A while back I wrote about how general relativity predicts gravitational waves. While we haven’t yet observed gravity waves directly, we know they exist. That’s because gravitational waves carry energy away from their source, just as light waves carry light energy.
Small Changes
One aspect of general relativity that always amazes me is the level of precision needed to distinguish it from Newtonian gravity. Take, for example, the advance of Mercury’s perihelion. When you count in the gravitational tugs from the sun and all the planets, Newton predicts Mercury’s perihelion will advance about 531.65 arcseconds per century. When we measure the orbit of …
The Planet That Never Was
While there were speculations about a planet closer than Mercury going back to at least the 1600s, it wasn’t until the 1850s that Urbain Le Verrier discovered the first indirect evidence for such a planet. Le Verrier carefully calculated the orbit of Mercury, and determined that the orientation of its orbit rotated slowly over time. This is known as a perihelion advance, and it is due to the small gravitational pulls from other planets.
Einstein and Eddington
Newton’s laws of motion and gravity predicted the motions of the planets almost perfectly. Newton’s laws are so accurate that we use them to accurately send robotic probes to Mars and other planets, but Newton’s laws aren’t perfect. The motion of some planets differ very slightly from Newton’s predictions. In the case of Uranus, its small deviation led to the discovery of Neptune. In the case of Mercury, however, its small deviation led to a completely new understanding of gravity.
Time After Time
Part 3 in the equations series. How a beam of light overturned 300 years of physics, and changed our view of the universe.
A Muse of Fire
Part 1 in the equations series: It’s Einstein’s most famous equation. It changed the political landscape of the world, and it gave us a true understanding of the stars.
Black Holes
The basic idea of a black hole is simple. Imagine tossing a ball into the air. It goes up to a certain height, and then back down. If you toss the ball faster, the ball rises higher, but it still eventually falls. Now suppose you could toss the ball as fast as you like. Could you toss the ball so fast it doesn’t fall back down?
Superluminal
There are examples of a mass of plasma (a jet) leaving a quasar at a speed that appears to be faster than light. But this turns out to be an interesting optical illusion.
The Color of Speed
In our everyday lives, we’re familiar with the Doppler effect as it applies to sound. You might notice when a car or train passes you, its sound shifts downward as it passes. This is because the sound waves from an object are bunched together as it moves toward you, and stretched apart as it moves away from you. For light a similar thing occurs.