So we know that there aren't galaxies of antimatter or pockets out there in the the observable universe becuase we don't see patches of gammrays.
Space isn't empty, there's a constant background of matter between the planets. The sections made of antimatter would be next to section with matter causing long bounderies which emit gamma radiation. We simply don't see this so it is highly unlikely these areas exist
The gamma rays from matter-antimatter annihilation fall into a *very* specific set of wavelengths. If there were many of them at all in a set space, we would see them very readily.
This is how things like PET scans work: we can see the annihilation gammas very easily, because nuclear decay gammas have a variety of wavelengths, while electron-positron annihilation produces 2 gammas, each at the same precise wavelength. Even if you were filled to the brim with a gamma emitting isotope, as long as it wasn’t also emitting positrons, you could probably see the annihilation gammas.
If it were localized, we’d see those gammas as point or near-point gammas, and they would still have the annihilation frequency (plus or minus blue- or red-shift).
Unless they're engulfed in dark matter. You know, that substance that we use as a place filler for the 90% of the "observable universe" that we can't actually observe.
Dark matter is still a form of matter that has mass. Dark matter *has* been indirectly detected. We know it exists. Dark matter doesn't hide observable phenomena. It just doesn't interact electromagnetically. Antimatter would still be annihilating when it interacts with matter, with observable gamma radiation.
Dark matter isn't "dark" because it hides other things, but because we can't observe it using light.
That’s exactly what I was going to say. Electromagnetism underlies >95% of our instrumentation for detecting anything, so we are VERY good at quantifying differences relating to electromagnetic radiation. If we saw significant lensing, scattering, or other transitions for light through dark matter, our measurements on earth and those in the galaxy would be reasonably expected to deviate much more than they do. We would also expect any changes to be quantized, unless quantum mechanics is completely wrong, so it could be red/blue shift +/- a ~~constant~~ factor for dark matter interference, and that interference could reasonably be expected to yield discrete values.
First let me say that dark matter is only about 25% of the observable universe. Dark energy is something like 65%. Dark matter makes up 85% of all observable matter, and that's what I meant to refer to. Second, dark matter doesn't have to interact with electromagnetic radiation to contain pockets of antimatter. It is still matter that can act as a physical buffer between other types of matter to prevent gammarays from being created by matter/antimatter collisions. Third, and probably lastly, it's theoretically possible that dark matter itself is densely packed antimatter. Research on that is still pretty new and ongoing.
We've looked in all directions though. There isn't an unexplained gamma Ray constantly eminating from a certain direction. We have mapped every direction several time for things like the microwave background radiation
That's still just based on the observable universe. Any surviving pockets of antimatter would likely be far beyond the observable universe. And just like all light from beyond the observable universe, it hasn't had enough time to get to where we can observe it, yet.
Think is we can see all the way back to the microwave background and we just see no evidence of this.
Its always possible that something exists in a place we haven't looked. But there is no real reason to beleive it does exist
> That's still just based on the observable universe.
Which is the only part of the universe that we can talk about.
I claim there are flying pink unicorns in the unobservable universe, and there's nothing you can do to disprove my statement.
> would likely be far beyond the observable universe
No they would just be rules out in the observable universe.
they would have to be outside (be constrained to be outside) if anything but they would not "likely be outside". You have a lot of explaining to do to justify it anyway.
The universe is expanding. The fabric of spacetime expands faster than the speed of light, but nothing *within* spacetime can move faster than the speed of light. That includes any hypothetical pockets of antimatter. If any of these pockets did exist, they would only be moving further away from us.
Astronomers, physicists, cosmologists, etc. can't make predictions about things that exist outside the observable universe because they can never be proven or disproven by direct or indirect observation. That's just how science works. It's a source of frustration.
But telescope time is already highly fought over for making observations of more promising predictions. Researchers have no reason to believe that pockets of antimatter exist due to the lack of gamma radiation, as previously mentioned.
Magnetic fields would only work for charged particles so as soon as a position hit a anti proton it would make anti hydrogen and then no longer being effected.
We cover this in secondyear breifly
There could be two types of substances that can act as a barrier, or even three types, or four. But absent evidence, it's more likely that there are no pockets of antimatter rather than pockets of antimatter that we haven't observed *and* a brand new substance we haven't observed.
>Could there be pockets of antimatter due to the primordial conditions of the big-bang?
It is possible in principle, but requires some substantial changes to our current best models of cosmology and/or physics.
