# Matter/antimatter imbalenc - forked from AMA ask a physicist



## Scott DeWar (Aug 24, 2015)

@Freyer, @_*Umbran*_, all the others who know their 'stuff', I will start with the last quote from the ama in the s block below:

[sblock=quote]


freyar said:


> Umbran does a pretty good job breaking down the  logical possibilities.  I'd like to elaborate, though, especially  because that wikipedia article is a bit disappointing compared to most  of the physics wikipedia articles.
> 
> The most important point to remember is that we really don't know the  answer to this question.  It's also quite likely we won't for a long  time, since there's very little way to test any of the possibilities ---  there are some potentially related effects we can test experimentally,  but those are really only good at ruling out options as opposed to  pointing toward the correctness of one.
> 
> ...



[/sblock]

1st, let me be clear that I understand that Wikipedia is never wrong can be rife with inaccuracies;
2nd, I understand that,as you have both mentioned, too little is understood, knowen and untestable AT THIS TIME AND DATE.



			
				wikki said:
			
		

> The CPT Theorem  guarantees that a particle and its antiparticle have exactly the same  mass and lifetime*[1],
> and exactly opposite charge. Given this symmetry, it  is puzzling that the universe does not have equal amounts of matter and antimatter.  Indeed, there is no experimental evidence that there are any  significant concentrations of antimatter in the observable universe. There are two main interpretations for this disparity: either the universe began with a small preference for matter (total baryonic number  of the universe different from zero), or the universe was originally  perfectly symmetric, but somehow a set of phenomena contributed to a  small imbalance in favour of matter over time. The second point of view  is preferred, although there is no clear experimental evidence  indicating either of them to be the correct one.




*[1] as it is posited that the lifetime is exactly the same for particle and anti particle, what is the possibility, not necessarily the probability, that there may be pockets of anti-matter in the universe in the dark corners that have not met up with its counter part? held in vacuum it is safely kept away, having been thrust away by the hot bang?

[2] are there expiraments in the science community working on discovering a way to test/find antimatter?
[2a] who is doing this?
[*[2b] I see you had answered that question. Sorry.

I have so very fallen in a pit of 'out of my depth here, so, ignore the links below. I had questions, But I can't get them to be printed. 

Here is my last question here:

[3]Is it possible, but not necessarily probable, that the anti-matter may be what is fueling the black holes? 
[3a] Any thoughts on how to approach a way to test this idea? 

Please note I labeled that as only an idea, and nowhere near a theory.

[sblock=references]

I hope I have given proper credit here:

1. Wikipedia - Baryogeneisis

2. Dirac equatioin

3. CPT Symetrey

4.  PDF on Sakharov Conditions for Baryogenesis ByDennis V. Perepelitsa,Columbia  University  Department  of  Physics;(Dated: November 25, 2008)

[/sblock]

More to come . . . . having some bad connectivity issues here, so this will be slow going . . . .Never mind. My brain is itching too much.


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## tomBitonti (Aug 24, 2015)

> I should also mention that the excess amount of matter is very tiny. In the early universe, the amount of matter and antimatter was essentially equal. For roughly every 10 billion matter/antimatter pairs of particles, there was one extra matter particle. Then all the 10 billion or so pairs annihilated each other away, leaving behind the one matter particle.




So many quotes ... I've left off the attribute of the above.

I've always wondered ... if so much matter/antimatter combined, wouldn't that create a huge excess of energy?  Where is that 10^10 factor of energy?

That is, particle/antiparticle annihilation doesn't destroy the energy of the particles.  Depending on the energy of the particles, very roughly speaking, either, a photon is produced, or a photon and some other particles are produced, or maybe just some new particles depending on the exact energy of the event.

Or does the energy recycle back into particles, but, considering the whole cycle, inefficiently, leaving a growing excess of matter?

But then, the fraction seems too high!  There would be so many creation/annihilation events in the early universe, one in 10 billion seems to to be too many.

Or do the events only happen in some narrow transition region, say, when matter and light decoupled?  Or very very early, such that the relevant time where the asymmetry mattered was very short?

Thx!

TomB


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## Umbran (Aug 24, 2015)

Scott DeWar said:


> *[1] as it is posited that the lifetime is exactly the same for particle and anti particle, what is the possibility, not necessarily the probability, that there may be pockets of anti-matter in the universe in the dark corners that have not met up with its counter part? held in vacuum it is safely kept away, having been thrust away by the hot bang?




The issue there is that there's no reason for it to have been "thrust away".  We would have expected the matter and antimatter to have been created in a homogeneous spread - where every matter particle created had its antimatter counterpart _right next to it_.  It'd be like having an incredibly large and dense bag of mixed vegetables, and finding somehow all the diced carrots spontaneously migrated to one corner of the bag.  



> [2] are there expiraments in the science community working on discovering a way to test/find antimatter?




Like anything else, you'd notice antimatter by its interactions.  Now, its interactions with other antimatter would look exactly like matter interactions with matter.  So, you can have a star of anti-hydrogen fusing away to anti-helium, and emitting light, and you'd be none the wiser - it'd just look like a star from far away.  You could have a whole galaxy of antimatter stars, and from a distance it would look normal...

...Except where it met a boundary with normal matter.  Then things go kablooey.  If there were large areas of antimatter within the visible universe, you'd expect to find boundaries between that and the region(s) with normal matter - at those boundaries, matter meets anti-matter, annihilates, and produces X-rays (If I recall the energies correctly - gamma rays if not X-rays).

There are, and have been, several X-ray telescopes.  I don't know if any have surveyed for precisely this effect, but a couple of previous telescopes did do full sky surveys.  I think they've looked at enough of the sky that they'd have seen it if it was there.  This suggest that there are no such regions in the visible universe.

This is where the hypothesis I mentioned in the other thread comes in.  It posits that, after the big bang, the only regions that fell out of inflation were regions that, for whatever reason (including just statistical variation), just happened to have at least a slight predominance of either matter or antimatter.  So, there's a multiverse of bubbles, separated by the vast inflating deeps, that are dominated by one or the other.  The next universe over may be an antimatter universe.  

And this fits nicely into the anthropic principle Freyar mentioned.  We live in the universe we do, because if it wasn't this way, it wouldn't be livable, or even exist.  If we were in a region that had even distribution of matter and anti-matter, it'd never have stopped inflating.


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## Janx (Aug 24, 2015)

Some extra Questions:

a) How do we know Anti-matter exists?
Is it possible we've made some stuff up because of our human love of symmetry?
This is likely explainable by Umbran, but it seems like a ground floor assumption to confirm.

b) what if the big bang was the collision of matter + anti-matter in an uneven mix?  All that energy went somewhere, our universe being the result. 


c) what is anti-matter made of and how is that different from normal matter (ex. protons, electrons, neutrons are made of things)?

d)Does Anti-Matter really matter?


