That's a very common misconception, but the answer is actually no!

While Albert Einstein is most famous for his theories of relativity, he was awarded the 1921 Nobel Prize in Physics "for his services to Theoretical Physics, and **especially for his discovery of the law of the photoelectric effect**."

### So, why not for relativity?

At the time, relativity was still considered too controversial and theoretical by the Nobel committee. There were two main reasons:

1.  **Lack of Conclusive Proof:** While Arthur Eddington's 1919 expedition had provided strong evidence for General Relativity by observing starlight bending during a solar eclipse, the results were still new and debated by some in the scientific community. The committee preferred to award prizes for work that had been unequivocally proven through experimentation.
2.  **It Was Too Revolutionary:** General Relativity completely overturned a 200-year-old understanding of gravity established by Isaac Newton. It was such a radical departure from established physics that many conservative members of the committee were hesitant to fully endorse it.

### Why the Photoelectric Effect?

Einstein's 1905 paper on the photoelectric effect was groundbreaking in its own right. It proposed that light could behave not just as a wave, but also as a stream of tiny particles (or "quanta," which we now call photons). This idea was a foundational pillar of quantum mechanics and, by the early 1920s, it had been solidly confirmed by experiments.

**In short:** The Nobel committee awarded him the prize for the groundbreaking work they could definitively prove, not for the even more revolutionary work that was still considered too new and speculative. The vague mention of "his services to Theoretical Physics" is often seen as a subtle nod to his other monumental achievements, like relativity.
