[Eternal Student]

Hi again,

   Thanks for the reply @Halc    I hadn't thought to look at a diagram like that, it does save a bit of time.  It looks like their scale factor is almost a linear function of time    a(t) ≈  k.t   except at early times.   They probably found a better solution for a(t) by running the Friedmann equations with our best estimates of the current proportions of matter, radiation etc.
    Anyway, just taking a(t) ≈ k.t   in  what I previously called [equation 1]  gives a maximum proper distance of approx. 5.1 BLY  which occurrs at a time that is about 5.1 BY after the big bang.   That's close enough to your diagram.  Especially since when you said  "...it crosses the Hubble sphere at t=~7.5 Gyr..."  you meant  4 Gyr or something under 5.

   Sorry for the distraction, Aeris, none of this is too important for your original questions.

Best Wishes.

[evan_au]

matter and antimatter are not inherently more attracted to each other

It's true that a neutron and an anti-neutron are not inherently attracted to each other, because:
- Gravity is negligible for subatomic particles
- neutrons & anti-neutrons have no electric charge (I understand that there is a slight magnetic moment, but small)
- The strong nuclear force operates over a small distance (around the diameter of a Uranium nucleus)
- The weak nuclear force has a very small range

However, for charged particles/antiparticles, there is a very strong electrostatic attraction:
- electrons (-) strongly attract positrons (+), briefly forming positronium
- protons (+) strongly attract antiprotons (-), forming protonium, half life 1us
       - Apparently, the protonium "atom" spends much of its short lifetime smaller than the width of a Uranium nucleus, so the strong nuclear force is actually more significant than the electrostatic force.

I didn't know (but I suspected) that there was a protonium, and it is listed in Wikipedia...
https://en.wikipedia.org/wiki/Protonium

[Halc]

I hadn't thought to look at a diagram like that, it does save a bit of time.  It looks like their scale factor is almost a linear function of time    a(t) ≈  k.t   except at early times.

That it is. Wiki has a scalefactor chart shown below. The magenta line is the one accepted not long ago, giving the 48BLY radius and the 13.8 age. If new tunings get closer to more recent observations, updating the radius of OU, the current age is probably updated as well.

The line is nearly linear up to the current time, except at early times. It matches the diagram I chose in the prior post.

Especially since when you said  "...it crosses the Hubble sphere at t=~7.5 Gyr..."  you meant  4 Gyr or something under 5.

Yea, I fixed that, even before you pointed out the error. Brain fart reading the numbers wrong.

Sorry for the distraction, Aeris, none of this is too important for your original questions.

Yea, we kind of got off track, but it came up discussing how far away antimatter would have to be to not notice it, and that would be the OU, not some closer boundary such as the event horizon.
I've posted elsewhere that I don't except the existence of state, unmeasured. If you accept that, it means there's no antimatter galaxies at all, but distant parts of the universe might be in superposition of having matter and having antimatter galaxies. If you don't accept that, then cause and effect can be separated by greater than light speed, and the the antimatter balance far further away than 100 BLY might have, in violation of the principle of locality, caused our part of the universe to be everywhere matter.

This is why I think we're not entirely off topic with the discussion.

[evan_au]

distant parts of the universe might be in superposition of having matter and having antimatter galaxies

Please clarify this. I don't understand:
- A sustained superposition of matter and anti-matter. Normally they annihilate
- How conservation laws exist in such a superposition
- If it occurs far away, why wouldn't it occur here (and be seen in the LHC, for example?)

[Halc]

distant parts of the universe might be in superposition of having matter and having antimatter galaxies

Please clarify this. I don't understand:
- A sustained superposition of matter and anti-matter. Normally they annihilate

No, they do that if they're both matter and antimatter. It isn't in that state any more than there is both a live and dead cat in the box.

How conservation laws exist in such a superposition

I don't think there's a conservation law with matter/antimatter since we're quite able to annihilate matter without first finding antimatter to die with it.
Given a closed system, I don't think it can be in superposition of say different total momentum, so I don't see how the superposition challenges any particular law.

If it occurs far away, why wouldn't it occur here (and be seen in the LHC, for example?)

No interpretation allows superposition to be self-detectable. Rovelli especially gets into that.
The answer to this is quite interpretation dependent, so maybe picking one is a good place to start.

[Eternal Student]

Hi again.

Regarding this part of the OP:

2. A lot of people say that there is a lot more matter in our universe than antimatter, but how certain can we really be about this? Like, are we absolutely certain that there is way more regular matter in our universe than antimatter? What’s wrong with the idea of the universe having equal amounts of both, albeit in places far apart from each other?

