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Earth Sci 1086 Exam 1 Notes.docx

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Earth Sciences
Earth Sciences 1086F/G
Wendy Pearson

CHAPTER 1: SCIENTIFIC THEORY AND THE BIG BANG  Sun, Moon and Earth are proper names of objects so don‘t use ―the‖  Hypothesis: an educated guess based upon observation (sometimes only one observation) o Can be supported or rejected through experimentation or more observation o It cannot be proven to be true  Theory: summarizes a hypothesis (or group of them) that is supported by repeated testing and observation o A theory is considered valid as long as there is no firm evidence to dispute it o Can be supported or rejected as more is learnt o Basically, if evidence accumulates to support a hypothesis, then the hypothesis becomes accepted as a good explanation of some phenomenon, and becomes a theory o It is not guaranteed to be true but it is the best we can formulate based on current evidence  Both hypothesis and theories explain the ‗WHY‘ of some action and theories are considered to be much better formulated and tested than hypotheses  Law: explains a body of observations o At the time it is made, no exceptions will have been found to that law o It explains things but does not describe them o It describes ‗HOW‘ something happens o Theory and law go hand in hand  The Big Bang Theory: effort to explain exactly what happened at the very beginning of the universe o The Big Bang created space and time  Singularity: an area in space-time where gravitational force is so high that all known laws of physics break down and do not apply  Gigantic expansion o To have an explosion there has to be space into which the explosion spreads  The Observations o There are several lines of observational evidence that support the theory, but there are three main ones called ―Three Pillars of Proof‖  Recession of stars/galaxies (as describes by Hubble‘s law)  The characteristics of cosmic microwave background radiation  The abundance of light elements  Hubble’s Law (#1) o Hubble lived from 1889-1953 and during that time he:  Demonstrated that there were many galaxies in the universe  He proved that the universe is expanding  He showed us how to measure distances in space o He fought to have astronomy recognized as belonging to the subject of physics o In 1990, NASA installed a huge optical telescope into Earth‘s orbit, naming it the Hubble Space Telescope o In order to understand Hubble‘s Law, we must make a comparison between a property of sound and a property of light o Doppler shift/effect: when an object coming toward you makes a sound, the sound waves are compressed by the motion of the noisy object and sounds differently to you than when the same sound waves are being carried away from you o Hubble observed apparent changes in speed of light and it meant the stars had to be moving away from Earth o It applied to everything he could see, the whole universe had to be expanding, and with the light waves moving through it o The more distant a galaxy is from us, the longer the light takes to arrive, thus the more ‗red-shifted‘ it appears when it finally arrives o So, the amount of redshift can be used to measure of a star or galaxy‘s distance from Earth o v = Hod o Where v is the speed expressed in kilometres per second; d is the distance of the star/galaxy away from Earth in parsecs (1 parsec = 3.26 times the distance light travels in one year), and Ho is the Hubble constant. That makes Ho the speed of expansion of the universe; Hubble assumed it was a constant (that has turned out to be somewhat wrong) o In simplest terms, you can calculate how far from Earth an object is by dividing its velocity (obtained from its amount of redshift) by the rate of expansion factor  Cosmic Microwave Background Radiation (#2) o Estimated that it was extremely hot in the first seconds of the universe and as it expanded it cooled o The hot light photons, produced in the early period, have since lost energy and dropped from the visible light energy range into the microwave energy range—and that constitutes the cosmic microwave background (CMB) that we can still see today  Scientists figure that CMB can be seen from anywhere in the universe because it comes from all directions and with nearly the same intensity o CMB was first discovered as noise in a very sensitive microwave radip receiver—and the researchers first thought it was the result of pigeons nesting in the antenna o The only explanation that makes any sense is that this CMB represents the very last remnants of the light/heat energy of the Big Bang‘s initial expansion  This is supported by the fact that while the general temperature of space should be 0 of the Kelvin scale, the actual average temperature in 2.726 K (-270.274 C)  Abundance of Light Elements (#3) o Has to do with the ratio of all the various atoms of the three lightest elements: hydrogen (75%), helium (25%) and lithium (trace) o The observed abundance of all the different atoms of those elements can be explained only in they originated from one single ratio of the first subatomic particles of matter that can be formed from a super-hot environment o The only way to get that one critical ratio is through a unique event like a Big Bang  Shape of the Universe o Knowing the shape of the universe is important for many reasons o 3 unique shapes o (1) Sphere—closed universe, this universe would be finite in size but without a boundary  In a closed universe, you could, in principle, fly a spaceship in one direction and eventually arrive back where you started from  Closed universes are also closed in time; they eventually stop expanding, and then contract in a ―big crunch‖ o (2) Open or negative curvature—sort of saddle-shaped  Also infinite and unbounded  Parallel lines eventually diverge  Open universes expand forever, with the expansion rate never approaching zero o (3) Flat—infinite in spatial extent and have no boundaries  Parallel lines are always parallel  Like saddle-shaped universes, flat universes also expand forever, but the expansion rate approaches zero o To all three of our models, a density parameter is critical. If space has a negative curvature, there is insufficient matter around to allow gravity to act and stop the expansion; let us say the density parameter is less than 1 o If space has a positive curvature, there is more than enough matter around to allow gravity to pull everything back together (we can express that as Ωo>1). o If space is exactly flat, we can say there is exactly the ‗critical‘ value of matter around that will prevent the universe from pulling back together or from expanding indefinitely to oblivion  So what is out there that affects gravity? o Conventional matter: stars, planets, asteroids, comets, etc.  Bit less than 4% of the universe o Dark matter: matter we have never seen because it gives off no electromagnetic energy, but we know it exists because we can detect its gravitational attraction to conventional matter  23% of he universe o Mysterious force constituting of 70-73% of the universe that acts opposite to gravity (repels matter) o Accept that the universe is ―flat‖ (slightest negative curvature)  Age of the Universe: there are several lines of investigation we can use to determine the age of things—even the universe.  Radioactivity (#1) o Certain elements have components that are radioactive—they breakdown at fixed rates to form other components and give off energy in the process o Used to interpret rocks on earth by (a) observing the compositions of gases around old stars (b) knowing the exact radioactive processes required to produce the gas compositions from the very first elements created in the Big Bang, and (c) knowing all the time factors involved in breaking down one component to yield others o This info gives us estimates ranging between 11.5 and 17.5 billion years o Known that the universe is older than 13.2 billiob years bc of a star  Hubble’s Expansion Constant o In order for Hubble to develop his equation that connected redshift with distance/velocity of light sources in the Universe, he had to propose a ‗constant‘ for the expansion rate (Ho). Since he produced that rather simple and elegant equation, there have been many refinements to Ho (based primarily on the shape/density matters we discussed previously). However, in any ‗rate‘ expression, there‘s a time factor (e.g. speed of your car: xx km/hour), so it certainly is possible to use Hubble‘s equation to determine the age of the most distant light sources we can find. o In 2002, the Hubble Space Telescope found some white dwarf stars – these are the remnants of stars that have consumed all their ‗fuel‘ and are sitting around cooling off. To have gone though the whole life cycle of a star means that a white dwarf is very, very old – thus a prime candidate for dating. All the white dwarfs found in this cluster gave dates between 12 and 13 billion years. Considering that it would have taken something less than 1 billion years for the cosmos to cool sufficiently (from the Big Bang event) to form a star, the age of the Universe had to fall between 13 and 14 billion years.  Cosmic Microwave Background Radiation o The cosmic microwave background signals offer the most accurate view to date of conditions in the early Universe. Based upon all the best physics available, a sophisticated model of the universe (from the time represented by that CMB signal map back to the time when the Big Bang produced those first photons) has been produced. Many assumptions have been made in order to get a coherent model. Assuming the right model has been developed (another assumption!), the universe is exactly 13.72 +/- 0.12 billion years This is the number nearly everyone uses these days – and we just hope it is close to correct.  