A detector at the Large Hadron Collider dedicated to resolving why our Universe is made of matter rather than antimatter has released new results.

The LHCb experiment has for the first time observed decays of particles known as Bs mesons that preferentially end up as matter, rather than antimatter.

However, the difference is still not enough to explain the preponderance of matter over antimatter in the cosmos.

The work, published online, has been submitted to Physical Review Letters.

Every member of the zoo of particles we know about has an antimatter cousin, identical in every way except for an opposite electric charge - the electrons and protons that in part make us up have positrons and antiprotons as their antimatter matches.

The current theory for how the Universe got its start holds that equal amounts of matter and antimatter were initially created. But whenever the two meet, they destroy each other in a flash of light.

Simply put, the Universe should have come to a blazing end just then. Something must have made for a slight excess of matter in order to lead to the matter-dominated Universe we see today.

Continues here.

I have a silly question relating to this, maybe someone can edumacate me?

If a distant star, or even galaxy, were made of anti-matter, could we tell from the light? Is it even possible for a cloud of antihydrogen to collapse and initiate fusion, creating antihelium? Would it live and die in the same way, choked to death by anti-iron, or collapse into neutron stars or whatever? Would the light be different in some way?

If it is possible to have anti-stars and anti-galaxies, presumably gravity would act on them in the same way, possibly slamming an anti-galaxy into a galaxy. What sort of energy release would that generate, something easily observable I would have thought.

Thoughts?

Antimatter is the same as matter except that the charges on the particles are the other way round. So, as you say, it responds to gravity in the same way as matter, and the energy it emits looks the same as the energy emitted by matter. Consequently

- you can't tell from the light (unless there is something that I don't know about, which is always possible!), and

- two galaxies composed entirely of antimatter and of matter respectively could well be attracted to each other by their gravity, in which case we would see the same annihilation of particles and anti-particles that we see on Earth (e.g. when cosmic rays enter the Earth's atmosphere), but on a somewhat grander scale!

The problem with this scenario is that, if there is a mechanism which has caused a net surplus of matter in our local environment in the universe (with effectively all the antimatter having disappeared by mutual annihilation with matter), it's hard to see why the opposite mechanism would have applied elsewhere in the universe. Without such a reason, the natural assumption is that mutual annihilation has caused a net matter surplus everywhere in the universe.

Even by dint of looking billions of years back in time through the strongest telescopes, we're not going to succeed in observing the universe before the process of matter-antimatter annihilation was finished. The furthest we can look back is the last scattering surface about 300,000 years in (and what we see there is the cosmic microwave background radiation), whereas the mutual annihilation of particles and anti-particles would have been effectively over in the first second or so after the Big Bang.

Evolving wrote:Antimatter is the same as matter except that the charges on the particles are the other way round. So, as you say, it responds to gravity in the same way as matter, and the energy it emits looks the same as the energy emitted by matter. Consequently

- you can't tell from the light (unless there is something that I don't know about, which is always possible!), and

- two galaxies composed entirely of antimatter and of matter respectively could well be attracted to each other by their gravity, in which case we would see the same annihilation of particles and anti-particles that we see on Earth (e.g. when cosmic rays enter the Earth's atmosphere), but on a somewhat grander scale!

The problem with this scenario is that, if there is a mechanism which has caused a net surplus of matter in our local environment in the universe (with effectively all the antimatter having disappeared by mutual annihilation with matter), it's hard to see why the opposite mechanism would have applied elsewhere in the universe. Without such a reason, the natural assumption is that mutual annihilation has caused a net matter surplus everywhere in the universe.

If we are completely unable to distinguish how many, if any at all, of the galaxies and stars visible in the night sky are formed of antimatter, then we cannot know anything about the preponderance of matter versus antimatter in the universe, I would have thought. Would it be true to say that our solar system represents the only matter we have any kind of certainty about? Presumably everything else could be made of antimatter and we would be blissfully unaware.

Evolving wrote:Even by dint of looking billions of years back in time through the strongest telescopes, we're not going to succeed in observing the universe before the process of matter-antimatter annihilation was finished. The furthest we can look back is the last scattering surface about 300,000 years in (and what we see there is the cosmic microwave background radiation), whereas the mutual annihilation of particles and anti-particles would have been effectively over in the first second or so after the Big Bang.

