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Is a public understanding of abstract physics concepts feasible?

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Is a public understanding of abstract physics concepts feasible?

Johannes P. Wessels InstitutfürKernphysikWestfälischeWilhelms-UniversitätMünster

and 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, communicatethese 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 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 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 10-2m…

…the closer…

…at 10-5m…

… ever more interesting …

…at 10-7m…

…till you see things that can’t be seen with ‘normal’ light…

…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

Synapses

The Biggest

The Smallest

Meters

Stars

K.H. Meier

Concept of Interaction - Force

Newton: actio = reactioforce fields work at a distance - potential

standard model: forces are mediated by the exchange of particles

Interaction entailsscattering

Time

Feynman-Graph

Position

4 Fundamental Interactions

falling apples,planetary orbits

strength: 10-39

range: infinite

mediator: graviton?

television, magnets,chemical binding

strength: 1/137

range: infinite

mediator: photon

nuclear stability,

quark confinement

strength: 1

range: 10-15 m

mediator: gluon

-decay, neutron stability, neutrinos

strength: 10-5

range: 10-18 m

mediator: W,Z-Boson

4 Fundamental Interactions

falling apples,planetary orbits

strength: 10-39

range: infinite

mediator: graviton?

television, magnets,chemical binding

strength: 1/137

range: infinite

mediator: photon

nuclear stability,

quark confinement

strength: 1

range: 10-15 m

mediator: gluon

-decay, neutron stability, neutrinos

strength: 10-5

range: 10-18 m

mediator: W,Z-Boson

4 Fundamental Interactions

falling apples,planetary orbits

strength: 10-39

range: infinite

mediator: graviton?

television, magnets,chemical binding

strength: 1/137

range: infinite

mediator: photon

nuclear stability,

quark confinement

strength: 1

range: 10-15 m

mediator: gluon

-decay, neutron stability, neutrinos

strength: 10-5

range: 10-18 m

mediator: W,Z-Boson

4 Fundamental Interactions

falling apples,planetary orbits

strength: 10-39

range: infinite

mediator: graviton?

television, magnets,chemical binding

strength: 1/137

range: infinite

mediator: photon

nuclear stability,

quark confinement

strength: 1

range: 10-15 m

mediator: gluons

-decay, neutron stability, neutrinos

strength: 10-5

range: 10-18 m

mediator: W,Z-Boson

4 Fundamental Interactions

falling apples,planetary orbits

strength: 10-39

range: infinite

mediator: graviton?

things we can relate to

television, magnets,chemical binding

strength: 1/137

range: infinite

mediator: photon

nuclear stability,

quark confinement

strength: 1

range: 10-15 m

mediator: gluons

-decay, neutron stability, neutrinos

strength: 10-5

range: 10-18 m

mediator: W,Z-Bosons

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 Electron

Time

Position

which interaction a particle is subject todepends on its charge (charges)

In case of the electron: participates in electromagnetic, weakand gravitational interaction

electrical charge couples to the poton

strength depends on the coupling constant a

In case of the weakinteraction charge -> weak charge and

weak coupling constant

In case of the gravitational interaction charge -> mass and

gravitational coupling constant

Example: Strong Interaction

Quarks 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

d

all strongly bound objects are color neutral.

they are either baryons

consisting of 3 quarks

or

mesons consisting of a quark and an anti-quark.

d

u

u

Proton

u

Confinement:There are no free quarks in nature.

How do we know about them and their properties?

Pion +

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

Accelerators

Acceleration of a charge in an electric field: E = q•U

For the LHC you would need 2 times 7000 trillion batteries

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.

Bubble ChambersOne of the first detectors to ‘view’ complex particle production events.

jpw - Single Cell 2008 - 24.11.2008

what constitutes seeing or evidence?

All Particles of the Standard Model

have been ‘seen’that way.

only the lightest

are stable!

their masses

differ hugely

Mass – a Puzzle

mass of the proton is 938 [units of mass]

it consists of 2 up- and 1 down-quark

mass(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 party

The 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.

Emmy AmaliaNoether (1882-1935)

All fine technical points aside, Noether\'s theorem can be stated informally

If a system has a continuous symmetry property, then there are corresponding quantities whose values are conserved in time.

time invariance -> energy conservation

translational invariance -> momentum conservation

rotational invariance -> angular momentum conservation

Symmetries appear to be a principle of nature

Dark Matter

Dark Matter interactsvia Gravitation. This leads togravitational lensing.

There are roughly 3000 invisible,

yet “tractable”, particles per

cubic meter of the universe.

all kinds of candidatesfor cold dark mattermay be produced at LHC

INVISIBLE!

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?

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