I stand to be corrected, but for A level I would adopt the tip: Take the W away from the baryon (and towards the lepton). Whether it is a + or a - will then be determined by what is needed to conserve charge. If a p is changing to a n then you will need a W+ away from the proton. If it is a n changing to a p then you need a W- away from the neutron.
On Amazon the best reviews on products are usually from users who've had the product for at least a year. Seen this video a year ago and have gone farther into the subject. Must say this video is remarkable and "stays with you". This instructor knows what is relevant, applying a unique approach focusing on the provocative things scientific minds appreciate. The video's value is that it is introductory -yes but at the same time provides artful preparation for advanced learning. Having seen other videos, the instructor's approach stands out by focusing on forces as a means to understanding particles. It is a very effective approach helpful in understanding Feynman diagrams. Great Video, Sir!
Great video. There is only one thing that is teached differently in our university: If there is an antiparticle involved, you should mark it as an arrow backwards in a diagram.
That's just stupid to be honest. There is no way that you can truly understand that at that level. Students just end up learning a set of arbitrary formulas and rules.
Really we should be learning more of this earlier on. Nobody studying physics is exploring Newtonian mechanics, Quantum Physics is where the future lies, yet senior schooling is stuck in the 1600's-1930's.
Aetrew While quantum physics is the new frontier it is NOT complete. And while with quantum mechanics you can predict a few things, it is not practical. Whereas Newtonian physics works and is practical to use in situations where it applies. Every theory of physics can be used at different scenarios and if you can not grasp this concept you should stop and think about it.
If there is a difference in mass between input particles and output particles then the difference is usually accounted for by E=mc**2. But in my previous comment I pointed out that much heavier particles can exist for a very short time if they borrow energy (and hence mass) from nothing provided they pay it back very very quickly. The diagrams dont explicitly say anything about KE, tho energy must be conserved in some form.
The same argument applies as below. At 6:48 the positron and the neutrino both travel in the same direction to conserve total lepton number. But a Feynman diagram with say a neutrino going one way can also be drawn with an antineutrino going the other way. Compare the diagrams at 6:02 and 8:58. They are virtually the same except in the former the anti-neutrino goes out, in the latter the neutrino goes in. A W- in the former going to the right has same effect as the W+ in the latter going left.
Some Feynman diagrams show antiparticles apparently moving backwards in time. This is a convention. But as far as I know, no one is seriously suggesting that antiparticles travel through time in the opposite direction. An antiparticle may be created and destroyed but in the interval between the two, time is moving forward.
Conservation rules. For example, baryon and lepton numbers have to be conserved. So when a proton changes to a neutron, positron and neutrino, the baryon number is conserved (proton in - neutron out) and the lepton number is conserved since a lepton and an anti lepton cancel out so lepton in =0 and lepton out = 1 + -1 = 0
When a neutron change into a proton in this reaction electron and anti neutrino produce. In its Feynman diagram the direction of anti neutrino should be inward.
No. The diagram at 6:02 for example has both the electron and the anti-neutrino traveling in the same direction (upwards). This is necessary to conserve the lepton number. No leptons come in. An electron (lepton number = +1) and an anti-neutrino (lepton number = -1) go out.
Because the strong nuclear force is confined. I deal with this in my current series on particle physics. The energy associated with the force between two quarks increases as you try to separate the quarks. It soon reaches a level where pair production arises and two new particles are created all within the radius of a nucleus.
A neutron star results from the gravitational collapse of a large star at the end of its life. The gravitational forces are sufficient to crush the atom and force the protons and electrons to merge into neutrons. So something similar to the situation at 8:00 must be happening.
The basic special relativity formula for mass is that the mass (at speed) = rest mass divided by the square root of (1 - v2/c2). When v approaches c, the mass approached infinity.
A Neutrino may be massless but current thinking is that it has a very small mass (much much smaller than that of an electron). Nevertheless your question is key. Indeed one might also ask how a W boson can be created from a proton/neutron which is 90x lighter. The answer is a version of Heisenberg's uncertainty principle which says that energy can be borrowed (from nothing) as long as it is paid back in a very short time. That is why the W boson exists for such a short time.
Thank you for taking the time to reply to my question- your videos are very helpful and what you're doing is great, my exam is tomorrow and it would be a disaster without your videos! Thank you again.
