Solving the Impossible in Quantum Field Theory

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Previous Episode:
Feynman’s Infinite Quantum Paths
• Feynman's Infinite Qua...
The equations of quantum field theory allow us to calculate the behaviour of subatomic particles by expressing them as vibrations in quantum fields. But even the most elegant and complete formulations of quantum physics - like the Dirac equation or Feynman’s path integral - become impossibly complicated when we try to use them on anything but the most simple systems. But physicists tend to interpret “that’s impossible” as “I dare you to try!” And try they did. First they expressed these impossible equations in approximate but solvable forms. Then they tackled the pesky infinities that kept appearing in these new, approximate equations. Finally, the entire mess was ordered into a system that mere humans could deal using the famous Feynman diagrams.
Written and Hosted by Matt O’Dowd
Produced by Rusty Ward
Graphics by Kurt Ross
Assistant Edit and Sound Design by Mike Petrow
Made by Kornhaber Brown (www.kornhaberbrown.com)
Comments answer by Matt:
Christian Haas
• Feynman's Infinite Qua...
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• Feynman's Infinite Qua...
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• Feynman's Infinite Qua...
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[@yolanankaine6063]

Matt : “But if you try calculate the self energy correction to an electrons mass using QED, you get that the electron has infinite extra mass. Ammm...This sounds like a problem” Haha I don’t know why this amuses me so much. Just picturing the physicists working on this calculation then getting infinity as the answer. Then all of them just sitting there , staring at each other like “ahh.. crud”

[@Tight_Conduct]

Never in this timeline has the past 40 years of the toil of physics been summed up so eloquently.

[@antoniolewis1016]

Kudos to you for wrapping up multiple Nobel Prize concepts into 15 minutes. That is badass!

[@emanueltrisnajati4957]

and kudos to you for understanding that 15 minutes wrap-up of those multiple nobel prize concepts

[@klyanadkmorr]

Or simply use the KISS process, KEEP IT SIMPLE STUPID

[@zes3813]

wrr

[@voidisyinyangvoidisyinyang885]

that's cuz he can't get out of those pants

[@Tiniuc]

@@klyanadkmorr that's an engineering principle.

[@markchadwick77]

This series keeps getting better. Finally, a lecture that isn't afraid to put up equations, but also doesn't use them exclusively for describing real interactions (like my Physics professors did).

[@TheRogueWolf]

Man, I'm glad these weird quantum mechanics rules don't govern regular physics. Imagine just going to a friend's house: "Hey, sorry I'm late. The Interstate was closed so I had to take a shortcut." "That's okay. Did you take Vine Street, Route 44 or the old dirt road?" "Yes."

[@MikeAbundo1]

"The Interstate was closed and not closed, so I had and did not have to take a shorcut."

[@supersonictumbleweed]

Mike Abundo "I took a longer route. I also took a shorter route and visited a friend. I also took a short route and got some food. Now I'm in a superposition of hungry and lonely."

[@garethdean6382]

They DON'T? Then why is it every time someone tells me they'll be with me 'in a minute' I end up waiting half an hour?

[@ashboon1625]

WA? HAHA? WAHAHAHA?

[@Niohimself]

I forgot to check my fuel level and ended up driving an infinite number of miles.

[@karstent8138]

Matt, you have the best tone, mood, wording,and rhythm for explaining these things I have heard up until now, Thank you (~8

[@DavidG2P]

Hey, a Feynman Diagram smiley

[@Mr.Nichan]

@@DavidG2P I was just scouring the internet trying to figure what that emoticon was. I see now that "(" = mouth, "~" = nose, and "8" = eyes. Maybe it could also be a Feynman diagram, though. Sort of like: ---->----, ,----

[@DavidG2P]

@@Mr.Nichan the strangest thing is that I have not the slightest idea what a Feynman diagram is and that I haven't wrote that comment 🤔

[@Mr.Nichan]

@@DavidG2P You're sure you never wrote that reply? Because that would be strange. Or are you just saying you didn't write the original comment so I shouldn't really be replying to you?

[@DavidG2P]

@@Mr.Nichan OK after watching the video and realizing that I had watched it already last year it could be that I maybe I DID write the original comment ;)

[@jona5820]

This is pretty amazing. To think you're actually making QFT videos for laymen. I didn't think it was possible. It's by far the toughest topic I have ever studied.

[@zjr5680]

Your guys work to make this type of information available to anyone willing to follow your videos is outstanding. I'm sure these lessons will go on to change lives of countless people. Thank you for all of your work and dedication.

[@mugu2416]

Honestly..... this information, in high quality, explained calmly and in detail, with full pictographs, analogies, and examples put in image, graph, and phrases to show you pretty complex things FOR FREE? Now that's worthy of some kind of nobel prize. Especially since this channel is not boring, makes funny references, sometimes uses meme pictures and answers commenters the video after. Why a channel like this has 1+Mil subscribers and useless individuals like logan paul or pewdiepie who provide ZERO productive or meaningful things make me sometimes WISH we would become extinct. 3 things that make intelligent civilizations extinct: Monetary wealth, Celebrities, and ignorance. Without money, we'd all be rich. Without celebrities, we'd all be famous. Without ignorance, we'd all be free of the both.

