Feynman Diagrams - a beginners guide

[mattb521]

I think representing time on the x-axis and space on the y-axis to be exceedingly more intuitive for many reasons

[warnford]

emission seems mis-spelt throughout

I s'pose if the site is called fizzicz, then no one is likely to notice

[lennythelabrat]

I think baryon number is conserved for electron capture rather than boson number.

[lblmer]

What a crock of bull. The atomic theory is bunk. Protons held strongly together by GLUONS? Stop promoting this false concept. I guess Feynman was wrong. There are 5 fundamental forces. Do something useful for mankind. Get a shovel an dig a ditch.

[seyoumeye]

This is well explained...but what surprises me is that "we" are still looking at these particles as if we are not made out them (consciousness is real!).

[j050227]

I don't get it and his accent annoys me like no other

[nachoseg]

wtf

[snevets123]

Has anyone got the time?

[fleminghell]

no...sorry...I got about 3 mins in, and yet again it slipped through my mental fingers.

too much staring out the window as a teenager instead of listening to the physics teacher!

[neoneoneofu]

I bet you have to study physics for many years until you get stupid enough to believe in this crap as a method for describing phenomena in nature :)

[jimbopumbapigsticks]

What's a fermion? Just a particle without any interaction (at a guess)?

[phara0h1]

@jimbopumbapigsticks Fermions are generally considered to be particles associated with matter, ie the quarks and leptons, as opposed to bosons which are force carrier particles.

Search the wiki article if you want a more accurate description.

[PhysicsMathMan]

@jimbopumbapigsticks fermions are a family of particles that obey fermi-dirac statistics. Opposed to this are bosons which obey bose-einstein statistics. I'd wiki both, but do not worry about understanding it too much -- I work on this stuff for a living and don't understand them fully to this day.

[ianbrooks]

i imagine fairly smart people watch this. so PLEASE, what is the name of the classical song in the first few seconds?

thanks

[Cheegro]

@ianbrooks

It is ''Air'' of the ''Orchestral Suite No. 3 in D major'' by Johann Sebastian Bach

To be specific, The piece you hear in this video is an interpretation by August Wilhelmj whom plays the piece on one of his violin Strings. G to be specific. So I would do a search for ''Air on the G-string'' (Yup G-String jokes coming up lol). Enjoy.

[TiiLLYYY]

At the feynman diagram for beta emission and a positron emission why is it that there isn't a particle going up that is producing the positron/electron and neutrino/anti neutrino. what produces this?

what is the n and p being repelled by to get the W- and W+ boson?

sorry for all the questions :)

[impCaesarAvg]

Feynmann didin't just (step 1 ) draw these diagrams. He used them as a guide to (step 2) write appropriate integrals, which he then (step 3) evaluated. The diagrams are easy, but I don't understand steps 2 and 3 at all. But he did, and then he moved on to (step 4) add the values of the integrals and square the sum to get the probablity of the process. I've never tried step 4, but I think I could do it.

[dandunleavy]

South Shields/Cleadon/Jesmond now Dallas/Regent's Park depending on spin.

[fizzicsorg]

Nice thought, unfortunately reality is much more mundane.

[fleurn0]

this may seem irrelevant, but could you please tell me what the piece playing in the intro is.

Nice to see videos on feynman diagrams on youtube

[Hardysamnin]

@fleurn0 - The intro is "Air on a G string"

[dandunleavy]

Geordies get everywhere!

[fizzicsorg]

Well spotted, dead right

[Prokopis1986]

as it is shown at 4:03, a W+ borns a netrino a positron by reversed arrow (means electron) which is wrong. W+ borns a neutrino and a positron

[Prokopis1986]

p+ is (uud) and not (ddu) as you show in the scheme

[rsr2500]

Why is the device so much more efficient in the pressure mode? That is, why does he have to hold the end of the hose away from the vacuum unit in the pressure mode, but can plug the hose all the way in - in the vacuum mode?

[DAILEYericCaryUSA]

Lose the ruler. Freehand is good.

[KKinsane2009]

what happens when three particles interact?

[HeaRTRiiPPeR]

Great video! :D

[adaseth]

Nice ruler :)

[jazzbobobo]

this diagram helps. thank you!

[TXRebelOK]

The antiparticles aren't really traveling back in time are they? It's confusing why antiparticles are depicted as backward arrows which seems to imply they are going backwards in time. Why not use a delta or an A to designate an antiparticle instead of an arrow which is universally understood as the direction of travel?

[TXRebelOK]

Left brain/ right brain is largely a myth. The brain is more hierarchical than anything else. And your post smells strongly of cognitive discontinuity seen in the mentally ill.

[jazzbobobo]

i agree that 'abookofverse''s post isn't well done, but i think it smells more like pot fumes than mental illness. the left brain/right brain postulate has been made into a popular idea, and myths do exist pertaining to it. however, the physiology of the brain does suggest that the two hemispheres interact in varying ways...the well known case of phineas gage for example.

