Big Bang Theory
In physical cosmology, the Big Bang is the scientific theory of how the universe emerged from a tremendously dense and hot state about 13.7 billion years ago. The Big Bang theory is based on the observed Hubble's law redshift of distant galaxies that when taken together with the cosmological principle indicate that space is expanding according to the Friedmann-Lemaitre model of general relativity. Extrapolated into the past, these observations show that the universe has expanded from a state in which all the matter and energy in the universe was at an immense temperature and density. Physicists do not widely agree on what happened before this, although general relativity predicts a gravitational singularity.
T h e t e r m B i g B a n g i s u s e d b o t h i n a n a r r o w s e n s e t o r e f e r t o a p o i n t i n t i m e w h e n t h e o b s e r v e d e x p a n s i o n o f t h e u n i v e r s e ( H u b b l e ' s l a w ) b e g a n - c a l c u l a t e d t o b e 1 3 . 7 b i l l i o n ( 1 . 3 7 × 1 0 1 0 ) y e a r s a g o ( ± 2 % ) - a n d i n a m o r e g e n e r a l s e n s e t o r e f e r t o t h e p r e v a i l i n g c o s m o l o g i c a l p a r a d i g m e x p l a i n i n g t h e o r i g i n a n d e x p a n s i o n o f t h e u n i v e r s e , a s w e l l a s t h e c o m p o s i t i o n o f p r i m o r d i a l m a t t e r t h r o u g h n u c l e o s y n t h e s i s a s p r e d i c t e d b y t h e A l p h e r - B e t h e - G a m o w t h e o r y .
F r o m t h i s m o d e l , G e o r g e G a m o w i n 1 9 4 8 w a s a b l e t o p r e d i c t , a t l e a s t q u a l i t a t i v e l y , t h e e x i s t e n c e o f c o s m i c m i c r o w a v e b a c k g r o u n d r a d i a t i o n ( C M B ) . T h e C M B w a s d i s c o v e r e d i n t h e 1 9 6 0 s a n d f u r t h e r v a l i d a t e d t h e B i g B a n g t h e o r y o v e r i t s c h i e f r i v a l , t h e s t e a d y s t a t e t h e o r y .
The Big Bang theory developed from observations and theoretical considerations. Observationally, it was determined that most spiral nebulae were receding from Earth, but those who made the observation weren't aware of the cosmological implications, nor that the supposed nebulae were actually galaxies outside our own Milky Way.
In 1927, Georges Lemaitre independently derived the Friedmann-Lemaître-Robertson-Walker equations from Albert Einstein's equations of general relativity and proposed, on the basis of the recession of spiral nebulae, that the universe began with the "explosion" of a "primeval atom" - what was later called the Big Bang.
In 1929, Edwin Hubble provided an observational basis for Lemaitre's theory. He discovered that, seen from Earth, light from other galaxies is red-shifted in direct proportion to their distance from the Earth. This fact is now known as Hubble's law. Given the cosmological principle whereby the universe, when viewed on sufficiently large distance scales, has no preferred directions or preferred places, Hubble's law suggested that the universe was expanding, contradicting the infinite and unchanging static universe scenario developed by Einstein.
This idea allowed for two opposing possibilities. One was Lemaître's Big Bang theory, advocated and developed by George Gamow. The other possibility was Fred Hoyle's steady state model in which new matter would be created as the galaxies moved away from each other. In this model, the universe is roughly the same at any point in time[6]. It was actually Hoyle who coined the name of Lemaître's theory, referring to it sarcastically as "this big bang idea" during a program broadcast on March 28, 1949 by the BBC Third Programme. Hoyle repeated the term in further broadcasts in early 1950, as part of a series of five lectures entitled The Nature of Things. The text of each lecture was published in The Listener a week after the broadcast, the first time that the term "big bang" appeared in print.
For a number of years the support for these theories was evenly divided. However, the observational evidence began to support the idea that the universe evolved from a hot dense state. Since the discovery of the cosmic microwave background radiation in 1965 it has been regarded as the best theory of the origin and evolution of the cosmos. Virtually all theoretical work in cosmology now involves extensions and refinements to the basic Big Bang theory. Much of the current work in cosmology includes understanding how galaxies form in the context of the Big Bang, understanding what happened at the Big Bang, and reconciling observations with the basic theory.
Huge advances in Big Bang cosmology were made in the late 1990s and the early 21st century as a result of major advances in telescope technology in combination with large amounts of satellite data such as that from COBE, the Hubble Space Telescope and WMAP. Such data have allowed cosmologists to calculate many of the parameters of the Big Bang to a new level of precision and led to the unexpected discovery that the expansion of the universe appears to be accelerating.