    I think people have already covered the basic ideas.   Although matter and anti-matter annihilations do seem to be a bit random, they do happen often and will be generally favoured or statistically likely.   As such, we would expect to see annihilation reactions going on where any pocket of anti-matter formed a boundary or border with a pocket of ordinary matter.  These annihilations would tend to produce gamma rays, which we just aren't observing.
    However, space is big and maybe we just haven't been looking in the right place.   One thing is that there just doesn't seem to be any reason why anti-matter would behave differently to ordinary matter, so it should be fairly evenly mixed up and distributed with ordinary matter.  There shouldn't be much reason for anti-matter to have attracted other anti-matter and ordinary matter to attract ordinary matter so that it would have separated into pockets of ordinary matter and pockets of anti-matter.  It should all be just fairly evenly mixed up.  If such pockets of ordinary matter and pockets of anti-matter exist then it is presumably just because over time there have been annihilations and there was a surplus of anti-matter or ordinary matter in those pockets to start with.  If this is just some random thing then we should be finding pockets of anti-matter all over the place.  In the simplest situation we should be finding some anti-matter in the particles that hit earth from outer space - but we don't seem to.   
    There are numerous articles and YT videos that discuss this issue and it is one of the main puzzles or problems with the mainstream models of cosmology that we have - why does there seem to have been a slight surplus of ordinary matter compared to anti-matter (at least in our observable region of space)?

    It's possible to imagine extreme situations where pockets of anti-matter might be kept quite separate from ordinary matter.  We can store anti-protons in magnetic bottles and prevent it from coming into contact with ordinary matter.  So it's possible to imagine some naturally occurring astronomical structures with magnetic fields that might act as giant bottles for anti-matter in the universe.  However this is speculation, I'm not aware of any such structures.
   If you assume that it is simply that the anti-matter is very far away from here, then the main problem is explaining why this peculiar distribution occurred during the evolution of the observable universe.  It could be just random chance but this chance would be incredibly small.  Antimatter should have been treated fairly equally with ordinary matter and we would expect them both to have been fairly evenly distributed.   However, if the universe is infinite then perhaps we can go with this random event occurring and argue along the lines of something like the anthropic principle.

Best Wishes.

[Eternal Student]

Hi again.

   I should probably have a look at the last remaining question in the OP.

3. Let’s say, hypothetically speaking (key word, hypothetically, NOT theoretically), I created a wooden, regular matter chair from a huge amount of energy without creating any antimatter whatsoever. It really doesn’t matter (no pun intended) how exactly I did this. All that matters is that I created lots of matter without creating even a little bit of antimatter. How many physical laws would I break from doing this?

    Well there has been some discussion of E=mc²  with at least one post talking about nuclear reactions where there is an overall mass deficit resulting in a large release of energy.  It's reasonable to assume that we can convert mass to/from energy.   Mass is just a property of some matter and it's surprisingly easy to adjust the mass of some piece of matter, we can just get it moving at relativistic speeds for example.  Alternatively we can just get some piece of matter very hot to increase its mass.  There is a difference between creating additional mass (which is easy) and actually creating an additional fundamental particle (which is hard). 

     We can put some photons into a box, we can have mirrors on the walls of box to keep the photons bouncing around inside.  We can put quite a lot of photons into the box if we want.  None the less, when we open the box and have a look inside there is usually just some photons in the box and not some particles of matter that have formed.  Energy density at some place does not force the formation of matter particles and vice versa  (particles of matter are under no obligation to change into some other form of energy).   E=mc² is just a relationship between two quantities (mass and energy) and not a prescription for actually creating new matter particles.

     There are very few ways of creating new matter particles that we know about.  We believe that there was some particle synthesis shortly after the big bang.   Specifically, that two energetic photons can combine under the right circumstances and create a fundamental particle of matter like a quark or a lepton.   Additionally we believe that the weak nuclear interaction is capable of changing one type of fundamental particle into another.   That's it, that's the only two ways I know of to bring about a new fundamental particle type in a place where there wasn't one before.
    (Well, I suppose there's a third option.... we can distort spacetime sufficiently and see how this might affect the permitted solutions of quantum field theory in the vicinity.  This is the kind of thing that happens with Hawking radiation, where particles do appear just outside the event horizon as far as an observer outside of the black hole would be concerned.  I'm just going to ignore this and I'm hardly competent to talk about it anyway).

    Now, let's have a careful look at your (Aeris) original question.    "(...suppose...) I created a wooden, regular matter chair from a huge amount of energy without creating any antimatter whatsoever".    The good news is that this is quite conceivable and doesn't violate any laws of science at all.  Just remember that "energy" isn't any kind of substance anyway.   So your supply of energy could have been some matter that you found lying about the place (matter has energy or some people might say matter is a form of energy).   Given some hand tools, it's possible to create a wooden chair from some wood and you don't usually create any anti-matter while you're doing this.   Even if you didn't have any actual wood but just some other matter available, we can imagine being able to convert the matter you have into some carbon-based wood matter using the weak interaction.
    This is probably not what you (Aeris) meant at all.  When you stated that you were creating a wooden chair from energy you probably had in mind some supply of photons that you were going to use.  Well, that's where it gets a bit tricky.  The synthesis of quarks and leptons (fundamental particles of matter) from photons does seem to involve the creation of  particle and anti-particle pairs.   I think Halc already mentioned that you could just throw all the anti-matter away if you wanted (for example fire it into a black hole).  It's technically still there and would persist on the event horizon for eternity as far as an observer outside the black hole is concerned - but it's not going to get much opportunity to interact with anything.

Best Wishes.
     

[Aeris (OP)]

Eternal Student

Hi again. I'm so sorry I haven't been as active as I was last week. I've just returned to college and I've already been showered in homework. I don't have enough time to go through every else everyone has said since my last comment on this topic, so I'm just gonna respond to this one in particular since it's the one that interests me the most.