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## Scott DeWar (Aug 24, 2015)

Umbran said:


> The issue there is that there's no reason for it to have been "thrust away".  We would have expected the matter and antimatter to have been created in a homogeneous spread - where every matter particle created had its antimatter counterpart _right next to it_.  It'd be like having an incredibly large and dense bag of mixed vegetables, and finding somehow all the diced carrots spontaneously migrated to one corner of the bag.



what is the possibility of being wrong on this? I know I have read that the mass is the same, but what if we are wrong on thiss too? If we are incorrect, we would be looking at the possibility of a "Brazil nut effect" (how the largest nuts float to the top of the can)



Umbran said:


> Like anything else, you'd notice antimatter by its interactions.  Now, its interactions with other antimatter would look exactly like matter interactions with matter.  So, you can have a star of anti-hydrogen fusing away to anti-helium, and emitting light, and you'd be none the wiser - it'd just look like a star from far away.  You could have a whole galaxy of antimatter stars, and from a distance it would look normal...



Did I read somewhere that anti-matter spins in the opposite direction or some such as that?



Umbran said:


> ...Except where it met a boundary with normal matter.  Then things go kablooey.  If there were large areas of antimatter within the visible universe, you'd expect to find boundaries between that and the region(s) with normal matter - at those boundaries, matter meets anti-matter, annihilates, and produces X-rays (If I recall the energies correctly - gamma rays if not X-rays).



I definitely understand this.



Umbran said:


> There are, and have been, several X-ray telescopes.  I don't know if any have surveyed for precisely this effect, but a couple of previous telescopes did do full sky surveys.  I think they've looked at enough of the sky that they'd have seen it if it was there.  This suggest that there are no such regions in the visible universe.



 I humbly point out: Our visible and known universe



Umbran said:


> This is where the hypothesis I mentioned in the other thread comes in.  It posits that, after the big bang, the only regions that fell out of inflation were regions that, for whatever reason (including just statistical variation), just happened to have at least a slight predominance of either matter or antimatter.  So, there's a multiverse of bubbles, separated by the vast inflating deeps, that are dominated by one or the other.  The next universe over may be an antimatter universe.
> 
> And this fits nicely into the anthropic principle Freyar mentioned.  We live in the universe we do, because if it wasn't this way, it wouldn't be livable, or even exist.  If we were in a region that had even distribution of matter and anti-matter, it'd never have stopped inflating.




I now have to admit, I am getting mentally exhausted. Yes, once again: Results of the coma. I am sure I read what you pointed out. I am now haveing absortion problems complicated by a wonky internet connection. I just hope I don't lose what I have on this post.


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## Morrus (Aug 24, 2015)

Janx said:


> Some extra Questions:
> 
> a) How do we know Anti-matter exists?
> Is it possible we've made some stuff up because of our human love of symmetry?
> This is likely explainable by Umbran, but it seems like a ground floor assumption to confirm.




We've seen it; and not just in space - on Earth, too. Cosmic rays hitting the atmosphere produces it, some radioactive decay produces it, we've even created it in very small quantities.  We even use it in some high end medical imaging procedures.


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## Scott DeWar (Aug 24, 2015)

Janx said:


> Some extra Questions:
> d)Does Anti-Matter really matter?




I just had a friend jokingly ask that question


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## Scott DeWar (Aug 24, 2015)

Morrus said:


> We've seen it; and not just in space - on Earth, too. Cosmic rays hitting the atmosphere produces it, some radioactive decay produces it, we've even created it in very small quantities.  We even use it in some high end medical imaging procedures.




So there is an existing  and verifiable test to prove the existance of ant-matter.

I will look up more on this. for the high end medical test equipment, what would that be?


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## tomBitonti (Aug 24, 2015)

Janx said:


> Some extra Questions:
> a) How do we know Anti-matter exists?




Anti-matter has been fabricated in laboratories, including not just particle/anti-particle pairs, but also whole anti-hydrogen molecules.

https://en.wikipedia.org/wiki/Pair_production

And:

https://en.wikipedia.org/wiki/Antihydrogen

At least the Positron occurs naturally, just not in large and durable quantities:

https://en.wikipedia.org/wiki/Positron

Actually, there are large quantities of anti-matter out there, but it is accountable for (kindof) as being generated by black holes:

http://www.dailygalaxy.com/my_weblog/2010/10/do-black-holes-eject-antimatter-.html

But on a cosmological scale, this is a tiny amount, and it won't last for long.  The cloud of positrons of the immediately preceding reference is gradually being destroyed (with, according to the article, the energy output of 11,000 stars!)

Thx!
TomB


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## Scott DeWar (Aug 24, 2015)

tomBitonti said:


> Anti-matter has been fabricated in laboratories . . . . .lots of good stuff . . . . . ..  The cloud of positrons of the immediately preceding reference is gradually being destroyed (with, according to the article, the energy output of 11,000 stars!)
> 
> Thx!
> TomB




I found this link[urlhttp://www.freepatentsonline.com/EP0050596.html=] FPO ip research & communities[/url] in a link on the "Procedure for transforming electrical energy to anti-matter with positron storage"

They have at the very opening:



> The positrons produced between the plates are then separated from the electrons with suitable magnetic fields and carried to suitable magnetic containers with magnetic guides, using mirror, toroidal or other type of magnetic field. The electrons produced are carried with a suitable magnetic guide to be used as a source for the accelerator beam in the procedure.




Just a thought: What if there was some super-magnetic force that separated the anti-matter from the matter to create the pockets of the anti-matter. Maybe this is the source of the development of the anti-matter universes previously mentioned?

And furthermore you need to keep the universes separated or . . . . .Kaboom!

https://www.youtube.com/watch?v=XN32lLUOBzQ


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## Morrus (Aug 24, 2015)

Scott DeWar said:


> I will look up more on this. for the high end medical test equipment, what would that be?




I had to look it up (I'm no medical student!), but the process is called positron emission tomography. It's used to detect tumours in oncology and, and also to detect some dementias.


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## Scott DeWar (Aug 25, 2015)

It sounds like using an electron scanning microscope without the destructive x-rays. An electron beam like that used with a CRT or electron microscope creates some nasty radiation. I guess the positrons  . . . I don't know. I am stuck on this.


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## freyar (Aug 25, 2015)

SO MANY GOOD QUESTIONS!  Sorry for shouting, just got a little carried away...

Let me pick up a couple of the fast ones, then I'll work through the others.  I think I'll kind of work backwards, as in starting with how we know there is antimatter and why you care and eventually getting to the more complex and abstract stuff.