[@smergthedargon8974]

+Mu Gu /r/im14andthisisdeep

[@ChinnuWoW]

@@mugu2416 Your last paragraph is bullshit. Without money, we'd all be poor since there wouldn't be any motivation to work hard. Without celebrities, we'd all be nobodies.

[@TadValente]

@@mugu2416 That last part he just pastes at the end of every comment.😂

[@donttouchmycoffee]

Matt, I love what you and the folks at Space Time are doing and have watched all of the videos dealing with QM, QED, and Special Relativity. I've watched them over and over, since I am a middle aged man with no background in higher maths or physics. I wouldn't want the episodes dumbed-down; I just with I could understand the maths and the very weird QM concepts more.

[@Locedamius]

Quantum Physics: If it makes sense, you're doing it wrong. Gotta love it! :)

[@spacebread501]

Can we please all agree to call Feynman Diagramms Feynman-Doodles from now on? :)

[@FloridaManMatty]

Diagrams by Richard Feynman: Dicky Doodles!

[@nachannachle2706]

Oh, I'm glad I caught this series now, rather than from its beginning. Quantum mechanics are absolutely FASCINATING. Bear in mind that this statement is coming from a non-physicist, non-mathematician, non-scientist, non-engineer person. I stumbled upon PBS spacetime while trying to dig into Einstein's "E=mc²". It has been a year and I'm still determined to absorb every bit of the discipline, from Classical mechanics through to Cosmology. Simply put, this channel is brilliant at popularising core concepts, while providing relevant links to explore the subject in detail. I have to say, Feynman's path integral is giving me the hardest time because it is both extremely logical and complex yet extremely unassuming and abstract. It's hard to believe that someone could manage to tidy up the QM mess in such elegant ways. Essentially, I've got more exploration to do...while waiting for the next episode of the QM series on PBS Spacetime! :)

[@markchadwick77]

I’ve subscribed to this channel for years. This video is still my favorite one.

[@jimbo9305]

Every time I see QED I think, "Done."

[@idiosinkrazijske.rutine]

Same with me when I see an empty square, any relations maybe?

[@pythoncure6755]

@@idiosinkrazijske.rutine hahah nice one👍

[@mastershooter64]

Lol pov pure mathematicians learn physics

[@while_coyote]

Could you go more in depth about how fields couple someday? This stuff is fascinating, never stop!

[@EvulDali]

These videos are just right for me. Not too dumbed down to make them fail describing complicated phenomena but still not too technical that a non physicist like myself cant understand anything. Fantastic!

[@JoshuaHillerup]

Now that you're covering the Standard Model, and you've already gone over a lot about General Relativity, will you do a video about some of the details of the problems that come from combining the two?

[@thedeemon]

Yep, now they're pretty close. They could describe metric tensor field as another quantum field with gravitons as its particles, then proceed to show how renormalization fails for such theory and infinities refuse to go away.

[@Henrique-hl3xk]

BEST PHYSICS CHANNEL ON KZbin!

[@samuraimath1864]

Feynman once scored 125 on an iq test. Basically the test didn't realize this was a trick subject and it failed.

[@OmegaSlaughter]

This is one of the reasons I think that intelligence can't be strictly measured until an individual exceeds a certain value. It is - at this point beginning - an own world full of inner thoughts of said individual which was shaped during life in its own way and stimulated intellectually on its own way. You can't measure this only with aspects of certain patterns during limited time. It is simply not enough.

[@fatix85]

I know a man, whose IQ score is around 85, and who still seems an intelligent guy. This guy's memory skills (photographic memory + good reasoning skills) allowed him ... to graduate from a university, work as a history museum curator and maintain healthy relations with his friends (all of whom had scored between 130 and 180 in IQ tests and none of whom had actually ever question this person's intelligence; they simply acknowledge this person KNOWS a lot and can interpret this information correctly, quite often startling them with his insight). IQ does not mean that someone is intelligent. It simply means that someone can, or cannot, do tests :).

[@poeslaw1648]

The IQ test had a max value of 130 in Feynman day and anything over 120 was known to be inaccurate. It took many years to calibrate IQ test to accurately measure people with an IQ over 130. Even today the general tests fail at 160 and specialize tests fail at 200. Also the test back then tested verbal skills more than math.

[@OmegaSlaughter]

Can't believe he scored that low. You have to take in consideration that at the time he did the test he maybe was irritated because of other things, had problems with concentration etc. Such tests put huge psychological pressures on people. Thats also a reason why I never intend to take one.

[@poeslaw1648]

OmegaSlaughter, ya IQ can be lowered by a lot of things. Alcohol drops it up to 30% based on how much has been consumed being hungry drops it 5-15 points. Sickness usually cuts it by 10 points ect. Even the general test is 2 hours of intense concentration which is timed. The comprehensive one that tests everything is 8 grueling hours and has to be given in one sitting since the above can change the values from day to day. Other than curiosity or to test for brain damage I wouldn't bother taking them. IQ is mostly used to understand why groups of people act the way they do or what effect it has on the society for the individual its kinda meh.

