Wednesday, March 03, 2010

Right the first time, Einstein

Following up from Wednesday's post, I wanted to take you all back to 1919 when Einstein's theory of relativity was demonstrated through experiment for the first time. It's an interesting story, and a more detailed account is given here.

The theory of relativity basically states that everything is relative to the observer. Even time. There is no absolute frame of reference where we can find out what time it is according to the universe. While time is a very important part of the universe, it can change for different folks moving at different speeds or living different distances from black holes.

Relativity also posited that gravity can bend light. So can a glass of water
(see the photo from PercepZone), but this was still a pretty freaky idea.

The only thing near enough to Earth with enough mass to bend a beam of light with its gravity would be the sun. But, the blinding light of the sun makes it nearly impossible to see the light of a star go anywhere near it. What to do?

Astrophysicist Sir Arthur Eddington had the great idea to try to look for the light-bending effects of gravity during an eclipse. If the sun passes between our telescopes and the light of a star, the gravity of the sun's mass will bend the light. If we can block the light coming from the sun, we can see these bending effects.

A six minute long eclipse took place in 1919, although total coverage was only visible in the southern hemisphere, so expeditions were sent to Africa and South America to watch it. The results confirmed Einstein's prediction.

Today we still use this concept to measure distances to far away objects. SLAC National Accelerator Laboratory just put out this awesome video to illustrate the concept. Scientists from SLAC also just published a nice paper showing that the method (called gravitational lensing) is just as precise as other methods of determining astronomical distances. Enjoy!

video

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