Big bang

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The big bang is the widely scientifically accepted theory of how the universe began. According to one version of the theory, all of space and time (spacetime) "began" about 13.7 billion (± 200 million) years ago, and has been expanding ever since.[1] Another version of the theory is that a hypothetical "multiverse" existed before our universe began.[2] While many details of the theory remain to be worked out, especially involving the first few instants of time, the big bang model is supported by many converging lines of evidence. The pillars of the big bang theory:

It is important to note that the big bang theory does not attempt to describe the initial conditions or first cause of the universe. It is intended to describe the development of the universe from its extremely dense and hot early stages into its present form. It is instructive not to think of it as a localized explosion from which all matter moves away, but rather as a uniform expansion of space itself. An observer at any point in the universe sees the same thing: a homogenous distribution of matter everywhere, with the more and more distant parts receding faster and faster.[3][4]

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[edit] Expanding universe

See the main article about this subject, expanding universe.

Up until the early 20th century, it had been assumed by scientists that the universe as a whole was static and unchanging. The first indication that this was not the case came in the 1920s, when Edwin Hubble's observations of distant galaxies revolutionized astronomers' understanding of the structure of our universe: he first proved that galaxies really were separate collections of stars, far from the Milky Way; and second, by observing the redshift of those galaxies, showed that they are receding from us. Hubble discovered an inverse relationship between a galaxy's distance and the speed at which it is receding from us. This relationship is known as Hubble's Law. By extrapolating back, this indicates that all the matter in the observable universe was very close together at one time, about 14 billion years ago.

[edit] Cosmic microwave background radiation

The early universe was extremely hot and dense. Matter emitted lots of radiation, the vestiges of which still exist in a much-cooled form (approximately 3 to 4 degrees K). It was first detected as unexplained noise in a highly sensitive antenna.

[edit] Ratios of chemical elements

Models of the early universe show that it was an ideal place for nuclear fusion to occur. Almost all of the deuterium ("heavy hydrogen"), as well as most of the helium, in the universe was created in the first few moments. Stars have converted some of the primordial hydrogen into helium, and the observed ratios of those two elements provide a rough estimate for the age of the universe.[5]

[edit] General relativity

A decade before Hubble made his observations, a number of physicists and mathematicians had established a consistent theory of the relationship between space and time by using Einstein's field equations of general relativity. Applying the most general principles to the nature of the universe yielded a dynamic solution that conflicted with the then prevailing notion of a static universe.

[edit] Inflation

One of the biggest problems with the original big bang theory is the extreme homogeneity of matter in the universe; the density of galaxies and gas clouds is the same no matter which direction we look. Scientists like Professor Alan Guth solved this problem, known as the horizon problem, by introducing the concept of inflation - shortly after the initial moment, the universe underwent a period of rapid expansion which smoothed out the density fluctuations. While it explains a few things, inflation leaves even more questions - most prominently, "what force of nature could cause that?".[6]

Chaotic inflation theory, or bubble universe theory, is an alternative model of inflation. Developed by physicist Andrei Linde and others in 1986, it solves a problem of the inflation theory, namely how to end the inflationary period.

[edit] Creationists

Of course, any time two scientists disagree about a minor aspect of the theory, the conversation is mined for any quotes which could be misrepresented to to support creationism. However, any discussion about the development of the universe is bound to be severely limited - the whole of our observations are made from one tiny corner of space, in the blink of an eye. We are not done learning yet.

[edit] How to create a universe

Dr. Guth and others hope to figure out how to create a universe in the labratory. [7] Guth once stated in an interview:

I in fact have worked with several other people for some period of time on the question of whether or not it's in principle possible to create a new universe in the laboratory. Whether or not it really works we don't know for sure. It looks like it probably would work. It's actually safe to create a universe in your basement. It would not displace the universe around it even though it would grow tremendously. It would actually create its own space as it grows and in fact in a very short fraction of a second it would splice itself off completely from our Universe and evolve as an isolated closed universe growing to cosmic proportions without displacing any of the territory that we currently lay claim to. [8]

[edit] Question

"What was there before the big bang?"

One possible answer is:

"The question is nonsensical, because there was no time (or space) for anything to exist in, so the word before is meaningless."

Another possible answer is:

"The multiverse existed before the Big bang.” [9]

As both the above are non-intuitive and go counter to all everyday human experience, it is the major point upon which popular understanding fails.

