QED

[EclecticSceptic]

This is so mad.

[Iberedmas]

I do not understand that much, but interesting.

[Suchtii22]

troll

[GamerIsCrazy]

lol

[TheTutsinHD]

troll

[Lavabug]

Absolutely AMAZING content. Finally some serious videos on QM! I love the joining the head to tail analogy, that is precisely the definition of the dot product and its what is used to calculate probabilities of outcomes.

[Jipzorowns]

Why does the spacing of the deffraction grating increase with different wavelenghts (colors) ?

[Jipzorowns]

thank you! had many "ahhhh thats why!" moments :)

[gmodruls]

how fast does the stopwatch go at the colour red? orange? yellow? green? blue? indigo? violet?. plz awnswer.

[cassiopeiaproject]

@gmodruls It runs at the frequency of the light.

[Yakeyglee]

@gmodruls Check out the table of frequencies on the Wikipedia page for the Electromagnetic Spectrum. A frequency in Hertz (Hz) is the number of oscillations per second which corresponds to the number of full turns in the clock shown in the video per second. (In reality, they turn much faster than shown in the video.)

[Nerfherder3]

Where does the coupling constant fit into all of this?

[CorporalHotdogs]

This guys voice....

it causes people to commit suicide.

[emwaver]

thank richard feynman for most of this...

watch his video on this (his new zealand lectures)... he says "i have no idea how this arrow thing really works, i just know it does"

[normanleto]

One question: we have a swarm of H20 particles,hitting each other. Some will join and stay together to form larger droplets, but some will bounce off by repulsion force. How exactly maseless photons involved in the electromagnetic force cause this bounce? Are photon wavefunctions (responsible for repulsion) emitted by electron wavefunction of the repelling H2O atoms? Or these force carrying photons wavefunctions are already "in the field" emitted before by any other sources?

...thanks

[aqouby]

@normanleto The first one. Photons are used in the repulsive process and they are a result of particle interaction. Cool question.

[SherryVapors]

Outstanding work. Thanks very much for making this video. It's a great help in beginning to understand path integrals and QED.

[me001ist]

I thought i heard that light was both particles and waves.

[MrGeoffrey834]

i thought they figured out that all light exists as waves, and that there were no photons

[cassiopeiaproject]

@MrGeoffrey834 Not Hardly.

[LIONEXable]

@cassiopeiaproject HAVE SEX

[itemushmush]

@MrGeoffrey834 It seems you are about 200-300 years behind in physics

[bacamd]

@MrGeoffrey834 Light exists as BOTH particles and waves. Crazy stuff.

[psycotria]

@tammas789 - He is trying to make it easy for even ignorant punks to understand. If you are concentrating on his voice, perhaps you just don't 'get it'.

[tammas789]

he got anoyng voice...gayish moron

[marksmanepsilon]

@tammas789 right... you are calling the guy explaining quantum physics a moron

[mjh012363]

"...photons are particals..."

Um..Yes and no. They are equally energy waves. It all depends how you "look" at them or if you "look" at them at all. :)

[Vocalallusive]

Probability is an expression for lack of insight. If we somehow could preconfigure the micro-world the photon is traveling though, it is a good reason to believe we can alter the statistics and by this get a slightly more deterministic interpretation. For all we know today, Higgs particle is responsible for the so called probability. This makes this interpretation, immature crap and not too to be taken serious when the goal is a complete theory. Prediction is not explaination, let alone evidence

[Indrius]

@Vocalallusive No. It's not about the probability, but the probability distributions. It is impossible to know how a particle travels from point A to point B. It's not as intuitive as with large objects that we see in our daily lives. They seemingly move in a straight line (if no forces apply) according to classical mechanics. But deep down below this concept is absent. No one can comprehend how a particle moves and interferes with itself. Look up superposition and learn more before spewing BS.

[gotnoshoes22]

Great video. A small explanation that the stopwatch and arrows account for interference of the probability wave would alleviate our guessing.

[shakagenghis]

So the "stop watch" is representing some oscillation of the photon as a wave or something? And why am I joining the "arrows?" What are these arrows representing exactly? Good video, though I am left asking more questions.

