# Presentation: 656249

## A Quantum Journey

## Atomic Theory

- “The present state of atomic theory is characterised by the fact that we not only believe the existence of atoms to be proved beyond a doubt, but also we even believe that we have an intimate knowledge of the constituents of the individual atoms ...”

*Niels Bohr (1885-1962*)

- Stockholm, 1922

- A Quantum Journey

- Peter Skands

## Atomic Theory

- Today, we even believe that we have an intimate knowledge of the constituents of

- nothing

- A Quantum Journey

- Peter Skands

## Overview

- A journey into the atom
- 1802: Mysterious lines in the Sun
- 1896: Unknown forms of radiation from Uranium salts
- 1897: Discovery of the electron
- Early 20th century: the Quantum Hypothesis
- The world seen by accelerators
- 1932: the first accelerator
- Fermilab and the “Standard Model”
- Beyond the known
- Five great questions for your Ask-A-Scientist session

- A Quantum Journey

- Peter Skands

## The trouble with the Rainbow

- William H. Wollaston (1802): 7 mysterious holes in the rainbow ...
- Joseph von Fraunhofer (1821): 500 lines ...
- Is the Sun made of salt?
- The eclipse of 1868
- A rainbow bridge to touch the stars
- The birth of spectroscopy!
- 1895: star stuff on Earth

- A Quantum Journey

- Peter Skands

## 1895: The X Rays

- “The Academy awarded the Nobel Prize in Physics to Wilhelm Conrad Röntgen ... for the discovery with which his name is linked for all time: the discovery of the so-called Röntgen rays or, as he himself called them, X-rays. These are, as we know, a new form of energy and have received the name "rays" on account of their property of propagating themselves in straight lines as light does. The actual constitution of this radiation of energy is still unknown.”

- Presentation speech, first Nobel prize, Stockholm, 1901

- Und nun ging der Teufel los ...

- A Quantum Journey

- Peter Skands

## Radio Activity 

- Becquerel’s inheritance
- Is there a relation between Röntgen’s vacuum-tube induced phosphorescence and natural phosphorescence?

- Pierre and Marie: call it “radioactivity”
- Two hypotheses
- An unknown sort of radiation fills all of space. The radioactive elements are the ones that are able to transform this radiation to observable forms

- A Quantum Journey

- Peter Skands

## Radio Activity

- “This leads to the supposition that the transformation is more far-reaching than the ordinary chemical transformations, that the existence of the atom is even at stake, and that one is in the presence of a transformation of the elements.”
- Helium production + existence of Radium  the alchemists were right!
- Radium becomes more expensive than gold and diamonds

- Pierre Curie, Stockholm, 1905

- PS : Eve Curie’s “Madame Curie” is a must read. (I saw it for $13 at amazon.)

- A Quantum Journey

- Peter Skands

## The Fruit of Knowledge

- It can even be thought that radium could become very dangerous in criminal hands, and here the question can be raised whether mankind benefits from knowing the secrets of Nature, whether it is ready to profit from it or whether this knowledge will not be harmful for it.
- The example of the discoveries of Nobel is characteristic, as powerful explosives have enabled man to do wonderful work. They are also a terrible means of destruction in the hands of great criminals who are leading the peoples towards war.
- I am one of those who believe with Nobel that mankind will derive more good than harm from the new discoveries.

- Pierre Curie, Stockholm, 1905

- A Quantum Journey

- Peter Skands

## A clumsy man

- British or German?
- Deflected by magnetic fields and producing charge accumulation  negatively charged particles?
- Not deflected by electric fields, penetrate thin metals  ether waves?

- J.J. Thomson, 1897

- “Thus the atom is not the ultimate limit to the subdivision of matter; we may go further ... the corpuscles appear to form a part of all kinds of matter ... it seems natural therefore to regard it as one of the bricks of which atoms are built up.”

- A Quantum Journey

- Peter Skands

## Corpuscle of Light

- Classical theory  ultraviolet disaster!
- Planck (1900): equation for black-body radiation with two constants: Avogadro + a new one, h
- Fits with experiment, but ... quanta ... ?
- Einstein (1905): Yes, light quanta!
- Photo-electric effect  direct proof of the existence of quanta

- Problems turned to proof:
- Variation of light intensity  variation of electron numbers
- Variation of light frequency  variation of electron energy

- A Quantum Journey

- Peter Skands

## Wollaston’s explanation

- Rutherford’s atom + Einstein and Planck’s quantum hypothesis  Niels Bohr (1913): There exist fundamentally only separate stationary states in the atoms
- Ephoton = h f = E2 – E1
- Applied to kitchen salt and sunlight, Wollaston’s rainbow, now 150 years old, was finally explained
- But what a strange explanation ...

