physics project : particle physics

8/14/2019 Physics Project : Particle Physics

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Physics Project

ParticlePhysics

What is UNIVERSE made from??????

By:Aditya quark TiwariTushant vacuum Jha

Yusuf string Jamal


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Preface

This topic is definitely less of Mathematics, and more of definitions, not because Particle Physics doesnt consider

mathematical aspects, but because our target audience maynot be able to comprehend that level of mathematics in just half an hour. To some, initially it may sound chemistrytoo, but then not our fault, its there in Physics Book too.

There is a video too, having basically some good ways toexplain the topic.

The project discusses The Standard Model of ParticlePhysics, by Tushant.

Then Yusuf and Aditya will discuss about Dark Matterand Dark Energy respectively.

We will also discuss about the Theory of Everything and

how it is different from 42 (obviously this is our PhysicsProject and not a Hitchhiker Guide)

We end our project on a note of hope

We thank Mrs. Vani Dutta maam to allow us take sucha topic.

(where at least a few students could sleep and ask noquestionssorry, it was just a comic relief)


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The Standard Model

of Particle Physics

The Standard Model refers to the compiled formulation

of all the elementary particles which have been both

observed and mathematically formulated.

Fermions [matter particles]:Fermions, or the so-called matter particles, are heavy

particles that make up our common matter. They arecalled so because they follow Fermi-Dirac Statistics.

They have half-integral spin that is -1/2, 1/2, 3/2, etc.

Spin is actually the quantized representation of Angular

Momentum. Handedness of Spin refers to similarity of

direction between direction of spin (z-component) and

motion of particle.

They also have electric charge, which makes them

interact through Photons. Actually its important to know

that any large enough collection of fermions (like this

sheet or even ink itself) is visible not actually because it

bounces back the photons (cmon, no one can bounce a

wave-particle so easily, at least I cant bat a rope) , but

because electrons and protons first absorb and then emitthem.

The Fermi-Dirac Statistics include Paulis Exclusion

Principle, which state no two fermions can have same

quantum numbers at same time and place.


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The Fermions are found in 3 generations, each generation

heavier and less stable than previous. It is important to

note that in Quantum Mechanics, stability is counted in

fractions of milliseconds.

All Fermions have their Anti-Matter Counterparts

which have exactly the opposite electric charge and

opposite handedness, and everything else same. When a

particle collides with its anti-particle (such as electron-

positron), energy is created equivalent to their masses

(E=mc2). As per Quantum Mechanics, at each and every

point of time, particle-antiparticle pairs are created and

destroyed (After all, its all uncertain[HeisenbergsUncertainty Principle])

The Fermions can be further classified into:

Quarks:These are the particles which make protons and neutrons.

They are of two types, more charged() and lesscharged()

They also have another kind of charge known as color

charge (not to be confused with visible colors, it is just a

naming convention). The color charge is of six types:

1.Red2.Blue

3.Green4.Anti-Red5.Anti-Blue6.Anti-Green

These color charges are named so because as mixing of

red, blue, and green lights give white lights, similarly all


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stable Baryons (called hadrons) are made only if there

are 3 quarks of different color-charge.

Or, a meson would be formed if two opposing colors

meet.

A Comic description by quarked.org


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Leptons:These are the light-weighted particles which include

electrons.

They also include neutrinos, which are so light that they

travel at relativistic speeds.Leptons act as particles to balance the electric-charge of

a system which is already color-neutral.

Bosons [Interactions]:Bosons, or the so-called force carriers, are particles

which follow Bose-Einstein Statistics, and have integral

spin. Bose-Einstein Statistics allow more than oneparticle of same kind to be at same place and same time.

All force in universe is ultimately made by these

fundamental forces. Have you ever thought that even

though 98% of atom is vacuum, whenever we push

something why dont we just get passed through it?? The

answer is E-M force.

At Plancks Time (the smallest unit of time) after Big

Bang, all Forces were unified as X and Y Bosons, but as

the universe cooled, the three (as far we have known)

main bosons were developed.

Gluons:The gluons are gauge bosons, which like

the photons, travel at c. It carries the

color charge and is called the

STRONG FORCE.


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Photons:These are the particles which carry electromagnetic field.

It is also the force that makes things visible.

Its energy can be given by E=h.

It is also subject to interference addition, that is:

Weak Force:Two kinds of W bosons exist with +1 and 1 elementary

units of electric charge; the W+ is the antiparticle of

the W. The Z boson (or Z) is electrically neutral and is

its own antiparticle. All three particles are very short-lived with a mean life of about 31025 s.

These bosons are heavyweights among the elementary

particles. With a mass of 80.4 GeV/c2 and 91.2 GeV/c2,

respectively, the W and Z particles are almost 100 times

as massive as the protonheavier than

entire atoms of iron. The masses of these bosons are

significant because they act as force carriers; their

masses thus limit the range of the weak interaction.


