Astrophysics question

[Vestnik]

I don't no nuthin' about no high-falutin' egghead science.

 

Well maybe I know a very little bit. Can somebody riddle me this?

 

As far as I understand things, prevailing theories of cosmogenesis hold that the Big bang should have created a universe 50% composed of matter and 50% of antimatter, and it is a matter of debate as to where this antimatter, assuming that it exists, is, since it obviously isn't around us.

 

Now my question is -- is it possible to determine from a astronomical distance whether an object is composed of matter or antimatter? Is there any way to determine whether e.g. Andromeda is composed of material of our type or of the "touch me and annihilation with result" type? Is there a dicernable difference?

 

Thanks all informed people!

[Starwolf]

Re: Astrophysics question

 

Actually your question resides in the realm of Particle Physics... and is onr of the unanswered questions in the science of physics. So far our discernable Universe is composed mostly of matter (as we know it). There is a miniscule amount of anti-matter that resides within stars (the annilihation of this anti-matter connecting with matter is part of the stars constant energy production). On earth very miniscule amounts are able to created in labs, but they connect to matter and annilihate so quickly that they are able to exist just barely long enough for scientists to stusdy some of the effects and properties. But as far as is known there are no blob of free floating anti-matter, no galaxies within our universe composed of anti-matter, etc.

 

Now could such things exist in your Star Hero campaign... sure it's your universe. Most SH games include FTL travel, and many including one that I play in uses voidspace where we actually enter an alternate universe/dimension to travel relatavistic distances without having to obey relatavistic rules

 

Oh I forgot heres a link about anti-matter http://en.wikipedia.org/wiki/Antimatter

[Vestnik]

Re: Astrophysics question

 

But as far as is known there are no blob of free floating anti-matter, no galaxies within our universe composed of anti-matter, etc.

 

Thanks. How can we tell? Theoretically, would an object made of AM "look" any differently from one made of "normal" matter"? I have a hazy understanding that AM and NM are pretty much identical except for the obvious mutual annihilation bit. (I may be 10000% wrong.)

[Comic]

Re: Astrophysics question

 

Uh.. cosmogenically, isn't matter-antimatter generation and annihilation an asymmetric process?

 

I'm a bit pressed for time at the moment to look it up, but I believe it's a not dissimilar ratio to left-handedness vs right-handedness in organic molecules, though of course for different reasons.

 

I'll try to recreate it experimentally, since I'm not really ready to do book research. All I need is an infinite void, an infinitessimal point containing the mass of the universe, and about a tenth of a second. I'll get back to you when I'm done.

[Cancer]

Re: Astrophysics question

 

The matter-antimatter asymmetry is one of the great unsolved problems in physics....

 

If there's equal amounts matter and antimatter in this Universe, then it is very well separated. We know our Solar System is matter, and we have a few unambiguous material samples that must be from outside the Solar System (the case I heard of most recently is carbonado diamonds) that are also matter.

 

When matter & antimatter come into contact, of course, they annihilate. This predominantly produces the 511 keV gamma-ray emission from electron-positron annihilation. We see this in places in the Galaxy, but always around compact objects, where the temperature is high enough that pair production occurs ... that is, the positrons doing the subsequent annihilation are being formed by a known process right there. We do NOT see big "sheets" of space giving off this radiation, which is what you'd expect at the boundaries of matter and antimatter domains, where the two flavors come into contact. Therefore, certainly in the Galaxy, we're all matter.

 

The same argument can be extended further out into intergalactic space ... there are no big zones of unexplained gamma ray emission.

[Clonus]

Re: Astrophysics question

 

Thanks. How can we tell? Theoretically' date=' would an object made of AM "look" any differently from one made of "normal" matter"?[/quote']

 

It would look a bit different because of all the antimatter explosions as it came in contact with the interstellar medium for our galaxy which we know to be matter because we aren't experiencing such explosions. Also we've sampled it. It's possible of course that other galaxies are all made out of antimatter...but not likely since there would be no way to separate the matter from the antimatter in the first few seconds after the big bang.

