is a public understanding of abstract physics concepts feasible? johannes p. wessels institut für...
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Is a public understanding of abstract physics concepts feasible?
Johannes P. Wessels Institut für KernphysikWestfälische Wilhelms-Universität Münsterand CERN, Geneva
Aspects of the nature of matter investigated at the Large Hadron Collider
• What is the nature of matter?• How do we study it?• What are our (physicists’) physics concepts?• If they appear to be abstract, how do we try to motivate, communicate
these concepts?
Analogies – do you find them useful?
How abstract is abstract? Opinions
Quantum Mechanics cannot be understood.Richard P. Feynman
The most incomprehensible about nature isthat she is so comprehensible. Albert Einstein
physics is looking for guiding principles of nature
Size of the Universe 3*1025m
each of the 9325 dots represents an entire galaxy
…at 1021m…
…our galaxy with its roughly 1011 “Suns”
…at 1020m…
…at 1014m…
…finally our solar system
…at 1011m…
…roughly six weeks of the earth’s path
…at 109m…
…the moon’s orbit
…at 107m…
…not so unfamiliar
…at 106m…
…a 1000 km of cultural heritage (and vacation)
…at 105m…
…space shuttle calling Geneva…
…at 104m…
…approaching GVA…
…at 103m…
…CERN just before landing
…at 102m…
…part of where CERN’s 10000 people work
…at 100m…
…in a beautiful setting
…at 10-1m…
…which gets moreand more interesting
…at 10-2m…
…the closer…
jpw - Single Cell 2008 - 24.11.2008
…at 10-3m…
…you look…
…at 10-5m…
… ever more interesting …
…at 10-7m…
…till you see things that can’t be seen with ‘normal’ light…
…at 10-8m…
…special light sources can even illuminate single molecules …
how abstract / real is this?
…at 10-10m…
…reaching atoms, that are essentially “empty” …
how familiar / correct is this?
…at 10-14m…
…almost the entire mass of the atom is concentrated in the nucleus, which consists of neutrons and protons…
How useful is it to know that, if the earth were of that density it would fit into a cube of 300x300x300 m3?
…at 10-15m…
…neutrons and protons in turn consist of quarks and gluons.These quarks may well be point-like particles. They can NEVER be seen in solitude.
THE matter investigatedat the LHC.
Physics - in Search for Similarities
The Complex
The Smallest The Biggest
K.H. Meier
Synapses
Stars Meters
Composition of the UniverseDynamics of the evolution governed by interations-> forces
23%
72%
Concept of Interaction - ForceNewton: actio = reactioforce fields work at a distance - potential
standard model: forces are mediated by the exchange of particlesTi
me
Position
Interaction entailsscattering Feynman-Graph
4 Fundamental Interactions
falling apples,planetary orbitsstrength: 10-39
range: infinitemediator: graviton?
television, magnets,chemical bindingstrength: 1/137range: infinitemediator: photon
nuclear stability,quark confinementstrength: 1range: 10-15 mmediator: gluon
-decay, neutron stability, neutrinosstrength: 10-5
range: 10-18 mmediator: W,Z-Boson
4 Fundamental Interactions
falling apples,planetary orbitsstrength: 10-39
range: infinitemediator: graviton?
television, magnets,chemical bindingstrength: 1/137range: infinitemediator: photon
nuclear stability,quark confinementstrength: 1range: 10-15 mmediator: gluon
-decay, neutron stability, neutrinosstrength: 10-5
range: 10-18 mmediator: W,Z-Boson
4 Fundamental Interactions
falling apples,planetary orbitsstrength: 10-39
range: infinitemediator: graviton?
television, magnets,chemical bindingstrength: 1/137range: infinitemediator: photon
nuclear stability,quark confinementstrength: 1range: 10-15 mmediator: gluon
-decay, neutron stability, neutrinosstrength: 10-5
range: 10-18 mmediator: W,Z-Boson
4 Fundamental Interactions
falling apples,planetary orbitsstrength: 10-39
range: infinitemediator: graviton?
television, magnets,chemical bindingstrength: 1/137range: infinitemediator: photon
nuclear stability,quark confinementstrength: 1range: 10-15 mmediator: gluons
-decay, neutron stability, neutrinosstrength: 10-5
range: 10-18 mmediator: W,Z-Boson
4 Fundamental Interactions
falling apples,planetary orbitsstrength: 10-39
range: infinitemediator: graviton?
television, magnets,chemical bindingstrength: 1/137range: infinitemediator: photon
nuclear stability,quark confinementstrength: 1range: 10-15 mmediator: gluons
-decay, neutron stability, neutrinosstrength: 10-5
range: 10-18 mmediator: W,Z-Bosons
things we can relate to
things we cannot relate to
All Partilces of the Standard Model
really all of them?
important symmetry:each particles has a corresponding anti-particle.creation always in pairs
Example: The Electronwhich interaction a particle is subject todepends on its charge (charges)In case of the electron: participates in electromagnetic, weak
and gravitational interaction
Tim
e
Position
electrical charge couples to the potonstrength depends on the coupling constant a
In case of the weak interaction charge -> weak charge and weak coupling constantIn case of the gravitational interaction charge -> mass and gravitational coupling constant
Example: Strong InteractionQuarks are subject to the strong interaction.The corresponding ‘charge’ is the color charge (r,g,b).The mediators (exchange particles) are the gluons.
