The primary reason given by people who don't believe in visiting extraterrestrial spacecraft is, the enormous distance between interstellar planets make it impossible. The primary logic behind this thinking is: (a)faster than light travel is not possible, therefore it would take far too long to travel the distance in any feasible time. (b)The fuel and other consumables required for such a trip, given the years it would take at near light speed, make it logistically unworkable.

However, insofar as the speed of light goes, gravity has an indeterminate speed. Experiments have shown the speed of gravity to be far in excess of light speed. If a craft can create it's own gravity, perhaps by way of focus and amplification of existing interstellar forces, then the speed of light limitation is circumvented. Furthermore, if gravity can be focussed by means of a type of lens then no fuel would be needed. And if interstellar space is a vacuum, once initial velocity is reached additional propulsion is only required to make incidental and course corrections. Creating ones own gravitational field would also cocoon the vehicle and it's occupants from inertia, and protect it from asteroids and other space rubble.
 
Some of the explanations put forward by disbelieving members of the scientific community are far more absurd than the proposal of extraterrestrial visitation. Examples of some well known explanations are: swamp gas, mass hallucination, lenticular clouds, ball lightning, Venus, or secret government technology. While I concede that the vast majority of UFO sightings are simple misidentification's of common phenomena such as satellites or aircraft, there are a number of encounters that one can hardly call into question. Instances of military personnel touching and photographing objects on the ground, and film of flying disks firing lazer-like beams at in-flight ICBM's are among well documented cases that stand on their own merit.
 
We need only look at advances made in human technology over the last couple of hundred years to realise how far we may advance over the next couple of hundred years. But progress in technology has not been the same the world over. Different cultures advance at different rates. Obviously the same would be true of civilisations spread throughout the cosmos. So why is it so difficult for bright people to accept the possibility that our planet has been visited by a more advanced civilisation? "Show me the evidence" they say, "grainy video and witness testimony is not evidence!" But there is good video, and highly credible witness testimony from people known to be beyond reproach. In some cases physical trace evidence and corroborating witness testimony has been thoroughly researched by scientists, and found to be un-attributable to known phenomena. So why the stubborn opposition?

If, as an advancing civilisation, we blindly accept the limitations we perceive, are we not placing a psychological barrier in the way of our own progress?

© A.C.Thursby-Pelham 2011

Ref: http://metaresearch.org/cosmology/speed_of_gravity.asp

Source: http://www.thursbypelham.com/2011/08/is-interstellar-travel-possible.html