Theory of relativity passes most extreme test yet

Editor's note: This story was originally posted 26 April 2013, but it's now graduated and become part of Astronomy 101!  Please be aware that any references to events that seem current may not actually reflect events happening right now.

Good news, everyone!  Our best theory of gravity, Einstein's general relativity, works in even the most extreme corner of the Universe yet detected.  Work carried out by researchers from the Max Planck Institute for Radio Astronomy in Germany has shown that measurements of a freakish pair of objects still obey one of the fundamental laws of physics.  The pair, a white dwarf and an unusually large pulsar, are among the densest objects in the cosmos.  Add to that the fact that the pulsar rotates at nearly the speed of light (an astonishing 25 times per second) and you have one seriously extreme environment.

An artist's rendition of what the space around a pulsar-white dwarf binary might look like.  See how the mass of these objects distort the space around them.  (Image credit: ESA)

Let's rewind for a moment, though, and ask how we got here.  If we jump back a century and a half, we find physics in a very different state.  Newton's law of gravity, published nearly two hundred years earlier, is still our best description of the most dominant force in the Universe.  But over the next couple of decades, cracks in this theory begin to appear.  Three classes of exceptions emerge: things which are very small, things which are very large, and things which are traveling very quickly.  By the early 1900s, Einstein had worked out a new law of gravity that would change the world.  In it, he put forth four groundbreaking ideas:

  1. Space and time are linked.  Changes in one affect the other.
  2. Observers in different places see the world in different ways.  There is no "true" reference frame
  3. Despite this, the speed of light is constant for everyone and nothing can travel faster than this.
  4. Mass and energy are equivalent (E=mc^2)

Heavy objects, like stars or planets, bend space around them, giving us the illusion of gravity.  Travelling close to the speed of light causes you to experience time more slowly than those who appear to be travelling slower than you.  Perhaps the most convincing proof Einstein provided of his new theory was the orbit of Mercury.  Mercury appears from Earth to have an impossible orbit, but it's one that makes sense in the realm of relativity.  This happens because Mercury is so close to the Sun, a very heavy object.

Today, relativity impacts our lives every day.  Probably the most obvious instance is GPS - without adjusting for relativity, your GPS directions would fail within hours.  But the question remains, is relativity completely true?  Or, like Newton's gravity, does it fall apart under extreme conditions?  This latest discovery shows that, even in the presence of both huge mass and extreme speeds, the theory's predictions are spot on.  Future tests will probably involve stars travelling near to black holes - the heaviest objects in the Universe.  Until then, Einstein's great theory remains safe.

Oh, and the question of the gravity of tiny objects?  That's still the most important unsolved question in physics.  So get busy!

Source: AFP

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