1123: "The Universal Label"

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Pfhorrest
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Re: 1123: "The Universal Label"

Postby Pfhorrest » Sat Oct 20, 2012 12:24 am UTC

watergrinder wrote:Probably should be "naturally flavored quarks"

I'd be more impressed with artificially flavored quarks.

kriskra wrote:The Universal Label
Ingredients:
Stardust


The Universal Label
Ingredients:
Stardust
Golden
Billion year old carbon

Warning:
This object attracts every other object in the universe with a force proportional to the product of their masses and inversely proportional to the distance between them.

(My old high school physics book actually had that warning label on it...)

Max™ wrote:Additionally, if you just have energy without a way to bias the production of matter over antimatter, you're just going to get a bath of gamma radiation.

It's not as simple as "just get a lot of energy and it will turn into matter", there was something in the early universe which produced that imbalance which was actually responsible for us being here at all.

Question: Is the equal production of matter and antimatter strictly guaranteed by the laws responsible for it, or is it merely a statistical thing? E.g. is it possible to condense a bunch of energy into just an electron or positron, but on average a volume of high energy density will condense into equal numbers of each; or does the production of an electron demand the production of a positron to maintain conservation of something?

If the former, then while one would expect the vast majority of possible universes to contain nothing but a sea of photons from the perfect matter-antimatter annihilation, progressively smaller numbers of possible universes would contain progressively greater imbalances of one over the other. It's then simply a question of how did we get so lucky, which on a many-worlds interpretation isn't really an important question.

Of course if it's not the former then nevermind...
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Re: 1123: "The Universal Label"

Postby Max™ » Sat Oct 20, 2012 1:05 am UTC

Pfhorrest wrote:
Max™ wrote:Additionally, if you just have energy without a way to bias the production of matter over antimatter, you're just going to get a bath of gamma radiation.

It's not as simple as "just get a lot of energy and it will turn into matter", there was something in the early universe which produced that imbalance which was actually responsible for us being here at all.

Question: Is the equal production of matter and antimatter strictly guaranteed by the laws responsible for it, or is it merely a statistical thing? E.g. is it possible to condense a bunch of energy into just an electron or positron, but on average a volume of high energy density will condense into equal numbers of each; or does the production of an electron demand the production of a positron to maintain conservation of something?

If the former, then while one would expect the vast majority of possible universes to contain nothing but a sea of photons from the perfect matter-antimatter annihilation, progressively smaller numbers of possible universes would contain progressively greater imbalances of one over the other. It's then simply a question of how did we get so lucky, which on a many-worlds interpretation isn't really an important question.

Of course if it's not the former then nevermind...


A gas of high energy photons will have a temperature, as you raise the temperature of that photon gas it will begin to produce pairs of particles, matter-antimatter pairs, at something like 106 K you get lepton/anti-leptons, around 109 K you get quark/anti-quarks.

The conditions of the early universe appeared to involve domain walls where the production of anti-quarks was slightly reduced on one side, which involves various arrangements of matter to produce the observed symmetry violations, it was a tiny effect, for every few million antimatter particles produced there were a few million and one matter particles.
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Re: 1123: "The Universal Label"

Postby Koyaanisqatsi » Sat Oct 20, 2012 1:13 am UTC

We are in space.

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Re: 1123: "The Universal Label"

Postby Pfhorrest » Sat Oct 20, 2012 2:15 am UTC

Max™ wrote:A gas of high energy photons...

Not to keep going of on tangents, but this raises another question:

Is a gas of photons gravitationally self-attracting? I.e. does the relativistic mass of photons distort spacetime in a way that curves the paths of other photons? Could you then have such a dense volume of photons that they kept each other in some complicated mess of orbits around their barycenter? In other words, are there any circumstances (however absent in the real universe, but under the same laws as it) where you could have, in effect, a star-like ball of photons floating alone in space?

I get the feeling that the answer will be "that would be a black hole", but I'm not certain.
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Re: 1123: "The Universal Label"

Postby Someguy945 » Sat Oct 20, 2012 4:14 am UTC

Pfhorrest wrote:
Max™ wrote:A gas of high energy photons...

