04. big bang

big bang theory

• all current and past matter and energy, space, and time in the Universe came into existence at the same time

  • occurred roughly 13.8 billion years ago

• matter was compacted into a very small ball with infinite density + intense heat called a singularity

  • suddenly, singularity expanded → universe (as we know) began

edwin hubble & the red shift

• Hubble observed that light from almost all galaxies were red-shifted and hypothesised that galaxies are therefore moving away from us

• light in the form of visible light → moves away from us, light shifts towards red end of spectrum

  • similar to doppler effect

red shift

• light emitted from stars moves away – light shifts towards the red end of the spectrum

• concluded:

  • almost all galaxies in the universe are moving away from the Milky Way galaxy

  • the further away a galaxy is, the more light is red-shifted

    • the more distant galaxies are moving away from the Milky Way faster than closer galaxies are

cosmic microwave background radiation

• afterglow of Big Bang

• detected as low-frequency background signals coming equally from all directions

  • due to heat of Big Bang, most energy would have been emitted as high frequency radiation

steady state theory

• universe is infinite in size with no beginning or end despite expanding

  • galaxies seemed to be evenly distributed in space

• matter is continuously created to form new stars and galaxies

difference between theories

• steady-state cosmology

  • matter is constantly created as the Universe expands

• Big Bang cosmology

  • matter dilutes as the universe expands