Unit 1 spaceship earth
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Unit 1 – Spaceship Earth. Hypothesis vs. Theory. Theory vs. Hypothesis. Hypothesis. What is a hypothesis: Is a guess as to why something happens A creative idea as to how a scientific event or entity came to be, based on a number of logical assumptions.

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Unit 1 spaceship earth

Unit 1 – Spaceship Earth

Hypothesis vs. Theory


  • What is a hypothesis:

    • Is a guess as to why something happens

    • A creative idea as to how a scientific event or entity came to be, based on a number of logical assumptions.

  • There is no scientific basis for a hypothesis, but the idea comes from logical assumptions.

  • In attempting to answer a question about the nature of the world, a scientist will form a hypothesis (or a guess) regarding the question's answer.


  • What is a theory?


  • An idea that results when a hypothesis is supported by observation and scientific inquiry.

The big bang
The Big Bang!

  • A widely held scientific theory that contends the creation of the universe, the Milky Way, and our solar system resulted from a violent explosion of matter.

  • Let’s look at how it went from hypothesis to theory.

1922 edwin hubble
1922 Edwin Hubble

  • Observed the universe was expanding

  • Calculated that the universe is expanding at 40,000 km/s

  • Picture of the M32 Galaxy

Hubble s law
Hubble’s Law

  • The velocity at which a galaxy is moving away from us is proportional to the distance of the galaxy from us.

    • If galaxy B is twice as far away as galaxy A, then it is receding twice as fast as galaxy A.

  • Basically, if the universe is expanding, then it is logical to assume that it was once infinitely smaller.

Georges lemaitre
Georges Lemaitre

Cosmic Egg

Belgian Astronomer

Albert einstein
Albert Einstein

  • Hypothesized that this cosmic egg exploded with such violence that its fragments are still flying out from the centre of the explosion billions of years later

Hair stylist

George gamow
George Gamow

1940s coined “Big Bang”

  • He hypothesized that the radiation that accompanied the explosion would still exist. Radio-wave radiation comes from all parts of the universe.

Russian Physicist

Arno penzias robert wilson
ArnoPenzias & Robert Wilson

1964 arno penzias robert wilson
1964 ArnoPenzias & Robert Wilson

  • Found the radio wave background radiation. Most astronomers believe that this is sufficient evidence to move the big bang from the category of hypothesis to that of a theory.

  • This occurred 15-20 billion years ago

    *Most astronomers accept that this is sufficient evidence to move big bang from the category of hypothesis to that of a theory!


  • Formed from giant eddies in the swirling cloud of dust after the explosion.

Solar systems
Solar Systems

  • Formed from smaller sub-eddies that formed in the bigger eddies

Hypothesis vs theory

  • Was formed as the gravitational pull of denser material at the centre of each sub-eddy drew matter inward until radioactive elements began to produce huge amounts of energy through thermonuclear fusion.


  • Formed from the 5% of the swirling cloud that was left after the stars were created.


  • Leftover chunks of material that were too small to form into planets

Hypothesis vs theory

Our Place in the Universe

Our study of Astronomy requires us to look UP and not DOWN. Humans today are not used to looking UP, we are not used to observing the sky – it appears to be of little use – and city living with its extensive light pollution often prevents us from seeing, and hence exploring, the “heavens”.

Most of us have some awareness that we are part of a system of planets encircling a star we call the Sun, and that we are part of a galaxy called the Milky Way, but beyond that our knowledge is often sketchy, cloudy, or even just plain wrong.

Hypothesis vs theory

The next picture slide summarizes our location within the Universe, something that can be briefly summarized as:

  • Earth– we all live somewhere on the surface of this spherical body we call Earth

  • Solar System – Earth is part of a system of different planets (in fact, Earth is the third planet out from the Sun) which all orbit a star (the Sun) in the same direction and almost all in the same plane in space

  • Milky Way Galaxy – our Solar System is part of a huge collection of stars (and dust and gas) known as a galaxy, which we humans have named the Milky Way

  • Local Group – galaxies (and there are billions in the Universe) tend to congregate in groups or clusters and our group is known as the local group

Hypothesis vs theory

  • Local Universe, something that can be briefly summarized as:Supercluster – groups of galaxies congregate in larger groups known as superclusters; thus, our local group belongs to the local supercluster

  • Universe– finally, all the superclusters comprise the Universe; as far as we know there are no other universes (we can’t even “see” to the edge of our own universe) although some science fiction writers have speculated about this notion