Thank you for the very interesting question.
We are all traveling in time in a linear fashion at, presumably, the
same rate until death.
Your question involves changing that rate or reversing the forward
linear movement of time travel. I'll answer each of your questions
specifically below.
1) Is time traveling possible?
-- Short answer...yes.
"Today, we know that time travel need not be confined to myths,
science fiction, Hollywood movies, or even speculation by theoretical
physicists. Time travel is possible. For example, an object traveling
at high speeds ages more slowly than a stationary object. This means
that if you were to travel into outer space and return, moving close
to light speed, you could travel thousands of years into the Earth's
future."
http://www.pbs.org/wgbh/nova/time/through.html
Albert Einstein's theory of special relativity allows for forward time
dilation that would ordinarily be called time travel.
"The theory holds that, relative to a stationary observer, time
appears to pass more slowly for faster-moving bodies: for example, a
moving clock will appear to run slow; as a clock approaches the speed
of light its hands will appear to nearly stop moving. However, this
effect allows "time travel" only toward the future: only forward,
never backward."
http://en.wikipedia.org/wiki/Time_Travel
This parculiar effect of special relativity is known as "time
dilation". The threory concludes that, "two observers who are moving
relative to one another, will get different measurements of the length
of a particular object or the time that passes between two events."
http://www2.slac.stanford.edu/vvc/theory/relativity.html
Here is another example:
"Consider two observers, each in a space-ship laboratory containing
clocks and meter sticks. The space ships are moving relative to each
other at a speed close to the speed of light. Using Einstein's theory:
* Each observer will see the meter stick of the other as shorter
than their own, by the same factor gamma (gamma- defined above). This
is called length contraction.
* Each observer will see the clocks in the other laboratory as
ticking more slowly than the clocks in his/her own, by a factor gamma.
This is called time dilation."
http://www2.slac.stanford.edu/vvc/theory/relativity.html
There is evidence for this theory. Particles have fixed half-lives,
yet when they are moving at speeds near the speed of light, there
half-lives have been observed to slow. Essentially, time is moving
more slowly for these fast moving particles and thus they decay much
more slowly than would be expected relative to a fixed state.
"Observations particles with a variety of velocities have shown that
time dilation is a real effect. In fact the only reason cosmic ray
muons ever reach the surface of the earth before decaying is the time
dilation effect."
http://www2.slac.stanford.edu/vvc/theory/relativity.html
Time slows as speed increases. (Only when viewed by another frame of reference)
"Time actually slows with motion but it only becomes apparent at
speeds close to the speed of light. Similar to length contraction, if
the speed reaches that of light, time slows to a stop. Again, only an
observer that is not in motion with the time that is being measured
would notice. Like the tape measure in length contraction, a clock in
motion would also be affected so it would never be able to detect that
time was slowing down (remember the pendulum). Since our everyday
motion does not approach anything remotely close to the speed of
light, the dilation is completely unnoticed by us, but it is there. In
order to attempt to prove this theory of time dilation, two very
accurate atomic clocks were synchronized and one was taken on a
high-speed trip on an airplane. When the plane returned, the clock
that took the plane ride was slower by exactly the amount Einstein's
equations predicted."
http://science.howstuffworks.com/relativity2.htm
This theory is very important to the notion of time travel and most of
the terminology of time travel, such as the Spacetime Continuam and
time dilation are related to Einstein's theory. Here is an overview of
some basic terminology:
Time
"Time is a fourth dimension. In normal life, time is a tool we use to
measure the procession of events of space. But time is something more.
Yes, we use time as a "tool", but time is essential for our physical
existence. Space and time when used to describe events can't be
clearly separated. Therefore, space and time are woven together in a
symbiotic manner. Having one without the other has no meaning in our
physical world. To be redundant, without space, time would be useless
to us and without time, space would be useless to us. This mutual
dependence is known as the Spacetime Continuum. It means that any
occurrence in our universe is an event of Space and Time. In Special
Relativity, spacetime does not require the notion of a universal time
component. The time component for events that are viewed by people in
motion with respect to each other will be different. As you will see
later, spacetime is the death of the concept of simultaneity."
http://science.howstuffworks.com/relativity1.htm
The importance of the "speed of light":
"Since light itself is just a form of electromagnetic radiation, the
speed of light is just an easy way of talking about the speed of
electromagnetic radiation in general. If you think about it, the speed
of light is the "speed of information". We can not acknowledge that an
event has occurred until the information about that event reaches us.
