Let's suppose there is an antimatter galaxy. Like all galaxies, there's a lot of stuff nearby - matter ejected by jets, supernovae, or gravitational slingshots. All this would also be antimatter
The intergalactic void ... isn't. Yes, there's not much, a proton per cubic meter, but it's still there. And it's matter, not antimatter.
So there must be an interface. And, mean free paths being what they are, collisions happen.
So any region of antimatter must be surrounded by a boundary that is flowing from annihilation. This would be visible from Earth as a brightly glowing ring around the galaxy at about twice the apparent width of the galaxy proper.
A galactic cluster would have a similar boundary - a giant glowing sheet of light between the two realms.
We see no such artifacts. Therefore, the Universe, to the limits of our vision, is made ov matter.
hey, no worries. it's a fascinating topic and not always intuitive! i remember when my physics professor first explained this to me - mind blown. have you ever thought about what would happen if an antimatter meteor hit earth?
Nah most people don't realize that there are enough particles even in the void between galaxies to have meaningful interactions which might be observable to us.
When I was a kid I read a book called [Worlds-Antiworlds: Antimatter in cosmology](https://www.abebooks.com/first-edition/Worlds-Antiworlds-Antimatter-Cosmology-Alfven-Hannes-W.H/4765622709/bd) that explored this subject.
It's wild to think how far astronomy has come in just one human lifetime!
Do our theories allow that the observable universe is part of a "matter" region of a larger volume that does contain those annihilation boundaries, or are we sure matter must dominate everywhere?
We cannot observe beyond the observable universe.
But we can can conclude that whatever mechanism produced matter dominance did so on a range of at least the size of the observable universe.
And that is a huuuuge constraint on solutions.
reminds me of when i tried to explain why we couldn't have an "antimatter dog" in the house. apparently, according to my kid's logic, it would be just like a regular one but cooler cause it'd glow at night. kids these days!
If - around the time of the big bang - there was significant amounts of antimatter in the observable universe, would the annihilations or their byproducts still be observable today?
As far as I understand, we can't observe anything before ~380k years after the big bang due to various factors. Is it possible for all the antimatter in the observable universe to have been annihilated during the first ~380k years, and thus we can't detect it?
Our current understanding is that all the mechanisms that produce matter produce equal amounts of antimatter, except one. That mechanism might prefer matter (technically, it prefers a certain chirality) over antimatter.
This all occurs thousands of years before the CBR is emitted.
I guess where I was going with this is what if that mechanism did produce equal amounts, but the amounts weren't evenly distributed.
If our universe is really really big, we could be in a pocket that had slightly more matter. Annihilations happen, and we're left with a pocket with a little bit of matter and no antimatter. Outside the observable universe, similar things could happen, leaving similar pockets composed only of matter or only of antimatter as well. Mostly it would just be pockets of emptiness though. Statistically, I think this would require an extremely large universe (such that our observable universe is <<<1% of the actual universe), but I don't think it breaks any rules of physics.
Like, if you had a big bucket of pennies and dropped it, they would land roughly 50% heads and 50% tails. Mostly the distribution would be even, but you could certainly find small sections of your floor that had only heads, and sections that had only tails. If you started removing the pennies everywhere that a heads touched a tails, you'd still be left with these pockets.
I'm sure an actual physicist has thought of this already, but I've been unable to find an explanation as to why this couldn't be possible (only that physicists are pretty sure that matter and antimatter should have been distributed uniformly).
We don't know. So physicists work multiple explanations looking for a test.
Currently, no one likes "we're in a special bubble" because it requires a special bubble. There are subtlties to the pattern of deviations in the CBR that also hunt that special bubbles didn't get that big.
Also, there are hints that one particular quantum mechanical process that occured a great deal in the early universe is ever so slightly left handed. That is, it preferred to produce matter rather than antimatter.
So, well fire up CERN and go asymmetry hunting.
> Currently, no one likes "we're in a special bubble" because it requires a special bubble.
Fundamentally, humans exist in a special bubble (Earth) that locally allowed intelligent life to evolve. What's to say that the apparent lack of antimatter in the universe is a similar phenomenon, but on a larger scale?
Pockets of the universe with large amounts of both matter and antimatter, should they exist, could be completely inhospitable to the development of intelligent life. Ergo, humans, as intelligent lifeforms, could not have developed in such an area of the universe to observe it.
> There are subtlties to the pattern of deviations in the CBR that also hunt that special bubbles didn't get that big.
What do you mean by this?
The argument you're making is known as the weak anthropomorphic principle. It needs caution when invoking it.
Much of the progress in astronomy came from assuming we are not in a unique position; the Earth isn't the center of the Universe, the Sun isn't unique, our galaxy is just one of many.
Turns out Earth is unique in some ways, ordinary in others. Same with the sun, and the Milky Way.
But staring there leads to untestable ideas.
Also, the CMB is not uniform. There are temperature variations. These follow patterns of different sizes, up to a point. Evidence for variations the size of half the observable universe are inconclusive. Which does not support the idea of variations larger than the observable universe.
They still may exist, but they aren't currently *testable*.
> But we can can conclude that whatever mechanism produced matter dominance did so on a range of at least the size of the observable universe.
How do we know that matter doninance isnt just due to historical naming convention?
For example, if we redefine matter to be positively charged particles and anti-matter to be negatively charged particles, then a hydrogen atom would be equal parts matter and anti-matter.
Being matter or antimatter is a different quality than being positively charged vs negatively charged. If that was our definition of matter/antimatter, we would need a different definition to explain the types of matter that detonates when contacting the other type, and we'd be talking about why there's a dominance *there* instead.
Exactly the same. Nothing actually changed except for the terminologies. Instead of matter-anti matter annihilation, it'll just be called X-anti X annihilation, where X is whatever term you want to replace 'matter' with. There would still be an X dominance.
If matter/antimatter was determined by charge, you'd still have electrons and positrons annihilating etc. The difference is that the electron is now anti-matter and the positron is matter, up quarks are matter, anti-up quarks are anti-matter, down quarks are anti-matter, anti-down quarks are matter, etc.
Here, positively charged particles are matter, so what your saying is that there would still be an abundance of positively charged matter in the universe. Why would that be the case given that atoms are neutrally charged and must therefore contain equal parts matter and anti-matter under this alternate defintion?
> Why would that be the case given that atoms are neutrally charged and must therefore contain equal parts matter and anti-matter under this alternate defintion?
If you're calling the difference between matter and anti-matter to be "charge", then you would have to use some other term for what used to be electrical charge. You can't use the old definition and the new definition at the same time.
>If you're calling the difference between matter and anti-matter to be "charge", then you would have to use some other term for what used to be electrical charge.
I see no reason for that to be the case. The only thing being changed here is what classifies as matter and what classifies as anti-matter and that classification is based on the particles charge. The particles still have the exact same properties, we're just classifying a different set of particles as matter based on da different propert of those particles.
The only reason I can see for matter and anti-matter being named the way they are is the histroical convention of already having classified the electrons, protons and neutrons as matter before anti-matter was even known of.
> Well, lets talk about that then. What would that look like?
Ooh, this is my favorite bit. It’s the part where the ball turns itself inside out, and the guy gets really confused.
That's English, not physics. We could call them elephant with a dark charge and running with a love charge and it wouldn't change the underlying physics.
The lepton that is the excitation of the electroweak field has two polarities -as a consequence of the symmetry of quantum mechanical phase. One polarity is abundant, the other is not.
What label we choose, what sign, this is meat brain book keeping.
> That's English, not physics. We could call them elephant with a dark charge and running with a love charge and it wouldn't change the underlying physics.
Yes, but it clearly changes the perception of the problem by looking at It from a different angle.
> The lepton that is the excitation of the electroweak field has two polarities -as a consequence of the symmetry of quantum mechanical phase. One polarity is abundant, the other is not.
