Time Travelling Aliens/Humans

Is it possible to travel from one point in time to another ? We've all seen the films "Back to the future" "The time machine". Many books written and even a prime time show (Doctor Who) on a Saturday evening are about it.  Now before I go further into this I know it is not physically possible for mankind to achieve this.... But, have beings from another planet manifested the power to do such a feat?


 The reason why i'm writing about this , is because of the amount of UFO sightings in around the time of major world events like 9/11, the first ever nuclear bomb testing at groom lake and the Apollo moon landings.
Are we being visited during these events by beings that already know where and when it is happening ?  It's certainly possible as anyone with a basic grasp in physics would tell you it is.
 General Relativity - General Relativity forms the basis of the space-time continuum, or a way of representing three dimensions of space and one dimension of time. By combining the two concepts into a single manifold, physicists are able to deal in a unified way with space times which attempt to explain the workings of the universe at both super galactic and subatomic levels. There may be an endless number of dimensions, though 4-D space time is as far as modern-day scientists know. Treating space and time on the same footing and as two aspects of a unified whole was devised by Hermann Minkowski shortly after the theory of special relativity was developed by Albert Einstein. Space-times are the arenas in which all physical events take place — for example, the motion of planets around the Sun may be described in a particular type of space-time, or the motion of light around a rotating star may be described in another type of space-time. In any given space time, an event is a unique position at a unique time.

Now Albert Einstein (E=mc2) calculated that nothing could travel faster than the speed of light, however the discovery of the Higgsboson  particle may prove that faster than light speed is possible. Other theories thrown around are folding space theory and the famously named warp speed.If Aliens have the ability to travel through time then maybe that's the reason UFOs seem to appear at the time of certain events. Have Aliens discovered a way of travelling through black holes and wormholes that have enabled them to jump to certain points in space and time at an instant or are they human?

My personal view to help understand this is maybe we are being visited by our future selves. Is this a human being maybe 5 million years in the future?  Has convergent evolution brought us to this? 
* Short in size because we are less mobile.
* Bigger heads because we've managed to enable the other 90% of our brains we currently don't use.
* Eyes and skin that have adapted to the environment of other planets we've inhabited.  


This is just a wee theory I have and it is pretty much out there there to be honest but i like it :-)


Greig