2903 Introduction: Science, Theories, Models, Laws and all that

What is Science?

The scientific approach to the examination of phenomena is a defence against the pure emotion of fear....This made for a kind of harmony and confidence. The sun came up about as often as it went down, in the long run...

Tom Stoppard, Rosencrantz and Guildernstern are Dead

• The Systematic Study of Phenomena? Note that this excludes (by definition), Political Science, Computer Science

  The most remarkable discovery made by scientists is science itself

Culture/Philosophy of Science:

• Primary Sources are not important (no one reads Newton)
• Knowledge is cumulative

  If I have seen further than other men, it is because I have stood on the Shoulders of Giants.
  Isaac Newton

• There are things we know that we know.... there are things that we know we don't know. ....... There are things we don't know we don't know. ..... And each year, we discover a few more of those unknown unknowns.
  Donald Rumsfeld

• An objective reality is assumed, which is not altered by one's viewpoint

  Reality: what a concept!!
  Robin Williams in Mork and Mindy

  ...........human kind
  Cannot bear very much reality.
  T.S. Eliot, Burnt Norton

• General principles exist, from which many consequences follow

  Essentia non sunt multiplicanda praeter necessitatem (Entities are not to be multiplied beyond necessity)
  William of Occam

  Hypotheses non fingo
  Isaac Newton

  (although he was lying!)

• practitioners totally ignore the critics (e.g. the philosophers, the sociologists, the social constructivists)

What is Physics?

• Physics is about the way the universe works: i.e. what are the laws of nature.
• How do we deduce laws from Nature?
• Guess them, and see what the consequences are
• How do we guess?
• Look for patterns in Nature
• e.g.

  Everything Stops

• This one happens to be false!

• We can think of this as a game, but what is a game? (Wittgenstein)

• There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
  Mark Twain

• An example which has nothing to do with physics: Eleusis: God makes up a rule, and the rest of the players try to guess it: e.g.
  A♣ K♥ 10♣ Q♦ 5♣ 6♥ 2♠ 6♦ 2♣ 7♦ 3♣ J♥ 9♠ 6♦ ..................
• But how about this one?
  10♣ Q♥ Q♦ K♦ 5♣ 7♠ 3♣ 8♠ 6♦ 8♦ 2♦ K♦ J♣ 9♠ 2♠ 6♦ ..................
• What we learn from this is
  • Rules don't need to be "fair"
  • There is no such thing as inductive logic
  • Half-right theories will work for a long time
  • It is very hard to abandon a theory which seems to work most of the time
  • Its easier to do "experiments" that you are almost certain will work than ones that you suspect won't
  • People, even physicists, are very stupid when they don't know the rules!!!!!!

• The distinguishing characteristic of a traditional folk game is that although it has rules they are not written. Nobody knows exactly what they are. The players have a tradition to guide them, but must settle among themselves the details of how to play a particular game.
  One Potato, Two Potato: the Secret Education of American Children, Mary and Herbert Knopp.

• We can have "rules" and "meta-rules". We assume in physics (and in Eleusis) there is a meta-rule that there is a rule!

  God is subtle but he is not malicious (Einstein)

• Other meta-rules:
  • Causality: i.e. all effects have a cause, which precedes it in time.

    Wind is caused by trees waving their branches (Ogden Nash, see also G. K. Chesterton)

  • Repeatability: any experiment when repeated under identical conditions will give the same answer.
  • Note: we don't do miracles!

    A♣ K♥ 10♣ Q♦ 5♣ 6♥ 2♠ 6♦ 2♣ 7♦ 3♣ J♥ 9♠ K♠ 6♦ J♣ 2♥ 8♣ 3♦ 4♣ 7♥ ..................

  • Rule is red-black-red-black.... except we can play the K♠ any time!
  • Verifiability/Falsifiability:

    It must be possible for an empirical system to be refuted by experience. Karl Popper

• Note it is often assumed that there is another meta-rule "The universe is constructed in such a way that we can understand it". There is NO basis for this rule: so far we have just been lucky, but wait till we hit quantum mechanics!

• Could we in fact cope with a universe that did not satisfy these meta-rules?
• Note this is not a matter of science (!): would a religion deal with an acausal universe?
• Can we even contemplate a universe where a large number of events occur without cause?

