Schroedinger, Erwin! Professor of physics!
Wrote daring equations! Confounded his critics!
(Not bad, eh? Don’t worry. This part of the verse
Starts off pretty good, but it gets a lot worse.)
Win saw that the theory that Newton’d invented
By Einstein’s discov’ries had been badly dented.
What now? wailed his colleagues. Said Erwin, “Don’t panic,
No grease monkey I, but a quantum mechanic….
Einstein played a leading role in the development of the ad hoc old quantum theory, but he was uneasy about it. Heisenberg’s mechanics seemed abstract to be a true representation of reality. On the other hand Schrodinger’s wave mechanics looked promising until Born came along and spoiled it with statistical interpretation….Einstein had been happier ….- You believe in the God who plays dice, and I in complete law and order in a world which objectively exists,and which I in a wildly speculative way am trying to capture…. Bohr responded to Einstein’s ideas with a series of brilliant arguments known as the “Copenhagen Interpretation” .
Einstein wasn’t the only physicist to object to the implications of quantum theory.Schrodinger initially believed his wave mechanics would return physics to an era of continuous differential equations and waves.De Broglie tried to retain some physical reality of wave – particle duality….
It’s wrong to think that the task of physics is to finde out how Nature is. Physics concerns what we can say about Nature.
Quantum theory leaves the future open and inhibits our ability to know the past.It’s hardly surprising that this radical shift in the interpretation of physical reality should shock and surprise physicists.Schrodinger was disturbed by these ideas and he published the amplification from quantum events. The Schrodinger cat thought experiment is the most famous in quantum theory.He involves a conscious creature – cat, whose fate depends on the detailed way in which the wavwfunction collaps. The cat must “exist” in a superposition of live and dead states until the experimenter opens the box and observes the state of the cat
incredible – who’s create the world?
Radioactive atom with 50% chance of decay in 1 hour
A cat is confined in a windowless box for 1 hour.The boh contains a fiendish apparatus that will administer a lethal dose of poison if triggered by decay of a single radioactive atom.
After 1 hour Schrodinger open the door of the box and see one of two possible outcomes
- atom has not decayed, cat still alive
- atom has decayed, cat is dead
The idea that the atom is in a superposition of decayed/undecayed states and the cat in a superposition of live /dead states prior to observation is disturbing.
However if superposition doesn’t take place it’s impossible to explain the appearance of interference effects in related experiments. Einstein couldn’t accept that quantum theory meant the end of an objective physics reality. He thought that quantum theory applied only to the average behavior of ensembles of particle, and wasn’t complete theory of the behaviour of individual particles.
Statistically speaking, the cat (goes the joke),
Is half a cat breathing and half a cat croaked.
To some this may seem a ridiculous split,
But quantum mechanics must answer, “Tough shit”..
I’ll be the first to admit this
is a bright but haunted age
I just don’t know now
now I just can’t say hey hey
And you keep slipping down the surface of things
I just cant take it now,
I just cant wait for more when you get down
down to the sub atomic part of it thats
when it breaks you know,
thats when it falls apart oh caveat emptor,
open the atoms core ….
the glory of the atom
begs a reverent word
the primary design
of the whole universe
yes, let us sing its praises
let us bow our heads in prayer
at the magnificent consciousness
the smallest unit of matter
with its orbiting electrons
echoing off the solar system
like a hawk in the hills at dawn
the smallest unit of matter
uniting bird and rock and tree
and you and me…
The idea that all matter is made from a combination of a small number of simple things goes back to the beginning of recorded history. The ancient Greeks proposed several unifying ideas one of which was a fairly atomic theory, attributed by the poet Lucretius in his poem “On the Nature of Things”.
“No rest is granted to the atoms throughout the profound void, but rather driven by incessant and varied motions,some after being pressed together then leap back with wide intervals, some again after the blow are tossed about within a narrow compass. And those begin held in combination more closely condensed collide with and leap back through tiny intervals….”
The name atom derives from atomos, meaning “uncuttable” a reflection of the Greek belief that all matter consists of an arrangement of few kinds of fundamental indivisible particles.
In the 19th century the atomic hypothesis developed into a powerful explanatory system, particularly with the work of Maxwell, Boltzmann, and Clausius. Some physicist took the atomic theory very seriously and assumed that atoms themselves are real, as Thomson – Lord Kelvin put it an atoms is”a piece of matter with shape, motion and laws of actions, intelligible subjects for scientific investigation..”
Various models were proposed for the atom including W. Thomson’s vortex rings in the
ether and J.Thomson’s “plum-pudding” model in which negative charges were embedded in a diffuse positive material. Two key discoveries led to the more familiar planetary model.
Model of the atom evolved through
- Rutherford’s nuclear atom
- Bohr’s quantised atom
- Schrodinger’s wawe-mechanical atom.