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The electromagnetic force, by contrast, has an infinite

range because its force carrier (the photon) is massless.

All three types have a spin of 1. The emission of

a W+ or W boson either raises or lowers the electric

charge of the emitting particle by 1 unit, and alters thespin by 1 unit. At the same time a W boson can change

the generation of the particle, for example changing

a strange quark to an up quark. The Z boson cannot

change either electric charge nor any other charges, only

spin and momentum, so it never changes the generation

or flavor of the particle emitting it

It is really important in Decays:udd uud + e + e

Comparative Strength:

As compared to E-M Force, we see that Strong Force is

stronger and Weak is weaker (wasnt that obvious by

their names?), but what amazes is that Gravity is much

weaker than even the Weak Force. But after all its E-M

which stops us going through floors.


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More Particles:There are still many questions left unanswered like why

things have mass, and to find the answers to these

questions, scientists are predicting new particles.

The Higgs Boson, as postulated by Peter Higgs, is a kind

of Boson which acts as a Higgs Field in the following

way:

Say a class is full of students (aka Higgs Bosons)

Now a boring guy (like me) enters, and then eventually

goes away.

But if a celebrity (say Orlando Bloom or Megan Fox)

enters, the whole class goes to take the autograph thus

making it difficult for heavy particle (celebrity) to move,

which it shows in form of Mass.


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Dark MATTERIn 1933, when Swiss Astrophysicist Fritz Zwicky, while

studying nearby Coma Cluster, suddenly found that the galaxies

were moving faster than expected, as if there was some ghostmaking them do so. It was later hypothesized that there existed a

non-baryonic species of matter which was exerting this unseen

gravitational effect. They couldnt be seen because they didnt

interact with Electromagnetic Waves, nor do they interact

through Strong force.

The Reason:

The Virial Theorem states that for a closed system,

EK= -(F*r)/2Where EKrepresents Kinetic Energy,

F represents Force,

r represents position

But Fritz observed 400 times more energy than calculated,

Since,

EK= mv2

And v couldnt had been 20 times more than what was

observed, it would mean that there was 400 time more mass inthe system.


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For 40 years after Zwicky's initial observations, no other

corroborating observations indicated the presence of dark

matter. Then, in the late 1960s and early 1970s,Vera

Rubin, a young astronomer at the Department of

Terrestrial Magnetism at the Carnegie Institution of

Washington presented findings based on a new

sensitive spectrograph that could measure the velocity

curve of edge-on spiral galaxies to a greater degree of

accuracy than had ever before been achieved. Together

with fellow staff-member Kent Ford, Rubin announced at

a 1975 meeting of the American Astronomical

Society the astonishing discovery that most stars in spiral

galaxies orbit at roughly the same speed, which impliedthat their mass densities were uniform well beyond the

locations with most of the stars (the galactic bulge).

This result suggests that either Newtonian gravity does

not apply universally or that, conservatively, upwards of

50% of the mass of galaxies was contained in the

relatively dark galactic halo. Subsequent to this,

numerous observations have been made that do indicatethe presence of dark matter in various parts of the

cosmos. Together with Rubin's findings for spiral

galaxies and Zwicky's work on galaxy clusters, the

observational evidence for dark matter has been

collecting over the decades to the point that today most

astrophysicists accept its existence. Recently,

cosmologists have mapped the presence of dark matter

with the help of gravitational lensing, or bending of lightdue to gravity.

As a unifying concept, dark matter is one of the dominant

features considered in the analysis of structures on the

order of galactic scale and larger. Dark Matter Halos in a


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galaxy are comparable to a

Christmas Tree. We see the

light bulbs (a.k.a. stars)

from far off but are unable

to see the structure on

which it rests, the Tree

(a.k.a. Halo).

Answers:

The possible solutions to

this problem are :

1.WIMPS, or WeaklyInteracting Massive

Particles which are

particles which

interact only through weak or lower.2.MACHO, or Massive Astrophysical Compact Halo

Objects, which attributes this stuff to star-decays. Itis also referred as Hot Dark Matter, as they will

travel at relativistic speeds

3.RAMBO, or Robust Associations of MassiveBaryonic Objects, which postulates quark-seas.

4.Or to check our Gravitational Concepts again.

But everything is just postulated, and most theories

themselves predict such particles which would bedifficult to observe (they could be passing through us

every second). Still, what we do know is that there is

something which is beyond Baryonic Matter but provides

gravitational structure to it.


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Dark Energy

When Albert Einstein first formulated his General Theory of Relativity,

he found it contradictory without an extra energy, which he termed

Cosmological Constant, to keep the universe static and counter theeffects of gravity. But as Edwin Hubble discovered that universe was

expanding, suddenly the utility of cosmological constant was put intoquestion. Einstein termed it as his biggest blunder.

