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indigofuzzy
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Shaving cometray ice with Occam's Razor? 
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Panache
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Wasn't it Jesus fighting with Allah, Santa Claus stepped in apparently
Actually if i wrote Jesus was fucking Allah (or visa versa) that would offend more irrationals however as this is not my priority i retract it and
apologise to everyone.
If you are offended by the Australian spelling of 'apologise' i aoplogise for this also.
Did you know Indigenous Australians only got the vote some 40 years ago, when did Native americans get the vote, for that matter African Americans.
Australian women (not the indigenous ones) got the vote in 1907, why the fuck it took us another 60 years to figure out aborigines where just as
important, relevant and the what who knows.
That Mr Stevens is getting to me again....
'..saturday night and I ain't got nobody..'
except i think Allah gave him a new name
Anyway thats my Dawkins-esc tirade over with and concerning the little event in Siberia 100 years ago. There will never be enough information to say
definitively, never ever ever, but i think my Jesus explanation is more likely than an advanced races', anti-matter tank's fuel gauge being faulty.
Wow that last sentence was difficult to punctuate.
8)
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Sauron
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I firmy believe it was one of the Great Old Ones, perhaps Yog-Sothoth, or Azathoth, stopping by to see to his pet shoggoths.
A Cthulhu mythos explanation is as valid as any of the utter rubbish being kicked about in this thread.
From my perspective, this century old event has generated little in the way of scientific data and way too much in the way of Fortean bald bullshit,
which for a hundred years has been embellished and embroidered by every crackpot psudoscience writer out there, and they are legion, until the
seperation of fact from half-fact and outright fabrication is well nigh impossible. Even Chris Carter's writers at The X Files had a go at it.
Idle speculation about antimatter, FTL drives, UFOs, cosmic anomalies etc. may be amusing but they are generally meaningless exercises in futility.
Engaging in such flights of fancy is not amateur science. This forum is about amateur science. Not flying saucers or close encounters. Go join
area51.com or something.
[Edited on 16-2-2008 by Sauron]
Sic gorgeamus a los subjectatus nunc.
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microcosmicus
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Wading through the nebula of deritus which has accreted upon the nucleus of this
thread, one gets to an original question which had scientific merit, namely how
far could a chunk of antimatter travel through interstellar space before being annihilated
by matter it met along the way. Time to do a back-of the-envelope estimate.
As our lump of antimatter, let's take an anti-meteor which consists of a mole of
anti-iron. Now, such an object weighs 56 grams and occupies a volume of 7 cc,
for simplicity, we may envision it as a cube 1.9 cm on each side. A cubic
centimeter of interstellar space will contain somewhere between 10^2 and 10^6
atoms of hydrogen, i.e between 1.7E-22 and 1.7E-18 moles. As a round average figure.
let us take something near the geometric mean, say 1E-20 moles.
Assume that each time our anti-meteorite encounters a hydrogen atom in it path,
the proton collides with a proton in an anti-Fe nucleus and that the energy liberated
wrecks that nucleus. (A reasonable assumption, because a(n anti-)proton weighs
a GeV, which is about twice the binding energy of an (anti-)Fe nucleus). Then we
can estimate that the distance which our anti-meteor travels before being
completely annihilated by the interstellar medium is such that the volume it
sweeps out is such as to contain a mole of the medium. Now, volume equals
base times height, so the ratio of the volume of the meteor to the volume it
sweeps is the ratio of the height of the meteor to the distance it travelled.
Thus, in order to run into a mole of interstellar medium it needs to travel
10^20 times its height, or 2E20 cm, which works out to around 2000 light-years.
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not_important
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Even though a proton/anti-proton annihilation releases enough energy to fully disrupt the nucleus, that doesn't make all that (anti) mass. You've
eliminated one anti-proton, but most of the nucleus is still there. From what I've read the annihilation kicks out 3 or 4 pions carrying 145 MeV
each, on the average. At least in the case of heavier nuclei, the nucleus remains mostly intact or fissions in the case of very heavy nuclei.
