Phil10015 Lecture Nine : Laws of Nature

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Phil10015 Lecture Nine Laws of Nature

• Dr Emma Tobin
• Philosophy
• Bristol

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Explanation Laws

• Hempels covering law model of explanation
  assumes that there is such a thing as a law of
  nature from which we can derive our scientific
  explanations.
• If scientific explanations do depend on laws then
  we must provide an account of laws.

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Q Why does Mars move in an ellipse?

• Answer
• P1 All planets move in ellipses (law of
  nature)
• P2 Mars is a planet
• Conclusion Mars moves in an ellipse.

Explanans
Explanandum
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• What is it to be a law of nature?
• How do we distinguish between laws of nature
  accidents?
• What role do laws play in explaining the world?

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Why do we believe in laws?

• The common-sense view
• The universe is ordered.
• We can predict and explain that order.
• We think that the order in the universe is the
  result of laws of nature.
• Intuition?
• There is also a rhythm and a pattern between the
  phenomena of nature which is not apparent to the
  eye, but only to the eye of analysis and it is
  these rhythms and patterns which we call Physical
  Laws.
• (Feynman 1965 13)

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Realism Laws

• Laws support explanations predictions.
• Laws lead credence to the generalisations they
  support.
• Disciplines with laws are scientific - Laws
  provide a possibility for demarcation.

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Laws in Physics

• Newtons second law of motion
• Force equals mass times acceleration. (F ma)
• Boyles Gas Law
• Under conditions of constant temperature and
  quantity, there is an inverse relationship
  between the volume and pressure for an ideal gas.
  

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Other Sciences

• Biology Bergmanns Law
• For species of warm-blooded vertebrates, races
  living in cooler climates are larger than races
  living in warmer climates.
• Economics The law of supply and demand
• In a market economy, the forces of supply and
  demand generally push the price toward the level
  at which quantity supplied and quantity demanded
  are equal.

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Laws Accidents

• Why are these two generalisations different?
• All the coins in my pockets are sterling pounds
• All planets move in ellipses
• Hempel would argue that (1) cannot be used in a
• scientific explanation because (1) is not a law.
• But on what grounds can we judge that (1) is not
  a
• law and (2) is?

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Accounts of Laws of Nature

• Regularity View (Hume/Lewis)
• Nomic Necessitation (Dretske/Tooley/Armstrong)
• Eliminativism (Van Fraassen/Mumford)

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The Regularity View

• It is a law that all Fs are Gs if and only if
  all Fs are Gs.
• (e.g. It is a law that All planets move in
  ellipses if and only if all planets move in
  ellipses.)

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Humes Problem of Induction

• P1) All knowledge is either known by experience
  (matters of fact) or intuition (relations of
  ideas).
• P2) We do not intuit the Uniformity of Nature.
• P3) We do not experience the Uniformity of
  Nature.
• ?We do not know that there is uniformity in
  nature.
• Humes argument vs. induction leads to the
  regularity
• view of laws.

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(1) The regularity view (Hume)

• We have sought in vain for an idea of power or
  necessary connection in all the sources from
  which we could suppose it to be derived. It
  appears that, in single instances of the
  operation of bodies, we never can, by our utmost
  scrutiny, discover any thing but one event
  following another without being able to
  comprehend any force or power by which the cause
  operates, or any connection between it and its
  supposed effect.
• (E Sec VII, Pt II 58)
• We only know one little event following another.

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Problems for the Regularity View (1) Accidental
Regularities

• It is a regularity that
• (1) All Moas die before fifty.
• Because (1) is a regularity then (1) Law
• (2) It is a law that All Moas die before fifty
  because all Moas die before fifty.
• But, all Moas died before fifty was because of a
  rare virus in
• the New Zealand environment (i.e. an accident).
• So, (2) ? Law.
• Popper ((1959) 427-8

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Problems for the Regularity View (2)
Uninstantiated Laws

• Newtons First Law of Motion An object in
  motion will remain in motion unless acted upon by
  a net force.
• This law tells us what happens to a body which is
  never acted upon by a force.
• But this may never or rarely be instantiated
  (i.e. it is not regularly the case) because all
  or most bodies are acted upon by some force.
• Yet, Newtons first law is still considered to be
  a law of nature.

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Laws with Exceptions

• Bergmanns Law For species of warm-blooded
  vertebrates, races living in cooler climates are
  larger than races living in warmer climates.
• Exception Animals that live in burrows

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Sophisticated Regularity Web of Laws

• What are the fewest and simplest assumptions,
  which being granted, the whole existing order of
  nature would result? What are the fewest
  general propositions from which all the
  uniformities, which exist in the universe, might
  be inferred. Mill (1846) IIIIV1 207
• A generalisation is a law of nature iff it
  appears as a
• theorem (or axiom) in each of the true deductive
  systems
• that achieve a best combination of simplicity and
  strength. Lewis (1973)

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Problems with the Sophisticated account

• The simplest and strongest system of laws is
  determined by us rather than the world.
• How do we determine a systems strength and
  simplicity?
• Epistemic account of laws vs. metaphysical
  account of laws.

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(2) Nomic Necessitation ViewArmstrong Dretske
Tooley

• A law is a relation of natural necessitation
  between two universals F G.
• N(F,G) Being F necessitates being G.
• The relation of necessitation binds F-ness and
  G-ness, so that when N(F,G) holds the
  corresponding regularity in the world also holds
  (i.e. Alls Fs are Gs).
• E.g. N(Being a planet, having an elliptical
  orbit.)

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Problems for Nomic Necessitation

• The Mysterious N Relation.
• What is natural necessitation? To say that there
  is a necessitation relation is not really to
  explain what this is.

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Van Fraassen

• (1) The Identification Problem - how to identify
  laws and distinguish them from accidents.
• (2) The Inference Problem - how to make a valid
  inference from laws to the regularities in the
  world.
• Regularity accounts solve (2) but not (1).
• Nomic Necessitation accounts solve (1) but not
  (2).

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(3) Eliminativism - No Laws?

• Is the notion of laws of nature just a metaphor?
• Laws as describers vs. laws as explainers.
• There are no laws in nature. (Mumford (2004)

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Physics The Special Sciences

• Are the laws of physics the only real laws in
  nature?
• How does the answer we give this question affect
  how we think about the scientific status of the
  other sciences (e.g. Biology/Chemistry/the
  medical sciences/the social sciences)

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Exam Help

• Office Hours Thursdays 10 - 12
• Room 2.2. 7 Woodland Road (Top of the Arts
  Graduate Centre)
• E-mail Emma.Tobin_at_bristol.ac.uk
• http//seis.bris.ac.uk/plemt/