead uses the ionization energy (13.6 eV) as the base unit of measurement? So the mass of the electron is about 37,500 times the energy required to separate one from a proton (from the lowest state).

I have a question concerning the vacuum energy of quantum fields and the cosmological constant. In my understanding, a positive cosmological constant makes the universe expand, i.e. acts as a kind of negative energy field causing anti-gravitation. The vacuum energy of the quantum fields from the zero point energy of the Fourier modes is positive, so it should make the universe contract due to additional gravitation. Therefore, the vacuum energy should contribute negatively to the cosmological constant, not positively, right? When you explained the "worst prediction in physics", i.e. the deviation of 120 orders of magnitude between vacuum energy and cosmological constant, how does this make any sense of they have opposite effect anyway? How are they comparable? Sorry as this would have better fitted into the Q&A of one of the last three episodes but I came up with the question just now. Would be nice if you could answer it anyway in a later Q&A when you go back to QFTs. Thanks a lot for this series!

eV as unit of energy, how did make the leap as units of mass, length and time?

I keep going back and forth, between Dr. Sean Caroll videos, and Dr. Sabine Hossenfelder videos ( and book ).

QUESTION: in an earlier episode you described moving from the very low entropy Big Bang to a higher entropy state now. Can you explain this? It seems to me that the primordial stew of particles immediate post Big Bang is high entropy, higher than organized stars and planets. Like evenly distributed gas in a box versus the gas being clumped together in parts of the box. Help!

What would happen if the Cellular Automata were to awaken and start digging around? I don't know, I am guess Sean just gets the created constructs flowing.

What about gravitons? Would a satellite orbiting the earth in a zero gravity orbit be able to measure them? Because I am starting to have weird suspicions about what we mean by particles in different frames of reference... Maybe the word particle has been stretched too far in order to respect the laymen intuitions.

If you had particles in the desert, say 10^18 eV, and you didn't know anything else about them, would you expect them to be weakly interacting with regular matter just because the energy scale is different? If there was a whole family or particles up there with fermions and bosons interacting with each other all at these high energies, would they still pass through regular matter undetected? Does it work like transparent glass where the photons don't interact because the energy states are too high?

I believe (not gonna say think cuz I dunno shit) that scale is pretty much the fundamental theme throughout the whole damn everything.

For a preview of scale as it relates to biology, see Sean's interview with Geoffrey West. Very good episode! kzfaq.info/get/bejne/jddmZsmk1Z_TYaM.html

I'm enjoying this series immensely, but as someone trained in mathematics, this discussion of dimensional analysis has me banging my head! [D] has dimensions ℏc/eV [T] has dimensions ℏ/eV. They aren't the same! Just because c is set to a value of 1 doesn't mean it has lost its dimensions. Take some distance measured in ℏc/eV: to convert it to time you need to divide it by c, just as you would if the distance were measured in light-seconds. A distance measured in light-seconds divided by the speed of light measured in light-seconds per second will give you a quantity measured in seconds -- a unit of time. [D] is NOT equal to [T]. [D/c] = [T]. Sigh. Physicists. Whadda ya gonna do, eh? With this in mind, I nominate Sean Carroll for the Paul Dirac Prize -- a (Lebesgue) measure of excellence in the productive misuse of mathematics. :)

What about X17 particle? Is that on this scale? CERN seems interested in it.

If a particle cannot be smaller than its Compton wave length, how can the electron be considered to be point-like?

At 22:00 the desert concept emerges. Can some one give references to learn more about this energy gap ?

~30ish "Most of us weigh more than one gram, sadly" Lol. Laughed harder at this than i maybe should have. I am a little disappointed miniature people are probably not possible. A shrink ray makes a person tiny in terms of length, this is a given. But what happens to their mass? Every movie or depiction of a shrink ray implies their mass gets really small too. For some reason I feel ok with shrinking space and length, but I'm not ok with shrinking mass. If you do shrink mass, that is a considerable energy delta to deal with

The bell is disabled on my iPad? Any ideas why? Only on this series

Is the large macroscopic scale of astronomical objects in some sense a result of gravity's weakness?

Why the eV is so mini in scale: It is like I'd say a litre of water is 10^6 milli grams (just thinking in the 13. minute of the video)

"Who does in everyday life? Moving electrons across 1 V batteries?" Well, not exactly 1 V, but we do all the time ... :D

How come there are unknown particles with very low energies? Shouldn’t they already have been observed at particle accelerators? Thanks!

What about the other desert betwern 1eV and 10⁵eV?

So, in natural units, energy and mass are interchangeable and same goes for length and time? As in, you cannot have mass without energy or move around without a clock ticking?

You might have answered this in a previous video, but related to the 'scale' of the electro-weak interaction being some point where the electromagnetic field 'combine' in some way with the weak force. A rephrasing of that is as the scale at which the weak force and the electromagnetic force 'separate'. Is there a similar point where the electric force and magnetic force 'separate'?

The most used unit for energy is probably kcal.