This means that a single collision is only going to reduce that mass by a (anti)proton mass, at least until most of the nuclei are reduced light ones.
And even light ones that are buried deep enough would yield hydrogen or helium trapped in the lump.
So it would seem that you need to interact with closer to 50 grams of hydrogen/protons, pushing your range out to 100 K light-years or about the
diameter of the galaxy.
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len1
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| Quote: | Originally posted by not_important
Even though a proton/anti-proton annihilation releases enough energy to fully disrupt the nucleus, that doesn't make all that (anti) mass. You've
eliminated one anti-proton, but most of the nucleus is still there. From what I've read the annihilation kicks out 3 or 4 pions carrying 145 MeV
each, on the average. At least in the case of heavier nuclei, the nucleus remains mostly intact or fissions in the case of very heavy nuclei.
This means that a single collision is only going to reduce that mass by a (anti)proton mass, at least until most of the nuclei are reduced light ones.
And even light ones that are buried deep enough would yield hydrogen or helium trapped in the lump.
So it would seem that you need to interact with closer to 50 grams of hydrogen/protons, pushing your range out to 100 K light-years or about the
diameter of the galaxy. |
I would argue against this factor of 50 on the grounds that the cross section for ppbar scattering gives tiny penetration depths into the target. The
energy release is nuclear decay is far in excess of the binding energy - thus the constant bombardment will make the outer surface of the meteorite
peal much faster than even the first approx suggests by disrupting the binding forces. Also the 10^2 - 10^6 H2/cm^3 is much too high, 10^6 is about
10^-15 down on the suns density, we would have to be about 5 orbits of pluto out from the sun to recreate the suns mass - that would be a substantial
correction to the orbit of pluto say. The figure for deep intestellar space is generally accepted at about 1 H2/cm^3
We also have baryon number conservation:
sum(antiprotons+antineutrons-protons-neutrons) = constant
That means unless the proton backward scatters out of the antimatter it must ultimately lead to the decay of at least one antimatter atom, it can not
equilibrate using pions.
[Edited on 17-2-2008 by len1]
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JohnWW
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I understand that many small iron spherules, which must once have been molten then widely dispersed by an explosion above ground, have been found in
and around the epicenter of the 1908 Siberian explosion. This would favor the meteorite theory, although what made it explode before hitting the
ground (no crater was found, only large numbers of trees blown oveer and pointing away from the epicenter) is unclear. It may have been an unusual
comet, consisting of a mixture of pieces of meteoritic iron (which also contains cobalt, nickel, and other heavy metals including platinum group
metals), and volatile compounds which vaporized due to atmospheric friction, thereby providing the propellants needed for the explosion.
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microcosmicus
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What I did was simply a crude first estimate to get the ball out of the
gutter and rolling again so I am glad you fellows are pointing out the
weak spots and making improvements. For my data on density, I simply
did a quick UTFSE and went with the figures which showed up, so
no big surprise if they're off  Continuing in this direction, here are some
more remarks.
Let's remember that proton-antiproton annihiliation is a strong process
and that the strong force is also what keeps nuclei together, hence it
should be easy for the energy released to be absorbed into the nucleus.
Consider the situation in more detail. If the proton and antiproton
were colliding in a vacuum, the energy released would be carried
away as kinetic energy of the outgoing pions. However, since the
proton happens to be part of a nucleus, one can expect recoil. The
exact amount will depend on the kinematics, but I would expect this
to be on the order of MeV's. Given that the chemical bonds holding
the nucleus in place are on the order of eV's. I would expect that, even
if all that happens is that a single nucleon gets removed. the remaining
nucleus would be knocked right out of its place in the crystal lattice.
This would produce defects, weakening the meteor.
