Naked singularities

  • Thread starter Tail
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  • #1
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Ok, just HOW could they exist, when the event horizon is just gravity, singularity is supposed to be infinitely contracted mass, and mass is supposed to have gravity?

Any insights at all appreciated...
 

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  • #2
Stingray
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Tail said:
Ok, just HOW could they exist, when the event horizon is just gravity, singularity is supposed to be infinitely contracted mass, and mass is supposed to have gravity?

Any insights at all appreciated...
Relativistic gravity is much much more complicated than newtonian gravity. In newton's version, you can go sufficiently far outside a lump of mass and find that the gravitational field is just given by the total mass of the lump and how far away you are from it. There is no analogous statement in GR (except in the weak field limit of course).

Gravity can't be described by a vector (or scalar potential) anymore, and it couples to more than just mass (also momentum and internal stresses/pressure). In many cases, its not even possible to define masses meaningfully in GR except in certain limits.

To add to the difficulty, an event horizon is an extremely nonlocal construct. It is not "real" in the sense that it could ever be measured exactly even in principle. Constructing an event horizon exactly requires knowing the entire future history of the universe. Otherwise, how would you know that nothing could ever escape?

The point of all that was to say that one's usual intuition doesn't apply here (and the math is very difficult). There actually are explicit solutions with naked singularities. They are not expected to exist in the real world for various reasons, but the point is that we can rule out specific examples, not the entire class.
 
  • #3
TeV
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Stingray said:
There actually are explicit solutions with naked singularities. They are not expected to exist in the real world for various reasons, but the point is that we can rule out specific examples, not the entire class.
Shapiro and associates constructed in 1990 the model (computer simmulation) of gravitational mass collapse starting from quasi-elipsoidal (?) mass distribution.At the 2 poles they got naked singularities existing for a finite time.GR cannot say anything about what could be seen in such situation despite only GR equations were used in creating the effect.
 
  • #4
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Still, they are supposed to be completely theoretical/ the result of complicated math?
 
  • #5
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Tail said:
Still, they are supposed to be completely theoretical/ the result of complicated math?
Better to say it was the result of computer simulation of Einstein equations for given boundary conditions(such problems very rarely have solutions explicible in closed math forms).
Yes,completely theoretical.Naked Singularities are clear sign that GR must meet theory of quanta in order to describe the phenomenon.
 

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