"We can put some photons into a box, we can have mirrors on the walls of box to keep the photons bouncing around inside.  We can put quite a lot of photons into the box if we want.  None the less, when we open the box and have a look inside there is usually just some photons in the box and not some particles of matter that have formed.  Energy density at some place does not force the formation of matter particles and vice versa  (particles of matter are under no obligation to change into some other form of energy).   E=mc² is just a relationship between two quantities (mass and energy) and not a prescription for actually creating new matter particles."

"There are very few ways of creating new matter particles that we know about.  We believe that there was some particle synthesis shortly after the big bang.   Specifically, that two energetic photons can combine under the right circumstances and create a fundamental particle of matter like a quark or a lepton.   Additionally we believe that the weak nuclear interaction is capable of changing one type of fundamental particle into another.   That's it, that's the only two ways I know of to bring about a new fundamental particle type in a place where there wasn't one before.
    (Well, I suppose there's a third option.... we can distort spacetime sufficiently and see how this might affect the permitted solutions of quantum field theory in the vicinity.  This is the kind of thing that happens with Hawking radiation, where particles do appear just outside the event horizon as far as an observer outside of the black hole would be concerned.  I'm just going to ignore this and I'm hardly competent to talk about it anyway)."

I actually didn't know that's what E = MC² actually meant. I always thought it quite literally meant that energy could be turned into matter (AKA electrons, protons and neutrons). It does raise some interesting questions though. Namely A) When a nuclear bomb or the sun converts matter to energy, is it actually just converting the mass of its matter into energy or are particles like electrons and protons decaying? B) If it turns out that particles like electrons and protons DON'T decay and last forever, does that mean that matter itself is eternal and has always existed? and C) Is there any evidence for particle synthesis and is it a process that we could theoretically recreate on Earth (be it now or in the distant future)?

"Now, let's have a careful look at your (Aeris) original question.    "(...suppose...) I created a wooden, regular matter chair from a huge amount of energy without creating any antimatter whatsoever".    The good news is that this is quite conceivable and doesn't violate any laws of science at all.  Just remember that "energy" isn't any kind of substance anyway.   So your supply of energy could have been some matter that you found lying about the place (matter has energy or some people might say matter is a form of energy).   Given some hand tools, it's possible to create a wooden chair from some wood and you don't usually create any anti-matter while you're doing this.   Even if you didn't have any actual wood but just some other matter available, we can imagine being able to convert the matter you have into some carbon-based wood matter using the weak interaction.
    This is probably not what you (Aeris) meant at all.  When you stated that you were creating a wooden chair from energy you probably had in mind some supply of photons that you were going to use.  Well, that's where it gets a bit tricky.  The synthesis of quarks and leptons (fundamental particles of matter) from photons does seem to involve the creation of  particle and anti-particle pairs.   I think Halc already mentioned that you could just throw all the anti-matter away if you wanted (for example fire it into a black hole).  It's technically still there and would persist on the event horizon for eternity as far as an observer outside the black hole is concerned - but it's not going to get much opportunity to interact with anything."

Since particle synthesis is the closest of those three methods you said to what you assumed I was describing in my question (which you were absolutely right about btw well done), that's the method I will choose to explain this question more thoroughly. Obviously a machine with the ability to do what the Big Bang did, even on a much smaller scale, would most likely be huge in size and require a level of energy akin to... well I actually don't know but I have no doubt in my mind it's probably an insane amount, so to make this slightly easier to answer, let's just pretend for a moment we're dealing with technology belonging to a type 2 or 3 civilization. I was mainly interested interested in knowing about what physical, universal laws would prevent a theoretical process like this from working. A perpetual motion machine of the first kind wouldn't work due to the first law of thermodynamics, and a perpetual motion machine of the second kind wouldn't work due to the second and third law of thermodynamics. Something like generating a wormhole however, is theoretically possible on paper (not everyone agrees with this statement, but many of them do), even though we currently don't know how to do it, so would a process involving the creation of matter from energetic particles like photons without the simultaneous creation of antimatter be impossible, or possible in theory? At least two people have brought up the fact that conversation of charge is safe due to the creation of electrically-neutral molecules, but evan_au brought up the fact that I violated conversation of lepton and baryon number, which left me confused since, like, aren't those number already uneven due to the universe having more matter than antimatter in it? If this really is impossible, how about a way to turn antimatter into regular matter? Would that also be impossible?

[Origin]

I actually didn't know that's what E = MC² actually meant.

The equation shows the relationship between energy and matter.

I always thought it quite literally meant that energy could be turned into matter (AKA electrons, protons and neutrons).

Energy can literally be turned into matter.  A photon with > 1.02 MeV can produce an electron - positron pair.

[Eternal Student]

Hi.

The equation 281a70c20b16a38d7781189936e1ac9f.gif shows the relationship between energy and matter.

