When you suck on a straw that has one end in water, you are causing a decrease in pressure in the straw. As a result the pressure in the straw is less than that in the surrounding air. The difference in air pressure is what drives the fluid into the straw.
In regards to it being impossible for aliens to come here due to prohibitive distances, it may be that they know something more than us mere human know about physics, that can be utilized by them to get here or to influence us...