causality in philosophy and physics

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Causality in Philosophy and Physics Mark Fox Department of Physics and Astronomy University of Sheffield Ponte di Legno 2003

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Ponte di Legno 2003. Causality in Philosophy and Physics. Mark Fox Department of Physics and Astronomy University of Sheffield. Outline. Why ?. Aristotle’s four causes Causality in classical physics Causality in quantum physics Trying to make sense of it all. The four causes. - PowerPoint PPT Presentation

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Page 1: Causality in Philosophy  and Physics

Causality in Philosophy and Physics

Mark FoxDepartment of Physics and Astronomy

University of Sheffield

Ponte di Legno 2003

Page 2: Causality in Philosophy  and Physics

Outline

Why ?

• Aristotle’s four causes

• Causality in classical physics

• Causality in quantum physics

• Trying to make sense of it all

Page 3: Causality in Philosophy  and Physics

The four causes

1. MATERIAL- what is it made of ?

2. FORMAL- what is the whole, the composition, the form ?

3. EFFICIENT- what is the source of changes ?

4. FINAL- what is the end, purpose ?

Physics, Book II, Chapter III

Aristotle384 - 322 BC

Page 4: Causality in Philosophy  and Physics

An example

1. Material cause: Bronze (paper or wood would have decayed)

2. Formal cause: Sir John Franklin(ie not Queen Victoria, David Beckham)

3. Efficient cause: The sculptor, the crane operator who put in on the plinth

4. Final cause: Born in Spilsby, Arctic explorer

Spilsby, Lincolnshire

Page 5: Causality in Philosophy  and Physics

Another example

1. Material cause: sodium atoms

2. Formal cause: gaseous sodium in a discharge tube

3. Efficient cause: The electrical current

4. Final cause: Lab experiments, street lighting

Page 6: Causality in Philosophy  and Physics

Causality in physics

Material : atomselectrons, protons, neutronsquarks, strings

Formal : macroscopic: solid, liquid, gas Microscopic: states of atoms, nucleiWave function ? *

Efficient : cause effect

Final: ?

* N. Gisin, EQEC, Munich, June 2003

Page 7: Causality in Philosophy  and Physics

Efficient causality

Effect must come after the cause

CAUSE: t = 0

EFFECT: t L / c

Signals cannot travel faster than light

L

Page 8: Causality in Philosophy  and Physics

Magic

CAUSE: t = 0

EFFECT:t < L / c

L

v

Observer can see effect preceding cause

Page 9: Causality in Philosophy  and Physics

Superluminal propagation ?

Clear message for causalityPhysics in Action: December 2003 Experiment confirms that information cannot be transmitted faster than the speed of lightEver since Einstein stated that nothing can travel faster than light, physicists have delighted in finding exceptions. One after another, observations of such "superluminal" propagation have been made. However, while some image or pattern- such as the motion of a spotlight projected on a distant wall - might have appeared to travel faster than light, it seemed that there was no way to use the superluminal effect to transmit energy or information.

Page 10: Causality in Philosophy  and Physics

Quantum philosophy ?

“We live in a remarkable era in which experimental results are beginning to elucidate philosophical questions. In no domain have the results been more dramatic than in quantum mechanics.”

Abner Shimony “The reality of the quantum world”

Scientific American , January 1988

Page 11: Causality in Philosophy  and Physics

Stern-Gerlach experiment (1924)

non-uniformmagnetic field

Force z Bz'

r

-ev+Ze

I

atom beam

or

Atomic magnet

Page 12: Causality in Philosophy  and Physics

Einstein-Podolsky-Rosen (1935)

specialradioactive

source

either

or

Page 13: Causality in Philosophy  and Physics

Interpretations

Einstein’sapproachor

Bohr’s approach

Page 14: Causality in Philosophy  and Physics

Bell’s theorem (1964)

• John Bell, 1928 -1990

• Measure at different angles

• Bohr and Einstein interpretations

predict different results

Page 15: Causality in Philosophy  and Physics

Modern EPR-Bell experiments with photons

a

SD2(1)

