Solving the Impossible in Quantum Field Theory | Space Time

  • Published on Jul 12, 2017
  • Viewers like you help make PBS (Thank you 😃) . Support your local PBS Member Station here:
    How do you calculate infinite quantum outcomes? Feynman Diagrams. Get your first two months of Curiosity Stream for free by going and using the promo code “spacetime” at sign up.
    You can further support us on Patreon at
    Get your own Space Time t­shirt at
    Tweet at us! @pbsspacetime
    Facebook: pbsspacetime
    Email us! pbsspacetime [at] gmail [dot] com
    Comment on Reddit:
    Help translate our videos!
    Previous Episode:
    Feynman’s Infinite Quantum Paths
    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 (
    Comments answer by Matt:
    Christian Haas
    Psy Kosh
    Special thanks to our Patreon Big Bang, Quasar and Hypernova Supporters:
    Big Bang
    Shane Robinson
    David Nicklas
    Eugene Lawson
    Joshua Davis
    Tambe Barsbay
    Max Levine
    Mayank M. Mehrota
    Mars Yentur
    Mark Rosenthal
    Dean Fuqua
    Chuck Zegar
    Jordan Young
    John Hofmann
    Joseph Salomone
    Martha Hunt
    Craig Peterson
    Prof. Dr. Kenneth Michael Beck
    Science Via Markets
    Thanks to our Patreon Gamma Ray Burst Supporters:
    Peter Durocher
    Michael Kers
    Chris Hicks
    Mark Vasile
    Patrick Murray
    Justin Lloyd
    Sultan Alkhulaifi
    Alex Seto
    Conor Dillon
    Jared Moore
    Michal-Peanut Karmi
    Bernardo Higuera
    Erik Stein
    Daniel Lyons
    Kevin Warne
    JJ Bagnell
    J Rejc
    Amy Jie
    Avi Goldfinger
    John Pettit
    Shannan Catalano
    Florian Stinglmayr
    Yubo Du
    Benoit Pagé-Guitard
    Nathan Leniz
    Jessica Fraley
    Loro Lukic
    Brandon Labonte
    David Crane
    Greg Weiss

Comments • 1 253

  • Mekratrig
    Mekratrig 7 days ago

    Who and when was the standard module created. Was it Feinman?

  • J LeMaire
    J LeMaire 15 days ago

    Someone scienced this dude a bit more pectoral mass.

  • Roy David
    Roy David 21 day ago

    I don't understand, but it sounds so cool :v

  • Nomen Nominandum
    Nomen Nominandum 23 days ago

  • violentauntie
    violentauntie 25 days ago

    Why not just call them 'FEYNAGRAMS'? You can have that for free...

  • Barrack Obama Vlogs

    This is so fucking useful.

  • Nad Senoj
    Nad Senoj Month ago

    could the electrons constant effect on the EM field, tie in somehow to pilot wave theory?
    I assume, (as a Layman) any radiated energy, would be inconceivably small. But so is an electron.

  • reynaldo velasco
    reynaldo velasco Month ago

    My son will solve this someday. Im too old now.

  • lolnope 64
    lolnope 64 Month ago

    2:35 if that's so, then we could use electrons as some sort of communication tool, or is that just the dumbest idea ever?

    • Silent Observer
      Silent Observer 5 days ago

      And that "communication tool" is called electricity, yep

  • Dave Brown
    Dave Brown Month ago

    I can't believe how much we still don't know, we make up theories on top of theories and still can't explain what gravity is?! We know the effects and can measure it but from the largest down to the smallest can't say what it is.

  • Barrack Obama Vlogs


  • wulphstein
    wulphstein 2 months ago

    You could consider a kind of virtual photon that has zero energy. It could still have frequency, energy, wavelength and momentum states. It would have c and h built into it, but zero energy, zero energized quantum states.

    • wulphstein
      wulphstein Month ago

      @Дмитрий Прищепа I interpret the \Delta E \Delta t > h, to mean that a virtual photon has no real energy, but the states can be measured in the same way that a gauge can happen to be on a value, but it doesn't mean anything.

    • Дмитрий Прищепа
      Дмитрий Прищепа Month ago

      All virtual particles kinda have no energy, only momentum.