So, first, how do we know antimatter exists?  As several people have said already, we see it quite a bit.  For example, there have been a number of satellite experiments with the capability to detect cosmic rays --- particles from outer space --- including antimatter.  There's a pretty sensitive one called the Alpha Magnetic Spectrometer (AMS) on the International Space Station right now, and the numbers of antiprotons and positrons (antielectrons) that it finds at each energy are of great interest for astrophysics and also dark matter physics.  We also see the results of antimatter annihilating with normal matter in astrophysics; the extreme environments around pulsars (highly magnetized, rapidly spinning cores of stars that are leftover after the rest of the star goes supernova) can produce positrons, which annihilate as they spread through the galaxy.

There are also some radioactive nuclei on earth that decay by producing positrons.  As noted, this is useful for medical imaging in positron emission tomography (PET).  The way PET works is that you stick some of those radioactive atoms in what's basically sugar otherwise, so it preferentially goes to highly metabolic areas of the body, like a tumor.  Then the nucleus decays, which releases the positron. The positron doesn't have to go very far to find an electron, so it then annhilates, producing 2 gamma rays that (usually) fly out of your body to a detector.  This lets you build up a nice clean picture of the tumor.  It's a powerful technique.  The cost of it is partly to do with producing the radioactive elements needed for it, since the one we use decays pretty quickly.  Right now, it's done at relatively few nuclear reactors around the world, but there's ongoing research into producing these nuclei using small particle accelerators that could be more common.  Anyway, PET does expose the patient to some radiation, but (a) usually it's only used when the disease is bad enough that the radiation isn't a concern and (b) we're fairly transparent to gamma rays.  It is true that PET gives you more of a radiation dose than other imaging techniques, though.

And, on the fun side, there is an experiment called ALPHA at CERN (home of the Large Hadron Collider experiment) that produces anti-hydrogen and tests some of its properties.  I know one of the scientists in charge of it a bit (his home institution is TRIUMF, the Canadian national particle physics lab).  As you might expect, one of the biggest challenge is keeping the antihydrogen atom away from regular matter long enough to make a measurement on it because otherwise it will just go POOF!


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## Umbran (Aug 25, 2015)

Janx said:


> a) How do we know Anti-matter exists?
> Is it possible we've made some stuff up because of our human love of symmetry?




As others have noted, we've observed, and outright used, anti-matter.  So, no, we aren't just making stuff up.



> b) what if the big bang was the collision of matter + anti-matter in an uneven mix?  All that energy went somewhere, our universe being the result.




Well, there are some issues with that.  Mainly, where did the matter and anti-matter come from, why were they colliding, and why was the mix uneven?  Moreover, the Big Bang is more than just about energy release - it is also about the origin and development of spacetime.  



> c) what is anti-matter made of and how is that different from normal matter (ex. protons, electrons, neutrons are made of things)?




Every fundamental particle has an anti-particle.  For electrons there are positrons.  For quarks (the things that make up protons and neutrons) there are anti-quarks.  Antimatter is made up of these anti-particles.



> d)Does Anti-Matter really matter?




Well, you aren't getting a PET scan without it.  So it may matter if you have brain cancer.


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## Umbran (Aug 25, 2015)

Scott DeWar said:


> what is the possibility of being wrong on this?




There is always a possibility.  But if you want a percentage chance, I can't give you one.  



> I know I have read that the mass is the same, but what if we are wrong on thiss too?




We have observed and experimented with anti-electrons, anti-protons, and anti-neutrons, and measured their masses.  They have the expected mass.



> Did I read somewhere that anti-matter spins in the opposite direction or some such as that?




You probably read such, but it doesn't mean what you probably think it means.  I'll try to avoid going too much into terminology, as when we start talking about quantum mechanics and "spin", there are a lot of terms.

There are a bunch of numbers we use to describe a particle, often called "quantum numbers".  Speaking broadly - an anti-particle will have all its quantum numbers reversed from a matter particle produced in the same way.  

So, say we have a *really* energetic photon.  Rather than just fly along forever, it may at some point spontaneously create a particle-antiparticle pair out of its energy.  Say it creates a positron and electron.  The electron has some angular momentum intrinsic to it.  In order to conserve angular momentum at the moment of creation, the positron must be created with the opposite angular momentum.  In that sense, we may say it has the opposite spin.




> I humbly point out: Our visible and known universe




In astrophysics, "visible" universe and "known" universe are synonymous.  Yes, there is a limit to the volume of space we know anything about.  It is possible that nearly anything could be going on outside that visible volume of space.  However, I note that the laws and constants we see are apparently *extremely* consistent across what space we can see.  You'd need a particular reason to justify why those laws then become different somewhere else.  Moreover, you'd have to deal with how, *just by coincidence* that weird thing happens to be out where we cannot see it.


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## Umbran (Aug 25, 2015)

tomBitonti said:


> I've always wondered ... if so much matter/antimatter combined, wouldn't that create a huge excess of energy?  Where is that 10^10 factor of energy?




All around you!  

We are talking about events at a time when the universe was extremely dense, just a plasma of particles.  Lots of particles and antiparticles tooth-by-jowl, so to speak.  When the particles annihilate, what you typically get* is photons**.  With things so dense, those photons get immediately absorbed by particles of matter***, and re-emitted.

Eventually, as the universe expanded, atoms formed, and the universe dropped to a density where photons could fly free without running into stuff.  What photons were left that didn't run into stuff to be absorbed became what we now call cosmic microwave background radiation.








*You sometimes get particle-antiparticle pairs instead, but then those annihilate, too, because everywhere you go there's stuff to annihilate with, so eventually you get back to photons.

** Freyar may correct me if I am wrong - this may be happening before the electromagnetic force and weak nuclear force decoupled, so we would then be looking at W and B bosons, carrying the electroweak force of the time, but the rest is about the same.

***We note there that "matter" in this case may also include so-called "dark matter" - while today it doesn't interact much, back in the day or high density it may have been a major contender- so some of that energy may be tied up in stuff you can't see now.


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## Umbran (Aug 25, 2015)

Scott DeWar said:


> I found this link[urlhttp://www.freepatentsonline.com/EP0050596.html=] FPO ip research & communities[/url] in a link on the "Procedure for transforming electrical energy to anti-matter with positron storage"




Note that "someone filed a patent" does not mean what they propose actually works.  The Patent Office is not a good place to go looking for how physical laws actually work.  The patent office are engineering applications of the laws, often for specific cases, such that they don't give you insight into the general case.



> They have at the very opening:
> 
> "The positrons produced between the plates are then separated from the electrons with suitable magnetic fields and carried to suitable magnetic containers with magnetic guides, using mirror, toroidal or other type of magnetic field. The electrons produced are carried with a suitable magnetic guide to be used as a source for the accelerator beam in the procedure."