[StGrimblefig]

Re: Astrophysics question

 

Didn't Hawking theorize that free antimatter particles could be "generated near a black hole? Something about matter-antimatter pairs coming into existence and annihilating each other all the time in the universe, but if the matter particle falls into a black hole before it collides again with its counterpart, the antimatter particle is then free to continue existing.

 

This is, if I remember correctly, related to the Hawking's theory that black holes "leak" particles. And, oddly enough, there is no restriction on the kinds or configuration of those leaked particles, so (to badly paraphrase an article I read a long time ago) a black hole could just as easily emit a '57 Chevy or the complete works of Shakespeare in 12 leather-bound volumes.

[Cancer]

Re: Astrophysics question

 

Well, the energy threshold for emitting baryons (protons and antiprotons, e.g.) is a lot higher than for emitting electrons and positrons, so it takes a MUCH hotter energy source to kick out protons and antiprotons. Also, particles and antiparticles are produced in pairs ... and near each other ... so they tend not to get far before hitting another particle and re-annihilating, so you tend to get just high-energy gamma-ray photons when viewed from a distance.

 

Once you get to the energy threshold for making baryons, the gamma rays are energetic enough that they photodisintegrate any composite nuclei that you might happen to assemble. The energy needed to break apart a nucleus is less than the rest-mass energy of two protons (which is what you need to have in order to make protons and antiprotons in the first place).

 

Then there's thermodynamic arguments about the probability of spitting out a macroscopically recognizable object...

[keithcurtis]

Re: Astrophysics question

 

I would think that antimatter people would object to a name with such a negative connotation.

 

Keith "differently charged" Curtis

[DarkGreen]

Re: Astrophysics question

 

Lots of very good info in this thread. Lots of high IQs in hero land.

 

Comic is right about handedness, that's how you tell them apart. There are particle physics interactions that have right handedness in matter and left handedness in antimatter. Until we can shoot a particle beam at distant galaxies and watch the results in high resolution though I don't think that there is a way to tell the difference at a distance.

 

Grimblefig is also right about the creation issue. You get lots of positive and anti matter near black holes and tend to lose one type of particle in slightly higher amounts into the event horizon due to the handedness issue. Thus you get net matter generation in matter neighborhoods and presumably the reverse in antimatter neighborhoods.

 

The handedness has also been shown to give galactic scale tendencies for matter and antimatter to cluster with like materials so that after the big bang an inhomogenous universe would develop to allow for matter galaxies and antimatter galaxies.

 

I once ran a star hero campaign where the PCs travelled through an ancient Farcaster network (with rooms of pure force in the travelways, so there were places to go "between" destinations). The creators of the network had cleverly designed the world gates so that one part would light up if you had the same matter status as the destination and another if you were different. When the PCs ran into their first contact the others help up cards for the PCs to point at to indicate which lights they saw on a nearby gate, thus allowing the NPCs to figure out if they could interact with the PCs without exploding

[Vestnik]

Re: Astrophysics question

 

Lots of very good info in this thread. Lots of high IQs in hero land.

 

Comic is right about handedness, that's how you tell them apart. There are particle physics interactions that have right handedness in matter and left handedness in antimatter. Until we can shoot a particle beam at distant galaxies and watch the results in high resolution though I don't think that there is a way to tell the difference at a distance.

 

Grimblefig is also right about the creation issue. You get lots of positive and anti matter near black holes and tend to lose one type of particle in slightly higher amounts into the event horizon due to the handedness issue. Thus you get net matter generation in matter neighborhoods and presumably the reverse in antimatter neighborhoods.

 

The handedness has also been shown to give galactic scale tendencies for matter and antimatter to cluster with like materials so that after the big bang an inhomogenous universe would develop to allow for matter galaxies and antimatter galaxies.

