Learning Goals: I will: 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. Learning 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?.

Disclaimer: This is a college lesson on theoretical astrophysics!! 

The End of the Universe

This will happen WAAAY SOONER!

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 Closed Universe Flat 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 of moving through space, but by space itself expanding…) This leads us to ask what is the shape of space-time, i.e., the curvature

The critical density: All observable matter  ~ 4% of ρc How the universe is “curved” depends on the density… The density which would make the universe flat is called the “critical density” ρc ρc ~ 9 x 10-30 g/cm3 (or 5 hydrogen atoms per cubic meter) ρ < ρc => open (not enough gravity) ρ > ρc => closed (too much gravity) All observable matter  ~ 4% of ρc

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?)

Origin and structure of the curvature: Inflation makes very specific predictions about the sizes of the fluctuations we on Earth should see in the CMBR… Inflation predicts these irregularities to be about 1o (in size) 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…

Flat Spacetime In essence, no curvature Infinite 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

Maybe it isn’t flat, but just appears that way…

https://www.youtube.com/watch?v=R5orcCuprG4

 In quantum mechanics, the vacuum itself should experience quantum fluctuations. In general relativity, those quantum fluctuations constitute energy that would add to the cosmological constant. However, this calculated vacuum energy density is many orders of magnitude bigger than the observed cosmological constant

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 H0 ~ 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

https://www.youtube.com/watch?v=4_aOIA-vyBo

How Many Years Until Heat Death of the Universe. 14,000,000,000 – Current age of the Universe

“What happens is you get just a quantum fluctuation that makes a tiny bubble of the vacuum the Universe really wants to be in. And because it's a lower-energy state, this bubble will then expand, basically at the speed of light, and sweep everything before it," the Fermi National Accelerator Laboratory theoretician said. “The universe wants to be in a different state, so eventually to realize that, a little bubble of what you might think of as an alternate universe will appear somewhere, and it will spread out and destroy us." Scary stuff. However, we need not panic for billions of years.

https://www.youtube.com/watch?v=ijFm6DxNVyI

Answer this Question of the Day Which of the four possible outcomes would you most like to have happen for the Universe and why?

Due Tomorrow at Midnight