The gauge boson column has nothing to do specifically with the fermions in the associated rows. Its just done like that for aesthetic reasons. If they find the Higgs, someone will have to put in another box. My advice would be to put the W and the Z in the same box and then use the spare box for the Higgs.
I prefer to show particles moving forward in time. Its not clear what moving back in time could mean. It's more intuitive to show an antiparticle being created and moving forward in time.
Its random and actually low probability - which is why the sun burns for 10 billion years. A W boson is 80x heavier than a proton and arises from a variation of Heisenberg's uncertainty principle which says that you can borrow energy for a very short amount of time. So a W boson can be created but it can only last for 10**−25 secs.
Rest mass energy is the inherent energy of a particle which has no kinetic energy ie is at rest. In non relativistic equations, the total energy = rest mass energy (mc^2 - where m is rest mass) + KE.
It might well toggle. But that will be determined by the probability of the exchange taking place. Think about the sun. Some protons on the sun must have been converted to neutrona on day 1 yet other protons might not be converted till 10 billion years later. So the probability for a lot of the potential toggling is very small.
I don't think we really understand the precise mechanics of exchange particles - and indeed it is misleading to describe quantum effects by analogy with the world we observe, but in A Level physics attractive forces are sometimes likened to two people throwing a boomerang to each other. The boomerang spins round and approaches the other person from behind thus pushing him towards to thrower (ie attractive force).
I got completely confused by my textbook. The exchange particle lines had no arrows, so i presumed they went both ways so i couldn't get my head around it, and then they also had some particles on the right hand side with an arrow pointing back down the page, which I now understand is impossible as the cannot travel back in time. I have been stuck for ages trying to work this out! Very helpfull video again. Jon
Its so awsome we can find such highly educational and so well explained information free on you tube . I need to study harder though , I don't have much of an education but hope I can get it all to sink in , this stuff is amazing , and you make it seem so easy . keep up the good work .
Why are they always interacting by weak force? How do you know if the exchanged particle is a gluon a photon or a W+-/Z?? How I know wich is the force that is interacting??
That's an easy enough explanation Either A) Causality has been laughing at humanity all along Or B) The entropy exchange that occurs collapses into a particle rather radiating, creating little moment where high entropy can become low entropy (not the same as A, see negative kelvin temperatures)
I'm assuming you mean an experiment where you fire particles (eg protons) at a target (eg a thin layer of gold) and a situation where you have two beams of protons travelling in opposite directions and made to collide. The latter gives more energy because each photon can be travelling at very close to c making the relative speed of collision very very close to c. Thus more energy.
You are usually given the starting products. But in general anything can happen as long as you obey the rules of conservation (charge, baryon, lepton etc)
Great videos I can understand you very well and these videos have been useful to me to study physics and concepts are wonderful thank you very much mister DrPhysicsA.
Question about arrow directions: Don't the arrows for anti particles point in the opposite direction of particles (ie. negative time)? Time points towards the address bar of this window. Therefore, the last two figures, the anti neutrino should point downwards, rather than upwards like the neutrino in the previous figure? It's a question that has got me very confused with Feynman Diagrams
It depends on the convention you use. Many people draw Feynman diagrams with antiparticles shown as travelling backwards in time. That is a convention. Antiparticles do not move backwards in time. I personally prefer therefore to show them travelling in the forward direction of time.
Unfortunately, nothing is gained by thinking of anti-particles as traveling back in time. Just because one can do it doesn't mean that one should. Like the new convention of electronics, teaching that electrons run from a relatively negative ground towards the direction of the positive voltage source. The desire to teach electrons rather than "holes" is just an additional and needless confusion factor for young students, now forced to learn the old heuristically developed convention running backwards. I would say that it's an additional stupidity factor, since electrons vs "holes" are really irrelevant to electronics engineering. The old model was developed for the purpose of wrapping ones mind around the subject, so why force new students to learn that model counterintuitively backwards? "Smart" professors are sometimes quite stupid.
for the nuetron-neutrino interaction, my textbook has the W- Boson instead of the w+ you displayed. Is this a mistake in the textbook, or can it be either w+ or w- depending on direction?
I have a question sir? Why do higgs boson decompose even if it is an elementary particle? As we all know, elementary particles do not compose into another smaller particles.
how the anti-neutrino in Beta minus and the positron in the Beta plus decay diagrams go up ? isn't anti particle suppose to go backwards in time?? the arrows are confusing ...
