Transcript gravity - in a secure place with other

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
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
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
For gravity  gravitons carry the instruction set
Particles can be screened because particles
interact with matter
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.
No earthly observations or experiments can
show that Newton’s theory is incomplete
But, remember the Anomaly
1859 precision observations of the orbit of
Mercury DISAGREE with Newtonian
Mechanics!
Now we need a new Theory

Einstein: Gravity = Curvature of Spacetime
Ouch, Curved Spacetime?




More mass = greater curvature (locally)
Affects time (locally at curvature)
E= mc2 means that photons have energy related
mass and therefore follow the curvature:
Need an Ant Universe to demonstrate:
The Need for Dark Matter


1970’s: Start to measure rotational properties of
other galaxies:
Invariably observe “flat” rotation curves:
Resolution:



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
Is there another explanation?
Maybe we still don’t understand
Gravity?




Maybe gravity works differently on different
acceleration scales? (GM/R2 = 9.8 m/sec2 on Earth)
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
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
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:
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