The Uncertain Nature of Gravity An Illustration of Science as a Process of Investigating Nature  Using observed motions of objects to infer physics

The Nature of Science Ideas are supported by testable and verifiable data or observation Science is a process or way to investigate nature. Scientific knowledge doesn’t mean possessing the truth. Science seeks consistency between observations and models

Once Upon a Time We were certain that: a)The Earth was the Center of the Universe b)The Earth was motionless c)All things fell toward the Earth unless they were located in the perfect celestial realm

Aristotelian Business Card: 1 Universe Place

Arrogance and the Anomaly Three Choices: 1. Ignore it 2. Fit it to your Bias 3. Throw out your Bias

Discovery in Science: How our understanding of gravity evolved Discoveries usually occur accidentally Discoveries usually occur accidentally Often is a first response to new instrumentation or new forms of thinking or new kinds of cultural interchange Often is a first response to new instrumentation or new forms of thinking or new kinds of cultural interchange May often be ignored depending on cultural bias May often be ignored depending on cultural bias Aristarchus of Samos: 225 BC

Newton’s Apple and Laws Apple always falls down? Gravity is an attractive force only? (so no anti-gravity!) All matter attracts each other? Why hasn’t the Universe collapsed?

Two Kinds of Mass

Equivalence Principle

Information and Communication Physics works by information exchange via particles Physics works by information exchange via particles For gravity  gravitons carry the instruction set For gravity  gravitons carry the instruction set Particles can be screened because particles interact with matter Particles can be screened because particles interact with matter But There is no such thing as a GRAVITY SCREEN! But There is no such thing as a GRAVITY SCREEN!

Is Newtonian Theory Complete? For all practical aspects we are done now: Newton’s laws provide the scientific foundation to engineer the planet. For all practical aspects we are done now: Newton’s laws provide the scientific foundation to engineer the planet. No earthly observations or experiments can show that Newton’s theory is incomplete No earthly observations or experiments can show that Newton’s theory is incomplete But, remember the Anomaly But, remember the Anomaly 1859 precision observations of the orbit of Mercury DISAGREE with Newtonian Mechanics! 1859 precision observations of the orbit of Mercury DISAGREE with Newtonian Mechanics!

Now we need a new Theory Einstein: Gravity = Curvature of Spacetime Einstein: Gravity = Curvature of Spacetime

Ouch, Curved Spacetime? More mass = greater curvature (locally) More mass = greater curvature (locally) Affects time (locally at curvature) Affects time (locally at curvature) E= mc 2 means that photons have energy related mass and therefore follow the curvature: E= mc 2 means that photons have energy related mass and therefore follow the curvature: Need an Ant Universe to demonstrate: Need an Ant Universe to demonstrate:

The Need for Dark Matter 1970’s: Start to measure rotational properties of other galaxies: 1970’s: Start to measure rotational properties of other galaxies: Invariably observe “flat” rotation curves: Invariably observe “flat” rotation curves:

Resolution: Galaxies must be surrounded by “Halos” of dark material than contain 90% of the total mass? Galaxies must be surrounded by “Halos” of dark material than contain 90% of the total mass? But what is this dark matter?  We still don’t know after 30 years of detailed investigation and theory But what is this dark matter?  We still don’t know after 30 years of detailed investigation and theory Is there another explanation? Is there another explanation?

Maybe we still don’t understand Gravity? Maybe gravity works differently on different acceleration scales? (GM/R 2 = 9.8 m/sec 2 on Earth) Maybe gravity works differently on different acceleration scales? (GM/R 2 = 9.8 m/sec 2 on Earth) This means the effective acceleration on an object changes so the force law changes  no need for dark matter This means the effective acceleration on an object changes so the force law changes  no need for dark matter Modified Newtonian Dynamics (MOND): empirically fits the data as well as the Dark Matter Theory Modified Newtonian Dynamics (MOND): empirically fits the data as well as the Dark Matter Theory But MOND violates the Equivalence Principle  therefore if its correct, Einstein’s theory has a major flaw But MOND violates the Equivalence Principle  therefore if its correct, Einstein’s theory has a major flaw

Reconciliation: An Extra Dimension Gravitons  the exchange particles in the gravitational force are different; they leak to another dimension Gravitons  the exchange particles in the gravitational force are different; they leak to another dimension Explains why the Gravitational force is so weak Explains why the Gravitational force is so weak

The Mysterious Dark Energy ACTS LIKE ANTI GRAVITY!

Summary We have a good understanding of how gravity works on the Earth What is the nature of the Dark Matter? If MOND is correct alternative, what is the nature of SpaceTime now that the equivalence principle is violated Does the extra dimension explain how gravity works throughout the Universe What is the nature of the Dark Energy?

Bottom Line Apparently Life is not so Simple anymore. There is much still to learn!

Our Current Response Will we Acquire Global Wisdom in Time?

The Coming Resource Scarcity The Decline of Oil: The Decline of Oil:

How the Universe Helps  It’s a big place, with much to discover  People think about it in scientific, philosophical and artistic terms  It is your ultimate environment – life is made from star dust  It reminds us of the great unknown and may help to humble us during our more arrogant moments

The value of Universities Provides a safe haven for discovery (both personal and intellectual) Instills critical thinking in terms of conflicts between discovery, comfort zones, and potential paradigm shifts Helps students appreciate the intrinsic value of research and asking questions Astronomy is a good venue to teach these attributes of science and discovery

Discovery is Everywhere

New Kinds of Solar Systems

A Tenth Planet?

Origin of Life?

STAR DUST

Perspectives  Science is Discovery  Most is Unknown  Certainty is unwarranted  Knowledge is contextual  Cultural Bias Drives our Decisions  Finite Resources require wisdom to Manage  Can we re-acquire this Wisdom?

The End