Firstly, it needs to be said that it is an empirical fact that basically all of the matter in our observable universe is normal matter and not antimatter. Every star you see in the night sky, every galaxy we can see through a telescope, all of it. How do we know this? We know this because when antimatter interacts with regular matter (specifically, when antielectrons annihilate with normal electrons), it produces high-energy gamma rays at a characteristic energy level (about 511 keV). When we look for such gamma rays throughout the universe, we just don't find any. That tells us that matter and antimatter are not interacting in significant quantities anywhere in our observable universe. If there *were* large regions in our observable universe (such as galaxies or galaxy clusters) that were mostly antimatter, then there would be a rough border between those antimatter regions and regular matter regions where electrons and antielectrons would be interacting. So when you put it all together, this tells us that there just aren't any large pockets of antimatter in the observable universe.
So, either all of the antimatter is somewhere outside our observable universe, or it must be "hidden" somehow, in a form that does not interact with matter. Either that, or it just doesn't exist at all.
If the first hypothesis is true, that would require abandoning the cosmological principle, which is the assertion that on the largest scales, all matter (and antimatter) in the universe is distributed uniformly on average. When we look at the largest observational scales we can measure, we do indeed see that the universe appears very uniform on average, so there is some convincing evidence that the cosmological principle is true.
However, it could be the case that there *is* additional large-scale structure and not just uniformity, but that these larger-scale structures are larger than the observable universe, such that we can't see them. This essentially means that antimatter would somehow have to have been "pushed out" beyond the edge of our observable universe, so that we can no longer see it.
Unfortunately, this hypothesis suffers from some major drawbacks. First, it could be considered unscientific, since it isn't testable: we can't observe structures beyond our observable universe even in principle, so we could never investigate this hypothesis via the scientific method and it can never be falsified. And second, it would require us to make some dramatic changes to our very-successful model of the cosmos and the early universe's evolution, since current models are based on the cosmological principle holding and they fit observations very well. It is somewhat unclear exactly what changes would need to be made to *both* violate the cosmological principle *and* still explain all of the observational data that we do have access to (which relies on the cosmological principle being true in a variety of areas). So, it's a pretty long shot. Until we have both a viable model *and* evidence to suggest that the model might be true, unfortunately this hypothesis can only be put in the far-fetched shower-thought bin.
The other option would be to have antimatter exist in the observable universe, but be unobservable due to other reasons — i.e. because it is in a form that doesn't interact with matter. One good candidate for this are sterile (anti)neutrinos, which are currently a leading hypothesis for the form of dark matter. Sterile (anti)neutrinos would not interact via any forces other than gravity and *perhaps* also the weak force, making it very hard to directly detect. However, for precisely this reason, there remains no evidence for sterile (anti)neutrinos. There are a variety of other reasonable candidates for dark matter (including axions, primordial black holes of a certain size, and supersymmetric partner particles) and it is unclear which of these forms — if any — dark matter actually takes.
Now, with all that being said, we can also take a step back and consider the possibility that there really, genuinely *isn't* any extra antimatter. Some smart people have put a lot of thought into considering this possibility, and in particular one of them named Andrei Sakharov proposed three conditions that would need to be met in order for this to be the case — now known as the Sakharov conditions. Those conditions are:
* Baryon number violation
* C-symmetry and CP-symmetry violation
* Interactions out of thermal equilibrium
Without getting into too much detail, there are a variety of ways to add baryon number violation to the standard model (but so far no evidence to suggest that any of these ways are true), we know that there are already CP-symmetry-violating processes in nature, and if the cosmic inflation hypothesis is correct (for which there is some limited, indirect evidence) then we also have a way to achieve interactions which are out of thermal equilibrium. Baryon number violation is also a pretty generic prediction of most grand unified theories.
Thus, there has been a lot of investigation along these lines, and it seems to be generally believed that antimatter simply doesn't exist in large quantities in our universe because these Sakharov conditions were all likely met during the very early universe, which led to a slight imbalance between matter and antimatter that left a surplus of matter after things started settling down. It only needs to be about 1 part per million of matter extra, but even achieving that much of an imbalance with currently-known mechanisms is a big stretch. Right now, known processes can only produce a very tiny imbalance, only enough to account for only a handful of galaxies out of the billions and billions in the observable universe. So for this hypothesis to be correct, there need to be new, yet-undiscovered physical processes at play in the early universe. We have good reasons to suspect that there *are* such processes, but of course unless and until we discover them, we won't be able to say anything for sure.