   This is fine as a turn of phrase and I'm sure that you know what it means, Origin but in this context where we're talking about creating new particles and explaining it to Aeris we have to take some care.   Matter has some mass but mass isn't a direct measure of how much matter is present.  (Inertial) Mass is the resistance to an applied force that would cause a change in momentum for an object.
    The  symbol  m  in  E=mc²  stands for mass and not  matter.   An amount of matter is measured in moles  (or mols) and this equation tells us nothing about how much energy is equivalent to one mole of substance.     Meanwhile mass is measured in Kilograms and is the only thing we can put into this equation.
    For example 1 mol of Hydrogen gas (H₂) has a mass of 2 grams at typical temperatures.   However, if we get it hot then we add internal energy and the mass of the Hydrogen will increase, even though there are still Avogadros number of molecules present.  The amount of matter hasn't changed but the mass of it has.  This sometimes takes a moment to think about.  If you put some hydrogen into a container then it requires a certain amount of force to make it accelerate at 1 m/s/s .   If you heat up that Hydrogen then it really does require more force to achieve that same acceleration even though there is exactly the same amount of Hydrogen there.
   We can can add energy to increase the mass of something easily but creating additional particles is more complicated.

Energy can literally be turned into matter.  A photon with > 1.02 MeV can produce an electron - positron pair.

   Yes but not on it's own.   We only observe this pair production when the photon is in the vicinity of a dense nucleus.   This process is also quite random, we sometimes observe a positron and an electron being created but sometimes we don't.    (https://en.wikipedia.org/wiki/Pair_production).
   If we don't follow a prescription or procedure (like firing the photon into a dense nucleus) then the high energy photon will just sail on through space and remain as a photon.  It doesn't spontaneously change into a positron and an electron all on its own  Indeed, it cannot do this because there would be no way to conserve momentum in all frames of reference without a nucleus that can be given recoil momentum.  As such it becomes a bit arbitrary to say that the photon just spontaneously changed into a pair of particles of matter.  There was some interaction that required a nucleus to be there and the nucleus is given recoil momentum at the end.
    Finally note that a photon is not "energy", it is something that has energy.  Energy does not have to be any kind of substance (it's just a conserved quantity).  Changing something with energy into some particles of matter is one thing, there are some procedures for doing this.  However, getting some energy density in one place does not automatically create a fundamental particle of matter like a lepton or a quark at that place.  You usually just have some energy density at that place.  There is no rest mass (or inertial mass) you could measure there and no fundamental particle of matter you can find there.   This was the main point being described earlier.  E = mc² does not imply that just getting some energy density in one place will automatically create a particle of matter, there's no obligation for one form of energy to spontaneously change into 'rest mass'. 

(already too long... I'm stopping).

Best Wishes.

[Origin]

This is fine as a turn of phrase and I'm sure that you know what it means, Origin but in this context where we're talking about creating new particles and explaining it to Aeris we have to take some care.

Yes, I meant to say mass, since that is what the m stands for.  It is an important distinction.

Yes but not on it's own.   We only observe this pair production when the photon is in the vicinity of a dense nucleus.

I never said what else was involved and I don't think it matters, the point was that photons can be directly converted into a electron and a positron. 

[Eternal Student]

Hi again.

I never said what else was involved and I don't think it matters, the point was that photons can be directly converted into a electron and a positron. 

    Yes, exactly -  and this relates to one of Aeris' questions in the most recent post....

C) Is there any evidence for particle synthesis and is it a process that we could theoretically recreate on Earth (be it now or in the distant future)?

1.   We can make positrons and electrons from gamma rays.  Just fire them toward some dense nuclei (like a lump of gold).   It's random but you get a fair chance for particle and anti-particle pair production if the nuclei have a high atomic number (like Gold) and also the gamma rays are of a frequency corresponding to an energy significantly above 1.022 MeV.

2.   There are also some reports where particle and anti-particle pairs have been created just by the collision of two photons  (i.e. without the need for a dense nucleus in the vicinity).   (see https://en.wikipedia.org/wiki/Matter_creation  but note that there are few credible sources and references on that article and I haven't read any of those myself).  It seems that this should happen and it is what we think must have happened in the early universe (since there wouldn't have been any dense nuclei around to get involved with matter creation until after there were already some nuclei).

3.   It is possible to create all fundamental particles in the standard model, including quarks, leptons and bosons using photons of varying energies above some minimum threshold, whether directly (by pair production), or by decay of the intermediate particle (such as a W− boson decaying to form an electron and an electron-antineutrino).  - quote from Wiki.   This is mainly a statement of theoretical possibility and I'm quite certain that we have NOT actually seen a great many heavy particles being created from photons in any experiments:   In no small part this is because the energies of the photons required are huge.  To create baryons like a proton and an anti-proton we should require photons in the hard gamma ray range,  > 1.88 GeV,  or  3 orders of magnitude higher than the experiments we have done to create electrons and positirons. 
    - - - - - -

It should be noted that in all of these particle synthesis reactions, we do seem to create everything in matter and anti-matter pairs.  This, along with the general theory suggests that quantities like "lepton number" and "baryon number" must be conserved.

Best Wishes.

[Aeris (OP)]

Eternal Student

"1.   We can make positrons and electrons from gamma rays.  Just fire them toward some dense nuclei (like a lump of gold).   It's random but you get a fair chance for particle and anti-particle pair production if the nuclei have a high atomic number (like Gold) and also the gamma rays are of a frequency corresponding to an energy significantly above 1.022 MeV."

