Big Bang Central2.com

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1920's, scientists thought that the universe was in a "steady state". The Steady State Universe Theorywas based on three assumptions, i.e. the universe was:

Uniform - has the same general make-upthroughout

Static - not expanding or contracting Infinite - it extends forever, but there was only

one galaxy - The Milky Way

Heinrich Olbers in 1800's - if the universe were infinitely large and infinitely old, then the whole sky

should have a "glow". That is, at all points of sight there. So all points in the heavens should have

some light. However, the the sky between stars was "very dark", with no signs of any glow: aOlbers'

Paradox.

In 1922 to 1924, Edwin Hubblepainstakingly developed a series of nebulae distance indicators

In 1922,Alexander Friedmann, a Russian cosmologist and mathematician, derived the Friedmann

Equationsfrom Albert Einstein's equations of General Relativity. indicating that the universe -either

expanding or contracting, but not static.

George Lematre,a Belgian physicist and Roman Catholic priest, interpreted Friedman's equations

and proposed that the recession of nebulae was due to the "expansion of the universe". (word

nebulae -galaxies outside the Milky Way; today nebulae means large clouds of gas and dust.)

However, both Friedman and Lematre were mostly dismissed, even by Albert Einstein. But, in

1929 Hubble discovereda correlation between "nebulae distance and recession velocity" meaning

indeed "the universe was expanding", a shock to most scientists of that time

Hubble's Law: (a) all objects in deep space have a red shiftrelative to earth and to each other; and

(b) the velocity of galaxies receding from earth is proportional to their distance from the earth and

other interstellar bodies.

The Cosmological Principle is that observers on earth do not occupy any privileged position within

the universe. It means that the universe looks the same wherever you are in it and the same laws of

physics apply everywhere.

RED SHIFT:

In a phenomenon called "doppler shifting:", the wavelength emitted by something moving away

from us is shifted to a lower frequency, and the wavelength of something moving towards us is

shifted to a higher frequency

wavelengths emitted by objects moving away from us are shifted towards the red part of the visible

spectrum or red shifted. And the faster they move away from us, the more they are red shifted. See

the picture to the right of a distant star moving away from us. The right portion is the distant star,


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the left portion is our sun, Likewise objects that are moving towards us are shifted towards the blue

part of the spectrum and are blue shifted.

If the universe is "expanding", then any light waves from another galaxy will be stretched out to

longer wavelengths. Hubble observed this looking at the distant galaxies- saw that their light was

"red shifted" therefore galaxy clusters were moving away from each other.

BIGBANG RIGHT:

1931 Georges Lematrefurther postulated that the expansion of the universe, if projected back in

time, would make the universe smaller and smaller until about ( 13.75 billion years ago) all the mass

of the universe would be concentrated in the size of ping pong ball. In 1949, Sir Fred Hoyle, an

English astronomer and mathematician, coined the term The Big Bangin a BBC radio .

ScientistsAlbert Einstein did not accept the theory.put cosmological constant in his eqn.s to

prevent universe from collapsing****.

The discovery of the Cosmic Microwave Background (CMB)in the 1960's convinced most

astronomers that theBig Bang Theoryhad merit. The "Hubble Expansion" is now one of three pieces

of evidence that support the Big Bang Theory. (The other two are theCosmic Microwave

Backgroundand Big Bang Nucleosynthesis.)

BIG BANG ISSUES AND INFLATION:

the early Big Bang Theory was based on Einstein's Theory of General Relativity, almost universally

accepted by scientists of the day, there were some technical issues with the initial version of the Big

Bang Theory. The original Big Bang Theory did not contain"inflation"and some scientists "rightly"poked holes in it.

solution was to add an extremely fast "exponential" expansion, called "inflation", into the first

micro-micro-seconds of the universe. Inflation caused the universe to grow by a factor of 100 billion

trillion trillion in just a few microseconds. (Note that the universe was not expanding into empty

space. Space-time itself was growing faster than the speed of light. Space-time is not limited by the

speed of light, only objects "within" space-time are.)

