- #1

Jaime Rudas

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- TL;DR Summary
- Is it problematic to assume that the universe is spatially infinite?

Section 5 (pg. 29) of the Michel Janssen's paper

1. From the above I understand that the application of general relativity to an infinite universe was considered problematic.

2. On the other hand, I understand that it is currently not considered problematic to obtain solutions of general relativity for a spatially infinite universe.

Are assertions 1 and 2 correct?

If they are, why was it problematic before and now it isn't? In other words, in what sense did the formulation change?

If the assertions aren't correct, is it currently problematic to assume that the universe is spatially infinite?

(*) http://philsci-archive.pitt.edu/4377/1/LoveMinusZero.pdf

*EINSTEIN’S QUEST FOR GENERAL RELATIVITY, 1907–1920*(*) says:General relativity retains vestiges of absolute motion through the boundary conditions at infinity needed to determine the metric field for a given matter distribution.

[...]

As he [Einstein] told De Sitter in February 1917: “I have completely abandoned my views, rightfully contested by you, on the degeneration of the ##g_{\mu \nu}##. I am curious to hear what you will have to say about the somewhat crazy idea I am considering now.” This “crazy idea” was actually quite ingenious: If boundary conditions at spatial infinity are the problem, why not eliminate spatial infinity? Einstein thus explored the possibility that the universe is spatially closed.

1. From the above I understand that the application of general relativity to an infinite universe was considered problematic.

2. On the other hand, I understand that it is currently not considered problematic to obtain solutions of general relativity for a spatially infinite universe.

Are assertions 1 and 2 correct?

If they are, why was it problematic before and now it isn't? In other words, in what sense did the formulation change?

If the assertions aren't correct, is it currently problematic to assume that the universe is spatially infinite?

(*) http://philsci-archive.pitt.edu/4377/1/LoveMinusZero.pdf

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