Science Flashcards
What is Cosmology?
Cosmology is the study of the origin, evolution and the ultimate fate of the universe
How did the universe begin?
Today, the most widely postulated theory is the Big Bang theory
What is the Big Bang theory?
Lemaître (1931-33) first proposed that the expansion of the universe started by singular, “something”
Big Bang theory
- Universe formed as the result of a violent ‘cosmic bomb’
- All the concentrated matter of the universe expanded outwardly as a hot gas to form both space and time
- The hot gas condensed to form stars and galaxies
- Galaxies eventually separated and are still moving away from us today
Hubble’s Law
The further away a galaxy is, the faster it is receding.
Big Bang may have had two distinct periods
- Inflationary Period
Very rapid period of expansion immediately following the start of the BigBang and all the energy and matter in the universe was created
- Post-Inflationary period (today)
the universe continued to expand in a “coasting” fashion and continues like this to this day
What existed before the Big Bang?
In theory, this question is illogical! The Big Bang theory assumes that this singular event was responsible for the creation of both space and time. Hence, we cannot really talk about what existed before it
What is Astrobiology?
Astrobiology is the interdisciplinary study of the origin, evolution, dispersion and future of life in the universe (NASA definition)
3 Astrobiology Epochs
- Cosmic evolution of biogenic compounds
- Prebiotic evolution involving the synthesis of increasingly complex biogenic compounds e.g. amino acids
- The evolution of simple unicellular organisms (from precursor biogenic molecules) and the continued evolution to increasingly advanced life forms
Give a credible, scientific definition of life
The ability to sustain metabolism, reproduce, and evolve
The absence of death
Explain the concept of Habitability Zones
These are zones around stars where the probability of finding life is elevated (“The Goldilocks Zone”)
For example
Massive stars have short main sequence lives, hence organisms may not have sufficient time to evolve.
Likewise, Low mass stars may not provide enough luminosity to maintain liquid water (there may be exceptions).
Explain the rudiments of prebiotic chemistry on earth, i.e. how simple molecules (carbon monoxide, carbon dioxide, molecular hydrogen and nitrogen, methane, ammonia) were processed by liquid water to eventually form amino acids
Prebiotic chemistry probably consisted of 3 levels
- The simple molecules like CO, CO2, NH3, H2O, H2, N2 and CH4 must have existed
- These then combined to compounds like formaldehyde (CH2O) and hydrogen cyanide (HCN), with the input of energy like radiation and heat from the Sun or heat from geological processes
- For level 3 compounds to form, bond energy was sufficient
Why was carbon dioxide important for the emergence and evolution of life on Earth?
- The early Earth was much colder than it is today as the Sun’s luminosity in its first 1 Ga was ~30% less than it is today
- CO2 compensated for the Sun’s initial low luminosity by creating a stable “greenhouse effect” which sustained liquid water, a key ingredient of life
- CO2 came from two main reservoirs
- Volcanic emissions
- Cometary bombardment
Summarize one theory, which accounts for the extinction of dinosaurs (and many other species) some 65 Ma ago
- Dinosaurs ruled the Earth for 135 Ma
- Most dinosaur extinction theories are cataclysmic/catastrophic
- Most popular theory (1980) suggests that an asteroid impacted the Earth at 64,000 km h-1 (1,778 m s-1, ≈5 Mach)
- It generated an enormous ejecta cloud that exploded outward
- There were tsunami’s
- The sky turned red and the heat generated burnt biomass and generated plumes of black smoke
- The sky cooled down after about an hour but remained black for many months
- The light loss produced freezing conditions and ceased much photosynthesis for perhaps three years…
What happened to Mars’ liquid water?
Mars is much smaller than Earth (circa half its diameter) and this has some important implications
- It has a lower gravitational field (35% of Earth’s), which allows liquid water to evaporate into interplanetary space. In this way, the Martian surface has become desiccated over time
- Small bodies lose internal heat more rapidly than larger bodies and internal heat powers geological activity.
