12Physics - Hubble's Law + Big Bang Theory

geocentric model

earth at the centre of the universe

heliocentric model

sun the centre of our solar system and earth orbits the sun

steady state theory

* universe has always existed - no beginning and end
* universe doesn’t change in appearance over time
* universe expanding constantly and creating matter

big bang theory

* all matter in the universe was created in one big bang at a particular time
* universe is expanding but no new matter or energy being created

Hubble’s law

the more distant the galaxy the faster the galaxy recedes

what does Hubble’s law show?

evidence for an expanding universe

how to measure the distance of a star?

knowing its brightness and luminosity

luminosity

measure of radiated electromagnetic power

cepheid variable stars

star that pulses in brightness with a well-defined stable period and amplitude

how did Hubble measure the velocity of galaxies?

doppler effect. thought since sound waves change wavelength and frequency when sound source is moving, light waves also change wavelength and frequency

source moving away from observer

* wavelength increase
* frequency decrease
* red shift

source moving towards observer

* wavelength decrease
* frequency increase
* blue shift

red shifted light

galaxy moving away from earth

blue shifted light

galaxy moving towards earth

red shift not due to recessional velocity of galaxies, BUT instead…

due to the expansion of space itself

what happens to wavelength and frequency during the expansion of space?

photon frequency decrease and wavelength increase

why do photons from distant galaxies undergo greater red shift?

takes more time for photon to reach earth and in that time the universe has expanded more

if the universe is expanding…

universe must’ve been smaller than it is now and must have a starting age

Big bang

expansion of hot dense universe into a less dense cooler universe

evidence of an expanding universe that started life very small, highly dense and hot

abundance of light elements

cosmic microwave background radiation (CMB)

record of the oldest electromagnetic radiation emitted in the universe when photons first escaped the plasma

Hubble’s constant

70km/sMpc