One of the most exciting things about dark energy is that it seems to live at the very nexus of two of our most successful theories of physics: quantum mechanics, which explains the physics of the small, and Einstein's Theory of General Relativity, which explains the physics of the large, including gravity.
In the context of general relativity, space almost is a substance. It can bend and twist and stretch, and probably the best way to think about space is to just kind of imagine a big piece of rubber that you can pull and twist and bend.
The star S0-2 orbits around Sgr A* every 16 years and will go through its closest approach in 2018. That's an opportunity to test Einstein's General Relativity theory through very precise measurements of this star's short period orbit.
I always found it satisfying that gravity was described by Einstein's geometric theory of general relativity.
Einstein had two new predictions from general relativity. One was that light would bend. That was tested in 1919, and basically, he was proven right. The second prediction was gravitational waves, which took us 100 years to prove. The theory itself, which is thought by most to be rather obscure, you use every day, probably.
In Einstein's general relativity the structure of space can change but not its topology. Topology is the property of something that doesn't change when you bend it or stretch it as long as you don't break anything.
The media thinks that only the cutting edge of science, the very latest controversies, are worth reporting on. How often do you see headlines like 'General Relativity still governing planetary orbits' or 'Phlogiston theory remains false'? By the time anything is solid science, it is no longer a breaking headline.
What you can show using physics, forces this universe to continue to exist. As long as you're using general relativity and quantum mechanics you are forced to conclude that God exists.
Gravitational waves will bring us exquisitely accurate maps of black holes - maps of their space-time. Those maps will make it crystal clear whether or not what we're dealing with are black holes as described by general relativity.
We have to have a combination of general relativity that describes the warping of space and time, and quantum physics, which describes the uncertainties in that warping and how they change.