This document discusses several theories of time travel, including Einstein's equations allowing for time travel under certain configurations of matter and energy, Gödel's mathematical solutions showing time travel is possible if the universe rotates, and Kip Thorne's work developing a serious proposal for a time machine using wormholes. While time travel remains theoretically possible, significant technological limitations exist, such as a lack of means to generate the exotic matter needed to stabilize wormholes. Paradoxes also pose challenges to changing the past through time travel.

1. The Theories of Time Travel
•Why it is theoretically possible?
•Who is responsible for these
conclusions?
•Why it is believed to be
impossible?

2. Einstein’s Equations of
Space-time
• Curvature of space and time is determined
by the matter-energy content of the universe
• Possible to find configurations of matter-
energy that can force the bending of time and
allow time travel
• When we find these configurations that allow
time to bend backwards Einstein’s general
relativity breaks down and quantum theory
becomes dominant

3. The Breakdown of Einstein's General
Relativity and Theory of Gravity
• Breakdown in large gravitational fields,
which are necessary for the backward
bending of time.
• However both quantum theory and the
theory of gravity are united in the Hyper-
space theory which exists in ten-
dimensional space.

4. Kurt Gödel
• Kurt Gödel was the first
person to find solutions to
Einstein’s equation that
allowed for time travel.
• This was the first solid
mathematical foundation
for time travel.

5. Kurt Gödel’s Solutions
• Assumed that the universe was filled with gas
or dust and that its was rotating.
• Concluded “By making a round trip on a
rocket in a sufficiently wide curve , it is
possible in these worlds to travel into any
region of the past, present, and future and
back again.”
• He found the first closed timelike curves,
CTCs, in general relativity.

6. Einstein's view of time
vs.
Gödel’s
• Einstien: a river flowing through space,
which could be moving at different
speeds dependent on it surroundings.
• Gödel: this river could be bent smoothly
backwards into a circle, much like an
eddy or whirlpool in real river.

7. What was wrong with Gödel’s
theory?
• Einstein was very perplexed by Gödel’s solutions
but could not find anything theoretically wrong
because Gödel used Einstein’s own equations.
• Weak spot was the in the assumption that the
universe was rotating.
• Experimentally we have found no evidence that
this is true, so for now Gödel’s results can be
ruled out , but still remains a possibility if the
universe did rotate then CTCs and time travel
would be physically possible.

8. Kip Thorne
• “ If Einstein is the
architect of the space-
time shortcut
(wormholes) then Kip
Thorne is its structural
engineer.”-Micheal
Moyer
• Along with
colleagues,
developed first
serious proposal for a
time machine.

9. How the idea of Wormholes
came about?
• 1935: Einstein and colleague Nathan Rosen
examined the scenario where an tiny rip in a
black hole connected to another tiny rip in a
different black hole.
• Know as the Einstien-Rosen bridge.
• Today referred to as a wormhole and creates
a shortcut through space-time.
• Thorne’s time machine centered around
wormholes.

10. The problem with wormholes
are:
• One: the gravitation forces at the center of the black
hole are astronomically large.
• Two: wormholes might be unstable, and that small
disturbances could cause the Einstein-Rosen bridge
to collapse.
• Three: in order to penetrate a wormhole to the other
side, one would have to go faster than the speed of
light.
• Four: the intense radiation given off by the black hole
might serve to close the wormhole by itself.
• Five: because time slows down in a wormhole and
comes to a complete stop at the center (point of
singularity), it would take an infinite amount of time to
travel through the wormhole.

12. How Thorne discovered his time
machine?
• He started by working the problem
backwards.
• He wanted a solution to Einstein’s
equations where the traveler would
survive a comfortable, round trip
through a stable wormhole, that would
be measured in days not millions of
years.

13. • At the beginning of these calculations and
theories, Thorne and colleagues stated that
this was a engineering problem for some
future civilization and had no realistic
applications for today or sometime in the near
future.
• Their solution for these black holes turned out
not to be the typical black hole solution.
• It was referred to as a “transversible
wormhole.”