"2.   There are also some reports where particle and anti-particle pairs have been created just by the collision of two photons  (i.e. without the need for a dense nucleus in the vicinity).   (see https://en.wikipedia.org/wiki/Matter_creation  but note that there are few credible sources and references on that article and I haven't read any of those myself).  It seems that this should happen and it is what we think must have happened in the early universe (since there wouldn't have been any dense nuclei around to get involved with matter creation until after there were already some nuclei)."

"3.   It is possible to create all fundamental particles in the standard model, including quarks, leptons and bosons using photons of varying energies above some minimum threshold, whether directly (by pair production), or by decay of the intermediate particle (such as a W− boson decaying to form an electron and an electron-antineutrino).  - quote from Wiki.   This is mainly a statement of theoretical possibility and I'm quite certain that we have NOT actually seen a great many heavy particles being created from photons in any experiments:   In no small part this is because the energies of the photons required are huge.  To create baryons like a proton and an anti-proton we should require photons in the hard gamma ray range,  > 1.88 GeV,  or  3 orders of magnitude higher than the experiments we have done to create electrons and positirons." 
    - - - - - -

"It should be noted that in all of these particle synthesis reactions, we do seem to create everything in matter and anti-matter pairs.  This, along with the general theory suggests that quantities like "lepton number" and "baryon number" must be conserved."

Ok neat, so this process is possible, but now I have 2 more questions I need you to take me through.

1. We can already create pairs of particles using this process, but can we potentially go a little further and create full-on atoms and molecules? Maybe some hydrogen gas or some water or something?
2. What are you referring to when you say when you say general theory?
3. When you say lepton number and baryon number must be conserved, what exactly do you mean by that. Are our current models of the universe dependent on those qualities being conserved, or will something terrible happen to the universe if they aren't conserved? Also, how are these numbers conserved? Is it like conservation of charge where the net amount of leptons and baryons in the entire universe is zero? Considering there's practically no antimatter in the entire universe, that seems quite unlikely to be the case, so what exactly is wrong with the idea of a process that results in the formation of only regular matter and no antimatter?   

[Halc]

1. We can already create pairs of particles using this process, but can we potentially go a little further and create full-on atoms and molecules? Maybe some hydrogen gas or some water or something?

They've already made anti-hydrogen, and have it stored in a fancy bottle.  Anything bigger requires fusion, and we already have such a hard time doing that with ordinary matter, it doesn't seem likely that they're going to make an anit-oxygen nucleus anytime soon.

When you say lepton number and baryon number must be conserved, what exactly do you mean by that. Are our current models of the universe dependent on those qualities being conserved, or will something terrible happen to the universe if they aren't conserved? Also, how are these numbers conserved? Is it like conservation of charge where the net amount of leptons and baryons in the entire universe is zero? Considering there's practically no antimatter in the entire universe, that seems quite unlikely to be the case, so what exactly is wrong with the idea of a process that results in the formation of only regular matter and no antimatter?   

Well obviously they're not conserved (not locally at least). This is a problem yet to be solved. So your assessment above is right. Maybe it has to do with some kind of imbalance during the inflation phase, where a random chance creation of matter or antimatter is multiplied by processes that don't obey conservation laws that have not yet been set up. This is a wild guess, undoubtedly wrong, but a solution to the problem will perhaps require thinking along such lines.
Maybe dark matter at sufficient densities has properties where matter or antimatter condense out, but not both.

[alancalverd]

It's important to remember that the "laws" of physics are descriptive, not prescriptive. They are how we observe the universe to work, not how some authority has ordained that it must work. So it's entirely possible that the creation of the observable universe did not follow some or indeed any of the laws we see in action every day, and even possible that we may occasionally observe some residue of the prior universe that seems to breach those laws.

[Eternal Student]

Hi again.
 

1. We can already create pairs of particles using this process, but can we potentially go a little further and create full-on atoms and molecules? Maybe some hydrogen gas or some water or something?

