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Travelling through time(2)...
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a) Special relativity
The speed of light is constantly independent of the reference system of
the observer. It is a limit that can't be exceeded by any kind of
matter
without transforming to energy. Each measurement of that speed will
have
the same value, no matter how fast you move. Whether you stand still or
move at 50% of light speed, the ray of light will always move at an
amazing
299 792,458 km/sec. That sounds strange; we would think when you move
at
50% of light speed along the ray of light, the measurement of that
speed
would be halved. But light speed is a universal constant, as is shown
in
many experiments. That means that time passes slower when you move than
when you stand still. If you move at a low speed, that difference is
extremely
small. But if you move at light speed itself, time stands still. If you
move faster than light speed, you could go back or forward in time
because
you can arrive somewhere before light does. That means you could travel
to the future or the past...
All this can be supported by the
calculations
of Einstein, but actually we only need the solution.
dt = dt' . (1 -
v²/c²)1/2
In this formula is * dt the time that passes when you move at a
speed
v
'--------------'
"
* dt' the time that passes when you stand still
"
this part is
called the
Lorentz-factor
* c the speed of light
or the time-bending
factor by speed
When you're moving, the Lorentzfactor is always smaller than 1,
therefore
we can conclude that, relatively seen, time passes slower in motion
than
when you don't move. When we reverse this factor, we can express how
many
times time passes slower in motion than at rest. The closer you get to
light speed, the slower time moves on. When you travel at light speed ,
you'll get 1-1=0
dt' . 0 = 0 --> time stands
still!!!!
Another example: If you travel to a star at 80% of light speed during
10
'earth' years, only 6 years will pass. An observer on earth with a
mighty
telescope would see you acting in slow-motion.
Nice to know: When a journalist asked Einstein what he would say if the
observations would not match with his theory of relativity, he
answered:
"I would pity the Lord, 'cause the theory is right anyhow."
b) General relativity
In this theory gravity has got an important influence. We will use the
'equivalent principle' here. This principle equals acceleration to
gravity.
That might sound strange, but it can be cleared out with one simple
example.
When you sit in a box that falls down to the earth, you fall with an
acceleration
of 9,81 m/s². In the box you don't move, you float. Now when your
box is far away of all star systems in space, and some kind of alien
(just
a way of explaining!!!) pulls your box at an acceleration of 9,81
m/s²,
you can think you're just falling to the earth, it's exactly the same.
The alien exercises the same power on you by acceleration than the
earth
does by gravity. Therefore, in this principle, acceleration equals
gravity.
All what will be written about gravity can also be interpreted for
acceleration.
Gravity has got it's influence on light, time and space.
Gravity deflecting light is not so difficult to understand. An example
is easily found: in space, the mass of, for instance, Mars deflects the
light of a shining star. Gravity influencing time and space is a little
bit more difficult to understand. But if you look in the previous
paragraph,
things will get more clear. Gravity equals acceleration, and we already
know that acceleration = 0 influences time (special relativity). I'll
explain
everything using Einstein's thoughts.
Assume there's a rotating disc somewhere in space, far away from all
gravity
fields. Our reference system is not rotating, and the middle of the
disc
is not rotating. We call this system C. We choose as a second reference
system C' the disc itself. So in the second reference system the disc
doesn't
move at all. Now we put three clocks (that tick exactly with the same
speed
in the same circumstances) and three sticks (that are exactly of same
length
in the same circumstances) on different places: in the middle of the
disc
(clock 1 and stick 1), on the edge of the disc (clock 2 and stick 2)
and
on the outside of the disc (clock 3 and stick 3). Clock 1, stick 1,
clock
3 and stick 3 don't move in C. Clock 1, stick 1, clock 2 and stick 2
don't
move in C'. Because clock 1 and clock 3 don't move in C, they tick
exactly
with the same speed. Clock 2 moves in C with acceleration = 0 (not
speed
= 0!!) and can be placed under special relativity. So this clock ticks
slower than clock 1 and 3.
Clock 1 and clock 2 don't tick
with the same speed. That's strange, because they're in the same
reference
system C'. This can only be explained by the fact that clock 1 and
clock
2 are not influenced in the same way by the field of gravity caused by
the rotation of the disk. The gravity of clock 1 is 0, and the gravity
of clock 2 is at maximum.
The same story with the sticks; stick 1 has got the same length as
stick
3 because they don't move in C. Stick 2 moves at a certain speed with
acceleration
= 0 in C and is shorter than 3 or 1. Stick 1 and stick 2 are in the
same
reference system C', but not of the same length because the disc
rotates.
It's only the gravitation of the disc that can do this, so gravity
bends
time and space.