Big Bang
Template:TOC-right The Big Bang is an important aspect of the theoretical model of the universe. The Big Bang means that essentially the universe began at Planck Time, 10-43 seconds, from a single point about 13.7 billion years ago, expanding at great speed to its current state. Prior to Planck Time, the Four Forces, strong, electromagnetic, weak and gravity, were united in one force.
At 10-35 seconds, the temperature of the Universe reached 1027 to 1028K and the initial inflation of the universe ended at 10-33 seconds.
The Universe continued to expand and its temperature dropped to about T=1013 K until 0.0001 seconds after the Big Bang. Antiprotons and protons annihilated each. For some reason, apparently most antimatter was annihilated but there were surviving protons and neutrons. There were also a very large number of photons per proton and neutron .
Eventually matter coalesced to form larger bodies, then stars and galaxies. The first stars formed about 100 million years after the Big Bang.
Unstable stars became supernovae, and when they exploded they spread all the elements from carbon, through through uranium throughout the Universe. Numerous galaxies then formed as dark matter, stars and gas coalesced and merged. Later, clusters of galaxies formed and eventually, the Solar System and Sun formed about 4.6 billion years ago.
The time now is 13.7 Gyr (billion years) after the Big Bang, and the temperature is T=2.725 K.
Evidence for the Big Bang Theory
The counter argument to the Big Bang has largely been the Steady State Theory. The Steady State implies simply that, the Universe is not changing or growing. Proposed in 1948 by Hermann Bondi (1919-2005), Thomas Gold (1920-2004) and Fredrick Hoyle (1915-2001), the Steady State adheres to the "Perfect Cosmological Principle", and assumes that the Universe is homogenous and isotropic (the same at all times in all places and in all directions respectively).
Given that observational data provides evidence that the Universe is expanding, the Steady State requires that density remains the same and matter, must thus, be continuously created. The Steady State Theory was a true scientific theory and as such it contained predictions that could be tested. Eventually those predictions were demonstrably incorrect.[4]
Some evidence for the Big Bang also provides evidence for the Steady State theory:
Olbers' paradox
The darkness of the night sky in a universe which is eternal and stars are homogenously distributed presents a contradiction: Why isn't the night sky uniformly bright? In the Steady State there are infinitely many stars so that every portion of the sky should have a star, and the entire heavens should be as bright as the sun. It would be like being in a hollow black body with a temperature of about 6000 degrees Centigrade. This is Olbers' paradox. Kepler in 1610 and Halley and Cheseaux in the eighteen century discussed this, but Olber takes credit for the 'paradox' because of his more extensive investigations in the nineteenth century.
Reasons as to why this would be possible--to uphold the Steady State and explain the paradox-- include
- There's too much dust to see the distant stars.
This presents a similar problem--the dust would have heated up as well resulting in a hot, glowing dust filled universe. Enough dust to reduce the radiation would obscure the sun.
- The Universe has only a finite number of stars.
While this may be correct, technically, the number of stars would still be large enough to light up the entire sky. This is because all the luminous matter together in the Universe is too extensive to allow for a dark sky. While there may not be an infintie number of stars, there are still enough to light up the heavens
- The distribution of stars is not uniform.
This would impose a certain restraint on the Steady State Theory. However, if there could be an infinity of stars and some are obscured behind others so that only a finite angular area is subtended by them, this may be correct in part. It has yet to be determined. If the stars are not distributed homogenously, that is they are distributed fractally, then there could be empty patches, and the sky would possibly appear dark in some areas.
- The Universe is expanding, so distant stars are red-shifted into obscurity.
As a star moves away, its light shifts to the red end of the spectrum, since the light waves are longer, reducing observed luminosity. This is considered to be correct and may be responsible in part for the dark night sky.
- The Universe is young. Distant light hasn't even reached us yet.
The proposed finite age of the Universe is probably the largest effect in explaining the dark sky. This does not support the classic Steady State Theory since it would mean that the Universe was not the same as it is now in the past. If we live inside an "Observable Universe", spherical and with a radius equal to the life span of the Universe, luminous objects over 15 billion years old are too far away for their light ever to reach us. [5]
The Hubble Law
Homogeneity
Isotropy
Time dilation in supernova light curves
Notes
- ↑ Big Bang Models Hyperphysics, Georgia State University
- ↑ Fundamental Forces Hyperphysics, Georgia State University
- ↑ Brief History of the Universe Wright, Edward L. Astronomy, University of California, Los Angeles
- ↑ Errors in the Steady State and Quasi-SS Models Wright, Edward L. Astronomy, University of California, Los Angeles
- ↑ Olber's Paradox Wright, Edward L. Astronomy, University of California, Los Angeles