If you are saying that the process of annihilation is over, then you are saying that there are no antimatter stars, are you not?

I mentioned a few possibilities in my answer here:

http://physics.stackexchange.com/questions/56355/antimatter-in-the-universe

twistor wrote in that other place:

However, there are some possibilities to look for the signature of photons that would be produced in large matter/antimatter annihilations

Yes, I was about to write (before I was rudely interrupted here by someone wanting me to do some work!) that if we had some regions in space that consisted of matter and others that consisted of anti-matter, they would presumably meet at the edges from time to time - especially if they were contained in the same galaxy - and we would therefore be able to observe gamma radiation from the resulting annihilation. So the fact that we don't observe that radiation suggests that any such regions must be separated from one another by a large void.

The polarisation idea is intriguing.

trubble76 wrote:

Evolving wrote:Even by dint of looking billions of years back in time through the strongest telescopes, we're not going to succeed in observing the universe before the process of matter-antimatter annihilation was finished. The furthest we can look back is the last scattering surface about 300,000 years in (and what we see there is the cosmic microwave background radiation), whereas the mutual annihilation of particles and anti-particles would have been effectively over in the first second or so after the Big Bang.

If you are saying that the process of annihilation is over, then you are saying that there are no antimatter stars, are you not?

Yes, and I was conscious when typing it that I was begging a question in doing so, or at least giving an incomplete reply.

The answer to that begged question is what I wrote in my first response:

it's hard to see why the opposite mechanism would have applied elsewhere in the universe

.

In other words, for the annihilation not to have been over everywhere in the first second, there would have to have been regions in which the annihilation produced a net anti-matter surplus by the end of that second, alongside the regions with the familiar matter surplus, and then the expansion of the universe would have to have happened too quickly for those regions to encounter each other.

Theoretically possible, in principle, but as I said: hard to see why it would happen.

twistor59 wrote:I mentioned a few possibilities in my answer here:

http://physics.stackexchange.com/questions/56355/antimatter-in-the-universe

So we can differentiate photons from antimatter sources by their polarity? So then we know that all the stars we can see are made of matter?

Evolving wrote:

trubble76 wrote:

Evolving wrote:Even by dint of looking billions of years back in time through the strongest telescopes, we're not going to succeed in observing the universe before the process of matter-antimatter annihilation was finished. The furthest we can look back is the last scattering surface about 300,000 years in (and what we see there is the cosmic microwave background radiation), whereas the mutual annihilation of particles and anti-particles would have been effectively over in the first second or so after the Big Bang.

If you are saying that the process of annihilation is over, then you are saying that there are no antimatter stars, are you not?

Yes, and I was conscious when typing it that I was begging a question in doing so, or at least giving an incomplete reply.

The answer to that begged question is what I wrote in my first response:

it's hard to see why the opposite mechanism would have applied elsewhere in the universe

.

In other words, for the annihilation not to have been over everywhere in the first second, there would have to have been regions in which the annihilation produced a net anti-matter surplus by the end of that second, alongside the regions with the familiar matter surplus, and then the expansion of the universe would have to have happened too quickly for those regions to encounter each other.

Theoretically possible, in principle, but as I said: hard to see why it would happen.

I must admit that I am not very satisfied with your answer, no offence intended. You seem to be saying you're pretty sure that there's no antimatter out there so we shouldn't bother looking.

No, no, that's not what I'm saying at all! On the contrary: people have been looking, and nothing indicating regions composed of antimatter has been observed.

The fact remains that it is a puzzle as to why almost all we seem to see is matter, because experimentally we see that matter and anti-matter are always created in exactly equal quantities. That suggests that, either that didn't apply at the Big Bang, or it did apply, but all the anti-matter is somewhere else: perhaps outside the observable universe.

My point, such as it was, about that first second and the differing regions referred to the fact that we would have had to have significant inhomogeneity in the material filling the universe in that first second, and it is hard to see why that material wouldn't have been, on the contrary, rather uniform.

it remains a puzzle.

trubble76 wrote:

twistor59 wrote:I mentioned a few possibilities in my answer here:

http://physics.stackexchange.com/questions/56355/antimatter-in-the-universe

So we can differentiate photons from antimatter sources by their polarity? So then we know that all the stars we can see are made of matter?

