SPACE

Document Sample
SPACE Powered By Docstoc
					SPACE
Introduction
        THE FIRST MOMENT
   At the birth of the universe all matter was
    compresses into a ‘fiery” mass of
    unimaginable density. The earliest
    moment that can be spoken of with
    certainty came after a period called the
    Planck time – the incredibly brief interval
    of 10-43 seconds.
        THE FIRST MOMENT
   The entire universe that is observable today –
    which may be only part of some unknown
    whole – occupied a space 10-20 times smaller
    than an atomic nucleus. And it is believed that
    an even earlier moment the four basic forces –
    gravitation, the strong and weak nuclear forces
    and electromagnetism – were unified into a
    single force. (We still do not know how this
    worked!!)
        THE FIRST MOMENT
   Present theories can be tentatively applied after
    the Planck time. But detailed information about
    the state of the universe at this time was
    irrevocably altered by the next major event in
    the history of the universe. When it was 10-35
    seconds old the era of inflation began: a period
    of fantastically rapid increase in size, during
    which the universe swelled up to at least 1050
    times its previous size.
        THE FIRST MOMENT
   Although the characteristics of inflation are
    incredible, theorists believe this idea – devised
    originally by Alan Guth in the US – must be
    correct, since it explains a number of puzzling
    features of today’s universe.
           THE FIRST MOMENT
   First it accounts for the fact that the closely packed
    infant universe expanded neither so slowly that
    gravitation could crush it back into nothingness, nor
    so fast that it could thin out before the galaxies and
    stars could form. Relativity tells us that space is in
    general curved, and that the amount of curvature
    depends on the amount of mass present in unit
    volume – the density. Too great a density and the
    universe would close round itself and collapse; too
    low a density and space would open out
    uncontrollably.
        THE FIRST MOMENT
   Mathematical analysis shows that to account for
    this fine balance the density of the universe must
    have had a particular, or critical, value, and no
    other, at a very early time. Indeed, at 10-33
    seconds after the Big Bang, it could not have
    differed from the critical value by more than one
    part in 10-49. Such a precise agreement is
    predicted by the theory of inflation, and no
    other way of explaining it is known.
        THE FIRST MOMENT
   Inflation also solves the “horizon” problem. In
    our present universe we see galaxies moving
    away from each other into the depths of space.
    There is a horizon beyond which we cannot see,
    since galaxies at that distance are receding at the
    speed of light. The horizon is different for each
    galaxy.
        THE FIRST MOMENT
   Consider two galaxies, close to our horizon
    but lying in opposite directions from us:
    they will both be able to see us, lying at
    their respective horizons, but not each other.
        THE FIRST MOMENT
   The problem that arises is this: such galaxies,
    which cannot receive signals from each other,
    are very similar in what they contain, and in the
    density and distribution of their matter. The
    cosmic background radiation, too, is exactly the
    same temperature, from whichever part of the
    sky it comes (later!!). Why would the universe
    be so homogenous when each part of it sees
    only a small part of the whole?
        THE FIRST MOMENT
   Certainly, as we go back ever closer to the Big
    Bang itself, these widely separated parts of the
    universe were closer together than they are now.
    But the time that had elapsed from the
    beginning was shorter too. There still had not
    been time for radiation to travel between them,
    evening out any possible differences. On the
    basis of the galaxies’ present motions, there
    would never have been any contact between
    these regions.
        THE FIRST MOMENT
   But the theory of inflation solves the problem.
    Before inflation occurred the presently
    observable universe filled a tiny volume, far
    smaller than the horizon distance of that time.
    All parts of it reached temperature equilibrium,
    with any differences evened out. We see this
    equilibrium today, long after the most widely
    separated parts of the universe have ceased to
    influence each other.
        THE FIRST MOMENT
   The universe we now see is indeed very
    “smooth” on the large scale. Inflation shows
    how any initial irregularity in the density of
    matter and energy would be ironed out to a
    vanishingly low level. The problem now is to
    explain how sufficient irregularity survived
    inflation to make it possible for matter to clump
    into galaxies and stars.
        THE FIRST MOMENT
   Lastly, physicists have discovered that
    presently the universe contains between
    100 million and a billion photons for each
    atom in the universe. Why it should be
    this number rather than any other is
    explained in the idea of inflation.
        THE FIRST MOMENT
   Inflation started when the strong force was
    beginning to separate from the electroweak
    force, but before their separation was complete.
    By the time this happened the temperature of
    the universe had dropped to a ten-thousandth of
    what it had been at the end of Planck time,
    although it was still at the enormous value of
    1028K. Inflation was triggered by extreme
    supercooling of the infant universe.
           THE FIRST MOMENT
   Supercooling occurs when a system falls below a
    temperature at which it normally changes state, yet
    fails to undergo that change. At 10-35 seconds the
    universe was on the brink of a change in state marked
    by the separation of the strong and electroweak
    forces. But it continued to cool until it was about 10-
    32 seconds old before this transition occurred. While

    it was in this supercooled condition, a false vacuum
    formed, the properties of which were very different
    from those of a true vacuum.
        THE FIRST MOMENT
   Usually the density of energy in any system –
    whether in the form of radiation or matter –
    decreases when the volume of the system
    increases and its particles become less densely
    packed. But the false volume state is one in
    which the energy density stays constant during
    expansion. Relativity theory shows that the
    existence of the false vacuum, with its constant
    energy density, would have caused a vast force
    of repulsion. Inflation occurred.
        THE FIRST MOMENT
   While the inflation period lasted the
    universe doubled in size every 10-35
    seconds. It doubled hundreds of times,
    with the result that its volume grew at least
    1050 times. The temperature plummeted
    from 1028 to 1023K.
          THE FIRST MOMENT
   Inflation ceased when the change of state had
    occurred and the strong force and electroweak
    forces had separated. The energy density of the
    false vacuum was released, rather as the latent heat
    stored in in steam is released when it changes state
    to become water. This burst of energy created a
    vast number of atomic particles, which reheated the
    universe to the temperature it had been when
    inflation began.
       THE FIRST MOMENT
 Inthis chaos of radiation and exotic
 particles began the building of matter
 as we know it today.
        THE FIRST MOMENT
   Matter, energy, space and time were created
    in an inferno of particles and forces
    unknown in the modern universe. Within a
    billionth of a second the initial force
    affecting all matter had frozen out into the
    forces known today. It took three minutes
    for the kaleidoscope of ephemeral particles
    to give way to stable atomic nuclei.
    Millennia were to pass before complete
    atoms were formed.
        THE FIRST MOMENT
   The colossal inflation of the universe was
    powered by the splitting of the GUT (grand
    unified theory) force into the strong and
    electroweak forces. The universe visible today is
    highly uniform because it lies in a “bubble” that
    was once within the horizon distance,
    throughout which physical conditions could be
    equalized.

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:6
posted:8/14/2012
language:English
pages:22