  • amir ali
    amir ali 2 months ago

    very very informative channel I like it

  • Rosolino Lo Sciuto
    Rosolino Lo Sciuto 2 months ago

    Quando una persona muore se ne rende conto all istante perche' la mente e' quantica e' il pensiero e' cosmico

  • brinbrin62 62200
    brinbrin62 62200 3 months ago

    This T-shirt do not fit you.

  • Alexander Daly
    Alexander Daly 3 months ago

    *existential angst screech*

  • WhimpyPatrol
    WhimpyPatrol 3 months ago

    Clearly, Feynman who lived in the 20th century was a modern quantum physicist. I don't understand how some caveman from prehistoric times was able to make this video about him.

  • shinzon0
    shinzon0 3 months ago

    @14:40, the sum of the real and the sum of the IMAGINARY components, not complex ;) - But of course great video!

  • Trog Veneerer
    Trog Veneerer 3 months ago

    How many love knots can yourself actually make and move with it????

  • priyank tamilsekaran
    priyank tamilsekaran 3 months ago

    can anyone guide me to find his videos in order, like from his 1st video

  • Tyler Hills
    Tyler Hills 4 months ago +1

    I strongly recommend to all physicists and mathematicians to abandon this concept of infinities

    • Andrew Sav
      Andrew Sav 3 months ago

      Well that seems like a rather absurd proposition, may I ask on what basis? The concept of infinity is implicit to the most important of mathematical constructs and unavoidably apparent in irrational numbers phi(derived itself from an infinite mathematical progression found in everything from spiral galaxies to sunflower seeds), euler's number(used extensively in financial mathematics to measure compounding interest), and pi(the number divisionally acquired from perfect circular geometry) the latter two of which are transcendental irrational numbers, i.e. not derivative from algebraic polynomial equations unlike phi. It is in the nature of such numbers to repeat without an identifiable pattern ad-infinitum. Furthermore, the square root of every prime number returns an irrational value that is itself infinite, from the sqrt of 2 to the sqrt of Mersenne's 50th prime (2^77, 232, 917)-1 a number with more than 24 million digits.

      I am both baffled and intrigued to hear your argumentative precedent for such a bold statement. As it would seem to me, infinity is not a conceptual conjuration from the mind of man so much as it is an observed reality. I may be more inclined to agree if you're arguing there is only one concept of infinity, or in other words, there are no lesser or greater infinities between numerical progressions just the same incommensurate outcome compounding to the same conclusion through a variety of paths(to reference the video above). Sorry for any incoherency or run-on sentences I'm a tad drunk but your comment kinda struck me.
      But cheers! lmao, looking forward to your response.

  • Tyler Hills
    Tyler Hills 4 months ago

    "this renormalization trick can be used to eliminate many of the infinities that arise in QFT" ... I.e. this trick of making up terms to soak in all the unexplainable errors is wonderfully useful 😂

  • Tyler Hills
    Tyler Hills 4 months ago

    I think in both worlds of mathematics and physics we need to stop using the words 1) infinite 2) infinitely many 3) infinitesimally etc and replace them with words like "unbounded". Doing so will mentally change our perspective to a MUCH more logical, grounded approach to all these subjects, starting with calculus. Not only would students benefit, but professional physicists and mathematicians as well and even the progress of all these subjects

  • Tyler Hills
    Tyler Hills 4 months ago

    Anyone else see a problem with, "physicists have geniously solved the problem of the 'inconvenient' mathematical infinities by folding in a term to correct for these errors" ... i.e. something has gone horribly wrong ... But it could be literally ANYWHERE from our base assumptions starting at the very beginning of the foundations of QFT to now ... But let's stick with our current path and "throw in an error term" i.e. a term to soak up all the error we've accumulated so far" 😂

    • Tyler Hills
      Tyler Hills 4 months ago

      Btw I am a mathematician currently doing research in QFT

  • The Truth of the Matter

    If we lived in a One Electron Universe then the electrons would have infinite mass right? Maybe that's why the equation keeps giving us an infinite electron mass.

    • Дмитрий Прищепа
      Дмитрий Прищепа Month ago

      If we live in a one electron universe the amount of electrons and positrons should be equal, but it's definitely not.

  • Joshua Scholar
    Joshua Scholar 4 months ago

    You said that superluminal paths add little to the probability - but not zero?