Not to keep going of on tangents, but this raises another question:

Is a gas of photons gravitationally self-attracting? I.e. does the relativistic mass of photons distort spacetime in a way that curves the paths of other photons? Could you then have such a dense volume of photons that they kept each other in some complicated mess of orbits around their barycenter? In other words, are there any circumstances (however absent in the real universe, but under the same laws as it) where you could have, in effect, a star-like ball of photons floating alone in space?

I get the feeling that the answer will be "that would be a black hole", but I'm not certain.


Gravity so strong that photons cannot escape it? Sounds like a black hole to me.

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Re: 1123: "The Universal Label"

Postby Max™ » Sat Oct 20, 2012 4:15 am UTC

Pfhorrest wrote:
Max™ wrote:A gas of high energy photons...

Not to keep going of on tangents, but this raises another question:

Is a gas of photons gravitationally self-attracting? I.e. does the relativistic mass of photons distort spacetime in a way that curves the paths of other photons? Could you then have such a dense volume of photons that they kept each other in some complicated mess of orbits around their barycenter? In other words, are there any circumstances (however absent in the real universe, but under the same laws as it) where you could have, in effect, a star-like ball of photons floating alone in space?

I get the feeling that the answer will be "that would be a black hole", but I'm not certain.

http://en.wikipedia.org/wiki/Kugelblitz ... physics%29

In theoretical physics, a kugelblitz (German: "ball lightning", not to be confused with ball lightning) is a concentration of light so intense that it forms an event horizon and becomes self-trapped: according to general relativity, if enough radiation is aimed into a region, the concentration of energy can warp spacetime enough for the region to become a black hole (although this would be a black hole whose original mass-energy had been in the form of radiant energy rather than matter). In simpler terms, a kugelblitz is a black hole formed from energy as opposed to mass.

According to Einstein's general theory of relativity, once an event horizon has formed, the type of mass-energy that created it no longer matters.

The best-known reference to the kugelblitz idea in English is probably John Archibald Wheeler's 1955 paper "Geons",[1] which explored the idea of creating particles (or toy models of particles) from spacetime curvature. Wheeler's paper on geons also introduced the idea that lines of electric charge trapped in a wormhole throat might be used to model the properties of a charged particle-pair.


Hadn't thought about that one for years, but yeah, that is an interesting tangent.
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Re: 1123: "The Universal Label"

Postby WIMP » Sat Oct 20, 2012 6:10 am UTC

Pfhorrest wrote:Question: Is the equal production of matter and antimatter strictly guaranteed by the laws responsible for it, or is it merely a statistical thing? E.g. is it possible to condense a bunch of energy into just an electron or positron, but on average a volume of high energy density will condense into equal numbers of each; or does the production of an electron demand the production of a positron to maintain conservation of something?


Always, 100% of the time, equal amounts of matter and antimatter are produced by any process, if you're purely counting antiparticles and particles. CP violation allows for some asymmetries, though. For example, a kaon decays very slightly more often into a positron and neutrino than electron and antineutrino. At the end of the day you've created as many particles as antiparticles (positron + antineutrino = neutrino + electron), but if all you care about is positrons and electrons, you've created more antimatter than matter. It's this kind of asymmetry, presumably amplified at the high energies of the early Universe, that led to today's apparent matter-antimatter imbalance. That is, lots of electrons (and baryons like the proton), not so many positrons (and antibaryons like the antiproton). But, many trillions of antineutrinos from the sun pass through your body every second, from above during the day and from below after passing through the Earth at night. Don't say antimatter doesn't exist in normal circumstances!

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Re: 1123: "The Universal Label"

Postby Max™ » Sat Oct 20, 2012 7:50 am UTC

WIMP wrote:
Pfhorrest wrote:Question: Is the equal production of matter and antimatter strictly guaranteed by the laws responsible for it, or is it merely a statistical thing? E.g. is it possible to condense a bunch of energy into just an electron or positron, but on average a volume of high energy density will condense into equal numbers of each; or does the production of an electron demand the production of a positron to maintain conservation of something?


