2.1 The major characteristics of dark matter and light propagation

The existence of dark matter in universal space confirms a simple fact that there is the medium of light propagation in the universe. The reasons is appearance, because the dark matter posseseses some basic properties that a midium posseses, for example:

The composed matter in WG (is certainly much smaller than elementary particles )and posseses an attractive force i.e. the gravitational force, it is a kind of long range force, which can be superpositioned.

Two composed matters can not be conbined to form a new bigger particle by the gravitational force between them (that already has been proved by physics because the gravitation is too weak to be a strong force). So the composed pratical object of dark matter  belongs to the item of elestic matter.

2.2 The principle method of measurement of photometrical        and the medium mass of light propagation.

            May be somebody will question me that since the dark matter is the medium of light propagation, why astrophysicists can not find it by optical instruments?
The answer is that todayís scientists can calculate the mass and energy of luminous objects by testing the colour temperature of emitted light and the temperature of any object. This only includes the mass and energy of luminance matter and the kinetic energy of relevant matter (especially for gas matter or fluid matter), ie. If itís true that the light propagates and transmits by the medium of dark matter, the measured results about the total universal mass by photometrical method only includes the luminance objects and the kinetic energy of matter in universal space, excluding the mass of the medium itself.