This analogy works for repulsive forces, if two electrons 'send out' virtual particles in all directions into its sourroundings, and the exchange between them transfers momentum between both electrons, then you would have to imagine a positron as a particle 'recieving' virtual particles from directions and disappearing in the positron, of course remember that they're called virtual because they represent the possibility of an interaction and not an interaction itself.
+Samixuos Lopes This. This was confusing when looking at diagrams after having done the A Level syllabus. Yes, it should go into the junction, but the A Level syllabus doesn't teach this, and so any arrows are ignored as long as the direction of time is apparent. In fact, it's kind of assumed that the student assumes that the arrows represent motion rather than anything else.
+Samixuos Lopes Some diagrams show the antimatter appearing to travel backwards in time. In my videos I wanted to keep it simple so I show all processes in terms of what produces what.
one simple question everbody say that only these are elementary particles and besides this brian cox in every video said that now we have zoo of new particles and we are outnumbered for giving name to them...kindly elaborate
Question, when you have a field and say you have a static situation where there is no motion or its in equilibrium, do you need a photon being exchanged to feel the electrostatic force? I mean, protons are everywhere and they all contribute to the final field, but that does not mean you need a photon from every proton to establish the field. There are photons but there is also the field. So isnt it true that you can have a force from the field but no photon exchanges required. Is there not a field and a photon?
In reaction of, let's say p + e- -> n + ve, how do we know that it's W+ going from neutron to electron and not W- going from electron to neutron? As far as I understand it, Feynman diagrams are supposed to be symetrical with respect to time. One more issue. On those diagrams, after exchanging the boson, both particles change direction a little bit. As far as I understand it, it's because exchange particle also carries some momentum and kinetic energy. Is that correct?
thank you so much, my exams on friday and i am bricking it, i get all the electronics, but the particle physics stuff is not quite there yet but this helped massively, thanks
The Z boson is associated with he transfer of momentum, spin, and energy when neutrinos scatter elastically from matter. i.e. when no charged particles are created or destroyed.
2) You said any charge conserving combination _can_ happen, but what causes it to happen? For example in the exchange at 8:00 it looks like a proton must convert into a neutron + w boson before the w boson can combine with the electron. Is this due to random decay, or can it be provoked?
You see for 8:45 the W+ Bosons has traveled from electron-neutrino to neutron thus being able to produce proton and electron. Wouldn't it be possible for the W- Boson to travel from neutron to electron-neutrino thus producing proton and electron. Just kinda confused
If photons are the force carriers of the EM force, therefore cause the interaction between charges, why is it that the W+ or W- transfers the postive/negative charge from the proton away into the electron/positron and the neutrino?
One more question... 5) why are the guage bosons in the column on the right? Do they share some property with the associated rows? If the Higgs is discovered, where would it go?
In your earlier comment 7 months ago, you advise to generally to take the W away from the baryon, towards the leptons. In the neutron-neutrino interaction at 8:45, the W particle goes from the leptons to the baryons, with the opposite W particle. Are both correct? i.e. a W- particle from the neutron to the leptons, or a W+ particle from the leptons? Thanks in advance. I really appreciate the videos - thankyou!
Its a case of "If it can happen (i.e. within the rules of conservation of baryon number, lepton number, charge etc) it will happen" So you can have an interaction with the W- moving one way or the W+ moving the other. The probability of each occurring may differ though.
On my AS textbook a neutron-neutrino interaction involves an exchange of a W- boson with the arrow going to the right. So is an W+ boson going to the left the same as a W- boson going go the right? Do they represent the same thing?
ZOD1189 I think he meant they do not mean the same thing, they are two different interactions but both of them exist so I guess it's not like it doesn't matter it's more like the direction of the arrow determines which interaction you're referring to but if that is not a concern then yeah it doesn't matter I guess cause both can happen, I'll just stick to what it says on my textbook for the exams just to be safe.
I'm really enjoying this series. I have a few questions...I'll spit them into comments so i dont run out of room. 1) Is the diagram you drew at 8:00 the exchange that takes place when a neutron star is formed?
If the neutrinos are neutral, how do you distinguish between the matter and antimatter versions? Apologies if you already covered this in another video.