Always, 100% of the time, equal amounts of matter and antimatter are produced by any process, if you're purely counting antiparticles and particles. CP violation allows for some asymmetries, though. For example, a kaon decays very slightly more often into a positron and neutrino than electron and antineutrino. At the end of the day you've created as many particles as antiparticles (positron + antineutrino = neutrino + electron), but if all you care about is positrons and electrons, you've created more antimatter than matter. It's this kind of asymmetry, presumably amplified at the high energies of the early Universe, that led to today's apparent matter-antimatter imbalance. That is, lots of electrons (and baryons like the proton), not so many positrons (and antibaryons like the antiproton). But, many trillions of antineutrinos from the sun pass through your body every second, from above during the day and from below after passing through the Earth at night. Don't say antimatter doesn't exist in normal circumstances!

That's only true if the Majorana mechanism holds for neutrinos, making them their own antiparticle, not a known fact. Currently the main source of antineutrinos is beta decay, solar processes produce neutrinos.
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Re: 1123: "The Universal Label"

Postby starslayer » Sat Oct 20, 2012 8:49 am UTC

Max™ wrote:A gas of high energy photons will have a temperature, as you raise the temperature of that photon gas it will begin to produce pairs of particles, matter-antimatter pairs, at something like 106 K you get lepton/anti-leptons, around 109 K you get quark/anti-quarks.
Your temperatures are waaay off. Stellar interiors do not have significant pair production, which you would expect if 106 K corresponded to MeV temperatures. 106 K is more like ~100 eV. 1010 K is where you start getting electron positron pair production. Mesons aren't made until you hit GeV temperatures.

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Re: 1123: "The Universal Label"

Postby Max™ » Sat Oct 20, 2012 10:22 am UTC

starslayer wrote:
Max™ wrote:A gas of high energy photons will have a temperature, as you raise the temperature of that photon gas it will begin to produce pairs of particles, matter-antimatter pairs, at something like 106 K you get lepton/anti-leptons, around 109 K you get quark/anti-quarks.
Your temperatures are waaay off. Stellar interiors do not have significant pair production, which you would expect if 106 K corresponded to MeV temperatures. 106 K is more like ~100 eV. 1010 K is where you start getting electron positron pair production. Mesons aren't made until you hit GeV temperatures.


Whoops, I was thinking of the times when it happened, 10-6 and 10-9 seconds after the big bang, good catch. For electrons it was 1010 K and 1013 K for protons/neutrons.
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Re: 1123: "The Universal Label"

Postby Envelope Generator » Sat Oct 20, 2012 11:19 am UTC

That's very nice, but I'm going to buy the one that also says "asbestos free".
I'm going to step off the LEM now... here we are, Pismo Beach and all the clams we can eat

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Re: 1123: "The Universal Label"

Postby SEE » Sat Oct 20, 2012 5:05 pm UTC

rmsgrey wrote:Ingredients (by mass): Hydrogen (75%), Helium (25%).


Hmm? No.

Ingredients (by mass): Dark Matter (84%), Hydrogen (12%), Helium (4%), Less than 1% Other Elements.

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Re: 1123: "The Universal Label"

Postby bmonk » Sat Oct 20, 2012 5:29 pm UTC

WIMP wrote:
Pfhorrest wrote:Question: Is the equal production of matter and antimatter strictly guaranteed by the laws responsible for it, or is it merely a statistical thing? E.g. is it possible to condense a bunch of energy into just an electron or positron, but on average a volume of high energy density will condense into equal numbers of each; or does the production of an electron demand the production of a positron to maintain conservation of something?