[@sansvoir]

Hey, Space Time, loving this recent series on the quantum realm. I really appreciate the deeper looks than you normally get with pop-science, while keeping it firmly within layperson's land.

[@ristopaasivirta9770]

"You are a hack!" "Oh my, thank you very much."

[@BrendanSteffens]

You guys are doing a fantastic job in particular with these QFT videos, in my opinion. I do hope that at some point in the future you will address the Feynman "antiparticles traveling backward in time" interpretation, and what came of that, historically speaking.

[@TilveranWrites]

Just a thought but... how complex do antimatter structures get? Could there be something like our solar system made of antimatter going "backwards" (relative to us)? Sometimes, time seems really odd. Almost like there's some illusion going on that satisfies us intuitively, while the reality could be well... more on the brain scrambling side. And what if there's more than forward and back? Well, maybe things are odd enough already.

[@jawtap1520]

Too much brain farts, maybe later

[@thereaction18]

Redneck version - Physics: Impossible Physicists: Hold my beer

[@RobCod2012]

Never has there been a faster video click time than when I saw the new Space Time video. I love your work mate, I wish I could have a personal conversation with you face to face matt, keep up the good work you bloody tank Cx

[@geordonworley5618]

I really appreciate these videos. This is amazing! Being able to see the diagrams and associated math would also be really cool.

[@NuclearCraftMod]

If anyone's wandering where the '1%' came from, it's to do with the value of the electric charge of the electron in natural units, as that is related to the 'coupling constant' that determines how strong the interaction is.

[@ozanerzos5774]

uuuum yeah! We all knew that! Go back to Electron Field Theory 101. ;)

[@unclerick1568]

The whole "self-energy" problem (maybe relating to quantum gravity) had my head spinning. I can never get enough of theoretical physics, but I'm just going to go to bed.

[@bonerici]

knocked this one out of the park. First time I have heard a lay person explanation of these concepts without horrible distortions and bad analogies.

[@robertschlesinger1342]

Excellent video. Very informative introduction and a must see for all science and mathematics students.

[@unvergebeneid]

Seriously, if we were living in a simulation, someone would have figured out a physics that's easier to compute.

[@garethdean6382]

'So I figure all the fundamental particles will have discreet locations and move in straight lines.' 'Well crud, I just copy-pasted this code, I dunno what it does, but it works. Best leave it.'

[@Loddfafnisodr]

Seriously, 12 year old stoners have more interesting thoughts.

[@unvergebeneid]

I don't think "interesting" is the problem. In fact, if I were in a meeting to create the rules for the next simulation and someone suggested QED to me, "interesting" might be the euphemism I'd use.

[@Loddfafnisodr]

No.

[@unvergebeneid]

Maybe get back to me when you're no longer on mobile and can spend more than three bytes on trying to express your thoughts?

[@jakobygames]

12am: Ill watch one more video, this QFT video series looks cool. 3am: I AM WAVES OF ENERGY ON INFINITE PLANES OF EXISTENCE. NOTHING IS REAL, THE FUTURE IS THE PAST AND THE PRESENT IS FOREVER

[@cristianm7097]

No free will, the future is predetermined

[@1Kapuchu100]

These videos are some of my favourite to watch, yet I understand so little of anything posted on this channel. I suppose the coolness of it all is the main reason it's so entertaining :P

[@manaoharsam4211]

I have liked almost all his videos. Does a good job in telling a short and effective description. Details can be found in other videos or text books.

[@thekingofcardboard]

I understood about 25% of this video, what I did understand amazed me.

[@Sam_on_YouTube]

Feynman's sum over histories is among the most underrated discoveries in physics. I used it in my philosophy thesis in college to show how even if you believe that only the present exists now, you can still take thw past as real because every past that COULD lead to the present actually DID happen. Though for macroscopic events, there aren't really important distinctions between one history and another.

[@marcosesteban6503]

May i read your thesis? I want to know your philosophical approach.

[@johannpohland2826]

Sam y please

[@ronaldderooij1774]

You should have taken Einstein's loaf of bread method for this. Google it and you will be amazed how artificial the terms past, present and future are in this universe. If it wasnt for the speed of light (=speed of information) we would be able to know present, past and future. According to Einstein, the universe includes past and future time as they both are part of the universe now.

[@Sam_on_YouTube]

Ronald de Rooij That would not have worked. I was taking the two common views in phosophy of time and updating them both to be compatible with relativity and quantum mechanics. One view is similar to the loaf of bread idea. That ia called "eternalism". I was using the sum over histories approach to prove that even if you believe in the other idea, "presentism", where you don't think the past is real, you can still treat it with precisely the same degree of certainty as if it were.

[@robertbower7461]

Ronald de Rooij It is my most fascinating subject . Like another dimension where past and future all exist still or ''always' have. !!!

[@empathon]

Great episode! I love when there is more math in your explanations!

[@X_Baron]

This is really excellent, even if I don't understand everything. For years and years I've seen Feynman diagrams and heard how good they are, without anyone actually bothering to explain what they mean.