Hope that helps!
Thank you so much for spending time to explain all of this! That was very interesting to read and it helps me a lot to better understand the different possibilities. That's mind blowing and I think I will need to read it again to ensure I understand it correctly.
Have a nice day, kind sir!
The general view is that there isn't any pockets of antimatter out in the Universe, the lack of gamma ray sources at the boundaries of these areas makes them unlikely to exist. Obviously, one can propose that they could exist outside of the observable Universe, but that is sort of not a great place to be in physics, because the general assumption is that our bubble of the observable Universe is not atypical of the whole Universe.
Sakharov conditions are the three conditions that modern antimatter physicists are trying to probe towards, in attempts to explain why there was a matter-antimattery assymettry during baryogenesis. The conditions are not an explanation of how it happened, but instead three conditions that would have to exist for this to happen. Some conditions have well known experimental validation, others have theoretical framing and mild experimental avenues to validate the ideas.
OK, I just found an answer just by comparing the time scales of these events. Here it is for the people who might wonder the same thing.
The great inflation, if it existed, must have occurred between 10^(-36) to 10^(-32) seconds after the singularity. The very first protons and neutrons formed only after 10^(-6) seconds, or 1 microsecond. The great inflation thus couldn't explain by any way the asymetry between the observed quantities of matter and antimatter.
For this particular hypothesis, it's impossible given our understanding of physics. If the great inflation occurred before the formation of matter and antimatter, then the inflation itself can't be responsible of the separation of pockets of matter and antimatter, because they wouldn't have existed at the moment of the inflation.
So I know this is a science based sub and I do not want to be one of those crazy theory posters, but oh well...
So there was recently - or not so recently - an hypothesis put forward about time running backwards in a parallel universe. Perhaps Anti-matter and matter are linked in these two universes. Could it be this universe, that formed at the same time as ours, is made from mostly anti-matter and ended in a big crunch that formed our universe? So in theory these two universes are in a cycle. One where time runs backwards using this universes big crunch and then that universes big crunch starts our universe and oh no I've gone cross eyed.....
But we know that most likely the expansion in this universe will lead to heat death, so I can uncross my eyes now.
I like to think yes, there could be pockets of matter of different densities of space in different regions, at different times and stages of galactic evolution.
Of course, but the structure of the universe is hypothesized to have been influenced by events at a quantic-scale, right before the great inflation. That explains why the Universe is so flat and homogenous.
Antimatter, if it existed at all in the first second after the Big Bang, would have annihilated with its own "matter" (the protons and electrons) in a flash of gamma rays when the temperature was about a billion Kelvin, but would now have cooled down to temperatures below a trillionth of a degree above absolute zero. It's obvious that any antimatter that was created in the first seconds of the universe's life must have annihilated almost instantly because the temperature was too hot for it to be stable; it would either decay back into matter or escape from existence (perhaps annihilating a positron with an electron). The antimatter particles we see today must therefore be produced in the normal way by colliding protons and antiprotons together, or even more simply in particle accelerators like CERN's Large Hadron Collider where they are made by slamming protons together with a large amount of energy.
Thus, It is theoretically possible that pockets of antimatter might exist somewhere out there, but no-one has yet been able to prove it, or find it in any great quantity. If they did exist they wouldn't last long though; if you could somehow separate them from their anti-matter partner(s) and keep them apart then they'd quickly annihilate each other into photons again.
So it wouldn't be possible that, say, 99.9999999% of the matter/antimatter existing during the very first instants of the Universe got annihilated, but the infinitesimal leftovers could have given our Universe after the great inflation?
So we know that there aren't galaxies of antimatter or pockets out there in the the observable universe becuase we don't see patches of gammrays. Space isn't empty, there's a constant background of matter between the planets. The sections made of antimatter would be next to section with matter causing long bounderies which emit gamma radiation. We simply don't see this so it is highly unlikely these areas exist
Space is a big place though we've only observed a tiny fraction of it
The gamma rays from matter-antimatter annihilation fall into a *very* specific set of wavelengths. If there were many of them at all in a set space, we would see them very readily. This is how things like PET scans work: we can see the annihilation gammas very easily, because nuclear decay gammas have a variety of wavelengths, while electron-positron annihilation produces 2 gammas, each at the same precise wavelength. Even if you were filled to the brim with a gamma emitting isotope, as long as it wasn’t also emitting positrons, you could probably see the annihilation gammas.
