Big Bang

The Big Bang Theory

At this moment in time the most popular theory for the creation of our universe as we know it is the ???Big Bang Theory??? which is estimated to have occurred 13.72(?±0.12) billion years ago1. There is much evidence to support this theory however it also posses some problems.

Evidence For the Big Bang

The first piece of evidence for the big bang I will be discussing is the observed red shift of the electromagnetic radiation of stars and galaxies. This effect was first noted by American physicist Edwin Hubble circa 1919 and in 1929 he published his findings2. His research had shown that the spectra of the light from distant light sources shift towards the red end of the electromagnetic spectrum3. The result of this is shown to the right. The two spectra compare the absorption lines of distant galaxies to the right with that of the Sun on the left. There is an obvious increase in the wavelengths expected from the distance source.

The reason for the increase in wavelength of the electromagnetic radiation from a distance is source is that the universe is expanding. This means that it appears that stars, galaxies and nebul? are moving away. The extent of the red shift of a source can be found by using the formula below:

[pic]

Where z is the red shift ratio, ?0 is the expected wavelength without considering the effect of red shift and where ? is the observed wavelength.

Hubble postulated that there is a linear relationship between the recessional velocity, v, and its distance, d, i.e. [pic]. To write this in the form of a formula we must include Hubble??™s constant, H0:

[pic]

The units of v, H0 and d, are km-1, km-1?·Mpc -1 and Mpc respectively.

The graph overleaf shows recessional velocity against the observed body from the observer.

[pic]

Using this formula we can also approximate the age of the universe as we know that [pic] and since [pic] then [pic]. However, this will only give an approximation of the universe??™s age as the rate at which the galaxies and other celestial bodies will have decreased due to the effects of gravitational attraction between the bodies. This estimate for the age of the universe gives a value of between 9-20 billion years3.

This proposed expansion of the universe means that the theory predicts that the universe had to have expanded from a single point. This point is called a singularity which in theory has almost infinite density as the entire mass of the universe is concentrated into a space smaller than the volume of an electron7.

Evidence that the universe is expanding also includes the distribution of the galaxies. The theory that space is expanding does not mean that the galaxies and stars themselves are moving but the space in between becomes stretched and therefore this means the galaxies become further apart. Their distribution is rather regular and this suggests that the expansion of the universe is the same throughout.

Further of evidence for the expansion of the universe, and therefore its origins being in the big bang, is the cosmic microwave background radiation throughout the universe. This is, as the name suggests, the constant presence of electromagnetic radiation, strongest in the microwave section of the electromagnetic spectrum, detected in any direction that a radio telescope is pointing. This was first discovered by American and German astronomers Robert Wilson and Arno Penzias in 19633. When they were using a radio antenna to study emissions of radio waves from space they noticed an emission in their spectra that was detected regardless of which way they directed their antenna. This was unusual because a source of electromagnetic radiation in space can normally be localised which was not possible with the emission they had detected here. The distribution of the cosmic background microwave radiation is show below ??“ the blue representing the least radiation and conversely the red represents the highest concentration of background radiation.
A Timeline of the Universe3, 9, 10, 11, 12, 13

t=0
The big bang creates the universe as we know it
Followed by the Planck era when the four fundamental forces, electromagnetism, gravity and the strong and weak nuclear forces, were all of equal strength and were possibly unified as one superforce.

t=10-43s
The Grand Unification epoch, during which the unification of all four forces begins to break down and the ratio of matter to antimatter begins to shift in favour of matter.

t=10-35s
The electroweak era allows the production of gauge bosons such as W?±, Z0 and the theorised Higgs boson. This period of time after the big bang is dominated by quarks and their antimatter counterparts.

t=10-10s
The hadron and lepton era leads to production of nucleons as quarks can become bound together with gluons, this also produces meson and other baryons. After this mutual annihilation of the matter and antimatter hadrons leaves the universe dominated by leptons and antileptons.

t=1s
Protons and neutrons are able to come together to form the nuclei of simple elements ??“ chiefly hydrogen, including deuterium, and helium as well as lithium.

t=10s
Mutual annihilation of many pair particles, mainly leptons and antileptons, leaves the universe being abundant in photons which interact with particles such as charged leptons, nuclei and protons for approximately the next 3?105 years.

t=180s
The first stable nuclei are able to form and by the time this era ends approximately 75% of the nuclei are hydrogen with about a third of the remaining nuclei being helium although there are very small amount of the nuclei of other elements.

t=3?105yr
Nuclei are finally able to combine with electrons resulting in the first atoms and the universe becomes transparent to cosmic background microwave radiation.

t=1?106yr
Stars are able to form for the first time as are protogalaxies along with quasars and these being to produce heavier elements than hydrogen and helium by nuclear fusion.

t=8?109yr
Our solar system comes into being with the Sun??™s gravitational attraction catching the remains of earlier stars and planets and satellites begin to form.

t=13.7?109yr
The present day.

One way in which we can look back in time is by studying high resolution images captured from space which show the light that left distance structures thousands, millions and billions of years ago. Below is the Hubble Ultra Deep Field image taken by the Hubble Space Telescope.

[pic]
Bibliography

1. http://adsabs.harvard.edu/abs/2009ApJS..180..330K
2. http://en.wikipedia.org/wiki/Hubble%27s_law
3. ???Quarks, Leptons and Hadrons??? by Jonathan Allday
4. http://en.wikipedia.org/wiki/File:Redshift.png
5. http://en.wikipedia.org/wiki/File:Redshift_blueshift.svg
6. ???Astrophysics and Cosmology??? by Roger Muncaster
7. http://atropos.as.arizona.edu/aiz/teaching/a204/images/Hubble_expansion.gif
8. http://www.rwc.uc.edu/koehler/astro/cmb.png
9. ???Stephen Hawking: Master of the Universe??? Channel 4
10. ???The Universe In A Nutshell??? Stephen Hawking
11. http://ssscott.tripod.com/BigBang.html
12. http://en.wikipedia.org/wiki/Timeline_of_the_Big_Bang
13. http://en.wikipedia.org/wiki/Graphical_timeline_of_the_Big_Bang
14. http://en.wikipedia.org/wiki/File:Universe_expansion2.png
15. http://en.wikipedia.org/wiki/File:Hubble_ultra_deep_field_high_rez_edit1.jpg
16. ???Understanding the Universe: From Quarks To the Cosmos??? by Don Lincoln
17. http://www.talkorigins.org/faqs/astronomy/bigbang.html
18. http://www.astro.ucla.edu/~wright/cosmology_faq.html
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