Chapter 15

MODERN COSMOLOGYWhat is cosmology?Cosmology is defined as the study of the entire Universe, including its origins and evolution with time.Cosmology has been the most difficult field of Astronomy to study observationally because of the vast distances and correspondingly faint and/or small apparent sizes of the individual objects of study.

Cosmology involves not only the study of individual galaxies and other objects, but also the characteristics of the cosmic microwave background radiationWhat is cosmic Microwave background radiation?The cosmic microwave background (CMB) was Discovered by the Hubble Space TelescopeOriginally discovered in the 1960sMapped out in 1990 at BerkleyEnergy waves (photons) left over from the original Big Bang in the form of microwavesThought to prove the Big bang theory

How old is the universe?The age of the Universe, until very recently, was not well established, but is now believed to be about 13.7 billion years, or about 3 times the age of our Solar System.

The Universe is thought to have originated in a point-like concentration (called a singularity) which began expanding outward in a big bang at the speed of light.

How did the universe begin?Option 1: Someone made the universe (Big Bang or creationist theory)

Option 2: The universe made itself (Inflationary or evolutionist theory)

Option 3: The universe has always been here (Steady State Theory)

Scientists now know that the cosmos had a beginning (due to proton decay and galactic motion) Therefore only options 1 and 2 are viable

The big bang theory (BBT)The current hypothesis concerning the origin of the Universe is that it started out from a point (or very compact) object, composed of pure energy, which exploded outward in a big bang at the speed of light, and has continued to expand outward at this speed ever since.

In the beginning13.7 billion years ago the Mass of the universe was the size of a head of a pin (called a singularity)Suddenly, an Unimaginable release of energy (an expansion- not a traditional explosion) occurred heating to trillions of degreesNobody knows how/why it happened (insert religion here)Release of energy Created space and time and the 4 main forces: gravity, strong, weak and electromagnetic forces.

How does the Bbt work?Stars (including our Sun) generate most of their energy by converting matter into energy by means of thermonuclear reactions (such as fusion of hydrogen to make helium and other, heavier elements).In the early Universe, the opposite process was at work, in which energy was converted into matter (elementary particles such as electrons, protons, and neutrons were converted into the light elements, hydrogen and helium).

Whats a red shift?Everything is made of elemental gases that emit specific wavelengths within the electromagnetic spectrum based on their chemical composition. Each gas emits certain wavelengths that are unique to that element. The combination of an objects elements which produce a pattern of spectral lines can be used to identify the object rather like a fingerprint or bar code.

The spectral lines of stars (and galaxies) coming towards Earth are shifted to the blue light end of the spectrum (shorter wavelength)

The spectral lines of stars (and galaxies) going away from Earth are shifted to red light end of the spectrum (longer wavelength)

Note: the objects themselves do not change color- just the spectral lines!

Red shift diagramRed shift is similar to doppler effect

What does red shift tell us?Blue Shift of Lightgalaxies moving toward us (contracting universe)Faster move toward us more blue-shiftedRed Shift of Lightgalaxies would be moving away from us (expanding universe)Faster move away from usmore redshifted

Since we see a red shift when we look at other galaxies, we know that they are moving away from us!However, we now know from the cmb that the galaxies are not moving on their own- space is carrying them away!Red shift animationWhen you click on the link below you will see a picture of the atomic spectra. The top half of the image will be your reference point. Slide the bar to the left or right to shift the spectra pictured on the lower half. Notice how the background image moves as a result of the shift in the spectra

Red Shift AnimationWhat does this all mean?Since we see galaxies redshifting, this means that the universe is still expanding!The rate of expansion, and its variation with time, are dependent on the total mass of the Universe.

observations of the redshifts of very distant galaxies have shown that the rate of expansion of the Universe is increasing with time, instead of decreasing with time, as previously assumed.

This can be explained only by the presence of previously unknown dark energy which uniformly permeates the entire Universe.These previously unknown contributions to the total mass and energy of the Universe constitute more than 95% of the total!

What is out there?

The cosmological principleThe cosmological principle states that the Universe is isotropic (homogeneous in its structure and distribution of galaxies)From this principle, we infer that there is not (to our current knowledge) a center or an edge of the Universe.

Therefore, no matter where we are located in the Universe, it will appear that we are at the center of the expansion, with generally uniform distributions of galaxies all around us

How will it all end?Existing theories include:The big freezeThe big ripThe big crunchmultiverseThe big freezeThis theory states that the universe will keep expanding until it is too cold to sustain life (essentially, the energy will be spread out so thin that there will be no heat)The big ripThis theory states that the universe will expand so rapidly that everything will get ripped apart. Dark energy is the culprit that will ultimately rip things apart.The big crunchThis theory states that at some point the universe will begin to collapse in on itself (blueshift) until it reaches a single point (singularity). Once it reaches that point the big bang will happen once again and the cycle will continue for eternity multiverseThis theory does not predict an end to the universe but suggests that there are many other universes that exist alongside our own.Other universes might appear like bubbles in water or parallel universes