  We compute the bispectrum of the 2dF Galaxy Redshift Survey (2dFGRS) and use
it to measure the bias parameter of the galaxies. This parameter quantifies the
strength of clustering of the galaxies relative to the mass in the Universe. By
analysing 80 million triangle configurations in the wavenumber range 0.1 < k <
0.5 h/Mpc (i.e. on scales roughly between 5 and 30 Mpc/h) we find that the
linear bias parameter is consistent with unity: b_1=1.04 pm 0.11, and the
quadratic (nonlinear) bias is consistent with zero: b_2=-0.054 pm 0.08. Thus,
at least on large scales, optically-selected galaxies do indeed trace the
underlying mass distribution. The bias parameter can be combined with the
2dFGRS measurement of the redshift distortion parameter beta =
Omega_m^{0.6}/b_1, to yield Omega_m = 0.27 pm 0.06 for the matter density of
the Universe, a result which is determined entirely from this survey,
independently of other datasets. Our measurement of the matter density of the
Universe should be interpreted as Omega_m at the effective redshift of the
survey (z=0.17).