The information is contained in the electromagnetic radiation from the
event via a radio signal, a flash of light etc. Any event is just an
occurrence of space and time, and any information that can be
transmitted about an event is emitted outward as radiation of some
sort. The information (electromagnetic radiation) from the event
travels at 186,000 miles/second in a vacuum."
http://science.howstuffworks.com/relativity1.htm
Reference Frames
"Einstein's special theory of relativity is based on the idea of
reference frames. A reference frame is simply "where a person (or
other observer) happens to be standing". You, at this moment, are
probably sitting at your computer. That is your current reference
frame. You feel like you are stationary, even though you know the
earth is revolving on its axis and orbiting around the sun. Here is an
important fact about reference frames: There is no such thing as an
absolute frame of reference in our universe. By saying absolute, what
is actually meant is that there is no place in the universe that is
completely stationary. This statement says that since everything is
moving, all motion is relative. Think about it - the earth itself is
moving, so even though you are standing still, you are in motion."
http://science.howstuffworks.com/relativity2.htm
Traveling back in time:
Time travel into the future, therefore, is possible according to this
theory. What about traveling back in time? Some have argued that,
theoretically, if one could travel FASTER than the speed of light than
reverse time travel may be possible. Einstein argues that time stops
at the speed of light. There are some major problems with this theory.
" If I am to believe that special relativity is correct, then I am
also to believe that the following events would occur. In order to
travel faster than the speed of light, I assume that you would at some
point have to travel at exactly the speed of light. For example, you
can not travel 51 miles/hour without having traveled 50 miles/hour at
some point, of course, this is providing that you were traveling 50
miles/hour or less to begin with. Now SR tells us that at the speed of
light, time stops, your length contracts to nothing, and your
resistance to acceleration becomes infinite requiring infinite energy
(as observed by a frame of reference that is not in motion with the
system). These conditions do not sound very conducive to life. Thus, I
conclude that time travel into the past, using the concepts of SR, has
some severe issues to overcome."
http://science.howstuffworks.com/relativity3.htm
A physicist named Ronald Mallett argues that reverse time travel is possible.
"Yes, according to Ronald Mallett, theoretical physicist and professor
at the University of Connecticut, recent experiments slowing light's
speed may make time-travel feasible. Mallet thinks he can harness
slow-light energy and turn the future into the past."
http://www.wonderquest.com/TimeTravel.htm
The technology to build a time machine may be attainable in the future:
"The physics of time travel is still in its infancy. While all
physicists today admit that time travel to the future is possible,
many still believe time travel to the past will never be easily
attainable. Don't believe anyone who tells you that humans will never
have efficient technology for backward and forward time travel.
Accurately predicting future technology is nearly impossible, and
history is filled with underestimates of technology:
"Heavier-than-air flying machines are impossible." (Lord Kelvin,
president, Royal Society, 1895)
"I think there is a world market for maybe five computers." (Thomas
Watson, chairman of IBM, 1943)
"There is no reason for any individual to have a computer in their
home." (Ken Olsen, president, chairman and founder of Digital
Equipment Corp., 1977)
"The telephone has too many shortcomings to be seriously considered as
a means of communication. The device is inherently of no value to us."
(Western Union internal memo, 1876)"
http://www.pbs.org/wgbh/nova/time/through2.html
2) Are there any records in history that show any time traveling activities?
--As noted above, observations have been made that validate time
dilation. However, in regards to human beings, the distance that one
has traveled into the future (from another's frame of reference)is
negligible.
--There are, however, some who believe that there is evidence of time
travelers from the future visiting the earth and impacting
civilization.
