From owner-biophysics@net.bio.net Sun Oct 04 23:00:00 1998 Path: biosci!news.stanford.edu!newsfeed.berkeley.edu!awabi.library.ucla.edu!164.67.43.25!news.ucla.edu!not-for-mail From: "Kevin Klapstein" Newsgroups: bionet.biophysics Subject: Re: gravity Date: 5 Oct 1998 20:28:15 GMT Organization: University of California, Los Angeles Lines: 55 Message-ID: <01bdf0a0$8926d8e0$1c9c8e95@gradlab_pc_2.biomath.medsch.ucla.edu> References: <6v30qv$cii@ednet2.orednet.org> <6v8e1h$q79$1@fremont.ohsu.edu> NNTP-Posting-Host: 149.142.156.28 X-Newsreader: Microsoft Internet News 4.70.1155 Matt Jones wrote in article <6v8e1h$q79$1@fremont.ohsu.edu>... > In article <01bdef2b$3adf8040$570dd9cf@TheDaniel> k, > klap@biomath.medsch.ucla writes: > >Spin 2 bosons, to be exact. They're called gravitons, and > >the spin 2 bit gives you a fource which is always attractive, > >never repulsive. > > > >Cheers, > > > >Kevin > > > Just to be clear, these particles remain hypothetical at present, do they > not? > > -Matt > Yes, unless you count the attraction of your coffee cup to the near by mass of the earth as a detection of gravitons. Rather a stretch. Still, you can only detect a particle by its' interaction with other particles. Gravitons couple only to mass, and so that's the only way to detect them. Because gravity is such a weak force, the effects on single particles are not likely to be seen, so it's back to the earth-and-coffee-cup size scale. About ten years ago, there was an experiment done to look for a difference in gravitational effects on electrons as opposed to positrons (the corresponding anti-particle). Theory says there should be no difference. Sadly, the gravitational effects were largely swamped by tiny electromagnetic effects: induced currents in near by metals due to a few positrons flying by, etc.. My reading of the paper was that the results were inconclusive because the experiment was just to difficult and riddled with unpredictable sources of noise. We can also tell that they have to be massless (like photons) because gravity follows a 1/r^2 decay law (like electromagnetism). The possibility exists that we're out to lunch on this one. Our theory of gravity is General Relativity, and our theory of particles is the standard model. The two have not been brought into agreement yet, and "quantizing gravity" from GR is still a hot topic of research for very clever masochists. If/when they succeed in quantizing GR, that should answer a lot of questions. Cheers, Kevin .