The Big Bang Theory

The Big Bang Theory

About 14 billion years ago, the Universe was much smaller and hotter. In the 1960s, Robert Dicke predicted a remnant “glow” from the Big Bang. In 1965, radio astronomers Penzias and Wilson discovered that glow, named the cosmic microwave background radiation. The CBR was seen in all directions in empty space, with a black body curve (temperature ~3K). About 1 second after the Big Bang, the Universe was very hot, at ~1 billion K. At 3 minutes, protons and neutrons combine to form the nuclei of atoms. The hydrogen/ helium ratio (3:1) found today is about the same as what’s expected after the Big Bang. Atoms were “ionized” with electrons roaming free without being bound. At 300,000 years after the Big Bang, the Universe becomes transparent with a temperature of 3,000K. Light red-shifted by a factor of 1000.

Big Bang: Timeline

*Recent measurements show the Big Bang at 13.75 billion years ago. Scientists recently discovered dark energy; the Universe is not only expanding, but accelerating in expansion. So, earlier estimates of the age of the Universe at 15 billion years have been reduced to 13.75 billion years.

The Universe: Main Points

  1. Expansion of the Universe
  2. Cosmic Microwave Background
  3. Primordial Nucleosynthesis
  4. Evolution of Galaxies and Large Scale Structure Over 14 Billion Years

The Universe: Composition

  • 0.03% heavy elements
  • 0.3% neutrinos
  • 4% stars and gas
  • 25% dark matter
  • 70% dark energy
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Expansion of the Universe

Expansion of the Universe

Hubble’s Law, written by Edwin Hubble in the 1920s, describes the expansion of the Universe.

Edwin Hubble & Expansion of the Universe – Timeline

1917: Vesto Slipher discovered that the spectra of galaxies were almost always red shift (moving away). Infact, most galaxies are moving away and 2 out of 15 spirals moving at over 2 million miles per hour.

1929: Edwin Hubble derived distances to these galaxies and showed that implied recessional speed, v1, is proportional to its current distance from us

  • Hubble’s Law: V – H0d, where  H0 is Hubble’s constant (71 km·s –¹/Mpc), v is velocity, and d is distance
  • The value of Hubble’s constant is how fast the Universe is expanding now; if Hubble’s constant is bigger, the Universe is expanding faster

1927: Belgian astronomer, G. Lamaitre, had a similar result, proving that the Universe is expanding

  •  Combined Einstein’s theory of relativity with the redshifts of spiral galaxies
  • Published a paper on mathematical  super structure connecting redshifts and expanding Universe of general relativity, but nobody noticed since he was only an obscure Belgian priest and mathematician
  • Universe began as a single pinpoint, a primordial soup

1998: Acceleration of the expansion of the Universe is caused by “cosmic anti-gravity” or “dark energy” (still unexplained)

Measuring Velocities of Red Shift

  • Light of a galaxy moving away from us will be “red-shifted,” or the wavelength gets longer
  • Light of a galaxy moving toward us will be “blue-shifted,” or the wavelength gets shorter
  • The faster the speed galaxies travel, the more the “red-shift”
  • Objects at the edges of galaxies tend to move faster than objects in the centers

Understanding the Expansion

  • Galaxies are all moving away from us: Does that mean we are at the center of the Universe?
    • No. There is “no” center. All points in space claim to be the center
    • e.g. Raisin bread rising: raising don’t expand, the space between them expands

Olbers’ Paradox— Why is the night sky dark?

  • In the 19th century, astronomer Wilhelm Olbers asked: If the Universe is finite, why isn’t the sky bright from starlight?
  • The solution is not that stars are increasing far away, but that the apparent brightness of a star decreases (1/d²), the area of shells of stars surrounding the Earth increases like d², so the effects cancel out
  • Another solution was that the Universe has finite size, so that not all of the light from all the stars has had time to reach us (Universe expanding); the Universe is 14 billion years old, and we only see “out” 14 billion light years distance from us