But later when Dark Matter was studied, cosmologists discovered that thenet energy of universe was more than first thought. The total amount of

Baryonic Matter and Dark Matter put together was observed to beinsufficient to produce the amount of Space-Time curvature we observe.Putting the newly found facts into Hubbles Theory, it was postulated that

the expansion of universe should decelerate as matter shows Gravitationaleffects.

In the 1998 and 1999 two teams of astronomers, the SupernovaCosmology Projectand theHigh-ZSupernova Search were looking fordistant type 1a supernovae in order to

measure the expansion rate of the

universe with time. They expected thatthe deceleration of expansion would be

indicated by the supernovae being brighter than their red-shifts as

the Hubbles Lawwould indicate.Instead, they found the supernovae to

be fainter than expected. Hence, the

expansion of the universe wasaccelerating!!!!!!


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Observations using the Chandra X-Ray Observatory have shown that the

growth of clusters of galaxies by gravitational attraction has slowed overtime. Astronomers think that this stifled development of larger and largerclusters of galaxies is likely caused by dark energy that is accelerating the

expansion of space between galaxies.

Also the Theory of Large Scale Structure, which governs the formation ofstructure in the universe (stars, quasars, galaxies and galaxy), suggeststhat the density of baryonic matter and dark matter in the universe is only

30% of the critical density. There should be something to account for the

remaining mass in and that something is dark energy. (Mass and Energyare related. Remember E=mc

2).

Thus Dark Energy was postulated, a

mysterious form of energy that physicists

believe is the single largest component of

the universe. Dark energy is spreadthroughout the universe and appears tomake up about 74 percent of its content.Dark energy is thought to be an inherent

property of space itself. Dark energy is the

only way to explain recent observations thatthe universe appears to be expanding at an

accelerating rate although the gravity produced by baryonic and darkmatter should have decelerated this expansion or even startedcontracting the space. It is found to be Vacuum Energy or the Energy

of Nothing as no matter or energy particle explains it, but only someproperty of space-time curvature.

Two Models of Dark Energy

1. Cosmological Constant:

A possible explanation of dark energy

that fits very simply within the

framework of Einsteins General

Theory of Relativity is the existence ofa cosmological constant. Einsteinoriginally introduced the cosmological

constant into his equations in an

attempt to render the universe static(neither expanding nor contracting).

Einsteins equations for general relativity predicted that the universecould not be static, but at the time Einstein formulated them, he and other


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scientists believed that the universe was unchanging. So Einstein

introduced the cosmological constant to balance gravity in his modifiedfield equations.

But after the discovery of expansion of Universe by Edwin Hubble in

1929, Einstein left this concept.The possibility that the equations of general relativity should include acosmological constant is now being seriously reconsidered because of the

discovery of dark energy. Instead of having the value needed to keep theuniverse static, however, the cosmological constant would now have thevalue required to make the expansion of the universe accelerate at the

observed rate.However, when this concept is applied to Quantum Field Theory it gives

its value of order 10120

which if applied actuallywould have accelerated the universe at unimaginable rate and neverallowed matter to form.

2. Quintessence:

To overcome the shortcomings of Cosmological constant, one such

theory proposed is that there may be a previously unknown type of forcein the universe that produces the observed acceleration. This would

constitute a fifth fundamental force. This class of theories is often

referred to as quintessence. These models predict that the nature of darkenergy changes over the lifetime of the universe, whereas the

cosmological constant is exactly thatconstant for all time. Precise

measurements are now being planned to determine whether the propertiesof dark energy do change with time.

Implications of Dark Energy on our Universe:

The concept that Einstein called his blunder is today found to be the

determining factor behind the fate of universe. If cosmologists couldrightly study the mechanism of Dark Energy, they could tell if theuniverse would die in fireorice.

Cosmologists estimate that the acceleration began roughly 5 billion yearsago. Before that, it is thought that the expansion was decelerating, due tothe attractive influence of dark matter and baryons.If the acceleration continues indefinitely, the ultimate result will bethat velocity of the expansion of space will exceed the speed of

light.This does not violate the Special Theory of Relativity as it only


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applies to flat space-time and not to curved space-time. Thus, local

clusters would soon be invisible to us.

Lambda-C.D.M. Model:The Lambda-CDM Model is the simplest known modelthat is in general agreement with observed phenomena. It

takes into account:

1. (Lambda), or the cosmological constant, which is

a dark energy term that allows for the currentaccelerating expansion of the universe. The

cosmological constant is often described in terms

of , the fraction of the energy density of a flatUniverse in the form of the cosmological constant.

