Anti-de Sitter space merges with de Sitter space

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Main Question or Discussion Point

what would happen, in terms of physics, if one region of the universe is de Sitter space and another region of the universe was anti-de Sitter space, and the two regions de Sitter space and anti-de Sitter space came into contact and merge?
 

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  • #2
strangerep
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How on earth would one model that? One region has +ve constant curvature and the other has constant -ve curvature. A huge discontinuity at the boundary sounds totally unphysical. But if you try smooth the discontinuity, you no longer have (A)dS spaces since the curvature is position-dependent.

[Aside: you might want to be careful with these "what if" speculative theory questions, lest you stray onto thin ice...]
 
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How on earth would one model that? One region has +ve constant curvature and the other has constant -ve curvature. A huge discontinuity at the boundary sounds totally unphysical. But if you try smooth the discontinuity, you no longer have (A)dS spaces since the curvature is position-dependent.

[Aside: you might want to be careful with these "what if" speculative theory questions, lest you stray onto thin ice...]
imagine a particle and it curves spacetime dS spaces and another particle curves (A)dS spaces. what happens when (A)dS and dS meet?
 
  • #4
strangerep
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it curves spacetime dS spaces
Sorry, I have no idea what you mean by this.
 
  • #5
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Sorry, I have no idea what you mean by this.
imagine a universe with dS spacetime colliding into a universe with AdS spacetime. what happens to the spacetimes?
 
  • #6
strangerep
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imagine a universe with dS spacetime colliding into a universe with AdS spacetime. what happens to the spacetimes?
A "universe" means "everything". So the concept of 2 universes somehow colliding (presumably inside some larger "universe") is self-contradictory.

[Sorry, but I'm going to exit this conversation now. PF is not the place for development of speculative theories.]
 
  • #7
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A "universe" means "everything". So the concept of 2 universes somehow colliding (presumably inside some larger "universe") is self-contradictory.

[Sorry, but I'm going to exit this conversation now. PF is not the place for development of speculative theories.]
string/m theory predicts a multiverse and that big bang may be caused by higher dimensional branes colliding.
 
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string/m theory predicts a multiverse and that big bang may be caused by higher dimensional branes colliding.
Multiverse is a concept in cosmology predicted by some models of inflation.
What you mean is called the string landscape which is the enormous number of possibilities for the properties of the compactification of extra dimensions(basically how those little dimensions look like) and those are different from branes that can have collisions among themselves. And I don't think branes in string theory can have non-trivial metrics like the (A)dS metric.
 
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The negative comments are wrong, this is actually a reasonable question in the context of inflation. With a complicated potential energy landscape, there may be a multitude of dS, Mink, and AdS vacua that can form as bubbles in an inflating universe.

I couldn't find anything specifically on a collision between dS and AdS, but "Colliding with a Crunching Bubble" considers collisions between a flat-space bubble and an AdS bubble.

@strangerep was almost right the first time, you get a cosmic domain wall at the boundary, possibly shielded by an event horizon. See the paper's last paragraph for one scenario: a cosmic sky showing a fractal distribution of black disks.
 
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  • #10
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The negative comments are wrong, this is actually a reasonable question in the context of inflation. With a complicated potential energy landscape, there may be a multitude of dS, Mink, and AdS vacua that can form as bubbles in an inflating universe.

I couldn't find anything specifically on a collision between dS and AdS, but "Colliding with a Crunching Bubble" considers collisions between a flat-space bubble and an AdS bubble.

@strangerep was almost right the first time, you get a cosmic domain wall at the boundary, possibly shielded by an event horizon. See the paper's last paragraph for one scenario: a cosmic sky showing a fractal distribution of black disks.
i was actually wondering in the context of say a particle say a neutrino generates a dS space around it, comes into contact with an antineutrino with an AdS space.

what is the physics that governs when dS space comes in contact with AdS space, and would a particle that generates dS space attract or repel a particle that generates AdS space
 
  • #11
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what is the physics that governs when dS space comes in contact with AdS space, and would a particle that generates dS space attract or repel a particle that generates AdS space
Long ago, I was perplexed by how two black holes could attract each other. The actual mass of either black hole is inside an event horizon, so how could it feel and respond to the gravitational field of the other object? The answer is that the actual attracting, the relative motion towards each other, occurs in the space outside the event horizons. The approximate solution to the two-body problem in general relativity patches together four regions of space-time: the interiors of two black holes, a shared exterior in which the external gravitational fields are distinct and interacting, and an asymptotic region in which they can be approximated as a single gravitational field. The dynamics of attraction happens in the second-last region.

A similar analysis seems to be required for your scenario. Incidentally, the issue of a boundary or transition between the (A)dS space immediately around the particle, and the surrounding space in which other particles move, arises even before we think about the two-body problem. Such geometric graftings are notoriously unstable - either the surrounding geometry dominates and the region of different geometry sourced by the particle shrinks to just an infinitesimal neighborhood of the particle, or the geometry sourced by the particle dominates and expands in all directions.

If your (A)dS regions are stabilized somehow, like the regions around a black hole of specified mass, charge, and spin, then a patchwork analysis like the four-region approach to the two-body problem can take place. But to say any more than this, requires a specific theoretical scenario. For example, it is conceivable that this scenario can be realized in some phase of string theory, as an interaction between positive branes and negative branes.
 
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  • #12
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is there any proof that all spacetime everywhere in the universe is dS? could there be pockets and regions of space that is AdS in our universe?
 
  • #13
ohwilleke
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The curvature need not be constant. If the curvature were +xve where x is the distance from the boundary point, and -xve, you'd get a topological saddle point with a single point that was topologically flat (e.g. the Big Bang in a bouncing cosmology of some type).
 
  • #14
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The curvature need not be constant. If the curvature were +xve where x is the distance from the boundary point, and -xve, you'd get a topological saddle point with a single point that was topologically flat (e.g. the Big Bang in a bouncing cosmology of some type).
so what happens when the 2 meet?
 
  • #15
Lisa Randall and Raman Sundrum were working on this problem 15 years ago with a Kaluza Klein Model.
3 D Branes crashing in an 5 D AdS
If they had been calculating your specific problem of an dS and AdS Brane? I don't know, but if could help to look for their publishings.
 
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