D2(0)

D1(1)

D1(0)

b

SD2(1)

D2(0)

D1(1)

D1(0)

EPR

BELL

Page 16: Causality in Philosophy  and Physics

Aspect experiments (1981-2)

orLocal hidden variablesinconsistent with the results

Sswitch

filter

PMT

PMT

a' b'

a b

PMT

switch PMT

filter

Einstein approach

Page 17: Causality in Philosophy  and Physics

“Spooky”* action at a distance

measurement

t = 0

“The EPR experiment is as close to magic as any physical phenomenon that I know of, and magic should be enjoyed.”

David Mermin, Physics Today, 1985(4), 38

* Einstein, letter to Max Born, 1947

Page 18: Causality in Philosophy  and Physics

Quantum teleportation

|

|

ALICE

BOBinput

output

ACME

Quantum teleportation machine

“Quantum information processing”

Page 19: Causality in Philosophy  and Physics

Teleportation of photons in the lab

EPR source

ALICE

BOB

input photon|

output photon|

classicalinformation

BSM

U

| | ||

Demonstrated with single photons across River Danube 2003

Page 20: Causality in Philosophy  and Physics

Philosophical implications

Two types of question:

1. If we cannot know what we have before the measurement is made, is it meaningful to consider objective reality existing independently of the observer ?

2. How do we preserve the notion of efficient causality with measurements producing effects instantaneously at space-time separated locations ?

Page 21: Causality in Philosophy  and Physics

Bell’s assessment

“Phenomena of this kind made physicists despair of finding any consistent space-time picture of what goes on on the atomic or subatomic scale. Making a virtue of necessity, and influenced by positivistic and instrumentalistic philosophies, many came to hold not only that it is difficult to find a coherent picture but that it is wrong to look for one - if not actually immoral then certainly unprofessional. Going further still, some asserted that atomic and subatomic particles do not have any definite properties in advance of observation. There is nothing, that is to say, in the particles approaching the magnet, to distinguish those subsequently deflected up from those subsequently deflected down. Indeed even the particles are not really there.”

J.S. Bell, Journal de Physique (1981), C2, 41-61

Page 22: Causality in Philosophy  and Physics

Is the moon there when nobody looks ?

“After we came out of the church, we stood talking for some time about Bishop Berkeley’s ingenious sophistry to prove the non-existence of matter, and that everything in the universe is merely ideal. I observed, that though we are satisfied his doctrine is not true, it is impossible to refute it. I never shall forget the alacrity with which Johnson answered, striking his foot with mighty force against a large stone, till he rebounded from it, ‘I refute it thus’.”Samuel Johnson

(1709-1784)from Boswell’s life of Johnson (year 1763)

*

* A. Einstein

Page 23: Causality in Philosophy  and Physics

Material or formal causality ?

• Wave function is the form of the system

• Measurement “collapses the wave function” i.e. changes the form

• Form is unknown prior to the measurement

• Measurement does not create the matter !

• Teleportation of form not matter (N. Gisin, EQEC 2003)

Does the act of observation create the reality ?

Page 24: Causality in Philosophy  and Physics

Efficient causality in quantum physics

• No surprise that quantum physics does not agree with classical concepts of efficient causality.

• Narrow definition of efficient causality resolves contradictions:

No predictable effects prior to their cause

No information-carrying signals travel faster than light

But is this satisfactory ?

• Form (wave function) of the particle is extended (non-local). Measurement changes the form.

Page 25: Causality in Philosophy  and Physics

Question for the philosophers

Can a cause be simultaneous with its effect ?

“Those causes which are particular and actual, are and are not simultaneously with the things of which they are causes.”

