By the way, there's something I've been wondering about for a long time.
I read somewhere that there are no antiphotons and antimatter emits light just the same as normal matter.
So, I assume that there's no way to tell whether a photon was emitted by antimatter or by matter.
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.
Empty space isn't completely empty, even between galaxies. There are traces of gas, almost entirely Hydrogen, between galaxies. If there were entire galaxies made of anti-matter then the areas where their clouds of inter-galactic anti-gas contacted normal inter-galactic gas would be rife with emissions due to annihilations. The amount of matter should be enough to be detectable even at tremendous distances.
I've wondered this myself. An explanation I have heard from a physisicist is: if there were regions of the universe where antimatter is dominant, the boundaries where they border normal matter space would be extremely bright from the annihilation reactions. Apparently even very thin interstellar gas would generate a lot of energy in matter/antimatter annihilations.
I think the way that is usually phrased is that "photons are their own antiparticles".
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.
If antimatter are repulsed by gravity, they might be in the outer shell of the universe being pushed further away. If antimatter also repulsed among themselves (??), then they won't have a chance to come together to create antimatter star.
Most people believe antimatter attract just like matter, so it's a moot point.
Well, the point of science is that we don't know until we observe it. So it shouldn't be that astounding since we've had a ridiculously hard time getting large amounts of neutral antimatter (everything before was charged, so EM affects overwhelmed gravitational). The consensus seems to be that antimatter will behave 'normally'. but we haven't seen it yet. Also, it turns out that certain frameworks where anti-matter is repelled by matter gravity doesn't violate anything else that hasn't already been violated (for example, CP and CPT symmetry have already be observed to be broken). And thus the uncertainty.
I've never heard anyone argue that it would react any differently to gravity than normal matter. After all, the only difference is the electrical charge of the particles. They have the same mass.
I'm with you on this one. If antimatter was just backwards everything then there'd be large conspicuous clusters of the stuff all over the cosmos because ordinary matter would be repelling it instead of annihilating it.
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...
It is actually great that they're doing this experiment 'cos if it turned out in a way that contradicted theory (which I think says "antimatter falls") then we might have to re-examine a whole lot of things!
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!
If it is proven that that anti-matter is repelled by gravity does that mean hover-boards will become a reality in our lifetimes? What are some of the potential practical applications?
Given that antimatter explodes violently when put into contact with regular matter, I kind of hope that's not how they go about achieving this. A kid who forgets to recharge his board, allowing the magnetic fields to collapse, could do a considerable amount of damage.
No. I am not a physicist, but my understanding is that certain devices that have been proposed for use in space manipulation devices (e.g. wormholes, alcubierre drive), require either a form of matter that has reverse gravity or thousands of times the available energy of the known universe.
Possibly with something like http://en.wikipedia.org/wiki/Laser_cooling, where you're not actually striking it with matter, but only with photons, though I don't know if photons react with antimatter (I presume not, but I am not a particle physicist).
Assuming 1kg of antimatter can be used to hover 1kg of matter and that your hoverboard could carry 80kg, should it's containment fail, it would detonate with the force of 3.4 gigatons of tnt. That's roughly equivalent with the entire present nuclear arsenal of the united states, and would cause 3rd degree burns out of direct thermal radiation over 300 kilometers away.
Ooooh, if antimatter is repelled by gravity, that means that cavorite actually is antimatter, and therefore possible? I've always thought that cavorite is the cleverest Science Fiction device ever imagined...
"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]
[+] [-] Typhon|15 years ago|reply
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.
[+] [-] InclinedPlane|15 years ago|reply
[+] [-] othermaciej|15 years ago|reply
[+] [-] aufreak3|15 years ago|reply
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.
[+] [-] ww520|15 years ago|reply
Most people believe antimatter attract just like matter, so it's a moot point.
[+] [-] ordinary|15 years ago|reply
[+] [-] icegreentea|15 years ago|reply
[+] [-] sp332|15 years ago|reply
[+] [-] monochromatic|15 years ago|reply
I am also surprised.
[+] [-] martinkallstrom|15 years ago|reply
[+] [-] anigbrowl|15 years ago|reply
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
[+] [-] enko|15 years ago|reply
[+] [-] kingsidharth|15 years ago|reply
[+] [-] aufreak3|15 years ago|reply
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!
[+] [-] dadro|15 years ago|reply
[+] [-] gecko|15 years ago|reply
[+] [-] jxcole|15 years ago|reply
http://en.wikipedia.org/wiki/Worm_hole#Traversable_wormholes http://en.wikipedia.org/wiki/Alcubierre_drive
[+] [-] danparsonson|15 years ago|reply
How do you cool something at this scale? And how about when it can't collide with any normal matter?
[+] [-] SeveredCross|15 years ago|reply
[+] [-] ljf|15 years ago|reply
[+] [-] Tuna-Fish|15 years ago|reply
So, umm, no.
[+] [-] civilian|15 years ago|reply
[+] [-] ww520|15 years ago|reply
[+] [-] wazoox|15 years ago|reply
[+] [-] mmaunder|15 years ago|reply
[+] [-] unwantedLetters|15 years ago|reply
[+] [-] coderdude|15 years ago|reply
"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...
[+] [-] eduardoflores|15 years ago|reply
[+] [-] unknown|15 years ago|reply
[deleted]
[+] [-] Apocryphon|15 years ago|reply
The civilizations of the galaxy call it... MASS EFFECT.