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…

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…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 Interactionsfalling 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 Interactionsfalling 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 Interactionsfalling 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 Interactionsfalling 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 Interactionsfalling 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

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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.

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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?

A physicists view on SEEING particles

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 interactionsleads 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, communicatethese concepts?does nature care?

• Analogies – do you find them useful?