[cassiopeiaproject]

@shakagenghis The stop watch is related to the frequency of the light. The arrows represent the probability of a certain path. Joining the arrows represents the probability of the event along all paths.

[sesshoumaru3st]

@cassiopeiaproject I understand everything.I kind get the place section of the video with the photons and electrons. But other than that i got it man XD hahaha YAY god damn i spend hours on this thing.

[marksmanepsilon]

@cassiopeiaproject at 16:34 is "n" the primary quantum number for that electron?

[emwaver]

@cassiopeiaproject glad you cleared that up; since watching feynman's lecture on this, i was concerned they would have to actually measure this extremely tiny amount of time.

[shakagenghis]

@shakagenghis

Thank you, that helps. Good video, the analogy was lost on me regarding the arrows.

So light never travels as a 'object,' just arrives as one. The universe shouldn't give a crap if we're observing it or not, so I have a hard time believing uncertainty has anything to do with observers, the inability to know velocity/position of an small object. It doesn't seem that the universe should care much about probability. Troubling

[VersionOnePointZero]

I'm sorry but this video doesn't do a very good job of explaining any of these concepts. You hand-hold the viewer on various concepts like vectors and apparently sinusoidal functions by calling them "arrows" and "stop watches," (without explaining the real mathematical basis for these things) while glossing over genuinely confusing concepts like obscure constants. As a layman, I genuinely had no idea of what was going on, and was just watching the pretty animations!

[av733]

These videos are the best, for explaining physics on YouTube.

[erivila]

wow, nice video, using stopwatch arrows to represent wavefunction interference. (and reversing the arrow because of it being a closed reflection)

Wouldnt it be easier to just refer to it as waves, though?

[ericsbuds]

i thought QED stood for quantum electro dynamics. or is the latin verison the same thing?

[cassiopeiaproject]

@ericsbuds It does. It also stands for the latin phrase quod erat demonstrandum which means "what was to be demonstrated". It is often quoted after a science or mathematical proof and in that context it indicates that the proof is finished and what was to be proven has been proven.

[sesshoumaru3st]

@cassiopeiaproject you said the probability each final outcome is the equal to adding all probability of each possible path.Would that make the probability of each final outcome 100%. I'm confused right there man .

[cassiopeiaproject]

@sesshoumaru3st We followed that statement with an example. Didn't the example help?

[alphatelescopii]

I don't get how the animation shows the light going in at say, near perpendicular to the mirror, and flying off to the photomultiplier at a low angle of near, say 30 degrees to the mirror. Wouldn't it go back up without going near the photomultiplier?

[Vocalallusive]

I'm sorry to say this ain't very convincing. Even when I trust the accuracy of the shown experiments I fail to see that your explaination of what is going on follows as a neccesity. In fact, in a brain spin on my part I'm able to come up with many different explainations for what's really going on, for each I obey the results of the experiments. I believe it's arbitary many explainations.

Maybe you physicists should start to be more self-critical and less religious?

[CathySander]

@Vocalallusive: Religious, huh? Physics ain't a religion. That the universe acts in these strange ways is a fact, not just something that physicists dreamed up in their spare time. We can make up stuff about what causes these things to occur, but for the time being, we'll just have to accept it as true...until further evidence arrives from the world. Simply because we can't understand it intuitively doesn't make it false.

[Vocalallusive]

@CathySander, no, it's not a fact. It's a choice of explaination which is not neither proven nor supported by enough evidence beyond reasonable doubt. Maybe you should look up "fact".

We should wait for more evidence before calling something a fact, stupid.

[magichristo]

How does a photon travel at all possible paths? How does that work? Doesn't that mean that it has to be at different places at the same time? Confusing shit!

[GrimHeaper460]

Ah, QED. A mathematician or physicist's time tested way of saying OH SNAP BITCH!!! Of course, in this sense, it refers to Quantam Electrodynamics.

[tnuh55]

What's with the narrator's voice? His intonation wrecks the video.

[jackp22]

Awesome 

[Netino78]

love the videos but it's so much information at once that by the time u grasp the concept of the phrase u just heard, 30 seconds have passed....and u have to watch these videos a few times to fit it all into your memory

[srosefx]

@Netino78 thats the point, to make us think and absorb and then question.

