Based upon the motions of visible matter, it is widely asserted that ordinary visible matter must make up only a minority of all matter, and that there must be vast quantities of other matter that interacts with visible matter only through gravity, or only through gravity plus much weaker forces. Otherwise we are unable to explain the motions of galaxies and galactic clusters.
We seem to understand gravity well in all testable circumstances, but on galactic scales where accelerations are measured in nanogravities or femtogravities, we cannot yet devise adequate tests for motion at ordinary (sublight) speeds. So my question is this: Which of the following two assertions is simpler, and therefore more scientifically valid?
1) There exists a vast amount of unseen matter, passing through us perhaps at every instant, obeying the laws of gravity and motion, but otherwise obeying completely unknown laws. The dark-matter equivalents of electromagnetism, the strong nuclear force, and the weak nuclear force are simply unknown, but such dark matter must exist because we understand gravity so very well.
2) We don't understand gravity at femto-meter-per-second accelerations and sublight speeds. There is no unknown set of physical laws governing an unknown set of forces and and unknown type of matter--we just have an imperfect understanding of gravity.
Hmmmmm. ----Daniel

• Interesting. - emperor__alikar - October 20, 2002 - 02:06 UTC
  • Particles that have no charge like axions - yaniru - October 20, 2002 - 03:15 UTC
    • Thanks (nt) - emperor__alikar - October 20, 2002 - 21:34 UTC
    • so... - fasteddy - October 21, 2002 - 03:24 UTC
      • Heaven is not physical - yaniru - October 21, 2002 - 11:01 UTC
  • Dark matter - danieldgj - October 20, 2002 - 13:07 UTC
    • Thanks (nt) - emperor__alikar - October 21, 2002 - 02:50 UTC
    • Another possibility endorsed by DrDick - yaniru - October 21, 2002 - 12:44 UTC
• gravity at femto-meter-per-second accelerations and sublight spe - yaniru - October 20, 2002 - 03:19 UTC
  • very gentle accelerations - danieldgj - October 20, 2002 - 13:28 UTC
    • What about supersymmetric particles? - harvey1 - October 21, 2002 - 03:58 UTC
    • Newton's theory needs to be saved as well - yaniru - October 21, 2002 - 11:24 UTC
      • vacuum energy - emperor__alikar - October 22, 2002 - 01:40 UTC
        • Vacuum energy - yanniru - October 22, 2002 - 19:15 UTC
      • More dark matter - danieldgj - October 22, 2002 - 03:55 UTC
        • Velocities are measured - yaniru - October 22, 2002 - 11:11 UTC
          • velocities - danieldgj - October 22, 2002 - 12:57 UTC
            • Do you have an alternative theory. - yanniru - October 22, 2002 - 19:20 UTC
              • Occam's razor - danieldgj - October 22, 2002 - 23:12 UTC
                • Gravitational colapse - emperor__alikar - October 22, 2002 - 23:56 UTC
                  • Time limits - danieldgj - October 23, 2002 - 22:22 UTC
                    • What if they dicover one day... - emperor__alikar - October 23, 2002 - 22:39 UTC
                      • The Sun fits - danieldgj - October 25, 2002 - 01:23 UTC
                        • Well, not really.... - kc2gwx - October 25, 2002 - 04:02 UTC
                • I don't think Occam's razor applies here - harvey1 - October 23, 2002 - 13:51 UTC
                  • What about nuetrinos - yaniru - October 23, 2002 - 13:56 UTC
                    • Neutrinos are plentiful. - danieldgj - October 23, 2002 - 22:35 UTC
                  • Either way, Einstein is approximate - danieldgj - October 23, 2002 - 22:33 UTC
                    • I agree with your objection to that assumption - harvey1 - October 23, 2002 - 23:02 UTC
                      • How does supersymmetry dispense with dark matter? - yaniru - October 24, 2002 - 15:11 UTC
                        • That's right - harvey1 - October 24, 2002 - 16:31 UTC
                          • Agreed - yaniru - October 24, 2002 - 17:21 UTC
                            • Yes and no. - danieldgj - October 25, 2002 - 01:27 UTC
                              • How do you know that - yaniru - October 25, 2002 - 02:37 UTC