Sorry, there’s no Physics API exposed and the underlying Matter.js is fully encapsulated as well as minified so there’s no way to access its structures (at least, without dramatic hacking and knowing how items are minified, meaning more WTF moments 
).
We’re generally conservative when it comes to adding API as we know we’ll need to support it forever. In the case of Physics, I’m in no way against adding API, but would want a good sense of what users are making with Hype and use cases for the API.
A good argument could be made that we should expose Matter.js, though at this time I’m still favoring flexibility for our Physics engine; you can think of our usage as an “implementation detail.”