[littlestymaar]

> Arguably, the photoelectric effect fits that notion better than GR or any other of Einstein's research

Today we could argue about it due to the importance of solar panels, but that was hard to forecast in 1921. Also, without GR there would be no GPS so it's not like it doesn't bring benefits to humanity.

[mr_mitm]

Einstein laid the foundation of quantum mechanics with his description of the photoelectric effect, so you could add transistors, lasers, LEDs, CCD sensors and more to the list. Although I agree that it's doubtful that most of this could have been foreseen then.

[zellyn]

Surely they would have just noticed a discrepancy in timing and added a few circles-upon-circles to effectively fix it up? Is deeply grokking relativity necessary for GPS to work?

On the other hand, it would be impossible to make those adjustments without someone coming up with GR :-)

[topaz0]

More to the point, photoemission spectroscopy has been a workhorse tool for understanding the electronic properties of materials for quite a long time now (though perhaps not yet in 1921).