   You've had a good answer from Halc concerning creation of anti-matter atoms.
I'm suspicious you wanted an answer about creating ordinary matter atoms and/or entire molecules.  I'm also suspicious you have an eye on the science ficition ideas of creating matter in something like a start trek transporter or whatever the thing is they make stuff in...  a replicator I think - where Captain Picard gets his cup of Earl Grey.
    Well,  making an entire atom all in one go,  or straight from a photon is asking a lot but I suppose it's not impossible.   The energy of the photon(s) has to match or exceed the total rest mass of the particles you are hoping to create.  So for an entire  atom of hydrogen  plus  its partner  anti-hydrogen  that  works out at a photon with an energy of  1.88 GeV or more.   I haven't done that calculation... just found it on a web-page but it looks about right.   The protons and anti-protons are much more massive than an electron and positron which you could create with just 1.022 MeV.     Or to say it another way, the protons need  about 1800 times more energy in the gamma ray because they are about 1800 times more massive than an electron.    I really don't know if we have equipment to create gamma rays with that frequency, its pretty serious cosmic ray stuff.
     Anyway supposing you can get the photons (you know.... on the Google shopping channel it's amazing what you can get these days), you could try and fire those at some dense nuceli and hope for some of them to change into hydrogen plus anti-hydrogen.   Now these photons are so energetic that their penetration and absorption characteristics are quite different to the soft gamma rays that produced position-electron pairs.  These hard gamma rays will frequently just go through a gold target as if it wasn't there.   You'd hope to fire millions of these gamma rays at a gold target and only get a few to interact.   There's also very little you can do to stop other particles being created.  It's not certain that a proton and an electron would appear, you might just get a proton (and it's anti-proton) and the remaining energy of the photon might just give those protons more kinetic energy than usual.   To say that another way, it's not certain that all the energy of the incident photon would be changed into rest mass, some of it might be converted into kinetic energy for a smaller particle.   Anyway... the whole process has become extremely random.   If you get anything at all it'll be a shower of assorted stuff, some of which would have very high velocities and you'd probably never be able to capture it - but maybe a small portion of that stuff would actually be an entire atom of hydrogen (and anti-hydrogen or bits of anti-hydrogen that have fallen apart).
    CERN do not make their anti-hydrogen this way.  It's far more efficient to make the smaller components like positrons and anti-protons and then they almost self-assemble themselves into anti-hydrogen.  They don't even try to make the anti-protons straight from photons but instead they bombard a metal target with ordinary protons and collect some anti-protons that are produced from that.  Even the positrons aren't synthesised from photons, instead these apparently come from a radioactive sodium source that just emits positrons as part of it natural decay process.   All they do at CERN is collect these components, slow them down and allow them to come into contact inside a trap and then just wait for self-assembly into anti-atoms.    (Information source:  https://newscenter.lbl.gov/2010/11/17/antimatter-atoms/).
   In principle if you have a pair of anti-hydrogen atoms close together (and cold, i.e. at low velocities) chemistry should take over and they should self-assemble into a complete molecule of  anti-Hydrogen gas  ( I think the molecular formula has a bar over the H    like   this      ).
    Anyway, just focusing on the oridnary matter and not the anti-matter.  It would be more efficient to just try and sythesise the protons and electrons (probably in seperate places) and then push those protons through a cloud of electrons.  Since they have opposite charges they will attract and self-assemble into atoms of hydrogen at-least a fair portion of the time.  We already know that chemisry can take over form here and two atoms of Hydogen in close proximity will self-assemble into a molecule of Hydrogen gas (provided they are cold, i.e. have fairly low velocities).
    It's a bit messy and extremely random with high energy gamma rays and high velocity particle fragments flying off all over the place, plus it's a bit of hybrid between sythesising some elementary particles and then just sitting back and waiting for ordinary physics and chemistry to build a molecule for you.   However, with a few years of refinement it might look a little bit more like the replicator where Captain Picard gets his cup of Earl Grey tea.

Best Wishes.

[Eternal Student]

Hi again.

2. What are you referring to when you say when you say general theory?

   I was being quite vague.   Most theories concerning the standard model of particle of physics (so that'll be Quantum Field theory mainly) state that the baryon number and lepton number is always conserved in any interaction.     (See, https://en.wikipedia.org/wiki/Baryon_number,  for example).
     The synthesis of matter from photons seems to do this by always creating matter and anti-matter pairs, whenever the process has been observed in experiments.
   

3. When you say lepton number and baryon number must be conserved, what exactly do you mean by that.

   For a system the Baryon number, B, is a quantum number defined by
B =
    Where n₁ = the number of quarks in the system    and  n₂ = the number of anti-quarks in the system.

Similarly Lepton number is   L = N₁  -  N₂   where  N₁   and  N₂ are the numbers of Leptons and anti-Leptons  respectively.

    Along with  statements like this:
In particle physics, lepton number (historically also called lepton charge)[1] is a conserved quantum number representing the difference between the number of leptons and the number of antileptons in an elementary particle reaction.[2] Lepton number is an additive quantum number, so its sum is preserved in interactions     - Taken from https://en.wikipedia.org/wiki/Lepton_number.

Examples include radioactive decay by  Beta^-  emission.
   n    →     p+  +  e^-   + 

Initially (on the left hand side) we had a neutron,      B = 1  and no leptons   L =0.
After the interaction we have a proton   B =1   and an electron (L=+1) but also an  electron anti-neutrino  (L = -1)  giving a total  L = 1 - 1 = 0  = exactly the same as we started with.

Is it like conservation of charge where the net amount of leptons and baryons in the entire universe is zero?

   Yes.  See above.   Technically, the conservation of lepton and baryon number only implies that whatever these numbers were to start with, they never change after any interaction.   So  they would be exactly 0 all the time    if and only if   they were 0 initially.   However if there were some leptons and baryons around just after the big bang then that is the total number that will be conserved from then on.    (We think that there was only radiation around just after the big bang and leptogensis and baryogensis happened shortly afterwards).   

Are our current models of the universe dependent on those qualities being conserved, or will something terrible happen to the universe if they aren't conserved?

   Conservation of these quantum numbers helps to explain why we don't observe some interactions. 

Lepton number was introduced in 1953 to explain the absence of reactions such as
    ν    + n   →    p  +    e−   - Taken from Wiki.

