Voyages of Discovery: Copernicus to the Big Bang   

  Telescope: Hunting the Edge of Space

  400 Years of the Telescope

    Early in this last century, astronomers believed that the
    Universe was eternal, infinite and unchanging. Edwin Hubble was
    interested in mysterious cloud-like objects known as nebulae. He
    turned the new Hooker telescope at Mt. Wilson on the fabled
    Andromeda nebula.


    Astronomer Sandy Faber points out: 

    "These giant telescopes, they are the only true time machines
    that human beings have and they are totally faithful. There's
    nothing hokey about this. You look through a giant telescope, you
    get a view of a very distant region of space, and it is as though
    you were a historian and could put your eye to a telescope and
    actually see Hannibal crossing the Alps and all those elephants
    trotting along. We are actually seeing the Universe and the
    things in it behaving as they did billions of years ago".

    "Andromeda was very important to Hubble because astronomers
    were wondering what all these little fuzzy blobs that we now
    call galaxies were. And there were lots of astronomers who
    thought that they were small little things that were just
    pieces of the Milky Way. But Hubble was able to discover stars
    in Andromeda that were -- that he could see were very much like
    stars in our own galaxy. And at this point everything clicked
    into place. He got the scale. He could see that it was far
    away. It was big. There was no way that it was a little piece
    of our own Milky Way".

    Hubble discovered that the Universe contains other galaxies --
    that it's far larger than we dared imagine. But he didn't stop
    there. He analyzed the light of distant galaxies, and found
    that it is skewed slightly to the red.

    This "redshift" is the result of the "Doppler Effect." It's
    like the sound of a train whistle that changes pitch as it
    speeds past. The redder the galaxy's light, the farther away it
    is, and the faster it is moving away from us. The Universe,
    Hubble found, is not static, but expanding rapidly in all

    "This discovery had a profound consequence. If the Universe is
    getting larger, we can make a movie, a cosmic movie, and we can
    run it backwards. It would look very comical. All the galaxies
    would be getting closer together and we can see that the
    expansion of the Universe implies that there was a first
    moment, a Big Bang".

    Even Albert Einstein's Relativity equations predicted that the
    Universe was not static an unchanging, but that it is dynamic
    and must either be expanding or contracting. Einstein found the
    idea of a changing universe so abhorrent that he tinkered with
    his equations.  

    To "fix" the problem of a finite universe he added the term, a 
    constant denoted with the Greek capital letter lambda, which
    balance the forces of gravity. Einstein's cosmological constant
    was a way of avoiding the consequences of an ever changing
    universe, a universe with a beginning and an ending. 

    When he learned of Hubble's discovery, something that
    Einstein's own equations could have predicted, he called the
    cosmological constant the greatest blunder of his career. So in
    1931, Einstein lent his prestige to Hubble's discovery. He
    conceded that his own model of the Universe was wrong. It was
    not a "repellent force" that kept the Universe from collapsing
    -- only its relentless expansion. 

  Where was the center of the Big Bang?



  The Hubble Space Telescope's prime mission, was to determine,
  once and for all, how fast the universe is expanding. Astronomers
  working with the Hubble telescope made lots of pretty pictures of
  exotica in space, but more important, they gathered reams and
  reams of data on Cepheid variable stars in an attempt to
  calculate the Hubble constant. After years of data the answer
  from Hubble is 72 km/s/Mpc!

  The Wilkinson Microwave Anisotropy Probe (WMAP) team made the
  first detailed full-sky map of the oldest light in the universe.
  The results from the first year of observing by the WMAP were
  announced in February of 2003, including the Hubble constant of
  H_o = 71 4 km/s/Mpc!

  How can the Universe be infinite if it was all concentrated into a 
  point at the Big Bang?

    The Universe was not concentrated into a point at the time of
    the Big Bang. But the observable Universe was concentrated into
    a point. The distinction between the whole Universe and the
    part of it that we can see is important. In the figure below,
    two views of the Universe are shown: on the left for 1 Gyr
    after the Big Bang, and on the right the current Universe 13
    Gyr after the Big Bang (assuming that the Hubble constant is
    H_o = 50 km/s/Mpc and the Universe has the critical density.)


    The size of the box in each view is 78 billion light years. The
    green circle on the the right is the part of the Universe that
    we can currently see. In the view on the left, this same part
    of the Universe is shown by the green circle, but now the green
    circle is a tiny fraction of the 78 billion light year box, and
    the box is an infinitesimal fraction of the whole Universe. If
    we go to smaller and smaller times since the Big Bang, the
    green circle shrinks to a point, but the 78 billion light year
    box is always full, and it is always an infinitesimal fraction
    of the infinite Universe.