From Rubber Bands to Big Bangs
The Universe has been expanding for almost 14 billion years from a smaller, hotter, denser form to its present cooler, larger, and less dense form. You might ask, “What is expanding, and how do we know that?” The Cosmic Microwave Background
Radiation (CMB) is scientific evidence that shows space itself is expanding. As space expands it cools and the original CMB waves have been stretched with this expansion of space. Although space has more than the two dimensions we will focus on with our rubber bands in this lab, we will gain a feel for the expansion of space.
rubber band (or elastic) pen stars ruler scissors
1) Make one cut in you rubber band so that it makes a flat piece.
2) Draw a wave pattern from one end to the other end.
3) Place 4 stars randomly on the rubber band. Number each star starting with number
4) Now stretch the rubber band and describe:
a) what happens to the distance between the stars.
b) what happens to the wavelength.
5) Pretend you are on a spaceship hovering near star 1, describe what you see
happening to the Universe. What would you see from your spaceship hovering star
2? star 3? star 4?
6) Now let’s look at this using measurements. Complete the following data table
before you stretch the rubber band and after:
Before stretching After stretching
Length of rubber band
Number of waves
Distance between stars 1-2
Distance between stars 2-3
Distance between stars 3-4
1) Since the rubber band represents space, and the stars represent stars or galaxies
(things made up of matter) explain what happens to matter as space expands.
2) What happens to the total number of waves as space expands?
3) As space expands what happens to the wavelength?
4) How does this relate to the Red Shift?
5) If you could continue to stretch the rubber band (and it did not break) what would
happen to the wavelength?
6) How are wavelength and temperature related?
7) Shortly after the Big Bang occurred, about 14 billion years ago, the Universe was
very hot, about 3000 K, why then today, is the CMB at about 2.7 K ?
8) How does the temperature of the CMB support the theory of the Big Bang?
9) What other evidence is there that supports the Big Bang Theory?
10) Why do scientists say that there is no center of the Universe or conversely
everywhere is the center? (Hint: think about procedure 5.)
Using the CMB’s peak wavelength of about 10^-3 m and its present temperature, calculate
its peak wavelength when it formed at the surface of last scattering. What type of electromagnetic (EM) wave was that at that time? What type of EM wave is it today?