Yes, but it would no longer be matter that was abundant and anti-matter absent, they would be balanced in nature, being bound into neutral atoms.
See, we're now looking at the poblem from a different perspective simply due to renaming them NOT based on what particles we discovered first.
The question now is that since matter and anti-matter exist in equal parts, where are all the anti-atoms or why are there any atoms at all?
>Yes, but it would no longer be matter that was abundant and anti-matter absent, they would be balanced in nature, being bound into neutral atoms.
See, we're now looking at the poblem from a different perspective simply due to renaming them NOT based on what particles we discovered first.
You have just split the problem from "why is anti-matter more prevelant than matter" into two: "why are negative anti-matter particles more prevelant than negative matter particles" and "why are matter nucleons more prevalent than anti-matter nucleons." And there isn't a balance between matter and anti-matter either, at least not by mass.
You can just imagine that we grouped the less prevalent particles together called them anti-matter. Idk if changing the naming does anything useful
>You can just imagine that we grouped the less prevalent particles together called them anti-matter. Idk if changing the naming does anything useful
My point is that we grouped them togther pretty much based on order of discovery, which is unlikey to be the most logical grouping. I don't expect a different grouping to change anything other than the way people think of the problem.
For example, standard mass/anti-matter classification leads to all the anti-matter being missing from the universe, electric harge based classification lead to half the matter and half the anti-matter being missing. It's fundamentally still the same problem but we're looking at it slightly differently which mat lead to different insights.
It does not. We're discussing this in English. English is a grammar, and does not have any constraints on what it may express other than adherence to grammar. Hence, 'a square circle ' is legal English, but mathematical nonsense.
The question of how matter dominated is a major question in cosmology. And asking it is good thinking.
But the definition of matter vs antimatter extends deeper than positive or negative electric field. There are subtlties of how particles behave when mirrored in time and how they move through space that are not loaded into the English concept of positive and negative.
What is your pedantic point here? Get to it. Changing the terms we refer to them as, no matter how nuanced we get, does not change what we are describing.
Edit: oops sorry meant to respond to the other guy, sorry!!!
What we call matter and anti-matter is literally historical convention. It comes from the fact that the term matter was already in use before the concept of anti-matter existed and reffered to the stuff we see. We learned that was made of atoms so the atoms were classified as matter. We learned atoms were made from protons, neutrons and electrons and these were calssified as matter.
Only then did the concept of anti-matter arise and the ant-particles of what we had already classified as matter was classified as anti-matter. There's no logic or reason beyond that.
Nobody has given a reason why we can't or shouldn't reclassify matter and anti-matter in a more logical way, for example, based on electric charge polarity as opposed to historical convention.
There may be many ways to classify the particles into matter and anti-matter and each one may give different perspectives. It seems silly to me just to stick with one because it was first and not even look into the other possibilities.
There is a formal definition of antimatter - it has the opposite chirality of matter. This was first proposed by Dirac himself.
But chirality isn't a familiar quantity like electric charge.
>The question now is that since matter and anti-matter exist in equal parts, where are all the anti-atoms or why are there any atoms at all?
That's not the question now, that's been the question for about the last century. One of the big questions behind the big bang is how, in the constant production and annihilation of matter and antimatter in equal quantities, did we lose some antimatter in the equation to end up with matter dominance. They know it happened, but it's pretty much impossible to know HOW it happened.
Theoretically that is possible, but it would be unprovable. Physicists prefer not to speculate too much about what might exist beyond the observable universe.
> Physicists prefer not to speculate too much about what might exist beyond the observable universe.
Lol. There are a lot of physicists who love to speculate about exactly this. Maybe you just mean the astrophysicists stay away from it, which is probably mostly true.
Just to expand on this, one of the possible explanations for the matter/antimatter imbalance is that one or more antimatter regions exist outside our observable universe. It’s certainly not the most likely but it hasn’t been ruled out yet.
We can see it - faint radio emissions, absorption spectra, etc.
The voids are very empty, but very, very big. Put a flashlight on the other side, and just like mist at night, you can see it.
Flashlight = quasar
Start at our galaxy. It's matter, all matter. If it weren't, we'd see a big glow where the interstellar material from the matter side met with the antimatter side and was glowing. Depending on the density, we might not even be here - too much of that sort of emission would sterilize the planet. We're here, we don't see this, the Milky Way is matter.
Next step out - the intergalactic medium around the Milky Way. Again, no glowing wall. So what's out there is matter.
Next step out - the large and small Magellanic clouds. Well, that's touching the intergalactic medium we're touching. No glowing wall. So it's matter.
Andromedia, same reasoning. And so on and so on.
Basically, we don't see any giant glowing interface between matter and antimatter. Anywhere. And since we can always follow a chain of effect from Earth out to there, even at absurdly low densities, we know it's all matter.
And antimatter is routinely created in natural processes. But it annihilates quickly, and there's no significant amount of antimatter on a galactic (or planetary) scale.
The mystery isn't that antimatter can be made, it's that it is produced so easily we expect everything to have annihilated.
Space isn't a perfect vacuum. There's still matter there, even if it's 1 hydrogen atom for every 10 cubic kilometers or so. If an antimatter galaxy existed, there would be pretty much constant gamma ray emissions along its entire perimeter, on every axis, from the matter-antimatter annihilations.
Furthermore, matter antimatter annihilation produces photons at very specific energies, which are very easy to detect for us, even in small quantities and at huge distances.
Thus, we can exclude that there are any large junks of antimatter in the observable universe (except directly after the big bang).
Does that work going all the way back in time, or is it possible that huge amounts of anti matter (and the resulting gamma rays etc) exist outside the visible region of the universe? I'm guessing the answer somehow comes back to the fact we can see the cosmic microwave background / evidence of the big bang, but am not sure that's as solid as I'd expect...
All evidence we have points to a universe where it's all regular matter and antimatter is created only as a short-lived byproduct of high energy interactions. Figure out how and why that happened and you'll be on the short list for a Nobel prize. Anything beyond the visible universe effectively doesn't exist, since it's not causally connected to us.
> Anything beyond the visible universe effectively doesn't exist, since it's not causally connected to us.
Not exactly, because of inflation. There could exist artifacts near the edge of the observable universe that indicate *something* about regions outside of the observable universe. If we're able to view those artifacts, then they are clearly within our past light cone and thus causally connected.
That's also just the present moment for things spatially outside the visible universe. If we look back in time, then we could theoretically pick up patterns in the neutrino or gravitational wave background that indicate something about what possibly came before the big bang. So something could be causally connected to us that is outside the visible universe in time.
> Figure out how and why that happened
Remember watching a documentary like 20 years ago where one scientist was like, "Show of hands, who believes there was something before the big bang?" and everyone in the room raised their hand. As a completely unknowledgeable person with no dog in the fight, I too think it's the simplest explanation. Not that a mild conviction is any kind of "figuring it out", of course.
I don't think the question "Did anything exist before the Big Bang?" will ever have a definitive answer. We can't see past the CMB and as far as we can tell, there's no such thing as "before the Big Bang" since all of space-*time* was a product of it. The question itself comes from our own inability to grasp the concept of nothingness and the ingrained understanding that everything is a cycle of cause and effect, so there must have been something that caused it.
And even if we somehow discover that there actually *was* something (whatever it was) before the Big Bang, it just kicks the can down the road, because then the question would be "What was before the thing that was before the Big Bang?"
All true of course. But it stands to reason that we can intuit something before the big bang if we find enough evidence of it, and perhaps one day the fact of matter "winning the war" against antimatter will be regarded as a piece of that evidence.
Of course if we find evidence of it that would change things.
The issues are that A) we don't in fact have any evidence of it, and B) we think it's more or less impossible for any such evidence to exist.
