It was suggested, as I had written a novel with alternate
time lines, and time paradox, that I should blog about time travel. Well, it
just so happens I did write something, about wormholes and time travel, about
ten years ago. So I pulled it out, dusted it off, and here it is. Take into
account this was written, as I say, ten years ago. This is based on a documentary,
and internet research, that I had done at the time. I, personally, find it
fascinating, but it's not everyone's cup of tea, and may even be used for those
that suffer from insomnia.
A paper discussing wormholes—wormholes first appeared in
Einstein's theory of gravity, in 1913—states that: To be stable, wormholes need
lots of negative energy—a rare commodity in the universe. Such energy has not
yet been found, but quantum mechanics suggests that it does exist. The problem
is that we don't know whether the laws of quantum mechanics allow enough
negative energy to be concentrated in such a way as to allow wormholes to
exist.
Although wormholes could exist throughout the universe—one
possible location is at the center of black holes—traveling through one of
these might prove extremely difficult since the wormhole would be so unstable
that it would collapse as soon as a spaceship, or even a ray of light, entered
it. This is because there would not be enough negative energy to hold it open.
In a paper on "Wormholes and Time Machines" by
Berndtson, Gunnarsson, and Johansson it states: The problem is that a
macroscopic wormhole is not static in structure, it's rather a shape that
expands from a singularity with zero throat radius to maximum radius and then
shrinks back to a singularity again. This expansion-reduction of the radius
would be very quick. Even light would not have a chance to pass through the
wormhole before it shrinks back to zero radius again. In fact, any now known
matter that would fall into the wormhole would pull it together through
gravity. If constructing a mathematical model of an open wormhole that allows
passage, the equations of general relativity says that matter with an enormous
negative pressure is needed to uphold the wormhole gravitationally. The
magnitude of the tension of the matter must be greater than the energy density
of the matter itself. This would leave us with a material that will have a
negative energy density relative to a light beam traveling through it.
We are talking of exotic matter, so-called because there is
no such matter now known. There are some indications that exotic matter can
exist. For example between two metal plates there can be field fluctuations
that have a negative energy density relative to the field fluctuations in free
vacuum. Evaporating black holes also imply that exotic matter can exist.
Another problem with wormholes is that fields can destroy
them. Fields are in some solutions able to increase their strength for each
passage through a wormhole. If the wormhole has a focusing effect, the total
field strength becomes infinite and will therefore destroy the wormhole. If the
hole is defocusing, it converges towards a finite value and the wormhole can
survive. The only matter that can make the wormhole defocusing is exotic
matter. If exotic matter exists and has the ability to uphold a wormhole
without interacting with and harming the traveler, then there is a physical
possibility of a traversable wormhole and for it to even work as a time machine.
A wormhole can be turned into a time machine by keeping one
mouth of the wormhole fixed while moving the other. This can be made through
gravitational attraction or by charging it electrically while moving it with
electric fields. Traveling from the stationary mouth to the moving and back
again could then send a traveler back in time.
A message sent through a wormhole would take a shortcut in
space-rime, arriving almost at once if the wormhole is short.
The lifetime of wormholes, however, are argued to be too
short lived for information to be communicated between the two external
regions.
The real problem with traversing a wormhole is that none of
the geodesics connecting these two external regions are time-like or
light-like. For information to cross from one external region to the other, it
would have to follow a space-like path during at least part of the journey. In
other words, in order for information to cross from one side of a wormhole to
the other without winding up hitting the physical singularities it would have
to travel faster than light in a way not allowed even by general relativity. If
information could do this, then the first problem of stability wouldn't be a
problem at all as the information could travel through the wormhole arbitrarily
fast and make it through before the wormhole connection was broken.
