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In the Big Bang theory, the universe began as very hot, small, and dense, with no stars, atoms, form, or structure (called a "singularity"). Then about 14 billion years ago, space expanded very quickly (thus the name "Big Bang"), resulting in the formation of atoms, which eventually led to the creation of stars and galaxies. The universe is still expanding today, but getting colder as well.
As a whole, space is growing and the temperature is falling as time passes. Cosmology is the name given to how the universe began and how it has developed. Scientists that study cosmology agree the Big Bang theory matches what they have observed so far.
Fred Hoyle called the theory the "Big Bang" on his radio show. He did not believe the Big Bang was correct. Scientists who did not agree with him thought the name was funny and decided to use it. Since then, Fred Hoyle's reasons for not agreeing with the theory have been proven wrong.
Scientists base the Big Bang theory on many different observations. The most important is the redshift of very far away galaxies. Redshift is the Doppler Effect occurring in light. When an object moves away from earth, it looks reddish because the movement stretches the wavelength. The reddish color occurs because red is the lowest wavelength on the visible spectrum. The more redshift there is, the faster the object is moving away. By measuring the redshift, scientists proved that the universe is expanding and can even work out how fast the object is moving. With precise observation and measurements, scientists believe that universe was a singularity approximately 13.8 billion years ago. Because most things become colder as they expand, the universe is assumed to have been very hot when it started.
Other observations that support the Big Bang theory are the amounts of chemical elements in the universe. Amounts of hydrogen, helium, and lithium seem to agree with the theory of the Big Bang. Scientists also have found "cosmic microwaves background radiation". This radiation is known as radio waves, and they are everywhere in the universe. Even so, it is now very weak and cold, but a long time ago it was very strong and very hot.
The Big Bang might also have been the beginning of time. If the Big Bang was the beginning of time, then there was no universe before the Big Bang, since there was no concept of "before" without time. Other ideas state that the Big Bang was not the beginning of time 13.8 billion years ago. Instead, some believe that there was a different universe before and it may have been very different from the one we know today.
Graphical timeline of the universe
A great deal happened in the first second of the universe's life:
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DateFormat = yyyy Period = from:-430 till:155 TimeAxis = format:yyyy orientation:vertical # order:reverse does not work ScaleMajor = unit:year increment:10 start:-430 # second ScaleMinor = unit:year increment:2 start:-430
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bar:Clock bar:Era bar:Dummy3 bar:Periods bar:Dummy4 bar:Events
fontsize:M pos:(240,75) text:Planck epoch pos:(250,50) text:Big Bang pos:(20,50) text:"0: Linear time" pos:(10,980) text:"Logarithmic time:" text:"10 · log10 second" pos:(154,946) text:"NEXT" pos:(117,931) text:The Stelliferous Era pos:(245,950) text:"Reionization"
layer:front at:123 frompos:358 tillpos:369 width:0.5 # Matter domination points:(369,878)(402,800) width:0.5 points:(402,800)(413,800) width:0.5
width:53 bar:Clock color:events align:right shift:(28,3) mark:(line,teal) at:-120 text:"One picosecond" at:-90 text:"One nanosecond" at:-60 text:"One microsecond" at:-30 text:"One millisecond" at:0 text:"One second" at:36 text:"One hour" at:75 text:"One year" at:105 text:"One thousand years" shift:(43,3) at:135 text:"One million years"
width:53 bar:Era mark:(line,white) align:center shift:(0,0) from:-430 till:135 color:era1 text:"The Primordial Era"
width:158 bar:Periods align:center shift:(0,0) mark:(line,white) from:-430 till:-360 color:period1 text:Grand unification epoch from:-360 till:-120 color:period2 text:Electroweak epoch from:-120 till:-60 color:period1 text:Quark epoch from:-60 till:0 shift:(-40,0) align:left color:period2 text:Hadron epoch from: 0 till:23 color:period1 text:Lepton epoch from: 23 till:131 color:period2 text:Photon epoch from:131 till:155 color:period1 text:"Dark Ages"
width:53 mark:(line,purple) textcolor:black fontsize:M bar:Events color:events align:left shift:(30,-4)
at:-430 shift:(30,-12) text:"Planck time, the smallest theoretically observable ~unit of time and the time before which science is ~unable to describe the universe. At this point, the ~force of gravity separated from the electronuclear ~force." at:-360 text:"Separation of the strong force from the ~electronuclear force." from:-360 till:-320 align:left shift:(-55,0) color:time1 text:"Inflationary epoch. The Universe expands exponentially" at:-320 shift:(30,4) text:"Reheating after inflation populates universe ~with quarks and anti-quarks." at:-120 text:"The weak force separates from the ~electromagnetic force resulting in the four ~separate forces we know today." at:-60 text:"Quarks become confined within hadrons." at:-30 mark:(line,white) text:"Formation of hydrogen nuclei." at:0 text:"Neutrinos cease to interact with other particles." at:23 shift:(30,-11) text:"Lepton/anti-lepton pairs annihilate." from:23 till:31 align:center shift:(0,-4) color:time2 text:"Big Bang nucleosynthesis" at:31 shift:(30,2) text:"3 to 20 minutes: Formation of helium nuclei" from:129 till:131 shift:(-114,-2) color:time1 mark:(line,white) text:"Recombination"
- at:123 shift:(30,-32) text:"70,000 years: Matter domination"
at:123 mark:(line,white) shift:(30,-83) text:"70,000 years: Matter domination" at:131 text:"379,000 years: Hydrogen and helium nuclei ~capture electrons to form stable atoms. Photons ~are no longer able to interact strongly with atoms. ~Cosmic microwave background radiation streams ~freely." at:155 text:"100 million years: First star begins to shine."
- NASA. "Universe 101:Big Bang theory". http://map.gsfc.nasa.gov/universe/bb_theory.html. Retrieved 2010-01-28.
- Sullivan, Walter (August 22, 2001). "Fred Hoyle dies at 86; opposed 'Big Bang' but named it". New York Times. http://www.nytimes.com/2001/08/22/world/fred-hoyle-dies-at-86-opposed-big-bang-but-named-it.html?pagewanted=1. Retrieved 2010-01-28.
- Chris LaRocco and Blair Rothstein. "The Big Bang: it sure was BIG!". http://www.umich.edu/~gs265/bigbang.htm. Retrieved 2010-01-28.
- Singh, Simon (2005). Big Bang: the most important scientific discovery of all time and why you need to know about it. Harper Perennial.