Maybe there are more forces than we are aware of (I'm not intending anything spiritual there, in case you wondered, although that's a thought.....
). The leaking thing sounds like conjecture. Why does it matter if gravity is so weak or rather why is that a mystery? Is gravity the same strength in the whole universe?
Also, how can the universe be expanding into nothing? Surely it's expanding into a space? My dad told me something recently about Einstein saying space has physical properties. I think it was 'space', can't remember now.

Also, how can the universe be expanding into nothing? Surely it's expanding into a space? My dad told me something recently about Einstein saying space has physical properties. I think it was 'space', can't remember now.

"The eternal mystery of the world is its comprehensibility"
Albert Einstein
Albert Einstein