Cosmology Past, present and future of the universe Is space flat or curved? Where is the center? What lies beyond our limit of vision? What is the universe expanding into? Did the physical laws exist prior to the Big Bang?

How old is the universe?

Globular Clusters Globular clusters are the oldest stellar objects observed that can be accurately dated Age of the globular clusters sets the minimum age for the universe The universe is older than these clusters

Where did the big bang occur? Everywhere It was an explosion of all space and time, NOT an explosion in space Since a singularity exploded and expanded, and the center of the singularity coincides with the singularity, the whole universe is just an enormous center

Space itself is expanding

Cannot really know Since we cannot see or find the edge of the center, we cannot determine the centroid (center of mass) of the center How does one find the center of this room? Look at the boundary walls and estimate the center What if one could not see the walls?

Other examples of disorientation Inside a tall cornfield In a whiteout blizzard

Cosmological redshift A wave of EM radiation, as it moves through the universe, will experience the same expansion as the universe As the wave travels farther and farther, it expands more and more By the time it is observed, it appears redshifted in proportion to the distance it has travelled

Background radiation The background radiation consists of X-ray and gamma-ray radiation that arose just after the big bang The wavelength of these shortwave radiations redshifted (expanded) as the universe expanded –The cosmological redshift The earliest of radiations has redshifted into the microwave portion of the universe

The microwave background radiation is the light from the oldest object in the universe – the universe itself

Cosmological Constant A factor used for adjusting how the universe expands Einstein’s thought it was his biggest blunder –He introduced the cosmological constant to make the universe stand still (static universe) Distant supernovae now suggest the value is not zero (like Einstein said!)

Distant supernovae now suggest that the universe is accelerating –Indicate motions that are slower than expected We do not know what causes it

Dark matter, dark energy Nearly 96% of the universe is invisible (does not glow like a star or galaxy) There may be enough dark matter to produce the critical density and halt the expansion of the universe Some say that the total of luminous and dark matter is at the critical density

The density of the universe determines if it will expand forever or stop expanding and collapse back on itself Not to worry – we won’t know for billions of years

Value of the critical density of the universe depends on the Hubble constant Critical density lies between the collapsing and expanding forever extremes

Hubble constant Somewhere between 50 and 75 We appear to be at the center of the Hubble flow Observers on all other galaxies also appear to be at the center of the Hubble flow All galaxies appear to be moving away from us Raisin cake analogy

Cosmological principle 2 assumptions Homogeneity and isotropy Homogeneity – one part of the universe is pretty much like any other part Isotropy – looks the same in all directions Therefore no edge and no center to the universe

Olber’s paradox Universe is homogeneous and isotropic If it is infinite in extent and unchanging in time, then the universe is uniformly populated with galaxies filled with stars Thus, one’s gaze should fall upon a star wherever one looked in the night sky and the night sky should be as bright as a star

However The universe is NOT infinite and it is expanding The expansion redshifts the starlight to longer wavelengths than the visible so distant stars cannot be seen by our eyes

Cosmological Redshift

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