Hence, Mars now has much less activity (volcanoes, earthquakes, etc.) than Earth that could melt water ice on or just below its surface
Summarize the three strands of evidence, which were originally presented by scientists proposing that the Martian meteorite, Allan Hills 84001, contains ancient evidence of life on the Red Planet
Mineral grains akin to those made by Earth bacteria
Within carbonate minerals, there are grains of iron oxide mineral magnetite (Fe3O4) and iron sulfide similar to some produced by bacteria on Earth and used as compasses to align themselves with the magnetic field. Note that similar grains can grow abiotically
Polycyclic aromatic hydrocarbons (PAHs), organic molecules that might be from decomposed organisms
Within carbonate globules are PAHs, ring compounds associated with the burning or decomposition of plants/animals. However, PAHs can also be synthesized abiotically
Objects that have comparable sizes and shapes to Earth bacteria
Rod-like objects on surfaces of carbonate globules were interpreted as fossilized bacterial colonies. They are ~0.01-0.1 µm long unlike Earth bacteria, which are generally >> 0.5 µm. However, “nanobacteria” have recently been discovered on Earth
Are there other theories about the origin of the universe?
No, but the “flawed” steady-state theory of Fred Hoyle et al. (1948) was, historically, a competitor
- It asserts that the universe has always existed and always will and that it is expanding
- Small amounts of matter are produced every year to support steady-state (~ 1 hydrogen atom per m3 per 109 years plus dark matter
- The theory is generally rejected by Cosmologists for several reasons, e.g. It fails to explain the 2.7 K CMB continuum
What evidence is there for the Big Bang theory?
The expansion of the universe
The expansion of the universe as deduced by observations of distant galaxies (“recession”) by Edwin Hubble and astronomers ever since
The 2.7 K Cosmic Microwave Background Radiation
- The Big Bang was a violent cosmic bomb
- We can observe the “cooled down remnant” of this fireball throughout the universe today as the CMB, a faint signal of the infant universe peaking in the microwave part of the spectrum
- Not perfectly isotropic
- CMB essentially identical to the theoretical spectrum calculated for a perfect radiator (perfect black body)
The nuclear abundances
The abundances of nuclei predicted by the Big Bang seem, at least superficially, to be in overall agreement with the nuclei we observe in the universe today
- Nuclear physicists can calculate how much hydrogen (H), helium (He) and deuterium were formed in the first three minutes after the Big Bang
- We can combine this work with the theory of the hot expanding universe to predict the types of elements produced
How old is the universe?
The universe is ~ 13.7 Ga
By measuring the rate of expansion of the universe and extrapolating it back to the start of the Big Bang, e.g. using the WMAP
The universe is ~ 11-18 Ga
By observing the oldest stars, they can give a lower limit to the age of the universe
Will the universe continue expanding forever?
The universe may stop expanding if there is enough matter in the universe (Critical Density)
- The galaxies are moving apart but their mutual gravities are trying to pull them together
- At some point in the future, the universe may stop expanding and start contracting (the “Big Crunch”)
What is Critical Density?
CD is a theoretical value at which the universe should cease expanding, stop, and then contract
Will CD affect the ultimate fate of the universe?
The critical density of the universe has not been established as astronomers can only observe a modest proportion of the total matter in the cosmos. This is because of dark matter (“missing matter”), which are bodies that are inferred to exist but appear invisible to astronomical detectors
What is dark matter?
= Matter assumed to exist but not directly observable (“dark”)
The precise composition of Dark Matter is still debated hotly in the astrophysics community but may include
- The elusive neutrino
- MACHOS (unobserved brown dwarfs, planets, mini galaxies, etc.)
- WIMPS (exotic particles)
- Other exotic contenders
Explanation
Astronomers could not explain the very rapid rotation of galaxies. Milky Way was behaving as if it was ten times more massive. A way of explaining these rapid motions is the existence of “Dark Matter”.
In the standard model of cosmology, data claims that:
26.8% = dark matter
What is Dark Energy?
Dark energy is a poorly characterized type of energy that is omnipresent in the universe and may explain the rate of expansion of the universe that we observe today
Explanation
Many cosmologists have argued that dark matter alone, cannot account for recent observational data and models of the geometry and total mass in the universe. The universe’s expansion is accelerating and dark energy can help explain this
• 68.3% = dark energy
Why was O2 (“free oxygen”) important for the evolution of life on Earth?
