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• Light/object moving toward

observer - shorter appearance of

wavelength. - shift to shorter

wavelength, blue end of spectrum; “Blue Shifting.”

Red 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.

PAST UNIVERSE

- Compressed, Spaced closer together.

- Hotter; only protons & electrons were

present

End of the Universe:Two major Theories

Heat Death

• the universe will stop expanding and everything will cool down to a temp. where no work can be done

Steady State

• the universe will stop expanding and collapse upon itself and start over with a new Big Bang

If we ever understand how quantum & gravity work together, we will have unlocked the secret of the creation of the universe.