14. Thorne’s Wormhole
• One way of creating this wormhole
involves two chambers each containing
two parallel metal plates and to induce
a huge electrical field, vastly greater
than anything possible today.
• This electric field rips the fabric of
space-time and creates a wormhole
between the two chambers.

15. Thorne’s Wormhole
• A second way to create a transversible
wormhole is to utilize already existing black
holes.
• The problem occurs at the center, because
no matter would be able to pass through it.
• Throne concluded that if an exotic matter with
anti-gravity properties was introduced to the
center it would in a sense widen the center
and allow matter to flow through it.

16. Thorne’s Wormhole
• Now we would have a stable wormhole
than moves objects geographically in
space-time, when Thorne really wanted
a wormhole that moved objects in time.
• To do this he applied Einstein's Special
Theory of Relativity.

17. Brief description of the Special
Theory of Relativity
• For Thorne’s purpose, he used the idea
that time slows down for objects that
move quickly,relative to the speed of
light.
• This principle, time dilation, is shown in
Lorentz’s transformations:
Δt=γΔt’ and
where γ=1/(1-(v²/c²))^½

18. The Birth of a Time Machine
• By surrounding the first chamber, the first
wormhole, in negative energy and towing it
around the universe at close to the speed of
light, it would age more slowly than the non-
moving chamber.
• Overtime the two cambers would become
desynchronized in space-time, i.e. the two
chambers would exist in different times.
• To travel back in time, an traveler would
enter the stationary end of the wormhole, the
second chamber, and exit at the moving
wormhole, the first chamber, many years
before he actually enter the second

19. Why we don’t have time machines today?
The Problems:
• The biggest and most obvious problem
is nature of the matter and energy
needed to create these wormholes was
know as “exotic.”
• This exotic matter does not violate any
laws of physics, a key idea that hints to
its possible existence.

20. Problem 2:
• The amount of energy needed to create
and maintain a wormhole with exotic
matter is like nothing we have
produced with today’s technology.
• There is theory that negative energy
can be used to create areas of space-
time in which time is bent into a circle
with transversible wormholes.

21. Negative Energy
• Was discover by Henrik Casimir, through the use
of quantum theory.
• Experimentally showed existence of negative
energy, by using two large neutral metal plates
separated by a very small distance, inside of a
vacuum.
• He used the Heisenberg Uncertainty Principle, to
say that in between the plate there exists trillions
of particles and anti-particles constantly
appearing and disappearing.
• Know as “virtual particles” and they create a
minute net attractive force between the plates.

23. Time Travel and String Theory
Richard Gott III
• Proposed that
Cosmic Strings
could be used to
allow backward time
travel.
• These strings are
infinitely long and
not wider than an
atom.

24. Time Travel and String Theory
• These strings have very strange gravitational
properties: a loop of string acts like a regular
body of mass, while a straight piece has no
direct gravitational force even though it has a
large amount of mass per length.
• Gott’s theory was that two parallel strings
traveling in opposite directions and at close to
speed of light would cause such a distortion
in space-time that a CTC would form and
allow matter to enter this riff then exit before it
ever entered.

25. The Problem with Time Travel in
String Theory
• We don’t know enough about Cosmic
Strings to find the correct configurations,
motions, and the physical properties of
their infinite extension.
• The downside is that we don’t have the
proper information to use Gott’s scenario,
but the upside is if we did, there are no
laws of physics that state it can’t
theoretically happen.

26. The Limitation of Time Travel
• So far to today, every plausible time
machine would not allow a traveler to
go back in time before the time machine
was created.
• This is the one consistent limitation of
time travel, but still does not explain the
paradoxes that could arise by traveling
to the past.

27. Paradoxes of Changing the
Past:
• Aside from the actual construction of a
time machine the most challenging part
would be the result of changing the past.
• Stephen Hawking proposed a simple
solution to this problem called the
Chronology Protection Hypothesis.
• It states that nature would always find a
way of preventing wormholes and other
ways of changing the past.

28. Paradoxes of Changing the
Past:
• Some physicists believe that most
paradoxes can be explained with
Quantum Mechanics and the Theory of
Relativity, using matrices and a series
of mixed states which are the possible
outcome of changing the past.
• This leads us to the theory of multiple
or parallel universes.

29. The End