## Happy 95th Anniversary, Relativity 120

StartsWithABang (3485481) writes

*"It's hard to believe, but there are people alive today who remember a world where Newtonian gravity was the accepted theory of gravitation governing our Universe. 95 years ago today, the 1919 solar eclipse provided the data that would provide the test of the three key options for how light would respond to the presence of a gravitational field: would it not bend at all? Would it bend according to Newton's predictions if you took the "mass" of a photon to be E/c^2? Or would it bend according to the predictions of Einstein's wacky new idea? Celebrate the 95th anniversary of relativity's confirmation by reliving the story."*
## 95 years but (Score:4, Interesting)

its less than that time if it was travelling at significant speed

## Re:Simultaneity is in the eye of the beholder. (Score:5, Interesting)

The truth is, relativity doesn't have to be as confusing as it's usually made out to be. The most accessible explanation I've found for time dilation came from Brian Greene's [wikipedia.org]:

The Elegant UniverseSuppose you have a race car that can only go 100 m/s, no faster, no slower. Suppose it's racing down a very wide track that's 1km in length . Depending on the angle at which the car travels, it may cross the finish line in 10 seconds, 20, 50 or however long, just no less than 10 seconds. So similarly, we can think of our journey through the universe as happening along a "time" direction as well as three "space" directions: the faster we travel through space, necessarily the slower we travel through time, but no matter what, we're travelling at c.

The math even works out, in terms of c=sqrt(v_x^2+v_t^2) where "v_t" (your velocity through time) is c*dtau/dt.

This analogy obviously only gets you so far, and the real "wow" of relativity comes from the concepts of simultaneity (I wish more SF authors realized that FTL and time travel are the same friggin' thing), but especially for non-majors this is a great way to get one's foot in the door and begin to understand what is a pretty alien concept.