So when it comes down to it we are not even sure that exotic
matter exists and if it exists it isn't very probable that we can collect
enough of it to feed a wormhole. We also have to find a macroscopic wormhole to
feed with this exotic matter. Current research indicates that it is impossible
to open a wormhole bigger than 10^-35 meters. Therefore it will take more
creative thinking before any scientist or novelist can fit a human into a
wormhole, especially one that small. The problems are many and if it really is
possible it will take many years before we overcome them.
In fact, physicists don't agree that time travel is
possible. Stephen Hawking wrote in 1993: "...the best evidence we have
that time travel is not possible, and will never be, is that we have not been
invaded by hordes of tourists from the future." Time travels might be
allowed theoretically but real ones are still science fiction at this point.
Then again, there is always the science of Ronald L.
Mallett. I recently watched a documentary on his theories and ideas and found
it fascinating.
According to Mallett, with the current technology it is
possible to send subatomic particles, at the very least, back into the past.
We've know for a long time that time travel is possible, in
theory. Mallett has a blueprint for a time machine, a means to achieve it.
Sending particles back in time would also allow information
to take the same route, it could be used to send scientific understanding from
the future...but then it would get a little strange.
Although the professor's underlying idea is new the science
is not. Time travel, travel in the fourth dimension, allows a person to be in
two places at once. And in fact has already been accomplished, although
admittedly only to a minute degree, by the Russian space program in the later
part of the 20th century. Traveling at 16,000 miles per hour has propelled them
a fraction of a second into the future.
Experimental physicist, Chandra Roychoudhuri, specializing
in laser technology, hopes to create a machine that will use the principle of
flexible time to send particles into the past.
In 1905, 26-year-old Albert Einstein showed how space, time,
and energy are linked. We know he got it right because his theory led directly
to the atomic bomb.
This is the very same theory that should allow real
practical time travel. It all has to do with the speed of light.
Einstein's big idea was that the amazing speed of light
holds the key to everything from the untold power of the atom to the
possibility of time travel.
The speed of light remains the same, no matter how fast you
are moving towards it or away from it, it will appear to pass you at the speed
of light.
Einstein's prediction that the speed of light is the same
for everyone is one the strangest in physics, but it's true. It's been shown by
hundreds of experiments that the speed of light remains the same no matter how
fast you are moving towards or away from it (something else is changing, and
that something is time). If an object is moving fast enough through space it
can alter its passage through time.
The faster you travel the slower time passes for you (so
what might appear an hour to you may be one hundred years to everyone else). In
effect, you would be traveling one hundred years into the future.
Then you have the grandfather paradox, which suggests things
are fixed not allowing for free will. You cannot change the past as it has
already happened.
And then you have Dr. David Deutsch, the world's leading
proponent of Parallel Universe Theory, who claims, that in addition to the
universe we see around us, there are vast numbers of other parallel universes.
Some are very like our own, differing only in the position of one atom, and
others are very different.
This idea comes from the study of subatomic particles. The
more we find out about them the more their behaviour seems absurd; which could
actually explain why the future is not fixed but fluid, in a weird sort of way.
If you look at the universe on a very small scale you begin
to see things that are very alien to our everyday experience.
In everyday life we are used to objects retaining their
identity, a pen is a pen. A subatomic particle typically might change into
another particle, or into two other particles, or particles might merge their
identity and become one.
Sometimes a subatomic particle can be traveling along and
then change course for no reason that we can observe. Or if this was the
subatomic world, we could put an object on the table and it could ooze right
through and pour to the floor.
This is the strange world of quantum mechanics, and
physicists still argue about what is going on.
What's really happening is that the universe we see is only
part of the physical reality. There are parallel universes, and each particle
in our universe has counterparts in many of the parallel universes, and under
some conditions these counterparts affect the particles that we can see. The
universes are interfering with each other all the time. So particles in our
universe could be hitting other particles in another universe, and neither
universe would really know about it, and in that parallel reality a very
different scenario could be playing out.
In a multiple universe time travel allows travel to take
place between two similar and yet different universes, and because you are not
in the universe you came from there is no need to fulfill any particular
destiny, so neither universe contains a paradox, some would postulate, however,
that this is not true time travel but inter-dimensional travel.
