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## Summary:

- Is a perfect vacuum able to expand in the way that we see the cosmos expanding even without any matter content? When viewing the expansion of space according to GR, it seems that the expansion is coming from a growth of space, rather than a physical acceleration of matter away from a local spot.

## Main Question or Discussion Point

The intention of this question is to get to the heart of the geometrical properties of space-time according to GR, and to focus entirely on what the theory allows, and not so much on what we actually see. I would like to consider a perfect vacuum, in a euclidian infinite void, completely devoid of matter and photons. I understand that there are quantum consideration when considering a perfect vacuum, but I am more interested in the pure mechanics of GR, and would like to avoid vacuum energy and only consider the lambda cosmological constant when further explaining the possible behaviors of space-time. Of course, I am prepared to be shown that GR must have some basic matter constituent to function, and I am also prepared to be told that a Euclidian space cannot exist for various reasons, but this is the thrust of my question. So a couple of thoughts. Can this empty void exist in theory, and if so, can I mathematically expand this space so that the metrics all begin to move away from one another at some fixed velocity and would this require energy? What would this question look like with a single electron in the infinite void, of perhaps two at inter galactic distances? Perhaps the entire void is simply an extremely rare and diffuse homogenous gas of hydrogen molecules far more diffuse than ever would be observed (just to add matter to stabilize things). I understand these molecules have their own sub speed of light random velocities and therefore, an extremely low temperature. You can replace the gas with a low level photon temperate of .0001 degrees if that helps the question. So I’m really just curious about he dynamics of this medium and if it’s expanded, is the momentum of expansion happening to the individual particles, or can this expansion be purely geometric? I apologize for the loosens of the question and if it’s irrational.