Aristotle, Physics II, 3

Page 26: Causality in Philosophy  and Physics

Summary

• Many issues resolved by distinguishing clearly between matter and form

• Concept of efficient causality in classical physics apparently at odds with quantum experiments. Resolve by narrowing definition of efficient causality

• New subject of “quantum information processing” beginning to exploit non-locality

Page 27: Causality in Philosophy  and Physics

The argument by designin Physics

Mark FoxDepartment of Physics and Astronomy

University of Sheffield

Ponte di Legno 2003

Page 28: Causality in Philosophy  and Physics

Outline

• Final causality

• Teleology: the purpose of the universe

• Design arguments in physics

Why ?

Page 29: Causality in Philosophy  and Physics

The four causes

1. MATERIAL- what is it made of ?

2. FORMAL- what is the whole, the composition, the form ?

3. EFFICIENT- what is the source of changes ?

4. FINAL- what is the end, purpose ?

Aristotle, Physics, Book II, Chapter III

Aristotle384 - 322 BC

Page 30: Causality in Philosophy  and Physics

Final causality in physics• Does everything have a purpose, e.g. atoms, photons, galaxies, the universe ? If so, what is it ?

TELEOLOGY

• Is intelligence necessary for final causality ?

Theme of next conference ?

Page 31: Causality in Philosophy  and Physics

The argument by design Thomas Aquinas, Summa Theologiae I, q. 2, a. 3.

The fifth way is taken from things’ being directed.We see that there are things that have no knowledge, like physical bodies, but which act for an end.

This is clear in that they always, or for the most part, act in the same way, and achieve what is best. This shows that they reach their end not by chance but in virtue of some tendency.

But things which have no knowledge do not have a tendency to an end unless they are directed by something that does have knowledge and understanding.

An example is an arrow directed by an archer.Therefore there is some being with understanding which directs all things to their end, and this, we say, is God.

Page 32: Causality in Philosophy  and Physics

Design arguments in biology

Why does evolution occur ?

Can natural selection by chance mutationexplain everything ?

Can intelligent life evolve spontaneously

Evolution of the eye

Page 33: Causality in Philosophy  and Physics

The God of the gaps in a clockwork universe

?

• Newton’s “proof” of the existence of God

• Laplace (1798-1857): “We did not need that hypothesis”

Page 34: Causality in Philosophy  and Physics

The anthropic principle

What conditions are required for human beings to exist ?• Stable stars• Planets• Carbon atoms• water• surface temperature between 0 ºC and 100 ºC

These conditions are very hard to achieve !

Planet earth is ideal for humans. Is this just a co-incidence ?

Page 35: Causality in Philosophy  and Physics

Carbon nuclear resonance

• Carbon is essential to life. Where does it come from ?• nucleosynthesis of heavy elements in stars

4 8 *

4 8 * 12 * 12

2 He + (99 6) keV Be

He + Be C C + 2

4 123 He C + 2

(a) LONG lifetime

(b) resonance at 7.7 MeV

• How does this occur ? (Salpeter, 1952, Hoyle 1954)

(c) 16O* level below 7.16 MeV prevents 12C + 4He 16O*

Steps (a), (b), (c) depend critically on: me, mp, h, c, e …..

Page 36: Causality in Philosophy  and Physics

Planet earth

Is planet earth unique ?

extra-solar planets:119 planets104 planetary systems13 multiple planet systems

• Life takes a very long time to evolve• Require stable conditions for billions of years• Importance of the moon

Page 37: Causality in Philosophy  and Physics

Quantum theory to the rescue“Although the uncertainties introduced by the quantum picture are often stressed, this same quantum picture is absolutely vital for the stability, consistency, and intelligibility of the physical world. In a Newtonian world, all physical quantities like energy and spin, can take any values whatsoever... Hence if one were to form a ‘Newtonian hydrogen atom’ … every pair of electrons and protons that came together would be different. There could not exist a well-defined element called hydrogen with universal properties.”

John BarrowTheories of everything: the quest for ultimate explanation

(Oxford, 1991)

Page 38: Causality in Philosophy  and Physics

The $6,000,000 question

WHY ?Why is there matter at all ?

Why isn’t there nothing ?

Why is there energy in the universe ?

meta - physics