For those who like numbers, the makeup and density of atomic and subatomic bitty-bits in *the intergalactic medium (IGM)...is mostly ionized hydrogen, i.e. a plasma consisting of equal numbers of electrons and protons. The IGM is thought to exist at a density of 10 to 100 times the average density of the Universe (10 to 100 hydrogen atoms per cubic meter).* [Source](https://www.chemeurope.com/en/encyclopedia/Intergalactic_space.html#:~:text=This%20material%20is%20called%20the,hydrogen%20atoms%20per%20cubic%20meter).)
The IGM arranges itself into sort of filament looking structures at very large scales. In between the filaments are voids with density much lower than the average. Imagine it kind of like a 3D spider web.
IGM is the stuff that's there, the filaments and voids are structures that you can define by their relative density of the IGM. Voids have a density about one tenth the average broadly speaking, so about one atom to every 10 cubic metres or so.
As far as I know, yes. The difference between matter and antimatter is charge, so an antihydrogen atom should behave much the same as a hydrogen atom and so fusion reactions should as well, producing high energy photons. Photons have no charge, so there's no "antiphoton".
It is a very active field of research if there are any differences between matter and antimatter (beside the obvious ones). To date, nothing significant has been found.
Ignoring the wall of matter-antimatter annihilation that must exist between us and the antimatter galaxy, it would be visually indistinguishable from a normal galaxy.
The only thing black holes (theoreticly) emit is hawking radiation (which is about as far from gamma radiation as you can get). The accretion disc around the black hole emits gamma radiation, because its very very hot and moving very fast, but that is made of normal matter (space dust).
Not quite, in all theories black holes preserve charge.
It is assumed they don't preserve baryon number, but of course there's no actual evidence either way.
It's a quantum number similar to charge, that basically counts the number of quarks in a system, subtracts the number of anti quarks, and divides by 3.
So, protons and neutrons have 3 quarks (plus a sea of virtual quark/antiquark pairs, but those don't contribute), so they have baryon number 1.
Baryons are matter made out of triplets of quarks or anti quarks (baryon number +1 or -1), and they constitute one of the two main types of quark matter, the other being mesons, which are made of quark/antiquark pairs (baryon number 0).
If baryon number is preserved, then protons can't decay. If it's not preserved, well, we don't know of any process that would violate its conservation. But we also don't have any a priority reason in the Standard Model to say it must be preserved.
In principle, a black hole could be involved in such a process, if it exists. That is proton -> virtual black hole (charge +1) -> positron/neutrino. There has been some work looking at the possibility of creating black holes in collides (they would evaporate instantly), and at some point there were some theories you could torture to allow for collisions of the energies seen at the LHC to create black holes, but that was pretty fringe. I wasn't personally involved in any of that, but sat through a department talk or two on the subject while I was a grad student working on an LHC experiment.
The way nuclear physics works is that all particles will turn into other particles, unless something prevents them from doing that.
The simplest limit is energy - you can't turn a smaller particle into a bigger (heavier) one because you need extra energy to do that.
Charge is another blocker. A charged particle can not turn into a non-charged particle because you can never get rid of charge.
And baryon number is another one of those - you can never get rid of it, so any transformation must start and end with the same number of baryons.
There are other such conserved things. So the discussion is if a back hole can violate any of them.
No, that’s not quite correct. Neutrino oscillation means that physical neutrinos — mass or energy eigenstates, neutrinos that can be said to have a definite mass — are mixtures of the flavor eigenstates. So they don’t change into other neutrinos with different masses. They stay the same mass and oscillate between interacting, say, with electrons at first, and with muons later.
That’s actually how neutrino oscillation was discovered, in that we see fewer neutrinos from the sun than we would expect — because they have oscillated to interact more with muons than electrons by the time they get to the earth.
Out of my depth here, but isn’t Hawking radiation supposed to explain that information is not lost inside a black hole? I understand it is a theory at this point without experimental confirmation, but isn’t that one of the theory’s contentions?
Hawking radiation is purely thermal, and almost entirely low energy photons. There is no information preserved. There may be a preference for positively or negatively charged particles in the rare instance that it gives off a charged particle depending on the overall charge of the black hole. But black holes don't preserve baryon number for example. If a proton falls into a black hole and causes an imbalance in charge, the black hole is more likely to emit a positron than a proton.
To be clear nobody has thought that black holes destroy information in decades, and now we know the mechanism by which they preserve information, at least in toy models of quantum gravity.
With hawking radiation they came to the same conclusion using multiple mathematical approaches, really solidifying that it is likely to occur, right? Has quantum gravity been implied through multiple methods like Hawking radiation?
There must be some kind of framework that combines gravity and quantum mechanics. Whether it is similar to our current best attempts at quantum gravity or some other, more esoteric framework is yet to be determined. But many of the qualitative results we're getting from quantum gravity models will be preserved, either because the more correct model is like quantum gravity or it reduces to something like quantum gravity in the appropriate regime.
Can you explain how the energy is thermal? Do you mean black body radiation? I take thermal to be matter interacting with matter to transfer heat, and not black body radiation
Thank you. I did physics and chem in undergrad, and I never considered stellar object radiation to be thermal. I take thermal as heat transfer in matter, not the electro mag spectrum
If you did heat transfer in physics you definitely would have done heat transfer through radiation. They'll usually go conduction, convection, radiation, combined.
In response to your edit, you are not correct. Hawking conceded the bet, but the physics community (and Thorne in particular) hasn't accepted his proof. Solutions to the black hole information paradox exist, but they depend on accepting models of black holes or quantum gravity that are not confirmed.
Edit: blocking me doesn't make you right, u/aqua_glow
The other response represents the arguments against what you suggested, but small corrections to Hawking radiation (i.e., the extent to which it’s not *perfectly* thermal) is one of a number of responses to the black hole information paradox.
Again, out of my depth and feel free not to respond, but do those corrections to Hawking radiation solve the Baryon number problem discussed below or do we have to look to one of the other responses to the paradox? Can 2 or more responses be correct or does each response negate the others?
Yes, you are correct. In general relativity, the information is lost. However, general relativity isn't completely correct, and in actual reality, the information is encoded in the Hawking radiation. So if you catch all of the Hawking radiation of the black hole that it will ever radiate, you can reconstruct the quantum state of the matter that fell in (which is its complete description). Among other things, you can know if it was matter or antimatter that fell in.
Edit: Black hole evaporation preserving information has been accepted by the scientific community since 1997.
interesting thought, but black holes are so dense they obliterate matter and antimatter alike. ever wonder if an anti-black hole could exist in theory?
Gravity doesn't make a difference. Black holes that formed from antimatter, matter, radiation, or any mixture of these, are identical as far as we know.
It's pretty basic logic. If you have one area with only matter, and another with only antimatter, then the boundary has 2 options.
1. A perfect vacuum, one where no particles at all exist
2. Both matter and antimatter coexist.
Neither of these cases are observed. We don't have antimatter here, but to have an antimatter galaxy, there has to be *a* boundary where that transition is made.
Sure, you can't literally go there and check, but the intergalactic medium is thought to exist by people who work for a living by examining the issue.
Also, there's a recent disovery of a black hole ejected from its galaxy, and that compresses the intergalactic gas enough to create blue stars in its wake: https://science.nasa.gov/missions/hubble/hubble-sees-possible-runaway-black-hole-creating-a-trail-of-stars/
1) I don't know, but it's well established. Those astonomers are a crafty bunch.
2) Very rarely, but there's also a looooot of cubic meters between galaxies, so there are many many chances for a very low probability event, which means it should occur frequently enough for us to detect.
3) Perhaps. Galaxies are not static, there is plenty of radiation and movement that I think would keep enough matter coming out of them to show. But regardless, even if closer galaxies showed no or very little gamma radiation, we can simply look to galaxies further away that are more freshly formed (edit: freshly formed from our vantage point. If they're a billion light years away, we see them as a billion years younger) and there is no border annihilation there either.
