I thought it was a really good basic start for anyone interested in the subject. And as my physics is a little ropey I'll give my view....
The fourth dimension is time, a solid principle if one considers time to normally act in a linear fashion with everything having a time limit. Whether it be a cell or a stone they are made up of very similar atoms, who knows maybe the same fundamental particle (Higgs particle anyone?) so it is logical to think they are subject to the same rules.
Now the question is how do you move in time - the grandfather principle suggests that anyone with Marty McFly ambitions of travelling back in time in a Delorean is out of luck because of the paradox it throws up - if you could alter the path of your ancestors then in theory you may not exist but you are there altering the path of your ancestors so you must exist.... and so on and so forth. However, what about travelling forward in time??
Well two views were suggested. Firstly if one travelled to 99% of the speed of light then time would slow down dramatically, however getting to this speed would require a lot of energy. The other, which I thought was a little more extreme, would be to encircle a super massive black hole... Indulge me if you will....
It has been proven from the 31 GPS satellites circling the globe that an object with a given mass actually distorts time. The GPS satellites have to have their internal clocks adjusted for the 3 billionth of a second they lose every week - apparantly if this wasn't done it would alter your google map results by about 6 miles! Now how does an object with a mass exert a distortion of time....? Simples!
If one is to imagine time as a river and the objects with masses as stones in that river it seems logical that to get past the stones the river is slowed down around it. The same is true for time - as time flows past masses like the Earth, time is actually slowed down. This phenomenon is a relationship that agrees with the river example. So in theory if you put a huge dam to bring the water to a stand still then logically the same is true for time? Sort of yes! So something with a huge mass like a supermassive black hole would slow time significantly! Amazing! Now this is the exciting bit - how to manipulate this into time travel... well the idea is to shoot a vehicle around a supermassive black hole in perfect synchronicity with the gravitational pull and the centrifugal force acting to keep the vehicle in a sort of orbit. This orbit around the supermassive black hole will reportedly slow time down by half to those in the vehicle. In other words for every year they spend orbiting it you would age two on earth... Seems a little extreme given the risk factor weighed up with the benefits but hey there you go.
So time travel is possible.... although dangerous, expensive and time consuming...
....I never wanted a Delorean anyway