   However, I'm not sure that it actually arises as a necessary condition from some piece of mathematics that describes the quantum mechanics.  It just seems to be an assumption in the standard model of physics and it is is empirically or experimentally supported (but I don't know for certain).
   Certainly there are some theories that suggest Lepton number and Baryon number do not need to be conserved.
   See:    "Violations of Lepton number conservation laws"   https://en.wikipedia.org/wiki/Lepton_number#Violations_of_the_lepton_number_conservation_laws   
  and also,    "Physics beyond the standard model"      https://en.wikipedia.org/wiki/Physics_beyond_the_Standard_Model

Will something terrible happen to our universe if they aren't conserved?  Well, the universe will presumably carry on doing what it's been doing regardless of whether we understand it or not.   We (human beings) will drop the assumption that Lepton number and Baryon number is necessarily conserved but I don't think it will shake the usefullness of the standard model of particle physics too much.  Under typical situations the standard model does seem to be a useful approximation or model even if there are some unusual situations (perhaps in the time close to the big bang) where it's not so good.
    As people have already mentioned, we do believe that there is more matter in our observable universe than anti-matter and so we are all expecting that there is at least some mechanism whereby lepton and baryon numbers are not conserved.

Considering there's practically no antimatter in the entire universe, that seems quite unlikely to be the case, so what exactly is wrong with the idea of a process that results in the formation of only regular matter and no antimatter?

   Many physicists do expect that there is (or was) such a process, or alternatively some process whereby anti-matter decays (presumably back into photons) faster or more preferentially than ordinary matter would undergo the same process.   It may have required conditions that were only around just after the big bang, so it may not be repeatable now.

Best Wishes.

[Aeris (OP)]

Eternal Student

"For a system the Baryon number, B, is a quantum number defined by
B =
    Where n₁ = the number of quarks in the system    and  n₂ = the number of anti-quarks in the system.

Similarly Lepton number is   L = N₁  -  N₂   where  N₁   and  N₂ are the numbers of Leptons and anti-Leptons  respectively.

    Along with  statements like this:
In particle physics, lepton number (historically also called lepton charge)[1] is a conserved quantum number representing the difference between the number of leptons and the number of antileptons in an elementary particle reaction.[2] Lepton number is an additive quantum number, so its sum is preserved in interactions     - Taken from https://en.wikipedia.org/wiki/Lepton_number.

Examples include radioactive decay by  Beta^-  emission.
   n    →     p+  +  e^-   + 

Initially (on the left hand side) we had a neutron,      B = 1  and no leptons   L =0.
After the interaction we have a proton   B =1   and an electron (L=+1) but also an  electron anti-neutrino  (L = -1)  giving a total  L = 1 - 1 = 0  = exactly the same as we started with.
   Yes.  See above.   Technically, the conservation of lepton and baryon number only implies that whatever these numbers were to start with, they never change after any interaction.   So  they would be exactly 0 all the time    if and only if   they were 0 initially.   However if there were some leptons and baryons around just after the big bang then that is the total number that will be conserved from then on.    (We think that there was only radiation around just after the big bang and leptogensis and baryogensis happened shortly afterwards)."

Ah, I get it now. The numbers have been set in stone and they (to our knowledge at least) cannot change.   

"Conservation of these quantum numbers helps to explain why we don't observe some interactions. 

Lepton number was introduced in 1953 to explain the absence of reactions such as
    ν    + n   →    p  +    e−   - Taken from Wiki.

   However, I'm not sure that it actually arises as a necessary condition from some piece of mathematics that describes the quantum mechanics.  It just seems to be an assumption in the standard model of physics and it is is empirically or experimentally supported (but I don't know for certain).
   Certainly there are some theories that suggest Lepton number and Baryon number do not need to be conserved.
   See:    "Violations of Lepton number conservation laws"   https://en.wikipedia.org/wiki/Lepton_number#Violations_of_the_lepton_number_conservation_laws   
  and also,    "Physics beyond the standard model"      https://en.wikipedia.org/wiki/Physics_beyond_the_Standard_Model

Will something terrible happen to our universe if they aren't conserved?  Well, the universe will presumably carry on doing what it's been doing regardless of whether we understand it or not.   We (human beings) will drop the assumption that Lepton number and Baryon number is necessarily conserved but I don't think it will shake the usefullness of the standard model of particle physics too much.  Under typical situations the standard model does seem to be a useful approximation or model even if there are some unusual situations (perhaps in the time close to the big bang) where it's not so good.
    As people have already mentioned, we do believe that there is more matter in our observable universe than anti-matter and so we are all expecting that there is at least some mechanism whereby lepton and baryon numbers are not conserved."

Yeah, I'll be honest, the way I worded that question made it sound like I was horrified at the prospect of the universe destroying itself through the violation of a fundamental law (or something pseudoscientific like that). I was primarily interested in knowing though since A) It's quite common for a single scientific discovery to overthrow and revamp entire models, and B) According to this https://www.quora.com/What-would-happen-if-the-law-of-conservation-of-charge-were-violated some conservation laws could cause VERY noticeable changes in our universe if they were ever violated and I was curious to know of the implications of a violation of baryon and lepton number. Actually, almost all of my questions stem from a place of curiosity, although I don't blame you for assuming I was interested in science-fiction (which admittedly I am, but that's not why I'm asking these questions).     