 

I once ran a star hero campaign where the PCs travelled through an ancient Farcaster network (with rooms of pure force in the travelways, so there were places to go "between" destinations). The creators of the network had cleverly designed the world gates so that one part would light up if you had the same matter status as the destination and another if you were different. When the PCs ran into their first contact the others help up cards for the PCs to point at to indicate which lights they saw on a nearby gate, thus allowing the NPCs to figure out if they could interact with the PCs without exploding

 

Given that galaxies do occasionally smack into each other, I would guess there would be a whopping big explosion if an AM and an M galaxy ever did so, and I assume that would happen from time to time if galaxies are divided 50/50 -- unless maybe the Bang sent the AM in one direction and the M in the other so never the twain shall meet. I assume no evidence of such an event happening has ever been seen?

 

(Is there enough matter between galaxies, to our knowledge, that the passage of a celestially-sized AM object would create enough of a gamma-ray trail to be observable?)

[Cancer]

Re: Astrophysics question

 

Given that galaxies do occasionally smack into each other, I would guess there would be a whopping big explosion if an AM and an M galaxy ever did so, and I assume that would happen from time to time if galaxies are divided 50/50 -- unless maybe the Bang sent the AM in one direction and the M in the other so never the twain shall meet. I assume no evidence of such an event happening has ever been seen?

 

(Is there enough matter between galaxies, to our knowledge, that the passage of a celestially-sized AM object would create enough of a gamma-ray trail to be observable?)

 

Depends on the form of the antimatter object. Make it a planet or rock, and it could be that it would escape notice, since the collision cross-section is so small: the volume of space where the annihilations would occur is rather small on a galactic scale.. If it's gas, though, it'd be just insanely luminous at gamma-ray luminosities. Heck, matter-matter galactic gas cloud collisions are very luminous, though not in gamma rays.

 

EDIT: Niven had a short story in Tales of Known Space IIRC, about an antimatter world passing through. I don't think he got the gamma-ray intensity right, but it's been 25+ years since I read the story, and never thought about it before in this way.

[DarkGreen]

Re: Astrophysics question

 

Given that galaxies do occasionally smack into each other, I would guess there would be a whopping big explosion if an AM and an M galaxy ever did so, and I assume that would happen from time to time if galaxies are divided 50/50 -- unless maybe the Bang sent the AM in one direction and the M in the other so never the twain shall meet. I assume no evidence of such an event happening has ever been seen?

 

Oooooh, neat thought!

 

My best answer is that I have no friggin idea . I'll mention that over lunch some time to some of the folks I work with who spend their time pondering just such things. I think you may be on the right track with the AM and M getting sent opposite directions though.

[Cancer]

Re: Astrophysics question

 

Given that galaxies do occasionally smack into each other' date=' I would guess there would be a whopping big explosion if an AM and an M galaxy ever did so, and I assume that would happen from time to time if galaxies are divided 50/50 -- unless maybe the Bang sent the AM in one direction and the M in the other so never the twain shall meet. I assume no evidence of such an event happening has ever been seen?[/quote']

 

Another thing ... the extreme smoothness seen in the microwave background measurements make any simple split in the Big Bang like you mention just about impossible. All the smart money now is betting that the matter-antimatter symmetry was broken very early on (no later than when the first nucleons formed, which is when the Universe was about three minutes old) and since then there's never been an appreciable amount of antimatter anywhere.

[Vestnik]

Re: Astrophysics question

 

Oooooh, neat thought!

 

My best answer is that I have no friggin idea . I'll mention that over lunch some time to some of the folks I work with who spend their time pondering just such things. I think you may be on the right track with the AM and M getting sent opposite directions though.

 

Please do! I'd love to hear what they say.

 

So, on the off chance that my pulled out of my ass idea is true, if the Big Crunch ever happens and all the stuff thrown out by the Bang cames together again, we get a huge universe-sized gamma-ray burst?

[Cancer]

Re: Astrophysics question

 

Yeah, but in a big crunch there'll be plenty of thermal gamma rays, not just annihilation gamma rays.