Here is one such account:
" The 'messenger in a bright light' reported by the founding prophets
of the world's various belief systems, refers to a Time Traveller;
The ancient 'oracle' that provided wisdom to ancient priests and
prophets concerning the 'future' was a computer used by the Time
Traveller;
The items portrayed as 'stones', 'tablets', 'wheels', or 'plates' as
being given to various prophets by 'the messenger' refer to historical
and astronomical compact disks;
The accounts in ancient texts taken to be of their past historical
events plus the descriptions of future revelations pertaining to a
particular 'End Time' war, the opening of a Sealed Book, and the
observation of associated Comets, are actually a retelling of a 'show
and tell' to those ancient peoples by a Time Traveller, of 1948 to
1998 modern historical and astronomical events;
All of the world's major religions since 5,000 BC have been based upon
their prophet's encounter with a Time Traveller and the viewing of
these CD-Roms;"
http://www.physicsforums.com/archive/t-24151_Evidence_of_Time_Travel_discovered_-_Source_of_ancient_Myths,_Legends,_and_Religions.html
Here is a website that claims to have "visual evidence" of time travel in history:
http://www.pphcstudygroup.org.au/
There are plenty of other references to time travel in history.
"Angelus Silesius, a sixth-century philosopher and poet, thought the
flow of time could be suspended by mental powers:
Time is of your own making;
its clock ticks in your head.
The moment you stop thought
time too stops dead."
http://www.pbs.org/wgbh/nova/time/through.html
"Another example is the Moslem legend of Muhammad carried by a mare
into heaven. After a long visit, the prophet returns to Earth just in
time to catch a jar of water the horse had kicked over before starting
its ascent."
http://www.pbs.org/wgbh/nova/time/through.html
Some argue that UFO's may be time machines.
"I have collated over 200 cases of events that I term ?Time Storms? -
in which strange glows and mists are encountered, and these often
involve similar physiological effects and atmospheric disruptions. As
a result it is not uncommon for witnesses to then report bizarre
alterations to the flow of both time and space. Today it is not rare
for these incidents to be interpreted in the context of a UFO - indeed
it is virtually the expected norm - with the effects felt then being
related to the consequences of the supposed UFO sighting with its
?alien? connotations. However, there is at least an arguable case that
the ?storm? occurs within the atmosphere - perhaps as a natural event
- and creates the physiological effects. The time disruptions (as in
time slip cases) and effects on the atmosphere (glowing clouds for
example) are simply misperceived as a UFO for want of a more
appropriate word in today?s cultural climate.
My book Time Storms (Piatkus, 2001) reveals the results of the
research into these cases and suggests that in fact we may be dealing
with a rare but very extreme form of disturbance within the space-time
framework that simply invokes time travels to take place by way of
quantum physics and relativistic processes. The threads that weave
these independent cases from all over the world into a pattern that
suggests a scientific reality is to me the best evidence on record
that time travel may indeed be possible."
http://www.bufora.org.uk/archive/timetravellers.htm
They argue that the conditions of most UFO sightings confirm this idea.
"Another observation if favour of the ?UFOs are time machines?
argument is that UFOs are often seen to materialise in mid-air. It
would make sense for a time machine to fly because switching times in
the vacuum of outer space is the only reasonably safe course. If you
move from a point on earth in the year 2001 to a point on earth in the
year 2051 you have no way of knowing what solid matter might occupy
that space at that moment, because a car, or a new house, or a
motorway might do so and your time travel visit to the future would
quickly be cut short as you ?land? inside a brick or get flattened by
a truck! In space, there is mostly vacuum and the orbits of planets
can be exactly calculated in advance. This is clearly the safest place
(though not totally safe) to make such a time jump."
http://www.bufora.org.uk/archive/timetravellers.htm
Some argue that anthropoligical evidence exists that suggests time
travelers may have visited.
"Of course, time travel being a theoretical possibility does not mean
that it is happening. We need to establish evidence for such a
prospect. Surprisingly, this is not absent. For example, there are
quite a few anomalies within geological science that are difficult to
comprehend without resorting to either the ancient astronauts theory
(human-like beings once visited our earth) or the time travel concept
(we visited - or rather one day will go back and visit - these areas
of our past ?timescape?). That is because signs of civilised human
habitation exist far back in time, long before it is conceivable that
humans could have roamed the earth according to our understanding of
anthropology."
http://www.bufora.org.uk/archive/timetravellers.htm
Some claim that figures from the past may have actually been influence
by those from the future.
