Section 7.3

Hubble’s Ideas... Edwin Hubble (1889-1953)

An American astronomer One of the first to study galaxies Two of his major findings changed

astronomy (1918-1929)

1. Confirmed many other galaxies existed beyond the Milky Way

2. Found that almost all galaxies are moving away from each other

This meant that the universe is expanding!! (this was stated by a man named Lemaître)

But how?

How did Hubble do this? Measured the distance from Earth of 46

galaxies Measured the speed of their movement Collected light from the galaxies and

examined their light spectrums (spectra) Visible light spectrum: the rainbow band of

colours into which white light separates when it passes through a prism

Hubble’s work and ideas remain the foundation of modern understanding of the nature and origin of the universe

The Big Bang Theory

The REAL Big Bang Theory

What is it? One of the most remarkable theories of the

20th century States that the universe formed when an

infinitely dense point suddenly and rapidly expanded in a single moment NO EXPLOSION!! All matter and energy today was created during

the early minutes of the hot, rapid expansion

Credited to George Gamow and Ralph Alpher

The Big Bang Theory

Evidence for the BBT

Commonly accepted that universe formed 13.7 billion years ago Beginning of universe and SPACE and

TIME!! What Hubble saw:

Looking at light spectra, figured out each galaxy’s speed moving away from ours

He saw that the farther away the galaxy was, the faster it was moving away

Loads of “light” elements (H and He)

The Wave Nature of Light

Electromagnetic radiation: energy that travels in waves of varying lengths E.g.: light, radio waves, microwaves,

ultraviolet radiation, X-rays Visible light is E.R. we can see with our

eyes When it is split into a rainbow of colours, it’s

called the visible spectrum

Electromagnetic SpectrumFull range of E.R. organized by wavelength from very long to very short

The Wave Nature of Light

Wavelength of red light is longer than the wavelength for blue light

Spectroscope This is an optical instrument that separates

light into its spectral colours Helps astronomers analyse star light

The Wave Nature of Light

•Spectral Lines

• Look like a UPC/bar code

• Created when each gas that makes up a star absorbs some of the light energy• Each gas does

this differently, creating different lines

•We can see the spectral lines of H in the spectra of almost all celestial objects, meaning H is present throughout the universe

Red-Shifted Spectral Lines Spectral Shifting

The change in position of spectral lines to the left or right of where they normally are in the spectrum of a light source that is not moving Astronomers noticed that in all galaxies

Hubble was studying, spectral lines were shifted to the red end This meant that the light source and

observer are moving away from each other at a high speed!!

Picture the Waves...a) In this picture, the

duck sits still, creating even ripples on the water

b) As the ducks starts swimming, ripples behind stretch out (wavelength is longer)

c) This is how Hubble knew galaxies were moving away from earth (expanding); he measured light wavelengths emitted from a galaxy to see if and where it was moving

Seeing Shorter VS Longer Wavelengths

Red-Shifted Spectral Lines Hubble saw this red-shift pattern in

many galaxies Gave support to theory that space was

expanding! Keck telescope in Hawaii repeated

Hubble’s work with 60 000 galaxies instead of 46 Added to Hubble’s work

Learning Checkpoint

1. What is a spectrum?2. What is the name given to the generally

accepted scientific theory that describes the origin and evolution of the universe?

3. How is it possible to know that the element hydrogen exists throughout the universe?

4. How does the idea that space itself is expanding relate to the observation that the spectra from distant galaxies are red-shifted?

Using Microwaves to Map Cosmic Background Radiation Critical question related to BBT:

Where was the energy left over from formation of the universe? First bit of universe was HOT with short

waves Then universe cooled and waves

lengthened where did the extra energy go?

All space should have evidence of this radiation

More Evidence for BBT

1965 Arno Penzias and Robert Wilson made the big discovery (found the radiation) Cosmic background radiation

Energy left over from the massive split-sec expansion

1992 & 2006 Radiation Maps Maps of cosmic background radiation collected

from most distant parts of visible universe CBR found fits with predictions consistent with

BBT