N Marbletoe As far as i know, All Leptons including neutrinos have lepton number of +1 and spin of ±1/2. So for example we have neutrino X and we want to distinguish between it and its anti-neutrino, the neutrino X will be having lepton number +1 and spin -1/2, then its anti-neutrino will be having Lepton number -1 and spin +1/2. For more info visit this link hyperphysics.phy-astr.gsu.edu/hbase/particles/neutrino3.html
Ramy Haddad cool link. it does seem to have an inconsistency, though: since neutrinos do appear to have some mass, they don't travel at c, thus it is possible to travel faster than a neutrino and see it's spin flip directions. i'm not sure if this means that a particle must be massless (and travel at c) to be it's own antiparticle, like the photon is its own antiparticle. i can't quite wrap my mind around Majorana vs Dirac fermions.
About the electron capture: as the weak interaction only works at very short ranges and as electrons must be at a certain distance from the nucleus due to the uncertainty principle (and also because they cannot have less energy than the allowed by quantization), how can the weak interaction between the proton and electron occur? from that, I think the proton and the electron couldn't come close enough so they are within the range needed for the weak interaction to take place... also, the interaction couldn't occur from afar because the boson would decay before it met the electron due to the boson's lifespan and thus would not turn the electron in a neutrino...
At 9:17, on the neuton-electron neutrino interaction, i think it should be the W- with an arrow pointing at the right. Can you please check that? Sorry if i made a mistake
4) at 8:45 you show that the equations are symetric. This is probably related to one of my other questions...what stops it from just toggling back and forth forever?
Can you consider a video on discussing how the diagrammed results from particle accelerators led to the concepts we are fed today about the nature of fundamental particles? Specifically, how are the traces, loops, squiggly lines, etc., interpreted as charge, mass, momentum, types of particles, etc. And how did they infer partial characteristics of quarks? Thanks.
when we say any particle with mass (be it electron or nutrino or protons) moving close to the spead of light, we say its mass increases , is there any equation for this to find out the mass in that instance?. In this scenario, what happens to the size of these partiles when mass increases?
I stand to be corrected, but for A level I would adopt the tip: Take the W away from the baryon (and towards the lepton). Whether it is a + or a - will then be determined by what is needed to conserve charge. If a p is changing to a n then you will need a W+ away from the proton. If it is a n changing to a p then you need a W- away from the neutron.
On Amazon the best reviews on products are usually from users who've had the product for at least a year. Seen this video a year ago and have gone farther into the subject. Must say this video is remarkable and "stays with you". This instructor knows what is relevant, applying a unique approach focusing on the provocative things scientific minds appreciate. The video's value is that it is introductory -yes but at the same time provides artful preparation for advanced learning. Having seen other videos, the instructor's approach stands out by focusing on forces as a means to understanding particles. It is a very effective approach helpful in understanding Feynman diagrams.
Great Video, Sir!
Great video. There is only one thing that is teached differently in our university: If there is an antiparticle involved, you should mark it as an arrow backwards in a diagram.
university??? we have to learn this in our first year of a levels.
That's just stupid to be honest. There is no way that you can truly understand that at that level. Students just end up learning a set of arbitrary formulas and rules.
Really we should be learning more of this earlier on. Nobody studying physics is exploring Newtonian mechanics, Quantum Physics is where the future lies, yet senior schooling is stuck in the 1600's-1930's.
Aetrew While quantum physics is the new frontier it is NOT complete. And while with quantum mechanics you can predict a few things, it is not practical. Whereas Newtonian physics works and is practical to use in situations where it applies. Every theory of physics can be used at different scenarios and if you can not grasp this concept you should stop and think about it.
Yes he is wrong.
Remember the adage - anything that can happen does happen. So I am just showing one outcome. The outcome with the W- is also a possibility.
Yes. Anything that can happen does happen. Its a different reaction but both can occur.
If there is a difference in mass between input particles and output particles then the difference is usually accounted for by E=mc**2. But in my previous comment I pointed out that much heavier particles can exist for a very short time if they borrow energy (and hence mass) from nothing provided they pay it back very very quickly. The diagrams dont explicitly say anything about KE, tho energy must be conserved in some form.
The same argument applies as below. At 6:48 the positron and the neutrino both travel in the same direction to conserve total lepton number. But a Feynman diagram with say a neutrino going one way can also be drawn with an antineutrino going the other way. Compare the diagrams at 6:02 and 8:58. They are virtually the same except in the former the anti-neutrino goes out, in the latter the neutrino goes in. A W- in the former going to the right has same effect as the W+ in the latter going left.