[Vestnik]

Re: Astrophysics question

 

Another thing ... the extreme smoothness seen in the microwave background measurements make any simple split in the Big Bang like you mention just about impossible. All the smart money now is betting that the matter-antimatter symmetry was broken very early on (no later than when the first nucleons formed' date=' which is when the Universe was about three minutes old) and since then there's never been an appreciable amount of antimatter anywhere.[/quote']

 

Broken how? (In layman's terms if possible please) Are there any dominant theories?

 

While I'm at it, here's something else that's been bugging me. As I understand things, stuff falls into a black hole and increases its mass. However, according to relativity, from the viewpoint of someone outside the hole the stuff falling into it never actually reaches it, but appears to be moving more and more slowly. Thus none of this stuff will ever actually (from the viewpoint of the the universe outside the hole) fall into it, and so the hole's mass will never increase. Am I missing something here? Is this a paradox?

 

I suppose a black hole would appear to be surrounded by a corona of stuff falling into it but never quite making it.

[Cancer]

Re: Astrophysics question

 

Broken how? (In layman's terms if possible please) Are there any dominant theories?

This is the regime of particle physicists, and I ain't one of those, and can't pretend to be one. This is the most exciting question in that game now, but I don't know that game at all. Sorry. My understanding of the Big Bang doesn't go further back than when the elements formed (H, He, Li), which is well after the matter-antimatter symmetry breaking took place.

 

While I'm at it, here's something else that's been bugging me. As I understand things, stuff falls into a black hole and increases its mass. However, according to relativity, from the viewpoint of someone outside the hole the stuff falling into it never actually reaches it, but appears to be moving more and more slowly. Thus none of this stuff will ever actually (from the viewpoint of the the universe outside the hole) fall into it, and so the hole's mass will never increase. Am I missing something here? Is this a paradox?

 

I suppose a black hole would appear to be surrounded by a corona of stuff falling into it but never quite making it.

That's sort of the idea. There isn't a paradox. It's the result of the photons that reach you from the fall-in event having themselves to crawl out from the edge of the hole. This isn't the right picture, but it's convenient to think that the closer the photons from the falling-in are to the event horizon when they start out, the longer it takes them to spiral their way out of the deep gravity well of the black hole. It just takes a while to get the signals from the very edge of the black hole; for the thing that's falling in, the experience is over very, very quickly.

[Comic]

Re: Astrophysics question

 

Okay, back.

 

Firstly, let me say, 'vacuum fluctuation' is an awesome term, repudiated or not.

 

Second, uh.. handedness.. Oh. Someone caught that.

 

Third, I got distracted and didn't watch closely during the matter-antimatter generation, so the experiment is a washout.

 

Plus, I now have this annoying microverse rapidly developing sentient species and religion has formed. They're asking 'Why do we exist?'

 

What should I tell them?

[Captain Obvious]

Re: Astrophysics question

 

Okay, back.

 

Firstly, let me say, 'vacuum fluctuation' is an awesome term, repudiated or not.

 

Second, uh.. handedness.. Oh. Someone caught that.

 

Third, I got distracted and didn't watch closely during the matter-antimatter generation, so the experiment is a washout.

 

Plus, I now have this annoying microverse rapidly developing sentient species and religion has formed. They're asking 'Why do we exist?'

 

What should I tell them?

 

If you tell them anything, they'll find reasons to kill each other over it.

[Cancer]

Re: Astrophysics question

 

Which is why advanced astrophysics courses are so bloody.

[austenandrews]

Re: Astrophysics question

 

Yeah, but advanced physicists have such cool weapons.

[L. Marcus]

Re: Astrophysics question

 

Kabom!

[tkdguy]

Re: Astrophysics question

 

God knows I've spent several nights struggling though homework and claiming my professor was the Antichrist.

[L. Marcus]

Re: Astrophysics question

 

My professor had a Vinnie the Pooh tie.