Identifying Dark Matter Interactions

Dark Matter bending the light from a background galaxy. In extreme cases the galaxy here is seen as the two arcs surrounding it. (Credit: NASA, ESA, and Johan Richard (Caltech, USA))
Fundamentally, the balance of the cosmos (or universal order) is considered as zero density: i.e. no positive density or negative density disruptions. In this respect, the photon presents a practical means for measure of this balance, as its very existence in zero density skirts the realms of both positive and negative density. Considering that the very definition of a photon is that it is constantly moving at the speed of light, “c,” it neither accelerates nor decelerates. Rather a photon instantaneously becomes a entity of energy upon its emission, and is embraced by the natural medium (or aether) of the universe. Like a fourth dimensional ripple in the aether of Space-Time, the energy is spherically radiated in all directions to be encapsulated into the form of a single energy entity (or packet) called the photon. Note: Energy can be considered as the tenable state that is reflective of the natural order of the universe; the traditional fourth dimensional ground state within the aether of the universe.
Needless to say, a single photon would go undetected, except on an atomic level, regardless of its resultant frequency or wavelength. Instead, what is detectable are the consolidations of these energy packets into continuous streams (or rays) to form a beams of radiation within the wavelength for light. So while there is literally a universe of photons traveling about, we can only visible (via the human eye)detect these beams that are capable of producing light. Similarly analogous to a one-sided echolocation, humans can detect these emitted light beams with their eyes. It is the interaction of these light beams with our eye’s retina that initiates a cascade of chemical and electrical events upon the absorption of these photons that, in turn, ultimately triggers nerve impulses that are interpreted by our brains. Still with the aid of other radiation detecting instrumentation, humans can also provide for the detection of these energy packets beyond their limited range of visible wavelengths that allow them to perceive visible light.
Still there are other problems with this kind of detection. Positive density matter within the universe hinders our capabilities to detect these streams of energy packets because they block the directed path of these continuous streams. In example, light emitted from a distance galaxy would not make it to us if it were blocked by another intervening galaxy or worse, by a black hole. While there are considerations of gravitational lensing that sometimes allows for light to bend around these intervening galaxies, one has to know the light is being bent to provide for proper cosmography.
Detection of these streams of energy packets with negative density matter is another consideration altogether. A common misconception is that light travels freely in the vacuum of space. Rather it depends on how one defines a vacuum. Light does travels freely in a vacuum of space, where the vacuum is defined as near or at zero density. Yet what would be the resulting issues due to interactions with greater negative density matter?
Currently an initiative is in place to consider how to detect proposed dark matter particles through non-gravitational means. The most widely accepted explanation for dark matter is that it is most probably composed of heavy particles that interact only through gravity and possibly the weak force; however, alternative explanations have been proposed, and there is not yet sufficient experimental evidence to determine which is correct.
Understanding the overriding principles for defining dark matter lends one to view dark matter as descriptive of negative density matter
as well. Both provide for an expectation of positive gravitational attraction. Based on the fundamental foundation for the force of gravity, relative to the acceleration of mass, the gravitational attraction (where mass volume remains positive and static, mass density becomes increasingly negative, and the gravitational constant is positive) is
Fg = m*a = (G(m1*M2))/r^2 for two positive mass densities
Fg = m*a = (G(-m1*-M2))/r^2 for two negative mass densities
As to the measure of degree by which negative density matter interferes with the detection of these streams of energy packets, we currently have none. However there have been promising experiments that have investigated the strong light-induced negative optical pressure arising from the kinetic energy of conduction electrons in plasmonic cavities. In the structure made of Drude (or plasma dispersion) metal and at frequencies in which the field penetrates the metal, most of the inductance is manifested as the kinetic energy of the electrons and only a small part in the magnetic field. The electric field energy becomes stronger than the magnetic field energy, and this difference induces strong optical forces in the plasmonic structure. Perhaps dark matter can be detected along these considerations, where the electric field energy becomes stronger than the magnetic field energy due to negative optical pressure within negative density matter.
Or perhaps the degree by which negative density matter interferes with these light beams is more subtle. Perhaps the negative density matter just depolarizes these light beams to create a distorted view of light as it passes through it to its destination.

Note in the figure above: Since there are many galaxies behind a Dark Matter halo, their shapes will correlate with its position.