Relativity in space
The theory of relativity holds a certain fascination for many people. At the same time it is often regarded as very abstract and difficult to understand.
Part of the difficulties in understanding relativity are due to the fact that relativistic effects contradict everyday experience. Motion, for example, is a familiar process and everybody "knows from experience" that it entails neither time dilation nor length contraction. A flight with half the speed of light could correct this misjudgement but is not on offer.
Space is commonly thought of as being absolute emptiness or nothingness. However, if space were sheer nothingness, it would not exist, and nothing could be located in it or move through it. Logically, space must have some kind of structure and therefore consist of substance, and unless this substance is assigned impossible, abstract properties (such as absolute continuity and homogeneity), space must consist of infinite interpenetrating grades of energy-substance. What to us is "empty space" is simply those regions of space containing no matter perceptible to our physical senses.
The Theory of Relativity
The Theory of Relativity, proposed by Albert Einstein in the early part of the 20th century, is one of the most significant scientific advances of our time. Although the concept of relativity was not introduced by Einstein, his major contribution was the recognition that the speed of light in a vacuum is constant and an absolute physical boundary for motion. This does not have a major impact on a person's day-to-day life since we travel at speeds much slower than light speed. For objects travelling near light speed, however, the theory of relativity states that objects will move slower and shorten in length from the point of view of an observer on Earth. Einstein also derived the famous equation, E = mc2, which reveals the equivalence of mass and energy.
When Einstein applied his theory to gravitational fields, he derived the "curved space-time continuum" which depicts the dimensions of space and time as a two-dimensional surface where massive objects create valleys and dips in the surface. This aspect of relativity explained the phenomena of light bending around the sun, predicted black holes as well as the Cosmic Microwave Background Radiation (CMB) -- a discovery rendering fundamental anomalies in the classic Steady-State hypothesis. For his work on relativity, the photoelectric effect and blackbody radiation, Einstein received the Nobel Prize in 1921.
Einstein's theories of both special and general relativity have been confirmed to be accurate to a very high degree over recent years, and the data has been shown to corroborate many key predictions; the most famous being the solar eclipse of 1919 bearing testimony that the light of stars is indeed deflected by the sun as the light passes near the sun on its way to earth. The total solar eclipse allowed astronomers to -- for the first time -- analyse starlight near the edge of the sun, which had been previously inaccessible to observers due to the intense brightness of the sun. It also predicted the rate at which two neutron stars orbiting one another will move toward each other. When this phenomenon was first documented, general relativity proved itself accurate to better than a trillionth of a percent precision, thus making it one of the best confirmed principles in all of physics.