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Lecture Two

Cosmic Forces

FROM ATOMS TO GALAXIES

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Curiosity Demands that We Ask Questions

• "Nothing exists except atoms and empty space - everything else is opinion“

Democritus of Abdera 430 B. C. Greece

• Matter is made of ATOMS.

• Different atoms for different ELEMENTS.

• What are Atoms?

• Atoms have a NUCLEUS of:

• PROTONS p+ Positive Electric Charge

• NEUTRONS n Neutral Charge

• The Nucleus is Surrounded by:

• ELECTRONS e- Negative Electric Charge

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The Simplest Atom

Carbon

• Uranium – heaviest natural atom: 92 protons, 143 neutrons, 92 electrons

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Atoms are VERY Small

• ~ 1 to 2 x 10-8 cm

• 10-8 cm = 1 ANGSTROM = 1 Å

• Size of Nucleus = 10-13 cm

• Your Thumb is made up of ~ 1024 ATOMS

Structure of Matter

• All things are made of ATOMS

• Little particles in perpetual motion

• Take water for example:

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Fundamental Laws of Nature

• Is there only one?

• Are the laws universal in Space and Time?

• The Test of Knowledge is always EXPERIMENT

• "My ambition is to live to see all of physics reduced to a single

formula so elegant and simple that it will fit on the front of my T-shirt"

Leon Lederman, 1993

The Scientific Method

• Observations

• Hypothesis

• Verifications

• “LAW”

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Evolution of Knowledge

• Laws are accurate... until they fail!

• DISASTER? NO!

• The discovery of a more accurate law.

• Example:

– Mass of an object is constant (Newton)

– Mass increases with velocity (Einstein)

Force: F = ma or a = F/m

• A force is that which can change the velocity of an object (either speed or direction).

– 1 dyne = g-cm/s2

– 1 Newton = kg-m/s2 (after Isaac)

= 105 dynes

• Forces cause acceleration!

• Example forces: Gravity

– Earth’s gravity: 980 g-cm/sec2

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Cosmic Forces

Name Relative Strength

1 Nuclear 1

2 Electromagnetic 1/137

3 Weak 10-13

4 Gravitational 10-39

Future: Grand Unified Theory (GUT) – 1+2+3

Theory of Everything (TOE) – 1+2+3+4

“Theory of Everything”

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Theory of Everything • Unite gravity with the other

fundamental forces. – Merging of gravity with quantum

mechanics and other forces.

• We don’t have a theory yet but the most promising ones involve “STRING THEORY” and “higher dimensions”

• String Theory suggests there are 11 dimensions (10 spatial + 1 time).

Gravity

• "Isaac Newton and the Apple" A.D. 1667

• F = Force of attraction (Newton)

• G = 6.67 x 10-11 m3kg-1sec-2

• m1 ; m2 = Masses (kg)

• d = Distance between objects (m)

2

21

d

mGmF

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Electromagnetic Force

• 1037 times stronger than Gravity

• Not all things attract

• Unlike particles attract - (+, -)

• Like particles repel - (+, + or -, -)

Electromagnetic Force

• ELECTROMAGNETIC FIELD AROUND THE PARTICLES

• Emitted energy propagates through this field

– Like a wave in the water

– With the speed of light

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Electromagnetic Energy

Atoms and molecules emit energy or "waves" of different "length" (or different energy).

Nuclear (Strong) and Weak Force

• Strong Force: Binding Force of Atomic Nuclei

– Keeps protons and neutrons together

– (A strong glue - "GLUONS")

• It has a VERY short range

• When released by nuclear interactions, vast amounts of energy are emitted.

• Weak Force: Gives rise to radioactivity

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New Revolution In Physics (1900 – 1930)

• Albert Einstein - Theory of Relativity

– No longer 3 dimensional space but 4 – Space-Time

– No longer a flat space but curved

• Quantum Mechanics

– Worked much better (more accurate) but predicted new unexpected results!

• Classical Physics is Rigidly Deterministic

– A given cause leads to a given result always and everywhere.

• In Quantum Mechanics, a given cause can lead to any of several results.

– Individual cases cannot be determined with certainty.

– The only laws are statistical ones for large numbers of instances.

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QM: The Uncertainty Principle

• The uncertainty principle of QM states that we cannot know both where something is and how fast it is moving.

• Thus we cannot predict exactly what will happen in a given experiment.

• The ‘Measurement’ problem

Uncertainty Principle

• For subatomic particles: Very important.

• However, the uncertainty becomes very small for larger things.

– Launch a rocket on a predictable path-- without worrying about subatomic particles.

– The behavior of an electron around the nucleus of an atom is more "Probabilistic"!

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Orbitals rather than orbits

• We don’t really see the electron in “orbit” around the nucleus.

• We have a probability of detecting an electron in a given location.

Humans have been able to explore the UNIVERSE from the very very small ATOMS to the very very large GALAXIES