[Indrius]

@Netino78 This video is based on Richard Feynman's lectures on quantum electrodynamics (they are here on youtube too). There's also a book called "QED: The Strange Theory of Light and Matter" which is based on those lectures too. It explains QED without using calculus (in fact, almost no maths). Highly recommended.

[TheIndrajit007]

theee explaintion given by cassion project are superb ,easy to understand ,i will be glad if can get my high school science chapters designed by the members of this group here

[666DRaZZ666]

This guys voice is annoying as HELL, He is also patronising as FECK. Why does he have to talk like THAT. Is there any real need for IT. Man it ruins a very interesting subject!

[Netino78]

@666DRaZZ666 once u get used to it, his voice and the way he talks makes your brain process the information easier

[jacobromu]

and deepak will take these properties of light and start talking about magic.

[AndyKong51]

Rainbow rotating arrow is kind of confusing. It's easier just to give a sin wave. And it doesn't really say much about j and magnetic moment.... I thought this video would tell me more about QED but instead, it adds more mistery to it. It's just my comment of this video. Thx.

[JOHNNYWADTON]

it's pretty easy, light was invented by general electric....... right?? no?? they hold the patent....

[sonofgong]

i'm going to start talking like that all the time

[beachcomber2008]

Fabulous. Well, no, REAL.

[vinayakaya]

light is also a wave, calling it a particle is overly simplistic and wrong as a result. The theory does produce predictable results, but that doesn't mean that the underlying explanation is correct.

[mrpossibilities]

This is a great video. And it really helps that the guy talks to me as if I was a retard. And yet, I couldn't quite grasp some things still.... but I'm almost there.

[AI2flesh]

hahahahaah my favorite friend mr QED. well what about thermodynamico? no mac 11 flights yet?

[zwxao]

is there an explanation on "why the light follows the least action principle?"

[yasminmansury]

this is the consequences of newton laws of  motion.

[yamjayamjabulba]

u wrote such a big example in ur description:

"light can be separated into colors you can see beautiful colors on a puddle if there is a little bit of oil on it..."

u could just have given the example of a rainbow....

thanx anyway for the nice video..

[sandwichtaster]

Rainbow doesn't show the thickness difference

[matatan69]

This video just thaugh me in 22 minutes what I was trying to understand in the past year. great work.

[YogiToad]

Remember the move about the Grinch when he heard the Who music and his heart came back to life and started growing and he writhed on the ground in pain, yea I'm holding my head right now.

[1RadicalOne]

These videos are excellent. They take something exceedingly complex and contrived, (like all of quantum mechanics, for example), and make it easy to understand.

[doogtoog]

Is there going to be a video on QCD?

I liked the teaching style of this video, and a similar one on QCD would be nice.

[cassiopeiaproject]

Perhaps. And until then, our "Standard Model" video includes the merged QCD into the larger picture.

[yamjayamjabulba]

Hey, can you please tell me what is actually the, "CassioPeia Project"?

[eythorb]

A very good animation of QED although I do think Feynman should be mentioned and given proper credit as the explanation for QED is taken almost directly from his book on QED.

[eythorb]

Okay, the book is credited in the end. It really should be in the description.

[angryangelhouse]

Theses vids are so great!

[GBTMK]

True

[SuperMerlin100]

Great video! Thanks! You explain it so well! cool!

[TonyBtheEG]

incredible.

[MrCropper]

21:50 "Quantum Electrodynamics is perhaps the single most successful theory ever devised."

This reminds me of the accuracy of Ptolemy's insane system, which sailors continued to use for over a century AFTER Copernicus's Heliocentric theory was published and widely known.

Accurate doesn't mean true.

[sbrenn]

But if accuracy is combined with simplicity (something Ptolemy's system certainly wasn't) it usually is.

[MrCropper]

3:50 "Each photon follows every possible path simultaneously..."

Wow, what a bunch of crap! How could this ever possibly be known? Believing that kind of stuff is like believing in unicorns and ghosts.

Did someone OBSERVE a photon that followed all possible paths AT ONE TIME? God, how stupid physicists can be!!!!!!!

[sbrenn]

Just go safely to bed tonight. We'll watch over you and you don't need to worry. I know it's all scary, but you're quite safe.