Some Feynman diagrams show antiparticles apparently moving backwards in time. This is a convention. But as far as I know, no one is seriously suggesting that antiparticles travel through time in the opposite direction. An antiparticle may be created and destroyed but in the interval between the two, time is moving forward.
Conservation rules. For example, baryon and lepton numbers have to be conserved. So when a proton changes to a neutron, positron and neutrino, the baryon number is conserved (proton in - neutron out) and the lepton number is conserved since a lepton and an anti lepton cancel out so lepton in =0 and lepton out = 1 + -1 = 0
When a neutron change into a proton in this reaction electron and anti neutrino produce. In its Feynman diagram the direction of anti neutrino should be inward.
No. The diagram at 6:02 for example has both the electron and the anti-neutrino traveling in the same direction (upwards). This is necessary to conserve the lepton number. No leptons come in. An electron (lepton number = +1) and an anti-neutrino (lepton number =
-1) go out.
Because the strong nuclear force is confined. I deal with this in my current series on particle physics. The energy associated with the force between two quarks increases as you try to separate the quarks. It soon reaches a level where pair production arises and two new particles are created all within the radius of a nucleus.
A neutron star results from the gravitational collapse of a large star at the end of its life. The gravitational forces are sufficient to crush the atom and force the protons and electrons to merge into neutrons. So something similar to the situation at 8:00 must be happening.
The basic special relativity formula for mass is that the mass (at speed) = rest mass divided by the square root of (1 - v2/c2). When v approaches c, the mass approached infinity.
Not necessarily. For example a W+ particle going one way is equivalent to a W- going in the other direction.
A Neutrino may be massless but current thinking is that it has a very small mass (much much smaller than that of an electron). Nevertheless your question is key. Indeed one might also ask how a W boson can be created from a proton/neutron which is 90x lighter. The answer is a version of Heisenberg's uncertainty principle which says that energy can be borrowed (from nothing) as long as it is paid back in a very short time. That is why the W boson exists for such a short time.
Thank you for taking the time to reply to my question- your videos are very helpful and what you're doing is great, my exam is tomorrow and it would be a disaster without your videos!
Thank you again.
The gauge boson column has nothing to do specifically with the fermions in the associated rows. Its just done like that for aesthetic reasons. If they find the Higgs, someone will have to put in another box. My advice would be to put the W and the Z in the same box and then use the spare box for the Higgs.
they found higgs bro
Thank you, your videos make understanding everything so much easier.
Have you found my nuclear physics playlist on my home page. Are there particular issues you would like covered?
I prefer to show particles moving forward in time. Its not clear what moving back in time could mean. It's more intuitive to show an antiparticle being created and moving forward in time.
Its random and actually low probability - which is why the sun burns for 10 billion years. A W boson is 80x heavier than a proton and arises from a variation of Heisenberg's uncertainty principle which says that you can borrow energy for a very short amount of time. So a W boson can be created but it can only last for 10**−25 secs.
Rest mass energy is the inherent energy of a particle which has no kinetic energy ie is at rest. In non relativistic equations, the total energy = rest mass energy (mc^2 - where m is rest mass) + KE.
No. Its a W+ because it is traveling from right to left. You could draw the same diagram with a W- traveling from left to right.
It might well toggle. But that will be determined by the probability of the exchange taking place. Think about the sun. Some protons on the sun must have been converted to neutrona on day 1 yet other protons might not be converted till 10 billion years later. So the probability for a lot of the potential toggling is very small.
I don't think we really understand the precise mechanics of exchange particles - and indeed it is misleading to describe quantum effects by analogy with the world we observe, but in A Level physics attractive forces are sometimes likened to two people throwing a boomerang to each other. The boomerang spins round and approaches the other person from behind thus pushing him towards to thrower (ie attractive force).
I was confused on this but your video cleared things up!!!! Thank you sm 🙌🏾🙌🏾 keep up the good work :)))
Best explanation I have seen so far on the diagrams.
I got completely confused by my textbook. The exchange particle lines had no arrows, so i presumed they went both ways so i couldn't get my head around it, and then they also had some particles on the right hand side with an arrow pointing back down the page, which I now understand is impossible as the cannot travel back in time. I have been stuck for ages trying to work this out! Very helpfull video again.