B a s e d o n m e a s u r e m e n t s o f t h e e x p a n s i o n o f t h e u n i v e r s e u s i n g T y p e 1 a s u p e r n o v a e , m e a s u r e m e n t s o f t h e l u m p i n e s s o f t h e c o s m i c m i c r o w a v e b a c k g r o u n d , a n d m e a s u r e m e n t s o f t h e c o r r e l a t i o n f u n c t i o n o f g a l a x i e s , t h e u n i v e r s e h a s a c a l c u l a t e d a g e o f 1 3 . 7 ± 0 . 2 b i l l i o n y e a r s . T h e a g r e e m e n t o f t h e s e t h r e e i n d e p e n d e n t m e a s u r e m e n t s i s c o n s i d e r e d s t r o n g e v i d e n c e f o r t h e s o - c a l l e d AC D M m o d e l t h a t d e s c r i b e s t h e d e t a i l e d n a t u r e o f t h e c o n t e n t s o f t h e u n i v e r s e .
T h e e a r l y u n i v e r s e w a s f i l l e d h o m o g e n e o u s l y a n d i s o t r o p i c a l l y w i t h a n i n c r e d i b l y h i g h e n e r g y d e n s i t y a n d c o n c o m i t a n t l y h u g e t e m p e r a t u r e s a n d p r e s s u r e s . I t e x p a n d e d a n d c o o l e d , g o i n g t h r o u g h p h a s e t r a n s i t i o n s a n a l o g o u s t o t h e c o n d e n s a t i o n o f s t e a m o r f r e e z i n g o f w a t e r a s i t c o o l s , b u t r e l a t e d t o e l e m e n t a r y p a r t i c l e s . A p p r o x i m a t e l y 1 0 - 3 5 s e c o n d s a f t e r t h e P l a n c k e p o c h a p h a s e t r a n s i t i o n c a u s e d t h e u n i v e r s e t o e x p e r i e n c e e x p o n e n t i a l g r o w t h d u r i n g a p e r i o d c a l l e d c o s m i c i n f l a t i o n . A f t e r i n f l a t i o n s t o p p e d , t h e m a t e r i a l c o m p o n e n t s o f t h e u n i v e r s e w e r e i n t h e f o r m o f a q u a r k - g l u o n p l a s m a ( a l s o i n c l u d i n g a l l o t h e r p a r t i c l e s a n d p e r h a p s e x p e r i m e n t a l l y p r o d u c e d r e c e n t l y a s a q u a r k - g l u o n l i q u i d ) i n w h i c h t h e c o n s t i t u e n t p a r t i c l e s w e r e a l l m o v i n g r e l a t i v i s t i c a l l y . A s t h e u n i v e r s e c o n t i n u e d g r o w i n g i n s i z e , t h e t e m p e r a t u r e d r o p p e d .
A t a c e r t a i n t e m p e r a t u r e , b y a n a s - y e t - u n k n o w n t r a n s i t i o n c a l l e d b a r y o g e n e s i s , t h e q u a r k s a n d g l u o n s c o m b i n e d i n t o b a r y o n s s u c h a s p r o t o n s a n d n e u t r o n s , s o m e h o w p r o d u c i n g t h e o b s e r v e d a s y m m e t r y b e t w e e n m a t t e r a n d a n t i m a t t e r . S t i l l l o w e r t e m p e r a t u r e s l e d t o f u r t h e r s y m m e t r y b r e a k i n g p h a s e t r a n s i t i o n s t h a t p u t t h e f o r c e s o f p h y s i c s a n d e l e m e n t a r y p a r t i c l e s i n t o t h e i r p r e s e n t f o r m . L a t e r , s o m e p r o t o n s a n d n e u t r o n s c o m b i n e d t o f o r m t h e u n i v e r s e ' s d e u t e r i u m a n d h e l i u m n u c l e i i n a p r o c e s s c a l l e d B i g B a n g n u c l e o s y n t h e s i s . A s t h e u n i v e r s e c o o l e d , m a t t e r g r a d u a l l y s t o p p e d m o v i n g r e l a t i v i s t i c a l l y a n d i t s r e s t m a s s e n e r g y d e n s i t y c a m e t o g r a v i t a t i o n a l l y d o m i n a t e t h a t o f r a d i a t i o n . A f t e r a b o u t 3 0 0 , 0 0 0 y e a r s t h e e l e c t r o n s a n d n u c l e i c o m b i n e d i n t o a t o m s ( m o s t l y h y d r o g e n ) ; h e n c e t h e r a d i a t i o n d e c o u p l e d f r o m m a t t e r a n d c o n t i n u e d t h r o u g h s p a c e l a r g e l y u n i m p e d e d . T h i s r e l i c r a d i a t i o n i s t h e c o s m i c m i c r o w a v e b a c k g r o u n d .
