Question: I heard a theory stating that an object which travels at light speed (or close to) is automatically becoming a black hole because it has endless mass, according to formula E=mc2, and starts to attack objects around it (I am oversimplifying but I think I wrote the essence of it). How much truth is in this theory?

Asked By: Smjesko Babic


For anything that is not moving at the speed of light, or is equivalently mass-less, you can stop its motion by a Lorentz boost.


Since that is the case, you can see where the discussion is going. No, a massive (but light) object moving at near light speed will never become a black hole.


This is pretty much an answer coming from the definitions of Relativity.


However, it is not too bad a guess. As is known from General Relativity, it is the energy and momentum of a system that determines the gravitational effects. This means that a highly speeding particle can jolly well distort spacetime strong enough to be macroscopically detectable.


By that, I mean that a particle may be moving so fast as to induce gravito-magnetic effects on nearby particles. However, such a whoopingly fast particle has never been observed.


In a universe with only one particle, or only one black hole, traveling at high speeds is meaningless.


Two particles moving in different directions, however, makes things possible. Even light itself, with enough energy, is expected to make black holes.




Sources / Further Readings:


Annoyingly, no textbook known to me deals with this issue, so I can only deduce this from the principles of General Relativity. Maybe they all thought that this problem is as simple as I have made it to sound (the theory would be useless if it were unable to deal with it this way, anyway).


Introductory texts on General Relativity (and Special Relativity) exist. I strongly recommend Sandar Bais' "Very Special Relativity" for a concise, maths-less pictorial introduction that has everything important in it.


Schultz introducing General Relativity is also one of the better written ones, as is Sean Carroll's.


Image Description: An artist's interpretation of how a black hole's aurora might look like close-up


Credit: Ian O'Neill/Discovery News



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