# Thread: Need help deciphering a paper (Linde/Vanturin multiverse)

1. ## Need help deciphering a paper (Linde/Vanturin multiverse)

I've tried to decpher this paper, but it's above my level.

Is this a multiverse, or just a large single universe with many inaccessable regions?

Are these regions subect to the same laws of physics, or different?

What are Freidmann geometries?

How could the same big bang produce universes with variant laws of physics?

2. I skipped to the Conclusions and that was when my brain went offline. I think they are saying there are a lot of universes but... ugh.

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[QUOTE=parallaxicality;2481738] I've tried to decpher this paper, but it's above my level.

Mine too, but It’s a fun way to learn. I’m reading “Faster than the speed of light” where Joao Magueijo describes that’s also what he tried to do when aged just 11 with Einstein’s papers, with the same result.

Originally Posted by parallaxicality
Is this a multiverse, or just a large single universe with many inaccessable regions?
Our best model for our universe is a Big Bang followed by a period of inflation.
Andrew Linde favours a model of the multiverse where a black hole produces the right conditions to replicate this. In other words, when a black hole forms in our universe, that “buds” off another universe with its own Big Bang and inflation.

Of course, there’s nothing that says our universe was “the first”, so you have eternal chains of universes budding forwards and back. He described it in this article if you can track it down :
https://www.scientificamerican.com/a...nflationary-u/

Originally Posted by parallaxicality
Are these regions subect to the same laws of physics, or different? ... How could the same big bang produce universes with variant laws of physics?
Short answer: different. As I understand string theory (not much !), our laws of physics (such as the properties of the fundamental particles, relative strengths of the forces, etc) are determined by how the strings can wrap around, which in turn is determined by the geometry of how space can be curled up (which I think is the number of false vacuums in the string theory landscape - that big 10^500 number). Upshot is that when a new universe buds off from its parent, the way the space curls would be changed, and therefore each will have its own physics.

As an aside, Lee Smolin has taken this idea a step further and proposed a sort of “natural selection” of universes - that universes whose physics maximise black hole production will therefore bud more child universes than those that don’t, so we shouldn’t be surprised to find ourselves in a universe with black holes.

Originally Posted by parallaxicality
What are Freidmann geometries?
I followed Roger.E.Moore’s example and went to the conclusion - so right at the end he had “locally-Friedman (ie approximately homogenous and isotopic) universes”

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4. Originally Posted by parallaxicality
I've tried to decpher this paper, but it's above my level.

Is this a multiverse, or just a large single universe with many inaccessable regions?
The paper is about the minimum number of locally-Friedmann (i.e. approximately homogeneous and isotropic) universes required to create a multiverse, given as 10^10^10^7. The paper also calculated how a human observer could only distinguish between 10^10^16 different universes maximum at any one time.

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