For centuries after Isaac Newton studied gravity, scientists accepted that gravity only exists between two objects that each have mass. However, new observations in the early twentieth century showed that even though light has no mass, it bends toward a planet as though it is forced by gravity. Albert Einstein used this observation, along with mathematical reasoning and many other observations, to redefine gravity and explain why both light and matter experience gravity’s effects. Einstein’s idea predicted many complex behaviors of nature that were later discovered, and because his idea consistently explains so many different observations it is now the basis for much of modern physics.

Which best describes Einstein’s new explanation of light and gravity?
a) Einstein created a new law, because his explanation of the interaction between light and gravity provided unity amongst many facts.
b) Einstein created a new law, because he discussed only light, mass, and gravity and made an easily observable, factual statement about them.
c) Einstein created a new theory, because his explanation of the interaction between light and gravity provided unity amongst many facts.
d) Einstein created a new theory, because he discussed only light, mass, and gravity and made an easily observable, factual statement about them.