Furthermore, what about those pions? Since they are emitted inside
a nucleus, I expect that many of them would interact with nucleons.
inelastic scattering of 140 MeV pion with a nucleon would knock it
out of the nucleus. Elastic scattering could destroy another nucleon
and make more mesons. Thus, the damage to to collision with
the hydrogen atom should be more substantial than just removing
a single nucleon.
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len1
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proton antiproton anihilation, as primarily an electromagnetic process, and not strong contrary to appearances. The primary vertex is
p pbar -> virtual photon -> anything
if the collision is of high enough energy to individuate the quarks its still an EM process
q qbar -> virtual photon
with spectator strong interactions. The interacting atom must change its identity leading to decay in almost all cases due to baryon number
conservation
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microcosmicus
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I primarily had in mind the spectator processes which rearrange the remaining quarks in mind
when I used the term "strong". Your point is well-taken, the choice of wording was not good,
what I was primarily getting at was that the result of a proton reacting with an antinucleus
would involve significant, quite energetic, disruption which would break up the meteor faster than
if each collision with a proton simply remove a single nucleon and not do much else. The main
point here is that pions interact with nucleons (after all, one can explain nuclear binding in terms
of virtual pion exchange) so I wouldn't expect 145 MeV pions produced in a nucleus to simply
carry away energy like neutrinos or photons.
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len1
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I agree, the meteor will disintegrate faster than single nucleon destruction, that was also my point.
regarding the pions, its unimportant because, as I keep saying, unless an antiparticle backscatters the total number of nucleons will decrease by 1.
It follows almost 100% that an atomic decay must occur.
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microcosmicus
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I agree with what you say about the pions and baryon number. The only role in which I
consider the pions important is as a means of transferring the energy
coming from annihilation towards disintegrating the meteor.
So, back to the main question. If we use a density of 1 atom / cc for deep space, then
our meteor would need to travel 200000 ly to have encountered a mole of H2. While
this would mean that only 1/56 th of the baryons would have annihilated, the meteor
would be in bad shape, falling into pieces. Now, breaking an object into pieces increases
the surface area, hence the annihilation and disintegration goes faster. Moreover,
once the thing goes to pieces, the pieces are going to drift their separate ways so,
after another light-year, we are going to have a diffuse cloud of disintegrating
meteorites and gas instead of a meteor. Thus, I think it reasonable to conclude that an
antimatter meteor which made it to Earth would have originated within our Galaxy
or, at any rate, the local group of galaxies.
Leaving aside the aliens and conspiracies, the only origin I can think of for macroscopic
quantities of antimatter would have been back in the early history of the universe when charge
conjugation symmetry broke. Given what we said above, primordial
antimatter would have no chance of surviving for cosmological times
in a matter-dominated galaxy. I highly doubt that the Andromeda
galaxy or other neighboring galaxies are made of antimatter either
or that dark matter and halos inbetween them are actually dark
antimatter (how would it stay dark?) so that pretty much rules out
possible places of origins, so I agree with xxxxx that an antimatter
meteor making it to Earth sounds implausible.
[Edited on 18-2-2008 by microcosmicus]
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chemoleo
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Just wondered - as antimatter-matter annihilations are extremely energetic, shouldn't this leave a noticeable identifiable residue in the cosmic
background radiation, even though it is red-shifted due to the universe expansion? I assume these annihilations occurred mainly during the early times
of the universe. Therefore, any annihilations in recent universe history, particularly in our galaxy, should be quite noticeable, right?
On the matter of meteorite impact at the 1918 tunguska explosion - I seem to have read very recently that apparently asteroids much smaller than
anticipated previously should also be capable of causing the devastation seen.
Plus, I think they have found a lake in the area which is roughly elliptical, and shows a bottom profile that would resemble a meteorite/asteroid
impact.
If you want I can dig the info out.
