What would the universe be like with less mass and energy?

Main Question or Discussion Point

So I have sort of a conceptual question about the big bang and gravity.

Imagine yourself in a universe, in which existed about the number of particles/energy in a 3X3 metre room at any given moment. This universe has the same laws of physics, constants and is identical in every way to our universe except that the amount of energy-mass is astronomically smaller.
Also in this imagined universe, the current time is a tiny fraction of seconds after the big bang, such that the universe has expanded to have the same pressure and mass -and by extension, volume- as that 3X3 metre room.
Now imagine that I suddenly appeared with a spacesuit on in that universe.
I've heard before that the universe is curved in some way. I'm not sure if it's 4-dimensionally curved and I'm not sure how it works, but the analogy of the universe as an expanding bubble is what I'm picturing here.
What would it feel and look like to live in that universe, would we be able to survive in it or would we be crushed/warped by the spherical shape of space or even ripped apart by the expansion of the mini-universe and are these questions that can't be answered using known laws of physics or do we not know enough about what's past the observable universe to say?

I've studied up to first year undergraduate physics but I do know a little bit about gravity and relativity however I'm not that great at math. If anyone could help me get a better grasp of the ideas needed to visualize this problem in their answer that would be great! I'm really just curious and want to try to understand how the universe works.

I appreciate any insight you can give!
Thanks.

phinds
Gold Member
2019 Award
... the analogy of the universe as an expanding bubble is what I'm picturing here.
then you are not imagining anything that resembles the universe we live in.

I'm really just curious and want to try to understand how the universe works.
I assume you believe that when you say it, but it doesn't really sound like it. You are asking about a universe that is nothing like ours so how does that help you understand the universe we live in?

Nugatory
Mentor
are these questions that can't be answered using known laws of physics or do we not know enough about what's past the observable universe to say?
These questions cannot be answered using the known laws of physics because those laws apply to the universe we live in, and you're talking about a completely different universe.

This thread is closed because there's no way of continuing the discussion within the Physics Forums rules.