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> Why the Universe is filled with matter, rather than > antimatter, is one of physics’ greatest mysteries. Why do we assume there is no anti-matter just b

by runeks 10y ago

> Why the Universe is filled with matter, rather than > antimatter, is one of physics’ greatest mysteries. Why do we assume there is no anti-matter just because we can't observe it? Our sensory organs were developed to survive on this planet. They're made out of matter and evolved to detect the presence of matter. And when we make a detector it's made out of matter too. I don't think it's farfetched to assume that matter-antimatter collisions occur all the time; they're just not that spectacular. It may even be a bit presumptuous to assume that it's even possible for matter to ever detect the presence of anti-matter. Because, detecting the presence of anti-matter just constitutes looking at the radiation left behind by a "collision" with matter. That's not observing anti-matter, it's an after-the-fact conclusion, that there must had been anti-matter before the radiation in question appeared. As soon as matter observes/comes in contact with anti-matter, it's no longer matter. So matter, in and of itself, seemingly cannot observe anti-matter (because it's transformed into something else at the moment it does). Reading Wikipedia, it also appears that the matter/anti-matter relationship is asymmetric: Bondi pointed out that a negative mass will fall toward (and not away from) "normal" matter, since although the gravitational force is repulsive, the negative mass (according to Newton's law, F=ma) responds by accelerating in the opposite of the direction of the force. Normal mass, on the other hand, will fall away from the negative matter. He noted that two identical masses, one positive and one negative, placed near each other will therefore self-accelerate in the direction of the line between them, with the negative mass chasing after the positive mass. Notice that because the negative mass acquires negative kinetic energy, the total energy of the accelerating masses remains at zero. Forward pointed out that the self-acceleration effect is due to the negative inertial mass, and could be seen induced without the gravitational forces between the particles. --- https://en.wikipedia.org/wiki/Anti-gravity#General_relativity_research_in_the_1950s https://en.wikipedia.org/wiki/Anti-gravity#General_relativit... Fascinating stuff!

dogma1138 10y ago
We know that there is no or very little anti matter in the universe because things are not blowing up, we also know that matter and anti matter have been created in equal amounts, hence were looking into what the frak happened to all the anti matter. Also anti matter reacts to the fundamental forces just like any other matter. It doesn't produce anti mass, anti gravity or anti anything. It does have an opposite charge and spin off its normal matter counterparts but other than that its pretty boring. weve made anti hydrogen, oxygen is pretty big so it would take a while before we can make anti water but it will be done also most likely.
- runeks 10y ago
  I guess I stand corrected on some points, but Wikipedia seems a lot less certain than you regarding anti-gravity. > Antihydrogen atoms should be attracted to other matter > or antimatter gravitationally with a force of the same > magnitude that ordinary hydrogen atoms experience. > This would not be true if antimatter has negative > gravitational mass, which is considered highly unlikely, > though not yet empirically disproven (see gravitational > interaction of antimatter). I'm not sure what the exact meaning of "highly unlikely" is in this context. https://en.wikipedia.org/wiki/Antihydrogen#Characteristics https://en.wikipedia.org/wiki/Antihydrogen#Characteristics https://en.wikipedia.org/wiki/Gravitational_interaction_of_antimatter https://en.wikipedia.org/wiki/Gravitational_interaction_of_a...
  - dragonwriter 10y ago
    I think it means that the theorized nature of antimatter in the dominant model has positive mass, other elements of that theory have proven out well, but we generate antimatter in the quantities we'd need to do good tests of gravitational interaction, so we haven't empirically verified its gravitational interaction.
  - dogma1138 10y ago
    Gravity is the result of matter(or energy) interacting (bending) spacetime. All massive objects bend space time hence they generate gravity, the mass of an anti proton is exactly the same as that of a proton. We haven't observed full gravitational interactions because we only create tiny amounts of anti matter, and even less of molecular anti matter. Since all anti matter must be kept in vacuum and electro magnetic containment it's a bit hard to check how does anti mater works with gravity. There are very little frameworks where anti matter actually interacts differently with gravity and hence space time. Even MTOG theories tend to treat anti matter in the same manner, it has a positive mass (we can verify that), if it has a positive mass it also has a positive energy, if it has that it should interact with gravity in the same manner as any other massive object.
drdeca 10y ago
Err, I'm pretty sure that anti hydrogen has been created and stored, and I'm pretty sure this included detecting it without it annihilating .
dozzie 10y ago
> Our sensory organs were developed to survive on this planet. They're made out of matter and evolved to detect the presence of matter. And when we make a detector it's made out of matter too. You don't understand how this "antimatter" thing works, do you?
cdumler 10y ago
In science, you never trust your own eyes. By using machines to do the observing we can see all kinds of things, such as X-rays and neutrinos. Those devices can pick up patterns of radiation are the hallmarks of matter/anti-matter collisions. We see those signs now, faintly. It can be tracked down to various processes, such as when cosmic rays strike the atmosphere of Earth. But, even though it is seen out in the cosmos, effects are far too small. We would expect that if galaxy-sized clumps of anti-matter existed, the anti-matter hydrogen would be aglow with anti-matter radiation as it collided with hydrogen from near by matter galaxies. We can observe back to almost the beginning of time by looking into the distance. Even there, we don't see the imbalance. This suggests that something happened right at the beginning.
scentoni 10y ago
Antimatter has positive mass. Negative mass is a hypothetical construct that does not appear to exist.
- runeks 10y ago
  Can you point me in the direction of the empirical evidence from which you conclude this?
  - TheOtherHobbes 10y ago
    The experiments to settle this are still being designed. But one of the most recent found no evidence for negative gravity up to a non-definitive but suggestive level of accuracy: http://alpha.web.cern.ch/node/248 http://alpha.web.cern.ch/node/248
deleted 10y ago
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by runeks 10y ago

