2.1 Senses and Instrumentation

"Seeing is believing," but should I believe what I see through a telescope? Or the reading I see on a thermometer? Instruments extend our experience of the world beyond our senses. Just as with our senses, we gain trust in scientific instruments through interactive exploration and comparison.

The Lesson in Context

This lesson links the idea that there's a shared reality "out there" and the beginnings of our comprehension about it. It does this by providing the foundation for why we can trust that the instruments we use are in fact measuring something real about reality. The lessons after this are about how we interpret the results of our measurements and start to unpack what they're actually telling us about reality.

Earlier Lessons

1.2 Shared Reality and Modeling

• Senses and instruments as means to study the shared reality.
• Ways to help us feel "real" about things we can't directly see.

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Later Lessons

2.2 Systematic and Statistical Uncertainty

• Accept that instruments are inaccurate or imprecise.
• Ways to quantify this inaccuracy and imprecision in our measurements.

6.1 Correlation and Causation

• The value of interactive exploration can be understood in terms of causation as "correlation under intervention."

Takeaways

Learning GoalsDefinitionsExamplesCommon MisconceptionsExpanded Learning Goals

After this lesson, students should

1. Place appropriate trust in instruments where direct observation is not possible (or is less precise/accurate).
2. Understand that interaction with reality through instruments can extend the belief of a shared objective reality to objects and phenomena to which our raw senses do not have direct access.
3. Understand the challenges of validating an instrument and general methods of validation.

Instrument

An instrument is a device you use to make some measurement about the world.

An instrument is not just something that provides information. A thermometer is an instrument but a weather app is not.

Students tend to overextend the category of "scientific instruments to enable wider observation" to appeals to authority like books and Google and to tools that add to rather than clarify observations, like PokemonGo and psychedelics.

Validation Challenges

There's lots of challenges that can make it challenging to validate instruments. For instance, when there is no objective gold standard (e.g. passage of time, what fluid to use in a thermometer). Another challenge is when direct observation is messy or impossible (e.g. radio waves, mass of a mountain).

Validation Techniques

Validation can either be done by the comparison of multiple instruments (e.g. thermometers) or by comparison to direct observation (e.g. naked sight compared to sight with a magnifying glass).

• Interactive Exploration

Testing an instrument by changing the thing it is measuring in ways you know through other means, and seeing if the instrument recognizes the changes appropriately (e.g. does hitting the gas pedal increase a car's odometer; see how singing higher and lower notes affects a sound spectrograph; sprayable electrons in Hacking reading).

Students are often confused about interactive exploration and often do not incorporate the validation of instruments into their understanding.

Instrument Ladder

We can build up an "instrument ladder" by comparing and building on results from previous instruments we've already tested. Instead of validating with our direct senses, we can validate with other instruments that were in turn validated by even more instruments as long as at some point the bottom rung of the "ladder" was validated with our senses, which were in turn validated against each other.

Exemplary Quotes

“It sure helped public health and medicine once we realized there were things affecting our health that were just a little too small to see. I wonder if we could have figured that out without the invention of the microscope. I guess we might have just thought there were more invisible entities out there.”

“It didn't occur to anybody that there was such a clear periodic pattern in the populations of those wolves and rabbits until somebody just started writing down every sighting—we're pretty bad at estimating and remembering times between occasional events.”

“It's amazing to first see a slow motion picture of a violin string making a note—wouldn't it be great if our eyes and brains were fast enough to do this?”

“Do you think that modern technology offering us more different vantage points fundamentally changes our position on any practical questions? For example, does it make a difference that in relatively recent decades we have gotten used to seeing the earth as a whole from space?”

Why should we trust our senses at all if they can be fooled by, say, optical illusions or hallucinations? Why should we trust instruments at all if they are imprecise and may have a defect?

It is important to teach that our senses and instruments don't have to be 100% infallible to be useful in making practical decisions. In fact, all instruments fail beyond a certain range of validity, but we can still use them to learn about our shared reality. We can check our observations against our own past observations, observations by other means, and the observations of others to become more confident that those observations are stable and reliable.

We can't really know anything about other galaxies, because we can only see them through fancy instruments and we can never know if the instruments are telling us the truth.

It's true that we can't measure detailed aspects of galaxies with our senses. However, we can use our senses to validate instruments and use those instruments to validate other instruments until we ultimately validate the instruments we use to measure distant galaxies.

After this lesson, students should

1. Attitudes
   1. Place appropriate trust in instruments where direct observation is not possible (or is less precise or accurate).
2. Concept Acquisition
   1. An instrument can have greater precision and accuracy than direct observation or the instruments used to test and calibrate it.
   2. Validity of a Measure: Is the measure yielding information about the target entity out in the world, given that the target is something real (i.e., the concept is valid).
   3. Challenges in validating the use of an instrument:
      1. When there is no objective gold standard (e.g. passage of time, what fluid to use in a thermometer).
      2. When direct observation is messy or impossible (e.g. radio waves, size).
   4. Techniques for validating instruments:
      1. Interactive exploration: Testing an instrument by changing the thing it is measuring in ways you know through other means, and seeing if the instrument recognizes the changes appropriately (e.g. does driving increase a car's odometer; see how singing higher and lower notes affects a sound spectrograph; sprayable electrons in Hacking reading).
      2. Comparison of multiple instruments (e.g. thermometers).
      3. Comparison to direct observation (e.g. naked sight compared to sight with a magnifying glass).
3. Concept Application
   1. Recognize the continuum from direct observation to indirect observation via instruments.
   2. Identify when and how interactive exploration, comparison of multiple instruments, and comparison to direct observation can be used to validate instruments.
   3. Identify cases in which instrumentation is needed to solve problems (e.g. entities or events that are too slow, too fast, or too small—those for which we cannot rely on our everyday senses and cognitive capacities), especially in policy contexts.
   4. Explain how our ability to use the techniques for validating an instrument above can lead to more or less confidence in a given measurement.
   5. Identify where challenges in validating an instrument (and the associated lack of confidence about what it is measuring) can make policy decisions more difficult.

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