O v e r t i m e , t h e s l i g h t l y d e n s e r r e g i o n s o f t h e n e a r l y u n i f o r m l y d i s t r i b u t e d m a t t e r g r a v i t a t i o n a l l y a t t r a c t e d n e a r b y m a t t e r a n d t h u s g r e w e v e n d e n s e r , f o r m i n g g a s c l o u d s , s t a r s , g a l a x i e s , a n d t h e o t h e r a s t r o n o m i c a l s t r u c t u r e s o b s e r v a b l e t o d a y . T h e d e t a i l s o f t h i s p r o c e s s d e p e n d o n t h e a m o u n t a n d t y p e o f m a t t e r i n t h e u n i v e r s e . T h e t h r e e p o s s i b l e t y p e s a r e k n o w n a s c o l d d a r k m a t t e r , h o t d a r k m a t t e r , a n d b a r y o n i c m a t t e r . T h e b e s t m e a s u r e m e n t s a v a i l a b l e ( f r o m W M A P ) s h o w t h a t t h e d o m i n a n t f o r m o f m a t t e r i n t h e u n i v e r s e i s c o l d d a r k m a t t e r . T h e o t h e r t w o t y p e s o f m a t t e r m a k e u p l e s s t h a n 2 0 % o f t h e m a t t e r i n t h e u n i v e r s e .
T h e u n i v e r s e t o d a y a p p e a r s t o b e d o m i n a t e d b y a m y s t e r i o u s f o r m o f e n e r g y k n o w n a s d a r k e n e r g y . A p p r o x i m a t e l y 7 0 % o f t h e t o t a l e n e r g y d e n s i t y o f t o d a y ' s u n i v e r s e i s i n t h i s f o r m . T h i s d a r k e n e r g y c a u s e s t h e e x p a n s i o n o f t h e u n i v e r s e t o d e v i a t e f r o m a l i n e a r v e l o c i t y - d i s t a n c e r e l a t i o n s h i p , o b s e r v e d a s a f a s t e r t h a n e x p e c t e d e x p a n s i o n a t v e r y l a r g e d i s t a n c e s . D a r k e n e r g y i n i t s s i m p l e s t f o r m u l a t i o n t a k e s t h e f o r m o f a c o s m o l o g i c a l c o n s t a n t t e r m i n E i n s t e i n ' s f i e l d e q u a t i o n s o f g e n e r a l r e l a t i v i t y , b u t i t s c o m p o s i t i o n i s u n k n o w n a n d , m o r e g e n e r a l l y , t h e d e t a i l s o f i t s e q u a t i o n o f s t a t e a n d r e l a t i o n s h i p w i t h t h e s t a n d a r d m o d e l o f p a r t i c l e p h y s i c s c o n t i n u e t o b e i n v e s t i g a t e d b o t h o b s e r v a t i o n a l l y a n d t h e o r e t i c a l l y .
A l l t h e s e o b s e r v a t i o n s a r e e n c a p s u l a t e d i n t h e õ C D M m o d e l o f c o s m o l o g y , w h i c h i s a m a t h e m a t i c a l m o d e l o f t h e B i g B a n g w i t h s i x f r e e p a r a m e t e r s . M y s t e r i e s a p p e a r a s o n e l o o k s c l o s e r t o t h e b e g i n n i n g , w h e n p a r t i c l e e n e r g i e s w e r e h i g h e r t h a n c a n y e t b e s t u d i e d b y e x p e r i m e n t . T h e r e i s n o c o m p e l l i n g p h y s i c a l m o d e l f o r t h e f i r s t 1 0 - 3 3 s e c o n d s o f t h e u n i v e r s e , b e f o r e t h e p h a s e t r a n s i t i o n t h a t g r a n d u n i f i c a t i o n t h e o r y p r e d i c t s . A t t h e " f i r s t i n s t a n t " , E i n s t e i n ' s t h e o r y o f g r a v i t a t i o n p r e d i c t s a g r a v i t a t i o n a l s i n g u l a r i t y w h e r e d e n s i t i e s b e c o m e i n f i n i t e . T o r e s o l v e t h i s p a r a d o x , a t h e o r y o f q u a n t u m g r a v i t a t i o n i s n e e d e d . U n d e r s t a n d i n g t h i s p e r i o d o f t h e h i s t o r y o f t h e u n i v e r s e i s o n e o f t h e g r e a t e s t u n s o l v e d p r o b l e m s i n p h y s i c s .
Big Bang Wikipedia
Cosmic 'treasure trove' revealed BBC - March 11, 2008
Nasa space probe measuring the oldest light in the Universe has found
that cosmic neutrinos made up 10% of matter shortly after the Big Bang.
What happened before the Big Bang? BBC - August 3, 2006
Big bang sound waves explain galaxy clustering New Scientist - January 2005
Big Bang 'soup recipe' confirmed June 2003 - New Scientist
A microsecond after the Big Bang, when the exploding fireball of the newborn
Universe was only a few kilometres across, all matter existed in a special state.
Cosmic polarization detected from South Pole September 2002 - New Scientist
Confirms cosmologists' view of the early Universe. Astronomers hope the discovery will lead to more
detailed measurements that will explain exactly how the Universe expanded in a fraction of a second after the Big Bang and how the first stars were formed.
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