- A Quantum Journey

- Peter Skands

## The Language of Atoms

- Correspondence
- From quantum mechanics, the classical laws must be obtained in the limit of large quantum numbers or small *h*
- Complementarity
- Mutually exclusive descriptions must be accepted. An experiment can show particle-like properties of matter, or wave-like ones, but not both at the same time.

*Niels Bohr (1885-1962*)

- A Quantum Journey

- Peter Skands

## The Copenhagen Interpretation

- The wave function only describes a (subjective) state of knowledge; it is not itself “real”
- Schrödinger’s cat can easily “be” both alive and dead
- Wigner’s friend can see a different wave function than Wigner
- EPR is not a paradox. Wave function collapse is subjective. Cannot be used to transfer information at v > c  anyway
- The uncertainty principle defines the limits of certainty
- Science is only about predicting the outcome of experiments. Additional questions are meta-physical (positivism)
- So the wave function is all you’re going to get
- Paraphrasing by Dirac: “Shut up and calculate”

- A Quantum Journey

- Peter Skands

## Antimatter

- "On August 2, 1932 ... the tracks shown in Fig. 1 were obtained, which seemed to be interpretable only on the basis of the existence [...] of a particle carrying a positive charge but having a mass of the same order of magnitude as that normally possessed by a free negative electron”

*Carl Anderson (1905-1991)*

- Dirac’s relativistic wave equation with spin  E2 = ...

- C. Anderson, “The positive electron”, Phys. Rev. 43 (1933) p.491

- A Quantum Journey

- Peter Skands

## The World Seen by Accelerators

- 1932: Cockroft & Walton built a system that could fire protons, like bullets, into metal targets: p + LiF  Be, He, O, ...

- “Transmutation of atomic nuclei by artificially accelerated atomic particles”

- Cavendish laboratory, ca. 1932

- A Quantum Journey

- Peter Skands

## Particle Accelerators

- The goal:

- Accelerators are ‘optical’ systems, with
- Light  charged particles
- Wave length shortening  particle acceleration
- Lenses  magnets

- E = mc2

- A Quantum Journey

- Peter Skands

## Collisions

- A Quantum Journey

- Peter Skands

## Detectors

- Tracking
- spatial vertexing and momentum measurement
- Calorimetry
- energy measurement
- Particle identification
- Muons are highly penetrating
- Hadrons are more penetrating than electrons and photons
- Photons aren’t charged so don’t leave tracks, electrons do
- ...
- And, please, with extremely high precision!

- A Quantum Journey

- Peter Skands

## The Tevatron at Fermilab

- Energy released by combustion of octane molecule ~ 50 eV
- About 1 eV per nucleon, typical for chemical reactions
- Neutron-induced fission of Uranium-235 ~ 200,000,000 eV
- About 1,000,000 eV per nucleon, typical for nuclear reactions
- Particle collision at the Fermilab Tevatron: 1,960,000,000,000 eV
- About 1,000,000,000,000 eV per (anti-)nucleon, typical for the “Terascale”
- Still, Dan Brown exaggerated a bit in Angels & Demons ...
- “If all of the antimatter ever produced at Fermilab had been collected, we would have a couple of nanogrammes ...”

- 1 eV = 1.602E-19 J.

- D. Van der Meulen, antimatter expert, Fermilab

- A Quantum Journey

- Peter Skands

## The LHC

- The Large Hadron Collider (LHC) at CERN, Geneva, will reach 10 times the energy of the Tevatron
- Scheduled to commence operations in May 2007
- Proton beams, colliding at 14 Tera-eV
- Mission 1: investigate the question of mass
- Mission 2: explore the “Terascale”
- At the Tera-eV scale theorists speculate new phenomena may reveal themselves
- Few things are known for certain about the nature of these phenomena
- Suggestions include the usual suspects: new symmetries, new forces, new matter, extra dimensions, and, of course, the unexpected ...

