Indirect and Direct Measurements in Physical Science

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The largest spans of space, the most infinitesimal movement of an atom; how do scientists measure what seems to be immeasurable? Scientists in the fields of astronomy, physics, chemistry, and earth science find themselves with the challenge of making indirect measurements to understand elements of science such as growth, density, and perception.

There are three different specific challenges for making direct measurements in the field of biology: tiny things that are too small to measure (like bacteria), internal responses that cannot be measured with scientific tools (such as emotions and perceptions) and biological processes that cannot be readily observed because of unreadable slowness. For example, counting the number of bacteria in a test tube would be nearly impossible and the process would be so slow that it would impede the progress of the experiment. The physics department at Illinois State University responded that they would, for example, use a spectrophotometer to measure the bacteria indirectly by shining a light through the test tube and measure the amount of light that gets through to the other side (2006); the less light that gets through the test tube, the more bacteria is in the test tube. 

While emotional responses can be measured by monitoring physical response, scientists may also use surveys to find out additional data regarding individual’s perceived level of fear, for example, but the history of the individual’s surveyed may influence the statistics. Surveys are considered an indirect measurement because the statistics gathered, while quantitative, are not directly gathered from measuring tools. The data is just as valid as direct measurement, it is simply dependent on what is being measured. For the example above, scientists consider the information in the same way that they record direct data. They would create a survey and look for possible issues in the administration and gathering of data, they would gather the data in a broad and extensive demographic of individuals and examine the data for patterns that exist.  

Some forms of indirect measurement are used if a process happens over a very long period of time and is difficult to measure; for example, the rate of photosynthesis is difficult to measure so scientists do a simple test involving samples from a leaf and how long it takes for the sample to sink in a beaker of Co2 and organizing the data to find the gross rate of photosynthesis (Wickliff & Chasson, 1964, p. 32-33). Indirect measurement is used in many fields of science, especially in biology, physics and astronomy where measurement may be too big, too small, or too slow to gather useful data.

The two most important tools or techniques in physical science are Heisenberg’s Uncertainty Principle and Arno Penzias and Robert Wilson’s discovery of cosmic microwave background radiation. The uncertainty principle has allowed quantum theory and quantum mechanics to grow into a respected and viable field of physics and has the potential to bring quantum computing and maybe even teleportation of physical objects. The uncertainty principle is the concept that “The position and momentum of a particle cannot be simultaneously measured with arbitrarily high precision” (Georgia State University, 2006). This means that there is flexibility in the data for scientists to examine areas of theoretical math and science that have not previously been explored. The discovery of cosmic microwave background radiation has also been groundbreaking because of the support it offers for Big Bang and refuted the steady state theory (Berkeley Lab, 1992). However, there are also some serious side effects to some scientific technologies.

Radiation is one serious hazard that scientists working in the physical sciences have to face when performing certain experiments and when using tools that incorporate radiation. While low levels of radiation can be mitigated by lead aprons, there may still be negative effects on the scientists who work with it for extended period of time. The Stanford University Radiation Safety Manual (2010) gives examples of shielding for different types of radiation, including plastic for beta emitters and steel or lead for gamma and x-ray emitters (p. 24). These types of shields have been used by scientists for a very long time and are used when patients are receiving medical x-rays, so the efficacy of shielding is very high. However, shielding should also be used in conjunction with dosing limits of radiation and individuals of different classifications (adult workers, declared pregnant women, general public and workers who are minors) should also be considered for safety’s sake (p. 35). While scientists have looked for a different tool to avoid the risks of x-ray radiation, no other viable solution is available.

Advancements in physical sciences can impact the safety of the global community in both positive and negative ways. Quantum mechanics, which embraces the uncertainty principle, can lead to the production of quantum computers that will secure secrets or finances in ways that scientists are just beginning to understand. Quantum mechanics has brought us the Large Hadron Collider and also means that there is even the possibility of having teleportation of subatomic particles that will rejoin as the original object. However, while these technologies may be groundbreaking, there are also possible negative uses for these technologies, such as quantum computers that can be used to hack into banks or government computers. Teleportation can also be used for negative uses, such as transporting stolen goods or money. The positive uses for this science outweigh the negatives, however, and with adjustment to laws to include teleported goods, the science can contribute a great deal to society.


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Wickliff, J.L. and Chasson, R.M. 1964. Measurement of photosynthesis in plant tissues using bicarbonate solutions. Bioscience, 14: 32-33.