Two assumptions underpinEinstein's special
theory of relativity. The consistent law principle,
which is founded on the notion that all motions
are relative to the chosen reference frame, is
the first principle. This principle can be stated as
follows:
The laws of physics are the same in all
frames of reference that are moving at a
constant velocity with respect to one another.
4.
The second principlehas something to do with the speed
of light. This is called the constancy of speed principle. It can be
stated as follows:
The speed of light in empty space has the same
magnitude for all observers regardless of their velocity.
That the speed of light in empty space is 3x108 m/s. An
observer traveling toward a light source would perceive light to
be traveling at 3x108 m/s. Light would appear to be traveling at
3x108 m/s to an observer who is not moving in relation to the
source. The speed of light would remain constant regardless of
the velocity of the source of light and the velocity of the
observer.
5.
Consequences of thePostulates of the Special Theory of
Relativity
The special theory of relativity is based solely on the
principles of consistency and the principle of constancy. These
principles have very interesting consequences if you are
observing from the ground. While on the ground, you may
compare the measurements of length, time, and mass of a very
fast airplane. While on the ground, you will find that:
1. an object’s length shortens while moving (length
contraction) – this means that the observer measures a
moving object’s length as smaller than it would be if it is not
moving;
6.
2. clocks runslowly while moving (time dilation) – this means the
slowing of the passage of time experienced by objects in
motion relative to an observer and it is measurable only at
relativistic speeds; and
3. the mass of objects increases while moving.
Therefore, we can conclude that time is relative. It flows at
different rates for different observers. Let us also consider the
fact that time and space are not independent. Special
relativity has been verified by countless experiments and the
predicted results always fit Einstein’s equations. This is no fiction
at all. This is how the universe works.
7.
General Theory ofRelativity
Einstein’s general theory of relativity has two
postulates.
• All laws of nature have the same form for observers in
any frame of reference whether it is accelerated or not.
• In the vicinity of any point, a gravitational field is
equivalent to an accelerated frame of reference in the
absence of gravitational effects.
8.
The general theoryof relativity predicted the existence of gravitational
waves. Some of the consequences of the theory is that ‘time is altered by
gravity.’
➢ A clock in the presence of gravity runs slower than when there is no
gravity.
➢ Evidence of the theory is the very slight shift in the orbit of Mercury.
➢ The differences between the Newtonian and Einsteinian
conceptions of gravity become significant only in regions where the
escape velocity approaches the speed of light.
➢ The properties of extraordinarily dense collapsed stars can be
explained by the general theory of relativity.
➢ Black holes, as they are called, are very dense that the escape
velocity exceeds that of light
