While there does seem to be a lot of dark matter out there, if it were actually antimatter and had opposite gravity to normal matter one would imagine there would be a huge discrepancy between cosmologists' models and observation. The high-end supercomputer simulations and regressions cosmologists employ have good predictive power, even though we lack a full explanation for the phenomena we can observe. Cosmologists deal with such far-out concepts to begin with (by definition) that it's not as if they'd be averse to a concept like antigravity if it had predictive utility.
toys idly with desk magnets while thinking about it
Then again, given that photons are massless maybe there could be such a thing as a gravitational dipole...
/timecube
The first property rules out baryonic antimatter as dark matter, since that would interact electromagnetically. The last two properties rule out anything that has a repulsive gravitational interaction as dark matter.
For example, if antimatter rises, there ought to be a statistical preference for black holes to emit antimatter.
One of the posters on that site said CPT violation would be another great thing to check. Hell yeah!
Don't worry. The design is impractical anyway - regulating the "anti-mass" would be extremely difficult. Just when you got it balanced, the kid would drink a glass of water and the board would sink into the ground.
Due caution would indeed be advisable when selling these gadgets, though. A matter-antimatter collision of 50kg would be equivalent to about 2.1 gigatons of TNT, or about 400 times more powerful than the most powerful hydogen bomb ever developed, so it would indeed caused a "considerable amount of damage".
We may still see some normal devices which use antimatter in one way or another.
http://en.wikipedia.org/wiki/Worm_hole#Traversable_wormholes http://en.wikipedia.org/wiki/Alcubierre_drive
the pieces of Universe that is more than 13B light years from us are moving with speed faster than light relative to us. The machinery behind it is space expansion. And by definition that is using energy less or equal to the universe's energy. So that is the start. The Alcubierre drive is the idea of how to use the same principle on much smaller scale. It is very doubtful that it would require more energy than moving the whole galaxies [which, let me repeat, are moving faster than light relative to us and to each other]
I would see no reason for Newton's law to not hold true around our scale, so repelling means F=Gm1m2/r^2 which only makes sense if one of the masses is actually negative. Just the thought of it looks like fun.
I am also surprised.
Therefore, how do we know distant galaxies aren't made of antimatter ?
Maybe there's an obvious answer, but as far as I know, the only thing we can know about these galaxies, we know because of the radiation they emit.
Rgd "anti matter galaxies", we do detect particle cosmic rays on earth that originate from outer space (outside the solar system), though I don't know either whether they might originate from as far as other galaxies.
However, gravity is weak compared to the other forces, so galaxies can be expected to eject fast moving matter in addition to radiation (just like our sun).
So, given my meagre understanding of physics, I wouldn't expect to have seen anti-matter galaxies without also seeing gamma radiation fields spanning the space between a matter and an antimatter galaxy as particles annihilate each other.
Most people believe antimatter attract just like matter, so it's a moot point.
So, umm, no.
Though strictly speaking, from a bomb-building point of view, it would be very difficult to design a weapon where matter-antimatter mixing happened more or less completely and simultaneously. Otherwise you "merely" have a series of uncontrolled multi-megatonne explosions in an increasingly large area, instead of a single multi-gigatonne explosion.
How do you cool something at this scale? And how about when it can't collide with any normal matter?
although iirc Dark matter is something does not interact with light.
"The long term storage of significant amounts of antihydrogen should soon settle the question of whether antimatter falls up or down."
One reason they would like to know if antimatter is repelled by gravity is that it could explain why the Universe is expanding at an accelerating rate.[1]
[1]: http://www.physorg.com/news/2011-04-antimatter-gravity-unive...
Would this mean that if I am "holding onto" a chunk of antimatter heaver than myself I will fall up into space?
The civilizations of the galaxy call it... MASS EFFECT.