The electron (discovered in 1897.) was the first subatomic particle.It was discovered in a particle accelerator (Crooke’s tube).
The idea that nuclei might contain a neutral particle was considered by Rutherford in the early 1920s.Rutherford suggested many ways in which the neutron might be formed or detected including the idea that hydrogen atoms might collapse to neutrons as electrons fall into the nucleus, but the crucial obsevations that led to descovery of neutron were made by
- Walther Bothe and Herbert Becker in 1930 – they are noted that beryllium emits a very penetrating nuclear radiation when alpha particles are fired at it
- Joliot – Curies in 1932. discovered that this radiation could eject protons from paraffin…
Becquerel like many physicist in early 1896. was intrigued by Rondgen’s discovery of X-rays.He wondered whether fluorescent and phosphorescent salts those that emitelight after apsorbing it, would also emit X-rays and began a series of experiments to find out. His experiments showed that the radiation persisted whether or not he excited the salt in any way, and wasn’t diminished when the salt was melted or dissolved. He also showed that the radiation produced ionisation in the air that could discharge an electroscope. The phosphorescent materials he used were uranium salt and he concluded that it was essential to the emission of radiation but the uranium. He discovered that it consisted of two parts – highly ionising rays with little penetration, which he called “alfa rays” and less strongly ionising but more penetrating rays which he called “beta rays”. (Villard were discovered gamma rays).
Marie Sklodowska Curie discovered radium and polonium and showed that radioactive decay must be an atomic process. Marie and Pierre Curie shared the 1903 Nobel Prize for Physics with Becquerel.
Radioactive decay is a nuclear process. It involves the decay of nuclei from one element and their transformation into nuclei of another element. Spontaneous decay occurs when the transformation results in a release of energy. This can be calculated using Einstein’s mass-energy equation.
Alfa decay is common in heavy nuclei with too many protons.Beta decay seems easier to explain using a proton-electron model then proton-neutron model.
How electrons are emitted?
Beta decay caused major problems for theoretical physicists….
The main problems were these:
- Where do the electrons come from?
- The emitted electrons have a continuous energy spectrum, what happens to the missing energy’?
How can a nuclear containing an even number of spin -1/2 particles emit another spin -1/2 particle?
The solution to these problems needed new physics and wonderful new discovery…..
In 1919 Rutherford ivestigated collisions between alpha particles and light nuclei including hydrogen. Rutherford had been known that the atomic mass number A of nuclei is a bit more than twice the atomic number Z for most atoms and that essentially all the mass of the atom is concentrated in the relatively tiny nucleus. As of about 1930 it was presumed that the fundamental particles were protons and electrons, but that required that somehow a number of electrons were bound in the nucleus to partially cancel the charge of A protons.it was known from the “uncertainty principle – confinement calculations that there just wasn’t enough energy available to contain electrons in the nucleus.An experimental breakthrough came in 1930 with the observation by Bothe and Becker that bombardment of beryllium with alpha particles from a radioactive source produced neutral radiation which was penetrating but non-ionizing. They presumed it was gamma rays, but Curie and Joliot showed that when you bombarded a paraffin target with this radiation, it ejected protons with energy about 5.3 MeV.Gamma rays are high frequency photons.They are emitted after an alpha or beta decay when the newly formed nucleus is an excited state. They take away energy but dont affect A or Z, they simply allow the nucleus to the de-excite.The existence of discrete gamma ray spectra led to the idea that nuclei, like atoms, can exist in a set of quantised energy levels. The necessary energy for the gamma ray explanation was much greater than any energy observed to be available from the nucleus, so the neutral radiation must be some kind of neutral particle.
Chadwick was able to prove that the neutral particle could not be a photon by bombarding targets other than hydrogen, including nitrogen, oxygen, helium and argon. Not only were these inconsistent with photon emission on energy grounds, the cross-section for the interactions was orders of magnitude greater than that for Compton scattering by photons.The task which remained for Chadwick was that of determining the mass of the neutral particle. He chose to bombard boron with alpha particles and analyze the interaction of the neutral particles with nitrogen. These particlular targets were chosen partly because the masses of boron and nitrogen were well known.
For this discovery (1932.) he was awarded the Nobel Prize for Physics in 1935. After Chadwick’s discovery of the neutron many physicists continued to think of it as a composite particle, a kind of collapsed hydrogen atom containing an electron and proton in tightly bound state. The idea that nucleons are bound by a new strong nuclear force developed through several distinct theoretical stages.
– In 1932 Heisenberg developed a theory of exchange forces. The essential idea in this theory is that neutrons and protons, neutrons and neutrons and protons and protons bind to one another by exchanging properties such as charge and position.
– In 1933 Fermi constructed a theory for beta decay using Pauli’s neutrino hypothesis and variation on Dirac’s quantum field theories.
