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
Expansion of the Universe
Cosmic Microwave Background
Evolution of Galaxies and Large Scale Structure Over 14 Billion Years
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