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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len1
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That is indeed so. All sorts of energetic processes contrinuted to the energy we see now as the microwave background. Less than a microsecond after
the universe formed we had a quark gluon plasma, mean kinetic energy exceeded the binding energy in nuclei - matter-antimatter annihilation was just
part of all proceses contributing to interactions at that stage. As the universe cooled the quarks combined into nuclei and we had a nucleon -
electron - photon plasma - some residual smoothing out of matter-antimatter fluctuations continued here. Later as the mean thermal energy dropped
below the ionisation energy of atoms the photons decoupled from matter and parted company, but there was plenty of time for the firball to
equilibrate, that is why the micerowave background is (too) uniform
[Edited on 19-2-2008 by len1]
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microcosmicus
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| Quote: |
Just wondered - as antimatter-matter annihilations are extremely energetic, shouldn't this leave a noticeable identifiable residue in the cosmic
background radiation, even though it is red-shifted due to the universe expansion?
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The microwave background is what is left of the photon gas pretty much as it was when atoms formed.
At that time, the density of the radiation outweighed that of the matter (hence "radiation dominated
era") so the effect of annihilations would not be quite as drastic as today in the sense that
turning matter and anti-matter into radiation would increase the energy density locally by a
moderate factor. Offhand, I wouldn't remember exactly what the ratio of matter (and antimatter) energy
density to radiation energy density was at the time of decoupling and it is too late to look that up
now so I will have to come up with the numerical value of that factor later. Morever, to some
extent the inhomogeneity would have diffused out. Depending on the values, the effect may
or may not turn out to be all that noticable.
| Quote: |
Therefore, any annihilations in recent universe history, particularly in our galaxy, should be quite noticeable, right?
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This was something I thought about as I imagined what a meteor gradually disintegrating from
colliding with interstellar medium would do. One tell-tale sign would be 511 MeV photons
coming from e+ e- annihilation. As for the hadrons, initially they make pions but these
decay; at the end of the day, one is left with more photons, neutrinos, electrons, and positrons.
The positrons will annihilate electrons from hydrogen atoms; between the widowed H+'s and
the e-'s from the decay, one would have a "smoke trail" of ionized interstellar medium.
Of course, a direct collision between an astronomical object made of antimatter with one
made of matter would be a much more dramatic event.
| Quote: |
Plus, I think they have found a lake in the area which is roughly elliptical, and shows a bottom profile
that would resemble a meteorite/asteroid impact. If you want I can dig the info out.
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If it's not too much trouble, post some of that information or a reference. Then maybe we
can dump some of the deritus about aliens and X-files in the bottom of the lake and move
on  At any rate, speculating about the fate of a lump of antimatter has certainly
been
a fun excursion into astronomy and particle physics.
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len1
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The temperature at which the photons decoupled from matter was of the order of the ionisation energy, 10000K, this is much less than the proton
annihilation energy, several GeV, hence matter-antimatter annihilation was very significant and rare at that stage
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tumadre
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http://www.space.com/scienceastronomy/070626_st_tunguska_cra...
The first expedition did not occur until 1926, giving plenty of time for this lake Cheko to be filled with water and overlooked.
Arguments against this lake as the impact site include the 1961 expedition which found "meters thick silt" and concluded that the lake was 5000 years
old. It is also 8 kilometers north-north west of the supposed center.
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chemoleo
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There's also more info, pics here (but article is in German which you can translate with babelfish)
http://www.spiegel.de/wissenschaft/natur/0,1518,490518,00.ht...
Cant find the article on the higher than anticipated impact of small asteroids, but it has been all over the news.
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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len1
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| Quote: | Originally posted by chemoleo
Just wondered - as antimatter-matter annihilations are extremely energetic, shouldn't this leave a noticeable identifiable residue in the cosmic
background radiation, even though it is red-shifted due to the universe expansion? I assume these annihilations occurred mainly during the early times
of the universe. Therefore, any annihilations in recent universe history, particularly in our galaxy, should be quite noticeable, right?
|
While the Siberian explosion is reasonably understadable and so not so interesting, the above quote has more to be said, in a way that can be
understood by people here, and hopefully give the a useful insight.
