head for understandable description of matter and forces at the most fundamental level n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Head for Understandable Description of Matter and Forces at the Most Fundamental Level PowerPoint Presentation
Download Presentation
Head for Understandable Description of Matter and Forces at the Most Fundamental Level

Loading in 2 Seconds...

play fullscreen
1 / 39

Head for Understandable Description of Matter and Forces at the Most Fundamental Level - PowerPoint PPT Presentation


  • 105 Views
  • Uploaded on

N. Head for Understandable Description of Matter and Forces at the Most Fundamental Level. N. Particles and Forces tell us about the beginning of the Universe. Is this a Belief System?. NO! Science does use the beauty of ideas, but ultimately relies on EXPERIMENT!!.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Head for Understandable Description of Matter and Forces at the Most Fundamental Level' - consuelo


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
head for understandable description of matter and forces at the most fundamental level

N

Head for Understandable Description of Matter and Forces at the Most Fundamental Level

Frank Sciulli - Lecture I

is this a belief system
Is this a Belief System?

NO!

Science does use the beauty of ideas, but ultimately relies on EXPERIMENT!!

Frank Sciulli - Lecture I

four lectures leading to the standard model of particle physics a paradigm

Illustrate, hopefully, that Physics (Science) has as ultimate

arbitrator

NATURE ! ! ! !

Four Lectures Leading to the Standard Model of Particle Physics - A Paradigm
  • Particles, Light, and Special Relativity
  • Quantum Mechanics, Atoms and Particles
  • Particles, Forces, and the Electroweak Interaction
  • Hadrons, Strong Force and the Standard Model

Frank Sciulli - Lecture I

approach to the subjects
Approach to the Subjects

Eclectic: factual, historical,

experimental, …

Lets start with pre-20th Century

  • Newton’s Laws (Galileo,…)
  • Energy and Work
  • Thermodynamics
  • Chemistry … atoms?
  • Optics, fluids, waves, ...

Particles and Forces:

Frank Sciulli - Lecture I

classical particles and waves

Single slit

Double slit

Classical particles and waves

Water waves hit slits

Classical particle scattering (balls)

Frank Sciulli - Lecture I

newton s laws for particles

Forces from elsewhere

Gravity, electricity, magnetism, ….

Newton’s Laws for Particles

Frank Sciulli - Lecture I

consolidation of electricity and magnetism by maxwell 1864
Consolidation of Electricity and Magnetism by Maxwell (1864)

Established clear rules for fields as the origin of EM force.

Made rules consistent!

They read

Source of E is charge (Gauss Law)

No magnetic charge

Faraday’s Law of Induction

Source of B is charge motion + Maxwell’s new Displacement Current

Frank Sciulli - Lecture I

implications electromagnetic waves
Implications: Electromagnetic Waves

Frank Sciulli - Lecture I

michaelson interferometer

Observer sees fringes

(light and dark pattern),

corresponding to constructive

and destructive interference:

For example, if 2d2 -2d1

changes by /2, fringe

pattern shifts

Michaelson Interferometer

Became important element in central problem of 100 yrs ago: why is

Frank Sciulli - Lecture I

slide11

But the velocity of the

mechanical wave relative to

the observer obeys the same rules

as a travelling particle:

relative velocities

Light also

has velocity

independent

of source

speed

PROBLEMVelocity of a mechanical wave depends only on the medium, not the velocity of the source (even though frequency and wavelength change - Doppler shift)

Example, it is possible for a

“listener” to travel faster than a

sound wave. In this case, the

sound will never catch up to the

listener. Sound wave in “A”

never catches “B” if v>c

But MEs state EM waves have v=c

Frank Sciulli - Lecture I

most obvious resolution luminiferous ether

V=30km/s

Earth motion

around sun

  • Essential element of scientific hypothesis: provides a possibility for testing!
Most obvious resolution:Luminiferous Ether
  • Provides transmission medium, in analogy with that required by mechanical waves
  • Provides a “special” frame of motion … where the laws of E&M (Maxwell’s Equations) are valid
    • All other frames of reference (in motion relative to the special one), Maxwell’s Equations are only approximately true!

Frank Sciulli - Lecture I

1887 michaelson morley idea
1887: Michaelson-Morley idea

Frank Sciulli - Lecture I

michaelson morley expt

Apparatus on bed of liquid mercury, rotate by 90 degrees

Michaelson - Morley Expt

Use velocity of Earth around the sun v =30km/s

Rotate apparatus by 90 deg… change in relative

phase of the two light rays by  is expected

Frank Sciulli - Lecture I

michaelson morley experiment big physics of 1887

Earth motion

around sun

V=30km/s

  5 10-7 m

Make d as

large as

possible

Michaelson Morley Experiment - “Big” Physics of 1887

CONCLUDE: No phase shift was observed

NO ETHER … ?!%*

Frank Sciulli - Lecture I

einstein s reasoning

Plane shoots rocket

Plane shoots laser

Einstein’s Reasoning

Maxwell’s Equations (eg Law of Induction at left)

do not depend on which is moving relative to what. So it is reasonable that the value of c coming out of the equations should not depend on state of motion of anyone! Sound a bit crazy? Not to Albert Einstein!

