(1) ELECTROMAGNETIC QUANTUM VACUUM

The zero-point fluctuations of the electromagnetic quantum vacuum may be approximated as a continuous flow of energy: randomly-phased plane-waves in the representation of stochastic electrodynamics (SED). Since the flow of radiation is on average the same in all directions, there is no net flux of energy or momentum as perceived by an observer in an inertial frame. However an accelerating observer will experience an asymmetry. Acceleration through the quantum vacuum results in the appearance of an electromagnetic effect -- a cousin of the well-known Unruh-Davies radiation -- whose strength is proportional to acceleration.

[STATUS: SED theory well developed since 1960s. See Rueda & Haisch (1998) papers on the Poynting vector of the zero-point fluctuations on the Scientific Articles page. See also SLAC physicist Pisin Chen's proposed experiment to measure Unruh-Davies radiation using an ultra-high-intensity laser (Chen and Tajima, Phys. Rev. Lett., 83, 256, 1999).]

(2) REST MASS: E=mc^{2}

A fundamental particle may be an intrinsically massless thing of some sort (string? spacetime deformation or singularity?) which continuously interacts with the quantum vacuum. Buffeted by the zero-point fluctuations of the electromagnetic quantum vacuum, a particle exhibits Brownian-like motion which Schroedinger named "zitterbewegung" (quivering motion). A tiny bit of the quantum vacuum energy is diverted into the kinetic energy of this zitterbewegung. We suggest that this is the origin of E=mc^{2} for a particle. If true, there would be no physically distinct mc^{2}. The physically real thing would be only the energy, E, associated with the zitterbewegung of the particle. In this view there is no need for any magic, mysterious conversion of mass into energy and vice versa. One could think of a particle as a localized concentration of zero-point energy which gravitates and resists acceleration for the reasons given below... no traditional "mass" needed.

[STATUS: Zitterbewegung and its connection to the zero-point fluctuations is well-developed. See for example the monograph by de la Pena and Cetto: "The Quantum Dice" (Kluwer 1996). The E=mc^{2} interpretation needs development. See H. E. Puthoff, Phys. Rev. A, 39, 2333, 1989.]

(3) INERTIAL MASS

Consistent with (2), inertial mass may also not be a physically real, innate property of matter. What we traditionally (since Newton's Principia) think of as inertial mass would in reality be a resistance of the quantum vacuum to acceleration. The fundamental particles (quarks and electrons) in an accelerating object interact with the electromagnetic quantum vacuum, whereby a drag force is generated that is proportional to acceleration. This could be the origin of F=ma. We refer to this as the quantum vacuum inertia hypothesis.

[STATUS: Well developed hypothesis. See numerous papers on Scientific Articles page.]

(4) ACTIVE GRAVITATIONAL MASS

As a consequence of (2) the greater the number of fundamental particles in a given volume of space, the greater the energy deficit of the electromagnetic quantum vacuum (since more of it is diverted into zitterbewegung). This may create an asymmetry in the energy-momentum flow of the zero-point fluctuations (in the SED representation). In other words a Newtonian gravitational field or a general relativistic curvature of spacetime produced by mass may in actuality be manifestations of a quantum vacuum energy asymmetry.

[STATUS: Tentative hypothesis. Need to reconcile this in detail with general relativistic spacetime curvature produced by mass-energy. See also a recent attempt to develop the polarizable vacuum gravitation perspective.]

(5) PASSIVE GRAVITATIONAL MASS

A particle at a fixed distance above a gravitating body such as a planet, will experience a downward force as a consequence of (4). This would be the origin of the force which we traditionally have called weight.

[STATUS: See Gravity and the Quantum Vacuum Inertia Hypothesis, Rueda & Haisch, Annalen der Physik, 2005.]

(6) PRINCIPLE OF EQUIVALENCE

Inertial mass and gravitational mass may be identical because they have an identical source process. Acceleration through the quantum vacuum and being held stationary in a gravitional field in which the electromagnetic quantum vacuum, being radiation, falls past on curved geodesics are, after all, identical processes.

[STATUS: See Gravity and the Quantum Vacuum Inertia Hypothesis, Rueda & Haisch, Annalen der Physik, 2005.]