Always, 100% of the time, equal amounts of matter and antimatter are produced by any process, if you're purely counting antiparticles and particles. CP violation allows for some asymmetries, though. For example, a kaon decays very slightly more often into a positron and neutrino than electron and antineutrino. At the end of the day you've created as many particles as antiparticles (positron + antineutrino = neutrino + electron), but if all you care about is positrons and electrons, you've created more antimatter than matter. It's this kind of asymmetry, presumably amplified at the high energies of the early Universe, that led to today's apparent matter-antimatter imbalance. That is, lots of electrons (and baryons like the proton), not so many positrons (and antibaryons like the antiproton). But, many trillions of antineutrinos from the sun pass through your body every second, from above during the day and from below after passing through the Earth at night. Don't say antimatter doesn't exist in normal circumstances!


That's not quite true. If 100% equal matter and antimatter is produced, then how does the observed universe have such an excess of matter? There are theories that some processes must create, or destroy, matter and antimatter unequally--even if only by a billionth of one percent or less--or no matter would remain at all.
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Re: 1123: "The Universal Label"

Postby Quarg Ranger » Sat Oct 20, 2012 7:07 pm UTC

Someguy945 wrote:
Quarg Ranger wrote:People talking about Energy -

Gravitational Potential Energy will exist between the hydrogen particles. Over time this will turn to kinetic energy. The other forces are implied by the existence of hydrogen.

Also, E=mc^2 says we have energy there, which will be released when fusion starts happening, as it inevitably will.


Why is any of this an issue? Does the ingredients section for a candy bar say "Electricity" anywhere on it?


This is my argument. We are on the same side here. It's just that people were saying that the list should be 'Hydrogen, Energy, Time', which I disagree with.

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Re: 1123: "The Universal Label"

Postby KrytenKoro » Sat Oct 20, 2012 7:28 pm UTC

Max™ wrote:If the former, then while one would expect the vast majority of possible universes to contain nothing but a sea of photons from the perfect matter-antimatter annihilation, progressively smaller numbers of possible universes would contain progressively greater imbalances of one over the other. It's then simply a question of how did we get so lucky, which on a many-worlds interpretation isn't really an important question.

I may just not be aware of one of the consequences of the interpretation, but I don't see how the "all possible states of a particle exist" posited by MWI would allow for fundamental imbalances in pair production. I mean, I can see how you could it would allow for regular matter to be kept far enough away from antimatter that it has time to form, but I'm not familiar with a formulation of MWI that allows it to also vary fundamental features like Baryon assymetry, etc.

I mean, I don't see any reason why there couldn't be distinct universes which came into existence with totally different setups for their fundamental constants, I just don't see how that has anything to do with MWI. Please inform me if I'm wrong.
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Re: 1123: "The Universal Label"

Postby Max™ » Sat Oct 20, 2012 8:10 pm UTC

KrytenKoro wrote:
Pfhorrest wrote:If the former, then while one would expect the vast majority of possible universes to contain nothing but a sea of photons from the perfect matter-antimatter annihilation, progressively smaller numbers of possible universes would contain progressively greater imbalances of one over the other. It's then simply a question of how did we get so lucky, which on a many-worlds interpretation isn't really an important question.

I may just not be aware of one of the consequences of the interpretation, but I don't see how the "all possible states of a particle exist" posited by MWI would allow for fundamental imbalances in pair production. I mean, I can see how you could it would allow for regular matter to be kept far enough away from antimatter that it has time to form, but I'm not familiar with a formulation of MWI that allows it to also vary fundamental features like Baryon assymetry, etc.

I mean, I don't see any reason why there couldn't be distinct universes which came into existence with totally different setups for their fundamental constants, I just don't see how that has anything to do with MWI. Please inform me if I'm wrong.

Wasn't my quote.
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Re: 1123: "The Universal Label"

Postby orthogon » Sun Oct 21, 2012 4:27 pm UTC

Pfhorrest wrote:Warning:
This object attracts every other object in the universe with a force proportional to the product of their masses and inversely proportional to the distance between them.

(My old high school physics book actually had that warning label on it...)

Your school textbook was made out some weird stuff that attracted objects according to an inverse (not inverse-square) law? Cool! Do you still have it? Or did it get sucked into the Sun? (If I didn't have a hangover I'd actually attempt the calculation.)
xtifr wrote:... and orthogon merely sounds undecided.