- Free oxygen (O2) was initially scarce as the dominant source of this gas (at least today) is biomass
- But increased O2 concentrations from photosynthetic cyanobacteria (like stromatolites) resulted in the first fully-assembled eukaryotic cells ~2 Ga ago
- Relatively sophisticated eukaryotic cells ultimately evolved into the multi-cellular animals/plants in the last 500 Ma (only)
Distinguish between different types of waves (mechanical, electromagnetic)
Mechanical wave
Is a disturbance of a medium due to the vibration (oscillation) of an object in contact with, or bonded to it
Mechanical waves are waves that require a medium in order to transport their energy from one location to another. Because mechanical waves rely on particle interaction in order to transport their energy, they cannot travel through regions of space that are void of particles. That is, mechanical waves cannot travel through a vacuum
Example: Sound
Needs a medium to travel through, molecules carry sound waves by colliding into each other. In space, there is no sound since there are no molecules around
Electromagnetic wave
Electromagnetic waves are waves that have an electric and magnetic nature and are capable of traveling through a vacuum. Electromagnetic waves do not require a medium in order to transport their energy
Example: Light
Do not need molecules to travel. They can travel through air and certain materials (e.g. glass, water) and through the vacuum of space
Describe some of the basic features of electromagnetic radiation: wavelength
Distance between one wave crest to the next. Is expressed in lambda, λ, in meters or nanometers
The concept applies to all types of waves
Explain the origin and name some basic characteristics of
electric fields
Electric field
A Region where forces are exerted on an electric charge by another electric charge or group of charges e.g. two adjacent protons, experience this force in the area around them
Created by
The mere existence of a charge
Electricity
- A basic, intrinsic, fundamental property of matter
- All matter is “electrical”
- A piece of “electrical matter” is called a “charge” (q)
- An electric charge (q) also has a mass (m)
- Examples of charge: electron (-), proton (+), ion (single or multiple + or -)
Explain the origin and name some basic characteristics of magnetic fields
Magnetic field
Invisible forces associated with electric currents and motions of electrons in atoms e.g. the field associated with a simple bar magnet
Created by
A charge in motion or vibrating
Magnetism
- A property of some matter
- Some matter is “magnetic”
Explain the physical origin of electromagnetic waves as deduced by Faraday, Maxwell and Hertz
Until 1820, electricity and magnetism were thought to be completely separate
Faraday
In 1832 he showed that you can produce electrical current by simply changing a magnetic field around a conductor.
An electromagnetic wave is generated by an electric charge which is non-stationary (moving or vibrating)
Maxwell
In 1873, he devised 4 elegant equations to describe the curl and divergence of electric and magnetic fields
- Magnetic fields also curl around a changing electrical field. This generates a magnetic field between the capacitor plates. Electric and magnetic fields are perpendicular to each other and the frequency of the vibrating charge is responsible for the frequency of the EM wave
Consequence: when an electric field vibrates the magnetic field generated induces more electric field, this causes EM waves rippling out from the vibrating charge: he predicted radiowaves = the origin of all EM radiation (“Radio to Gamma”)
Heinrich Hertz (1857-1894)
Soon produced radio waves - as predicted by Maxwell - using vibrating charges. He measured wavelength and velocity and showed that they possessed many of the properties of visible light
Explain the model of the wave-particle duality
The concept in quantum mechanics that light may be described as either a
- wave
- particle
- EM radiation
Electromagnetic waves display both wave characteristics (e.g. reflection, refraction, diffraction) and particle characteristics (e.g. Einstein’s Photoelectric Effect, BB radiation)
Explain what is meant by Multi-Wavelength Astronomy and give examples of the types of astrophysical objects observed at different wavelengths
Multi-Wavelength Astronomy means observations made at all wavelengths. More energetic (hot) objects are observed at shorter wavelengths while colder bodies are generally observed towards the radio end of the spectrum
Radio
Temperature < 10K
cosmic background, cold interstellar medium, regions near neutron stars and white dwarfs
Infra-Red (IR)
T = 10-103 K
cool stars, planets, comets, asteroids
Visible
T = 103-104 K
planets, galaxies, stars, nebulae
UV
T = 104-106 K
supernova remnants, very hot stars, quasars
X-Rays
T = 106-108 K
cluster of galaxies, neutron stars, supernova remnants
Gamma-Rays
T = More than 108 K
pulsar or neutron stars, accretion dusks around black holes
Describe some of the basic features of electromagnetic radiation: frequency
Number of cycles of a wave to pass some point in a second. Is expressed in cycles per second, or Hz (1 Hertz = 1/s)
Concept applies to all types of waves
Describe some of the basic features of electromagnetic radiation:
Speed in vacuum
All electromagnetic waves travel in a straight line trough space
v = c = constant in a vacuum (3 x 108 m/s)
Describe some of the basic features of electromagnetic radiation: Planck’s Law
E = h v
- E is the energy of the radiation
- V is the frequency of the radiation in Hz
- h is Planck’s Constant, 6.626 x 10-34 Js
Describe some of the basic features of electromagnetic radiation: visible spectrum
Our eyes can see just a relatively narrow frequency band of electromagnetic waves, the so-called visible light.
