This may not count as practical, but with high-enough resolution on time we can start to make direct observations of relativistic effects. There are physicists

This may not count as practical, but with high-enough resolution on time we can start to make direct observations of relativistic effects. There are physicists like Ivette Fuentes starting to do direct experiments with time dilation [1]. When Einstein made his thought experiments with light clocks and described what should be observed, he didn't think we'd actually make light clocks... but we have the technology to do that literally (really, truly, actually... so sad we no longer have a word in English that means that). [1] https://www.youtube.com/watch?v=y5V9qAETcw8 https://www.youtube.com/watch?v=y5V9qAETcw8