Newtonian mechanics with objects or

(mechanical) waves: velocity is relative

to motion of observer! OLDTHINK…

Frank Sciulli - Lecture I

slide17

ConundrumEITHER light is like mechanical waves: E&M only valid in one frame!?OR light is NOT like mechanical waves; E&M valid in all frames, independent of their motionEinstein chose the latter

Einstein “Laws of Physics the same in all inertial frames”

MEANS

Maxwell’s equations valid in all non-accelerating coord. systs

BUT this implies that velocity of light = c in vacuum

no matter where

the light comes from and how fast you are moving

Frank Sciulli - Lecture I

slide18

Einstein Postulates (1905) require(a) speed of light (in vacuum) same in all inertial frames(b) speed of light (in vacuum) independent of the motion of sourceCARRY MANY IMPLICATIONS

Lorentz Contraction

+

Time Dilation

+

Frank Sciulli - Lecture I

transformations of position and time
Transformations of Position and Time

Frank Sciulli - Lecture I

reversible
Reversible

Check if these equations

give correct answer:

For x’=ct’ ….. x=ct ?

Frank Sciulli - Lecture I

limiting cases

v << c

= v/c

Limiting cases

So this  is essentially ONE unless the object is near the velocity of light… where it rises very rapidly.

Frank Sciulli - Lecture I

time dilation and lorentz contraction
Time Dilation and Lorentz Contraction

Happening in S’ at x’=0

over t’

Rod at rest in S’, with length L0

Length in S is L, measure ends

at same time: t=0

Frank Sciulli - Lecture I

relativistic invariants
Relativistic Invariants

Frank Sciulli - Lecture I

implications of relativity for particle momentum and energy
Implications of Relativity for Particle Momentum and Energy

Relativistic

Nonrelativistic

Implication: Matter is a form of energy. At v=0, E=mc2.

Frank Sciulli - Lecture I

transformation of momenta energy
Transformation of Momenta/Energy

Frank Sciulli - Lecture I

energy momentum mass and units

X

X

eV eV/c eV/c2

MeV MeV/c MeV/c2

GeV GeV/c GeV/c2

Energy/Momentum/Mass and Units

Universal energy

units are joules (traditionally);

but a much simpler one for dealing with particles:

(with electric charges that are multiples of the electron)

Frank Sciulli - Lecture I

mass is energy and vice versa

N

Mass is Energy and vice versa
  • Macroscopic systems, mass stays essentially the same and
  • kinetic energies small compared to rest mass energy: separate!
  • Microscopic systems (atoms), energies of electrons are small
  • compared to mass of system:
  • in hydrogen atom, U=13.6 eV but M~109 eV/c2
  • Note that mass of proton is ~ 1 GeV/c2
  • Ultra - microscopic systems (nuclei and smaller), energies of
  • constituents get comparable or larger than their rest mass

What about

EM fields?

Frank Sciulli - Lecture I

mass disappears energy appears fusion

N

Mass Disappears-Energy AppearsFUSION

Mass difference of .0304u = 28.3 MeV/c2 becomes energy

Frank Sciulli - Lecture I

relativity is the way the world works
Relativity is the way the world works

Example: NAVSTAR Satellite system to track velocity of airplanes uses Doppler shifts.

If non-relativistic Doppler formula were used, precision on velocity would be about 21 cm/s.

If relativistic Doppler formula used, precision  1.4 cm/s

Examples: Real-life everyday observations in particle and nuclear physics, where new matter is made

and it spontaneously decays

Frank Sciulli - Lecture I

metastable matter radioactive decay makes a clock

Characterized by lifetime ()

or half-life (T1/2 =  ln2 = 0.7 )

1000

100

10

1

Metastable Matter(Radioactive Decay makes a clock)

Example 128I nuclide

with T1/2 = 25 minutes.

Compare:

14C has T1/2 = 5730 yrs.

 has T1/2= 3.75  10-8 sec

Frank Sciulli - Lecture I

working with unstable matter can make for problems

N

Working with Unstable Matter Can Make for Problems!

Just kidding … It’s actually not that hard!

Here we use pions, unstable particles with mass of 140 Mev and lifetimes of ~ 3 10-8 sec

Frank Sciulli - Lecture I

real world test of relativity fermilab complex

15 story high rise

Four mile circumference Tevatron Ring

Real World Test of Relativity: Fermilab Complex

Frank Sciulli - Lecture I

accelerators raise kinetic energy using electric fields

measure

velocity

= v/c

Accelerators Raise Kinetic Energy using Electric Fields

Each loop, the energy of protons are raised by increment determined by electric potential: E =eV

 = E/m

Proton total Energy

versus velocity

Frank Sciulli - Lecture I

accelerated protons have very large energy

Beam protons hit stationary

target (Et=m) with

very large kinetic energy

 = Eb/m

Extracted protons have

energy E  800 GeV

Accelerated protons have very large energy

What happens????

Frank Sciulli - Lecture I

collision of 300 gev proton with stationary nucleon
Collision of 300 GeV proton with stationary nucleon

New kinds of particles made out

of kinetic energy: mesons (pions)

with mass of 140 MeV each.

Frank Sciulli - Lecture I

beams of pions made from collisions of high energy protons

Beams of pions made from collisions of high energy protons

WRONG!!

Beam line, 0.78 km long,

transports 140 GeV ’s made at tgt

Frank Sciulli - Lecture I

right answer lab perspective

v

Right answer: Lab perspective

Right!!!

Frank Sciulli - Lecture I

right answer pion perspective

v

Right answer: pion perspective

Right!!!

Frank Sciulli - Lecture I

conclusions special relativity
Conclusions - Special Relativity
  • Relativity was required by experimental information at the time it was invented (1905)
  • It is essential now to describe the world, especially since we can directly observe objects travelling near the speed of light
  • The rules are, in fact, simple - see handout or website!
  • Do the problems and prove the simplicity!

Frank Sciulli - Lecture I