"Whilst we might speculate about the likes of Leonardo da Vinci -
whose skills at creating machines that simply could not then be built
(such as helicopters and submarines) are stunning - especially as
these have been proven entirely practical by today?s standards. Of
course, human geniuses do get born and it is perhaps too easy to
imagine that they came from elsewhere (or elsewhen!) if a simpler
answer is more probable.
However, when you couple cases of anomalous appearances like this with
those of equally mysterious sudden disappearances (people seen to
literally vanish into thin air apparently never to return) it is easy
to wonder if by some process we might not be naturally projected
through time by forces outside of our control. And if we are do we
literally get stuck in the past (or the future?) creating these
occasional anomalies? "
http://www.bufora.org.uk/archive/timetravellers.htm
Reported "time slips" could involve time travel.
"In most cases there is reason to suppose this is a visionary
experience, not a literal reality. However, there are a few rare cases
where people claim to have spent long periods of time living in the
past. In the claims of two Kent couples (the Simpsons and the Gisbys)
- whom I have met - they believe they stayed overnight in a hotel that
does not seem to have existed since the early 20th century. They did
so on an overnight drive near Montelimar, France in 1979 and
interacted with, over many hours people apparently from that time
(including a policeman who did not recognise the French word for
motorway!)."
http://www.bufora.org.uk/archive/timetravellers.htm
3) Can a time machine be built? What are the possible theories
suggested? How can you build a time machine
(theortically)?
Malett believes he can experimentally test time travel and possibly
develop a "time machine".
"Mallett thinks time travel is not merely theoretically possible but
doable, given the speed-of-light breakthrough. He and a group of
scientists at University of Connecticut are designing the first
experiment to test Mallett's ideas. They plan to build a time-travel
device.
Matter distorts space and time. Clocks, for example, run slower in
Earth's gravitational field than they do in outer space. Get a really
massive object, say the Universe, spinning and you can twist space and
time into a ring. So time, instead of marching straight ahead in a
line from past to future, curves around. The future can meet the past
and you, following the ring, can return to a particular moment."
He argues that he can use light to create a vortex.
"Light causes space to bend. Last year Mallett published a paper in
Physics Letters describing how a circulating laser beam creates a
vortex in space within its circle. The bent laser light actually
causes space to whirl around like a twister within the circle.
Mallett deduced that, if he adds a second laser beam shining in the
opposite direction and increases its intensity enough, he can warp
time into a loop. Unfortunately, once again the energy required is out
of reach.
Then he saw an answer. His equations show the slower the light moves
within the laser circle, the more space and time distort. Bingo. He
can get the needed energy from slow-moving light. The whole crazy
notion suddenly became maybe, just maybe, feasible."
http://www.wonderquest.com/TimeTravel.htm
"To twist time into a loop, Mallett worked out that he would have to
add a second light beam, circulating in the opposite direction. Then
if you increase the intensity of the light enough, space and time swap
roles: inside the circulating light beam, time runs round and round,
while what to an outsider looks like time becomes like an ordinary
dimension of space.
A person walking along in the right direction could actually be
walking backwards in time -- as measured outside the circle. So after
walking for a while, you could leave the circle and meet yourself
before you have entered it."
http://www.spacedaily.com/news/timetravel-01a.html
New discoveries on how to slow light has increased the possibility of
a feasible time travel device.
<<Though it seems counter-intuitive, light gains inertia as it is
slowed down. "Increasing its inertia increases its energy, and this
increases the effect," Mallett says.
As luck would have it, slowing light down has just become a practical
possibility. Lene Hau of Harvard University has slowed light from the
usual 300,000 kilometres per second to just a few metres per second --
and even to a standstill (New Scientist, 27 January, p 4).
"Prior to this, I wouldn't have thought time travel this way was a
practical possibility," Mallett says. "But the slow light opens up a
domain we just haven't had before.">>
http://www.spacedaily.com/news/timetravel-01a.html
Many still believe that travel back in time in this fashion is still impossible.