What Banged? o Suggested the Big Bang represents just one stage in an infinitely repeated cycle of expansion and contraction (sort of like clapping your hands in very slow motion?), and that neither time nor the universe has a beginning or end. How does it all work? I will give you a reference to follow, but basically Turok proposes a universe consisting of two infinitely extensive sheets, separated by a very thin layer of energy (you could call it dark energy, it does not really matter). This is a ‗sandwich‘ model. Every once in a while, the intermediate layer becomes unstable at some point, gravity starts pulling things together, the layers bounce together, and – from the point of the contact – sufficient energy is generated to produce another Big Bang. From then, until the next period of instability (perhaps some trillion years in the future), the universe continues its life of expansion. NOTE ON DARK ENERGY  Dark matter is all the rest of the matter out there that we can‘t see through a telescope – it is essentially invisible to us. We know it‘s there, however, because the mass of the matter we CAN see is not enough to account for all the gravitational effects observed in the universe. Therefore we know that there is much more mass accounting for these gravitational effects, but we just can‘t see it – and we call this dark matter.  The universe is expanding, and what‘s even more unexpected is that the expansion is accelerating! So there must be some other mechanism going on here. We call this somewhat mysterious effect dark energy. As space increases in an increasingly accelerating expansion of the universe, so does the amount of dark energy in the universe.  If dark energy did not exist, we would expect that at this stage after the Big Bang, the expansion of the universe would be decelerating, dark energy counterbalances this and instead makes it accelerate faster and faster  ***Dark matter has a gravitational pull, whereas dark energy repels matter and is what is thought to be responsible for the accelerating expansion of the universe*** CHAPTER 2: TIME AND SPACE  Light Years o Used to measure distances in space o A light-year is the distance that light travels in one year o Light travels at about 300,000 km per second; there are 31,500,000 seconds in a year o When looking through an optical telescope, you must realize you are looking at light that existed one million years ago  Measuring Light Years o Different measurement techniques are needed for different distant ranges, and the middle range work (500 to 500 million light years distant) is the most complex o Up to 500 light years distant  To gauge "near" distances, astronomers use the same method as you do (unthinkingly) every time you take a walk. The nearby tree, viewed against a more distant field, appears to move slowly behind you as you pass it by. This phenomenon, called trigonometric parallax, relies on an object appearing to be at a different place relative to the background, depending on your viewpoint. o 500 to 500 million light years distant  The first technique for stars in this range deals with the brightness of stars. Astronomers use a chart, called a Hertzprung-Russell Diagram, relating the luminosity of stars (equivalent to brightness) to their temperature (related to colour; see bottom and top scales on diagram) (Fig. 2.2). Sun, like most of the stars we see, falls in the class defined as ―Main Sequence‖; if we were to draw a best-fit line through the field labeled Main Sequence in Figure 2.2, the plus/minus variation is not too bad.  Using a calibrated colour chart, we determine the exact colour of the star we are studying (which allows us to know the exact temperature of the star since the two are tightly related – and we have already defined that relationship). Now we draw a vertical line from that colour-determined temperature to intersect our Main Sequence average best-fit line on the H-R diagram, and measure (using a horizontal line), on the brightness scale (left side of the diagram) what the ‗true brightness‘ (called ‗intrinsic‘ brightness) of that star must be. However, a star‘s brightness dims with distance, so the brightness you see from Earth (called the ‗apparent‘ brightness) is rather less than true. That is all you need! To get distance, you use the following equation: Apparent brightness (which you see and measure) = Intrinsic brightness (graph) / (distance)2  This method of determining distance from colour is called main- sequence fitting, and it is good for distances up to about 150,000 light years away, which is beyond the Milky Way.  The second technique for determining distance in this middle range makes use of ‗marker stars‘ that have a special property: they have a pulsing brightness that peaks with absolute regularity (its ‗period‘), which is completely related to the star‘s brightness. We call these Cepheids, after the first one discovered. Here is how it works: We find
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