– In 1934 Irene Curie and Frederic Joliot discovered beta plus decay, the emission of a positron from proton-rich nucleus. They were awarded the Nobel Prize for Chemistry in 1935.
-In 1937 – “heavy electron” now called a muon. Yukawa’s theory of the strong nuclear force. Nucleons exchange mesons. This binds them together. He was awarded the Nobel Prize for Physics in 1949. Yukawa’s work changed the way about forces…..
A neutron walks into a bar. ‘I’d like a beer’ he says.The bartender promptly serves up a beer. ‘How much will that be?’ asks the neutron. ‘For you?’ replies the bartender, ‘no charge’
Hardly any mass at all
Always teased for being small
Whizzing at the speed of light
Never stopping day or night.
That’s not fair
I do the work
They just sit there.
Crammed up in a ball
Weighing down the atom
hoping to change the end
im not very happy with it
The idea that hadrons might be combinations of simpler more fundamental particles occurred to a number of physicists.In 1964 Gell-Mann and Zweig suggested that the meson nonet and baryon octet and decuplet could all be derived by combining three distinct spin – 1/2 particles, and their associated antiparticles. These new fundamental particles were called quarks. In 1967 Feynman suggested an intuitive model of what hapens when protons conteining quarks collide with other particles. He was able to derive certain characteristics of scattering that could be related back to the quark/parton model. In 1968 Freidman, Kendall and Taylor directed high-energy electrons at protons at SLAC(Stanford Linear Accelerator Center).One thing stood out, the pattern of scattering was the same at all collision energies. They discovered that they could account for the scattering by identifying the partons with quarks and introducing some additional particles moving between the quarks.
Deep inelastic scattering – when high-energy electron beams were fired at fixed targets some of electrons suffered large angle scatterings rather like those of the alfa particles in original Rutherford scattering experiment.
The electrons must be interacting with highly concentrated charged particles inside the protons.The scattering takes place via the exchange ofhigh-energy photon.
The 1990 Nobel Prize for Physics was shared by Friedman, kenall and Taylor for their pioneering investigations concerning deep inelastic scattering of electrons on protons and bound neutrons, which have been of essential importance for the development of quark model in particle physics….
Quark is hypothetical particle that carries a fractional charge. There are four different kinds of quarks, each having antiparticle called Antiquark. These quarks are called:
The Up Quark (u)
The Down Quark (d)
The Strange Quark (s)
The Charm Quark (c)
The charges on the four quarks u, d, s, c are +2/3, -1/3, -1/3, +2/3 that of the electron charge. Antiquarks have opposite charges. All quarks and antiquarks have equal spins which is ½. These quarks combine to form different elementary particles. For example: Protonsare composed of three quarks (uud) and neutrons (udd). Each meson can be conceived as the union of a quark and an antiquark.
There are two main types of particle: fermion (with half-integer spin) and bosons (with integer spin). Particles can also be classified by their interactions:
– hadrons (baryons and mesons) interact by the strong force.Half-integer spin hadrons (such as protons and neutrons) are called baryons and integer spin hadrons are called mesons (such as the pion)
– leptons not affected by strong interaction.
The first generation of leptons – electron (electron – neutrino).
The second generation of leptons – muons (don’t take part in the strong interaction but do behave just like electrons would if their mass was increased 207 times, except that they are unstable. When they decay they do so by creating an electron and anti-neutrino which is not the same as the anti-neutrino emitted in beta decay).
The third generation of leptons discovered in 1974 Martin Perl -the tau particle (tau – neutrino).
The 1988 Nobel Prize for Physics was awarded to Lederman, Schwartz and Steinberger for the neutrino beam method and the demonstration of the doublet structure of the leptons through the discovery of the muon-neutrino.
In 1995 the Nobel Prize was awarded to Martin Perl for the discovery of the tau lepton and Frederick Reines for the detection of the neutrino.
O divine neutrino!
“Neutrinos they are very small.
They have no charge and have no mass
And don’t interact at all.
The earth is just a silly ball
To them,through which they simply pass
Like dustmaids down a drafty hall…”
The problem with neutrinos is that they only interact with matter through the weak force, so they are extremely difficult to detect:
- spin (-1/2) hadrons such as the proton and neutron called baryons
– integer spin hadrons like the pion called mesons
Baryon decay always results in a proton and some other particles since the proton is the lightest and probably stable. Baryons cannot decay to mesons, so protons don’t decay to pions.
Mesons decay to lepton.
Rochester and Butler discovered in 1946 heavy meson – the kaon. The ions are formed by the strong interaction and decay by the weak interaction.Kaon were called “strange particles” because of this.
Kaons were created in collisions between pions and protons, the kaon was always accompanied by another strange particle it never came with a pion….