As I said before matter-antimatter annihilation was much more common in the early universe. Now that it has cooled it can not be frequent as else it
would severly distort the mwave background to which chemoleo refers. Indeed it places a limit on the inhomogeneity of matter/antimatter regions -
they must be separated by at least 3-10kpc - the radius of the milky way.
The ratio
number barions + antibarions in universe now
/
number barions + antibarions in universe at big bang
gives the effectiveness to which mass has annihilated.
This equals roughly
number barions + antibarions now / number photons now.
Number photons we know from Stefans Law - for 2.7K mwave background it is 410 cm-3. Number barions we know from Hubbles expansion - how fast galaxies
are receeding from us. When this is measured it directly determines R(t) in the simplest metric
ds^2 = dt^2 - R^2(t) dr^2
when this metric is put into Einsteins equations, whose essence is to relate metric to particle density, we get the matter density - 10^-7 cm-3.
So the ratio of baryons to photons is about 10^-10 which is much larger than simple cosmological models can explain. One of the problems in
cosmology.
[Edited on 8-3-2008 by len1]
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pyrochemix
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nuclear explosion releases bout .7% of the nucleo-chemical energy stored in an atom through fission, when antimatter and matter collide they release
100%, therefore (bomb dropped on hiroshima was about a square foot or so i think of uranium) therefore the same amount of antimatter would have
destroyed the lower center part of russia.
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franklyn
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A small sample
www.reuters.com/article/2013/02/15/us-russia-meteorite-idUSB...
Approach => www.youtube.com/watch?v=90Omh7_I8vI
Shockwave => www.youtube.com/watch?v=Np_mpGYSBSA
.
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bfesser
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Beat you to it. 
<a href="viewthread.php?tid=23380">New Thread</a>
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Traveller
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I thought they were only called meteorites after they landed .
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IrC
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Stop it. You are using Occam's razor to ruin perfectly good conspiracy theories.
"Science is the belief in the ignorance of the experts" Richard Feynman
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zenosx
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Quote: Originally posted by neutrino  | Someone a few posts up mentioned the object's shape from eyewitness accounts. I have to doubt these descriptions for two reasons.
First, an object entering the Earth's atmosphere usually comes in at such a high speed that it travels through the entire troposphere in a matter of
seconds. That means that it would only be visible to someone not looking at it with a powerful telescope for only a tiny fraction of a second. How
anyone could make out the shape of a small object in a few milliseconds I don't know.
Second, how could anyone have gotten close enough to this thing to see the object clearly and live to tell about it? Anyone close enough would
probably have been killed instantly by the massive explosion.
My two cents. |
I have to disagree with this statement based on personal experience.
It's been a few years ago, but I personally witnessed a meteor streak across the sky to eventually impact with a VERY large flash bright enough to
make midnight look like noon for about a second. Like a lightning flash.
The meteor itself was very visible and at least towards the surface, while travelling very fast, was still visible.
Where I do agree however is that this item, and others look like long tubes from the ionized gas flowing behind the object from friction. Even a
spherical object will look long and tube-like in this regard. They could not have seen the actual object because of this gas/fire, only the bright
blaze.
I am not sure about the exact specifics, but at least as far as smaller meteors go (like this one), the atmosphere creates enough resistance to reduce
the object to terminal or slightly over velocity. Only meteors of very large size (I know more than 10 mi. width count here) have absolutely NO
interaction with the atmosphere for all intents and purposes and smacks the planet as if there was no atmosphere.
They hypothesize this type of impact was what wiped out the dinosaurs (perhaps with century long volcanic eruptions in the Asia sector), and it hit
around the ocean/Columbia interface if I remember correctly. Sorry off topic a bit there.
A question that sometimes drives me hazy: am I or are the others crazy?
Albert Einstein
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