Abstract:  A traveling black hole or other mass and even 
radiation may encounter a slowdown effect of its forward 
velocity due to gravitational (warped spacetime) curvatures 
continually generated as the mass is passing through space.

That is, as the giant black hole travels through space it 
warps spacetime on an ongoing basis as well as dilating 
time.

My suggestion or hypothesis is that this process absorbs 
energy.  Space has a hypothetical suggested property that is 
somewhat analogous to viscosity, like our 10-40 oil or 0-40 
oil.  The more and heavier the curvature of space that is 
continually generated due to mass and mass movement of the 
cruising black hole, the more viscouslike this activity in 
space becomes.  At least, that is the hypothesis.  The 
reality may lie elsewhere.  For my part, it is just a 
hypothetical suspicion to date.

A note however:  viscosity is just an analogic word to 
describe the 'back' resistance of space to a black hole 
traveling through space.  obliquely somewhat like back 
emf... well sortof...

This may be the reason why the components of the Cosmos 
appears to be somewhat 'stationary'.  

This 'slowdown' effect, if it in fact exists, we can 
temporarily rename as the 'viscosity' of space.

The viscosity of space may be mathematically somewhat like 
gravity in that objects, no matter what their mass will all 
'slowdown' in their forward movement at the same rate.

Radiation is not exempt from the viscosity effect of the 
cosmos.  A gradual deterioration in energy, it is suggested, 
may occur; a redshift if you please.

As stated above, this viscousness of space 'thickens' as an 
object passes through sections of the universe that contain 
increased dilated time and curved space components generated 
from the many black hole systems that are present.

So a velocity vectored black hole or specimen ship, passing 
between two slowly orbiting much larger black holes very 
near or upon the zero gravity plane generated by the binary 
orbiting systems will encounter a much 'thicker' space due 
to the net increased curvature and time dilated situation 
there.  But the wanderer better stay on the zero gravity 
plane or it is history. Any minor wandering off the zero 
gravity plane's track and into the black hole the wanderer 
or the speciman, goes.   

The net effect from traveling through the time dilated area 
will be to generate a different and less elapsed time 
compared to those who traveled the same distance but did not 
take the same route through the zero gravity plane of the 
monster binary black hole system.

A father traveling through the system compared with his 
young child taking the alternate route of a same elapsed 
time, may come out 'younger' than his child, who, having 
traveled the distance under nominal gravitational conditions 
is now 'older' than his own father.

If the travel is of an appropriate length, the father will 
end the journey arriving with his son a bent old man.

And even worse, perhaps only his son's descendants will be 
there to meet him at a very long journey's end.

Here there is no traveling back or foward in time, just 
traveling forward in Time at different rates.

Science fiction writers, have long beat a similar concept to 
death.

Radiation, passing through the various areas of warped 
spacetime, might be gravitationally bent distances as well 
as slowed down because of passing through viscous areas of 
space that have been time dilated and curved due to a mass 
being present along its travels.

This theoretical, yet unproven property of space, its 
viscousness, may offer a lot of unseen and hidden problems 
to the hapless navigator.

Darkness hides its secrets.