Jon
Its so awsome we can find such highly educational and so well explained information free on you tube . I need to study harder though , I don't have much of an education but hope I can get it all to sink in , this stuff is amazing , and you make it seem so easy . keep up the good work .
Jack Specht keep learning dude 👍
this helped me so much in my exam today! THANKYOU
This is gold!!! I love your videos !!
Thanks for the video it really helped me get my head round feynman diagrams unlike any of the other videos I've watched :)
Why are they always interacting by weak force? How do you know if the exchanged particle is a gluon a photon or a W+-/Z?? How I know wich is the force that is interacting??
Hey, I didn't understand this lesson from my teacher but you explained it very well! Hopefully I ace my test. Thanks
Did you ace your test?
That's an easy enough explanation
Either
A) Causality has been laughing at humanity all along
Or
B) The entropy exchange that occurs collapses into a particle rather radiating, creating little moment where high entropy can become low entropy (not the same as A, see negative kelvin temperatures)
I'm assuming you mean an experiment where you fire particles (eg protons) at a target (eg a thin layer of gold) and a situation where you have two beams of protons travelling in opposite directions and made to collide. The latter gives more energy because each photon can be travelling at very close to c making the relative speed of collision very very close to c. Thus more energy.
Thank you x 100! This video helped me tremendously!
For the bottom example at 8:20, why is it not the other way around with a W- coming from the electron side?
Thank you so much. I think I finally get this!
Quick question:
how do you know which product goes on which side of the squiggly line?
You are usually given the starting products. But in general anything can happen as long as you obey the rules of conservation (charge, baryon, lepton etc)
Thanks for the quick responses.
Bless this guy!! What a lifesaver, thank you!!
Great videos I can understand you very well and these videos have been useful to me to study physics and concepts are wonderful thank you very much mister DrPhysicsA.
Question about arrow directions:
Don't the arrows for anti particles point in the opposite direction of particles (ie. negative time)? Time points towards the address bar of this window. Therefore, the last two figures, the anti neutrino should point downwards, rather than upwards like the neutrino in the previous figure?
It's a question that has got me very confused with Feynman Diagrams
It depends on the convention you use. Many people draw Feynman diagrams with antiparticles shown as travelling backwards in time. That is a convention. Antiparticles do not move backwards in time. I personally prefer therefore to show them travelling in the forward direction of time.
Unfortunately, nothing is gained by thinking of anti-particles as traveling back in time. Just because one can do it doesn't mean that one should. Like the new convention of electronics, teaching that electrons run from a relatively negative ground towards the direction of the positive voltage source. The desire to teach electrons rather than "holes" is just an additional and needless confusion factor for young students, now forced to learn the old heuristically developed convention running backwards. I would say that it's an additional stupidity factor, since electrons vs "holes" are really irrelevant to electronics engineering. The old model was developed for the purpose of wrapping ones mind around the subject, so why force new students to learn that model counterintuitively backwards? "Smart" professors are sometimes quite stupid.
DrPhysicsA i think this means that Feynman Diagrams simply don't have an absolute arrow of time. we can read them either way.
for the nuetron-neutrino interaction, my textbook has the W- Boson instead of the w+ you displayed. Is this a mistake in the textbook, or can it be either w+ or w- depending on direction?
thanks so much for these videos, so much help and clarity
I have a question sir? Why do higgs boson decompose even if it is an elementary particle? As we all know, elementary particles do not compose into another smaller particles.
how the anti-neutrino in Beta minus and the positron in the Beta plus decay diagrams go up ? isn't anti particle suppose to go backwards in time?? the arrows are confusing ...
Should we write the arrow downwards for antiparticles such as positrons?
Thank you i got my as exam tomorrow this really helped!
This analogy works for repulsive forces, if two electrons 'send out' virtual particles in all directions into its sourroundings, and the exchange between them transfers momentum between both electrons, then you would have to imagine a positron as a particle 'recieving' virtual particles from directions and disappearing in the positron, of course remember that they're called virtual because they represent the possibility of an interaction and not an interaction itself.
all a level students should watch and learn
Hi, the video really helped me! I just have one question about the n+V --> p+e- . why does the boson direction go backwards (to the left) ?
hi. very nice video, thank you.
by the way, shouldn't the positron (in onw of the diagrams), have an arrow flipped back (downwards) ?
