Our Strange Universe

Abstract

Astronomical observations of the past century have shown that we live in an expanding universe that originated a long but finite time ago in an incredibly dense and hot initial state called the Big Bang. Apart from matter, also space is an essential ingredient of our universe, and the observed expansion of the universe implies that the amount of space increases in the course of time. In the past there was less space and in the future there will be more. This appears strange and opposite to our daily experience, from which we know space to be a fixed quantity, such as the volume of our room. Physics tells us, however, that space—even if it is pure vacuum (completely empty space that contains no atoms or molecules)—is an essential ingredient of the universe, that contains hidden particles and energy, and can expand or contract. A strange discovery made in 1998, thanks to the measurements of the brightness of very distant exploding stars, is that the empty space of the universe contains the bulk (about 70 %) of all energy of the universe. This energy manifests itself by a mysterious force, still not understood, that causes the expansion of the universe to accelerate. The remaining about 30 % of the energy of the universe (according to Einstein, mass and energy are equivalent) manifests itself as the mass of “real” matter, which exerts gravitational attraction. Of this real matter, only about one sixth is ordinary matter, consisting of atoms and molecules, and five sixth is mysterious Dark Matter, which does exert gravitational attraction, but whose nature is still completely unknown.

The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them.

Sir William Bragg, British physicist (Nobel laureate)