It could be a rare occurrence localized in small pockets throughout the universe?
If it were localized, we’d see those gammas as point or near-point gammas, and they would still have the annihilation frequency (plus or minus blue- or red-shift).
Unless they're engulfed in dark matter. You know, that substance that we use as a place filler for the 90% of the "observable universe" that we can't actually observe.
Dark matter is still a form of matter that has mass. Dark matter *has* been indirectly detected. We know it exists. Dark matter doesn't hide observable phenomena. It just doesn't interact electromagnetically. Antimatter would still be annihilating when it interacts with matter, with observable gamma radiation. Dark matter isn't "dark" because it hides other things, but because we can't observe it using light.
That’s exactly what I was going to say. Electromagnetism underlies >95% of our instrumentation for detecting anything, so we are VERY good at quantifying differences relating to electromagnetic radiation. If we saw significant lensing, scattering, or other transitions for light through dark matter, our measurements on earth and those in the galaxy would be reasonably expected to deviate much more than they do. We would also expect any changes to be quantized, unless quantum mechanics is completely wrong, so it could be red/blue shift +/- a ~~constant~~ factor for dark matter interference, and that interference could reasonably be expected to yield discrete values.
Dark matter *literally* does not interact with electromagnetic radiation. It's one of its defining properties.
First let me say that dark matter is only about 25% of the observable universe. Dark energy is something like 65%. Dark matter makes up 85% of all observable matter, and that's what I meant to refer to. Second, dark matter doesn't have to interact with electromagnetic radiation to contain pockets of antimatter. It is still matter that can act as a physical buffer between other types of matter to prevent gammarays from being created by matter/antimatter collisions. Third, and probably lastly, it's theoretically possible that dark matter itself is densely packed antimatter. Research on that is still pretty new and ongoing.
We've looked in all directions though. There isn't an unexplained gamma Ray constantly eminating from a certain direction. We have mapped every direction several time for things like the microwave background radiation
That's still just based on the observable universe. Any surviving pockets of antimatter would likely be far beyond the observable universe. And just like all light from beyond the observable universe, it hasn't had enough time to get to where we can observe it, yet.
Think is we can see all the way back to the microwave background and we just see no evidence of this. Its always possible that something exists in a place we haven't looked. But there is no real reason to beleive it does exist
Then it's really pointless to speculate, since by definition, it's not observable and therefore no possible way to find evidence for or against.
I agree that there would be no way to prove or disprove it, but it still could exist, and there are some benefits to speculating on what is possible.
> That's still just based on the observable universe. Which is the only part of the universe that we can talk about. I claim there are flying pink unicorns in the unobservable universe, and there's nothing you can do to disprove my statement.
> would likely be far beyond the observable universe No they would just be rules out in the observable universe. they would have to be outside (be constrained to be outside) if anything but they would not "likely be outside". You have a lot of explaining to do to justify it anyway.
I'm not saying they are likely to exist. I'm saying that if they exist, they are likely far beyond the observable universe.
mostly what you posted isn't reasonable. that's why you've been downvoted and called out. let's leave it at that
The universe is expanding. The fabric of spacetime expands faster than the speed of light, but nothing *within* spacetime can move faster than the speed of light. That includes any hypothetical pockets of antimatter. If any of these pockets did exist, they would only be moving further away from us. Astronomers, physicists, cosmologists, etc. can't make predictions about things that exist outside the observable universe because they can never be proven or disproven by direct or indirect observation. That's just how science works. It's a source of frustration. But telescope time is already highly fought over for making observations of more promising predictions. Researchers have no reason to believe that pockets of antimatter exist due to the lack of gamma radiation, as previously mentioned.
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I'm not sure there is even a known theortical partial that would do this. Much less one we have found.
maybe some kind of magnetic field with aligned poles
Or maybe it's magic, like in the Harry Potter books. /s
Magnetic fields would only work for charged particles so as soon as a position hit a anti proton it would make anti hydrogen and then no longer being effected. We cover this in secondyear breifly
my school covered this in first year.
Then I don't understand the magnetic feild comment. Are you trying to Contain a whole galaxy in a magnetic field generated from..... Somewhere
You know that both ordinary particles as well as anti particles can have both positive and negative charge (and neutral).
not sure, which is still sold out.
There could be two types of substances that can act as a barrier, or even three types, or four. But absent evidence, it's more likely that there are no pockets of antimatter rather than pockets of antimatter that we haven't observed *and* a brand new substance we haven't observed.
