AtomsandNature of Science

Mr. FinnFall, 2013

Richard Feynman

If, in some cataclysm, all scientific knowledge were destroyed, and only one sentence passed on the the next generation of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis (or atomic fact, or whatever you wish to call it) that all things are made of atoms - little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another. In that one sentence you will see an enormous amount of information about the world, if only just a little imagination and thinking are applied.

Richard Feynman (Nobel Prize, Physics 1965)

Greek “atomos”

Leucipus of Miletus435 BCE

"The Cheerful Democritus"Charles-Antoine Coype

Piece of gold:- cut gold in half repeatedly- is there a limit to process?- reach "smallest" piece of gold?

"a-tomos" = un-divided

How do we “know” atoms are real?

1. We can smell objects at a distance.

2. Chemical compounds consist of small, whole number ratios of elements.

3. Crystal form simple geometric shapes based on atomic packing.

4. Ideal gas law can be derived from kinetic theory of gases.

5. We can observe “Brownian motion” or random motion of objects due to collisions with atoms.

Powers of Ten• Prefixes• Tera (T) = 1012 - centi (c) = 10-2

• Giga (G) = 109 - milli (m) = 10-3

• Mega (M) = 106 - micro (μ) = 10-6

• Kilo (K) = 103 - nano (n) = 10-9

- pico (p) = 10-12

Images of AtomsScanning electron microscope

Scanning tunneling electron microscope

What is the world made of?

Democritus

Lucretius

"By convention sweet is sweet, bitter is bitter, hot is hot, and color is color. But in reality there are only atoms and empty space. That is, the objects of sense are supposed to be real, but it is customary to regard them as such but in truth they are not. Only the atoms and empty space are real."

"All nature then, as it exists by itself, is founded on two things: There are bodies and there is void in which these bodies are placed and through which they move about."

Modern View – All that exists are fields

and space-time

Inner structure of atoms

Helium atom

nucleus: protons & neutrons

(size ≈ 10-14 to 10-15 m)

electron cloud (quantized orbitals)

1 Å = 10-10 m

How do we “know” the inner structure of atoms?

1. Rutherford scattering experiment showed that most of atom is empty space.

2. Atomic spectra shows energy levels are quantized

3. Chemical bonding is explained by “sharing” of outer electrons

4. Periodic table is consistent with patterns in electron orbitals.

Max Born

"I believe that ideas such as absolute certitude, absolute exactness, final truth, etc. are figments of the imagination which should not be admissible in any field of science. This loosening of thinking seems to me to be the greatest blessing which modern science has given us. For the belief in a single truth and in being the possessor thereof is the root cause of all evil in the world.”

Max BornNobel Prize in Physics (1954)

What is Physics?

• Biology is the study of "living" organisms• Chemistry is the of the composition/structure of matter• Astronomy is the study of stars and other celestial

objects

• Physics is the study of ...

[Hint: root of physics is "PHYSIS" (ΦΥΣΙΣ) = nature]

Reductionism

“Scientific Truth”

“Truth” in science is …

- based on a “dialog” between data and theory

- provisional or based on only currently available data

- falsifiable or true only to the extent that it is capable of being proven wrong by experiment – but its testable predictions have withstood rigorous testing until now.

- focused best on being “useful” (or being simple, predictive) rather than “true”

Black BoxPour water into top

(apply voltage to atoms)

Measure water leaving bottom(spectra of light emitted)

Infer inner structure …without directly “seeing” the inside?