This visible light consists of the colors in a rainbow.
Each of these colors actually corresponds to different energy (frequency) and a different wavelength e.g. blue light has more energy and a shorter wavelength than red light
Describe some of the basic features of electromagnetic radiation: Electromagnetic spectrum
Give examples of light behaving as a particle
The photoelectric effect
Einstein explained why UV radiation ejects electrons (photoelectrons) from metals, the so-called Photoelectric Effect.
Einstein noted that the maximum energy of the emitted electrons (maximum kinetic energy, Kmax) increases with frequency. He argued that some incoming photons possessed enough energy to release the metallic electrons. This explanation is only feasible if light can behave as a particle
Black body radiation
Max Planck explained the emission of a hot black body by assuming that the energy is carried by discrete “bundles” or “packages” of energy called “photons”
- A perfect black body is a theoretical object that absorbs 100% of incident radiation
- It is a perfect radiator
Wien’s displacement law
When the temperature increases, the peak of emission shifts toward lower λ (higher frequency → higher energy). The peak of the emission spectrum depends on the temperature of the source e.g. healthy human beings maintain a temperature of 310 K (37.0°C)
Atomic Emission spectrum
These spectra are characteristic of thin gases, where electrons become temporarily excited and emit a photon of characteristic energy. These emissions are manifested in colorful emission lines
Atomic absorption spectrum
An absorption spectrum occurs when light from a warm body, e.g. the Sun, passes through a cool, dilute gas and atoms in the gas absorb at characteristic frequencies. Dark lines that can be seen in the spectra as the re-emitted light is unlikely to be emitted in the same direction as the absorbed photon
Give examples of light behaving as a wave
Reflection
Angle of incidence = angle of reflection
Refraction
Refraction is the bending of light when the beam passes from one transparent medium into another e.g. starlight passing from interplanetary space into Earth’s atmosphere
Polarization
Light and other EM radiation can be polarized i.e. the wave can have vibrations confined to a single plane that is perpendicular to the direction of motion. The incident wave is vibrating in the same vertical plane as the polarizerand will be transmitted (see picture).
However, the transmitted wave will be absorbed by the analyzer, which has a perpendicular vertical plane
Interference
Where two or more waves interact with each other constructively (increasing in magnitude) or destructively (decreasing in magnitude). Light also shows interference
Diffraction
The effect of a wave spreading as it passes through an opening or goes around an object e.g. sound waves can easily be heard around corners
Describe the internal structure of the Earth and the origin of Earth’s magnetic field
The internal structure of the Earth is composed by outer parts (they are rocky) and inner parts (they are metallic):
- crust
- upper mantle
- lower mantle (silicate composition)
- outer core (Iron and sulfur liquid composition)
- core (iron and nickel solid composition)
The Earth’s magnetic field results from the self-exciting dynamo effect in the outer core. It is generated by the convective motion of ferromagnetic materials (Fe, Ni, Co, some REE)
Explain important, rudimentary terms in Solar Physics:
Solar flares
Flares are explosions that happen when energy stored in twisted magnetic fields around sunspots is violently released as hot plasma. They release a stream of atoms, ions, electrons and radiation into space
Explain the origin of Earth’s magnetosphere and be able to state some of its basic characteristics
Solar wind interacts with the Earth’s magnetic field (deflects and traps some charged particles, and deforms and compresses it), resulting in the magnetosphere
- The particles spiral back and forth along field lines
- Most such particles (not deflected by the bow shock) are concentrated in the two Van Allen Radiation Belts
Characteristics
- Earth’s magnetic field shields us from much of the solar wind. Solar wind largely deflected “like water around the bow of a ship” (bow shock)
- The region of space sitting behind the bow shock and surrounding Earth is termed the magnetosphere: 60-80,000 km (“sunny side”) and out to > 300,000 km away from Sun.
