Jack Gelfand Cosmic Microwave Background


An Instrument for the Detection of the Cosmic Microwave Background for Amateurs

Jack Gelfand PhD

Portland, Maine USA


As the universe cooled after the Big Bang, it entered a stage in which it was a uniform, ionized plasma. As the plasma cooled further, the electrons and protons recombined to form a neutral, transparent gas. When we look into the sky today we see back in time to the light left over from that transition. Because of the cosmic red shift, we now see that light red shifted to microwave frequencies. This radiation called the Cosmic Microwave Background (CMB) is the most ubiquitous electromagnetic radiation in space and fills the entire sky in all directions. By carefully studying small spatial fluctuations in the CMB, astronomers have been able to learn much about the early universe.

Dispite the ubiquitous nature of the CMB, amatuers do not try to observe it. One reason is that there is a substantial amount of information about the implications of the Big Bang and the CMB in the popular press, but there is little information available to amateurs about designing and building an instrument to observe the CMB. This site describes an apparatus that I have built and provides enough information to allow you to build one yourself.

The original homogeneous, dense plasma of the Big Bang absorbed all light. A property of a material that completely absorbs radiation is to radiate in a mathematically specified way called a black body radiator. Astronomers detect the CMB as extra noise equivalent to a black body radiating at a temperature of 2.73 K. They do this with an instrument called a microwave radiometer. A radiometer is a radio telescope that is calibrated with known temperature sources. A professional apparatus utilizes the temperature of liquid helium, 4.2K, to calibrate the temperature scale and cool the electronics.

With some simplifications, though, it is possible for an amateur to construct a similar apparatus to detect the CMB. I have found that you can obtain a reasonable level of performance with inexpensive electronics operating at room temperature, and a temperature calibration using liquid nitrogen. The configuration of my instrument is adapted from earth-based and balloon-borne instruments and has all of the essential elements of a professional apparatus. Some components are simplified while retaining the critical elements of the design. This puts the complexity and cost of a CMB apparatus within the reach of an amateur observer.

You can read about the details by downloading the following sections.
Origin and Discovery Download
Design and Construction Download
Data Analysis Download
Correction for Atmospheric Emission Download
Matching Impedance of Cold Load and Free Space Sources
Component List
Other Amateur Systems

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