Let's say that we have a particle flying through space, at a collision course with a planet. As seen from an observer on this planet, the particle has an enormous energy, and its wavelength is just slightly bigger than the Planck length. As the particle falls down the gravitational well of the planet, it gets blue shifted enough to gain the last bit of energy, and the particles wavelength shrinks below the Planck length, which transforms the particle to a black hole. The person on the planet observes this black hole. The whole scenario is also seen by a different observer, flying with great speed, also toward the planet, in the trajectory of the particle. In her system, the wavelength of the particle isn't that close to the Planck length, and the gravity of the planet surely isn’t enough to transform it into a black hole. Now what does she see? Will the particle behave “nice” in her system, and not turn into a black hole? In that case, two contradictory histories are being observed. On the other hand, if all observers agree on the fact that the particle has turned into a black hole, that would be very weird indeed (because I can always make up some system for which the wavelength of the particle is less than the Planck length). Any ideas about how to resolve this?