B_The big Bang.ppt

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How the Universe got its

Spots

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Goals

• Where did the Universe come from? • Where is it going?

• How can we see the past?

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What do you think about

concepts like these?

• Nuclear reactions and the weak interaction _{Nuclear reactions and the weak interaction}the rules the rules that govern the universe are foreign by everyday

that govern the universe are foreign by everyday standards, but

standards, but there are still rulesthere are still rules; we can know them ; we can know them in detail, and use them to study other phenomena.

in detail, and use them to study other phenomena.

• Dark matter and dark energy_{Dark matter and dark energy} the universe is the universe is controlled on large scales by

controlled on large scales by entities unlike usentities unlike us; there ; there is no problem with this – it’s exciting, and probably is no problem with this – it’s exciting, and probably solvable.

solvable.

• Big bang theory _{Big bang theory}the universe is vast in space and the universe is vast in space and

time and evolves over time like our world does, but it time and evolves over time like our world does, but it is

is notnot beyond our ability to measure with precision! beyond our ability to measure with precision!

• Origin and evolution of life _{Origin and evolution of life}we appear to be we appear to be part of a part of a cosmic system

cosmic system, organized and tweaked chemically on , organized and tweaked chemically on Earth in a way that could have happened elsewhere Earth in a way that could have happened elsewhere too.

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The Future from the Past

• Is the Universe:

– Slowing down? – Speeding up?

– Staying the same velocity?

• In the past, was the Universe:

– Going faster? – Going slower?

– Going the same velocity?

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Time line: Cosmic Soup,

Radiation Era, Matter

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The Big Bang

• Big Bang: the event from which the Universe began expanding.

• Into what did the Universe expand? • Where was the Big Bang?

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Consequences

• If everything is moving away from us and things farther are moving faster

• Then the Universe is expanding!

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Expanding Universe

• Space itself is expanding, not matter flying apart within space.

• Examples:

– dots

– rubber band – raisin bread

– ants on a balloon

 It does not mean we are at the center

of the Universe

 every part of the Universe sees everything

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Looking Back in Time

• Remember it takes time for light to reach us

– travels at 300,000 km/s

– So we see things “as they were” some time ago

• The farther away, the further back in time we are looking

– 1 billion LY means looking 1 billion years back in time

• So the greater the redshift, the further back in time

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Big evidence for Big Bang

• 1992 COBE satellite :Cosmic Background Explorer satellite : Background radiation

• _{“it’s the discovery of the century, if not for all time…”} Stephen Hawking

• _{“the handwriting of God…”}

Dr. George Smoot, astrophysicist,

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Galactic Redshifts

• Edwin Hubble (1889-1953) and colleagues

– measured the spectra (light) of many galaxies – found nearly all galaxies are red-shifted

• Redshift (Z)

(Doppler effect) Z = v/c (for speeds approaching c,

we’ll need a relativistic version of this equation.)

rest rest    -= observed

Z Andromeda galaxy

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Redshift

Quasars & Cosmology

Department of Physics, Applied Physics & Astronomy, RPI

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Hubble’s Law

• Galaxies are moving away from us.

• The farther away the faster they go.

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Expanding Universe

• If galaxies are all moving away, then at some point they were all much closer.

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Look back Time

• We see everything as it once was.

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Age of the Universe

• Since all galaxies are moving away from us, how long has it been since all galaxies were together?

time = distance / velocity velocity = H_o x distance

time = distance / (H_o x distance) time = 1/H_o

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Luminosity and Distance

• Brightness goes as 1/D2_.

• Move light:

– 2x farther away, one quarter as bright. – 3x farther, one ninth as bright

– 10x farther, one hundredth as bright.

• If you know:

– How bright it looks

– How bright it SHOULD be

– You know how far away it must be.

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60s

Baby Boomer

Universe

90s

80s

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Density of the Universe

• Add up all the mass we see and _o = 0.01 • But we know there is some dark matter in

galaxies and clusters. • How much?

• Think ~10 x more dark matter than “light” matter.

• Cosmologists think _o < 0.3

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V

Distance (Lookback time) Present Past

Are We Slowing Down?

• In our experience, things slow down over time.

• Is the Universe slowing down at all?

• Plot distance versus velocity.

• Use supernovae as

“standard candles.”

– Distant supernovae (large lookback time). Accelerating

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Are We Slowing Down?

• Unseen mass making stars move fast:

Dark Matter

• Unseen energy

accelerating galaxies:

Dark Energy Slowing

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The End of the Universe

• Will the universe expand forever?

• Depends on the density of the Universe.

• Too big: Big Crunch – Closed Universe

– Bound Universe

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Some references

• John D. Barrow and Frank J. Tipler, The Anthropic

Cosmological Principle (New York: Oxford University Press, 1996)

• J. P. Moreland (ed.), The Creation Hypothesis (Downers Grove, Illinois: InterVarsity Press, 1994)

• Charles B. Thaxton, Walter L. Bradley, and Roger L. Olsen, The Mystery of Life’s Origin: Reassessing Current Theories (Dallas: Lewis and Stanley, 1992)

• Robert Shapiro, Origins: A skeptic’s guide to the creation of life on earth (New York: Summit Books, 1986)