There is a great deal of hand-waving in the words "suitable".  Yes, you can manipulate moving charged particles with magnetic fields.  But doing so is complicated - it generally requires all the particles to be sorted to be moving in the same direction, with known momentum (speed and mass), have known charge, and sometimes also be spinning in a known direction.



> Just a thought: What if there was some super-magnetic force that separated the anti-matter from the matter to create the pockets of the anti-matter.




In the early universe, the matter and antimatter are of mixed type (some heavy some light), mixed charge (some of the antimatter is positively charged, some negatively charged, some electrically neutral), moving in random directions (not a beam) with a random distribution of spins.  There no simple way to sort a random mix like that with the known forces available.  

Moreover, we are talking about a time with densities such that the universe was not "transparent".  Right now, space is basically empty, so photons, carrying the electromagnetic force, right now can go pretty much forever without hitting anything.  But back then things were so dense that they couldn't reach anything but their very nearest neighbors.  Reaching out to a distant particle of antimatter, and getting it from point A to point B without hitting anything along the way?  Not realistic.

Basically, the universe can't sift though all the particles in itself as if they were M&Ms, and you want all the green ones in a separate bowl.


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## tomBitonti (Aug 25, 2015)

Umbran said:


> In the early universe, the matter and antimatter are of mixed type (some heavy some light), mixed charge (some of the antimatter is positively charged, some negatively charged, some electrically neutral), moving in random directions (not a beam) with a random distribution of spins.  There no simple way to sort a random mix like that with the known forces available.




I thought your idea of expanding bubbles arising from local statistical concentrations of matter or anti-matter was interesting.

There are a couple of problems though: Relative to a single bubble, points are distinguished by how far they are from the edge of the bubble.  Unless the bubble immediately detaches from the larger universe.  Also, that makes for a much larger universe than we can observe, so it seems hard to test.

Of course, "local statistical concentrations" could be quite large, if the universe is much much larger than the billions of light years which we can observe.

Thx!
TomB


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## freyar (Aug 25, 2015)

Umbran's covered a lot of stuff, so I will be relatively brief compared to my usual rambles.  Just wanted to go through a couple more basic issues right now.

There's a question upthread about the difference between matter and antimatter and whether antiparticles have the opposite spin than normal particles.  I'll just add a couple of things to what Umbran has said, which is first of all that each particle has an antiparticle.  In some cases, the antiparticle is the same as the particle itself; this is the case for photons (quantum particles of light).  As Umbran said, the "charges" of antiparticles are always opposite of the corresponding particles.  That includes electric charge but also more mathematically abstract things.  For example, the neutron is electrically neutral but has "weak charge," so the antineutron has opposite "weak charge."  (I am grossly oversimplifying that.)  Quarks have three types of "strong nuclear force charges" a.k.a. colors, known as red, green, and blue, but antiquarks have anticolors, which you might colloquially call cyan, magenta, and yellow.  

Spin is a little more complicated in that it's a more technical definition.  But, using suitable definitions of "spin" and "antiparticle," yes, they have opposite spins.  This isn't too big of a deal, though, as most types of particles can spin in either direction, which means their antiparticles can too.  Neutrinos are a bit weird, however.  Neutrinos can only "spin left" (technical definition), which means antineutrinos can only "spin right."  Theoretically, "right-handed neutrinos" could exist (and could explain some puzzles about neutrinos), but they don't interact with any types of particles we know about, so we've never been able to observe them.



			
				Umbran said:
			
		

> So, say we have a *really* energetic photon. Rather than just fly along forever, it may at some point spontaneously create a particle-antiparticle pair out of its energy. Say it creates a positron and electron. The electron has some angular momentum intrinsic to it. In order to conserve angular momentum at the moment of creation, the positron must be created with the opposite angular momentum. In that sense, we may say it has the opposite spin.



Just want to correct this quickly.  A photon can never just split into an electron and positron because that would violate energy and momentum conservation.  A photon that hits something, though, can create an electron and positron.  Photons also have intrinsic angular momentum (spin), and total angular momentum coming in always has to equal total angular momentum coming out.  So keeping track of spin is important in calculating particle interaction possibilities.


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## Umbran (Aug 25, 2015)

freyar said:


> Just want to correct this quickly.




Not so much correct, as complete.  The fact that this transition must be mediated was something I was leaving out for sake of brevity.  Concept first, then details!

Same reason I left out discussion of "spin" vs "helicity".


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## freyar (Aug 25, 2015)

Umbran said:


> Not so much correct, as complete.  The fact that this transition must be mediated was something I was leaving out for sake of brevity.  Concept first, then details!
> 
> Same reason I left out discussion of "spin" vs "helicity".




Fair enough, though the photon also has spin, so the electron and positron wouldn't necessarily have the opposite spin as each other, either.  In fact, if the thing the photon hits doesn't flip spins and has negligible recoil, the electron and positron need to have the same spin.


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## freyar (Aug 25, 2015)

tomBitonti said:


> So many quotes ... I've left off the attribute of the above.
> 
> I've always wondered ... if so much matter/antimatter combined, wouldn't that create a huge excess of energy?  Where is that 10^10 factor of energy?
> 
> ...






Umbran said:


> All around you!
> 
> We are talking about events at a time when the universe was extremely dense, just a plasma of particles.  Lots of particles and antiparticles tooth-by-jowl, so to speak.  When the particles annihilate, what you typically get* is photons**.  With things so dense, those photons get immediately absorbed by particles of matter***, and re-emitted.
> 
> ...




Umbran has this covered in the basics, so I just want to fill in a couple of tomBitonti's particular questions and address the footnote.

Any matter/antimatter annihilation can create just about anything it has enough energy to make (oversimplifying a bit again).  In particular, that can include dark matter, electrons, protons, etc, etc.  The very early universe (after inflation, if you know what that is) was a very hot, very dense soup of particles, so these annihilations happened all the time as Umbran said.  But, one peculiarity of an expanding universe is that it cools things down, so what annihilations have enough energy to make eventually gets to be lighter and lighter particles, and the heavier things basically go away.  In the last stages, you have some left over protons and neutrons (antimatter is all gone, so they can't annihilate), electrons and positrons, and photons.*  When the electrons and positrons annihilate (with a few electrons left over), the energy can only go into photons (like Umbran said).  At the time, that meant almost all the energy was in photons.**  However, the universe continued to expand and cool, and photons cool down much more quickly than protons and electrons, etc.  So by now, the photons have cooled off a lot (to a temperature of less than 3 Kelvin (ie, 3 Celsius-sized degrees above absolute zero)) and make up very little energy compared to the matter.  As Umbran said, these photons are the cosmic microwave background (CMB).  A neat thing about the CMB is that you can see it.  If you have an analog TV antenna and set your TV to a station that's not there, about 1% of the static snow is due to the CMB.  The CMB is also immensely useful to understand the early universe, since it's nearly unchanged since quite early times.  One thing it tells us is what the starting conditions were like for the formation of structures like galaxies, etc.

