Quantum Electrodynamics (QED) 

Feynmann was the man! I have a book of his, and it's amazing how he could explain quantum theory in such a easy way for a layman (like me) to understand. That's pure genius.

Fields are very much still involved in QFT. The core assumption is that just as you made x and p into operators in basic quantum mechanics, you make the fields themselves into operators. That means that thatthere is an operator associated to fields at each point in spacetime or space, depending on if you are in the schrödinger or heisenberg picture. Particles emerge from these quantum fields, as the energy of free fields is as if they would represent multiple particles and add their energy together. And of course you can construct a particle number operator that is consistent with this. Feynman diagrams are in no way a fundamental building block of QFT, they are just a tool to represent certain terms in perturbative expansions, and they only work for weakly interacting theories. They emerge in the following way: you split the hamiltonian into two parts, the free hamiltonian and the interaction hamiltonian. You switch to the interaction picture, and in that picture the time evolution operator can be approximated by the dyson series. The nth term in the dyson series is associated with feynman diagrams with n vertices in them. Each term in the dyson series further splits into the sum of different terms using wicks theorem. It's these terms that are kn 1 to 1 correspondence with the feynman diagrams. Fields are still fundamental, feynman diagrams are just a tool to get terms in a series without doing the boring algebra required to obtain them otherwise.

Man. This was clear and concise.

Helpful indeed... Thank you

You are doing a great job am from india and your videos are awesome

thanks for the explanation through the animation

Very well explained

Thanks Dave. I like your style

Very Helpful sir...

I'm confused. Shouldn't these "virtual photons" all have different frequencies? Therefore, different energy? If so, shouldn't the change in momentum between two electrons, due to virtual photons exchange be different each time? Or is it that the virtual photon being manifested by the electron like you said, already quantized so the change in momentum is always the same betwen two electrons?

this is amazing thanks

Appreciate your work professer thank you

Excellent video, thank you!

However, how do then opposite charges interact? Do they also send out photons, and somehow still attract to each other?

thanks dave

A good explanation. A bit ruff around some edges but in general very good. I mean we haven't truely merged quantum theory with general relativity and virtual photons are just a simplification for the exitations in its field and saying fields have come abundant for the transmission of forces when indeed the quanta that transmit forces are merely exitations in the regarding fiel feels a little weird but I guess this is nit picking.

thank you :)

Beautiful explanation

Thanks. You are nice expleiner!

I went from extreme confusion to a vague understanding in 3:54 how??? Thank you. I'm young so when I don't understand concepts in physics I end up convincing myself I can't. Guess maybe I can kind of learn some physics. (I read in a book if you think you understand quantum physics, you don't)

This material makes me really excited to learn about these phenomena in my physics class :) Thanks so much Professor Dave! Do you know what field of math is involved in order to understand the math behind these behaviors? I'd love to try my hand at perusing through them to get a scope of what is to come/what I'm missing haha

This video is the perfect length

Thanks for you

ありがとうございます❗

Thanks Dave, well explained in simple terms !

Can someone help me? How do protons and electrons interact? Wouldn't the virtual photons emmited by the electron just push the proton away? How do the virtual photons make the electrons stay around the nucleus?

How about the electromagnetism? How the electric field generate this force.?

Interesting to hear about getting something from nothing. I wonder if that may be due simply to, we humans not possessing all of the pieces to the quantum puzzle. Could this be linked back to the possibility of there being more dimensions than we can observe account for and understand? Is there a way to gain knowledge of unobservable and unverifiable dimensions of existence? This stuff seems pretty heady. Out of my head anyway, but very interesting.

thank you so muuuchhhhh

Do we have anti virtual particles to make things have neagative mass?

❤Thank you very much

I don't get it: First I doubt if someone can even imagine that two pieces are attracted to each other or push each other away because they exchange a package. Secondly, I still don't understand what these two kinds of electric charges are. Different spices, salt and pepper?

can you please explain me the SPDF configuration

the photo exchange explains the repulsive nature but what about the interaction of particles of different nature (electron-proton interactions) how do you explain that? how do they attract each other? please reply

Ummm. No, fields are still not outdated as a concept. Particles are just a convinient way of describeing mathematically the state of a quantum field. The underlying idea behind all of this is still the field concept. This is illustrated by the use of lagrangian density in every quantum field theory.

By QED can you explain the attraction between positively charged particle with negatively charged particle

Thanks for your videos . I have a theory about why the speed of light is the speed limit of the universe . If you find the time ,I would like to discuss it with you and heve your reflection on the matter.

I have a question... so can we think that all of electric forces interaction that happens in the macroscopic level that seem to be continuous and smooth are all just emerged from exchanging virtual photons or many other quantized interactions in quantum level??

I don't get why the fields had to he discarded and exchange of virtual photons had to be used instead??

Even though QED works just fine, quantum gravity doesn't work out because trying to merge quantum mechanics and general relativity produces a lot of infinities. Precisely, it produces an infinite number of infinities, which is annoying because it's tricky to get rid of that number.

I thought momentum was related to mass. How could light have momentum? I would like an explination, please. What is momentum if not mV? I would honestly like to know.

I understand how the transfer of momentum could cause repulsion but not attraction

It seems to me that EM force is different than QED. From what I read, EM force can be felt from one end of the galaxy to the other. This QED seems to be interactions between nearby electrons. Why call Feynman peculiar? Who isn't peculiar in one way or another?

A physics professor once told me that quantum electrodynamics is the most beautifil thing the human intellect has ever achieved. I really wish i understood why.

Wow he's good! Teaches clearly, simply, relating to non-scientists. I never heard nor read anyone before say what he did about we aren't capable of picturing gravity due to our two dimensional limitation. Even the great Elon Musk erred when he recently retweeted a science magazine about magical gravity (Newtonian) attraction.

Could it be that virtual photons (emmited by protons and electrons) affect space-time in a similar way as a body of mass, and thus cause attraction? Since the electrons and protons would create virtual photons all around, it would naturally be that more virtual photons exist in between a proton and electron. Thus more virtual photons between the electrons and protons would cause that area in between to get "heavier" (i.e. more energy), so the protons and electrons sink towards each other? I'm no physicist, so don't berate me for just throwing out a layman's thought. But id love for someone to tell me how I'm wrong in this (I'm sure I'm wrong, but I need someone to show me how).

But in quantum field theories aren't every thing including matter , excitations in Quantum field?

Waiting for 1 million

I don’t really grasp how a photon, which has no mass, can divert the path of an electron, which has mass. To divert a path, a force is required and an object with no mass can not exert any force (as stated in Newton’s equation F=m*a).

professor dave , that means there may be a particle responsible for gravitation force to attract something ...so is this mysterious particle already discovered??..thanks

Can electric fields exist without a medium like magnetic fields?

1:30 ..

Meanwhile on suspicious observers "the earth could very well be flat"

you said that virtual photon have no mass or charge and then you said these virtual photons carry momentum. this doesn't make sense because you cant have momentum without mass. F=ma

you forgot the part when they erase the infinity part...

WOW! How could this guy put up this video? He knows these exchanges or "electrons" are actually merely exchanges of energy in the EM field, vibrations, that emerge and we observe as particles. Why do this if you cannot do it right?

Thank you science jesus 🙏

does this dude know everything

There is an electromagnetic field, it's just quantum. And it produces the photon.

I am the most intelligent person on the earth and I am very great at managing the money. So I am the richest and the most good looking.

0:23-0:40 flat earth confirmed

Please 👎👎