Salvation, for one editor at least, came with the Planck Time. The Planck Time is the shortest meaningful length of time. It is somewhere around 10-43 seconds, which is extremely short, but not zero. It is not possible to know what happened less than one Planck Time after the big bang. Indeed, it is not just not possible to know what happened, it is actually meaningless to even ask the question. That being the case the question of what happened before the big bang is also meaningless. We just have to lump it and get on with asking questions which are meaningful.

Hawking's book A Brief History of Time gives a reasoned explanation of the big bang and subsequent events, but is popularly reckoned to be intensely dense to the point of unreadability. Another book A Briefer History of Time has since been published.[10]

Julian Barbour suggests that reality simply terminates on nothing at the alpha point, as a brute fact, in the same way that England abuts the sea at Land's End without requiring an explanation.

[edit] Theory of everything?

It is notable that the disciplines of quantum physics, relativity and astrophysics all converge in the big bang theory - a first for science.

[edit] Addendum: God?

Theists of all stripes have attempted to use the theory as a "proof" of the existence of God. Well Goddidit:

"How was the big bang initiated, if not by a supernatural being?" they ask.
To which there is only one reply necessary:
"How was the supernatural being created if not by a supernatural being?"
And so on ad infinitum.

This paradox is unsolvable, so in the end, it comes down to a question of faith, or lack thereof.

In A Brief History of Time, Stephen Hawking outlines the mathematical use of imaginary time which results in the descripton of the universe as being of a hyperspherical nature without start or end - these being merely points on a "surface" undistinguished from others. The upshot is that the requirement for "start" and "cause" are removed, as is the need for faith (a concept which has no place in science).

Interestingly enough, the big bang theory was first proposed by Catholic priest and professor of physics Georges Lemaître. He first brought the theory to public attention after the discovery of redshift of nearby nebulae, although it was Fred Hoyle who coined the actual name as a derisory term. Compared with current big bang theory, which incorporates aspects such as inflation, LeMaitre hypothesized that all matter for the universe came forth from a "primeval atom", today more commonly described as a singularity.

[edit] So what happens next?

The universe, from this point, could:

  1. Keep expanding, until it expands so far it cannot collapse back upon itself. Eventually matter and energy would be so spread out that no particles would interact again. This is called "the heat death of the universe".
  2. Keep expanding, but reduce the rate of expansion by a fraction, eventually reaching nearly 0.
  3. Keep expanding, but at slower and slower rates, until gravity takes over, compressing all the mass back into a singularity, perhaps kicking off another big bang.

A fourth option, which was only recently discovered, is that the expansion will keep accelerating until the universe is torn apart at the atomic level. Recent studies into the cosmic microwave background radiation, gravitational lensing, and, most importantly, improved measurements of supernovas have led to the discovery that expansion really is accelerating. A possible explanation for this acceleration is the fact that, as the universe expands, the density of dark matter decreases while the density of dark energy remains constant, thus leading to an eventual predomination of dark energy which in turn drives the expansion.

[edit] See also

[edit] Footnotes

  1. ↑ [1] "The age of the Universe can also be estimated from a cosmological model based on the Hubble constant and the densities of matter and dark energy. This model-based age is currently 13.7 +/- 0.2 Gyr. But this Web page will only deal with actual age measurements, not estimates from cosmological models. The actual age measurements are consistent with the model-based age which increases our confidence in the Big Bang model."
  2. ↑ See Wikipedia on speculative physics beyond the Big Bang
  3. ↑ Scientific American Special Edition - The Cosmic Life Cycle, 1994-2007: "The Evolution of the Universe", P. James E. Peebles, David N. Schramm, Edwin L. Turner and Richard G. Kron.
  4. ↑ Cosmos, Carl Sagan. 1985.
  5. ↑ 'The End of Cosmology?', Lawrence M. Krauss and Robert J. Scherrer. Scientific American, March 2008
  6. ↑ Scientific American Special Edition - The Cosmic Life Cycle, 1994-2007: "Inflation in a Low-Density Universe", Martin A. Bucher and David N. Spergel.
  7. ↑ Physicist Aims to Create a Universe, Literally, Malcolm W. Browne, The New York Times, 1987.
  8. ↑ Parallel Universes (transcript), BBC, 2002.
  9. ↑ Big Bang, Wikipedia
  10. ↑ A Brief History of Time, ISBN: 0-553-34614-8 A Briefer History of Time, ISBN: 0-553-80436-7
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