Black holes
suck in objects but  according to Einstein's general theory of
relativity that time reversal is possible  objects that travel through
black holes could theoretically be spewed out of other holes. Such holes
are called white holes. The tunnels that connect black and white holes
are known as wormholes.
The spacetime tunnels of another world
Black holes are the final stage of a star's development. But in
extraordinary times, such as the start of the Universe, wormholes could
be created. If the changing nature of space and time is considered, it's
better to think that wormholes appear and disappear. By thinking closely
about wormholes, it's possible to understand that there is a different
world to the one we live on. If we consider both these worlds as being
parallel, wormholes are like a spacetime tunnel that joins our world to
the other.
Wormholes present time travel opportunities
Kip Sone, a relative theorist, devised a theory where wormholes could
act as time machines. He believed that, according to the principles of
quantum mechanics, if a space ship was strong enough to travel at
something near light speed through a wormhole, time would travel
backwards. By following the principles of the special theory of
relativity that say time moves slower for objects traveling at the speed
of light, it would be possible to travel in time.
Stephen Hawking has dismissed the possibility of creating time
machines
There are a number of factors working against the theory of creating a
time machine and it's better at this stage to consider its construction
impossible. Stephen Hawking has often said that if the effects of
quantum mechanics are considered, the construction of a time machine is
not possible in the real world.
Time warps
Ever see "Back to the Future"?
Well, I have and it really made me think. Could we travel back through
time? Would it be a twoway trip? Here's what I have to say... At first
I thought, no way, time travel can't be achieved! But when I really
think about it, why not? Let's talk about Einstein. Space and time coexist.
Giant gravitational forces (such as stars) cause "dents" in this spacetime
fabric. Could we possibly "jump" over these dents? In the future maybe,
but for now we have to think realistic. If you don't know already, if
you travel even close to the speed of light, time starts to slow down.
Back on Earth though time goes at normal speed therefore the people on
Earth will age faster since time is going faster for them. That's one
way you could get to the future faster.
What about going back in time? You'd
need a giant ferris wheel o' time travel. It would of course have to
spin at the speed of light and it would have to have tremendous mass!
You could in theory beat the light to where it was heading and again in
theory arrive back in time by beating the light to it's intended
destination.
Here's where I try to explain
complicated things. Hold on. Twoway time travel is going to a point in
time and then returning to the point you came from. Such a journey is
said to open a closed timelike loop (CTL). The problem with this is, if
you go back in time and cause the (accidental, inadvertently, whatever)
death of your maternal grandmother before you mom was born you would
have therefore never been born and never made the trip. So the journey
never happened and granny didn't die after all. In which case the time
traveler HAS been born...and so on. Causality is a hypothetical law that
says causes always precede effects. That theory does give us reason to
believe we can open a CTL.
When an electron/positron pair is made
out of gamma radiation, the positron may annihilate with a different
electron, leaving it's original partner free. Feynman pointed out that
this is exactly equivalent to a single electron bouncing off a gamma ray
and traveling backward in time before bouncing off a second gamma ray
and continuing it's path into the future. Got it?
Many geniuses, in my opinion, have
come up with their theories of twoway time travel. From tipping light
cones to my rotating cylinder theory, it is complex! Thanks to John
Gibbin's book, "Unveiling the Edge of Time", I better understand these
ideas and it's the source of my information.
Curved space time
It isn't space which is curved
it's spacetime. When I talk about curved space I'm not being very
accurate. The reason I do talk about curved space is because it's easier
to understand than curved spacetime. Spacetime is a fusion of space and
time; we put the two together because they are not independent. They may
appear to be independent in every day life but they're noticeably
connected if you travel at near light speed.
What does it mean for space to be curved? Moving through curved space is
not the same as driving down a curved road, because when you're moving
through curved space, you think you're travelling in a straight line.
How can this be? Imagine approaching an area of great curvature, which
therefore is very hard to traverse. The easiest way to get to the other
side is to go around, rather than through. Thus the line (which is the
shortest distance between two points, as defined by geometry) of your
path is not straight, but curved. Such a line is called a geodesic.
In our universe, things travel along geodesics of spacetime.
Because these geodesics are curved by the presence of matter, an
object's geodesic will curve inward toward a massive body. We observe
this effect as gravitation. Light, too, travels along geodesics, and its
path is bent and curved as it speeds through spacetime.
