How did the universe create?

There were two theories supporting this:1. Steady state theory - states that the universe has always existed and will continue to survive

without noticeable change2. Big bang theory - states that the universe was created in a massive explosion-like event billions of

years ago 

Evidence for big bang

1. Red shift

This happens with light too. Our sun contains helium. We know this because there are black lines in the spectrum of the light from the sun, where helium has absorbed light. These lines form the absorption spectrum for helium.

When we look at the spectrum of a distant star, the absorption spectrum is there, but the pattern of lines has moved towards the red end of the spectrum, as you can see below.

This is called red shift. It is a change in frequency of the position of the lines.Astronomers have found that the further from us a star is the more its light is red shifted. This tells us that distant galaxies are moving away from us, and that the further a galaxy is the faster it is moving away. Since we cannot assume that we have a special place in the universe this is evidence for a generally expanding universe. It suggests that everything is moving away from everything else. The Big Bang theory says that this expansion started billions of years ago with an explosion.

2. Cosmic microwave background radiation Scientists discovered that there are microwaves coming from every direction in space. Big Bang theory says this is energy created at the beginning of the universe, just after the Big Bang, and that has been travelling through space ever since.A satellite called COBE has mapped the background microwave radiation of the universe as we see it. Big Bang theorists are still working on the interpretation of this evidence.

In 1963, Arno Penzias and Robert Wilson, two scientists in Holmdale, New Jersey, were working on a satellite designed to measure microwaves. When they tested the satellite's

antenna, they found mysterious microwaves coming equally from all directions. The radiation that Penzias and Wilson discovered, called the Cosmic Microwave Background Radiation, convinced most astronomers that the Big Bang theory was correct. For discovering the Cosmic Microwave Background Radiation, Penzias and Wilson were awarded the 1978 Nobel Prize in Physics.

After Penzias and Wilson found the Cosmic Microwave Background Radiation, astrophysicists began to study whether they could use its properties to study what the universe was like long ago. According to Big Bang theory, the radiation contained information on how matter was distributed over ten billion years ago, when the universe was only 500,000 years old.

At that time, stars and galaxies had not yet formed. The Universe consisted of a hot soup of electrons and atomic nuclei. These particles constantly collided with the photons that made up the background radiation, which then had a temperature of over 3000 C.

Soon after, the Universe expanded enough, and thus the background radiation cooled enough, so that the electrons could combine with the nuclei to form atoms. Because atoms were electrically neutral, the photons of the background radiation no longer collided with them.

When the first atoms formed, the universe had slight variations in density, which grew into the density variations we see today - galaxies and clusters. These density variations should have led to slight variations in the temperature of the background radiation, and these variations should still be detectable today. Scientists realized that they had an exciting possibility: by measuring the temperature variations of the Cosmic Microwave Background Radiation over different regions of the sky, they would have a direct measurement of the density variations in the early universe, over 10 billion years ago

Radiation from the Big Bang was demonstrably warmer at earlier times throughout the universe. Uniform cooling of the cosmic microwave background over billions of years is explainable only if the universe is experiencing a metric expansion, and excludes the possibility that we are near the unique center of an explosion.

One day When Penzias and Wilson reduced their data they found a low, steady, mysterious noise that persisted in their receiver. This residual noise was 100 times more intense than they had expected, was evenly spread over the sky, and was present day and night. They were certain that the radiation they detected on a wavelength of 7.35 centimeters did not come from the Earth, the Sun, or our galaxy  Both concluded that this noise was coming from outside our own galaxy—although they were not aware of any radio source that would account for it. just 60 km (37 mi) away, were preparing to search for microwave radiation in this region of the spectrum. Dicke and his colleagues reasoned that the Big Bang must have scattered not only the matter that condensed into galaxies but also must have released a tremendous blast of radiation. With the proper instrumentation, this radiation should be detectable, albeit as microwaves, due to a massive redshift.

its discovery is considered a landmark test of the Big Bang model of the universe. When the universe was young, before the formation of stars and planets, it was denser, much hotter, and filled with a uniform glow from a white-hot fog of hydrogen plasma. As the universe expanded, both the plasma and the radiation filling it grew cooler. When the universe cooled enough, protons and electrons combined to form neutral atoms. These atoms could no longer absorb the thermal radiation, and so the universe became transparent instead of being an opaque fog.

Interpreting the evidence

A summary of some of the evidence of the Big Bang and its interpretation

Evidence Interpretation

The light from other galaxies is red-shifted.

The other galaxies are moving away from us.

The further away the galaxy, the more its light is red-shifted.

The most likely explanation is that the whole universe is expanding. This supports the theory that the start of the universe could have been from a single explosion.

Cosmic Microwave Background

The relatively uniform background radiation is the remains of energy created just after the Big Bang.

3. Heavy elements

Astronomers are not only interested in the fate of the universe; they are also interested in understanding its present physical state. One question they try to answer is why the universe is primarily composed of hydrogen and helium, and what is responsible for the relatively small concentration of the heavier elements.

With the rise of nuclear physics in the 1930s and 40s, scientists started to try to explain the abundances of heavier elements by assuming they were synthesized out of primordial hydrogen in the early universe. In the late 1940s, American physicists George Gamow, Robert Herman, and Ralph Alpher realized that long ago, the universe was much hotter and denser. They made calculations to show whether nuclear reactions that took place at those higher temperatures could have created the heavy elements.

Unfortunately, with the exception of helium, they found that it was impossible to form heavier elements in any appreciable quantity. Today, we understand that heavy elements were synthesized either in the cores of stars or during supernovae, when a large dying star implodes. Gamow, Herman, and Alpher did realize, though, that if the universe were hotter and denser in the past, radiation should still be left over from the early universe. This radiation would have a well-defined spectrum (called a blackbody spectrum) that depends on its temperature. As the universe expanded, the spectrum of this light would have been redshifted to longer wavelengths, and the temperature associated with the spectrum would have decreased by a factor of over one thousand as the universe cooled.

4. Hubble’s law5. Primordial gas clouds (Wikipedia) 6. Galactic evolution and distribution (Wikipedia)