A theory or Law must

The logical flow should be:

• In fact it is always more complex than this ideal

The process of discovery:

• Success in research needs the 4 g's: Gluck, Geduld, Geshick und Geld. (Luck, Patience, Skill and Money) (Paul Ehrlich)

• Most worthwhile experiments nowadays require these in combination:
• e.g. Sudbury Neutrino Observatory (SNO) Designed to see why our theories of how the sun works seem to be wrong
  • Patience: idea formulated in 1985, construction started in 1990, First results in Fall 2000
  • Money: (depending on what you include) M$ 40 - M$ 100
  • Skill: meant constructing a device that has never existed before
  • Luck: Could only be built in Canada because of a political boondoggle, but more seriously:
  • if we are lucky (we were!), we could
  • Understand how the sun works
  • Understand how neutrinos work
  • If there is a supernova explosion, understand how these work
  • If we had been unlucky, may just have found the previous experiments were wrong!

Jenner

• the story of Jenner and smallpox:
• Milkmaids do not catch smallpox
• They do catch a much less serious disease (cowpox)
• Therefore cowpox protects against smallpox
• Test: give a child cowpox, and then inoculate him with smallpox
• [the story is a bit more complex, and you wouldn't get that past an Ethics committee nowadays!]

• Find an experiment to distinguish them
• Choose the simpler (???????) which is known as Occam's Razor

• e.g. Aristotle
• Motion can be divided up into "Natural" and "Unnatural"
• e.g. it is natural for a stone to fall, and a force must be supplied to stop it
• It is natural for a cart to stop moving, and so a force must be supplied to keep it moving, so the motion is "unnatural"

• e.g. Galileo/Newton
• All forms of motion are the same
• e.g. A stone has a gravitational force that acts on it and causes it to fall. To stop it falling , an equal upward force must be applied
• A cart has a frictional force which slows it down: to overcome this force, a force in the direction of motion must be applied.
• SIMPLER?? Aristotle didn't need to introduce these extra forces. However, Galileo/Newton theory makes more predictions

Critical Test:

• Aristotle: Heavy objects fall faster than light
• Galileo/Newton's: All things should fall at same speed

• First get your facts, then you can distort them at your leisure (Mark Twain)

• Note how dangerous it is to do one step in this process: theory without experiment is bad.

  It is contrary to reason to say that there is a vacuum or a space in which there is absolutely nothing. Descartes

• Particularly dangerous is developing theories based on assumptions which are so obvious that you don't write them down: e.g.
  • Time is the same whether you are moving or not
  • The world is 3-dimensional
  • The simplest objects in the universe can't have a "handedness"

Models

• This is a theme we keep returning to
• Life is Difficult (usually too difficult!)

• Ball will have air resistance, gravity will vary, sun and moon will attract ball, ball won't be a perfect sphere.................

• Model is

  Note that the world has become an infinite flat plain,we have ignored air-resistance, the child is irrelevant.....

• e.g for a satellite in orbit, we need to consider the earth as a perfect sphere, 6500 km in radius

• e.g for the earth in orbit around the sun, we need to consider the earth as a point with some mass

• Note that these models for the earth are not only different, they are not even consistent! The earth cannot be an infinite flat plane, a sphere and a point at the same time!

What is an electron?

What is an electron?

1. I have no idea
2. A very small negatively charged particle
3. It's a very stupid question
4. A wave that moves around a nucleus

What is an electron?

e.g

• What colour is an electron?
• What shape is an electron
• Is soft or hard?
• How big is it?

• e.g What colour is an electron? Colour comes from reflected light: an electron is too small (actually, it reflects light of all colours, so ....)
• What shape is an electron? To decide what shape something is, we need to "see' it
• Is soft or hard? What can we "poke" it with?
• How big is it? Depends on how you measure size; best assumption is that it's a point.

• "What is an electron?" is not a good question
• How does an electron behave?
• It behaves like a solution of the Dirac Equation

• But for a model of an electron:: A model is a spinning ball of negative charge

• Note: this is not reality, but a convenient crutch for thinking!!!!

• ..Any picture of the atom that our imagination is able to invent is for that reason defective. AN understanding of the atomic world in that primary sensuous fashion ..is impossible. Heisenberg

• This is a computer generated event for the ATLAS detector showing a mini-black-hole being created and decaying.

• Several hundred thousand lines of code + minutes of CPU time on a computer farm.
• and it's probably wrong since mini-black-holes may well not exist!

Four short case studies in the scientific method

There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy.