  • Risto Paasivirta
    Risto Paasivirta 4 months ago +2

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

  • David Wilkie
    David Wilkie 5 months ago

    Feynman Diagrams get closer to a systematic way of showing the external properties of the "Pacman" dimension and Renormalization = instantaneous to eternal zero-infinity range of Temporal Superposition Holography?

  • Q.D. White
    Q.D. White 5 months ago

    If any path that can happen does happen, I'm disappointed they didn't call it Quantum Murphy's Law.

  • Dr B. C.
    Dr B. C. 5 months ago

    Wow, I am your biggest fan! You probably hear this a lot, and it must be very tiresome. But hey, I am here now, so it will be a easier from now on. Anyway keep up the good work. And at least you have one person who can understand what you are trying to do.

  • Smoked Paprika
    Smoked Paprika 5 months ago

    This video deserves more views.

  • Michael Cox
    Michael Cox 5 months ago

    Poor Matt, having to balance on his toes all the time.

  • Dmitry Miserev
    Dmitry Miserev 6 months ago

    Nice video. Just a little moment to clarify. When you were giving examples of higher order diagrams contributing to the scattering amplitude of two electrons (or 4-point electron correlation function), you included the diagrams corresponding to the dressing of external electron lines. These diagrams should not be included for any correlation function. It is what's called amputation of external legs. Technically, it's seen from the definition of correlation functions where you take the vacuum average from the T-ordered product of the operators in the interaction representation which can be rewritten as the T-ordered product of the Heisenberg operators (bare operators) and the S-matrix (and do not forget to divide the result by the vacuum average of the S-matrix). It is easy to show that only connected diagrams with amputated external legs contribute to the interaction part of the correlation functions. Thank you.

  • Leo Marrah
    Leo Marrah 6 months ago

    Does anyone else notice all the background clicking?

  • Alpha Beta
    Alpha Beta 6 months ago

    In August the eclipse is? Really????? Which YEAR????, Do you even understand that you do not exist in time? Please specify the time you are referencing too when talking on your videos, sigh. and yes I mean the pun psi

  • W Serba
    W Serba 6 months ago

    If light is our medium of information exchange, and that our intimate knowledge of the universe is limited to that which interacts with light, how can we definitively claim those other possibilities don't actually exist if they don't interact with light? Those other fundamental fields must also be mediums of information exchange, but how does one wrap one's mind around how they really are? Must one be familiar with the raw data? Is there any living human being who could legitimately do that given our short life span? I imagine that's what a Feynman diagram really is, a conceptual model that agrees with the data. If we must use our imaginations to perceive these things as they really are, isn't the rabbit hole of analogies that approach the real meaning an inevitability, even between those with PhDs? In the game of signifier and signified, are you sure you're all on the same page? Is that why Feynman preferred to use so many examples? With more examples of concept comes more clarity of concept, i.e. the more descriptive one becomes the more precise one becomes?

  • TheHorizonTries
    TheHorizonTries 6 months ago

    So smug when he ends EVERY EPISODE by working in the last words "space-time"

  • Christian Vulpescu
    Christian Vulpescu 6 months ago

    Referring to the QFT: They tried to proof the Plank units in space by measuring the crispness of light from verry distant objects and the pictures were to crisp.
    Could it be, that the photons don't have to pass the real Plank units in space but could travel as field exitationes - so to say: under the radar- to us and materialize in our telescopes?

  • Ben
    Ben 6 months ago

    I guess you can say he was a fine man?

  • Alex Gregor
    Alex Gregor 6 months ago

    Again this guy!
    Can't watch this

    SWAYAM G. 8 months ago

    What about PROTONS, u only talked about ELECTRONS

  • Shawn Elliott
    Shawn Elliott 8 months ago +2

    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 RUclip.

  • Anarchy
    Anarchy 9 months ago

    Not sure how I got here to this video but I'm glad i did

  • John von Horn
    John von Horn 9 months ago

    The dude reminds me of Jesus

  • David Hand
    David Hand 9 months ago

    Hypothesis: In a universe containing *nothing* but one electron, the mass of that electron *is* infinite. The absorption of many of those photons by other particles is what limits the mass to a finite number.
    Shoot me down.

  • Arby
    Arby 9 months ago

    What if you impossed the rule that the total energy of a particular Feynman interaction is constant. Hence the sum of an electrons self energy plus it's remaining mass must be constant. I don't know what forces govern an electron to emit and re-absorb a photon with, say, an energy equivalent to half it's mass, but I think it's safe to assume that it doesn't happen very often (otherwise electrons would give off heaps of UV light). So this a wild guess, but could the relationship between the sum of the self energy be explained by an inverse probability relation (i.e. 1 - (photon energy)/(total energy of electron))?