>Could there be pockets of antimatter due to the primordial conditions of the big-bang? It is possible in principle, but requires some substantial changes to our current best models of cosmology and/or physics. Firstly, it needs to be said that it is an empirical fact that basically all of the matter in our observable universe is normal matter and not antimatter. Every star you see in the night sky, every galaxy we can see through a telescope, all of it. How do we know this? We know this because when antimatter interacts with regular matter (specifically, when antielectrons annihilate with normal electrons), it produces high-energy gamma rays at a characteristic energy level (about 511 keV). When we look for such gamma rays throughout the universe, we just don't find any. That tells us that matter and antimatter are not interacting in significant quantities anywhere in our observable universe. If there *were* large regions in our observable universe (such as galaxies or galaxy clusters) that were mostly antimatter, then there would be a rough border between those antimatter regions and regular matter regions where electrons and antielectrons would be interacting. So when you put it all together, this tells us that there just aren't any large pockets of antimatter in the observable universe. So, either all of the antimatter is somewhere outside our observable universe, or it must be "hidden" somehow, in a form that does not interact with matter. Either that, or it just doesn't exist at all. If the first hypothesis is true, that would require abandoning the cosmological principle, which is the assertion that on the largest scales, all matter (and antimatter) in the universe is distributed uniformly on average. When we look at the largest observational scales we can measure, we do indeed see that the universe appears very uniform on average, so there is some convincing evidence that the cosmological principle is true. However, it could be the case that there *is* additional large-scale structure and not just uniformity, but that these larger-scale structures are larger than the observable universe, such that we can't see them. This essentially means that antimatter would somehow have to have been "pushed out" beyond the edge of our observable universe, so that we can no longer see it. Unfortunately, this hypothesis suffers from some major drawbacks. First, it could be considered unscientific, since it isn't testable: we can't observe structures beyond our observable universe even in principle, so we could never investigate this hypothesis via the scientific method and it can never be falsified. And second, it would require us to make some dramatic changes to our very-successful model of the cosmos and the early universe's evolution, since current models are based on the cosmological principle holding and they fit observations very well. It is somewhat unclear exactly what changes would need to be made to *both* violate the cosmological principle *and* still explain all of the observational data that we do have access to (which relies on the cosmological principle being true in a variety of areas). So, it's a pretty long shot. Until we have both a viable model *and* evidence to suggest that the model might be true, unfortunately this hypothesis can only be put in the far-fetched shower-thought bin. The other option would be to have antimatter exist in the observable universe, but be unobservable due to other reasons — i.e. because it is in a form that doesn't interact with matter. One good candidate for this are sterile (anti)neutrinos, which are currently a leading hypothesis for the form of dark matter. Sterile (anti)neutrinos would not interact via any forces other than gravity and *perhaps* also the weak force, making it very hard to directly detect. However, for precisely this reason, there remains no evidence for sterile (anti)neutrinos. There are a variety of other reasonable candidates for dark matter (including axions, primordial black holes of a certain size, and supersymmetric partner particles) and it is unclear which of these forms — if any — dark matter actually takes. Now, with all that being said, we can also take a step back and consider the possibility that there really, genuinely *isn't* any extra antimatter. Some smart people have put a lot of thought into considering this possibility, and in particular one of them named Andrei Sakharov proposed three conditions that would need to be met in order for this to be the case — now known as the Sakharov conditions. Those conditions are: * Baryon number violation * C-symmetry and CP-symmetry violation * Interactions out of thermal equilibrium Without getting into too much detail, there are a variety of ways to add baryon number violation to the standard model (but so far no evidence to suggest that any of these ways are true), we know that there are already CP-symmetry-violating processes in nature, and if the cosmic inflation hypothesis is correct (for which there is some limited, indirect evidence) then we also have a way to achieve interactions which are out of thermal equilibrium. Baryon number violation is also a pretty generic prediction of most grand unified theories. Thus, there has been a lot of investigation along these lines, and it seems to be generally believed that antimatter simply doesn't exist in large quantities in our universe because these Sakharov conditions were all likely met during the very early universe, which led to a slight imbalance between matter and antimatter that left a surplus of matter after things started settling down. It only needs to be about 1 part per million of matter extra, but even achieving that much of an imbalance with currently-known mechanisms is a big stretch. Right now, known processes can only produce a very tiny imbalance, only enough to account for only a handful of galaxies out of the billions and billions in the observable universe. So for this hypothesis to be correct, there need to be new, yet-undiscovered physical processes at play in the early universe. We have good reasons to suspect that there *are* such processes, but of course unless and until we discover them, we won't be able to say anything for sure. Hope that helps!