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Re: 1123: "The Universal Label"

Postby blackcoffee42 » Sun Oct 21, 2012 6:52 pm UTC

Shouldn't the Universal Label be:
Ingredients: Quantum Fluctuations, Time

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Re: 1123: "The Universal Label"

Postby addams » Mon Oct 22, 2012 4:37 am UTC

MAX!! I was able to see the graphics of the early Universe. Very nice.
Yes. That is the way I learned it. I don't want to unlearn it and learn something new on a whim.

The graphics make sense and they are pretty.

All that universe out there for sooo long. We get to think we can see and understand some of it.

I am at the mercy of the hardware. Sometimes it says, "YES". Sometimes it says, "No".

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Re: 1123: "The Universal Label"

Postby gerv » Mon Oct 22, 2012 9:25 am UTC

Presumably this label could also be stuck on humans?

If all you are is hydrogen and time, same as a star or a rock, then how can things like personality, morality, value or obligation have any real meaning? The big bag of fizzing chemicals which is me behaves one way; the other big bag which is you behaves another. Who is to say which is "better"? Where does the idea that there is such a thing as "better" even come from? It's all just hydrogen and time.

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Re: 1123: "The Universal Label"

Postby Technical Ben » Mon Oct 22, 2012 11:20 am UTC

You could make anything out of thyme and time. Given sufficient amounts of either.
It's all physics and stamp collecting.
It's not a particle or a wave. It's just an exchange.

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Re: 1123: "The Universal Label"

Postby rmsgrey » Mon Oct 22, 2012 11:50 am UTC

SEE wrote:
rmsgrey wrote:Ingredients (by mass): Hydrogen (75%), Helium (25%).


Hmm? No.

Ingredients (by mass): Dark Matter (84%), Hydrogen (12%), Helium (4%), Less than 1% Other Elements.


You left out energy...

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Re: 1123: "The Universal Label"

Postby Beatrice The Golden » Mon Oct 22, 2012 12:00 pm UTC

gerv wrote:If all you are is hydrogen and time, same as a star or a rock, then how can things like personality, morality, value or obligation have any real meaning?


Right. This label is simply depressing...
There is but one universal ingredient from which all matter is created.

And it's not hydrogen.

The Universal Label
Ingredients: Love
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Re: 1123: "The Universal Label"

Postby mathmannix » Mon Oct 22, 2012 2:37 pm UTC

SEE wrote:
rmsgrey wrote:Ingredients (by mass): Hydrogen (75%), Helium (25%).


Hmm? No.

Ingredients (by mass): Dark Matter (84%), Hydrogen (12%), Helium (4%), Less than 1% Other Elements.


"Dark Matter" is just normal matter in the 8 adjoining universes which are close enough for us to indirectly detect.
I hear velociraptor tastes like chicken.

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Re: 1123: "The Universal Label"

Postby Max™ » Mon Oct 22, 2012 6:13 pm UTC

rmsgrey wrote:
SEE wrote:
rmsgrey wrote:Ingredients (by mass): Hydrogen (75%), Helium (25%).


Hmm? No.

Ingredients (by mass): Dark Matter (84%), Hydrogen (12%), Helium (4%), Less than 1% Other Elements.


You left out energy...

If you have matter, you have mass, so the stress energy tensor is nonzero, i.e. you have gravity, which is more than enough energy to do everything else we're interested in.
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Re: 1123: "The Universal Label"

Postby KarenRei » Mon Oct 22, 2012 11:29 pm UTC

(message lost to dark energy-accelerated expansion)
Last edited by KarenRei on Wed Oct 24, 2012 1:41 am UTC, edited 1 time in total.

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Re: 1123: "The Universal Label"

Postby Max™ » Tue Oct 23, 2012 12:38 am UTC

I'm amazed you didn't notice all the people who pointed that out already. :P

Still, if you start with enough hydrogen, over enough time you will wind up with all the elements we see around us.
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Re: 1123: "The Universal Label"

Postby ijuin » Tue Oct 23, 2012 1:28 am UTC

Pfhorrest wrote:
watergrinder wrote:Probably should be "naturally flavored quarks"

I'd be more impressed with artificially flavored quarks.

