THE ACCELERATING UNIVERSE A.Rahman Mohtasebzadeh (11/16/2012)

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Content

• Cosmology through ages

• Basic Concepts

• Nobel Prize in Physics (2011)

• Conclusion

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“Twinkle twinkle little star, how I wonder where you are..”

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Figure 1

“Twinkle twinkle little star, how I wonder where you are..”

• Egyptian (~1534 BC)

• Greek (~300 BC)

•  Indian (~200 BC)

• Chinese (~180 BC) SN185 (Chinese calendar)

• Persian/Islamic (11 century) (Persian calendar)

• European (16 century)

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Redshift • Doppler Effect and Redshift

Doppler effect causes the wave to be stretched

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Figure 2

Redshift • Doppler Effect and Redshift

Doppler effect causes the wave to be stretched

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Figure 3

The displacement of spectral lines toward longer wavelengths (the red end of the spectrum).

Redshift • Doppler Effect and Redshift

Doppler effect causes the wave to be stretched Observed wavelength

Emitted wavelength

In 1916 Vesto Slipher Measured velocities to nearby galaxies, and discovered they were all moving away from us. He studied the spectra of light that is coming from the galaxies. And observed that their lights are stretched. But how did he do that ?.....

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Standard Candle

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Figure 4

Standard Candle

• Stellar brightness is quantified using �visual magnitude� scale

• Hipparchus ranked stars from 1 to 6: 1 being the brightest in the sky, 6 the dimmest (with unaided eye)

• Now we quantify magnitude:

where m is apparent magnitude, d is distance, and M is the absolute magnitude--the brightness of the object from a distance of 10 parsecs (pc)

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m = M + 5 • logd

10 pc"

# $ $

%

& ' '

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Standard Candle •  In 1929, Hubble used brightest stars to measure the

distance to the nearest galaxies

• He assumed that the brightest stars are all the same brightness

•  The faster the galaxy was moving, the fainter the stars!

• Easy way to imagine expanding universe

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The expanding Universe

NOW time (t1) FUTURE time (t2)

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Figure 7

The expanding Universe

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Standard Candle

•  The most distant objects are speeding away from us

•  The error of factor 10 ! Because he didn’t have well measuring equipment

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Figure 5

Standard Candle

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Figure 6

Einstein’s Theory of General Relativity

•  1905 – published equations of general relativity

• Gravity and acceleration are equivalent – Curvature of Space – Dynamic Universe (cosmological constant)

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Figure 8

Einstein’s Theory of General Relativity Left-Hand Side = Right-Hand Side Curvature = Energy-Momentum Gµν + Λgµν = 8πGTµν

What can contribute to Energy-Momentum?????? "the greatest blunder of my life"

If we weight the universe we can understand it’s shape!!

The Cosmological Constant

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Einstein’s Theory of General Relativity

By measuring all these masses we can measure how much stuff are in the universe

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Figure 9

Einstein’s Theory of General Relativity In the first case, there is enough mass to slow down and stop the present expansion. The universe is not infinite, but has no boundaries (you can picture it as a sphere, you cannot call any point on the surface of the sphere an end). Eventually, the universe will collapse producing what we call Big Crunch. (closed) In the second case, there is not enough mass to stop the expansion. The universe will expand forever and has no boundaries. (open) In the third case, there is exactly enough mass to stop the expansion, after an infinite amount of time. In other words, the universe will expand forever and has no boundaries. (flat)

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Figure 11

Einstein’s Theory of General Relativity

• Ω total amount of stuff in the universe

• Ωm = matter density

• ΩΛ = “dark energy” density

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Figure 10

Three possible cases for the universe

•  If Ωm>1 , ΩΛ=0 means the universe is dominant by mass, such a universe decelerates.

•  If 0<Ωm<1 , ΩΛ>0 means the universe is dominant by

unknown stuff (“dark energy”) and accelerates

•  If Ωm=1 , ΩΛ=0 means universe is moving with a constant speed and it’s flat.

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Nobel Prize-Physics 2011 •  The Supernova Cosmology Project (SCP) was initiated in 1988 by

Saul Perlmutter of Lawrence Berkeley National Laboratory (LBNL), USA.

•  Another team leaded by Brian Schmidt of the Mount Stromlo Observatory in Australia and Adam Reiss from University of John Hopkins in Maryland, USA.

Saul Perlmutter Brian Schmidt Adam Reiss

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Supernovae • Extremely luminous fireworks in the universe. Happen few

once or twice per century in a galaxy, when a star runs out of fuel. •  Supernova Type Ia •  In a binary system when

when one star feeds the dwarf star with it’s fuel, until dwarf star reaches critical mass (1.4 Mass of the sun) or Chandrasekhar limit.

•  For Type Ia supernova,

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M ≈ −19.3

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Figure 12

Hunting Supernovae Type Ia

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Figure 13

Observation Results

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Figure 14

Observation Results

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Figure 15

Conclusion •  The study of distant supernovae constitutes a crucial

contribution to cosmology.

•  This will lead us to further understanding of our strange universe and will help us answer many cosmological related questions

• A good foundation for further understanding “dark energy” and “dark matter”

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Resources •  http://www.physicsoftheuniverse.com/

topics_bigbang_accelerating.html •  http://atramateria.com/the-shape-of-the-universe/ •  http://www.spaceandmotion.com/cosmology-history-

astronomy-universe-space.htm •  http://www.youtube.com/watch?

feature=endscreen&NR=1&v=qMawNji-sXo •  http://www.nobelprize.org/nobel_prizes/physics/laureates/

2011/perlmutter-lecture.html

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Thank you !

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