The Big Bang Theory
Unit: Space
Birth of a Theory
• Hypothesis: Educated Guess.
• Theory: Hypothesis that’s supported by
consistent results & experimentation.
• Scientific Law: A rule that correctly describes a
natural phenomenon; well established theory.
Light & the Doppler
Effect
•Spectrum: Rainbow of colors
passing through a glass prism.
(spectra)
•Wavelength: Distance from
crest of wave to crest of next
wave.
•Each color spectrum has
a wavelength.
•Light passes through
prism  each
wavelength is bent dif.,
resulting in spectrum.
Bright-Line
Spectrum:
• Series of thin colored lines spaced at uneven
intervals.
• Elements produce bright-line spectrums when
heated.
• Every element has a unique bright-line
spectrum.
Doppler Effect:
- Used to determine an objects speed
relative to an observer.
Doppler Effect: (continued)
Blue Shifting
Red Shifting
• Light/object moving toward
observer 
- shorter appearance of
wavelength.
- shift to shorter wavelength,
blue end of
spectrum; “Blue Shifting.”
• Light/object moving away from
observer 
- longer appearance of wavelength
- shift to longer wavelength, red
end of
spectrum; “Red Shifting.”
Doppler Effect: (continued)
• The faster the light
source, the
greater the
spectrum shift.
http://hea-www.harvard.edu/~efortin/thesis/html/doppler.html
Evidence
Spectroscopes
• Used to determine what elements are in stars.
• Separates light into a spectrum of colors &
wavelengths.
• Dif. chem. elements emit light of dif. colors when
heated, so astronomers use this to examine light
given off by stars (like the sun), when using
spectroscopes.
• By determining the dif. colors of light emitted by
a star, you can determine what elements it
contains, it’s age, & it’s inside temp.
Spectroscope Evidence
• Starlight spectra gives us info. about Universe.
• Spectra of most galaxies (large systems of stars) show a
shift toward red end of spectrum (Red Shift), indicating
that almost all galaxies in universe are moving away
from Earth.
• By examining degree of red shift, determine speed of
traveling galaxies. Farthest galaxies, moving the fastest
(most red shift).
• Conclusion, Universe is expanding= Big Bang Theory
Background Radiation Evidence
• Using radio telescopes, scientists detected low
levels of energy (Background radiation),
evenly distributed throughout the universe.
• The presence of evenly distributed energy
convinced most scientists that the Big Bang
Theory was correct.
Big Bang Theory Explained
• Billions of yrs ago, all matter & energy was
compressed into extremely small volume.
• About 18 b.y.a. an event (Big Bang- cause:
Gravity) sent all matter & energy outward in a
giant cloud.
• As cloud expanded, some matter gathered into
clumps, galaxies evolved.
• Today the universe is still expanding & galaxies
continue to move away from each other, causing
the red shift in the spectra of galaxies.
Big Bang Theory:
• All stars in universe appear to be moving away
from same point. (balloon example)
• This is due to Doppler shifts (red/blue) in light
emitted by stars, the distribution of stars
throughout the universe, & the discovery of
background radiation.
Misconception
Galaxies are Not flying away from us,
the space between them is growing
Limitations of the Big Bang Theory:
• Does not explain formation of galaxies, stars,
etc.
• Can’t explain very early universe.
• Doesn’t answer where universe came from or
what came “before” it.
End of the Universe:
Two major Theories
Heat Death
Steady State
• the universe will stop
expanding and
everything will cool
down to a temp. where
no work can be done
• the universe will stop
expanding and collapse
upon itself and start
over with a new Big
Bang