" But even Adams isn't convinced that the experiment will work. That's
hardly surprising, as time travel raises disturbing questions. Could
you go back and murder your grandparents, making your birth
impossible? There may be ways out of this problem, but most physicists
think that any attempt to mess with history should be impossible. The
Cambridge astrophysicist Stephen Hawking calls this the "chronology
protection conjecture".
The general theory of relativity, which Mallett used to work out his
theory of time travel, does not take account of quantum mechanics.
Could this be the crucial omission that means time machines won't work
in the real Universe?
Hawking and Thorne say that any time machine would magnify quantum
fluctuations in the electromagnetic field, and destroy itself with a
beam of intense radiation. But to know for sure, we need a theory of
quantum gravity -- a theory that merges quantum theory with
relativity."
http://www.spacedaily.com/news/timetravel-01a.html
Wormholes
"Thorne believes there could be another type of tunnel-like structure
existing in the universe that could be used for a time travel portal.
Wormholes, also called Einstein-Rosen Bridges, are considered to have
the most potential for time travel if they do exist. Not only could
they allow us to travel through time, they could allow us to travel
many light-years from Earth in only a fraction of the amount of time
that it would take us with conventional space travel methods."
http://science.howstuffworks.com/time-travel4.htm
Wormholes could be used for time travel.
" If wormholes could be discovered, it might allow us to travel to the
past as well as the future. Here's how it would work: Let's say the
mouth of the wormhole is portable. Then person B in the example above,
who traveled at 50 percent of light speed into space for a few hours,
could carry one wormhole mouth into space, while the mouth at the
opposite end of the wormhole would stay with person A on Earth. The
two people would continue to see one another as person B traveled into
space. When person B returned to Earth a few hours later, a few years
may have passed for person A. Now, when person A looks through the
wormhole that traveled into space, that person will see him or herself
at a younger age, the age he or she was when person B launched into
space. The cool thing about it is that the older person A would be
able to step into the past by entering the wormhole, while the younger
person B could step into the future."
http://science.howstuffworks.com/time-travel4.htm
Cosmic Strings
"Yet another theory for how we might travel back and forth through
time uses the idea of cosmic strings, proposed by Princeton physicist
J. Richard Gott in 1991. These are -- as their name suggests --
string-like objects that some scientists believe were formed in the
early universe. These strings may line the entire length of the
universe and are under immense pressure -- millions upon millions of
tons.
These cosmic strings, which are thinner than an atom, would generate
an enormous amount of gravitational pull on any objects that pass near
them. Objects attached to a cosmic string could travel at incredible
speeds, and because their gravitational force distorts spacetime, they
could be used for time travel. By pulling two cosmic strings close
together, or one string close to a black hole, it might be possible to
warp spacetime enough to create closed time-like curves."
http://science.howstuffworks.com/time-travel5.htm
How a time machine may be created using cosmic strings.
"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. However, there is still much speculation as to whether
these strings exist, and if they do, in what form. Gott himself said
that in order to travel back in time even one year, it would take a
loop of string that contained half the mass-energy of an entire
galaxy. And, as with any time machine, you couldn't go back farther
than the point at which the time machine was created."
http://science.howstuffworks.com/time-travel5.htm
Using massive spinning cylinders
"Another approach, developed by Frank Tipler, involves a spinning
cylinder. If a cylinder is long, and dense, and spins fast enough
about its long axis, then a spaceship flying around the cylinder on a
spiral path could travel back in time (or forward, depending on the
direction of its spiral). However, the density and speed required is
so great that ordinary matter is not strong enough to construct it. A
similar device might be built from a cosmic string, but none are known
to exist, and it doesn't seem to be possible to create a new cosmic
string.