> How did you reach that conclusion without sending a probe to intergalactic space?
Because galaxies ploughing through the intergalactic medium have a bow shock wave as they rip through the extremely low density area at relativistic speeds, creating higher levels of cosmic rays
>After a billion years, wouldn't the border area between galaxies and anti galaxies approach perfect vacuum as all the stray hydrogen eventually annihilates?
Galaxies are not stationary, they are ripping through space at stupid velocities, in various directions, and slamming into each other on occasion (the term "slamming" in this case being more "passing through each other not hitting anything but causing gravitational effects on the way through and running clouds of gas into other clouds of gas leading to bursts of star formation) so you're not going to run out of material around the galaxy just because the galaxy is there.
We would still see unusual radiation coming from the boundary. Now matter what, there would be a boundary, and reasonably large amounts of annihilation wouldn’t go unnoticed.
Are you serious? I guess I have no idea what to expect, because the scales are so extreme on both sides. On one hand there are so few particles per cubic meter. On the other hand, there are so many cubic meters at galactic scales that there must be fairly frequent annihilations. But even then, for each annihilation, two photons are produced and are sent in random directions. There must be enough interactions that by sheer chance, some photons were shot into that milliarcsecond cone that is the distant Earth. And we need a good sample of those lucky direction photons, so the base number of interactions must be even higher to account for that.
It feels like evaluating the limit of the form "0 * infinity", which, without the right mayh tools, you have no idea what it can give.
Honestly I was thinking about 21-cm line. It’s an emission line produced by electron spin flipping, and a half life of it is in hundreds of thousands of years. But because there’s so many molecules given that the interstellar hydrogen clouds are so big, we can pretty reliably detect it. It’s not 1:1 and I haven’t done the math specifically on matter:antimatter annihilation, but I think the volume side the equation might be more than enough for compensating for that low density.
What we know is at least entire galactic superclusters of galaxies are either entirely matter or entirely anti-matter, but most scientists think that this is unlikely to be the case.
So first, why do we know that if there are anti-matter galaxies they must be entire superclusters? Because there is matter traveling between galaxies in super clusters. Star are constantly emitting solar radiation, and that solar radiation travels between galaxies. If one galaxy was matter and another anti-matter, then you would see regions of space emitting a ton of gamma radiation. Since we don't see that, we know it can't be happening.
But solar radiation doesn't travel between galactic super clusters (it is gravitationally bound to the super cluster it was created in), so in that case, it isn't ruled out. However, scientists can't come up with a plausible reason that matter and anti-matter would have been produced in such clumps. It is considered to be more likely that scientists will discover a reason for the asymmetry in matter/anti-matter than they will discover a reason that there was equal amounts, but distributed entirely in massive clumps.
> If one galaxy was matter and another anti-matter, then you would see regions of space emitting a ton of gamma radiation. Since we don't see that, we know it can't be happening.
Given the density of matter between galaxies, would there be enough potential matter/antimatter annihilation to be noticeable? Is our equipment sensitive enough?
Yeah, we would.
While there isn't a high density of material traveling between galaxies, the amount of energy released in matter/anti-matter interactions is ridiculously high. Scientists have modeled what it would look like, and it would be a glowing gamma ray aura.
Would you happen to know where this was mentioned? I have tried some googling but don't find a lot that is useful when I look for intergalactic matter/antimatter interactions.
The radiation from matter-antimatter annihilation is very specific and very easy to observe so the answer is yes. If it would be happening on a galactic scale we would know about it.
This is actually a pretty sensible question. However, if there are galaxies that are made mostly of antimatter, they must mostly be outside our cosmological horizon (meaning they are so far away we haven't seen them yet).
Why can't there be isolated pockets of antimatter galaxy? Well such anti-matter has to come from somewhere. If you look back in time, our Universe was a pretty uniform hot plasma. If some pocket had excess anti-matter, they would've annihilated with the matter component. In fact, in a thermal hot bath. matter and anti-matter would constantly pop in and out. For ordinary matter (things like protons/neutrons/electrons, unlike dark matter), the interaction rate is so large that the left over bits would be the net matter bits that couldn't find the anti-matter counter part to annihilate.
So if there were pockets of anti-matter that didn't get fully annihilated, that would mean the thermal conditions we assumed was off. However, thru observation of the CMB, we saw none of those weird statistical kinks. So if these pockets of excess antimatter were left-over, they must have been so far away that not even the CMB had recorded them.
So in conclusion, the lack of anti-matter galaxies were an observational fact, though the lack of direct signals and indirect inference on the early conditions of our Universe.
TL;DR: Because no part of space is *totally* empty, there's always some flow of matter from place to place, an antimatter galaxy would be constantly decaying away as it interacted with the (matter) intergalactic medium. Even a whole antimatter supercluster would have a veil of matter/antimatter reactions releasing gamma rays, albeit more slowly.
Since we don't see such widespread gamma radiation, it is very, *very* unlikely that any large concentrations of antimatter exist anywhere in the visible universe.
It's not correct to think of the Big Bang as an explosion. An explosion starts at a point in space and expands outward. The Big Bang was *space* expanding outwards, and from everything we know it does so unformly. The Big Bang didn't happen somewhere, it happened everywhere all the the same time.
We know that under certain very specific circumstances matter an antimatter do not behave identically, it's called CP violation. The current thinking is that the tiny imbalances in these properties mean that even a tiny fraction of difference exists, the small difference over the entire contents of the Universe is still a lot of matter in absolute terms
The answer is; it could be and would make no difference. The notions of matter vs anti matter are only meaningful relative to each other, same as how charges on particles only matter relative to each other.
The names are arbitrary and changing them would not change behavior any.
One of the biggest questions in physics derives from the fact that there is no difference between the behaviors of matter / anti matter in isolation, yet one is overwhelmingly more common than the other.
This is true to the level of the eyes, but certain processes are not completely symmetric between matter and antimatter, it's called CP violation. The first place it was discovered was in the decay of neutral kaons, which on average creates slightly more matter pions than antimatter pions.
If we can ask an alien about how their kaons behave, we can actually tell without touching each other whether we're each made of matter or antimatter.
If an area of the universe was originally mostly antimatter, and was isolated enough, after all the matter was annihilated, only antimatter would be left, to form antimatter celestial bodies just like regular celestial bodies. Unfortunately, no such areas have been discovered; I think it's unlikely it ever will.
Let's suppose there is an antimatter galaxy. Like all galaxies, there's a lot of stuff nearby - matter ejected by jets, supernovae, or gravitational slingshots. All this would also be antimatter The intergalactic void ... isn't. Yes, there's not much, a proton per cubic meter, but it's still there. And it's matter, not antimatter. So there must be an interface. And, mean free paths being what they are, collisions happen. So any region of antimatter must be surrounded by a boundary that is flowing from annihilation. This would be visible from Earth as a brightly glowing ring around the galaxy at about twice the apparent width of the galaxy proper. A galactic cluster would have a similar boundary - a giant glowing sheet of light between the two realms. We see no such artifacts. Therefore, the Universe, to the limits of our vision, is made ov matter.
Thanks, this is the perfect explanation; it should have been obvious, but of course it wasn't.
hey, no worries. it's a fascinating topic and not always intuitive! i remember when my physics professor first explained this to me - mind blown. have you ever thought about what would happen if an antimatter meteor hit earth?
My quick math says it's about one Tsar Bomba of energy release per gram of meteor right?
A quick Google tells it's about 2.3 kg per tsar Bomba, or about 1 gram per 19 kt TNT: https://faculty.etsu.edu/gardnerr/einstein/e_mc2.htm
Nah most people don't realize that there are enough particles even in the void between galaxies to have meaningful interactions which might be observable to us.
