Portals are not Aperture Science's only remarkable scientific accomplishment. Among their other inventions is the Light Bridge, that provides a stable and seemingly immaterial surface that people can stand on. The bridge can also be turned on or off instantly.
You heard it like me, someone just asked about the physics of Aperture Science's neat Portal Gun. I'll try to give an account of what we know from the material that Aperture recently made available and from what can be deduced from demonstrations of the product.