1. Atoms and Nature of Science
Mr. Finn
Fall, 2013

2. 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)

3. Greek “atomos” Piece of gold: - cut gold in half repeatedly
Leucipus of Miletus
435 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

4. How do we “know” atoms are real?
We can smell objects at a distance.
Chemical compounds consist of small, whole number ratios of elements.
Crystal form simple geometric shapes based on atomic packing.
Ideal gas law can be derived from kinetic theory of gases.
We can observe “Brownian motion” or random motion of objects due to collisions with atoms.

5. Powers of Ten Prefixes Tera (T) = 1012 - centi (c) = 10-2
Giga (G) = milli (m) = 10-3
Mega (M) = micro (μ) = 10-6
Kilo (K) = nano (n) = 10-9
- pico (p) = 10-12
Powers of Ten = 9 min

6. Images of Atoms Scanning electron microscope
Scanning tunneling electron microscope

7. What is the world made of?
"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."
Democritus
"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
Lucretius

8. Inner structure of atoms
Helium atom
nucleus: protons & neutrons
(size ≈ to m)
electron cloud (quantized orbitals)
1 Å = m

9. How do we “know” the inner structure of atoms?
Rutherford scattering experiment showed that most of atom is empty space.
Atomic spectra shows energy levels are quantized
Chemical bonding is explained by “sharing” of outer electrons
Periodic table is consistent with patterns in electron orbitals.

10. 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 Born Nobel Prize in Physics (1954)

11. 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]

12. Reductionism

13. “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”

14. Black Box Pour water into top (apply voltage to atoms)
Infer inner structure …
without directly “seeing” the inside?
Measure water leaving bottom
(spectra of light emitted)

15. Brownian Motion

16. Image of thorium atoms
Albert Crewe
(1927 – 2009)

17. Cesium atoms on GaAs surface
STM image, 7 nm x 7 nm, of a single zig-zag chain of Cs atoms (red) on the GaAs(110) surface (blue).
Reference: Geometric and Electronic Properties of Cs Structures on III-V (110) Surfaces: From 1-D and 2-D Insulators to 3-D Metals, L.J. Whitman, J.A. Stroscio, R.A. Dragoset, and R.J. Celotta, Phys. Rev. Lett. 66, 1338 (1991).

18. Electrons on copper surface
Reminiscent of formal Japanese rock gardens, here we see ripples surrounding features on the copper (111) surface. The artists' fortunes took a major turn upward when they determined that the ripples were due to "surface state electrons." These electrons are free to roam about the surface but not to penetrate into the solid. When one of these electrons encounters an obstacle like a step edge, it is partially reflected. The ripples extending away from the step edges and the various defects in the crystal surface are just the standing waves that are created whenever a wave scatters off of something. The standing waves are about 15 Angstroms (roughly 10 atomic diameters) from crest to crest. The amplitude is largest adjacent to the step edge where it is about 0.04 Angstroms from crest to trough

19. Ring of Iron atoms From IBM's "STM Image Gallery":
Here they have positioned 48 iron atoms into a circular ring in order to "corral" some surface state electrons and force them into "quantum" states of the circular structure. The ripples in the ring of atoms are the density distribution of a particular set of quantum states of the corral. The artists were delighted to discover that they could predict what goes on in the corral by solving the classic eigenvalue problem in quantum mechanics -- a particle in a hard-wall box.

20. Heinz Pagels (1939-1988, physicist)
"Physical theory without experiment is empty. Experiment without theory is blind. It is the experimentalists who keep the theorists honest.

21. William James (1842-1910, philosopher)
"We have to live today by what truth we can get today, and be ready to call it falsehood."

22. Karl Popper (1902-1994, philosopher)
What is a "scientific" theory?
"1. It is easy to obtain confirmations, or verifications, for nearly every theory - if 
we look for confirmations.
"2. Confirmations should count only if they are the result of risky predictions ...
"3. Every 'good' scientific theory is a prohibition: it forbids certain things to 
happen. The more a theory forbids, the better it is.
"4. A theory which is not refutable by any conceivable event is non-scientific. 
Irrefutability is not a virtue of a theory (as people often think) but a vice.
"5. Every genuine test of a theory is an attempt to falsify it, or to refute it ...
"6. Confirming evidence should not count except when it is the result of a 
genuine test of the theory; and this means that it can be presented as a serious 
but unsuccessful attempt to falsify the theory ...
"7. Some genuinely testable theories, when found to be false, are still upheld by 
their admirers - for example by introducing ad hoc some auxiliary assumption, 
or by reinterpreting the theory ad hoc in such a way that it escapes refutation. 
Such a procedure is always possible, but it rescues the theory from refutation 
only at the price of destroying, or at least lowering, its scientific status."

23. Claude Levi-Strauss (1908-2009, anthropologist)
"The scientist is not a person who gives the right answers, but he is one who asks the right questions."