Chapter 3: Experiment

What is this thing called Science? (Alan Chalmers)

Science as Knowledge Derived from the Facts of Experience

In Chapter 1 and 2, we saw that observation is active, public, and theory-dependent. Today, we investigate Experimentation as the true factual basis of science.

Learning Objectives:

1. Explain why passive observation of naturally occurring events is insufficient for science.
2. Critique the naive view that experimental facts are "straightforwardly given" via the senses.
3. Analyze historical examples showing how advances in technology and theory transform the experimental base.
4. Evaluate how scientists avoid circularity when using theories to design the very experiments that test those theories.

1. Not Just Facts, but RELEVANT Facts

A naive empiricist might say: "To build science, we must collect all observable facts."

Chalmers' Critique:

• The vast majority of observable facts are completely irrelevant to science.
  • Example: Counting the number of books in your instructor's office, or recording the exact color of your neighbor's car.
• To make a meaningful contribution, we need to know which facts are relevant.
• Relevance is always relative to the current state of development of a science.
• Science poses the questions, and ideally, observation provides the answers.

The "Cow Pat" Controversy

How do we establish the cause of a natural phenomenon? Chalmers tells a story from his youth:

• The Observation: Grass grows noticeably longer around cow pats in a field.
• Theory A (The Brother): It is due to the fertilizing effect of the dung.
• Theory B (Chalmers): It is due to a mulching effect (dung traps moisture and inhibits evaporation).
• The Reality (Scientific Resolution): Neither was entirely right. Cows are simply disinclined to eat the grass around their own dung!
• The Epistemological Point: You cannot resolve this dispute by passive observation. You must intervene practically.

Student Task 1: The Cow Pat Challenge

Format: Small Group Brainstorm (4-5 students)

The Scenario: You are 19th-century agricultural scientists investigating the "Cow Pat" growth phenomenon. You have three competing hypotheses:

1. Fertilization (nutrients)
2. Mulching (moisture retention)
3. Bovine selective grazing (bovine behavior)

Your Task:

• Design a series of practical experimental interventions that isolate and test the magnitude of each effect.
• List what disturbing factors you must eliminate and how you plan to do so.
• Hint: Think about how you might simulate dung without nutrients, or how you might study the grass with and without cows present.

The Complexity of Nature: Falling Leaves

Why can't we discover physical laws by just watching the world as it naturally exists?

• The Natural Scene: Watch a leaf fall from a tree.
• The Forces at Play: The leaf is simultaneously acted upon by:
  • Gravity
  • Air resistance
  • Changing winds
  • Physical decay of the leaf tissue
• The Result: The leaf flutters, drifts, and falls in a highly chaotic path.
• The Lesson: Watching falling leaves will never yield Galileo’s law of uniform acceleration ().
• To isolate the law of gravity, we must practically intervene to eliminate air resistance and wind. We must construct a vacuum.

2. Getting Experiments to Work

Experimental results are not straightforwardly given. They are hard-won achievements.

The Practical Struggle:

• Getting an experiment to work can take months or years of struggle.
• It requires specialized know-how and physical craftsmanship.
• It requires knowing what the potential disturbing factors are and possessing the technology to eliminate them.

Chalmers own experience as an experimental physicist in the 1960s:

• The Goal: Scatter low-energy electrons from gas molecules to determine molecular energy levels.
• The Technical Challenges:
  • To get a clean reading, electrons had to collide with exactly one target molecule. This required pushing vacuum technology to its absolute limit to remove background air.
  • Gas molecules ionized by the electron beam would collect on the metal electrodes, creating spurious electric potentials (erroneous voltages).
  • The Solution: Coating electrodes with "aquadag" (a carbon-based solvent) to minimize these spurious potentials (their American competitors gold-plated their electrodes, which was better but out of Chalmers' budget!).
• Outcome: His patience and research scholarship ran out before getting significant results!

Theory-Dependence of Experiments

Experimental facts are deeply interrelated with background theory.

1. Identifying Distortions: To design an adequate experiment, we must presuppose theories about what disturbing factors exist.

• Example: If our theory of electrostatics is wrong, we won't realize that gaseous ions are collecting on our metal plates and distorting our electron beams.

2. Fallibility: If our background theoretical assumptions are defective, our experimental results will be faulty.
3. Revisability: Experimental facts are regularly updated, replaced, or set aside as irrelevant when our technology or theoretical understanding advances.

3. Transforming the Experimental Base: Hertz vs. Thomson

In the late 19th century, scientists disputed the nature of cathode rays (electric discharges in glass tubes). Are they waves or charged particles?

Heinrich Hertz's Experiment (Early 1880s):

• The Hypothesis: If cathode rays are charged particles, they must be deflected by an electric field.
• The Setup: Hertz applied an electric field across a discharge tube containing cathode rays.
• The Result: No deflection was observed.
• Hertz's Conclusion: Cathode rays are not charged particles; they must be waves (like light).
• Hertz was one of the greatest experimentalists of his era. Why was his result false?

Thomson's Breakthrough (1897)

J.J. Thomson succeeded where Hertz failed because of improved vacuum technology and a deeper understanding of gas ionization.

• The Problem with Hertz's Setup:
  • Hertz's tube had too much residual gas.
  • The cathode rays (electrons) collided with these gas molecules, stripping away their electrons and ionizing the gas.
  • These positive gas ions collected on the metal plates, creating a spurious shielding charge that neutralized the electric field Hertz was applying.
• Thomson's Intervention:
  • Baked the glass tube for days to drive out residual gases from the surfaces.
  • Ran vacuum pumps continuously to achieve an ultra-high vacuum.
• The Result: The rays deflected beautifully, proving they were particles (electrons).