Position
Time
Gluons carry color charge, therefore, they interact amongst themselves strongly.
Confinement
all strongly bound objects are color neutral.
they are either baryonsconsisting of 3 quarks
or
mesons consisting of a quark and an anti-quark.
Proton
u u
d
u d
Pion +
Confinement: There are no free quarks in nature.
How do we know about them and their properties?
The “Right” Light to Look Inside of Things
Vision works byscattering of‘visible’ light
“Vision” of even smaller structures viascattering of particles
= 400-700 nm
= h/p
The “Right” Light to Look Inside of Things
Vision works byscattering of‘visible’ light
“Vision” of even smaller structures viascattering of particles
= 400-700 nm
= h/p
AcceleratorsAcceleration of a charge in an electric field: E = q•U
For the LHC you would need 2 times 7000 trillion batteries
jpw - Single Cell 2008 - 24.11.2008
ALICE
LHC
SPS
…the “Light” from Large Accelerators
Either shoot on stationary target or collide beams
Recall Einstein’s famous equation E=mc2 for particle production
…Seeing? - we have no sense for particle radiation.
So, we need suitable detectors.
jpw - Single Cell 2008 - 24.11.2008
Bubble Chambers
One of the first detectors to ‘view’ complex particle production events.
jpw - Single Cell 2008 - 24.11.2008
jpw - Single Cell 2008 - 24.11.2008
L3
LEP
SPS
fully electronic “eyes” - here L3
…so we can “see”!
what constitutes seeing or evidence?
The general public’s view on particles
All Particles of the Standard Model
have been ‘seen’that way.
only the lightestare stable!
their massesdiffer hugely
Mass – a Puzzle
mass of the proton is 938 [units of mass]
it consists of 2 up- and 1 down-quarkmass(up) = 1.5 – 3.3 [units of mass]mass(down) = 3.5 – 6.0 [units of mass]
mass(proton) = 2 x mass(up) + 1 x mass(down) = 9.5 – 12.3 [units of mass]
Proton
strong binding force leads to the mass of the proton
again - E=mc2 ?
How do Elementary Particles Acquire Mass? - Higgs (1)
in strict analogy to a cocktail partyThe room is filled with physicists, entertaining lively discussions aka as small talk. They constitute the Higgs-field (which is everywhere not just in this room!).
How do Elementary Particles Acquire Mass? - Higgs (2)
A famous (or perhaps very good looking) physicist enters the room.
He immediately attracts a group of admirers. A local distortion of the field is generated and propagates.
How do Elementary Particles Acquire Mass? - Higgs (3)
It is getting ever more difficult for him to move.
He seems to gain mass. Just like a particle moving through the Higgs-field.
How do Elementary Particles Acquire Mass? - Higgs (4)
The same mechanism works for a simple message.
The buffet is open!
How do Elementary Particles Acquire Mass? - Higgs (5)
Again a distortion develops.
This is how the Higgs particle itself acquires its mass.
All Particles of the Standard Model
Crucial theoretical prediction
Evidence slowly emerging
K.H. Meier
Emmy Amalia Noether (1882-1935)
All fine technical points aside, Noether's theorem can be stated informallyIf a system has a continuous symmetry property, then there are corresponding quantities whose values are conserved in time.
time invariance -> energy conservationtranslational invariance -> momentum conservationrotational invariance -> angular momentum conservation
Symmetries appear to be a principle of nature
wikipedia
Supersymmetry - SUSY
The world as we know it A whole new world?
Standard Particles SUSY Particles
Dark MatterDark Matter interactsvia Gravitation. This leads togravitational lensing.
There are roughly 3000 invisible,yet “tractable”, particles percubic meter of the universe.
INVISIBLE!
all kinds of candidatesfor cold dark mattermay be produced at LHC
Summary
• What is the nature of matter?
concept of elementary constituents and their interactions
leads to proper description of processes in nature. • How do we study it?
just like looking – by scattering of particles.• What are our (physicists’) physics concepts?
detailed description in so-called quantum field theories.• If they appear to be abstract, how do we try to motivate, communicate
these concepts?
does nature care?• Analogies – do you find them useful?
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