*There is also some dark matter, which either has no anti-dark-matter left over (and nothing to annihilate with) or else is too dilute to annihilate efficiently, and neutrinos, which don't interact with the other stuff I mentioned much.
** and neutrinos.


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## Scott DeWar (Aug 25, 2015)

I know what I am going to ask is going to make my head spin, but this dizzy trip is starting to get to be fun - if I can survive the accompanying headache . . . . 

Next Subject: 
Neutrinos

1. You mentioned that do not react with some forms of matter. Why? Are they too high of an energy particulate? 

1a. how do they move at such high velocities sometimes, but not all times? 

Ref: At University of Missouri-Columbia Research Reactor, the core sits in a pool of water with a blue glow around it. It is explained that the glow is caused by neutrinos escaping at near 'C' velocities; however the neutrinos do not move that fast in open air.

2. What is a neutrino exactly, if that is known. I know of neutrino detection labs deep in the earth, the detectors set in these deep chambers and the slow gathering of data that is accomplished.

3. Has there been any purpose for these neutrinos as yet - such as the anti-electron has done.

4. hidden in all of these answers there might be an answer to this next question and I am sorry if I missed it, but, Is there an anti-neutrino?

4a. if there is an anti-neutrino, does it react the same as other antiparticles? That is annihilating and producing a gamma wave?

That should be enough for now, I think. I am giving my self that head spin and headache.


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## freyar (Aug 26, 2015)

These I can answer pretty quickly before I get to the other stuff....



Scott DeWar said:


> I know what I am going to ask is going to make my head spin, but this dizzy trip is starting to get to be fun - if I can survive the accompanying headache . . . .
> 
> Next Subject:
> Neutrinos
> ...



It isn't an energy issue but a "what type of force" issue.  We say we know of 4 fundamental forces: electromagnetic, strong nuclear, weak nuclear, and gravitational (technically, we can now add a 5th, the Higgs force, though it hasn't yet been observed in all the same ways the others have).  For particle physics experiments, gravity is so feeble as to be non-existent, so let's not count that.  While electrons feel the electromagnetic and weak forces, neutrons feel the strong and weak forces, and protons feel all three, neutrinos only feel the weak force.  As you might guess from the name, the weak force  doesn't affect things very strongly, which is due to the fact that it is very short range.  So neutrinos just don't have the capability to interact with other particles easily.

Here's another way to put it.  Imagine you are a fundamental particle.  If you look around, other particles appear to be carrying targets sized according how easy they are for you to hit.  If you're an electron or neutron, a proton looks really big.  However, if you're a neutrino, other particles look super-tiny.  To give you some perspective, if you had a beam of neutrinos, half of them would make it through a wall of lead more than a light year thick.  This means neutrino detectors have to be very big to catch a very few out of a fantastical number of neutrinos.




> 1a. how do they move at such high velocities sometimes, but not all times?
> 
> Ref: At University of Missouri-Columbia Research Reactor, the core sits in a pool of water with a blue glow around it. It is explained that the glow is caused by neutrinos escaping at near 'C' velocities; however the neutrinos do not move that fast in open air.




In addition to interacting very weakly, neutrinos have a very small mass, no more than one-millionth that of electrons, which are the next lightest massive particles.  At the energies we've ever observed neutrinos, they are so relativistic to be moving at a speed indistinguishable from c, the speed of light in vacuum.  And most any neutrino produced has enough energy to be moving that fast.  (Since neutrinos do have mass, it is technically possible to have one moving slowly, but I don't know of a way, for example, you could easily produce them in an experiment or astrophysical event and have them come out slowly.)

That blue light in the reactor is called Cherenkov radiation and deserves a bit of explanation.  Light moves at c, "light speed," only in vacuum.  In air, light moves a bit more slowly and even more slowly in water.  What's happening in that reactor is production of a bunch of neutrinos with a lot of energy.  A small fraction of these neutrinos hit electrons in the water so hard that the electrons start moving very close to c and *even faster than light moves in water*.  Just like an object moving faster than sound in air creates a sonic boom, those electrons create a "light boom," which is the Cherenkov radiation.



> 2. What is a neutrino exactly, if that is known. I know of neutrino detection labs deep in the earth, the detectors set in these deep chambers and the slow gathering of data that is accomplished.




Bear with me, mini-lecture ahead.  There are two basic types of fundamental particles, force-carriers like photons (called bosons), and matter particles like electrons (fermions).  The fundamental matter particles are 6 types of quarks, electrons, muons (heavier version of electrons), taus (even heavier versions of electrons), and neutrinos.  Now, as far as the weak nuclear force is concerned, these matter particles come in pairs: 3 pairs of quarks, electrons and electron neutrinos, muons and muon neutrinos, taus and tau neutrinos (yes, imaginative naming, I know).  So there are actually 3 types of neutrino.

As for other properties of the neutrinos (all 3 types), we've already covered that they only interact through the weak force and that they have a very small mass.  The other very important thing about neutrinos is that they can change type as they fly along.  In other words, you could create a whole bunch of electron neutrinos and send them off to a detector.  But by the time they reach the detector, some will have changed into muon neutrinos or tau neutrinos.  This is what the big neutrino experiments are trying to understand, for the most part --- what is the precise physics that causes neutrinos to change type.  This is one of the things we know about particle physics that tells us the Standard Model is incomplete, and it might be telling us that there are even other types of neutrinos that don't even feel the weak nuclear force (called "sterile" neutrinos), and these might be the dark matter we observe in astrophysics (or a part of it).  Anyway, one of my colleagues at my university works on one of these neutrino experiments.  



> 3. Has there been any purpose for these neutrinos as yet - such as the anti-electron has done.




I assume you're asking about technological uses.  Neutrino technology is in very early stages since they're very slippery particles, but there are some ideas. As you've noticed, nuclear reactors produce lots of neutrinos, so a sophisticated neutrino detector could act like an "x-ray machine" to look inside of nuclear reactors where you can't send equipment due to the high radiation.  This could help with monitoring non-proliferation agreements or the Fukushima accident site.  There have also apparently been some experiments using neutrinos for communication purposes, but I don't know details.




> 4. hidden in all of these answers there might be an answer to this next question and I am sorry if I missed it, but, Is there an anti-neutrino?
> 
> 4a. if there is an anti-neutrino, does it react the same as other antiparticles? That is annihilating and producing a gamma wave?
> 
> That should be enough for now, I think. I am giving my self that head spin and headache.




Yup, there are anti-neutrinos.  Certainly, neutrinos and anti-neutrinos can annihilate and could even produce gamma rays or at least photons of some energy.  But the odds of that happening are astronomically slim, so I'm pretty certain no one's ever seen that happen.

