1

• First: Kepler’s Laws

Nature of Physical Laws

2

First Law: The orbits are ellipses with the Sun at a focus

Kepler’s laws

3

• The line joining the planet to the Sun sweeps out equal areas in equal times

Kepler’s Second Law

Modern terminology: Gravity is a central force, angular momentum is conserved

4

• The ratio of the squares of the period of revolution is equal to the cube of the ratio of their semimajor axes

Kepler’s Third Law

The Force of Gravity diminishes as 1/R2

5

If we use the “natural units” from the Earth of 1 year and 1 A. U. (Period /1 year) = (Semimajor axis/ 1AU)3/2

(Semimajor axis/ 1AU) = (Period /1 year)2/3

Mars period is 1.88 years

So its Semimajor axis is (1.88)2/3 AU = 1.52AU

So, now all distances are known if the AU is known

Calculating…

6

• Kepler 1571- 1630 • laws of planetary motion that made a convincing

case for Heliocentric theory • Newton 1643 - 1727 • laws of motion • law of gravity (explains Kepler, comets, tides,

precession of equinoxes) • calculus • optics • alchemy, religion

7

Aristotle: Motion is a property of the bodies seeking their natural place:

Earth, air, fire and water had their “natural place” and moved vertically to find it

The heavens didn’t change as the elements “were in their place”. The unchanging circular motions was a property of their “quintessance” (literally “fifth element or essence”)

PHYSICAL LAWS!

8

Different bodies with different laws and properties

On the Earth, bodies in motion found their place and stopped

In the heavens the motions continued in their uniform circular motion

Different laws for Earth and the Heavens

A Naturalist approach to Physical Law

9

One dealt with unchanging relationships while the other was the laws of change

While there was quantitative work, there was no overarching principle that a theory was in trouble if it didn’t fit the data to the accuracy of the data

Modern physicists have a near obsession with this as we are always looking for clues for the next generation theory or new objects or new….

Aristotle thought Math had no place in Physics

10

• Born on Xmas day after the death of his father • lifelong interest in religion, occult, alchemy

• Was slow to publish his “whispers from God” • Published gravity after Robert Hooke published

an incorrect theory • “If I have seen further it is by standing on the

shoulders of giants.” • His notes total 10 Million words, 1 Million are on

alchemy.

Newton

11

• Clear Physical Laws in The Principe

• Invented the mathematics needed to capture them (integral calculus for gravitational potentials, differential calculus for motions)

Newton

12

The motions of Uranus don’t match the predictions of Newton’s laws of gravity including all the perturbation of the planets

=> Neptune is proposed and discovered The motions of stars and gas in the outer parts of

galaxies doesn’t match what is expected from the gravity of the visible material

=> Dark matter is proposed and finds repeated confirmation

Modern examples of disagreements between theory and experiment

13

The dynamics of the Universe, brightness of distant objects, numbers of distance objects all show anomalies within the theory

=> Dark energy is proposed and confirmed In the late 19th century, it is impossible to “build

stable matter”. The basic theory of the atom has the electron moving around the nucleus. It should radiate and it’s orbit should “decay”

=> quantum mechanics enables a stable theory of matter

More…

14

The orbit of Mercury is off by a miniscule 43 seconds of arc per century using Newton’s laws of gravity

=> General relativity fixes this problem

The laws of physics blow up at very high energies => Still working on this one, “string theory” looks

like the best bet so far

More…

15

• The greatest excitement comes from “being wrong” or discovering differences between theory and experiment

• Physical theories are only “right so far”, we are constantly trying to show that they are wrong and find the next big thing

• The best way to spot a nut is somebody who thinks that they are right and the scientific community is persecuting them by trying to show that they are wrong: this is the scientific process

Lessons learned:

16

It worked for most of the phenomena in the solar system and helped discover Neptune and helped clearly show it’s own problems

It is a “limiting case” of General Relativity that works with velocities that aren’t too great, accelerations that aren’t too great

It is taught in every freshman physics course But, yes, it some sense it is wrong, but it was the

“best of its’ time” and is a “limiting case” that is useful

Is Newton’s Law of Gravity Wrong?