+Samixuos Lopes This. This was confusing when looking at diagrams after having done the A Level syllabus. Yes, it should go into the junction, but the A Level syllabus doesn't teach this, and so any arrows are ignored as long as the direction of time is apparent. In fact, it's kind of assumed that the student assumes that the arrows represent motion rather than anything else.
+Samixuos Lopes Some diagrams show the antimatter appearing to travel backwards in time. In my videos I wanted to keep it simple so I show all processes in terms of what produces what.
one simple question everbody say that only these are elementary particles and besides this brian cox in every video said that now we have zoo of new particles and we are outnumbered for giving name to them...kindly elaborate
You explain things so well!!
Question, when you have a field and say you have a static situation where there is no motion or its in equilibrium, do you need a photon being exchanged to feel the electrostatic force? I mean, protons are everywhere and they all contribute to the final field, but that does not mean you need a photon from every proton to establish the field. There are photons but there is also the field. So isnt it true that you can have a force from the field but no photon exchanges required. Is there not a field and a photon?
how do you tell which particles will give and which will receive the exchange particle
So can we say that the electro-magnetic field is nothing but photons?
Yes
Is it antielectron neutrino or electron antineutrino?
Thank you for educating me.
Such a useful video, thank you very much !
Fantastic Video. Onto the next video ...
In reaction of, let's say p + e- -> n + ve, how do we know that it's W+ going from neutron to electron and not W- going from electron to neutron? As far as I understand it, Feynman diagrams are supposed to be symetrical with respect to time.
One more issue. On those diagrams, after exchanging the boson, both particles change direction a little bit. As far as I understand it, it's because exchange particle also carries some momentum and kinetic energy. Is that correct?
thank you so much, my exams on friday and i am bricking it, i get all the electronics, but the particle physics stuff is not quite there yet but this helped massively, thanks
A Feynman diagram paints a thousand equations.
Where does the z boson come in? Every Feynman diagram I've seen on the AS level course involves only either photons or w bosons.
It is basically a Z^0 boson. It has no charge.
The Z boson is associated with he transfer of momentum, spin, and energy when neutrinos scatter elastically from matter. i.e. when no charged particles are created or destroyed.
2) You said any charge conserving combination _can_ happen, but what causes it to happen? For example in the exchange at 8:00 it looks like a proton must convert into a neutron + w boson before the w boson can combine with the electron. Is this due to random decay, or can it be provoked?
This video was very helpful thanks a lot!
You see for 8:45 the W+ Bosons has traveled from electron-neutrino to neutron thus being able to produce proton and electron. Wouldn't it be possible for the W- Boson to travel from neutron to electron-neutrino thus producing proton and electron. Just kinda confused
If photons are the force carriers of the EM force, therefore cause the interaction between charges, why is it that the W+ or W- transfers the postive/negative charge from the proton away into the electron/positron and the neutrino?
6:56 shouldn't the arrow for the positron be pointing backwards because it is an anti-particle?
even the electron anti-neutrino
thats what i thought too.
yeah that should also be the case for anti-neutrino in the beta minus decay
in a-level we're just taught to draw the arrows the same for both to make things simple i guess
Also thanks for a video with an explanation that makes sense!
One more question...
5) why are the guage bosons in the column on the right? Do they share some property with the associated rows? If the Higgs is discovered, where would it go?
In your earlier comment 7 months ago, you advise to generally to take the W away from the baryon, towards the leptons. In the neutron-neutrino interaction at 8:45, the W particle goes from the leptons to the baryons, with the opposite W particle. Are both correct? i.e. a W- particle from the neutron to the leptons, or a W+ particle from the leptons? Thanks in advance. I really appreciate the videos - thankyou!
Its a case of "If it can happen (i.e. within the rules of conservation of baryon number, lepton number, charge etc) it will happen" So you can have an interaction with the W- moving one way or the W+ moving the other. The probability of each occurring may differ though.
Doesn't a W+ boson carry mass, if so where does that mass go in the electron capture feynman diagram?
Its a combination of "borrowing" from the vacuum - as long as you pay it back very quickly; and mass/energy exchange.
Particle physics is mildly confusing, thanks for the reply, you explained the topic very well :D
On my AS textbook a neutron-neutrino interaction involves an exchange of a W- boson with the arrow going to the right. So is an W+ boson going to the left the same as a W- boson going go the right? Do they represent the same thing?
Its a different interaction but as they say, if its possible it can happen.
DrPhysicsA Then the direction of the arrow doesnt matter as far as i obey the the rules of conservation?