Which flavors? Up, down, top, bottom, strange, or charm? ^_^

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Re: 1123: "The Universal Label"

Postby Max™ » Tue Oct 23, 2012 1:48 am UTC

I've been trying to cut back on quarks, you can never have just one, you see.
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Re: 1123: "The Universal Label"

Postby addams » Tue Oct 23, 2012 6:21 pm UTC

Beatrice The Golden wrote:
gerv wrote:If all you are is hydrogen and time, same as a star or a rock, then how can things like personality, morality, value or obligation have any real meaning?


Right. This label is simply depressing...
There is but one universal ingredient from which all matter is created.

And it's not hydrogen.

The Universal Label
Ingredients: Love


Some one memorized the names of the quarks. What would make a person do such a thing?

A desire to be Loveable?

It works. Strange and Charm are my favorites; Because! It's so true.
Life is, just, an exchange of electrons; It is up to us to give it meaning.

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Re: 1123: "The Universal Label"

Postby WIMP » Wed Oct 24, 2012 11:32 pm UTC

bmonk wrote:
WIMP wrote:
Pfhorrest wrote:Question: Is the equal production of matter and antimatter strictly guaranteed by the laws responsible for it, or is it merely a statistical thing? E.g. is it possible to condense a bunch of energy into just an electron or positron, but on average a volume of high energy density will condense into equal numbers of each; or does the production of an electron demand the production of a positron to maintain conservation of something?


Always, 100% of the time, equal amounts of matter and antimatter are produced by any process, if you're purely counting antiparticles and particles. CP violation allows for some asymmetries, though. For example, a kaon decays very slightly more often into a positron and neutrino than electron and antineutrino. At the end of the day you've created as many particles as antiparticles (positron + antineutrino = neutrino + electron), but if all you care about is positrons and electrons, you've created more antimatter than matter. It's this kind of asymmetry, presumably amplified at the high energies of the early Universe, that led to today's apparent matter-antimatter imbalance. That is, lots of electrons (and baryons like the proton), not so many positrons (and antibaryons like the antiproton). But, many trillions of antineutrinos from the sun pass through your body every second, from above during the day and from below after passing through the Earth at night. Don't say antimatter doesn't exist in normal circumstances!


That's not quite true. If 100% equal matter and antimatter is produced, then how does the observed universe have such an excess of matter? There are theories that some processes must create, or destroy, matter and antimatter unequally--even if only by a billionth of one percent or less--or no matter would remain at all.


Because the observed particles are the equivalent of the electron, and the unobserved particles are the equivalent of the antineutrino. That is, the Universe is dominated by protons and electrons, not antiprotons and positrons, but something else somewhere is picking up the slack for antimatter.

The dominant theory for the imbalance is enhanced CP violation in the early Universe (ie a "dynamical" source). CP violation *does not* produce one electron and nothing else. It produces an electron and antineutrino more often than a positron and neutrino (or vice versa, and the equivalents for other particles). For example, the long lived kaon decays to a positron and neutrino (plus other stuff) more often than to an electron and antineutrino (plus other different stuff), to the tune of a part in 10,000 if memory serves. That is not the same thing as decaying to an electron and neutrino alone, thus cutting antimatter out of the equation entirely. The decay treats matter and antimatter differently, meeting the definition of CP violation, and at first glance it appears to produce antimatter more often than matter, but only if you're biased towards easily detectable particles (electrons and positrons) instead of hard-to-detect particles (the neutrinos).

It is impossible, in the fundamental structure of quantum field theories, to produce unequal amounts of matter and antimatter. CP violation treats matter and antimatter differently, allowing for an imbalance in, say, electrons and positrons (this is what's observed in the Universe--in favor of electrons), but not an overall matter-antimatter imbalance (so there'd be, for example, a reverse imbalance in favor of antineutrinos over neutrinos). The Standard Model CP violation is far too small to account for the observed effect, so there must be enhanced CP violation at high energies, but the mechanism is widely agreed to be similar to the small effect seen at low energies, just on a different order of magnitude.