- “God does not play dice ...” (A. Einstein)  ... “Einstein! Don’t tell God what to do” (N. Bohr)

- A Quantum Journey

- Peter Skands

## The ILC

- When the LHC takes over the energy frontier, the shutdown of Fermilab’s Tevatron will make way for new projects
- The future of the lab (and accelerator-based particle physics in America in general) may well lie with a proposed machine called the International Linear Collider (ILC)

- “Only” 500 GeV (or maybe 1 TeV), but shoots electrons on positrons  higher precision

- A Quantum Journey

- Peter Skands

## The “Standard Model”

- You often hear: there are 6 quarks, 3 leptons, and 3 neutrinos, or things to that effect.
- Let’s count degrees of freedom:
- Quarks: 3G ( NC  ( uR + uL  + dR + dL ) + antiquarks ) = 72 quark dof
- Leptons: 3G ( eL + eR +  νL + antileptons ) = 18 lepton dof
- Force particles: photon: 2 dof + gluons: 8 x 2 dof + (W+,W-,Z) :3 dof = 27 dof
- Higgs: 1 dof
- So the Standard Model really has 118 individual degrees of freedom (124 if we add right-handed neutrinos, 128 if we add another “Higgs doublet”, 256 if we make that “supersymmetric”, etc).
- As far as we know, these 100-odd degrees of freedom, plus gravity, represent the dynamic content of the universe

- A Quantum Journey

- Peter Skands

## Beyond the Known

- What is it that produces the special concentration of energy around particles known as ‘mass’?
- What is ‘Dark Matter’? Can we produce it?
- What about ‘Dark Energy’?
- How does gravity fit in? Are all forces one?
- Are there undiscovered principles of Nature? What physical laws exist beyond the known?

- “There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.”

- Hamlet (act I, sc v)

- A Quantum Journey

- Peter Skands

## Mass

- Consider an ether ‘field’ distributed evenly across the Universe, of uniform strength
- Suppose that different particles experience this field as being more or less transparent, i.e. that different particles couple to it with different strength
- Suppose that the nature of the interaction is such that the ether ‘condenses’ around particles which couple to it, causing an increased energy density around the particle
- This is essentially the Higgs mechanism

- A Quantum Journey

- Peter Skands

## The Higgs Particle

- If correct, the Higgs mechanism makes one spectacular prediction: it should be possible to excite a wave in the Higgs field itself, an ether wave
- This wave would quickly dissolve (decay) into massive particles, but should be detectable via its decay products
- Made out of pure ‘Higgs’ ether, in particle form this wave is known as the ‘Higgs particle’ or ‘Higgs boson’
- We are searching intensely for it here at Fermilab, but so far it has remained elusive

- A Quantum Journey

- Peter Skands

## The Composition of the Universe

- A Quantum Journey

- Peter Skands

## Dark Matter

- August 2006: Clowe et al.: **“A direct empirical proof of the existence of dark matter”**

- astro-ph/0608407, accepted for publication in ApJL

- A Quantum Journey

- Peter Skands

## The Undiscovered Country

- Open-minded “model building”:
- There could be new fundamental matter
- “Fundamental” matter might be composite
- There could be new fundamental forces
- Known forces might not be fundamental
- What is gravity, at the fundamental level?
- There could be new symmetries of space and time
- Known symmetries might break down
- There could be extra dimensions

- Spacetime

- Matter

- Force

- A Quantum Journey

- Peter Skands

## What can we say beforehand?

- Spacetime

- Matter

- Force

- A] A _*complete*_* *theory should:
- explain the origin of mass
- explain dark matter and dark energy
- explain neutrino masses
- unitarize WW scattering
- agree with all measurements so far
- address the *hierarchy *problem
- incorporate quantum gravity
- B] A complete theory _*could*_:
- involve grand unification (we have hints of it)
- involve measurable new physics in the near future
- be aesthetic and natural
- be simple

- A Quantum Journey

- Peter Skands

## A Natural Cause

- We glibly talk
- 	of nature’s laws
- But do things have
- 	a natural cause?
- Black earth turned into
- 	yellow crocus
- Is undiluted
- 	hocus-pocus

- P. Hein, friend of Niels Bohr

- A Quantum Journey

- Peter Skands