Another fun fact about neutrinos and anti-neutrinos: we talked a bit earlier about the spin of particles.  Most matter particles, like electrons, can spin in two basic ways.  However, neutrinos can only spin one way --- we call them left-handed.  Anti-neutrinos can only spin the other way --- they are right-handed.  This is another complicating feature for neutrino theory.  Where are the right-handed neutrinos?  Are they the sterile neutrinos?  Do they exist at all?  There are lots of models to explain this fact along with the way neutrinos change type, but we just don't have the data yet to say what's right.


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## Umbran (Aug 26, 2015)

freyar said:


> Fair enough, though the photon also has spin, so the electron and positron wouldn't necessarily have the opposite spin as each other, either.  In fact, if the thing the photon hits doesn't flip spins and has negligible recoil, the electron and positron need to have the same spin.




And here, we see perhaps some fundamental difference in communication philosophies.  All of what you say is entirely true, but not necessary for the point - that the example given did not lead to being able to separate matter and anti-matter in the overall universe!

The point is that one of the possible handles we have to separate the pair requires information to use.  Putting this back in context of the patent - the target is a slab of metal, so we don't know, and cannot measure, the spin state change or recoil of the individual atoms in the interaction.   The electron and positron spins are correlated, such that their creation adds no new net angular momentum to the system, but we still don't know what way they'll be pointing.  So, separating on the basis of that is not simple.

I was also trying to stay away from the details of quantum mechanical spin, helicity, and magnetic moment, as those can be *really* confusing to laymen.


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## Mustrum_Ridcully (Aug 26, 2015)

Umbran said:


> Moreover, you'd have to deal with how, *just by coincidence* that weird thing happens to be out where we cannot see it.



Maybe any spot where it would be visible would also be harmful to human life, or hinder the forming of biological life? Not quite satisfying, of course, but that's always the issue with theanthropic principle.


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## freyar (Aug 26, 2015)

Umbran said:


> And here, we see perhaps some fundamental difference in communication philosophies.  All of what you say is entirely true, but not necessary for the point - that the example given did not lead to being able to separate matter and anti-matter in the overall universe!
> 
> The point is that one of the possible handles we have to separate the pair requires information to use.  Putting this back in context of the patent - the target is a slab of metal, so we don't know, and cannot measure, the spin state change or recoil of the individual atoms in the interaction.   The electron and positron spins are correlated, such that their creation adds no new net angular momentum to the system, but we still don't know what way they'll be pointing.  So, separating on the basis of that is not simple.
> 
> I was also trying to stay away from the details of quantum mechanical spin, helicity, and magnetic moment, as those can be *really* confusing to laymen.




Yeah, there are different communication styles, which is perfectly fine.  But I thought we were answering the question about whether antiparticles have the opposite spin of their corresponding particles, right?


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## freyar (Aug 26, 2015)

Mustrum_Ridcully said:


> Maybe any spot where it would be visible would also be harmful to human life, or hinder the forming of biological life? Not quite satisfying, of course, but that's always the issue with theanthropic principle.




The problem is that it wouldn't be a big deal for human (or other intelligent) life unless the boundary were quite close.  Even a supernova, which would be much more inimical to life, would have to be within 100 lightyears or so of earth to kill off life here.  And that's just no distance at all in terms of cosmology.


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## Scott DeWar (Aug 26, 2015)

freyar said:


> These I can answer pretty quickly before I get to the other stuff.... . . . . edit lots of stuff . . . . .
> That blue light in the reactor is called Cherenkov radiation and deserves a bit of explanation.  Light moves at c, "light speed," only in vacuum.  In air, light moves a bit more slowly and even more slowly in water.  What's happening in that reactor is production of a bunch of neutrinos with a lot of energy.  A small fraction of these neutrinos hit electrons in the water so hard that the electrons start moving very close to c and *even faster than light moves in water*.  Just like an object moving faster than sound in air creates a sonic boom, those electrons create a "light boom," which is the Cherenkov radiation.



 for lack of a better way for me to put that, that is so kool! further on you mention usin neutrinos -possibly-  in a technological use of an "Xray for reactors" of sorts. That would have so many positive implications that is almost astounding!



freyar said:


> Bear with me, mini-lecture ahead.  There are two basic types of fundamental particles, force-carriers like photons (called bosons), and matter particles like electrons (fermions).  The fundamental matter particles are 6 types of quarks, electrons, muons (heavier version of electrons), taus (even heavier versions of electrons), and neutrinos.  Now, as far as the weak nuclear force is concerned, these matter particles come in pairs: 3 pairs of quarks, electrons and electron neutrinos, muons and muon neutrinos, taus and tau neutrinos (yes, imaginative naming, I know).  So there are actually 3 types of neutrino.



that we know if anyway. you mention that sterile neutrinos might be dark matter for all that we know



freyar said:


> As for other properties of the neutrinos (all 3 types), we've already covered that they only interact through the weak force and that they have a very small mass.  The other very important thing about neutrinos is that they can change type as they fly along.  In other words, you could create a whole bunch of electron neutrinos and send them off to a detector.  But by the time they reach the detector, some will have changed into muon neutrinos or tau neutrinos.  This is what the big neutrino experiments are trying to understand, for the most part --- what is the precise physics that causes neutrinos to change type.  This is one of the things we know about particle physics that tells us the Standard Model is incomplete, and it might be telling us that there are even other types of neutrinos that don't even feel the weak nuclear force (called "sterile" neutrinos), and these might be the dark matter we observe in astrophysics (or a part of it).  Anyway, one of my colleagues at my university works on one of these neutrino experiments.
> 
> I assume you're asking about technological uses.  Neutrino technology is in very early stages since they're very slippery particles, but there are some ideas. As you've noticed, nuclear reactors produce lots of neutrinos, so a sophisticated neutrino detector could act like an "x-ray machine" to look inside of nuclear reactors where you can't send equipment due to the high radiation.  This could help with monitoring non-proliferation agreements or the Fukushima accident site.  There have also apparently been some experiments using neutrinos for communication purposes, but I don't know details.



 perhaps for ftl communications for interstellar communications?? *shrug*



freyar said:


> Yup, there are anti-neutrinos.  Certainly, neutrinos and anti-neutrinos can annihilate and could even produce gamma rays or at least photons of some energy.  But the odds of that happening are astronomically slim, so I'm pretty certain no one's ever seen that happen.
> 
> Another fun fact about neutrinos and anti-neutrinos: we talked a bit earlier about the spin of particles.  Most matter particles, like electrons, can spin in two basic ways.  However, neutrinos can only spin one way --- we call them left-handed.  Anti-neutrinos can only spin the other way --- they are right-handed.  This is another complicating feature for neutrino theory.  Where are the right-handed neutrinos?  Are they the sterile neutrinos?  Do they exist at all?  There are lots of models to explain this fact along with the way neutrinos change type, but we just don't have the data yet to say what's right.



re: right handed neutrinos, 
if anti neutrinos are sterile neutrinos and ignoring 'the proverbial target' of other mass, and possible other normal matter neutrinos, could this be what anti matter of non neutrino typs are also doing? Maybe it is somehow out of some sort of quantum phase as the rest of the universe? thus able to 'miss' touching any other of matter?

on an aside,
**- [NEW QUESTION ALERT!! BEWARE!!!]-**
I see much talk of such as the electron and positron annihilating each other as with the anti-proton/proton and neutron/anti neutron pairs respectfully, but what if a positron makes contact with a proton?


