Basing what is possible on current thinking puts a vast amount of things in the "impossible" sphere! Take it back a few decades and very few would have thought flat screens, wrist portable communicators and eye glasses that could access more literature than the British library holds to be impossible. Technology becomes outdated fast and the pace is increasing with far more now possible and in fact relatively easy to do than ever previously thought. Give it time and ways to make Dyson spheres and other even greater things will become possible!