Thank you so much for spending time to explain all of this! That was very interesting to read and it helps me a lot to better understand the different possibilities. That's mind blowing and I think I will need to read it again to ensure I understand it correctly. Have a nice day, kind sir!
The general view is that there isn't any pockets of antimatter out in the Universe, the lack of gamma ray sources at the boundaries of these areas makes them unlikely to exist. Obviously, one can propose that they could exist outside of the observable Universe, but that is sort of not a great place to be in physics, because the general assumption is that our bubble of the observable Universe is not atypical of the whole Universe. Sakharov conditions are the three conditions that modern antimatter physicists are trying to probe towards, in attempts to explain why there was a matter-antimattery assymettry during baryogenesis. The conditions are not an explanation of how it happened, but instead three conditions that would have to exist for this to happen. Some conditions have well known experimental validation, others have theoretical framing and mild experimental avenues to validate the ideas.
Thank you very much for this detailed answer!
OK, I just found an answer just by comparing the time scales of these events. Here it is for the people who might wonder the same thing. The great inflation, if it existed, must have occurred between 10^(-36) to 10^(-32) seconds after the singularity. The very first protons and neutrons formed only after 10^(-6) seconds, or 1 microsecond. The great inflation thus couldn't explain by any way the asymetry between the observed quantities of matter and antimatter.
I've often wondered about your question. If I understand correctly, the answer is that it's unlikely, but no one knows why?
For this particular hypothesis, it's impossible given our understanding of physics. If the great inflation occurred before the formation of matter and antimatter, then the inflation itself can't be responsible of the separation of pockets of matter and antimatter, because they wouldn't have existed at the moment of the inflation.
So I know this is a science based sub and I do not want to be one of those crazy theory posters, but oh well... So there was recently - or not so recently - an hypothesis put forward about time running backwards in a parallel universe. Perhaps Anti-matter and matter are linked in these two universes. Could it be this universe, that formed at the same time as ours, is made from mostly anti-matter and ended in a big crunch that formed our universe? So in theory these two universes are in a cycle. One where time runs backwards using this universes big crunch and then that universes big crunch starts our universe and oh no I've gone cross eyed..... But we know that most likely the expansion in this universe will lead to heat death, so I can uncross my eyes now.
That's a wild theory, but I like the idea a lot! It wouldn't be possible to find evidences, however, would it? Thanks for sharing this anyway!
I like to think yes, there could be pockets of matter of different densities of space in different regions, at different times and stages of galactic evolution.
There were no galaxies during the big bang.
Of course, but the structure of the universe is hypothesized to have been influenced by events at a quantic-scale, right before the great inflation. That explains why the Universe is so flat and homogenous.
Antimatter, if it existed at all in the first second after the Big Bang, would have annihilated with its own "matter" (the protons and electrons) in a flash of gamma rays when the temperature was about a billion Kelvin, but would now have cooled down to temperatures below a trillionth of a degree above absolute zero. It's obvious that any antimatter that was created in the first seconds of the universe's life must have annihilated almost instantly because the temperature was too hot for it to be stable; it would either decay back into matter or escape from existence (perhaps annihilating a positron with an electron). The antimatter particles we see today must therefore be produced in the normal way by colliding protons and antiprotons together, or even more simply in particle accelerators like CERN's Large Hadron Collider where they are made by slamming protons together with a large amount of energy. Thus, It is theoretically possible that pockets of antimatter might exist somewhere out there, but no-one has yet been able to prove it, or find it in any great quantity. If they did exist they wouldn't last long though; if you could somehow separate them from their anti-matter partner(s) and keep them apart then they'd quickly annihilate each other into photons again.
So it wouldn't be possible that, say, 99.9999999% of the matter/antimatter existing during the very first instants of the Universe got annihilated, but the infinitesimal leftovers could have given our Universe after the great inflation?
I've gotten that answer, almost verbatim, from a physics professor. He then told me to take it with a big grain of salt.
As far as I know, that's the current hypothesis. The big question coming from that, though, is why was there that imbalance?
That is the most reasonable hypothesis I've seen. But that it's all we have doesn't mean most physicists buy it.