|I have heard that (theoretically) one could
travel into the past by moving faster than the
speed of light. Again, I do know that to our
current knowledge moving faster than light is
impossible, but for the sake of the example lets
say that it is possible. So anyway, if you were
to travel faster than the speed of light, wouldnt
time "move" backwards for YOU? If so, then how
would you be "traveling" into the past, in general?
When doing special relativity, the assumption
is that everyone has their own personal clock.
Due to this, the rate at which time passes for you
according to you never changes. One second seems
like one second to you. However, you will observe
others' time to be moving different than yours.
One of their seconds might seem like several of
your seconds. Even if you don't pass the speed of
light this is true. therefore, what the math
states is that beyond the speed of light, you
would observe others' time (the people going
slower than light in your reference frame) to be
moving in a reverse fashion.
like the mathematical solution says that there's a
possibility that the height of a swing increases
due to friction as it continues swinging (instead
of decrease due to friction like we usually see),
we consider both of those cases (the swing as well
as the past time travel) to be the "time-reverse"
of what is the real physical answer. In the case
of the swing, if you reverse time for the growing
solution, you'll see a dying solution where it
swings lower with each swing. The special
relativistic case of going faster than light is
just a reversal around the speeds between infinity
and the speed of light, instead of 0 and the speed
of light (notice that 1/0 approaches infinity.
Therefore it's a reverse around the fraction of
the speed of light you are traveling). Due to the
mathematical formulations scientists like to use,
you can take time to be (-1) x time and it will
provide no new information. But we never observe
those things in nature. And so scientists believe
that it's just the same solution with t -> -t in
the math, and not something real that can happen.
I think the place you heard that was Star Trek.
Their physical understanding is frequently
In Einstein's theory of general
relativity, space-time continuum can be visualized
as a four-dimensional hyper-surface existing in a
five-dimensional space,just as the surface of the
Earth can be visualized as a two-dimensional
surface in a three-dimensional space. On t his
surface, three of the dimensions are what we know
as space; the fourth is time. The curvature of
space-time is caused by the presence of mass, and
the converging curvature of different points is
what we know as the force of gravity. Just as an
object traveling along the Earth's surface follows
a curved "geodesic" path, so must an object in
space follow a curved path in space and time. The
reason why you can't go faster than light has to
do with the fact that hyper-surface of space and
time cannot connect two points in space without a
certain distance in time between them.
Science-fiction writers and some physicists
have speculated that it might be possible to bore
a hole through the fabric of space-time and move
freely through this five-dimensional space, then
you could travel anywhere in space and time at
your leisure. The simplest way to envision this is
to create a tube-like surface connecting two
distant places in space and time. This
hypothetical tube-like shape of space-time is
called a wormhole. If you were to travel through a
wormhole, then you would experience time passing
as you travel through it according to the length
of the tube in the time dimension. Other means
have also been envisioned, however.
wormholes or other means of traveling not in
space-time have ever been observed, although
quantum physicists theorize that they do exist at
extremely small spatial and short temporal scales
(about 10^-33meters and 10^-41 seconds). These
also remain unobserved, but the grounds for
suspecting their existence is that the theory of
Einstein does not agree with quantum mechanics, so
one of the theories must be wrong where the two
physical principles intersect. If theoretically,
you could depart from space-time, then you could
travel into the past - or into the future -at any
speed that you desired.
Most science fiction treatments of time travel
assume you're in a "bubble" of some kind (a ship
in a warp field, etc.). If you're inside the
bubble, time moves normally: clocks appear to move
correctly, a dropped glass breaks, etc. But if
you're inside looking outside the bubble, the rest
of the universe would seem to be running backward
toward the big bang. And similarly for an
outsider looking in: life in the bubble would seem
to happen backwards.
How to generate the
bubble and propel it faster than the speed of
light is... um... a "nontrivial problem."
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