Opposite of Black Hole - Matter Repulsion?

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Discussion Overview

The discussion revolves around the concept of a theoretical entity that would act as the opposite of a black hole, specifically one that repels matter rather than attracting it. Participants explore the idea of "negative pressure" and its implications in the context of black holes and white holes.

Discussion Character

  • Exploratory, Debate/contested, Conceptual clarification

Main Points Raised

  • One participant suggests the existence of a theoretical "hole" that would push matter away, akin to negative pressure.
  • Another participant mentions white holes as a theoretical possibility that aligns with the initial proposal.
  • A subsequent reply clarifies that white holes do not exhibit repulsive gravity but rather have attractive gravity, similar to black holes, and that both are vacuum solutions with zero pressure.
  • The same participant notes that for a scenario involving "negative pressure," one would need to consider alternatives like a cosmological constant or a scalar field, indicating that the original concept may not fit within current theoretical frameworks.

Areas of Agreement / Disagreement

Participants express differing views on the nature of white holes and their relation to the concept of repulsive gravity. The discussion remains unresolved regarding the feasibility of a repulsive entity analogous to a black hole.

Contextual Notes

The discussion highlights limitations in the definitions of black holes and white holes, as well as the assumptions regarding vacuum solutions and the conditions necessary for negative pressure scenarios.

Felix Quintana
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Since black holes takes matter to a singularity, theoretically could there be a hole that does the opposite? As in push everything away like negative pressure.
 
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Oh cool! Thanks!
 
Drakkith said:
A white hole, which does exactly what you proposed

Not really. A white hole has attractive gravity, not repulsive gravity. See below.

Felix Quintana said:
could there be a hole that does the opposite? As in push everything away like negative pressure.

No. A black hole, and its time reverse, a white hole, are both vacuum solutions; there is zero pressure everywhere (and also zero energy density). The white hole has things coming out of it and decelerating as they rise away. The black hole has things falling into it and accelerating as they fall. Gravity is attractive in both cases.

For a solution with "negative pressure", you need either a cosmological constant or something like a scalar field, i.e., not vacuum.
 
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