Physicist Robert Forward noted that a naïve application of general
relativity to quantum mechanics suggests another way to build a time
machine. A heavy atomic nucleus in a strong magnetic field would
elongate into a cylinder, whose density and "spin" are enough to build
a time machine. Gamma rays projected at it might allow information
(not matter) to be sent back in time. However, he pointed out that
until we have a single theory combining relativity and quantum
mechanics, we will have no idea whether such speculations are
nonsense."
http://en.wikipedia.org/wiki/Time_Travel
Using spooky action at a distance
http://en.wikipedia.org/wiki/Time_Travel
"Quantum mechanical phenomena such as quantum teleportation, the EPR
paradox, or quantum entanglement might appear to create a mechanism
that allows for faster-than-light (FTL) communication or time travel,
and in fact some interpretations of quantum mechanics such as the Bohm
interpretation presumes that some information is being exchanged
between particles instantaneously in order to maintain correlations
between particles. This effect was referred to as "spooky action at a
distance" by Einstein.
Nevertheless, the rules of quantum mechanics curiously appear to
prevent an outsider from using these methods to actually transmit
useful information, and therefore do not appear to allow for time
travel or FTL communication. This misunderstanding seems to be
widespread in popular press coverage of quantum teleportation
experiments. The assumption that time travel or superluminal
communications is impossible allows one to derive interesting results
such as the no cloning theorem, and how the rules of quantum mechanics
work to preserve causality is an active area of research."
Problems with Time Travel
"If we are ever able to develop a workable theory for time travel, we
would open up the ability to create very complicated problems called
paradoxes. A paradox is defined as something that contradicts itself.
Here are two common examples:
* Let's say, for the sake of argument, that 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?
* Possibly 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? If we could change the past, it would
create an infinite number of paradoxes.
Another theory regarding time travel brings up the idea of parallel
universes, or alternative histories. Let's say that you do travel back
to meet your grandfather when he was a boy. 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. For
instance, if you were to travel back in time and kill one of your
ancestors, you've only killed that person in one universe, which is no
longer the universe that you exist in. And if you then try to travel
back to your own time, you may end up in another parallel universe and
never be able to get back to the universe you started in."
http://science.howstuffworks.com/time-travel6.htm
"Stephen Hawking has even proposed using wormholes to connect our
universe with an infinite number of parallel universes. Edward Witten
is working hard on superstring theory, which has already created a
sensation in the world of physics because it can explain the nature of
both matter and spacetime. By realizing that the fundamental laws of
physics appear simpler in higher dimensions, string theory can unite
Einstein's theory of gravity with quantum theory in ten dimensions.
Our heirs, whatever or whoever they may be, will explore space and
time to degrees we cannot currently fathom. They will create new
melodies in the music of time. There are infinite harmonies to be
explored."
http://www.pbs.org/wgbh/nova/time/through2.html
The possibility of paradoxes
http://en.wikipedia.org/wiki/Time_Travel
"The Novikov self-consistency principle and recent calculations by Kip
S. Thorne indicate that simple masses passing through time travel
wormholes could never engender paradoxes?there are no initial
conditions that lead to paradox once time travel is introduced. If his
results can be generalized they would suggest, curiously, that none of
the supposed paradoxes formulated in time travel stories can actually
be formulated at a precise physical level: that is, that any situation
you can set up in a time travel story turns out to permit many
consistent solutions. The circumstances might, however, turn out to be
almost unbelievably strange."
Additional Links
Nova Time Travel Site
http://www.pbs.org/wgbh/nova/time/
Paul Davies, About Time ISBN 0684818221
How to Build a Time Machine ISBN 0142001864
J. Richard Gott, Time Travel in Einstein's Universe: The Physical
Possibilities of Travel Through Time ISBN 0618257357
Paul J. Nahin, Time Machines: Time Travel in Physics, Metaphysics, and
Science Fiction ISBN 0387985719
Clifford A. Pickover, Time: A Traveler's Guide ISBN 0195130960
Frank J. Tipler, Rotating Cylinders and the Possibility of Global
Causality Violation, Physical Review D 9 (1974), 2203
Google Search Strategy
"time travel"
"evidence of time travel"
"special relativity"
"time machines"
Thanks for the interesting question. I hope this helps.
Regards,
Anthony (adiloren-ga)
University of Tasmania's excellent online lecture series on time travel
http://www.utas.edu.au/docs/humsoc/philosophy/Time_Travel/lectures.htm
Time Travel: A How-To Insider's Guide
http://www.amazon.com/exec/obidos/tg/detail/-/1892062046/002-4105567-8676060?v=glance |