Unfortunately it's not quite as simple as that. The paper twistor quotes writes (among other things):

During normal star processes, the photons lose the initial polarization state while
diffusing out of the star, but during a supernova explosion the photons produced by the
56Ni decay chain could be detectible.

So apparently it might be possible to identify a region of anti-matter if we are able to observe a supernova explosion in that region. It seems quite speculative, however, though intriguing.

Evolving wrote:No, no, that's not what I'm saying at all! On the contrary: people have been looking, and nothing indicating regions composed of antimatter has been observed.

The fact remains that it is a puzzle as to why almost all we seem to see is matter, because experimentally we see that matter and anti-matter are always created in exactly equal quantities. That suggests that, either that didn't apply at the Big Bang, or it did apply, but all the anti-matter is somewhere else: perhaps outside the observable universe.

My point, such as it was, about that first second and the differing regions referred to the fact that we would have had to have significant inhomogeneity in the material filling the universe in that first second, and it is hard to see why that material wouldn't have been, on the contrary, rather uniform.

it remains a puzzle.

But why is it considered a puzzle that we don't observe antimatter when it seems we only have an incredibly tenuous and unproven method of observing it?

We know that there is no significant amount of anti-matter in regions that are in contact with other regions, because we would see gamma radiation at the edges of those regions when they encountered each other. Since we don't, the conclusion must be that any regions of anti-matter must be separated by a void from regions of matter.

Bear in mind that not only interstellar but also intergalactic space is generally far from empty.

The idea of using the polarisation of light emitted by a particular reaction during a supernova explosion would be relevant (if it indeed works) to test regions that are separated by a void, to see whether they perhaps consist of anti-matter.

Evolving wrote:We know that there is no significant amount of anti-matter in regions that are in contact with other regions, because we would see gamma radiation at the edges of those regions when they encountered each other. Since we don't, the conclusion must be that any regions of anti-matter must be separated by a void from regions of matter.

Bear in mind that not only interstellar but also intergalactic space is generally far from empty.

The idea of using the polarisation of light emitted by a particular reaction during a supernova explosion would be relevant (if it indeed works) to test regions that are separated by a void, to see whether they perhaps consist of anti-matter.

Okay, so in reality we know how to spot antimatter/matter collisions in most cases and we don't see any. We therefore know that most of the universe is devoid of antimatter because we know everything we can see is matter. There can't be antigalaxies because no galaxies are sufficiently separated from other galaxies, meaning they would annihilate and we would see it.

Am I getting there? I must admit, I'm not sure I understand it fully.

I'm not sure that anyone has systematically sifted through the observable universe for signs of the radiation that would occur if regions of matter and anti-matter encountered one another, and it may well be that there are regions which are sufficiently isolated from our part of the universe and which therefore might, for all we can tell, consist of anti-matter.

What we can say is the negative result, that no such radiation has hitherto been observed, so that we can certainly be pretty sure that our Local Cluster (the cluster of galaxies which contains our Milky Way) is matter rather than anti-matter, and with rather less certainty I suspect we can say the same about other clusters.

Actually one thing that does occur to me is that, if there were indeed, after the Big Bang, regions of matter and other regions of anti-matter which separated from one another as the universe expanded, then the mutual annihilation at their edges in the past would tend to have created just such a void as we are requiring now to account for the absence of observed annihilation today. (Bearing in mind that "today", in astronomy, can mean an awfully long time ago for distant galaxies.)

trubble76 wrote:
Am I getting there?

Yes!

A question that hasn't been empirically answered yet is the gravitational interaction of anti matter. It turns out to be fairly difficult to test.

http://en.wikipedia.org/wiki/Gravitatio ... antimatter

That's an interesting link, klazmon. Setting out the various possibilities that exist, logically, in the absence of direct experimental evidence - and that absence is exactly what one would expect, since the antimatter we can observe with certainty is so rare and so short-lived, and gravity has such weak effects compared with electromagnetism, when we are looking at individual particles.

Similarly the link that twistor provided is fascinating for setting out the various ways in which one might conceive of detecting regions of antimatter.

Wikipedia wrote:

the overwhelming consensus among physicists is that antimatter will attract both matter and antimatter at the same rate that matter attracts matter

Indeed: what I have been saying in this thread is academic orthodoxy, i.e. the stuff that I do exams in! Academic orthodoxy has been wrong before.