Bob and I have been enjoying the Oct. 17, 2015 issue of Science News magazine, which contains an article about how well Einstein’s Theory of General Relativity seems to be holding up. Very well, indeed, as it turns out.
Much of the Theory is way beyond me, especially the math, but there are some concepts that I can understand The one I’m thinking about right now is that gravity is actually not a force that pulls on things (instantaneous action-at-a-distance) which is how Sir Isaac Newton conceived of it. In reality, Einstein discovered, gravity is the curvature of space: a massive body will have a gravitational field that is actually space curving around the massive body and forcing objects to fall to the ground. Additionally, this gravity causes time to flow more slowly in the presence of a massive body.
A lot of Relativity phenomena are not noticeable in “normal living”—they tend to show up in more extreme cases, such as bodies being accelerated close to the speed of light, light bending during solar eclipses, and so on.
However! There is one phenomenon that we are all noticeably affected by. Science News reports: “A GPS receiver records the precise time that signals arrive from multiple satellites; those arrival times can be used to calculated how far away the satellites are. The receiver can then compute its own position based on the distances to the satellites…this approach requires clocks on the ground to be synchronized with clocks on the satellites. But because of gravitational time dilation, clocks on the ground run slower than those on the satellites. After just a day, your GPS would misplace your location by about 10 kilometers (six or seven miles) if the calculations weren’t corrected for relativity’s effects.”