Hertz's Radio Waves & The Trouble with Walls

Even great experimentalists run into limits of space and geometry.

• The Breakthrough: In 1888, Hertz successfully generated and detected radio waves, confirming Maxwell's electromagnetic theory.
• The Experimental Anomaly: Hertz tried to measure the speed of these waves. His calculations indicated that waves of longer wavelength traveled faster in air than along wires, and faster than the speed of light (violating Maxwell's theory).
• The Real Culprit: The Laboratory Walls!
• The radio waves were reflecting off the stone walls of his small laboratory, creating standing wave interference that distorted his measurements.
• Hertz's Famous Reflection: "Care in making the observations cannot make up for want of space. If the long waves cannot develop, they clearly cannot be observed."

The "Tragedy" of 19th-Century Chemistry

How can highly precise, perfectly executed experiments become completely irrelevant overnight?

• The Historical Achievement: Throughout the 19th century, a distinguished galaxy of chemists dedicated their entire careers to measuring the exact atomic weights of chemical elements to extreme decimal precision.
• The Theoretical Shift: The discovery of isotopes in the early 20th century.
• The Epistemological Realization:
  • Elements in nature are mixtures of isotopes with different weights in arbitrary ratios.
  • Measuring the "average" atomic weight of naturally occurring chlorine has no fundamental chemical significance.
• Chalmers' Verdict: Their life's work was reduced to "the determination of the average weight of a collection of bottles, some of them full and some of them more or less empty."

Student Task 2: Spot the Spurious Fact

Format: Class Discussion / Think-Pair-Share

Consider the following historical experimental "facts." For each, identify whether the error arose from (a) poor observation skills, (b) inadequate technology/setup, or (c) defective background theory.

1. Hertz's finding that cathode rays are not deflected by electric fields.
2. Aristotelians observing that flames naturally ascend into the sky because their natural place is at the boundary of the sub-lunar sphere.
3. Chemists measuring the precise atomic weight of naturally occurring neon to four decimal places.
4. Galileo measuring the angular diameter of a star using a hanging cord. (Recall Chapter 2: this was spurious due to the optical illusion of irradiation).

4. Escaping the Circularity Trap

If we use theories to build instruments and judge experimental setups, aren't we caught in a circular argument when we use those experiments to test the theories?

         [Theory under Test]
                │
                ▼ (used to design/validate)
         [Experimental Setup / Instruments]
                │
                ▼ (produces facts that confirm)
         [Theory under Test]

If this circle is closed, science becomes a self-validating echo chamber.
How do scientists break out of this loop?

Case Study: The Deflecting Coil

Chalmers shares a story from his schoolteaching days to illustrate circularity:

• The Physics Lab: Pupils were asked to test the theory that the deflection of a suspended wire coil in a magnetic field is directly proportional to the electric current passing through it.
• The Setup: They hooked up a battery, a deflecting coil, and an ammeter to measure the current.
• The "Success": Students who got a perfect straight-line graph of deflection vs. current passed.
• The Hidden Circularity: The ammeter used to measure the current already worked on the exact same principle of a coil deflecting in a magnetic field!
• The experiment presupposed the very law of proportional deflection it was designed to prove.

Breaking the Circle: Independent Validation

How do we fix the circular ammeter experiment?

• The Solution: Measure the current using an independent physical principle that does not rely on electromagnetism.
• Alternative Method: Chemical Electroplating.
  • Pass the current through an acid bath and measure the mass of copper ions deposited on an electrode over time (Faraday's Law of Electrolysis).
  • This relies on chemistry and mass, not magnetic deflection.
• The Epistemological Rule: The theories presupposed in the operation of our experimental instruments must not be identical to the theory being tested. Good experimental design requires theoretical independence.

The Ultimate Arbiter: The World Decides

Despite the theory-dependence of design, experimental results are ultimately determined by the physical world, not by our theories.

• We can adjust our theories, gold-plate our electrodes, and write elegant equations.
• But once the apparatus is built and the switches are thrown...
  • The needle either deflects or it doesn't.
  • The screen either flashes or it remains dark.
  • The chemical either changes color or it remains clear.
• We cannot force the physical world to conform to our expectations.
• This stubborn independence of the material world is what makes experimental testing a meaningful, objective quest.

Student Task 3: The "Switches & Currents" Debate

Format: Structured Classroom Debate (Divided Class)

The Motion: "Experimental results can never truly falsify a high-level theory because the experimental setup itself is always built upon theoretical assumptions."

• Team A (Proponents): Argue that because experiments require auxiliary assumptions and background theories (e.g., vacuum physics, instrument calibration), a scientist can always blame a failed experiment on the apparatus rather than the theory under test. (Cite Hertz's defense).
• Team B (Opponents): Argue that the physical world exerts an unyielding constraint on experiment. If Thomson can remove gas and force a deflection, the world is dictating the facts, not the theory. (Cite Thomson's breakthrough).

Summary & Key Takeaways

1. Passive observation is not enough: Science requires active, practical intervention (experimentation) to isolate causal processes from the chaotic noise of nature.
2. Experimental facts are hard-won: They are not "straightforwardly given" via the senses. They require physical craftsmanship, high technology, and deep know-how.
3. The experimental base is fallible and revisable: Failed experiments (like Hertz's) are often due to an inadequate setup rather than bad observation, and are updated as technology (vacuum pumps) improves.
4. Circularity can be avoided: By ensuring that the theories underlying our instruments are independent of the theories we are testing, we preserve the objective power of experimentation.