From: Andy Benn 27/09/2001 7:46:22 Subject: Anti Matter post id: 429626 What is Anti matter From: Geraint ® 27/09/2001 7:49:27 Subject: re: Anti Matter post id: 429627 Its the same as ordinary matter, except the charge is the opposite. So, when a proton has a positive charge, an anti-proton has a negative charge. There are subtle differences between the interaction of anti-matter when compared to matter, but if we replaced all the matter in the universe with antimatter we would be none the wiser. From: Zardoz ® 27/09/2001 7:50:28 Subject: re: Anti Matter post id: 429628 The discovery of antiparticles fell into the - in my opinion - most interesting era of physics research: the time between 1920 and 1950. The first `piece' of antimatter to be found was the positron - the positively charged counterpart of the electron. The theoretical physicist Paul Dirac discovered it in 1927 `at the tip of his pen'. He had derived an equation (which we now call the `Dirac Equation') in order to describe the relativistic behaviour of electrons. Amazingly, this equation has solutions not only for electrons, but also for other particles with the same characteristics of electrons but with opposite charge. Much later, in 1977, Dirac wrote: ``I was reconciled to the fact that the negative energy states could not be excluded from the mathematical theory, and so I thought, let us try and find a physical explanation for them.'' And that was exactly what he did; he refused to throw away those solutions as a mathematical curiosity and had the courage to take them as a serious hint on new physics. He postulated that there must be particles which ``look'' exactly like electrons except for their opposite charge. But, as you might know, a theoretical prediction is worthless if it can't be confirmed by experiment. In 1932, Carl Anderson performed cloud chamber experiments to investigate high-energy cosmic radiation. Some of the tracks he identified had to be attributed to the very particle whose existence Dirac had predicted five years before! Astonishingly, he didn't know very much about Dirac's work. Later he wrote about Dirac's papers: ``[Their] highly esoteric character was apparently not in tune with most of the scientific thinking of the day... The discovery of the positron was wholly accidental.'' Scientific discovery seems to have its own, strange rules. This has not changed very much in the course of the last 60 years. As to your second question, there are many many ways to produce antiparticles in the laboratory. One possibility is pair production: A photon with enough energy (more than twice the rest energy of an electron) can spontaneously transform into an electron-positron pair if there is another massive particle around (such as a nucleus) to take some of the momentum (without this additional condition, pair production out of a single photon is impossible because energy and momentum cannot be conserved simultaneously). In collisions of heavy nuclei, as they are performed e.g. at CERN or at Brookhaven, other types of antiparticles emerge: Antoprotons, antineutrons, antimuons etc etc. The basic requirement is that there is enough energy around to produce the particle. You might have noticed that I've hesitated so far to use the term `antimatter'. This is so because this term should be reserved for something which is what we usually observe as `matter': atoms and molecules. The most simple `piece of antimatter' would accordingly be an antihydrogen atom, which is a positron bound to an antiproton. This has been produced only recently. In 1995, a research collaboration at CERN has managed to create 11 atoms of antihydrogen. The difficulty with this is that the positron and the antiproton must have a relative kinetic energy which is so low that they can form a bound state (and not just pass each other with a shy glance :-). Many interesting experiments could be done if we had antihydrogen in lab-scale quantities. One of the most interesting questions is whether antimatter is affected in the same way by gravity as ordinary matter. http://ikpe1101.ikp.kfa-juelich.de/ps210/" The CERN-experiment that proved the existence of Antihydrogen http://www.madsci.org/posts/archives/mar97/857469573.Ph.r.html From: B.C. ® 27/09/2001 8:02:27 Subject: re: Anti Matter post id: 429633 Interesting point......After the BB there was presumably a surplus of matter over anti matter, so after all the anti matter was anhiliated with matter we had left over normal matter. If this had been different, in other words if there had been more anti matter than matter, we would probably still be here..there would be no difference....we would be calling normal matter anti matter, and anti matter normal matter. From: MichaelT 27/09/2001 8:05:11 Subject: re: Anti Matter post id: 429634 "If this had been different, in other words if there had been more anti matter than matter" And if it had been different in that there was the same amount? Silly question - not worth thinking about. From: Geraint ® 27/09/2001 8:06:34 Subject: re: Anti Matter post id: 429635 Hi BC - Yeah, (just about) everything would be the same. The difference would appear at the particle level as we see CP violation, our antimatter cousins would see the opposite. From: Chris (Avatar) 27/09/2001 9:49:25 Subject: re: Anti Matter post id: 429742 And if it had been different in that there was the same amount? Matter and antimatter annihilate when they meet, so equal amounts would mean little or no matter or antimatter in a radiation filled universe. This is not so different from our own universe. Radiation dominates matter by a factor of a billion times (ie there are 1 billion photons for every particle of matter in the universe). By extension you can see that the matter over antimatter domination in the early universe must have been as small as one part in a billion to produce the radiation/matter ratio we see today. Hope this helps! Chris From: John Devers ® 28/09/2001 2:26:06 Subject: re: Anti Matter post id: 431195 So are you guys that are saying there is no difference trying to convince me that anti-matter is not made out of anti-quarks? AFAIK the only thing the same about matter and anti-matter is the way it interacts with light in a spectrometer. It is not made of the same stuff as matter and has less points in common with matter than it does points in common with matter, From: John Devers ® 28/09/2001 2:46:57 Subject: re: Anti Matter post id: 431196 Above should read, It is not made of the same stuff as matter and has more points in That are not in common with matter than it does points that are in common with matter. In other words anti-matter is only the same as matter when matter and antimatter are pure energy being carried by a photon. As a pure form of antimatter particle I would have to say they are almost completly different. This forum is un-moderated. The views and opinions expressed are those of the individual poster and not the ABC. The ABC reserves the right to remove offensive or inappropriate messages.