ZOD1189 I think he meant they do not mean the same thing, they are two different interactions but both of them exist so I guess it's not like it doesn't matter it's more like the direction of the arrow determines which interaction you're referring to but if that is not a concern then yeah it doesn't matter I guess cause both can happen, I'll just stick to what it says on my textbook for the exams just to be safe.
Ooo that makes sense :) thank you
Why is the exchange particle for the n+νe an W+ boson isn't it meant to be a W- boson ? please correct me if am wrong.
whether it is a plus or minus sign will depend on whether the W Boson is carrying away a positive or negative charge.
Thank you so much for the lesson!!
is there a feyman diagram for z bosons?
sir u r superb, really good explanation
What boson is present when 2 atoms go to fusion. I know some reactions can create muons, which implies a boson
I'm really enjoying this series. I have a few questions...I'll spit them into comments so i dont run out of room.
1) Is the diagram you drew at 8:00 the exchange that takes place when a neutron star is formed?
Beautiful.
If the neutrinos are neutral, how do you distinguish between the matter and antimatter versions? Apologies if you already covered this in another video.
From the direction of spin and lepton number, both are reversed.
hope this help.
Ramy Haddad i thought i heard that neutrinos might be their own antiparticle. how would this work in terms of spin and lepton number?
N Marbletoe As far as i know, All Leptons including neutrinos have lepton number of +1 and spin of ±1/2. So for example we have neutrino X and we want to distinguish between it and its anti-neutrino, the neutrino X will be having lepton number +1 and spin -1/2, then its anti-neutrino will be having Lepton number -1 and spin +1/2. For more info visit this link
hyperphysics.phy-astr.gsu.edu/hbase/particles/neutrino3.html
Ramy Haddad cool link. it does seem to have an inconsistency, though: since neutrinos do appear to have some mass, they don't travel at c, thus it is possible to travel faster than a neutrino and see it's spin flip directions.
i'm not sure if this means that a particle must be massless (and travel at c) to be it's own antiparticle, like the photon is its own antiparticle. i can't quite wrap my mind around Majorana vs Dirac fermions.
Great video, thanks.
how do you know which way your arrow should point with the W+/- bosons? also are there any interactions with Z bosons? Thank you.
About the electron capture: as the weak interaction only works at very short ranges and as electrons must be at a certain distance from the nucleus due to the uncertainty principle (and also because they cannot have less energy than the allowed by quantization), how can the weak interaction between the proton and electron occur? from that, I think the proton and the electron couldn't come close enough so they are within the range needed for the weak interaction to take place... also, the interaction couldn't occur from afar because the boson would decay before it met the electron due to the boson's lifespan and thus would not turn the electron in a neutrino...
1:55 I can't figure what symbol he's using to represent the force of gravity...
Can't make out the handwriting.
Is that an S or an integral?...
I believe he just wrote "Grav"
At 9:17, on the neuton-electron neutrino interaction, i think it should be the W- with an arrow pointing at the right. Can you please check that? Sorry if i made a mistake
I dont think you made a mistake, I think it just depends on how you want to draw it. Your way should still work too. ~ The Astronomer
4) at 8:45 you show that the equations are symetric. This is probably related to one of my other questions...what stops it from just toggling back and forth forever?
Why, in the diagrams, was there always a W+ exchange instead of perhaps a W- in the opposite direction?
How can there be a graviton if gravity is caused by the warping of space? Thanks for the interesting clip!
3) The input mass doesn't equal the output mass. I assume the difference goes into the velocities. Do the diagrams say anything about kinetic energy?
has the graviton been measured?
Can you consider a video on discussing how the diagrammed results from particle accelerators led to the concepts we are fed today about the nature of fundamental particles? Specifically, how are the traces, loops, squiggly lines, etc., interpreted as charge, mass, momentum, types of particles, etc. And how did they infer partial characteristics of quarks? Thanks.
when we say any particle with mass (be it electron or nutrino or protons) moving close to the spead of light, we say its mass increases , is there any equation for this to find out the mass in that instance?.
In this scenario, what happens to the size of these partiles when mass increases?
Great video but couldn't the W boson be positive in one direction and negative in the other direction? eg in the diagram at 8:13
Depends on the charge the W boson is carrying away.
how does a supermassive W+ boson combine with a light electron to create a massless particle?
Very useful, thank you