Explain fundamental Planetary Science terms:
heliosphere
The heliosphere is the region of our Galaxy in which the Sun’s magnetic field and the solar wind dominate the interstellar medium
(Heliosphere) is similar to a planet’s magnetosphere, e.g.
- An outer bow shock
- A boundary called the heliopause, where energy of solar wind particles < winds from nearest stars
Give one example of a theory proposed to explain why the inner four planets of the Solar System are rocky (Terrestrial) in composition while the outer ones are dominantly fluids (Fluid Giants)
Fred Hoyle (1915-2001) explained the Sun’s low angular momentum and how hydrogen and fine dust were displaced to the outer Solar System
- The young Sun had a strong magnetic field and the hydrogen ions (H-, H+) would have acted as tiny “magnets”
- Eventually, their period of rotation would have matched that of the Sun. Transfer of momentum (“Sun to gas”) would have slowed Sun’s rotation
- Acceleration of the gas may have been sufficient to move them along with the tiniest dust grains to the outer Solar System where they may have accreted into Gas Giants in the new “gas-rich” environment
- The inner planets would have accreted from the remaining, larger solids (mostly silicate and oxide grains) in a “gas-free” environment
Explain why the elemental abundances found in meteorites (with the exception of the more volatile elements) are very similar to those observed in the Sun’s photosphere
Chondrites: Stone meteorites that are literally “a piece of the Sun”. This is why abundances in type I carbonaceous chondrites are linear with solar abundances
sun and asteroids formed by the same starting ingredients 4.6 billion years ago
Quantify the relations between wavelength, frequency and energy
Speed of wave = wavelength x frequency
Highlight some of the consequences of mean motion resonance in the solar system
Resonances affect the stability of orbits in planetary systems and play a significant role in the evolution of planetary systems
Explain the concept of tidal forces and their consequences for planetary bodies
Tidal forces can be explained by taking into account that the orbiting bodies have volume, that is to say, not all points of the first body are in the same distance from the second body. Thus, they experience unequal gravitational forces. The net effect is the stretching of the body.
Consequences
- Tidal forces can alter the orbit of satellites, making a moon spiral outwards or inwards (Orbit expansion of the Moon and the inner satellites of Jupiter, Saturn and Uranus, Orbit decay of Phobos and Triton)
- The movement of mass that creates the tidal bulges creates a lot of energy and can cause heating and volcanism (tidal heating).
- Tides transport angular momentum between planetary rotation and satellite orbits. It is the reason most major moons have a synchronous rotation rate with their planets (spin-orbit lock).
- If the moon approaches too close to the planet, it may reach a point when its internal forces cannot resist the tidal forces and it fragments (breaks apart). That point is called the Roche limit. The fragments can then continue to orbit in a ring formation.
Provide a theory on the creation of planetary rings
Explain what the Late heavy Bombardment is and provide a theory for its origin
Explain the axiom: “Stars are born, evolve, and die in different ways, largely depending on their (initial) mass”
Cycle
Stars are born, evolve, and die in different ways, largely depending on their mass
- *Low mass stars**
(0. 08-1.4 solar masses) evolve through a red giant phase stars and ultimately white dwarfs
High mass stars
(>2 solar masses) evolve to supernovae producing heavy elements, leaving behind a neutron star or black hole
Give an example of a nuclear chain reaction associated with H or He burning in a star’s core
3 phases
- 2 atoms of H fuse into Deuterium
- 1 more atom of H joins Deuterium making 3 He
- 3 He is bombarded with another 3 He, make 4 He and releases 2 atoms of H, which restart 1
A star is in equilibrium if nuclear and gravitational forces are equal
- Other reaction chains exist (CNO as catalysts)
- The greater the mass of a star, the further it contracts until radiation pressure can counter-balance gravity
Explain the two, evolutionary paths observed by stars of ‘low’ and ‘high’ initial masses
Big Bang
Stars
Low Mass vs. High Mass
Red Giants vs. Red Super Giants
Planetary Nebulae vs. Supernova
White Dwarf vs. Neutron Star or Black Hole