[@awabqureshi814]

I would love if you could do a video on the Einstein Feild Equations

[@takisally]

Peter Dinklage's taller , physcist brother!

[@joejohns3543]

I feel like Feynman represents a big gap in a more complete understanding of spacetime for most people. I am really excited you guys made these two videos. Spacetime 4 ever! -coolascats

[@mokopa]

I love the cold correctness of the part where he says "obviously electrons do not have infinite mass and we know that because we've measured that mass"...like, just to make sure that they aren't infinitely massive, we went ahead and confirmed our suspicions that they're not...obviously. Lol. This channel has the perfect mix of ELI5 and ELIPhD and is one of extremely few I'll consider sponsoring.

[@frogstud]

ADS/CFT so lit though

[@TimmacTR]

What now? "Virtual" electrons???? Physics, you again..!!

[@pierrecurie]

It's a mathematical convenience. Just pretend they don't actually exist; under the rug they go.

[@lydianlights]

I finally understand what perturbation theory actually is (or rather, how it's actually applied to physics). I love that you present these episodes at a perfect level of complexity for enthusiasts like me who never had a chance to formally study physics but have always been in love with the subject.

[@Frediloc8]

I was reading up on re-normalization and these "infinities" last week, and although I have some physics education background, it was still difficult for me to grasp. This was a very effective breakdown of these complicated subjects!

[@treblot04]

best episode, by far!!! I love how you are posing questions to try and find a physicist who is the diamond in the rough. looking through the comments for the similar effect that a three year physicist student has toward current physics theories! you have a great platform for theoretical physicists to take new ideas and theories and run with

[@Tomyb15]

You mentioned that with Feynman's equation, you can explain antimatter as matter travelling back in time (or something like that). Does it have anything to do with the fact that how a charge moves when attracted to an object of opposite charge in a video played backwards looks the same as if that charge had the opposite charge (and thus, the same as the charge of the object) and the video played normally? (Disclosure: I said video but that fact isn't important to the hipothetical example)

[@yuryeuceda8590]

I got addicted to your videos. They and you are great. Thanks Professor

[@josevalero3543]

Thanks for this videos! you made me kind of understand very difficult concepts!

[@DDvargas123]

The sum of infinite terms in the electron mass making a finite number reminds me of how "the sum of all integers is -1/12"

[@garethdean6382]

That sum actually makes a lot of appearances in physics so you're not too far off.

[@Yemeth42pis]

Could you give me an example of where it appears ? I've watched some of numberphiles video on it, the only example there were was in a string theory book. Is it use in a experimentally verified theroy ? I think I read somewhere it appears in the equation about the casimir effect, is it true ?

[@DDvargas123]

But that's what I meant by my original comment. The sum of all integers is in NO WAY convergent but we still have a way to assign it a number.

[@garethdean6382]

The application is in an area known as 'zeta functions'; in QM an QFT they're used to deal with 'self-adjoint operators' (en.m.wikipedia.org/wiki/Self-adjoint_operator ) this is not a simple thing to explain, as the link will quickly show. An example is (Deep breath) In flat space, in which the eigenvalues of Laplacians are known, the zeta function corresponding to the partition function can be compute. If you have a scalar field φ contained in a box of volume V in flat spacetime at the temperature T = β−1. The partition function is defined by a path integral over all fields φ on the Euclidean space obtained by putting τ = it which are zero on the walls of the box and which are periodic in τ with period β. What? Exactly. So it's a bit more complex then finding out there are infinite waves somewhere that add up to a particle having negative mass or something, it's deeply involved stuff. On the upside this also means that there's no 'real' case where a supposedly infinite force, energy or mass sums to -1/12.

[@vacuumdiagrams652]

Self-adjoint operators are a bit more general than this. Any observable such as position or momentum corresponds to a self-adjoint operator (mathematical subtleties abound when it comes to the terms "self-adjoint" and "Hermitian", which physicists pretend are synonymous even though they aren't). The zeta function thing is more restricted. The technique called "zeta-function regularization" consists of defining a "determinant" for an operator by analogy to what is done with the Riemann zeta function. The Riemann zeta function is the sum of inverses of integers to a certain power, that is, it is 1/1^s + 1/2^s + 1/3^s + 1/4^s + 1/5^s + ..., where s can be anything, even a complex number. If Re[s] > 1 you can just add up this series. It converges nicely. If Re[s] = 1 (x = 1 is excluded, but x = -1 or x = -i are not). The cooler thing is that this is the _only_ expression that works (and is an analytic function), so we can use it to *define* what we mean by 1 + x + x² + x³ + ... outside the region of convergence. For example, I can use this expression to say that 1 + 2 + 4 + 8 + 16 + ... = 1/ (1 - 2) = -1, or 1 + 3 + 9 + 27 + ... = 1/(1 - 3) = -1/2. Technical details aside, this is the exact same argument that we use for saying that 1 + 2 + 3 + 4 + ... = -1/12. In this form it is used directly in the Casimir effect, as I stated. But the main application is to find the determinant of certain operators. It's essentially the same technique, but for other sums.