Just close your eyes and... sleep....

[MrCropper]

"Just go safely to bed tonight. We'll watch over you and you don't need to worry. I know it's all scary, but you're quite safe... Just close your eyes and... sleep...."

An example of the idiot soothing his doctor. : )

[sbrenn]

Well, if the doctor doesn't know anything about quantum physics, that would make sense. :)

I advice you to watch Feynman's lectures (especially those from Auckland - 70's)

Go to video.google. com and search for Feynman Lectures Quantum Mechanics. It's in two parts each more then an hour.

You'll enjoy it. Feynman is a joy to listen to.

[SuperMerlin100]

Yes photons have been observed to follow every path. The double slit experiment.

Quantum mechanics is science

not religion.

[AtheistThatsATheist]

Its amazing the amount of people who can watch one video and think themselves more of an expert than the people who dedicate their lives. These comments tend to be only insulting & rarely offer an alternative(I dont mean an invisible man just made it that way) Which is intelligent and based on know science, or even a logically thought out thought experiment.

Do u care to offer an explaination or cause it doesnt make sense to u, is enough reason in your eyes 4 this comment? I reserve Judgement

[RationalEmotive]

Everyone, do not believe the wildly speculative debaucheries of cassiopeiaproject:

A young attractive woman has nothing to do with the daily life of normal physicists. Well, maybe quantum physicists but certainly not condensed matter physicists.

[kahnicles]

jealous much?

[doogtoog]

Well, considering about half of their videos have to do with simplistic astrophysics, biology, and basic mechanics (the subjects being mostly condensed matter physics) you shouldn't trust mechanics either. many of them are about chemistry and nuclear physics (based on mostly quantum mechanics), so atom bombs don't work and the pH scale is useless since cassiopeiaproject sais otherwise.

[RationalEmotive]

I wasz joking, dude.

I think it is a well-done and above average public understanding of science or science communication project, It ain't Carl Sagan, but hey.

If Americans would tune in to this every other Sunday instead of FoxNews sports, there would still be global warming, overpopulation, the industrial military complex and the church, distribution problems of wealth and HIV,... but at least people would not fill the aerial aether with pointless information about sports results.

[barsoapdish]

doogtoog,

could you enlighten me about where did Cassiopeia Project stated that atom bombs don't work and pH scale is useless?

[CathySander]

@doogtoog: Surely you know that you use other reliable sources...

[evilelton]

just because you used 2 SAT words doesn't make you any less of a dumbass

[Trajedya84]

COOL STORY BRO

[nickharvey7]

Great video! But what about the problem of infinities that can only be put right in a process called renormalization. This is a mathematical problem the calculations for each coupling on a Feynman diagram are infinite. These infinities can only be canceled out by renormalization. Also we can understand how to do these calculation but we have no understanding of why we have to do them. It would make sense if each photon electron coupling radiates out in a light sphere of quantized waves

[cassiopeiaproject]

Feynman won the Nobel prize for solving the problem of renormalization. He showed that the infinities that plagued QED at small distance couplings only involve the two theoretical numbers "n" and "j" that are mentioned in the video.

[kurtu5]

So in that part you are basically rehashing his prize winning work?

BTW thanks.

[cassiopeiaproject]

Yes, the material in this video came directly from his book displayed at the end of the video.

[TheExpandedPicture]

@cassiopeiaproject

for the second experiment, wouldn't you have to reverse the direction of the arrows since the light was reflecting off the glass (and you stated before, whenever you have reflection you would always reverse the direction of the arrow)?

[cassiopeiaproject]

@TheExpandedPicture You only reverse the direction of the arrow when the reflection occurs at the FRONT surface of the glass.

[dibbuck]

nice video. But understanding the arrows represent the phase of a wave and their subsequent interference makes it more intuitive. But that is the point I suppose - providing a particle interpretation... nice video

[ProcInc]

I love your genius use of word play here using QED, referring to quantum Electro dynamics but also Quod erat demonstrandum (said at the end of something Definitive)

I'm assuming it was intentional

[ProsperosCloset]

Sorry, Proclnc but are you being sarcastic?

[ProcInc]

"Sorry, Proclnc but are you being sarcastic?"

