[roywiggins]

Adding in a single extra particle is a lot simpler than rejiggering the entirety of our theories of gravitation. It's also a lot easier to test, just go out and find the particle. This worked for neutrinos, antimatter, the Higgs boson...

The Higgs boson took a long time to be discovered, but people thought it would be there because the alternative was the Standard Model being wrong. And so they looked, and there it was. Perfectly compatible with the Standard Model.