Expert: James Gort - 4/19/2010

Question
Hi again. Thankyou for your last reply, it was very helpful. Just one more question please that arose on reading your answer. Can any of the observations we make CURRENTLY on the universe distinguish if it is anti matter we are 'looking' at? Im guessing the answer is no. So we have no way of knowing if we are the exception? Neighbouring galaxies may be anti matter? Could it even be possible that parts of our own galaxy are anti matter? Is it unlikely...or impossible, that some bodies in our galaxy could be anti matter. Is there evidence that the big bang created a slight discrepancy in matter to anti matter-do theories point to this? Or is that just speculated because we,and matter, are here! I am just feeling if we have no test/observation of anti matter, the universe could be empty of it, or teeming with it. And finally, do we absolutely know that any phenomena we see isn't a result of matter/anti matter annihilation such as supernova etc-put another way are there some things out there that COULD be a result of annihilation? Thankyou very much for your time again  Regards Richard.

Answer
Hi Richard,

Just a follow-up and a suggestion.  Get the book "Antimatter" by Frank Close.  It's a small paperback from Oxford University Press, fairly inexpensive, but written by a high energy physicist for the general audience.  Again, hope that helps.  

Prof. James Gort


Previous answer:

We have no direct observational proof that anti-matter exists (or doesn't exist) as the main constituent in other stars or galaxies.  We just can't tell for sure.  The light we see would be identical.  But we have indirect evidence that antimatter stars (or even galaxies) are probably not close.  And some people have postulated that anti-matter galaxies are unlikely anywhere in the universe.

The reasoning goes like this:  IF the current universe "began" as a big bang (hot dense matter and energy in rapid expansion), then it is likely equal (or nearly equal) matter and anti-matter would be produced (the universe doesn't usually play favorites, although there are exceptions - the magnetic field around an electric current follows a "right-hand" rule - not a "left-hand" rule).  So most of the matter and anti-matter would have annihilated in a very short time (after all, it's dense material - particles are close and would interact).  The result would be lots of energy released (photons).  Since we're here, it all couldn't have annihilated.  The best guess is that for every billion anti-matter particles produced in the big bang, a billion and one matter particles were produced.  This can be guess-timated from the observed photon density in the cosmic microwave background and the energy density.  Anyway, when the universe expanded and cooled, almost all the matter left was regular matter.  

Another way of showing (indirectly) that anti-matter stars are probably not nearby is that we haven't yet found anti-matter elements in cosmic rays.  Stars are always ejecting material, and supernovae eject a lot of material.  If any anti-matter stars were in our galaxy (or even in neighboring galaxies), we should have detected some anti-hydrogen or other elements in cosmic rays.  None have been found.

Now the problem with some of the above:  What if there was no big bang?  Many scientists think there are alternatives, and the universe may be in a steady state or oscillatory.  If you'd like a little reading on this subject by leading scientists, see "Seeing Red" by Halton Arp or "A Different Approach to Cosmology" by Hoyle, Burbidge, and Narlikar.

If there was no big bang, there is every reason to expect that there would be whole anti-matter galaxies elsewhere in the universe.  If there weren't any, that would be the real surprise!

Your last question relates to observations which could be the result of matter / anti-matter annihilation.  The quick answer is that no observations have been identified which require that for an energy source.  A possible candidate might be Quasars.  These are the most luminous objects in the universe.  Until the 1980's, there wasn't much of a consensus on what powers them.  Now, it is thought that they're the result of accretion of material into super-massive black holes in the nuclei of galaxies.  That doesn't mean the consensus is right.  They might someday be found to be two stars interacting - either just their atmospheres or their entire cores.  If one star was matter and the other anti-matter, the energy released could explain Quasars' brilliance.

To summarize, the majority view is that there are not significant areas of anti-matter either in our galaxy or anywhere in the universe.  But as sometimes happens in science, the majority can be proven wrong.