Inflation equations: Alan Guth, currently a Professor of Physics at MIT (and his alma mater) added to

the big bang theory*****.

Expansion was accelerating:

Astronomers from the Supernova Cosmology Project (U. of California Berkeley Labs) and the High-z

Supernova Search Team (Australian National University and John Hopkins University) were using

"land-based" telescopes for preliminary data and then the Hubble Space Telescope for fine detail.

Instead of slowing down as everyone had expected, the dimness of the supernovas showed that

they were 10% to 15% farther out than anticipated, indicating that expansion had accelerated over

the ensuing billions of years. Far from decelerating under the influence of gravity as was commonly

thought at the time, the expansion of the universe was in fact accelerating


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Issues With The Original Big Bang Theory

Einstein's original general theory of relativity was not compatible with a static universe. The

equations indicated that the universe was either expanding or contracting. Einstein also thought the

universe was static, so he modified his original equations to incorporate a static universe. When

Edwin Hubble discovered that the universe was expanding, Einstein retracted his modifications,

calling it the biggest mistake of his life.

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The definition of a "horizon" in cosmology is the inability to receive any type of signal from a verydistant source because of the finite speed of light. The microwave background radiation coming from

extremely distant parts of the universe all have exactly the same average temperature but are too far

apart to have ever communicated with each other, even with signals traveling at the speed of light.

Temperatures of the background radiation were just "assumed" to be the same everywhere in the

original Big Bang Theory. Hence the "horizon issue" - How did the temperatures get to be exactly the

same everywhere?

Based on Einstein's General Relativity, the original Big Bang Theory assumed that the universe was"mathematically flat" (explained in the next paragraph) in all directions. If not "flat", it would have

collapsed on itself shortly after the Big Bang or it would have flown apart so quickly that galaxies

would never have been able to form. The original Big Bang required the universe to be flat within one

part in 10^59 (one with 60 zeros following it). This is obviously possible but is it realistic?

The term "flat" is a mathematical term that represents the rate of expansion of the universe, meaning

the expansion rate will neither increase or decrease, i.e. it will remain the same (or be "flat"). Being

mathematically "flat" has nothing to do with the shape of the universe, it is a term to describe (poorly)

the rate of expansion in all directions. It means the universe is a spherical type object expanding

equally fast in all directionssort of like blowing up a balloon.

Current theory of sub-atomic particle physics predicts that very massive exotic particlescalled magnetic monopoles should have been produced by the Big Bang. There should be many of

these monopoles in the universe today. However, no one has ever found any monopole particles. Any

particle left over from the early, hot stages of the universe is called a "relic particle". The big bang

model predicts that we should be able to observe these relic particles today, but none have ever been

seen.

INFLATION:

Inflation Theory, initially developed in 1981 by Alan Guth of MIT, and extended by Andrei Linde,

Paul Steinhardt, and Andy Albrecht, introduces a period of extremely rapid (exponential) expansionof the universe prior to the more gradual Big Bang expansion. Inflation was extremely rapid, itincreased the size of the "observable" universe by a factor of about 10^70 in only a small fraction of a

second! Inflation is now considered an extension of the Big Bang theory since it explains the above


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issues very well while retaining the basic concept of a homogeneous expanding universe. Here is howthe above three issues are explained by Inflation:

The tremendous expansion of inflation means that regions that we see widely separated in the skynow were much closer together before inflation and thus could have been in contact.

Inflationary Theory predicts unequivocally that the universe should be exactly flat. The universeappears to be flat out to the farthest distance that we can see. The recent satellite WMAT found the

universe to be "flat" with an error of only 0.5%.

The rapid expansion of the universe tremendously diluted the concentration of any magneticmonopoles that might have been produced. Calculations indicate that they have become so rare in any

given volume of space that it would be very unlikely to ever encounter one in an experiment to search

for them.