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## Umbran (Aug 27, 2015)

Scott DeWar said:


> **- [NEW QUESTION ALERT!! BEWARE!!!]-**
> I see much talk of such as the electron and positron annihilating each other as with the anti-proton/proton and neutron/anti neutron pairs respectfully, but what if a positron makes contact with a proton?




Note that "makes contact with" is kind of a misapprehension.  We have this idea of "contact", like when we put a hand on a table, and we think that we are really touching, matter to matter.  But, on the really small scale, we are not.  The electron clouds of my atoms get close to the electron clouds of the table's atoms, and eventually the electric repulsion keeps them apart.  Some photons are exchanged to do that, but the electrons never *touch*, per se.  The electrons are so close to being mathematical points that the concept of 'touching" is of questionable meaning.

So, we while we tend to speak of them "colliding", really, they get close to each other, and start exchanging force-carrying particles (like photons), until something interesting happens.

In this case, they don't just annihilate into energy, if that's what you are asking.  A particle annihilates with its own antiparticle.  It isn't a general, "if you are 'antimatter' you annihilate with *anything* that is matter".

Oh, hey, look, someone has studied this a bit:  
https://en.wikipedia.org/wiki/ZEUS_(particle_detector)
http://www.hep.ucl.ac.uk/undergrad-projects/3rdyear/photons-at-HERA/pshera.htm

The basic interaction at the energies of these experiments seems to be scattering.  They are both positively charged, so getting them close enough to get the positron to go *into* the proton is really hard.  Instead, the electrostatic repulsion has them just bounce off each other.

In these interactions, they exchange an energetic photon (that carries the electromagnetic force) in the scattering .  Sometimes, that photon is big enough to crack the proton open, and you get a cascade of hadrons* (mostly mesons, I expect).  Sometimes, the photon is big enough to produce particle-antiparticle pairs of its own (a meson, in this case), as discussed earlier, and that whams into the proton and you get a cascade of hadrons, slightly different than if the photon did it directly.


*Hadron = particle made of quarks and antiquarks - the proton and neutron are hadrons.  There are mesons made of quark-antiquark pairs as well.


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## freyar (Aug 27, 2015)

Scott DeWar said:


> that we know if anyway. you mention that sterile neutrinos might be dark matter for all that we know



Yes, though right now we don't know if sterile neutrinos exist. 



> perhaps for ftl communications for interstellar communications?? *shrug*



Not FTL --- neutinos travel at light speed --- but for SETI a neutrino telescope has an advantage that one detector can see in all directions, since neutrinos pass right through the earth.  Or an advanced civilization could use a neutrino beam to communicate through a nebula or something.  

The real advantage of neutrino communication is that they can pass through matter, so you could for example communicate with Australia or China from the US without bouncing the signal off a satellite.  I looked into it, and people seem a bit excited about the possibility for communication with submarines. It would be very low bandwidth, but submarines already have low bandwidth communications since they have to use extremely low frequency electromagnetic waves that can't be modulated quickly (radio waves can't penetrate water).



> re: right handed neutrinos,
> if anti neutrinos are sterile neutrinos and ignoring 'the proverbial target' of other mass, and possible other normal matter neutrinos, could this be what anti matter of non neutrino typs are also doing? Maybe it is somehow out of some sort of quantum phase as the rest of the universe? thus able to 'miss' touching any other of matter?




Remember that antimatter particles interact the same was as the corresponding matter particles but with opposite charge.  So positrons -- anti-electrons -- interact by electromagnetism just as strongly as electrons do.  Also, I might have been a bit confusing in my first post: sterile neutrinos would be some whole new type of particle, not antineutrinos (the antiparticles of neutrinos).  We have lots of observations of antineutrinos.  You also seem to be thinking about why sterile neutrinos don't feel the electromagnetic, strong, or weak forces.  One answer is that they just don't.  Of course, there are highly speculative theories that give reasons, like maybe most matter is at one place in extra dimensions and sterile neutrinos are somewhere else.  It's not "quantum phase" like sometimes messes up people in Star Trek, but it is kind of out there.



> on an aside,
> **- [NEW QUESTION ALERT!! BEWARE!!!]-**
> I see much talk of such as the electron and positron annihilating each other as with the anti-proton/proton and neutron/anti neutron pairs respectfully, but what if a positron makes contact with a proton?



What Umbran said.


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## Umbran (Aug 28, 2015)

test post for page 4

(okay, something was a little weird, that seemed to make page 4 inaccessible.  I'm leaving this no-content post here, in case the problem is with the post above, so the thread has a good post in this page to reach.)


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## MarkB (Aug 28, 2015)

Scott DeWar said:


> 3. Has there been any purpose for these neutrinos as yet - such as the anti-electron has done.




One concept the SF writer Larry Niven used in his novels was "Deep Radar", a RADAR-like detection system using neutrinos, which had the advantage of being able to observe structures deep underground. 

I suspect the main difficulty of making such a device practical would be producing a sufficient torrent of neutrinos to get anything like a decent resolution. As mentioned, only a tiny percentage of neutrinos will interact at all with even a planet sized object, and the deep-radar detector would be looking for the several-orders-of-magnitude-smaller percentage of neutrinos that interacted in such a way as to bounce back towards the detector,  and then ineracted with the detector itself.


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## Umbran (Aug 28, 2015)

MarkB said:


> O
> I suspect the main difficulty of making such a device practical would be producing a sufficient torrent of neutrinos to get anything like a decent resolution.




The is the problem with any practical use of neutrinos.  You need so many of them, and your detector probably needs to be very large, that they become impractical.