17

If it only applies in extremes, what’s the point? The extremes are exciting: the Universe, black

holes, binary pulsars, collisions of black holes and neutron stars….

Without GR corrections, GPS wouldn’t work, so not

so exotic

Is General Relativity so exotic that it is nearly irrelevant?

18

Is there anything better?

What does it mean to be “a theory”? Can continually test hypotheses

What does it mean to be “just a theory”

19

• A scientific theory must be testable. It must be “falsifiable”

• Experiments are the sole judge of scientific “validity”

• Scientific method: observations, hypothesis/theory, experiment (test), revision, repeat

What is a Scientific Theory?

20

Correlations don’t prove cause, must do controlled experiments to test for cause

Correlations versus causation

21

• Induction… Taking examples and trying to make a reasonable generalization This step is very tricky and the process is extremely difficult to describe as

it’s the most creative/artistic element of science

Test and revision seems turnkey, but how do we start?

22

• No matter how much evidence that we have, the conclusion could still be false (if it can’t be falsified, it’s not a scientific theory after all)

• A hypothesis is confirmed not proven • The most positive the results of tests, the more

comfortable we are using a theory in new circumstances • One can make true conclusions from false data and false

conclusions from true data • Though we can’t prove theories true, this doesn’t make

them false or “slight”

More principles of the method

23

Positivism (aka “logical positivism): ask not why gravity is attractive, ask only how it attracts, emphasis on “how” rather than “why”, attempt to make the entire activity “hyper-rational” and objective. A popular philosophical notion until mid-century, still the notion that most scientists might give you

The Philosophical backdrop I.

24

Materialism: emphasis on objects, “biological states” with a denial of “mind”

This really doesn’t figure into the scientific method, but is one more way that scientists attempt to claim that they are “not in the picture”

The Philosophical backdrop II.

25

Classical Idealism (Plato), use of thought and consciousness to bring the Universe into “being” or “meaning”. Many quantum physicists appealed to classical idealism as part of a quantum theory of measurement

The Philosophical backdrop III.

26

• Wave function evolves deterministically • if you know the wave function at any time, you

can calculate it into the future • Entanglement of Wave Function leads to a variety

of effects: Quantum computing, “spooky action at a distance”. Difficult measurements, but all support QM

• “Hidden variables” have consequence, QM is always shown to be correct without “hidden Vs”

• The transition regime to Classical behavior is bewildering 100 years after

Quantum mechanics

27

●What is the quantum wave function? What does it mean? QM evolves this wave function deterministically. ●How and why does the wave function collapse? Due to measurement? Due to the change in knowledge of an observer? Due to a “handshake” between waves? Or does it never collapse, but instead, the universe splits? ● Why cannot we know simultaneously the precise values of certain quantities like position and momentum or energy and time?

Questions Raised by Quantum Mechanics

QM Interpretations

CopenhagenMany Worlds

Uses “observer knowledge” to explain wave function collapse and non-locality. Advises “don’t-ask/don’t tell” about reality.

Uses “world-splitting” to explain wave function collapse. Has problems with non-locality. Useful in quantum computing.

“DeCoherence of the Wavefunction” Interaction with the environment doesn’t collapse the wave function but it decoheres and becomes part of the environment

29

The sad tale of Schrodinger's cat. A quantum process can trigger the release of cyanide with a 50:50 probability, Quantum theory requires that the system develops into a ghost-like hybrid state of live cat / dead cat until an observation is made, when either a live cat or a dead cat will be perceived.

30

31

32

33

34

Science provides a way of testing and interacting with the physical universe that will better our understanding of the physical universe.

Science is a human effort and is subject to all of the best and worst of cultural biases existing at the time.

Most scientists are interested in how things work, not why things work they way they do.

Though the assumption is not necessary for science, many scientists assume that science needs to consider only the physical, concrete objects around us.

