2.1 Senses and Instrumentation

Science uses both our direct senses and a variety of instruments to extend our ability to observe phenomena. We trust our instruments for the same reasons we trust our senses; 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.

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.

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

After this lesson, students should

Place appropriate trust in instruments where direct observation is not possible (or is less precise/accurate).
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.
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.

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.

Useful Resources

Discussion Slides Template

The discussion slides for this lesson.

Interactive Exploration Worksheet

Worksheet used for all the activities in this lesson.

iOS Spectrogram App

iOS app used for the spectrogram activity.

Android Spectrogram App

Android app used for the spectrogram activity.

Do We See Through a Microscope?

Do you think you "see" through an ordinary microscope? What about an electron microscope? Does using the word "see" imply that what you see is what is really there?

Recommended Outline

Before Class

Have students download a spectrogram app on their phones for the first activity.
Review and print worksheets for students.
Get all materials for activities:
- Slinkies (may need a weight with each, one per group)
- Gas lamp (also called a discharge tube) (any kind will do, one per class)
- Diffraction grating (one per person)
If you want, bring a musical instrument to class to use with the spectrograph.

During Class

1 Minute	Hand out worksheets.
1 Minutes	Introduce the lesson and go over the plan for the day. Make sure people have groups, spokespeople, etc.
3 Minutes	Ask the warm-up question to loosen the students up and get them ready to be convinced of their capacity to understand reality.
20 Minutes	Do activity 1 (sound spectra).
20 Minutes	Do activity 2 (light spectra).
20 Minutes	Do activity 3 (slow motion camera).
15 Minutes	Ask the post-activity discussion questions.

Lesson Content

This is a logistically heavy lesson. Make sure to prepare far in advance to plan and prepare the necessary materials. You may need to contact your institution's physics demo office.

Warm-up Question

Which statement best captures your stance?

I think our understanding of reality is mostly wrong.
I think most of our understanding of reality is mostly wrong, but we might have a few bits basically accurate or close to accurate.
I think a good bit of our understanding of reality is probably generally accurate or close to accurate, with a lot of errors.
I think most of our understanding of reality is mostly accurate or close to accurate, with some important errors.
I think nearly all of our understanding of reality is accurate, with few important errors.

This question has no "correct" answer, but it's nice to get a sense of where your students stand and have them argue their responses with each other.

Spectra of Sound

Instructions for Android users.

In this activity, students use a spectrogram app on their phones to interactively explore the frequency composition of different sounds and voices. Seeing the spectrogram immediately and consistently respond to different sounds should give the students a sense that it's measuring something real.

To make the Android app display readings in the same way as the iOS one, students may have to push the button that says "1D" at the bottom of the screen. This switches the app to "2D" mode.

Instructions

Prior to class, make sure the students download one of the spectrogram apps on their phones.

2 Minutes	Introduce the activity by opening the app on your phone and singing or whistling out loud into it. But, don't show them the results of your measurement.
10 Minutes	Have the students explore different sounds with the apps. They will investigate the sounds of their singing/whistling and different voices/sounds as well as high and low pitched notes from any musical instruments if they have them available. Encourage them to look at the differences between the spectra for the different voices and sounds.
4 Minutes	Have the students discuss the discussion questions in small groups.
4 Minutes	Discuss the questions as a class. You can skip this step if you're running short on time.

Sound Discussion Questions

Based on your observations, how could you distinguish the various sounds, if you were given the spectrogram alone (but not your own sense of sound)?
How do you know that the instrument is showing something real about the world? How does interaction help you test it?

Spectra of Light

This activity has students use small diffraction gratings to look at the spectrums produced by various light sources. By interactively observing the different patterns diffracted out by different types of lights, the students should be able to see that there is some structure to light that they can't easily observe with their naked eyes. The students can trust their instruments because they see the results consistently and in direct response to their measurements.

