2. Two coordinates are is
Only one coordinate
Three coordinates are y
required to specify a
required to specify a point Y
point in one dimensional
in three two dimensional
dimensional
space
space X
z
X
3. •It is impossible to imagine a four-dimensional space.
•However, it is easy to draw diagrams of two-dimensional
spaces
T
i
m
e
sun Alpha Centauri
Distance
4. LIGHT CONE
The light spreading out from an a
Maxwell suggested that if
event forms of(three-dimensional)
if a pulse a light is emitted
cone in (the four-dimensional)
at a particular time at a
Similarly
space-time. This cone is called the
particularcone of the event. In
future light point in
space, thenwe can draw
the same way as time goes
on it will spread out as a
another cone,
called theof light whose sizeis
sphere past light cone, which
the set of events from which a
and position able to reach the
pulse of light is are
independent of the speed of
given event
the source.
5. Event when Sun
Future Light
dies
Cone of Event
Sun
Death of sun does not The Earth enters the future
effect us immediately Earth cone of death of sun after
because we are not in approximately 8 minutes
the future light cone
0 1 2 3 4 5 6 7 8 9 10
7. • Think of a train moving on a track and a person in the train
sitting on the seat. If he bounces a ball and catch it. He will say
that he threw the ball in a vertical path and if the height was h
then the ball traveled 2h distance.
h
Train Compartment
8. An Observer on the platform would see the ball moving on
such a path defined below
Another observer can also say that train is at rest and track
is moving or earth is moving in reverse direction
9. Earth is also moving on a path round the sun and Sun is
also moving on a round path in galaxy and Galaxy is
also moving on a milky way. So there is no absolute
space or position.
Earth
Sun
10. • There is no absolute space means that Space is not
independent of universe. Similarly Time is also not
absolute. But Pre-Einstein theorem did not say
anything about absolute time.
• After 1915 Einstein made the revolutionary theorem
Which was called “General Theory of Relativity”.
11. GENERAL THEORY OF RELATIVITY
• He said that space is not flat. It is curved by the distribution of
mass and energy in it.
• Bodies like the earth are not made to move on curved orbits by
a force called gravity.
• They follow the nearest thing to a straight path in a curved
space.
• In general relativity, bodies always follow straight lines in four-
dimensional space-time, but they nevertheless appear to us to
move along curved paths in our three-dimensional space.
12. CURVED SPACE DUE TO MASS
The mass of the sun curves space-time in such a way that although the
earth follows a straight path in four-dimensional space-time, it appears to
us to move along a circular orbit in three-dimensional space.
13. • Another prediction of general relativity is that time
should appear to slower near a massive body like the
earth.
• Energy of light is directly promotional to the frequency
of light.
• As light travels upward in the earth’s gravitational
field, it loses energy, and so its frequency goes down.
To someone high up, it would appear that everything
down below was making longer to happen.
14. TEST OF CONCEPT
• This prediction was tested in 1962, using a pair of
very accurate clocks mounted at the top and bottom
of a water tower. The clock at the bottom, which was
nearer the earth, was found to run slower, in exact
agreement with general relativity.
17. • A Person on the platform will say that ball is moving on a
triangular path due to the motion of the train on a horizontal
track.
The distance travelled by ball h
will be 2√(h2+t2).
18. • It can simply be said that distance 2h travelled by ball
in the train is less than the travelled distance according
to the outer observer.
• It is also clear that the time examined by the outer
observer will be more that the time according to the
observer in the train.
20. • Clocks on satellites are used to “triangulate” locations.
But the timing needs to be very accurate. (~ 20 ns)
• The satellites are at altitudes of ~ 20,000 km
where the gravitational field of the Earth is much less
than at the surface of the Earth.
• Clocks run faster in this environment and this needs
correcting for (+45000 ns/day).
• The satellites are also moving fast enough (14000 km/h)
to need corrections from Special Relativity too (slow
down by -7000 ns/day).
• GPS would fail after a few minutes without these
corrections
22. • Time can not exist without space and likewise space
cannot exist without time. This relation is called space-
time continuum.
• Traveling faster than the speed of light could open up
the possibility of time travel to the past as well as to the
future.
• The problem is that the speed of light is believed to be
the highest speed at which something can travel.
• But time travel in the other direction is not as
difficult, and the future may one day be a possible
destination.
23. For time travel , Writers have developed so many
theories and ideas with the help of imagination an
scientific facts.
Most theories of time travel don't rely on machines.
Instead, time travel will likely be done by way of
natural phenomena that will transport us instantly
from one point in time to another.
24. Three Phenomena , which we are not
even sure exist, include:
• Rotating black holes
• Wormholes
• Cosmic strings
26. Black Holes have such strong gravitational field that even
light cannot escape it might be possible to pass through them
and exit out of a "white" hole. A white hole would have the reverse
action of a black hole. These white holes would be our way to
enter other times or other worlds.
28. In space, masses that place pressure on different parts of the
universe could eventually come together to form a tunnel .
A wormhole could be a type of tunnel-like structure existing in
the universe that could be used for a time travel portal.
30. • The latest is the String theory proposed by
Princeton physicist J. Richard Gott in 1991.
• Scientist believes that string-like objects were
formed in the early universe.
• These strings may line the entire length of the
universe and are under immense pressure.
• These cosmic strings, which are thinner than an
atom, would generate an enormous amount of
gravitational pull on any objects that pass near
them.
31. • Objects attached to a cosmic string could
travel at incredible speeds, and because their
gravitational force distorts space-time, they
could be used for time travel.
• A spacecraft could be turned into a time
machine by using the gravity produced by the
two cosmic strings, or the string and black
hole, to propel itself into the past. To do this, it
would loop around the cosmic strings.
33. • You could travel back to a time before
you were born. The mere fact that you
could exist in a time before you were
born creates a paradox. If you were
born in 1960, how could you exist in
1955?
34. • The most famous paradox is the grandfather
paradox.
• What would happen if a time traveler went back and
killed one of his or her ancestors before the traveler
was born?
• If the person killed his or her grandfather, then how
could that person be alive to go back and kill his or
her grandfather?
37. PARALLEL UNIVERSE
• Theory regarding time travel brings up the idea of parallel universes, or
alternative histories.
• In the theory of parallel universes, you may have traveled to another
universe, one that is similar to ours, but has a different succession of
events.
• The idea here is that every action causes the creation of a new
universe, and that there are an infinite number of universes that exist.
• When you killed your ancestor, you created a new universe that was
identical to your own up until the time you changed the original
succession of events.
38. Time is complicated but still very
interesting. We still need so many
years to understand the nature and
time and one day we will be able to
build time machine.