1. Dreams
2. Egryn Lights
3. Meteorites
4. Ball Lightning

Dreams

• Problems: too much data (we all dream)
• Freud took data and a model (mind consists of id, ego and super-ego) and developed a theory: Dreams represent subconscious (Id) desires, usually sexual, which are filtered out by super-ego and can only make it to the brain during sleep.
• From this a massive applied superstructure => psychoanalysis.
• NO scientific content at all, and very dangerous (led to probably reliable cases of sexual abuse being discounted). Also Eysenck pointed out that patients treated have a much lower chance of recovery than those ignored!
• So what are dreams? Need more data

• We dream during Rapid-eye movement (REM) sleep (~ 10% of total, short bursts of ~ 5 minutes)
• People prevented from dreaming rapidly become psychotic (in contrast to people who are just randomly woken)
• Thought (more precisely neural transmission) works by complex process

  .

• Sodium, potassium and chlorine are all involved.
• Probably imbalances build up during the day, and need to be "reset" during sleep. This stimulates the nerve, producing random images.

• What do dreams mean?

• Nothing!

Egryn Lights

• observed in Wales, near Harlech, during four months in 1904 and 1905, associated with the Welsh revivalist movement, and assumed to be divine manifestations at the time. Both locals, and (presumably fairly cynical) journalists saw these, and in several cases many witnesses were involved.
• If the observations are plotted on a map, they lie in an almost straight line, which traces out a geological fault in the rock, the Mochras fault.
• Triboluminescence. Many minerals when crushed emit light. In earthquakes and fault zones, rocks are in motion producing huge shear forces, which result in crushing of the material.
• Cannot be all of the explanation: does not explain why the lights were be visible above the ground when the crushing is taking place well underground, but it provides a plausible starting point.

Meteorites

"In fact even the realization that meteors seen in the heavens are associated with stones falling from the sky is very recent. The French Academy appointed a committee, led by the chemist Lavoisier, in 1772, to consider the reports of stones falling form the sky, and published such a damning report that museums were persuaded to throw away their specimens. Only around 1800 were the "thunderstones" accepted as real, following anecdotal reports that involved a whole town, and thus were difficult to ignore."

Ball Lightning

• The evidence:

  e.g. "Quite suddenly we were aware of a large sphere (I think coloured blue and 60 cm in diameter), traveling very rapidly towards us. It struck the ground a few yards from us with a loud explosion"

  ---

  "One flash seemed to produce a small fireball which came form outside and entered one of the ventilating windows... the ball was of greenish colour, about 13 cm in diameter and was visible for long enough for me to leave the steel and stand on a wooden climbing board. The ball did not strike the steel supports but moved between them" Several thousand reports of ball/globe lightning (kugelblitz)

More dubious (factoids!)

• Energy content? One fell into water butt and boiled it -> 10⁴ kJ, one traveled along a phone wire and melted a handset. Several other compatible observations
• no radioactivity above background, no observers have ever suffered radiation sickness <100 rad)
• small mag field (~150 G)
• O₃,NO , NO₂ observed
• Temp ~ 5000-10000 ºK (based on colour)
• Note there is a severe paradox here: if T = 10⁴K, then Power ~ 100 MW

What is it?

138 models of the nature of ball lightning

• Fraud/stupidity: Always possible, but observations are too consistent.
• After-images in the eye: Can be produced, but don't vanish rapidly. However, many observations are multiple observer, and photos are hard to explain!
• Chemical
  1. e.g. O₃ or NO created by strike. ~100 kJ in 50 cm sphere of ozone
  2. e.g. flammable gases: propane air mixes can produce small short-lived balls not naturally spherical,
  3. Silica Aerogels. Density must be ~ air, can do this by making "fractal structures". as in (e.g. )exploding wires
  4. e.g. carbon (coal and candle-flame models: O₂ diffuses in slowly from outside, similarly heat diffuses out slowly

• Explosions?
• Nuclear models
• Electrical models
  • Coronal discharges (e.g. St Elmo's Fire): Insects can produce coronal discharges, often form large clouds in humid weather. Would expect these to be discharged by lighting strikes, not created?
  • Some sort of plasma. Plasma balls can be produced, but decay via radiation in ~ 10^-3 s, rather than explosive process
  • e.g. Kapitza: resonant microwave absorption of microwaves by plasma: 10 cm size implies l ~ 35 cm or 1GHz: rather weakly produced by storms
  • e.g. non-linear conduction

• i.e. we don't know what it is!

Periodic Table and Mendeleev [1869] (Needs quantum mechanics to understand it 1925)

Continental Drift

• We know a lot
• We don't know everything
• We have methods for extending our knowledge
• We can speculate on what we don't know
• So we want to look at Science Fiction