Instructions

2 Minutes	Get everyone set up with their diffraction gratings and demonstrate looking through one. If you don't have access to diffraction gratings, you can use old CDs.
10 Minutes	Have the students look at different sources of light. They should try looking at the sunlight (but not at the sun directly), any lamps in the room, and the LED lights on a phone or other electronic device. If you have special lamps from the physics department, have them look at those too.
4 Minutes	Have the students discuss the discussion questions in small groups.
4 Minutes	Discuss the questions as a class. You can skip this step if you're running short on time.

Light Discussion Questions

What do you see through the grating that differentiates the different light sources?
How can you interact with this grating film/CD to assure yourself that the instrument is showing something real about the world?
Based on your observations, how could you distinguish the various light sources, if you were given the diffraction grating film alone (but not your actual sense of vision)?

Hint

Light can warm things up.

Slinky Drop

For this activity, each group will need one slinky and one smartphone with slow motion camera capability.

How a Slinky Falls in Slow Motion

Additional video explaining the phenomena in this lesson.

How to Drop

These and all other instructions for the activity are provided in the handout.

Hold on to one end of the slinky and let the whole slinky naturally hang down. The bottom of the slinky should not touch the ground. If the slinky is too long, you may hold onto many rings at once, so that the remaining length does not touch the ground.
Once the slinky is steady (not bouncing or swinging), release it to let it to fall to the ground.

Slinky Question 1

What is happening to the bottom of the slinky just after you release it?

It is falling at the same speed as the top of the slinky.
It is falling slightly slower than the top of the slinky.
It is falling slightly faster than the top of the slinky.
It is not falling at all.
It is moving upwards.

Slinky Question 2

What is happening to a ring in the middle of the slinky just after you release it?

It is falling at the same speed as the top of the slinky.
It is falling slightly slower than the top of the slinky.
It is falling slightly faster than the top of the slinky.
It is not falling at all.
It is moving upwards.

Next Steps

Have other group members repeat this.
Now, with one person holding the slinky as in the first drop, have a second person record a slow motion video of the slinky from a distance using a smartphone camera.
As a group, review the slow motion video and answer the above questions again.

You can maximize slowness on iPhones by clicking the number in the upper right corner from 120 to 240 (frames per second). Other phones may have "slo mo" and "super slo mo" options. Make sure the video includes the entire slinky and the floor. Keep the camera steady throughout the recording.

Play Around

What else can you do with a slinky? Can the slow motion camera help you see other movements of the slinky more clearly? (E.g. stretch out the slinky between two people and have one person jolt it, while a third person records.) Feel free to play around and experiment. How does your interactive exploration of the slo mo videos of the slinky help you believe the video is showing what's happening AND reveal how the slinky is really moving?

Skip playing around if you're running short on time.

Final Discussion Questions

Question 1

In all the instruments we've looked at, we've directly compared them with our senses. How do we check our senses when we are unsure of them? How do we do that for our instruments?

Our senses can be validated just like any other instrument. Since the things we see, hear, smell, touch, and taste allow us to navigate through the world, for which those senses are our only direct input, and they tend to line up with each other, they have some stability and reliability. And, as with testing instruments against each other, we can compare our senses with the observations of others (shared reality!). Since they tend to fit with the reports of others, for the most part, that is our shared reality, such as it is. (Whatever else we might mean by 'reality,' it's hard to say it's not all the stuff that seems to have similar effects on us and everyone else we talk to and observe.)

Furthermore, no instrument needs to be 100% accurate to tell us something about the world. As long as there is some regime in which some of our senses work, we can use that as a basis to start validating other tools and exploring some aspect of the world.

Question 2

How can we observe a thing that we can never perceive directly with our senses?

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.

Question 3

Not all instruments are as directly interactive as the ones we've used here. Describe an entity which you believe exists for which you have only very indirect evidence.

Why do you believe it exists?
Is there anything that might convince you it did not exist?
Is there anything that might convince you that although something like it does exist, it has quite different properties than you had thought?

Examples

Electrons, quarks, black holes, dark matter, etc.

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