dogma1138 10y ago

We know that there is no or very little anti matter in the universe because things are not blowing up, we also know that matter and anti matter have been created in equal amounts, hence were looking into what the frak happened to all the anti matter. Also anti matter reacts to the fundamental forces just like any other matter. It doesn't produce anti mass, anti gravity or anti anything. It does have an opposite charge and spin off its normal matter counterparts but other than that its pretty boring. weve made anti hydrogen, oxygen is pretty big so it would take a while before we can make anti water but it will be done also most likely.

runeks 10y ago
I guess I stand corrected on some points, but Wikipedia seems a lot less certain than you regarding anti-gravity. > Antihydrogen atoms should be attracted to other matter > or antimatter gravitationally with a force of the same > magnitude that ordinary hydrogen atoms experience. > This would not be true if antimatter has negative > gravitational mass, which is considered highly unlikely, > though not yet empirically disproven (see gravitational > interaction of antimatter). I'm not sure what the exact meaning of "highly unlikely" is in this context. https://en.wikipedia.org/wiki/Antihydrogen#Characteristics https://en.wikipedia.org/wiki/Antihydrogen#Characteristics https://en.wikipedia.org/wiki/Gravitational_interaction_of_antimatter https://en.wikipedia.org/wiki/Gravitational_interaction_of_a...
- dragonwriter 10y ago
  I think it means that the theorized nature of antimatter in the dominant model has positive mass, other elements of that theory have proven out well, but we generate antimatter in the quantities we'd need to do good tests of gravitational interaction, so we haven't empirically verified its gravitational interaction.
- dogma1138 10y ago
  Gravity is the result of matter(or energy) interacting (bending) spacetime. All massive objects bend space time hence they generate gravity, the mass of an anti proton is exactly the same as that of a proton. We haven't observed full gravitational interactions because we only create tiny amounts of anti matter, and even less of molecular anti matter. Since all anti matter must be kept in vacuum and electro magnetic containment it's a bit hard to check how does anti mater works with gravity. There are very little frameworks where anti matter actually interacts differently with gravity and hence space time. Even MTOG theories tend to treat anti matter in the same manner, it has a positive mass (we can verify that), if it has a positive mass it also has a positive energy, if it has that it should interact with gravity in the same manner as any other massive object.

drdeca 10y ago

Err, I'm pretty sure that anti hydrogen has been created and stored, and I'm pretty sure this included detecting it without it annihilating .

dozzie 10y ago

> Our sensory organs were developed to survive on this planet. They're made out of matter and evolved to detect the presence of matter. And when we make a detector it's made out of matter too. You don't understand how this "antimatter" thing works, do you?

cdumler 10y ago

In science, you never trust your own eyes. By using machines to do the observing we can see all kinds of things, such as X-rays and neutrinos. Those devices can pick up patterns of radiation are the hallmarks of matter/anti-matter collisions. We see those signs now, faintly. It can be tracked down to various processes, such as when cosmic rays strike the atmosphere of Earth. But, even though it is seen out in the cosmos, effects are far too small. We would expect that if galaxy-sized clumps of anti-matter existed, the anti-matter hydrogen would be aglow with anti-matter radiation as it collided with hydrogen from near by matter galaxies. We can observe back to almost the beginning of time by looking into the distance. Even there, we don't see the imbalance. This suggests that something happened right at the beginning.

scentoni 10y ago

Antimatter has positive mass. Negative mass is a hypothetical construct that does not appear to exist.

runeks 10y ago
Can you point me in the direction of the empirical evidence from which you conclude this?
- TheOtherHobbes 10y ago
  The experiments to settle this are still being designed. But one of the most recent found no evidence for negative gravity up to a non-definitive but suggestive level of accuracy: http://alpha.web.cern.ch/node/248 http://alpha.web.cern.ch/node/248

deleted 10y ago

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