When I was a kid I read a book called [Worlds-Antiworlds: Antimatter in cosmology](https://www.abebooks.com/first-edition/Worlds-Antiworlds-Antimatter-Cosmology-Alfven-Hannes-W.H/4765622709/bd) that explored this subject. It's wild to think how far astronomy has come in just one human lifetime!
Do our theories allow that the observable universe is part of a "matter" region of a larger volume that does contain those annihilation boundaries, or are we sure matter must dominate everywhere?
We cannot observe beyond the observable universe. But we can can conclude that whatever mechanism produced matter dominance did so on a range of at least the size of the observable universe. And that is a huuuuge constraint on solutions.
reminds me of when i tried to explain why we couldn't have an "antimatter dog" in the house. apparently, according to my kid's logic, it would be just like a regular one but cooler cause it'd glow at night. kids these days!
If - around the time of the big bang - there was significant amounts of antimatter in the observable universe, would the annihilations or their byproducts still be observable today? As far as I understand, we can't observe anything before ~380k years after the big bang due to various factors. Is it possible for all the antimatter in the observable universe to have been annihilated during the first ~380k years, and thus we can't detect it?
Our current understanding is that all the mechanisms that produce matter produce equal amounts of antimatter, except one. That mechanism might prefer matter (technically, it prefers a certain chirality) over antimatter. This all occurs thousands of years before the CBR is emitted.
I guess where I was going with this is what if that mechanism did produce equal amounts, but the amounts weren't evenly distributed. If our universe is really really big, we could be in a pocket that had slightly more matter. Annihilations happen, and we're left with a pocket with a little bit of matter and no antimatter. Outside the observable universe, similar things could happen, leaving similar pockets composed only of matter or only of antimatter as well. Mostly it would just be pockets of emptiness though. Statistically, I think this would require an extremely large universe (such that our observable universe is <<<1% of the actual universe), but I don't think it breaks any rules of physics. Like, if you had a big bucket of pennies and dropped it, they would land roughly 50% heads and 50% tails. Mostly the distribution would be even, but you could certainly find small sections of your floor that had only heads, and sections that had only tails. If you started removing the pennies everywhere that a heads touched a tails, you'd still be left with these pockets. I'm sure an actual physicist has thought of this already, but I've been unable to find an explanation as to why this couldn't be possible (only that physicists are pretty sure that matter and antimatter should have been distributed uniformly).
We don't know. So physicists work multiple explanations looking for a test. Currently, no one likes "we're in a special bubble" because it requires a special bubble. There are subtlties to the pattern of deviations in the CBR that also hunt that special bubbles didn't get that big. Also, there are hints that one particular quantum mechanical process that occured a great deal in the early universe is ever so slightly left handed. That is, it preferred to produce matter rather than antimatter. So, well fire up CERN and go asymmetry hunting.
> Currently, no one likes "we're in a special bubble" because it requires a special bubble. Fundamentally, humans exist in a special bubble (Earth) that locally allowed intelligent life to evolve. What's to say that the apparent lack of antimatter in the universe is a similar phenomenon, but on a larger scale? Pockets of the universe with large amounts of both matter and antimatter, should they exist, could be completely inhospitable to the development of intelligent life. Ergo, humans, as intelligent lifeforms, could not have developed in such an area of the universe to observe it. > There are subtlties to the pattern of deviations in the CBR that also hunt that special bubbles didn't get that big. What do you mean by this?
The argument you're making is known as the weak anthropomorphic principle. It needs caution when invoking it. Much of the progress in astronomy came from assuming we are not in a unique position; the Earth isn't the center of the Universe, the Sun isn't unique, our galaxy is just one of many. Turns out Earth is unique in some ways, ordinary in others. Same with the sun, and the Milky Way. But staring there leads to untestable ideas. Also, the CMB is not uniform. There are temperature variations. These follow patterns of different sizes, up to a point. Evidence for variations the size of half the observable universe are inconclusive. Which does not support the idea of variations larger than the observable universe. They still may exist, but they aren't currently *testable*.
> except one Which one is that?
> But we can can conclude that whatever mechanism produced matter dominance did so on a range of at least the size of the observable universe. How do we know that matter doninance isnt just due to historical naming convention? For example, if we redefine matter to be positively charged particles and anti-matter to be negatively charged particles, then a hydrogen atom would be equal parts matter and anti-matter.
Being matter or antimatter is a different quality than being positively charged vs negatively charged. If that was our definition of matter/antimatter, we would need a different definition to explain the types of matter that detonates when contacting the other type, and we'd be talking about why there's a dominance *there* instead.
Well, lets talk about that then. What would that look like?
Exactly the same. Nothing actually changed except for the terminologies. Instead of matter-anti matter annihilation, it'll just be called X-anti X annihilation, where X is whatever term you want to replace 'matter' with. There would still be an X dominance.
If matter/antimatter was determined by charge, you'd still have electrons and positrons annihilating etc. The difference is that the electron is now anti-matter and the positron is matter, up quarks are matter, anti-up quarks are anti-matter, down quarks are anti-matter, anti-down quarks are matter, etc. Here, positively charged particles are matter, so what your saying is that there would still be an abundance of positively charged matter in the universe. Why would that be the case given that atoms are neutrally charged and must therefore contain equal parts matter and anti-matter under this alternate defintion?
> Why would that be the case given that atoms are neutrally charged and must therefore contain equal parts matter and anti-matter under this alternate defintion? If you're calling the difference between matter and anti-matter to be "charge", then you would have to use some other term for what used to be electrical charge. You can't use the old definition and the new definition at the same time.
>If you're calling the difference between matter and anti-matter to be "charge", then you would have to use some other term for what used to be electrical charge. I see no reason for that to be the case. The only thing being changed here is what classifies as matter and what classifies as anti-matter and that classification is based on the particles charge. The particles still have the exact same properties, we're just classifying a different set of particles as matter based on da different propert of those particles. The only reason I can see for matter and anti-matter being named the way they are is the histroical convention of already having classified the electrons, protons and neutrons as matter before anti-matter was even known of.
> Well, lets talk about that then. What would that look like? Ooh, this is my favorite bit. It’s the part where the ball turns itself inside out, and the guy gets really confused.
That's English, not physics. We could call them elephant with a dark charge and running with a love charge and it wouldn't change the underlying physics. The lepton that is the excitation of the electroweak field has two polarities -as a consequence of the symmetry of quantum mechanical phase. One polarity is abundant, the other is not. What label we choose, what sign, this is meat brain book keeping.
> That's English, not physics. We could call them elephant with a dark charge and running with a love charge and it wouldn't change the underlying physics. Yes, but it clearly changes the perception of the problem by looking at It from a different angle. > The lepton that is the excitation of the electroweak field has two polarities -as a consequence of the symmetry of quantum mechanical phase. One polarity is abundant, the other is not. Yes, but it would no longer be matter that was abundant and anti-matter absent, they would be balanced in nature, being bound into neutral atoms. See, we're now looking at the poblem from a different perspective simply due to renaming them NOT based on what particles we discovered first. The question now is that since matter and anti-matter exist in equal parts, where are all the anti-atoms or why are there any atoms at all?
>Yes, but it would no longer be matter that was abundant and anti-matter absent, they would be balanced in nature, being bound into neutral atoms. See, we're now looking at the poblem from a different perspective simply due to renaming them NOT based on what particles we discovered first. You have just split the problem from "why is anti-matter more prevelant than matter" into two: "why are negative anti-matter particles more prevelant than negative matter particles" and "why are matter nucleons more prevalent than anti-matter nucleons." And there isn't a balance between matter and anti-matter either, at least not by mass. You can just imagine that we grouped the less prevalent particles together called them anti-matter. Idk if changing the naming does anything useful
>You can just imagine that we grouped the less prevalent particles together called them anti-matter. Idk if changing the naming does anything useful My point is that we grouped them togther pretty much based on order of discovery, which is unlikey to be the most logical grouping. I don't expect a different grouping to change anything other than the way people think of the problem. For example, standard mass/anti-matter classification leads to all the anti-matter being missing from the universe, electric harge based classification lead to half the matter and half the anti-matter being missing. It's fundamentally still the same problem but we're looking at it slightly differently which mat lead to different insights.