I didn't watch until the end when I posted the comment. I initially didn't know whether or not QED was intended to be a double entendre.

To everyone who does watch the video I will sound extremely sarcastic now, dammit

[AMGarrett09]

Really excellent presentation! I read Feynman's book, QED: The Strange Theory of Light and Matter earlier this year, and although it was fairly easy to understand, seeing in a video like this definitely made things clearer.

Generally it's also nice to see some accurate videos about quantum mechanics here on Youtube, as opposed to the countless half-baked consciousness-driven interpretations.

[DustyMay1944]

Then YouTube is either messing with your presentations or my comments. The latter may be true since I just found other comments removed from other channels.

Sorry for doubting you; it is indeed an excellent QED presentation as are your many others. Thanks.

[DustyMay1944]

Brian;

Do you always remove comments that disagree with your preaching? It would be best if you also present the wave mechanics of light also; not just the QED interpretations.

[cassiopeiaproject]

We don't remove any comments. Feel free to repost whatever comment you believe was removed.

[uni4dfx]

How much time does 1 degree on the stopwatch correspond to?

[cassiopeiaproject]

Once around for the hand of the stopwatch corresponds to the frequency of the color of light... typically a little less than a billionth of a second or so.

[uni4dfx]

Ah yes, that makes sense.

Thank you so much yet again!

[soulplayxXx]

I got lost along the way.. but I continued watching.. I'll just watch it again somtime.. ^^

tnx for the upload! I really appreciate your videos.. :D

[RyuDarragh]

Oh, forgot: This is an example of the Complementarity Principle of Uncertainty.

Lovely demo of refraction :)

[MaDrung]

Oh and this... If we then place 2 different counters of photons, will then both show the same photon comming in?

I'm not completely sure about how QM works, since I don't know if most probable things hgappens, or they all do at the same time. Bah, confused :D

[cassiopeiaproject]

Only one photon counter will register the photon. A probability amplitude expresses the likelihood of which one will register. The arrows and clocks are the method for calculating the probability amplitude.

[RyuDarragh]

Why claim light is a particle when it's a *quanta* pf energy? Solitons can interact as if they were solid particles, even though they are made up of nothing but waves. The universe is stranger than we think it is and we suffer from a kind of "anthropic myopia" (where the anthro has nothing to do with "man", but with "being").

[MaDrung]

I love cassiopeia project!

But still no mather how muchvideos of QM I watched, I still can't believe world works like that, even tho I know it was tested pretty much.

Let me ask: If I have a glass like in this video (basicly same concept) If I shoot a photon directly out of center of glass so the path is longer, then there is no way of it travelling the smallest path because its most probable like shown in this video.

In my thinking it goes where you send it to, not where its most probable. :/

[cassiopeiaproject]

If there are multiple paths a photon can take, it will take them all. You cannot determine what path it takes.

[sinxcosxtanx]

OMG, that is really hard to understand. I missed something for sure since I've lost you in the first 5 minutes. I don't understand why arrows and clocks have something to do with reflectivity. And why in your mirror experiment light beam can avoid the law incidence = reflexion.

[MaDrung]

Clocks represents one cycle, andarrows shows the dirrection at the exact time. Bcause proceses repeat it is shown in circle, cause every cycle stops where it beggins.

I might interpreted it wrong tho

[cassiopeiaproject]

Classical ideas like "angle of incidence = angle of reflection" don't apply at the quantum level. Instead, a probability amplitude expresses the likelihood of each possible path a photon could travel. The arrows and clocks are the method for calculating these probability amplitudes.

[sinxcosxtanx]

Oh I see, I'll re watch it. Good day sir.

[tjd07x]

Phenomenal. Bravo.

[ILYIAB]

Great vid.

The "theory" ppl will still object. Dumb asses.

[notscooter952]

I'm not sure what your background in physics is, but I wouldn't resort to ad hominem attacks before knowing a thing or two about the photoelectric effect, thin film interference, or even young's double slit experiment. Theories are what makes science... science. If we didn't have people questioning the way of doing things, we'd all still be living in a catholic world where the earth is at the center of the universe.

[ILYIAB]

Sorry. I think you missunderstood my comment. I was sarcastic.

Have a great day!