As a bonus, Inflation also explains the structure of the current universe. Prior to Inflation, the portionof the universe we can "observe" was microscopic. Quantum fluctuations in the density of matter on

microscopic scales expanded to astronomical scales during Inflation. Over the next several hundredmillion years, these higher density regions condensed into stars, galaxies, and clusters of galaxies inthe universe as we now know it

BIG BANG NUCLEOSYNTHESIS:

What caused Inflation to happen? Cosmologists are not sure of this and several theories exist. Guth

proposed that the super cooling initiated a anti-gravitational field which then caused a violent

growth spurt

After Inflation, the universe slowed down to the normal "Hubble Rate" and was filled with radiationand elementary particles, sometimes called "quark soup". As the universe continued to cool, new

particles were formed out of pre-existing ones. This early formation phase is called theBig BangNucleosynthesis(BBN). With the temperature falling below 10 billion Kelvin, BBN took place from

about ten seconds to about twenty minutes.The diagram at the left illustrates two of the common nuclear reactions which occurred during theBBN. It shows single proton ions and neutron ions combining to form deuterium nuclei, D,(containing one proton and one neutron) plus the emission of high energy photons, . Subsequently itshows two deuterium nuclei fusing to produce one nucleus of helium-3 (with two protons and one

neutron) and one free neutron. Note that "atoms" were not yet forming, the above reaction shows justthe "nuclei" of future atoms forming from ions. Experiments can be done in labs today demonstrating

these early BBN nuclei reactions.

The BBN theoretical calculations result in a nuclei abundance of about 75% hydrogen (1 protonnucleus), about 25% helium (2 protons and 2 neutrons in the nucleus), and about 0.01% of deuterium

(1 proton and 1 neutron nucleus). Without this abundance of hydrogen nuclei, there would be nowater and therefore no life as we now know it. That the observed hydrogen and helium

abundances in early distant galaxies are very consistent with the above theoretical calculations

is considered "strong evidence" for the Big Bang Theory.Big Bang Nucleosynthesis is one of thethree pillars of support for the Big Bang Theory. Measurements from the WMAP satellite over nineyears of collecting data (2001 to 2010) has recently confirmed the above ratios with much greaterprecision.One nice feature of the BBN is that the physical laws that govern the behavior of matter at theseenergy levels are very well understood. Hence the BBN lacks some of the speculative uncertaintiesthat characterize earlier periods in the "theoretical" life of the universe. During all this time, electronsand photons interacted with each other so intensely (instantaneous collisions) that the universe wasopaque, i.e. dark, no light (photons) could escape.


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PHOTON ERA:

About 70,000 years after the Big Bang, radiation and matter were about equal in density, shortlythereafter matter began to dominate.Recombination (380,000 Years) For the next 310,000 years the universe continued to expand andcool, but was still fiery hot and dark. Any visible light was immediately scattered by collisions with

the ubiquitous electrons and protons. It contained only the simplest elements, mostly hydrogen andhelium ions. As the universe cooled further, the electrons (with a negative charge) begin to getcaptured by the ions (with a positive charge) forming atoms (electrically neutral). This processhappened relatively fast and is known as "recombination". The first bits of structure began to form.These small clumps of matter grew in size as their gravity attracted other nearby matter. At about380,000 years of cooling, light (photons) began to travel through the spaces between the atoms whichnow "bond" the electrons in their orbits. The universe had become transparent

Cosmic Microwave Background (CMB). The first early radiation that could freely travel was theCMB, the remnants of which we can detect in the current universe 13.75 billion years later. 380,000

years is the earliest point in time we can ever look back and "see" because everything before that waspart of the dark ages.Note the CMB picture to the left taken by the European Space Agency (ESA) Planck satellite. The

Planck satellite launched in 2009 is the third satellite exclusively designed to map the early CMB.NASA has previously launched the COBE in 1989 and the WMAP in 2001.Check out theCosmicMicrowave Backgroundweb page.Currently, the earliest galaxywe can "see" is MACS0647-JD which is believed to have formed about420 million years after the Big Bang.
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