Earth Sciences 1086F/G Study Guide - Midterm Guide: Hubble Space Telescope, Milky Way, Triangulum Galaxy
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Chapter 1: The Scientific Method
An educated guess based upon observation – sometimes, only one observation
Usually, a hypothesis can be supported or rejected through experimentation or more observation
It cannot be proven to be true
summarizes a hypothesis (or group of hypotheses) that is supported by repeated testing and
considered valid as long as there is no firm evidence to dispute it
theories can also be supported or rejected as we learn more
if evidence accumulates to support a hypothesis, it becomes accepted as a good explanation of some
phenomenon, and becomes a theory
theory is not guaranteed to be true, but it is the best we can formulate based on current evidence
both hypotheses and theories attempt to explain the ‘why’ of some action and theories are
considered to be much better formulated and tested than hypotheses
explains a body of observations
At the time it is made, no exceptions will have been found to that law
Scientific laws explain things, but they do not describe them
A quick way to tell the difference between a theory and a law is to ask if the statement explains
"why" something happened; if it does, it is a theory, not a law
If it describes "how" something happens, it is a law
theory and law go hand-in-hand
o EX. Newton developed a Law of Gravity which predicts the behaviour of an object as it falls
– but Newton’s Law of Gravity does not explain why an object falls.
o EXAMPLE OF THE SCIENTIFIC METHOD: Observation: Every swan I’ve seen this year is white
Hypothesis: All swans must be white Experiment/Test: A random sampling of swans
from each continent where swans are indigenous produces only white swans Publication
of my hypothesis: “My global research has indicated that swans are always white, wherever
they are found” Further testing: Every swan any other scientist has ever observed in any
country has always been white Theory: All swans are white Prediction: The next swan I
see will be white
THE BIG BANG
The Big Bang theory is an effort to explain exactly what happened at the very beginning of the universe.
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: Not the equivalent of a giant explosion. To have an explosion there has to already be
space into which the explosion spreads. But the Big Bang created space (and time), so perhaps we can
think of an infinitesimally small balloon, which in the tiniest fraction of time, suddenly expands – and
keeps on expanding. In this tiny instant, time and space had a finite beginning (at least if you are inside
the balloon).This is really confusing – and there is no pretense otherwise! If this sequence occurred (a
singularity, a Big Bang, and creation of time and space), then can it be true that before that singularity
there was nothing: no space, no time, no energy? That is what the Big Bang theory, as currently
expressed, states. Let us go over the observations that suggest that the universe really was produced by a
Big Bang event (Please review the appendix provided at the end of this chapter, entitled “What
Theories and Hypothesis that Support Big Bang
``The Three Pillars of Proof “
1. Recession of stars/galaxies (as described by Hubble’s Law)
2. The characteristics of cosmic microwave background radiation
3. The abundance of light elements.
1) Recession of stars/galaxies
Edwin Hubble: 1889 to 1953; demonstrated that there were many galaxies in the universe – not just the
one we are in (the Milky Way Galaxy).
He proved that the universe is expanding & showed us how to measure distances in space.
Hubble fought to have astronomy recognized as belonging to the subject of physics. After his death, the
Nobel Prize Committee officially made this recognition (unfortunately, he was never awarded a Nobel
Prize, as they are not awarded posthumously).
In 1990, however, scientists at NASA installed a huge optical telescope into Earth’s orbit, naming it the
Hubble Space Telescope (many of the observations that appear throughout this course came from
evidence collected by the Hubble telescope).
Light’s Redshift and Hubble’s Law
In order to understand the observations that led to
Hubble’s Law, we have to make a comparison (as Edwin
Hubble did) between a property of sound and a property of
light. You all know that if you stand by the side of a railroad
and a train passes blowing its horn, the sound pitch is very
different when the train is approaching (the wavelengths of
sound are compressed and shortened) than when it is
moving away (the wavelengths of sound are stretched and lengthened; Fig. 1.3a).
The change in sound is called the Doppler Shift, or the Doppler Effect.
Doppler 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 off away from you
Hubble knew that waves of light would behave somewhat like waves of sound when the light source was
moving toward or away from the observer (as had been proven in a science lab around 1918 by a scientist
called Keeler) (Fig. 1.3b).
If the light source is moving toward the observer the light wavelength appears to shorten (i.e., to move
into the blue spectrum, or “blue-shifted”), and if the light source is moving away from the observer the
light wavelength appears to lengthen (i.e., to move into the red spectrum, or red-shifted) (Fig. 1.3b)
In fact, Hubble realized that the faster the light-emitting object was moving, the greater the shift
The speed of light is fixed and cannot change, so when Hubble observed apparent changes in speed of
light (from a star), it meant the stars had to be moving away from Earth
In fact, applied to everything he could see, the whole universe had to be expanding, and with it the light
waves moving through it.
More distant a galaxy is from us = the longer its light takes to arrive, thus the more ‘red-shifted’ it appears
when it finally arrives
Amount of redshift can be used as a measure of a star or galaxy’s distance from Earth.
Equation for Hubble’s Law: v = H˳d
V= speed expressed in km/second
D= distance of the star/galaxy away from Earth in parsec (1 parsec =3.26 x the distance light travels in one
Ho= hubble constant , the speed of expansion of the universe
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
Always remember your assumption: your calculation assumes that Ho (the expansion factor) is a
constant; if the expansion of the Universe has changed over time, your calculation will be inaccurate
2) Cosmic Microwave Background Radiation
It is estimated that it was extremely hot in the first seconds of the universe and as it expanded, it cooled
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.
As you can see from the map made of CMB (Fig. 1.5; signal converted to temperature), it shows the same
pattern of distribution throughout all parts of the Universe
An educated guess based upon observation sometimes, only one observation. Usually, a hypothesis can be supported or rejected through experimentation or more observation. At the time it is made, no exceptions will have been found to that law. A quick way to tell the difference between a theory and a law is to ask if the statement explains. Scientific laws explain things, but they do not describe them. why something happened; if it does, it is a theory, not a law. If it describes how something happens, it is a law theory and law go hand-in-hand: ex. Newton developed a law of gravity which predicts the behaviour of an object as it falls. But newton"s law of gravity does not explain why an object falls: example of the scientific method: observation: every swan i"ve seen this year is white. The big bang theory is an effort to explain exactly what happened at the very beginning of the universe.