Learnin g Goals: I will: understand the properties of different types of galaxies. understand how the universe come to be what we observe today. understand how astronomers use astronomical objects (standard candles) as a distance ladder to estimate the size of the universe and to measure large distances in the universe. understand how astronomers determine the age and size of the universe?. 4. Complex Knowledge: demonstrations of learning that go above and above and beyond what was explicitly taught. 3. Knowledge: meeting the learning goals and expectations. 2. Foundational knowledge: simpler procedures, isolated details, vocabulary. 1. Limited knowledge: know very little details but working toward a higher level.

5/5/16 What is the most distant thing we can see? What is the oldest thing we can see?

FYI: Seniors The ABSOLUTE last day I will accept a single piece of late work from a senior is tomorrow. Don’t even try to turn it in after tomorrow. If you are absent tomorrow…bummer for you, it goes in as a 40 percent!

Disclaimer: This is a college lesson on theoretical astrophysics!! This is the last lesson of “new” material for seniors

WMAP data reveals that its contents include 4.6% atoms, the building blocks of stars and planets. Dark matter comprises 23% of the universe. This matter, different from atoms, does not emit or absorb light. It has only been detected indirectly by its gravity. 72% of the universe, is composed of "dark energy", that acts as a sort of an anti-gravity. This energy, distinct from dark matter, is responsible for the present-day acceleration of the universal expansion. WMAP data is accurate to two digits, so the total of these numbers is not 100%. This reflects the current limits of WMAP's ability to define Dark Matter and Dark Energy.

Fates of the Universe Depends on density of the universe, which also determines its geometry (curvature) Gravity Pulling in –Matter and Dark Matter vs. Anti-Gravity Pushing out –Dark Energy Questions to we need to ask –Which is stronger? In or out –Will Dark Energy Last forever? –Will Dark Energy Increase? –Will there be yet some other force involved?

Fates of the Universe Open Universe –Big Rip Closed Universe –Big Crunch Flat Universe –Big Freeze

The shape of space and time: On the whole, the universe looks the same in every direction (with the exception of local variations) – “isotropic” And also uniform – “homogeneous” Isotropy + homogeneity  “ cosmological principle ”  Any observer sees the same general features If you accept this, then there can be no edge, and no center (The redshifts of very distant objects are produced, not by the Doppler effect, but by space itself expanding…) This leads us to ask what is the shape of space-time, i.e., the curvature

The critical density: How the universe is “curved” depends on the density… The density which would make the universe flat is called the “critical density” ρ c ρ c ~ 9 x g/cm 3 ρ open (not enough gravity) ρ > ρ c => closed (too much gravity) All observable matter  ~ 4% of ρ c

Open Spacetime If the density of the universe is less than the critical density then the geometry of space is open (infinite), and negatively curved like the surface of a saddle. This implies that initially parallel photon paths diverge slowly, slowly becoming farther and farther apart After enough time, everything will be moving away from each other faster and faster in what is known as the Big Rip!  Negative curvature  Infinite in extent  Will expand forever

Closed Spacetime If the density of the universe exceeds the critical density: then the geometry of space is closed and positively curved like the surface of a sphere. –This implies that initially parallel photon paths converge slowly, eventually cross, and return back to their starting point (if the universe lasts long enough). After enough time the universe will collapse in on itself in the Big Crunch!  Positive curvature  Finite  Will collapse (big crunch/oscillate?)

Curvature: Three possibilities: Open  Negative curvature  Infinite in extent  Will expand forever Closed  Positive curvature  Finite  Will collapse (big crunch/oscillate?) Flat  In essence, no curvature  Infinite  Expansion will stop at t = infinity Open, closed, or flat?:

Flat Spacetime If the density of the universe exactly equals the critical density then the geometry of the universe is flat like a sheet of paper, and infinite in extent. –This implies that initially parallel photon paths will stay parallel forever Expand Forever After enough time, everything will be moving away from each having no more interactions until all energy has been used up, this is known as heat death, or “The Big Freeze” The simplest version of the inflation theory, predicts that the density of the universe is very close to the critical density, and that the geometry of the universe is flat  In essence, no curvature  Infinite  Expansion will stop at t = infinity

Wormholes:

Inflation makes very specific predictions about the sizes of the fluctuations we on Earth should see in the CMBR… WMAP mapped the CMBR at high accuracy  reveals small irregularities If these irregularities were produced by inflation, then the size of them depends on the speed of the universe at the time of recombination… Inflation predicts these irregularities to be about 1 o if the universe is flat, smaller if open, and larger if closed… Origin and structure of the curvature:

Predictions of inflation in the three panels to the left, the observed CMBR in the last panel Observations fit well with a flat universe (which is exactly what inflation did… it “flattened” the curvature of space-time!) This also indirectly confirms dark energy and acceleration…

Read the article at your table

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Latest analysis of the properties of the universe: AN OVERVIEW Seems to be flat Accelerating Will expand forever Age: 13.7 billion years 4% baryonic matter 23% dark matter 73% dark energy H 0 ~ 71 km/s/Mpc Inflation on strong ground Cosmological constant supported, but quintessence not entirely ruled out Dark matter is mostly of the “cold” variety in order to clump and produce the universe we see today

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Final Question of the Day Which of the three possible outcomes would you most like to have happen for the Universe and why?

Origin and structure of the curvature: Study the distribution of galaxies, “large scale structure” Measure distance & position and plot the results (i.e., create a map of the universe) Seems like the universe tends to cluster along filamentary structures… This presents a puzzle… The CMBR seems to be uniform (corresponds to the time of recombination – the universe was uniform then)… The look-back time to the farthest galaxies is 93% of the way back to the beginning… How did this uniform gas coagulate so quickly to form galaxies and the structure we see? Why filaments? The Two-Degree-Field (2DF) survey mapped the position and distance of ~ 250,000 galaxies and 30,000 quasars Analysis of the distribution also confirms the acceleration independent of the Type Ia’s and that of Chandra…

Theoretical models of large-scale structure: Quantum fluctuations in space would have been stretched and enhanced at the time of inflation  filaments

Origin and structure of the curvature: Graphically, the data also fit well with predictions of a flat universe…

The modern picture:

Evidence of the Big Bang 1. The expansion of the universe Edwin Hubble's 1929 observation that galaxies were generally receding from us provided the first clue that the Big Bang theory might be right.

Evidence of the Big Bang 2. The abundance of the light elements H, He, Li The Big Bang theory predicts that these light elements should have been fused from protons and neutrons in the first few minutes after the Big Bang. Predicted abundance of elements heavier than hydrogen, as a function of the density of baryons in the universe (expressed in terms of the fraction of critical density in baryons, Omega_B and the Hubble constant)

Evidence of the Big Bang 3. The cosmic microwave background (CMB) radiation The early universe should have been very hot. The cosmic microwave background radiation is the remnant heat leftover from the Big Bang.

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