Some scientists assume that thought or consciousness is the most fundamental reality.

Summary:

35

There are several ways that people “come to knowledge” in everyday life

Experience Testimony Authority Revelation/Vision

Science requires strong empirical elements of observation/experiment

The role of dogma in science?

36

• Possible ways of knowing: testimony, authority, revelation, mystical visions, scientific method.

• Observational experience is a crucial part of scientific knowledge. • The experience must be objective and communicable in public language. • Scientific theories must logically agree with known physical truths or well-

established physical laws. • No matter how much logical deduction and mathematical analysis is used,

the scientific theory must be checked against the real world to confirm the theory.

• However, the exploration of the implications of a logical train of thought is a vital part of the scientific process.

• The best ideas are those that enable us to make connections between rational theories and the physical world.

Knowing…

37

• No, only our ideas about them • although they can be “time dependent”

• We have to battle preconceived notions and entrenched thought

• The challenge: question everything, maintain idealism, reject nihilism

Do Physical Laws Change

38

• A basic assumption of science: fundamental physical laws do exist in the universe and do not change. Our understanding of those laws may be incorrect or incomplete.

• Recent developments in our knowledge of the universe cause some scientists to challenge this basic assumption. Our perception may affect the physical laws or events.

• Scientists must be aware of the assumptions they make and how those assumptions affect our understanding of the universe.

Whither physical law…

39

“Discovery Science” Look in new domains: space, time, precision,

frequency --> find new things… The Cosmic Microwave Background Pulsars discovered by radio survey with timing Quasars White Dwarfs ……

The Tyranny of “Hypothesis” and “Stories”

40

• Global surveys: Genome project to other “omes”, transcriptome, proteome, …..

Biology is trying to shake free of the “Hypothesis tyranny”

41

• Linda is single, outspoken and very bright. As a student, she was deeply concerned with issues of discrimination and social justice.

• Which is more probable: • (1) Linda is a bank teller. • (2) Linda is a bank teller and is active in the

feminist movement.

• “the Linda problem.”

“Thinking Fast and Slow”, Daniel Kahneman

42

• and have difficulty distinguishing between a story and a theory

We love stories!

43

44

45

46

• Reproducibility rate in Biology is 10-15% •publication bias—the top journals want to publish amazing sensation

results. A synonym for these adjectives is “incredible” and it is.•author’s narrative bias—after settling on a narrative, things are made to fit,

they scientists drift into a mode where “believing is seeing”. Results that spoil the story are not incorporated. Unintentional and well-intentioned fraud becomes the norm.

•reviewer’s narrative bias—for a positive review, the authors must sell the narrative to the reviewer. Once the reviewer has accepted the narrative, they will overlook results that lack statistical significance.

Theory vs. “Story”

47

•proposer’s preliminary narrative bias—funding proposals require narratives based on limited preliminary results: pledges to deliver a final story before the results warrant it. This accelerates the “believing is seeing”. A compelling proposal narrative is also a pledge to avoid risk and innovation, despite claims that these should be rewarded.

•plot spoiler bias—failures to reproduce aren’t published because the complex narrative of the original paper is far greater than the one irreproducible result. Every plot has weak points, but the movie gets made and enjoyed.

Reproducibility II

48

Good stories

49

• Various versions, on Friday afternoons, a high correlation was claimed between beer and diapers in shopping carts. Story told about Target and Walmart, was evidently Terradata working on OSCA drugs “carts”. Eventually debunked.

Diapers and Beer

50

• The claim was that by watching the frequency of people googling “flu” and “flu symptoms”, the flu was tracked better than the CDCs means of alerts

• One off, never shown to work again, but you can Google “google” and “flu” and read the story:)

Google, the Flu and the CDC

51

52

• Science Matters • launched in Zurich by our Faculty

New Journal Paradigm

53

• New journal: sciencematters.io

• “Thinking Fast and Slow”, Daniel Kahneman

Promised links