[@peoplez129]

When he says "reality" at the beginning it looked like it hurt.

[@DeathBringer769]

Objective "reality" is tricky business, after all...

[@22222Sandman22222]

These are always as fascinating!

[@nhandam80]

Thank you for explaining Feynman diagram. I am in business field and customer service. But physics and science fascinated me and really stretch my imagination. Thank you again and keep on discovery and invention.

[@ohno5988]

Can you make a video explaining the particle anti particle pairs. Such as the virtual electron and positron pairs. Im not fully understanding what they truly are or how they even exist

[@garethdean6382]

Indeed, there's a lot of simplification with them that leads to more questions than answers. There needs to be more focus on how they really DON'T exist as sensible particles rather than the standard description.

[@Garganzuul]

If we can make gamma-ray lasers, we can possibly make kugelblitz black holes and find out for sure.

[@MrSh1pman]

Wait a second. At 7:50, does the virtual positron in Feynman's diagram go back in time?!

[@vacuumdiagrams652]

There is no notion of forwards or backwards in time for virtual particles. They go forward or backward depending on your perspective, but that's okay because they cannot be observed by definition.

[@lucrativelepton]

It looks like it is but I think that's a misrepresentation. My guess is they'd technically be overlapping but it's just modified so we can see both separately.

[@tetraedri_1834]

I haven't yet learned QFT, but to my u derstanding in Feynmann diagrams the antiparticles are modelled as particles moving backwards in time. Just draw a picture on space-time diagram of electron annihilated by positron and follow the line, it will become quite apparent why this is not as crazy interpretation as it first sounds.

[@ezzmansour7226]

Antimatter here is treated as matter that goes backwards in time

[@Garganzuul]

Time travel has a bad rep, but it is a recurring theme in physics. Perhaps we can design quantum computers which bring us messages from the future? It is not expressly forbidden by the equations we know, and nature bends the rules wherever it can...

[@lendypradhana4744]

Great!! Thanks for giving me such deep knowledge in just 15 minutes instead of 1 semester lecture..

[@TheSatiah]

I've stopped to understand what are we talking about few episodes ago, but just can't stop watching. O.o

[@vrixphillips]

-sigh- you make me regret going into literature and philosophy rather than maths and theoretical physics lol

[@stasyszy]

philosophy and theoretical physics are cousins

[@Sam_on_YouTube]

stasyszy I majored in the philosphy of theoretical physics in college.

[@sumsar01]

A cousin who has a job though.

[@ankitaaarya]

@@sumsar01 gahahaha

[@SupLuiKir]

Is there always a finite number of Feynman Diagrams at each group of Feynman Diagrams of a certain vertex count?

[@vacuumdiagrams652]

Yes. Since there is always the same number of lines coming out of each vertex, you can only assemble a finite number of diagrams from a finite number of vertices. The more interesting question is whether the sum of all diagrams for a given process converges. Sure, there are a finite number of diagrams at each order, and each individually contributes less, but the more vertices, the more diagrams you can assemble. And the answer is no. The sum of diagrams diverges!

[@Nick-oj2rt]

That's a brutal result... it probably means we're missing something important (*cough* quantum gravity *cough*)

[@NuclearCraftMod]

+Vacuum Diagrams sorry, I don't think I quite understood you - are you saying that the sum of all diagrams over all orders diverges? If so, why should we allow ourselves to ignore diagrams above a certain order?

[@vacuumdiagrams652]

Yep, that's exactly what I'm saying. The usual convergent series become better and better approximations the more orders are included. For example, 1 + x + x² + x³ + ... (where x is smaller than 1) becomes a better and better approximation to 1/(1 - x) the more terms you include. The types of series generated by Feynman diagrams is _not_ like that. It is what is called an asymptotic series. Typically there is an optimal order of truncation; if you add more terms past that order, for your hard work you get a _worse_ approximation to the quantity you're calculating than if you'd simply left them out. When a series diverges you can often tease out a result for the sum anyway, just like we say that 1 + 2 + 3 + 4 + ... = -1/12. Unfortunately, for the interesting case of Feynman diagrams, this procedure is ambiguous and doesn't lead to a unique answer. There is a fascinating new subject called "resurgence" that is an attempt to deal with this problem in a more precise way. In several interesting special cases, it can be shown that the ambiguity exactly cancels out some non-perturbative contributions that don't come from Feynman diagram calculations but rather objects known as "instantons", and surprisingly enough, this fixes the problem. It hasn't been comprehensively applied to QED as far as I know, but the results in simplified theories are very nice.

[@ChenfengBao]

Yes, the sum of all diagrams over all orders diverges. It's probably an artifact of how we do perturbation, not an inherent feature of the theory. There're more elementary examples in math where you can start out from a finite expression and end up with a divergent series after some manipulations. What happens is that somewhere in your manipulation there's an "equal sign" that's not *really* an equal sign, but better read as "associated with". For example, in a first course to QFT, when deriving the formalism of perturbation theory, there's probably a place where you (and the textbook, and the lecturer) stealthily switch the order of two limits without justification. That could be a (maybe naive) understanding of why the series diverges. But this divergence doesn't mean that the first few orders of the series couldn't serve as a useful approximation to the true (finite) value.

