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ASTRO110 The Big Bang - OPEN University
Course Description
In this unit, we present the three main lines of
experimental evidence pointing to the big bang origin of the Universe:
(i) the recession of the galaxies; (ii) the microwave remnant of the
early fireball; and (iii) the comparison between the calculated
primordial nuclear abundances and the present-day composition of matter
in the Universe.
A data sheet of useful information is provided
as a pdf for your use. You may wish to print out a copy to keep handy as
you progress through the unit.
Click 'View
document' to open the S357_1 data sheet.
View document
By the end of this unit you
should be able to:
- describe the
characteristics of light emitted by stars, and hence the
information of cosmological interest that can be deduced from it;
- distinguish between true and false statements relevant
to the
distribution and motion of stars within galaxies, and of galaxies within
clusters and superclusters;
- outline the methods
used for estimating the distances to stars and to
galaxies;
- explain and apply Hubble’s law;
- distinguish between various sources of redshift and
estimate their
relative importance in a given situation;
- describe
the cosmic microwave radiation in terms of its origin, its
thermal nature, and how its temperature has changed with time;
- explain how observations of thermal radiation are
affected by the
motion of the observer with respect to it;
- outline
the evidence concerning the isotropy of the Universe;
- describe the most important basic nuclear reactions
taking place in the
early stages of the big bang, and how the final mix of elements produced
provides evidence today for the big bang.
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Introduction
 Introduction
Resource- In this unit, we present the three
main lines of experimental evidence pointing to the big bang origin of
the Universe: (i) the recession of the galaxies; (ii) the microwave
remnant of the early fireball;...
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1 Introducing cosmology
- 1 Introducing cosmology Resource
- General relativity has a very
different conceptual basis from that of Newtonian mechanics. Its success
in accounting for the precession of Mercury's orbit, and the bending of
light by massive objects like...
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2 Radiation from the galaxies
- 2 Radiation from the galaxies Resource
- Stars occur in great collections
called galaxies. The distribution and motion of galaxies provide us with
the first important experimental information on which we shall build
our understanding of the type...
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3 Distances of galaxies
- 3.1 First steps towards a distance
scale Resource
- As you will see from Table 2, when
it comes to astronomy and cosmology, one is called on to deal with a
wide range of distances. (Note that a light-year (ly) is the distance
light travels in one year,...
- 3.2 Some general properties of
galaxies Resource
- Firstly, we note that galaxies
tend to occur in clusters rather than singly. The mutual gravitational
attraction of galaxies naturally tends to hold them on paths that remain
close to each other. Typically...
- 3.3 Extending the distance scale Resource
- Having reviewed some of the
properties of galaxies, we are now in a position to return to the
question of how we are to develop further our methods of measuring
distance.
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4 The variation of redshift with distance
- 4.1 Hubble's discoveries Resource
- In this section, we bring together
two important features of galaxies – their redshifts and their
distances.
- 4.2 Evidence for a big bang Resource
- Having interpreted the redshift as
indicating a recessional speed proportional to distance, one may
extrapolate into the future to predict how the positions of the galaxies
will evolve with time. One can...
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5 The microwave background radiation
- 5.1 A second major discovery Resource
- In the introduction to this unit,
we said that there were three pillars of evidence for the big bang. We
now turn to the second. It rests on a discovery that ranks in importance
with that of Hubble's law....
- 5.2 The origin of the 3 K radiation Resource
- In speaking of the radiation as
having a cosmic origin, what do we have in mind? Essentially this:
- 5.3 The redshift of the 3 K
radiation Resource
- The temperature, T, of the
radiation is proportional to the most probable photon energy, E, which
as we have said is proportional to f, and hence inversely proportional
to the wavelength λ. Thus,
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6 The angular distribution of the 3 K
radiation
- 6.1 Basic isotropy Resource
- As we have said, the photons in
the 3 K background have been practically free from interaction with
anything since about 4 × 105 years after the instant of the big bang.
The present angular distribution...
- 6.2 The effect of the motion of the
Earth Resource
- The speed of the Earth in its
orbit round the Sun is 29.8 km s−1, in a heliocentric frame. But to
specify the velocity vector, it is not sufficient to specify the Sun as
the origin of the coordinate system;...
- 6.3 Anisotropies in the Universe
itself Resource
- Having subtracted the dipolar
anisotropy due to the motion of the Earth relative to the 3 K radiation,
we are left with radiation that is exceedingly isotropic. So, we have
to ask whether there are any...
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7 The primordial nuclear abundances
- 7.1 Introduction Resource
- So far we have presented two
pieces of evidence pointing to the occurrence of a big bang: the
redshift of the galaxies (indicating the continuing expansion of the
Universe), and the 3 K radiation (the...
- 7.2 The temperature of matter and
radiation Resource
- The different reactions by which
neutrons and protons came together soon after the instant of the big
bang to produce heavier nuclei will have proceeded at different rates
according to the energies of...
- 7.3 The formation of light nuclei Resource
- It is the very high temperatures
that make the early stages of the big bang relatively simple to
calculate. When it comes to the formation of the first nuclei, we are
looking at a temperature that has...
- 7.4 Nuclear abundances as evidence
for the big bang Resource
- What we have seen is that a
theoretical model based on the assumption that there was a big bang, and
incorporating an assumption about the present-day value of the baryonic
density, ρb,now, leads to definite...
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8 Conclusion
- 8 Conclusion
Resource
- We have seen that there are three
independent pieces of evidence, all of which point to the occurrence of a
big bang: (i) the recession of the galaxies; (ii) the cosmic microwave
background; and (iii)...
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Summary
- Summary
Resource
- 1 The visible matter in the
Universe, stars and interstellar gas, is concentrated into galaxies,
which are collections of ∼1011 stars. The galaxies themselves are
usually to be found in clusters with typically...
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References and Acknowledgements
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Copyright 2007,
by the Contributing Authors.
Cite/attribute Resource.
administrator. (2010, January 30). ASTRO110 The Big Bang - OPEN University. Retrieved July 31, 2010, from Free University Courses OCW Courses OpenCourseWare Freeversity Foundation Web site: http://www.freeversity.org/science-and-mathematics/astronomy/astro110-the-big-bang-open-university.
This work is licensed under a
Creative Commons License
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