"Many physicists do expect that there is (or was) such a process, or alternatively some process whereby anti-matter decays (presumably back into photons) faster or more preferentially than ordinary matter would undergo the same process.   It may have required conditions that were only around just after the big bang, so it may not be repeatable now."

It's highly possible you'll respond to this with a "We don't know", but... do you think you could tell me what exactly those conditions were by any chance? Could you at least tell me what we think those conditions were?

Also this isn't relevant to your recent posts, but it is something that just crossed my mind earlier today that I didn't realize two days ago when you brought up particle synthesis. You said that "two energetic photons can combine under the right circumstances and create a fundamental particle of matter like a quark or a lepton.". You also said that such a process happened moments after the Big Bang. If matter didn't exist yet at this point in time, that means that electromagnetic fields didn't exist either. Photons are vibrations of electromagnetic fields, so how can photons exist moments after the big bang if electromagnetic fields did not?

Also not relevant to your recent posts, I'm having a fun time talking about this stuff with you guys you're really helping me out.   

[Eternal Student]

Hi again.

do you think you could tell me what exactly those conditions were by any chance? Could you at least tell me what we think those conditions were?

    Around the time of the big bang we expect the temperature, pressure and energy density to be extraordinarily high.  Physicist's often lump all of these descriptions and properties together and just say they are high energy conditions.  There may be other conditions like the inflaton field having only just switched off and/or the Higgs field having only just switched on (i.e. fields that we don't seem to be able to influence at the moment).
    There doesn't seem to be the technology available to recreate and also safely contain these extremes conditions and there are some theoretical limits anyway:  Since energy density and pressure are both sources of gravitation we could easily create a black hole by accident  (which would obviously tend to conceal what had actually happened during the experiment).   We are talking about establishing conditions that are within a hairs breadth of causing a singularity.   After all, baryogenesis and leptogenesis were thought to have occurred only a few moments after a singularity.
    At these sorts of energies it's thought that most of physics would be quite different.   Most of the theories we have are thought to be only low-energy approximations to the underlying principles.

If matter didn't exist yet at this point in time, that means that electromagnetic fields didn't exist either.

    That's not necessary.   The electromagnetic field exists and permeates all of space,  independently of whether there is matter there or not.   For example, an electric field exists even across a vaccum and any charged particle you had on the one side of that vaccum would still feel a force from a source on the other side of that vaccum.   EM radiation can certainly exist in and travel through a vaccum (infact it only has the speed c when it is doing this).
  (Technically the electromagnetic field is terminology associated with a classical field theory of electromagnetism and at these sorts of energies and relativistic conditions we should probably be using a quantised version but the principle would be the same.  Matter is not required).

Best Wishes.

I'm having a fun time talking about this stuff with you guys you're really helping me out.

   Great.  You're going to be helping me out in a few years and probably not just with some physics.

Best Wishes.

[Aeris (OP)]

Eternal Student

"Around the time of the big bang we expect the temperature, pressure and energy density to be extraordinarily high.  Physicist's often lump all of these descriptions and properties together and just say they are high energy conditions.  There may be other conditions like the inflaton field having only just switched off and/or the Higgs field having only just switched on (i.e. fields that we don't seem to be able to influence at the moment).
    There doesn't seem to be the technology available to recreate and also safely contain these extremes conditions and there are some theoretical limits anyway:  Since energy density and pressure are both sources of gravitation we could easily create a black hole by accident  (which would obviously tend to conceal what had actually happened during the experiment).   We are talking about establishing conditions that are within a hairs breadth of causing a singularity.   After all, baryogenesis and leptogenesis were thought to have occurred only a few moments after a singularity.
    At these sorts of energies it's thought that most of physics would be quite different.   Most of the theories we have are thought to be only low-energy approximations to the underlying principles."

Sooooo... the asymmetry that allowed regular matter to triumph over antimatter was brought about by the early universe being in a state of insanely high energy? It's that simple? Also theoretically speaking, if we COULD find a way to replicate this process, how much matter could we create before we unintentionally spawn a black hole? 

"That's not necessary.   The electromagnetic field exists and permeates all of space,  independently of whether there is matter there or not.   For example, an electric field exists even across a vaccum and any charged particle you had on the one side of that vaccum would still feel a force from a source on the other side of that vaccum.   EM radiation can certainly exist in and travel through a vaccum (infact it only has the speed c when it is doing this).
  (Technically the electromagnetic field is terminology associated with a classical field theory of electromagnetism and at these sorts of energies and relativistic conditions we should probably be using a quantised version but the principle would be the same.  Matter is not required)."

Ah, I see. So even if we found a way to magically remove the virtual particles popping in and out of existence all of the time, we would still have underlying, universal fields in space representing each of the four fundamental forces that hold all of existence together, thus preventing it from ever being truly empty. That also means that photons (and all forms of electromagnetic radiation) can exist independently of matter. Sweet!   

"Great.  You're going to be helping me out in a few years and probably not just with some physics."

Considering that you are the one researching, simplifying and explaining this stuff to me, it seems highly unlikely that, if I ever did take up a career in the world of science and physics, you'd be one of the people I'd teach. But still, thank you for the kind remark

Sorry for the late reply btw. Twas my Dad's birthday today.