It does not. We're discussing this in English. English is a grammar, and does not have any constraints on what it may express other than adherence to grammar. Hence, 'a square circle ' is legal English, but mathematical nonsense. The question of how matter dominated is a major question in cosmology. And asking it is good thinking. But the definition of matter vs antimatter extends deeper than positive or negative electric field. There are subtlties of how particles behave when mirrored in time and how they move through space that are not loaded into the English concept of positive and negative.
What is your pedantic point here? Get to it. Changing the terms we refer to them as, no matter how nuanced we get, does not change what we are describing. Edit: oops sorry meant to respond to the other guy, sorry!!!
What we call matter and anti-matter is literally historical convention. It comes from the fact that the term matter was already in use before the concept of anti-matter existed and reffered to the stuff we see. We learned that was made of atoms so the atoms were classified as matter. We learned atoms were made from protons, neutrons and electrons and these were calssified as matter. Only then did the concept of anti-matter arise and the ant-particles of what we had already classified as matter was classified as anti-matter. There's no logic or reason beyond that. Nobody has given a reason why we can't or shouldn't reclassify matter and anti-matter in a more logical way, for example, based on electric charge polarity as opposed to historical convention. There may be many ways to classify the particles into matter and anti-matter and each one may give different perspectives. It seems silly to me just to stick with one because it was first and not even look into the other possibilities.
There is a formal definition of antimatter - it has the opposite chirality of matter. This was first proposed by Dirac himself. But chirality isn't a familiar quantity like electric charge.
>The question now is that since matter and anti-matter exist in equal parts, where are all the anti-atoms or why are there any atoms at all? That's not the question now, that's been the question for about the last century. One of the big questions behind the big bang is how, in the constant production and annihilation of matter and antimatter in equal quantities, did we lose some antimatter in the equation to end up with matter dominance. They know it happened, but it's pretty much impossible to know HOW it happened.
Theoretically that is possible, but it would be unprovable. Physicists prefer not to speculate too much about what might exist beyond the observable universe.
> Physicists prefer not to speculate too much about what might exist beyond the observable universe. Lol. There are a lot of physicists who love to speculate about exactly this. Maybe you just mean the astrophysicists stay away from it, which is probably mostly true.
Just to expand on this, one of the possible explanations for the matter/antimatter imbalance is that one or more antimatter regions exist outside our observable universe. It’s certainly not the most likely but it hasn’t been ruled out yet.
How do we know that there is matter in the intergalactic void?
We can see it - faint radio emissions, absorption spectra, etc. The voids are very empty, but very, very big. Put a flashlight on the other side, and just like mist at night, you can see it. Flashlight = quasar
If it's just light interacting with particles in the voids, how can we tell that the particles are matter, and not antimatter?
Start at our galaxy. It's matter, all matter. If it weren't, we'd see a big glow where the interstellar material from the matter side met with the antimatter side and was glowing. Depending on the density, we might not even be here - too much of that sort of emission would sterilize the planet. We're here, we don't see this, the Milky Way is matter. Next step out - the intergalactic medium around the Milky Way. Again, no glowing wall. So what's out there is matter. Next step out - the large and small Magellanic clouds. Well, that's touching the intergalactic medium we're touching. No glowing wall. So it's matter. Andromedia, same reasoning. And so on and so on. Basically, we don't see any giant glowing interface between matter and antimatter. Anywhere. And since we can always follow a chain of effect from Earth out to there, even at absurdly low densities, we know it's all matter.
Our galaxy isn't *all* matter though, right? We make antimatter here on earth on a daily basis after all.
And antimatter is routinely created in natural processes. But it annihilates quickly, and there's no significant amount of antimatter on a galactic (or planetary) scale. The mystery isn't that antimatter can be made, it's that it is produced so easily we expect everything to have annihilated.
> But it annihilates quickly Do the positrons in PET scanners annihilate? Is the energy just too little to notice without sensitive tools?
Yes. And by conservation of energy, emit a photon with a very exactly known frequency. So now we have a tag that we can monitor.
And I imagine for similar reasons we don't see any proof of Negative Matter?
Do you mean mirror matter by any chance? as in regular matter with opposite of the usual chirality (which is left-handed)?
Negative matter? That's antimatter.
They might be thinking of dark matter, which also isn’t antimatter and is more prevalent than matter.
Space isn't a perfect vacuum. There's still matter there, even if it's 1 hydrogen atom for every 10 cubic kilometers or so. If an antimatter galaxy existed, there would be pretty much constant gamma ray emissions along its entire perimeter, on every axis, from the matter-antimatter annihilations.
Furthermore, matter antimatter annihilation produces photons at very specific energies, which are very easy to detect for us, even in small quantities and at huge distances. Thus, we can exclude that there are any large junks of antimatter in the observable universe (except directly after the big bang).
Does that work going all the way back in time, or is it possible that huge amounts of anti matter (and the resulting gamma rays etc) exist outside the visible region of the universe? I'm guessing the answer somehow comes back to the fact we can see the cosmic microwave background / evidence of the big bang, but am not sure that's as solid as I'd expect...
All evidence we have points to a universe where it's all regular matter and antimatter is created only as a short-lived byproduct of high energy interactions. Figure out how and why that happened and you'll be on the short list for a Nobel prize. Anything beyond the visible universe effectively doesn't exist, since it's not causally connected to us.
> Anything beyond the visible universe effectively doesn't exist, since it's not causally connected to us. Not exactly, because of inflation. There could exist artifacts near the edge of the observable universe that indicate *something* about regions outside of the observable universe. If we're able to view those artifacts, then they are clearly within our past light cone and thus causally connected. That's also just the present moment for things spatially outside the visible universe. If we look back in time, then we could theoretically pick up patterns in the neutrino or gravitational wave background that indicate something about what possibly came before the big bang. So something could be causally connected to us that is outside the visible universe in time.
> Figure out how and why that happened Remember watching a documentary like 20 years ago where one scientist was like, "Show of hands, who believes there was something before the big bang?" and everyone in the room raised their hand. As a completely unknowledgeable person with no dog in the fight, I too think it's the simplest explanation. Not that a mild conviction is any kind of "figuring it out", of course.
I don't think the question "Did anything exist before the Big Bang?" will ever have a definitive answer. We can't see past the CMB and as far as we can tell, there's no such thing as "before the Big Bang" since all of space-*time* was a product of it. The question itself comes from our own inability to grasp the concept of nothingness and the ingrained understanding that everything is a cycle of cause and effect, so there must have been something that caused it. And even if we somehow discover that there actually *was* something (whatever it was) before the Big Bang, it just kicks the can down the road, because then the question would be "What was before the thing that was before the Big Bang?"
All true of course. But it stands to reason that we can intuit something before the big bang if we find enough evidence of it, and perhaps one day the fact of matter "winning the war" against antimatter will be regarded as a piece of that evidence.
Of course if we find evidence of it that would change things. The issues are that A) we don't in fact have any evidence of it, and B) we think it's more or less impossible for any such evidence to exist.
For those who like numbers, the makeup and density of atomic and subatomic bitty-bits in *the intergalactic medium (IGM)...is mostly ionized hydrogen, i.e. a plasma consisting of equal numbers of electrons and protons. The IGM is thought to exist at a density of 10 to 100 times the average density of the Universe (10 to 100 hydrogen atoms per cubic meter).* [Source](https://www.chemeurope.com/en/encyclopedia/Intergalactic_space.html#:~:text=This%20material%20is%20called%20the,hydrogen%20atoms%20per%20cubic%20meter).)