And the comment about Majorana neutrinos is correct but in the opposite direction. What I say is *false* in a sense if neutrinos turn out to be Majorana particles, and true iff they are Dirac particles. You can make a case that Majorana neutrinos make sense, but there is an ever so slightly more compelling case that they're Dirac particles, and that's the Standard Model interpretation. I'll come back and edit this if anyone finds neutrinoless double beta decay == they're Majorana. :)

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Re: 1123: "The Universal Label"

Postby Max™ » Thu Oct 25, 2012 2:19 am UTC

I brought up Majorana as that is the situation when they are their own antiparticles.
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Re: 1123: "The Universal Label"

Postby ijuin » Thu Oct 25, 2012 9:11 am UTC

Given that Neutrinos do not attract/repel through the Electromagnetic or Strong Nuclear forces, and that they only collide with the (much larger than themselves) atomic nuclei at a rate of something like one per several tons of solid matter per year (i.e. one collision per year for approximately 10^30 nuclei), it's quite plausible that there are a comparable magnitude of antineutrinos as neutrinos flying about, since only a very rare direct collision between a neutrino and an antineutrino would ever produce an annihilation (akin to shooting down an incoming bullet with another bullet, only both bullets are going at the speed of light and are a thousand times smaller than protons).

If there are lots of antineutrinos out there, and neutrinos turn out NOT to be their own antiparticles, then gamma ray detectors in orbit ought to detect the occasional gamma photon of the right energy for neutrino/antineutrino annihilation (just as they pick up the occasional electron/positron annihilation). Slightly problematic however is that we don't KNOW the exact rest mass of neutrinos, so we aren't quite sure how much energy would be released per neutrino/antineutrino collision.

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Re: 1123: "The Universal Label"

Postby WIMP » Sun Oct 28, 2012 1:44 am UTC

ijuin wrote:Given that Neutrinos do not attract/repel through the Electromagnetic or Strong Nuclear forces, and that they only collide with the (much larger than themselves) atomic nuclei at a rate of something like one per several tons of solid matter per year (i.e. one collision per year for approximately 10^30 nuclei), it's quite plausible that there are a comparable magnitude of antineutrinos as neutrinos flying about, since only a very rare direct collision between a neutrino and an antineutrino would ever produce an annihilation (akin to shooting down an incoming bullet with another bullet, only both bullets are going at the speed of light and are a thousand times smaller than protons).

If there are lots of antineutrinos out there, and neutrinos turn out NOT to be their own antiparticles, then gamma ray detectors in orbit ought to detect the occasional gamma photon of the right energy for neutrino/antineutrino annihilation (just as they pick up the occasional electron/positron annihilation). Slightly problematic however is that we don't KNOW the exact rest mass of neutrinos, so we aren't quite sure how much energy would be released per neutrino/antineutrino collision.


Neutrino rest energy wouldn't matter, since they're always relativistic. It's total energy that's liberated by annihilation events, which means neutrino annihilation events would have variable energy and are (a small) part of the continuum gamma ray background processes. Positrons and electrons produce consistent 511 keV photon pairs when they annihilate at nonrelativistic speeds because their kinetic energies are dwarfed by their rest energies (511 keV each); not so for neutrinos. Neutrinos are also unlikely to annihilate to photons, since they don't interact with them directly. They're more likely to annihilate to relativistic fermion-antifermion pairs through an intermediate Z boson, although they can go to photons through a loop similar to how a Higgs can decay rarely to two photons despite not interacting with them.

If neutrinos and antineutrinos are in fact the same particle, this doesn't affect their annihilations. It just makes certain exotic processes like neutrinoless double beta decay possible.

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Re: 1123: "The Universal Label"

Postby ijuin » Sun Oct 28, 2012 7:21 am UTC

The question is, then, how do we go about detecting (and recognizing) neutrino-antineutrino annihilation events, if such actually occur? Detecting such events would be a big step towards being able to determine the amount of antineutrinos in the universe


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