The physical principle is basic inertia. You need to accelerate a container large enough to hold a human being plus the systems needed to keep that person alive to 17,000 mph, and then decelerate them again without cooking them alive or smushing them into a paste against the inside of the vessel.
Your 747 argument is specious. The energy in a stick of firewood is comparable to that in an equivalent mass of dynamite. I invite you to set both on fire and report back on the difference.
So, your argument is that oh noes, there's Too Much Energy! (gasp). That clueless scientist's "proof" of the impossibility of heavier-than-air flight rested on a speed of 600 mph being "unobtainable."
Color me impressed!
Really the hurdle for rocketry to LEO has to do with the horrendous increase of reaction mass in the rocket equation. With the enthalpies available from chemical reactions, the required delta-V for earth is just on the cusp of impractical, requiring mass-fractions just at the edge of our practical fabrication technologies.
But we are not inherently limited by the energies of chemical bonds or by the rocket equation.
Your 747 argument is specious. The energy in a stick of firewood is comparable to that in an equivalent mass of dynamite. I invite you to set both on fire and report back on the difference.