The theory implies that there are an infinite number of
these parallel universes and that time travel would simply involve skipping
from universe to universe to universe. A working time machine would, in effect,
test this extraordinary idea. If it's correct then not only does free will
exist but the nature of reality itself is very strange indeed.
Mallett says that the paradoxes that people talk about are
only going to be resolved after we build the first time machine. Then we will
know whether or not free will enters into it, whether there's multiple
universes, or whether the universe is determined. That's going to have to be
understood experimentally.
Although Einstein correctly worked out that traveling very
fast sends you into the future, a further development of the theory should
allow travel into the past.
The crux of Mallett's theory starts with intersecting
powerful rings of laser light that twist time into a loop, an effect that
Einstein predicted but was never able to prove.
The way it works is, a circulating beam of light creates a
rotating region of space as though you were stirring a cup of coffee and in
addition to twisting space in Einstein's theory, space and time are linked so
you cause a twisting of time as well.
We think of a time-line as being a link from the past, to
the present, to the future. If you can close that time-line into a loop you can
go from the past, to the present, to the future, but we're on a loop so we can
go from the future back into the past.
The basic form a time machine would take is a stack of
lasers creating layers of circulating light and around them would be
circulating loops in time. In building a time machine we would need to exceed
the speed of light without breaking the laws of physics. We already have the
answer. We know it exists, and we know where to find it. The problem is getting
there.
What you need is a rotating black hole. A black hole that is
spinning has a very interesting effect on the space and time around it. It
drags them around with it and that means one can evade the rule about not
exceeding the speed of light. As we already know a black hole's denseness
creates a gravitational pull that is so strong not even light can escape it.
This incredibly strong gravitational pull is able to grab the empty space
around it and pull it towards its center like a whirlpool. Here physics is
pushed to its absolute limit.
One can travel into the region where space and time are
being dragged around the black hole, remain in that region traveling around
with it and emerge at a time before we went in.
This natural time machine occurs only because the black hole
has the power to move empty space. The phenomenonm, as you are most likely
familiar with, is called frame dragging, one of Einstein's lesser known ideas.
Within that rotating region of space you can travel speeds
up to the speed of light. To someone outside it would appear as though you are
traveling faster than the speed of light and for them you will disappear from
sight as you are traveling back into the past. However, black holes are not
always readily available.
This is where Mallett had a stroke of inspiration. He
realized that Einstein's theory was hiding the secret. Something that would be
even better at twisting space than a black hole. It turns out that light is
much more effective at twisting space and time. As stated before, his idea is
to use a circulating light beam to twist space and close time into a loop. The
key technical challenge is trying to get enough laser power to cause this
twisting of space and time.
Modern laser technology is extremely advanced, some lasers
can create conditions as hot as the center of the sun. An array of such devices
could be rigged to fire at the same time and that could produce a cylinder of
light with enough power to actually twist space.
An elementary particle fired on a corkscrew-shaped path down
this tunnel would wind its way into the past. Seen from outside this experiment
this would have some pretty bizarre consequences (this is where the strange
part comes in).
Says Dr. Mallett: "I expect that particles might just
simply appear out of nowhere, even though I didn't put anything into the
machine. And those would be particles that would be from experiments that I
performed next week, or a year from now, in which I am sending particles back
to my time.
"This is a real time machine and that means that when
you turn it on today, and you leave it on, it will only act during the time you
have it on. So if I turn it on today and I leave it on for a hundred years, I
can then travel from a hundred year from now up to today, but I cannot travel
to a time before the machine was turned on.
"So, it's conceivable that the moment the machine is
turned on that you might immediately start receiving messages from the future.
"If a machine can be created that would be stable
enough to keep twisting time for a century or more it could become, in effect,
a phone line through time. Anyone with future access to the machine could send
messages back which begin to be recovered the moment it is turned on."