[@otakuribo]

The quantum mechanics series has been my favorite topic so far! 👍👍

[@Zahlenteufel1]

8:30 Nice how you added that antiparticles can be seen as moving backwards in time!

[@biswapratim11]

As every particle is an oscillation of their own field like electron, proton and other fundamental particles then everything is a combination of vibration as atoms are made up of electron proton and other fundamental particles and atoms are made up of them ? means what we see and feel all are vibration at a large scale ?

[@archersterling4044]

Somebody call Mr or Mrs Smith

[@MakeMeThinkAgain]

Protons aren't fundamental. And going there takes us away from Feynman and into the really strange world of QCD. God help us all.

[@thedeemon]

Yes, what we see and feel are all those vibrations. Just don't be fooled by the word "vibration", in this context it means quite specific things from QFT, not simple wobblings of stuff.

[@MakeMeThinkAgain]

Well... the way we perceive the "simple wobblings of stuff" is a whole other topic. You can think of Quantum Field Theory as just the latest way of talking about what Kant called the "thing in itself."

[@materiasacra]

Yes. Matter is not a thing, but a dance.

[@feynstein1004]

Quantum mechanics is so unsettling. No wonder Einstein didn't like it. Also, when will we get a video about the Kaluza-Klein theory that light is vibrations in the 5th dimension? That'd be really interesting to watch.

[@frankschneider6156]

+Feynstein 100 Kaluza-Klein is indeed interesting, but led unfortunately nowhere, when trying to integrate the other 2 forces. Also I'm personally (so that's just my problem) very skeptical of everything that requires more than 3 spatial dimensions, because that violates reality as it is included with many inverse square laws (Yes I know the additional dimensions are "compactified"/roled up ... but imho that's just an excuse to negate reality and continue playing around with higher dimensions).

[@feynstein1004]

+Frank Schneider I wasn't aware of that. I just read about it in Michio Kaku's Physics of the Impossible and found it very interesting.

[@frankschneider6156]

+negativlex32 You are right. But according to the scientific method we need some hard observational evidence to consider higher dimensions (although mathematically possible) to be a real hypothesis and not just speculation. Also do the inverse square law - forms of many laws clearly show, that space is exactly 3-dimensional (if there would be e.g. 4 spatial dimensions, they would be of the form 1/r³ and not 1/r²). I don't say it's generally impossible, but according to the scientific method, convincing empirical, observational evidence in favor of it is requred, before taking such hypothesis for real.

[@Musigreg1]

Hey Matt, just became a Patreon from France . You're the only channel worth disabling my adblock. PLEASE keep making videos! Please don't stop, and please don't change host again ;-p I still have troubles getting a grip on that diagram, but man.... I'll watch you again and again until I get a grasp. Love you Matt ! See ya !

[@rickrose5377]

Best vid yet in terms of elucidating some complex concepts. I knew that renormalization was critical to eliminating those pesky theoretical infinities from the math, but I didn't really know how until now. Thanks, ST.

[@RealCottonCandyKid]

Correction: every vertex reduces the probability of the interaction with about 10%, or the square root of the fine structure constant, if i'm not mistaken. The reason about every extra interaction reduces the probability to about 1% is that these vertices always come in pairs.

[@materiasacra]

You seem to forget about Born. The probability is the absolute square of the amplitude. If you had one vertex (which QED does not allow) the probability would be proportional to the fine structure constant (~1%). An amplitude with two vertices upon squaring yields the fine structure constant squared (~10^-4). Etc.

[@nmarbletoe8210]

anybody confirm or contradict this? it's a very interesting question

[@pierrecurie]

He was being fast and loose with his language. It is true that every vertex contributes sqrt(alpha), but vertices always come in pairs. The odd ones are always 0, and I think it's related to furry's theorem.

[@dAvrilthebear]

RealCottonCandyKid at 8:10 are the numbers correct? 4 vert. - 0.001% 6 vert. - 0.0000001%

[@jawtap1520]

Well ill tell you , but first are you a RealCottonCandyKid?

[@deusexaethera]

I have a question. How can I calculate my own (approximate) mass in electron-volts? Assume I'm at-rest, because that's the truth -- I'm sitting on my ass watching KZbin.

[@cristianm7097]

Earth and Sun move your ass through the galaxy

[@RalphDratman]

Superb exposition. Thank you very much!

[@Blubb5000]

My head just exploded. Brilliant!

[@Nick-oj2rt]

So, if the electron's fundamental mass is unknown, and there is no limit to how much self energy it can have. Is it possible that electrons have no fundamental mass, and are made up entirely of self energy?

[@archersterling4044]

nicholas Aiello Untill observed probably yes.

[@sebotas2000]

nicholas Aiello they are, energy from the Higgs field

[@vacuumdiagrams652]

Depends on how you think of it. You can solve the Higgs mechanism to lowest order exactly and then the mass is just the mass. You can also treat the interaction with the Higgs vaccum perturbatively, and then the mass is due to a kind of self-energy. The corresponding diagrams have no loops though, so it's not quite the same type of self-energy that Matt was talking about.