  • DJ Toddles
    DJ Toddles 9 months ago

    9:00 I wonder if electrons have a weight watchers program for dealing with their infinite mass

  • That Should Work
    That Should Work 9 months ago

    maybe there is a static underlying field, that particles interact with as we hurdle through space

  • Ilya Kostolomov
    Ilya Kostolomov 9 months ago

    Damn, physics Jesus knows his shit

  • Abhi Abhi
    Abhi Abhi 9 months ago

    Why should light should travel why can't it be in one place

  • MetraMan09
    MetraMan09 10 months ago

    The electrons don't bounce off each other, they actually just pass through each other like waves but 4-dimensional wave crests smack into each other and affect their source waves. The math works out.
    9:30 The math works out if you calculate mass(time). Yes, infinite kinetic mass energies are possible but they last for so little time that they average out to the known electron kinetic mass. It is actually why an electron increases in mass as it goes faster and faster: the electron's time dilation makes the infinite kinetic mass last longer from our pov and thereby creating relativistic mass.

  • Mr. Lee
    Mr. Lee 10 months ago

    This is a beautiful person.

  • Tabulanis Morris
    Tabulanis Morris 11 months ago

    I would like to say thanks PBS spacetime. You guys are on it. I wanted to request something.
    I have seen a lot of lectures and salons about the many worlds interpretation and how it works. They seem to always say "Then the universe splits in two." This seems really counter to the idea. I always thought it was always many worlds. No plitting needed. In fact the case for the many is already there I think. One has to remove worlds to make a "split" If it's all quantum, then wouldn't it be more about wich worlds one "sees" and not what world is created? That way it can all be quantum just not all observable. I get that some folks think this is useless as it can't be proven, but I think it's important to show that observation shows us some possible particular state of the universe, not THE state of The Universe. Like, say all quantum systems in the whole are in superposition but connected through likelihood. Maybe even entanglement. I don't think it's useless just misunderstood.
    I mean what if you can only "see" one chunk of time and no others. Just your chunk. Your chunk is a lifetime long and as big as all that you see in that time.
    Like if you take the whole city of New York and every possible thing in a day that can be observed without any filter. You have nonsense. Just random junk everywhere. Add a video camera and we limit our perspective. Now we see objects interacting though time. That's how it seems to me. I would love to see a more indepth look at these ideas. We can't prove what happens inside a black hole but we still try, and that work has been very revealing.

  • douchebag patrol
    douchebag patrol 11 months ago

    wish u could just use perturbation theory in exams to justify ur answer lol
    near enuf is good enuf :D

    • Cosmic Landscape
      Cosmic Landscape 10 months ago

      douchebag patrol it’s very difficult actually ^^

  • Poes Law
    Poes Law 11 months ago +1

    Electron go in and electron go out, you can't explain that without QED

  • James Elger
    James Elger 11 months ago

    Ha ha ha! What happened to Lambda!?

  • Q&science
    Q&science 11 months ago

    I got rather confused at the beginning when you talked about the exchange of one virtual photon between the two electrons. There are two electrons which cause two excitations in the electron field, therefore shouldn't they cause two excitations in the electromagnetic field, which means that the pair of electrons would exchange not one, but two virtual photons in one repulsion?
    Would really appreciate it if someone can answer this. My head hurts.

    • Q&science
      Q&science 11 months ago

      Oh, ok I just watched the part up to 5:47, and I realised that the two electrons can cause random excitations and it just depends on the exact circumstance (if I understood correctly)

  • Mekratrig
    Mekratrig Year ago

    Why would a virtual photong come into existence between an approaching pair of particles? What governs the origin point of such. Can virtual particles be something other than photons?

  • Aditya Das. Mr.COSMOS

    Very nice

  • Michsel Holiday
    Michsel Holiday Year ago +1

    The secret is the Heisenberg uncertainty principle but elaborating further on that the particles of measurement also along with its energy it's borrowed from the future and it's like moving through a soup of these particles and using 1 using using one only once we going to the next one

    • Michsel Holiday
      Michsel Holiday Year ago

      Also you must consider that causality has the speed limit and not light