Currently, 0.74, implying 74% of the energy

density of the present universe is in this form.

2.Cold dark matter is the model where the darkmatter is explained as being cold (i.e. its velocity is

non-relativistic or

much less than c at

the epoch of radiation-matter equality),

which is possibly non-

baryonic,

dissipationless (can

not cool by radiating

photons) and

collisionless (i.e., the

dark matter particles interact with each other andother particles only through gravity). This

component makes up 22% of the energy density of

the present universe.

3.The remaining 4% is all of the matter (and energy)that makes up the atoms (and photons) that are the


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building blocks of planets, stars, and gas clouds in

the universe. This fraction of universe (strangely

having more matter than anti-matter) is involved in

nucleosynthesis in stars.

4.It also assumes that universe has noobservable topology or space-time rips, so that the

universe is much larger than the observable particle

horizon. These are predictions of cosmic inflation.

5.It takes many parameters like:a.Hubbles Constant, which describes the speed

of recession between galaxies.

b. Baryon Density, the absolute density of

baryonic matterc. Dark Matter Density, the density of dark

matter present in universe

d.Critical Density, the relation between gravityand anti-gravity (dark energy), etc.

Lambda-CDM model as of 2006 is consistent with a

series of increasingly rigorous cosmological

observations, the latest being the 2005 Supernova LegacySurvey.


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Theory of EverythingStrings, Superstrings, Fields, Extra Dimensions,

and Everything else

Scientists have been working on to GENERALISE, that

is to define more than one concept in just one theory.

An intellect which at a certain moment would know all forces thatset nature in motion, and all positions of all items of which nature is

composed, if this intellect were also vast enough to submit these datato analysis, it would embrace in a single formula the movements ofthe greatest bodies of the universe and those of the tiniest atom; for

such an intellect nothing would be uncertain and the future just like

the past would be present before its eyes.

Essai philosophique sur les probabilits, Introduction, Pierre-

Simon Laplace, 1814

The history of a quest for such a theory is long, but

recently the efforts of unification have seen many ups-and-downs

1713: Newton unifies Galileos on terrestrial

gravity, Kepler's laws of planetary motion, and the

astronomical studies on Jupiters and others Moons into a

single law of universal gravitation

1873: Maxwell works on previous works of Oerstedand Faraday to unify Electricity and Magnetism into

mere 4 equations.

1915: After General Relativity, Einstein tries to unify

E-M with Gravity, but fails


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1919: Theodor Kaluza adds a fifth dimension to

General Relativity to adjust it for differences between E-

M and Gravity.

1930s: Uncertainty Principle hinders development of

Theory of Everything

1940s: Heisenberg works on S-Matrix approach,

triggering work on Unified Field Theory.

1960s: Strong and Weak discovered. But now Gravity

has no place in newly formed Standard Model

1964: Higgs Boson proposed to accommodate in

Unified Field Theory

1967: Abdus Salaam and Steven Weinberg unify E-

M and Weak, thus forming ElectroWeak Theory

1969: Few Scientists propose that everything is madeof strings

1974: Scientists propose Grand Unified Theory,

combining all forces

1980s: Dark matter and dark energy discovered, pose

problems

1990s: Scientists work on modified version of initial

String Theory, now called Superstring Theory, predicting

up to 26 dimensions.


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says that everything is made from

some kind of vibrating strings, obviously this could

account for Particle-Wave duality. According to it all

particles are made from different tones of vibration in

strings.

But the one of the few problems this has is that it predicts

many smaller dimensions, but first lets understand what

is a smaller dimension:

So in a similar way there more

dimensions which dont really affect us,

but at quantum

levels, it can have

amazing impacts

being the medium

for vibration of strings.

But String Theory, to some extent, contradicts General

Relativity, as it asks for a particle to mediate gravity,

while relativity attributes gravity to space-time curvature.


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The importance of extra dimensions, as many scientists

say, lies in making the universe possible. The universe

is possible only because there are about 20 constants

which have fine tuned. eg.- If the ratio of Dark Matter

and Hubbles Constant would have had been changed,

the universe would have had crunched long before we

could evolve. The Multiple Dimensions allow parallel

universes, thus making our universe one of the

privileged universes.

But String Theory has a problem, its too difficult to test

it

due to the high-energy required to test its effects.


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Sources:

WIKIPEDIA (thats obvious)

Elegant Universe, NOVA TV-

PBS, by Brian Greene

Particle Adventure, CPEP

Youtube, etc.

We shall hope that one day scientists are successful in unifying Standard Model, Lambda-CDM Model, General Relativity,

Superstring Theory, and Unified FieldTheory into one consistent Theory of

Everything (definitely not 42)so thatthe twenty years down the line students

dont make group project but individualones on this topic.

physics project : particle physics

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