[@ashkara8652]

en electron has several masses, to be completely correct. Its charge-to-mass ratio in a spectrometer, its rest mass, its self mass as explained in this video, including its relativistic mass using the full form of E=mc^2. Different experiments are used to calculate these different types of masses for an electron. For particles so small and traveling that fast, their masses do seem to change depending on their velocities, as expected. Sorry for over- complicating things, maybe I got a few things wrong, but just wanted to point out the different working definitions of mass.

[@Nick-oj2rt]

If it was made up entirely of self energy (i.e. photons interacting with the EM Field), wouldn't it not interact with the Higgs Field at all?

[@BattousaiHBr]

i know photons carry momentum, but what would happen if you pointed a trillion trillion trillion trillion watt laser at a black hole? would it push the black hole away? or would it stay in the same place? or would the black hole be pulled towards the laser (since photons also have gravity)?

[@garethdean6382]

The hole would move; while attracted to the laser and its light the momentum would push the two apart. (Not just the hole but the laser is being pushed back, both equally in fact. What you essentially have is a 'light rocket' launching you away from the hole.) The total effect will be not only that the laser and hole get further apart (action, reaction) but that the hole itself will move from where it initially was. (Though not by much if it has any mass at all.)

[@chinkeehaw9527]

The laser will be destroyed due to too much energy.

[@nathaniellavery1862]

BattousaiHBr

[@LuisAldamiz]

You'd make the black hole slightly larger. Photons do not "have gravity" (i.e. mass) they are just affected by it because gravity is not a force but the bending of space-time.

[@fadingbeleifs]

BattousaiHBr nothing would happen. youd just be wasting yourr time.

[@eldizo_]

QFT looks like an unholy spaghetti mess that somehow works out in the end

[@Adiso424]

Thanks for all your efforts Dr. Matt , yourself and your whole team . The dept of knowledge can never be payed back . Thanks for eternity ❤️

[@alexispulido398]

who was a subscriber before they started advertising?

[@bassisku]

Udit Gupta Imo he talked wayyyy too fast, especially for such a hard topic.

[@gospizana]

Udit Gupta I hated the other guy. it always felt as if he was upset and screaming at you.

[@vampyricon7026]

Wait... They advertise? Be prepared for more "I didn't understand a word of this" comments.

[@alexispulido398]

Vampyricon yes have u not seen the ads?

[@jpphoton]

it was a good run we had there Hank

[@_dr_ake]

Quick physics question! So, we're told we live in three dimensions which represents space, right? If time is actually a fourth dimension we experience then in reality would your beard tickle me if we kissed?

[@Michelle4PTG]

They told me that any object can be described and measured using a 3 dimensional grid and can track and calculate its motion using time as extra dimension. They never told me if those dimension are a real thing, only that they are used to accurately describe our reality and are useful to make predictions. So I see physics and math as a way to describe and talk about our reality in a universal way.

[@Michelle4PTG]

Yup, Wealthy Pepsi. Thats true. But you got to start small and simple. Can't start with explaining how the whole universe work on the first school day.

[@_dr_ake]

Michel_ I'm not a physicist obviously so please excuse me if I'm misunderstanding you! So if we think of time or any other dimension as something not actually real but just as a means of mathematically describing our reality, then time really would stop for me if he were to kiss me *just right*?

[@Michelle4PTG]

No, _ Drake. The time wouldn't really stop or slowdown. You might experience as if time slowed down for you but thats because you mind is focus on one moment.

[@danechegoyen3550]

One of their best! Great broad view!

[@austinnguyen9107]

Was experiencing SPACETIME withdrawal..., but SPACETIME always coming through at the right SPACETIME!

[@mansamusa1743]

*insert unoriginal/stolen comment*

[@watsisname]

Nice try, but you're not getting my unoriginal and/or stolen goods that easily!

[@amisfitpuivk]

That's Fine, man

[@jackmuller5478]

+Sotiris Krol the irony

[@andrewmcilveen4917]

*insert unoriginal/stolen comment*

[@5prayerfaust]

Wow, good effort on the visuals. Excellent video.

[@LoanwordEggcorn]

Fun stuff! Thanks for the introduction!

[@TheArtofFugue]

kudos for wrapping up noble prize winning concepts in such a short time. never could explain such with an infinite amount of time. Thanks! very easy to understand as well, being i am not a native english speaker.

[@complexham]

Im a programmer, but i love physics! and this channel makes me love it even more!

[@dendrofilen]

Tip for future episode: Holographic theory. It was briefly explained in a discussion on quantum mechanics on World Science Festival when talking about hawking radiation of black holes. I would love to know more about it.

