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The Big BangThe Theory of Universe

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The Big Bang

• The universe begins~13.7 Billion years ago• The universe begins as the size

of a single atom• The universe began as a violent expansion

• All matter and space were created from a single point of pure energy in an

instant.

Image 1: Beginning of Big Bang

The Beginning of TimeThis lecture is the intellectual property of Professor S.W.Hawking. You may not reproduce, edit, translate, distribute, publish or host this document in any way with out the permission of Professor Hawking.

In this lecture, I would like to discuss whether time itself has a beginning, and whether it will have an end. All the evidence seems to indicate, that the universe has not existed forever, but that it had a beginning, about 15 billion years ago. This is probably the most remarkable discovery of modern cosmology. Yet it is now taken for granted. We are not yet certain whether the universe will have an end. When I gave a lecture in Japan, I was asked not to mention the possible re-collapse of the universe, because it might affect the stock market. However, I can re-assure anyone who is nervous about their investments that it is a bit early to sell: even if the universe does come to an end, it won't be for at least twenty billion years. By that time, maybe the GATT trade agreement will have come into effect.

The Quran on the Expanding Universe and the Big Bang Theory

A microwave map of the leftover from the Big Bang that gave birth to the universe. (Courtesy: NASA)

It is mentioned in the Quran:“He (God) is the Originator of the heavens and the earth…” (Quran 6:101)“Is not He who created the heavens and the earth Able to create the likes of them? Yes; and He is the Knowing Creator. His command is only when He intends a thing that He says to it, ‘Be,’ and it is.” (Quran 36:81-82)The above verses prove that the universe had a beginning, that God was behind its creation, and all that God needs to do inorder to create is to say “Be,” and it is. Could this be an explanation as to what triggered off the explosion that brought about the beginning of the universe?

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EXPANDING OF THE UNIVERSE

The space between galaxies expands, not the galaxies themselves; objects held together by their own gravity are always contained within a patch of nonexpanding space.Example: raisins in a loaf of bread.

As the dough rises, the overall loaf of bread expands; the space between raisins increases but the raisins themselves do not expand

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Dark Energy73%

Normal Matter4%

Dark Matter23%

Figure 1: Materials of Universe

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Evidence for Dark Energy - supernovae as distance indicators - step 1

Image 12: A dying star becomes a white dwarf.

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Evidence for Dark Energy - supernovae as distance indicators - step 2

Image 13: The white dwarf strips gas from its stellar companion….

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Evidence for Dark Energy - supernovae as distance indicators - step 3

Image 14: ….and uses it to become a hydrogen bomb. Bang!

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Evidence for Dark Energy - supernovae as distance indicators - step 4

Image 15: The explosion is as bright as an entire galaxy of stars….

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Evidence for Dark Energy - supernovae as distance indicators - step 5

Image 16: and can be seen in galaxies across the universe.

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How Everything Began~ Several hundred thousand yearsafter Big Bang

• ATOMS form (specifically Hydrogen and its isotopes with a small amount of Helium.)

• The early Universe was about 75% Hydrogen and 25% Helium. It is still almost the same today.

Figure 2: Atom Formation.

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~200 to 400 million years after Big Bang

• 1st stars and galaxies form

Image 17: ~200 to 400 million years after Big Bang

History of the Universe - gravitational waves are hypothesizedto arise from cosmic inflation, an expansion just after the BigBang

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Hubble’s Discovery

• Edwin Hubble’s observations of remote galaxies, and the redshift of their spectral lines (1924).

• Hubble noticed that the further away the galaxy, the greater the redshift of its spectral lines.

• This linear relationship is called Hubble’s Law.

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Redshift

•The wavelengths of the light emitted by distant objects is elongated as it travels to earth.

•Longer the light travels, the more it gets redshifted.

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Hubble’s Lawv = H0d

v = recessional velocity of the galaxy

H0 = Hubble constantD = distance of galaxy to earth

Galaxies are getting farther apart as time progresses, therefore the universe is expanding.

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Hubble’s Constant

•Expansion rate measured using Type 1A Supernovae.

•The age of the universe can be derived from Hubble’s constant:

•T0 = d T0 = 1 H0d H0

For example, if H0 = 73 km/s*Mpc, then

T0 = 13.4 Billion years old

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Age of Universe•Currently, after taking into account differences in expansion rate over time and our movement through space:

T0 ~ 13.7 ± 0.2 byo•Age of stars: ~13.4 byo ± 6%

Therefore, oldest stars are younger than the age of universe.

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Big Bang evidence

1) Universal expansion and Hubble’s Law2) 3 degree background radiation3) Quasars4) Radioactive decay5) Stellar formation and evolution6) Speed of light and stellar distances

1. Universal expansion and Hubble’s Lawa) Hubble observed the majority of galaxies are moving away from us and

each otherb) The farther, the faster they movec) Red Shift

2. Back ground radiation

a) Noise radiation (static) is evenly spread across space

b) The amount of radiation matched predictions

c) C.O.B.E satellite confirmed for the entire universe that noise radiation (static) is evenly spread

d) Law of conservation of energy (energy can neither be created or destroyed) – energy remains constant over time

3. Quasars - super large (solar system size) galactic cores that put out more light than whole galaxies

• Only found 10-15 billion light years away

• Found nowhere else• Nothing exists past them

6. Speed of light and stellar distances

• The speed of light is a universal constant of 300,000 km/s2

• We observe stars millions/billions of light-years away

• A light-year is the distance that light travels in 1 year – the light we see today from a star 500 light years away is 500 years old

• The furthest stars away are 10-15 billion light years away

• We have telescopes that can see further, but there isn’t anything viewable

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Conclusions – Till Now

• Big Bang model describes our current understanding of the universe.

• New discoveries, such as dark matter and accelerating expansion (Dark Energy), lead us to refine our model,

but there is no crisis in our understanding (yet).• Science is an ongoing process - forcing us to test our model

through prediction and observation. • The more tests it passes, the greater is our confidence in it.

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