READING: Discovery 1.1, Appendix 1&2, Prologue P.1
Theories MUST be testable and MUST be tested.
1) Theory: The Sun shines by burning coal.
2) Prediction: If its mass is made up entirely of coal, it can shine for (100 / 1,000 / 10,000 / 1,000,000) years
3) Observation: The Solar System is approximately 5,000,000,000 years old
This theory FAILS its observational test. Now we MODIFY it, and start over!
1a) Theory: The Sun shines by fusing hydrogen to helium in its core...
We are going to avoid writing big numbers like the one I used in the example above. For example:
Speed of Light = 299,792,458 meters per second (m/s)
Light-year = 9,460,000,000,000 kilometers (km)
Instead, we are going to use SCIENTIFIC NOTATION:
Speed of Light = 2.99 x 108 m/s
Light-year = 9.46 x 1012 km
Remember:
100 = 1
101 = 10
102 = 100
103 = 1,000
106 = 1,000,000
109 = 1,000,000,000
1012 = 1,000,000,000,000
So 9.46 x 1012 means 9.46 x 1,000,000,000,000 or 9,460,000,000,000
Let's do a quick question
Besides using scientific notation to avoid writing out large numbers, we can also use different UNITS.
For distances, we will use light travel times. Here is an analogy to units we are more familiar with:
It is roughly 180 miles to the New Jersey border. You might tell a friend that it is "3 hours" to the New Jersey border. Well, an hour is a unit of time, right? What you mean is that on the highway in a car going about 60 miles an hour, it takes a car 1 hour to go 60 miles. So in 3 hours, a car will cover about 180 miles.
So we define 1 car-hour as the distance a car can travel on the highway in 1 hour, which is roughly 60 miles.
The distance to NJ = 3 car-hours
The distance to IL = 10 car-hours
The distance to CA = 44 car-hours
Remember, the speed of light is about 3 x 105 km/s, so 1 light-second is 300,000 kilometers. 1 light-minute is 300,000 x 60 or 1.8 x 107 kilometers, 1 light-hour is 300,000 x 60 x 60 or 1.1 x 109 kilometers, and 1 light-year is 9.5 x 1012 kilometers.
Let's do another quick question