[@BarryKort]

"Schroedinger's equation is a special case of a more general formulation of QM. In Schroedinger's equation, all the particles are tracked according to one universal master clock. In Feynman's approach, each particle is tracked according to its own proper time clock, which can vary its tick speed depending on how fast the particle is traveling. Derivation of Schroedinger from Feynman requires approximating all of the separate proper time coordinates to give a single time coordinate. That approximation is OK at low speeds, but breaks when things get close to the speed of light." ~Matt @13:35 Carry that thought over to the derivation of Bell's Inequality, where (instead of the wavefunction) we have the presumptive hidden variable, λ(x,t). One member of the twin particles has a position +x at time t, while the twin has a position -x at time t. But note that Bell adopts a common clock, so that λ(x,t) can be algebraically canceled out by λ(-x,t), regardless of the function λ(•). If you appreciate that a gravitational gradient perturbs timekeeping so that the particles speeding off in opposite directions age at their own idiosyncratic rates, then one can no longer algebraically cancel out λ. The derivation of Bell's Inequality breaks down; the presumptive hidden variable λ(x,t) remains present. Indeed one can say the hidden variable is time itself. In Aspect's experiment, λ(x,t) could be Maxwell's Equation for the photon, or (equivalently) Feynman's rotating vectors. But recall that photons traversing a gravitational gradient gain or lose energy and thus change their wavelength (or color) accordingly. The two photons are thus represented by sinusoids which are not perfect mirrors of each other and thus cannot be algebraically canceled out. They will have a residual nonzero "beat frequency" which remains present, thus spoiling Bell's convenient cancellation of λ(x,t) midway through his derivation. That's why Bell's Inequality doesn't hold in the real cosmos where there is no universal master clock that keeps identical time everywhere and everywhen.

[@ikarienator]

This, gentleman, has been the best layman's description of renormalization I've ever encountered.

[@myhandsspeak1925]

My favorite channel. Please don't stop

[@danthepyroman1]

I'm super excited for the Space Time eclipse glasses

[@ManyHeavens42]

you dont need electricity to activate a Crystal, Use frequency, Frequency Creates light, light creates life Your so Smart.

[@TheAgentJesus]

You guys are honestly incredible, and you have my eternal gratitude for all you've taught me over the years. Great episode, as usual. That's said, if I can make one single request: please, Please, PLEASE make an episode on Loop Quantum Gravity!!! It's often heralded as one of the most promising alternatives to String Theory as a theory of Quantum Gravity, and yet there's little to no accessible material out there explaining it for non-physicists! Sounds to me like a job for you beautiful people at SpaceTime XD

[@trucid2]

Thanks, this is one of the better episodes.

[@colinellesmere]

These are brilliant videos. So well thought out and explained. It's still tough going but bit by bit through more viewing of related topics I am getting a clearer mental map of the terrain. The internet has a lot to answer for in term of allowing dumbing down of issues and sensationalisation and bias. This is an example，and there are many others，where it is a force to open up minds to a greater and more humble appreciation of our place in the Universe. From the presenters knowledge perhaps this is a relatively simplistic explanation but I suspect he has had to think long and hard about how to formulate these ideas and that the process has increased his own understanding. We can't all get up to speed on the Maths as that is a high level career calling for a select few that some how can quickly understand complex maths. But to begin to understand this conceptually is not at all easy. It requires a great deal of consideration over time. I have great admiration for communicators like this. They want us to know and learn. That is a very compassionate thing to do.

[@norbertprebeck9724]

Thank you very much for presenting your insights.

[@jasonmann42]

Nicely done Matt!

[@maltebergman5242]

If you see this, I love this guys keep it up! Really nice videos for an interested non-academic =)

[@Newsflash-Channel]

I know this isnt related to the topic of this Video, but could you do one about The Great Attractor? Love your Show!

[@RatusMax]

Not gonna lie, I ran when i got here in physics (the professor even made it easy for us but i at the time felt like it was a mental overload. Then I had to deal with personal problems) and went straight to CS. Such an easier concept and it gave me more time to go to work and have money to eat. Now, although there are probably code that do it, I am reading my physics books and writing my own code making the functions for the physics equations. This is actually helping me see physics in a different way. I might go back for a phd when i turn 30. (I need to get my life together now) In the U.S.A money first, discovery later. Unless you have a full ride scholarship then go all out. I am not worried though. I met this genius kid in physics he was 100X better than I was. It was a treat to see him do his thing and worth the debt I got trying to pay for classes. It showed me who I could become. Anyways, for some reason after his PhD in physics, he went to go into machine learning. Since I was in CS, I was introduced to it and decided to go in that direction. I think he, like I have, realized there is something there that will help in future physics endeavors.

[@bethbartlett5692]

Really like this presenter - pleased I found this channel. Is there a presentation on "The Unified Field Theory"? I viewed Dr Hagelin's - adore that man, just would like another presentation perspective.

[@memeeeeh]

I'd like to point out, i'm probably to stupid to understand half of this, yet i keep watching every upload.

[@rayzorray4151]

Wow wow Wow . . . Equations hiding in plain sight, now im realy hooked . . .

[@a52productions]

Seems funny that one of the major stumbling blocks of QFT was a problem with infinite electron energy -- when avoiding infinite electron energy was the reason Planck came up with quantum theory started in the first place.

[@LuciFeric137]

Excellent lecture