%0 Journal Article %T Determining the Cosmological Constant Using Gravitational Wave Observations %A Thomas L. Wilson %J Journal of Modern Physics %P 1-8 %@ 2153-120X %D 2020 %I Scientific Research Publishing %R 10.4236/jmp.2020.111001 %X It is shown in Einstein gravity that the cosmological constant ¦« introduces a graviton mass m_g into the theory, a result that will be derived from the Regge-Wheeler-Zerilli problem for a particle falling onto a Kottler-Schwarzschild mass with Λ ¡Ù 0. The value of mg is precisely the Spin-2 gauge line appearing on the Λ - m2g phase diagram for Spin-2, the partially massless gauge lines introduced by Deser & Waldron in the m2g, Λ) phase plane and described as the Higuchi bound m2g= 2Λ/3. Note that this graviton is unitary with only four polarization degrees of freedom (helicities ¡À2, ¡À1, but not 0 because a scalar gauge symmetry removes it). The conclusion is drawn that Einstein gravity (EG, Λ ¡Ù 0) is a partially massless gravitation theory which has lost its helicity 0 due to a scalar gauge symmetry. That poses a challenge for gravitational wave antennas as to whether they can measure the loss of this gauge symmetry. Also, given the recent results measuring the Hubble constant H_o from LIGO-Virgo data, it is then shown that Λ can be determined from the LIGO results for the graviton mass m_g and H_o. This is yet another multi-messenger source for determining the three parameters %K Gravitation %K General Relativity %U http://www.scirp.org/journal/PaperInformation.aspx?PaperID=97598