Curvature of
space
The effect of this is so little it can be ignored in all cases when:
 Velocities (speeds) of objects are much smaller than the
speed of light
 The ratios of masses divided by the distances separating
their centres of mass are much smaller than the ratio of speed of light squared
Newtonian gravitational constant.
A good image is to think of a weight of a massive object which stretches the trampolinelike spacetime
fabric, which results in trajectories around this dent being curved due to the
slope and the pull of gravity.
Curvature of space explains why mercury is the closest planet to the sun, and moves faster
than any other planet, but also is more curved that any other planet.

Time dilation
Time dilation is the slowing down of the passage of time experienced by people or objects in
relation to the observer.
This effect is so significant that Global Positioning System (GPS) need to correct
with respect to the
effects of time dilation.
The effect is extremely small until speed approaches 30,000kmph (1/10 the speed
of light)
Lorentz factor  Behind the calculations for Time
dilation
T_{0} = passage of time measured by a stationary observer
T_{1} = measured by observer travelling at velocity v
v = velocity
c = speed of light
Basically, the nature of the universe must not change for an observer if
their inertial state changes.
The speed of light is the same to all inertial observers, is the same in all
directions, and does not depend on the velocity of the object emitting the
light.