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## Scott DeWar (Aug 28, 2015)

Umbran said:


> Note that "makes contact with" is kind of a misapprehension.  We have this idea of "contact", like when we put a hand on a table, and we think that we are really touching, matter to matter.  But, on the really small scale, we are not.  The electron clouds of my atoms get close to the electron clouds of the table's atoms, and eventually the electric repulsion keeps them apart.  Some photons are exchanged to do that, but the electrons never *touch*, per se.  The electrons are so close to being mathematical points that the concept of 'touching" is of questionable meaning.
> 
> So, we while we tend to speak of them "colliding", really, they get close to each other, and start exchanging force-carrying particles (like photons), until something interesting happens.
> 
> In this case, they don't just annihilate into energy, if that's what you are asking.  A particle annihilates with its own antiparticle.  It isn't a general, "if you are 'antimatter' you annihilate with *anything* that is matter".



I never really thought about that, but it does make sense.


Umbran said:


> Oh, hey, look, someone has studied this a bit:
> https://en.wikipedia.org/wiki/ZEUS_(particle_detector)
> http://www.hep.ucl.ac.uk/undergrad-projects/3rdyear/photons-at-HERA/pshera.htm



Squirrel!!


Umbran said:


> The basic interaction at the energies of these experiments seems to be scattering.  They are both positively charged, so getting them close enough to get the positron to go *into* the proton is really hard.  Instead, the electrostatic repulsion has them just bounce off each other.
> 
> In these interactions, they exchange an energetic photon (that carries the electromagnetic force) in the scattering .  Sometimes, that photon is big enough to crack the proton open, and you get a cascade of hadrons* (mostly mesons, I expect).  Sometimes, the photon is big enough to produce particle-antiparticle pairs of its own (a meson, in this case), as discussed earlier, and that whams into the proton and you get a cascade of hadrons, slightly different than if the photon did it directly.
> 
> ...



thus tthe 'Hadron' of the LHC, I am guessing.


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## Scott DeWar (Aug 28, 2015)

do opposite sides of quark pairs attract each other? such as up/down, does an up quark attract a down quark anywhere like a proton and elecytron pull at each other? 

if so, is this the binding force that keeps a nucleus together [protons/neutrons]?


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## Scott DeWar (Aug 28, 2015)

Can you produce neutrinos such as, but not necessarily the same as, an electron is produced in a tube?

then focus the neutrino with a deflector shield array?
sorry about my inner Trekkie


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## Scott DeWar (Aug 28, 2015)

Another question: Are you guys tired of my questions?


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## Umbran (Aug 28, 2015)

Scott DeWar said:


> Another question: Are you guys tired of my questions?




I will answer this first:  No.  I like exercising my teaching skills.  Ask away!


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## Scott DeWar (Aug 28, 2015)

Umbran said:


> I will answer this first:  No.  I like exercising my teaching skills.  Ask away!



good!


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## freyar (Aug 30, 2015)

First off, ask away!



Scott DeWar said:


> Can you produce neutrinos such as, but not necessarily the same as, an electron is produced in a tube?
> 
> then focus the neutrino with a deflector shield array?
> sorry about my inner Trekkie




When you say "an electron is produced in a tube," I guess you're talking about electron guns found in old cathode ray tube televisions, etc.  In those, free electrons are produced by heating a piece of metal to a high enough temperature that the electrons "boil off." Then an electric field is used to pull the electrons away from the metal and accelerate them.

Neutrinos, on the other hand, are trickier.  They are produced in nature; for example, the sun makes a lot of them, some radioactive decays produce neutrinos, a supernova produces a tremendous number, etc.  But we also want to make neutrinos for experiments to study them.  Some experiments use nuclear reactors, since various nuclear reactions including radioactive decay of unstable "daughter" nuclei can make neutrinos.  There are also experiments that need a high intensity beam of neutrinos, which takes a multi-step process.  First, you accelerate protons to very high energies, and then you smash them into a fixed target (like a piece of graphite).  This produces a bunch of junk, including some short-lived subatomic particles called pions.  Some pions are charged, so you can separate them from the other particles by sending everything through a magnetic field and selecting only the pions.  Then the pions decay, producing neutrinos and electrons/positrons, which you then just let hit a wall or something.  Meanwhile, the neutrinos just go right through the wall to your detector, which can sometimes be hundreds of miles away through the earth.


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## Scott DeWar (Aug 30, 2015)

A crt or any vacuum tube is exactly what I was thinking of.

Ah, so it is possible, being done and being experimented with. Very interesting.

behaving my self.

ony one question.

Gah! Why graphite?


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## freyar (Aug 31, 2015)

Scott DeWar said:


> do opposite sides of quark pairs attract each other? such as up/down, does an up quark attract a down quark anywhere like a proton and elecytron pull at each other?
> 
> if so, is this the binding force that keeps a nucleus together [protons/neutrons]?




For quarks, up/down, charm/strange, and top/bottom are sort of like "weak force charges" for quarks (very very roughly, think of the first of the pair having one charge and the second a different charge), though it's somewhat more complicated than that.  But the weak nuclear force is extremely short range and can't really reach even across a nucleus very well.  To understand the binding of a nucleus, we need to talk about the strong nuclear force.  

First off, protons and neutrons are made of fundamental particles called quarks.  Quarks carry "strong force charge" known as _color_.  There are three colors (red, green, and blue) for quarks (anti-quarks have anti-colors, which you might call cyan, magenta, and yellow or less imaginatively anti-red, etc).  The strong force is actually strong enough that you can't have a colored object like a quark sitting around by itself.  If you tried to pull the quarks of a proton apart (by, for example smashing the proton with something), the energy you'd need to do that would actually be sufficient to produce (lots of) quark/antiquark pairs from the vacuum, which would the assemble with the original quarks from the proton.  So, in the end, every particle we see on it's own is color-neutral: you can either have a quark/antiquark bound together (so it would have a color plus the corresponding anti-color, which adds to no color) or three quarks with one red, one green, one blue so the colors add to "white."  Quark/antiquark states are called _mesons_ and include the pions I mentioned earlier, and the three-quark states, including protons and neutrons, are _baryons_.  Together, mesons and baryons are called hadrons, as Umbran already said.  *Short version:* the quarks in protons and neutrons are held together by the strong force, and protons and neutrons are therefore strong-force-neutral.

But even though protons and neutrons don't carry color, the strong force still holds them together.  The analogy is the van der Waals force between electrically neutral atoms: if two atoms are close together, the electrons and nuclei inside can move around so there is a net attraction between the atoms.  It's much much more complicated (to the point where we don't have a good way to calculate it from first principles), but protons and neutrons in a nucleus are held together by the strong force version of the van der Waals force.  And, yes, that is strong enough to overcome the electromagnetic repulsion among the protons (which all have the same electric charge).  

Last note: there have also recently been discoveries of 4-quark and 5-quark bound states (_tetraquarks_ and _pentaquarks_) but not a lot is known about them yet.  Tetraquarks have two quarks and two antiquarks; pentaquarks have 4 quarks and one antiquark.  The question is whether they are one big blob of quarks or something like a meson orbiting another meson/baryon.  These qre quite unstable, though.


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