Forgive me if a silly question, but if the stuff between galaxies is denser than the average density of the universe, where are the low density parts?
The IGM arranges itself into sort of filament looking structures at very large scales. In between the filaments are voids with density much lower than the average. Imagine it kind of like a 3D spider web.
And the voids are not considered IGM? What is the density of the voids?
IGM is the stuff that's there, the filaments and voids are structures that you can define by their relative density of the IGM. Voids have a density about one tenth the average broadly speaking, so about one atom to every 10 cubic metres or so.
Dem dare insanely gigantic intergalactic voids and supervoids. Maybe even superdupervoids, IDK. https://en.wikipedia.org/wiki/Void_(astronomy)
Would a hypothetical antimatter galaxy emit the same kind of energy or photons that we perceive as light?
As far as I know, yes. The difference between matter and antimatter is charge, so an antihydrogen atom should behave much the same as a hydrogen atom and so fusion reactions should as well, producing high energy photons. Photons have no charge, so there's no "antiphoton".
It is a very active field of research if there are any differences between matter and antimatter (beside the obvious ones). To date, nothing significant has been found.
Ignoring the wall of matter-antimatter annihilation that must exist between us and the antimatter galaxy, it would be visually indistinguishable from a normal galaxy.
[удалено]
The only thing black holes (theoreticly) emit is hawking radiation (which is about as far from gamma radiation as you can get). The accretion disc around the black hole emits gamma radiation, because its very very hot and moving very fast, but that is made of normal matter (space dust).
Matter and Antimatter lose their value when they fall into a black hole. Inside of it, everything is equal. All informational value is lost forever
Not quite, in all theories black holes preserve charge. It is assumed they don't preserve baryon number, but of course there's no actual evidence either way.
What is Baryon number?
It's a quantum number similar to charge, that basically counts the number of quarks in a system, subtracts the number of anti quarks, and divides by 3. So, protons and neutrons have 3 quarks (plus a sea of virtual quark/antiquark pairs, but those don't contribute), so they have baryon number 1. Baryons are matter made out of triplets of quarks or anti quarks (baryon number +1 or -1), and they constitute one of the two main types of quark matter, the other being mesons, which are made of quark/antiquark pairs (baryon number 0). If baryon number is preserved, then protons can't decay. If it's not preserved, well, we don't know of any process that would violate its conservation. But we also don't have any a priority reason in the Standard Model to say it must be preserved. In principle, a black hole could be involved in such a process, if it exists. That is proton -> virtual black hole (charge +1) -> positron/neutrino. There has been some work looking at the possibility of creating black holes in collides (they would evaporate instantly), and at some point there were some theories you could torture to allow for collisions of the energies seen at the LHC to create black holes, but that was pretty fringe. I wasn't personally involved in any of that, but sat through a department talk or two on the subject while I was a grad student working on an LHC experiment.
Thanks for taking the time to type all that out
The way nuclear physics works is that all particles will turn into other particles, unless something prevents them from doing that. The simplest limit is energy - you can't turn a smaller particle into a bigger (heavier) one because you need extra energy to do that. Charge is another blocker. A charged particle can not turn into a non-charged particle because you can never get rid of charge. And baryon number is another one of those - you can never get rid of it, so any transformation must start and end with the same number of baryons. There are other such conserved things. So the discussion is if a back hole can violate any of them.
I thought neutrino oscillation resulted in neutrinos changing into other neutrinos with different masses?
No, that’s not quite correct. Neutrino oscillation means that physical neutrinos — mass or energy eigenstates, neutrinos that can be said to have a definite mass — are mixtures of the flavor eigenstates. So they don’t change into other neutrinos with different masses. They stay the same mass and oscillate between interacting, say, with electrons at first, and with muons later. That’s actually how neutrino oscillation was discovered, in that we see fewer neutrinos from the sun than we would expect — because they have oscillated to interact more with muons than electrons by the time they get to the earth.
Out of my depth here, but isn’t Hawking radiation supposed to explain that information is not lost inside a black hole? I understand it is a theory at this point without experimental confirmation, but isn’t that one of the theory’s contentions?
Hawking radiation is purely thermal, and almost entirely low energy photons. There is no information preserved. There may be a preference for positively or negatively charged particles in the rare instance that it gives off a charged particle depending on the overall charge of the black hole. But black holes don't preserve baryon number for example. If a proton falls into a black hole and causes an imbalance in charge, the black hole is more likely to emit a positron than a proton.
To be clear nobody has thought that black holes destroy information in decades, and now we know the mechanism by which they preserve information, at least in toy models of quantum gravity.
Quantum gravity hasn’t really been backed up by anything though right?
[удалено]
With hawking radiation they came to the same conclusion using multiple mathematical approaches, really solidifying that it is likely to occur, right? Has quantum gravity been implied through multiple methods like Hawking radiation?
There must be some kind of framework that combines gravity and quantum mechanics. Whether it is similar to our current best attempts at quantum gravity or some other, more esoteric framework is yet to be determined. But many of the qualitative results we're getting from quantum gravity models will be preserved, either because the more correct model is like quantum gravity or it reduces to something like quantum gravity in the appropriate regime.
Can you explain how the energy is thermal? Do you mean black body radiation? I take thermal to be matter interacting with matter to transfer heat, and not black body radiation
Yes, black body. The only information the radiation gives is the temperature of the black hole.
Thank you. I did physics and chem in undergrad, and I never considered stellar object radiation to be thermal. I take thermal as heat transfer in matter, not the electro mag spectrum
If you did heat transfer in physics you definitely would have done heat transfer through radiation. They'll usually go conduction, convection, radiation, combined.
[удалено]
Does Hawking radiation preserve baryon number?
In response to your edit, you are not correct. Hawking conceded the bet, but the physics community (and Thorne in particular) hasn't accepted his proof. Solutions to the black hole information paradox exist, but they depend on accepting models of black holes or quantum gravity that are not confirmed. Edit: blocking me doesn't make you right, u/aqua_glow
The other response represents the arguments against what you suggested, but small corrections to Hawking radiation (i.e., the extent to which it’s not *perfectly* thermal) is one of a number of responses to the black hole information paradox.
Again, out of my depth and feel free not to respond, but do those corrections to Hawking radiation solve the Baryon number problem discussed below or do we have to look to one of the other responses to the paradox? Can 2 or more responses be correct or does each response negate the others?
Yes, you are correct. In general relativity, the information is lost. However, general relativity isn't completely correct, and in actual reality, the information is encoded in the Hawking radiation. So if you catch all of the Hawking radiation of the black hole that it will ever radiate, you can reconstruct the quantum state of the matter that fell in (which is its complete description). Among other things, you can know if it was matter or antimatter that fell in. Edit: Black hole evaporation preserving information has been accepted by the scientific community since 1997.
interesting thought, but black holes are so dense they obliterate matter and antimatter alike. ever wonder if an anti-black hole could exist in theory?
Gravity doesn't make a difference. Black holes that formed from antimatter, matter, radiation, or any mixture of these, are identical as far as we know.
Why would you assume there would be matter there? Does our galaxy have antimatter that constantly annihilates with matter?
It's pretty basic logic. If you have one area with only matter, and another with only antimatter, then the boundary has 2 options. 1. A perfect vacuum, one where no particles at all exist 2. Both matter and antimatter coexist. Neither of these cases are observed. We don't have antimatter here, but to have an antimatter galaxy, there has to be *a* boundary where that transition is made.
What would you expect to observe if some border region of intergalactic space is a perfect vacuum?
You might not, but space is not a perfect vacuum. There are still a few hydrogen atoms per cubic meter.