[Tapecutter59]

@TXRebelOK - Left brain/ right brain is largely a myth.

Nope, you have two brains joined by a bundle of nerves called the corpus collusum. One brain lives in the moment, the other serializes moments into time and memories. Look up the TED talk from a neurologists who describies a stoke she had suffered in her talk. Also the "system" it uses is more like the internet than a hirearchical structure.

[TXRebelOK]

I'm going to medical school to become a neurosurgeon. I'm well away of the corpus callosum and other inter hemispherical nervous pathways. You do have interesting effects when you sever this nerve bundle to help patients with chronic seizures. The brain is modular and if you block communication between modules you'll see effects. The left brain being all logical and the right brain being creative is just simple incorrect. If you PM me I'll send you links of neuroscientist discussing this.

[Tapecutter59]

"The left brain being all logical and the right brain being creative is just simple incorrect." - That's not what I claimed. The rest of what you said agrees with what little I understand of the subject.

Perhaps you were unclear or perhaps I just misread but I think we are talking about different "myths". Also I'm a computer scientist, to me "modular" and "hierarchical" are two very different things.

[TXRebelOK]

Yes, they are different and both are true. There are debates about the extent of modularity of the brain. Obviously there are parts dedicated to specific tasks like in modular programming, but they are also extremely interconnected with other modules and create a massively non-linear or sometimes referred to as a dynamic system. When I said hierarchical, I meant evolution has just slapped complex higher ordered neuronal systems on top of primitive systems.

[Tapecutter59]

Yes, the maths of the "dynamic system" is very similar to that used in simulating physical processes such as in "virtual windtunnels", climate simulations, neclear bomb simulations, etc.

I agree the anatomy of the stem and layered hemispheres is hierarchical.

[psychobollox]

actually, it's essentially five brains: the two cerebral halves, the two cerebellar halves and the more primitive parts of the brain that 'live' in the brain stem, between the spinal cord and the brain itself.

[Tapecutter59]

Five brains, now were talking. Plus there are a bunch of tiny brains that 'live' in the spine.

[psychobollox]

in a sense, you're right... because of the phenomenon we refer to as the 'spinal arc reflex response' - where the response to something occurs via afferent (sensation) nerves arcing through neural circuits in the spinal cord before the response is made by activation of muscles because of signals taken down and efferent (motor) nerve,

The Finnish have a saying: 'went into the spine', meaning that something has become second nature to that person.

[Tapecutter59]

If you havent already seen it you might be interested to googgle IBM's "Blue Brain" project.

They have recently built a "molecular level" computer model to simulate the mammalian neocortex and are hoping to do the same for the entire brain.

The model is a FEA type model, it was built from brain scan data and extrapolates the brains physical/chemical behaviour using the laws of physics and chemistry.

The project is aimed at medical research but has also been used for AI research.

[psychobollox]

have to check that out sometime...

[Techra]

it would be cool if the -on suffix for particles wasn't around in physics so that the Boson would be called a Boso and pronounced Bozo

[pindanot]

now that is what i call QED for layman!

[DickDude2007]

the diagrams you showed were of relatively simple interaction between two particles. Including self-energy is more complicated and is not that understandable for me.

[bphysicsguy]

An interesting point about the diagram at 4:43. If the boson is drawn with a positive slope, it is a W-. Drawn with a negative slope it is a W+. Its easier to keep track of the charge if you chose one or the other, but they are actually describing exactly the same reaction.

[fizzicsorg]

A good point. There is no generally agreed convention on the legends which are used, however that would be a useful addition.

[calexculux]

2:58 my textbook shows the antineutrino pointing upwards why is urs downwards? also can u try explaining more slowly. Thanks anyway.

[fizzicsorg]

A rule that is used by the Institute of Physics is that anti particles point downwards (see 1.55 on video) however this convention is not used by everyone.

If you are taking exams then you need to check the convention used by the authority that sets the exams.

[fizzicsorg]

Not absolutely instant, but very, very short

[calexculux]

time and space, does it start from 0 since the line isn't close. 0:40

[fizzicsorg]

The diagrams are representative of the broad changes, they are not intended to be scale diagrams or graphs. There is no attempt to suggest absolutes in terms of time or space.

[calexculux]

why not explain urself  clearly? this is for beginners isn't it?

[fizzicsorg]

I try and yes in that order.

[marjan15]

Is the boson interaction instant in time according to these diagrams shown?

[marekesz]

Oh, well... Is there a mistake at 3:20? I think, the result of the transition should be udu (since before was udd and the third quark has changed to u).

[fizzicsorg]

Yes, sorry, there is a mistake. I'm just a bit too idle to go back and change it.

[contrail2k8]

awesome :)

[quantiseduniverse]

Great!

A slight typo at 3:18... 'up' quark should remain 'up'.

[schnugglepup1]

Awesome!