A brief history of the Universe

• About 15 billion years ago, the Universe came into existence - don't know how or why.
• Amazingly, we know something about its state in its youth. It was very different: hot and dense and made of light
• In the first few minutes, the pure energy was transformed into the basic particles we see today: protons, neutrons, and electrons
• As time passed, the Universe expanded rapidly and cooled off
• After about a million years, the matter in the universe which was smoothly distributed collapsed into blobs under the force of gravity. In the centers of these blobs, stars were formed.
• The stars and gas around them separated into distinct groups in space which we now call galaxies
• Each star in each galaxy acted as a nuclear reactor, converting simple elements into more complex ones and producing light in the process
• Some of the stars exploded, sending the more complex elements back into the gas, from which new stars were formed. Around some of these stars, some of the complex elements condensed into rocky balls which we call planets.
• About 5 billion years ago, a star was formed in the outer region of one of the galaxies. Around this star, a system of nine planets formed. The size and temperature of the 3rd planet from the star was such that liquid water existed on its surface.
• On this planet, the combination of elements along which the light from the star allowed chemical reactions to take place which allowed the formation of simple life.
• Over 5 billion years, the life forms changed and evolved. Very recently, only a few million years ago, humans appeared on the planet They lived simply for millions of years. They probably looked at the stars and wondered about them, not dreaming that they in fact were made of stardust themselves.
• Astronomy has also been used practically by humans. Very recently (on the astronomical time scale), humans developed agriculture and depended on their observations of the sky to help them determine when to plant crops
• It's a particularly interesting time for astronomy because of recent technological developments. This technology allows us to see much more of the Universe than we can by eye, and our view of the Universe has changed dramatically.
  • Where Earth was thought to be large and immutable, changing gradually, if at all, we now have seen Earth from space and realized how small and fragile it is in the overall scheme of things. We know that the very continents move around and collide with each other. It's possible that the history of Earth is dramatically influenced by the impact of comets on its surface.
  • Where people once saw the Sun an unchanging, we now know it is quite dynamic
  • Where people once saw planets as bright points of light, we now see them as worlds of their own, with rapidly changing atmospheres and systems of moons and rings around them. Some of these worlds have active geology and perhaps even harbor some form of life.
  • Where people once saw unchanging stars and planets, we now see material between stars, newly forming stars, and exploding stars
  • People now see galaxies and can measure their motion through space and understand that the Universe itself is expanding
  • New technologies of big telescopes and telescopes in space allow us to look far back into time and see what the Universe looked like long ago.
  • We realize that there are astrophysical phenomena operating on all time scales, from the slow evolution of stars and galaxies on timescales of billions of years, to supernove and gamma ray bursts on the timescales of days and seconds.

  • There are lots of recent astronomical developments
    • 2003 Science news of the year: the contents of the Universe (WMAP map of the microwave sky , Sloan Digital Sky Survery , contents of the universe)
    • 2004: A rover on Mars! (Mars globe , Spirit landing site , the scenery!)

  • The development of a fundamental understanding of the universe is still in progress. Just in the past few years, astronomers have revised their ideas about the overall shape, age, and contents of the Universe. In the current picture, large fractions of the Universe are thought to be in some still-unknown forms of ``dark matter'' and ``dark energy''.

• Although we think we know a lot, there's a good chance we don't. Mankind has been around for only a tiny fraction of the time the Universe has been around, and the technological age has been only a tiny fraction of that. If the history of the universe were placed into the framework of a week, mankind would have appeared about a minute before midnight on the last day of the week, and the technological age just a fraction of a second before midnight.