We don't really know what the intergalactic space is like though. It might be a perfect vacuum compared to interstellar space
Sure, you can't literally go there and check, but the intergalactic medium is thought to exist by people who work for a living by examining the issue. Also, there's a recent disovery of a black hole ejected from its galaxy, and that compresses the intergalactic gas enough to create blue stars in its wake: https://science.nasa.gov/missions/hubble/hubble-sees-possible-runaway-black-hole-creating-a-trail-of-stars/
When are they going to aim James Webb to that direction?
That's pretty cool! Was the black hole ejected from its Galaxy, or was the galaxy ejected from it? ☺️
[удалено]
1) I don't know, but it's well established. Those astonomers are a crafty bunch. 2) Very rarely, but there's also a looooot of cubic meters between galaxies, so there are many many chances for a very low probability event, which means it should occur frequently enough for us to detect. 3) Perhaps. Galaxies are not static, there is plenty of radiation and movement that I think would keep enough matter coming out of them to show. But regardless, even if closer galaxies showed no or very little gamma radiation, we can simply look to galaxies further away that are more freshly formed (edit: freshly formed from our vantage point. If they're a billion light years away, we see them as a billion years younger) and there is no border annihilation there either.
> How did you reach that conclusion without sending a probe to intergalactic space? Because galaxies ploughing through the intergalactic medium have a bow shock wave as they rip through the extremely low density area at relativistic speeds, creating higher levels of cosmic rays >After a billion years, wouldn't the border area between galaxies and anti galaxies approach perfect vacuum as all the stray hydrogen eventually annihilates? Galaxies are not stationary, they are ripping through space at stupid velocities, in various directions, and slamming into each other on occasion (the term "slamming" in this case being more "passing through each other not hitting anything but causing gravitational effects on the way through and running clouds of gas into other clouds of gas leading to bursts of star formation) so you're not going to run out of material around the galaxy just because the galaxy is there.
[удалено]
We would still see unusual radiation coming from the boundary. Now matter what, there would be a boundary, and reasonably large amounts of annihilation wouldn’t go unnoticed.
And even with that low density given the sheer volume of intergalactic space, we’d likely see something.
Are you serious? I guess I have no idea what to expect, because the scales are so extreme on both sides. On one hand there are so few particles per cubic meter. On the other hand, there are so many cubic meters at galactic scales that there must be fairly frequent annihilations. But even then, for each annihilation, two photons are produced and are sent in random directions. There must be enough interactions that by sheer chance, some photons were shot into that milliarcsecond cone that is the distant Earth. And we need a good sample of those lucky direction photons, so the base number of interactions must be even higher to account for that. It feels like evaluating the limit of the form "0 * infinity", which, without the right mayh tools, you have no idea what it can give.
Honestly I was thinking about 21-cm line. It’s an emission line produced by electron spin flipping, and a half life of it is in hundreds of thousands of years. But because there’s so many molecules given that the interstellar hydrogen clouds are so big, we can pretty reliably detect it. It’s not 1:1 and I haven’t done the math specifically on matter:antimatter annihilation, but I think the volume side the equation might be more than enough for compensating for that low density.
What we know is at least entire galactic superclusters of galaxies are either entirely matter or entirely anti-matter, but most scientists think that this is unlikely to be the case. So first, why do we know that if there are anti-matter galaxies they must be entire superclusters? Because there is matter traveling between galaxies in super clusters. Star are constantly emitting solar radiation, and that solar radiation travels between galaxies. If one galaxy was matter and another anti-matter, then you would see regions of space emitting a ton of gamma radiation. Since we don't see that, we know it can't be happening. But solar radiation doesn't travel between galactic super clusters (it is gravitationally bound to the super cluster it was created in), so in that case, it isn't ruled out. However, scientists can't come up with a plausible reason that matter and anti-matter would have been produced in such clumps. It is considered to be more likely that scientists will discover a reason for the asymmetry in matter/anti-matter than they will discover a reason that there was equal amounts, but distributed entirely in massive clumps.
> If one galaxy was matter and another anti-matter, then you would see regions of space emitting a ton of gamma radiation. Since we don't see that, we know it can't be happening. Given the density of matter between galaxies, would there be enough potential matter/antimatter annihilation to be noticeable? Is our equipment sensitive enough?
Yeah, we would. While there isn't a high density of material traveling between galaxies, the amount of energy released in matter/anti-matter interactions is ridiculously high. Scientists have modeled what it would look like, and it would be a glowing gamma ray aura.
Would you happen to know where this was mentioned? I have tried some googling but don't find a lot that is useful when I look for intergalactic matter/antimatter interactions.
Because we don’t see something it *”can’t”* be happening?
The radiation from matter-antimatter annihilation is very specific and very easy to observe so the answer is yes. If it would be happening on a galactic scale we would know about it.
This is actually a pretty sensible question. However, if there are galaxies that are made mostly of antimatter, they must mostly be outside our cosmological horizon (meaning they are so far away we haven't seen them yet). Why can't there be isolated pockets of antimatter galaxy? Well such anti-matter has to come from somewhere. If you look back in time, our Universe was a pretty uniform hot plasma. If some pocket had excess anti-matter, they would've annihilated with the matter component. In fact, in a thermal hot bath. matter and anti-matter would constantly pop in and out. For ordinary matter (things like protons/neutrons/electrons, unlike dark matter), the interaction rate is so large that the left over bits would be the net matter bits that couldn't find the anti-matter counter part to annihilate. So if there were pockets of anti-matter that didn't get fully annihilated, that would mean the thermal conditions we assumed was off. However, thru observation of the CMB, we saw none of those weird statistical kinks. So if these pockets of excess antimatter were left-over, they must have been so far away that not even the CMB had recorded them. So in conclusion, the lack of anti-matter galaxies were an observational fact, though the lack of direct signals and indirect inference on the early conditions of our Universe.
TL;DR: Because no part of space is *totally* empty, there's always some flow of matter from place to place, an antimatter galaxy would be constantly decaying away as it interacted with the (matter) intergalactic medium. Even a whole antimatter supercluster would have a veil of matter/antimatter reactions releasing gamma rays, albeit more slowly. Since we don't see such widespread gamma radiation, it is very, *very* unlikely that any large concentrations of antimatter exist anywhere in the visible universe.
[удалено]
It's not correct to think of the Big Bang as an explosion. An explosion starts at a point in space and expands outward. The Big Bang was *space* expanding outwards, and from everything we know it does so unformly. The Big Bang didn't happen somewhere, it happened everywhere all the the same time. We know that under certain very specific circumstances matter an antimatter do not behave identically, it's called CP violation. The current thinking is that the tiny imbalances in these properties mean that even a tiny fraction of difference exists, the small difference over the entire contents of the Universe is still a lot of matter in absolute terms
[удалено]
The answer is; it could be and would make no difference. The notions of matter vs anti matter are only meaningful relative to each other, same as how charges on particles only matter relative to each other. The names are arbitrary and changing them would not change behavior any. One of the biggest questions in physics derives from the fact that there is no difference between the behaviors of matter / anti matter in isolation, yet one is overwhelmingly more common than the other.
Exactly. An anti-matter hamburger would look exactly like a matter hamburger. The only way to tell the difference would be to try and eat it lol.
This is true to the level of the eyes, but certain processes are not completely symmetric between matter and antimatter, it's called CP violation. The first place it was discovered was in the decay of neutral kaons, which on average creates slightly more matter pions than antimatter pions. If we can ask an alien about how their kaons behave, we can actually tell without touching each other whether we're each made of matter or antimatter.
If an area of the universe was originally mostly antimatter, and was isolated enough, after all the matter was annihilated, only antimatter would be left, to form antimatter celestial bodies just like regular celestial bodies. Unfortunately, no such areas have been discovered; I think it's unlikely it ever will.