10/17/2012. Lecture Two. Cosmic Forces FROM ATOMS GALAXIES

Size: px

Start display at page:

Download "10/17/2012. Lecture Two. Cosmic Forces FROM ATOMS GALAXIES"

Dorcas Russell
5 years ago
Views:

1 Lecture Two Cosmic Forces FROM ATOMS TO GALAXIES 1

2 2

3 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 3

4 The Simplest Atom Carbon Uranium heaviest natural atom: 92 protons, 143 neutrons, 92 electrons 4

5 Atoms are VERY Small ~ 1 to 2 x 10-8 cm 10-8 cm = 1 ANGSTROM = 1 Å Size of Nucleus = cm Your Thumb is made up of ~ ATOMS Structure of Matter All things are made of ATOMS Little particles in perpetual motion Take water for example: 5

6 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 Observations The Scientific Method Hypothesis Verifications LAW 6

7 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/s 2 1 Newton = kg-m/s 2 (after Isaac) = 10 5 dynes Forces cause acceleration! Example forces: Gravity Earth s gravity: 980 g-cm/sec 2 7

Cosmic Forces Name Relative Strength 1 Nuclear 1 2 Electromagnetic 1/137 3 Weak 10-13 4 Gravitational

8 Cosmic Forces Name Relative Strength 1 Nuclear 1 2 Electromagnetic 1/137 3 Weak Gravitational Future: Grand Unified Theory (GUT) Theory of Everything (TOE) Theory of Everything 8

9 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 Gm1m F 2 d F = Force of attraction (Newton) G = 6.67 x m 3 kg -1 sec -2 m 1 ; m 2 = Masses (kg) d = Distance between objects (m) 2 9

10 Electromagnetic Force 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 10

11 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 11

12 New Revolution In Physics ( ) 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. 12

13 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"! 13

14 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 14

Forces and Nuclear Processes

Forces and Nuclear Processes To understand how stars generate the enormous amounts of light they produce will require us to delve into a wee bit of physics. First we will examine the forces that act at