# Presentation: 109589

## The Four Fundamental Forces... and Beyond!

**Jerry Blazey**
**Physics Department**
**Northern Illinois University**

- Four Fundamental Forces

## This could be a talk about anything
Army, Navy, Air, Coast Guard
Political, Economic, Social, Religious
...
But we’ll limit ourselves to physics and to “the primary agents that cause motion or change”*
Describing these “primary agents” leads us into the microscopic world and ...
	extra dimensions!

* Webster’s has nearly 30 definitions of force!

**Army, Navy, Air, Coast Guard**
**Political, Economic, Social, Religious**
**...**
**But we’ll limit ourselves to physics and to “**_**the primary agents that cause motion or change**_**”***
**Describing these “primary agents” leads us into the microscopic world and ...**
**	****extra dimensions!**
*** Webster’s has nearly 30 definitions of force!**

- Four Fundamental Forces

## The Familiar Forces

**	****	****	****Gravity**
**Frictional (Static & Kinetic)**
**Centrifugal/Centripetal**
- Tension
- Normal Forces
**	****	****	**
**	****	****Electrical**
**	****	****	****Magnetic**

**Newton’s Laws**
**1687**
**Force = **
**Mass * Acc.**

**James Clerk Maxwell**
**1865**
**Maxwell’s Equations**

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## Unification

_**Unification**_

**There’s a natural tendency toward unification of forces**
**For instance electrical and magnetic phenomena where unified by Maxwell’s equations into **_**electromagnetism**_**.**
**In essence all electrical and magnetic phenomena can be described by the motion of charged particles. **

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## And a drive towards simplicity

**All of the “familiar forces” are due to just gravity & electromagnetism.**
**Consider friction: this is just the residual force left over from the charged atoms on the two surfaces interacting electromagnetically!  The same can be said for the normal and tension forces.**
**As for centripetal forces, these can be due to gravity, if you’re a satellite, or the normal force (electromagnetism), if your in a car and restrained by your seat belt!**

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## The Situation ~1900

_**The Situation ~1900**_

**So at the turn of the last century most phenomena could be explained by **
**gravity **
**electromagnetism.**
**But some annoying things started cropping up because of improved instrumentation:**
**X rays (Roentgen 1895)**
**Radioactivity (Becquerel 1896)**
**The electron (Thomson 1897)**
**The nucleus (1911 Rutherford)**

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## The Quanta

**  ****All these discoveries led to the description of matter and radiation as particles or small quanta**
**The quantum idea (Planck 1900)**
**Light as quanta (Einstein 1905) **
**The nucleus (Rutherford 1911)**
**The atom (Bohr 1913)**

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## The Atom*

_**The Atom***_

**Let’s consider the atom:  In 1900 it was  thought to be a solid sphere **
**After the quantum revolution it was understood to be composed of a nucleus and electrons. **
**The electron has negative charge and the nucleus positive charge.  The entire thing is held together by electromagnetism**
**	*****By the way atom is a  misnomer since it’s Greek “********” for “that which cannot be divided”!**

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## Light as a Manifestation of a Fundamental Force

**By emitting or absorbing a photon, the electron can change its average position or energy in an atom.  **
**In every day life, the illumination from your light bulb is just a very great number of photons emitted from the excited filament atoms.**
**This is a **_**classic electromagnetic interaction**_** and our first **_**manifestation of a fundamental force**_**!**

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## A Characteristic of Fundamental Forces

**As the light bulb hinted, charged objects interact by exchanging photons.**
**In the atom the electron and nucleus are held together by exchanging photons.**
_**In fact all fundamental forces involve the exchange of a fundamental particle.**_
**... ****to go any further in our discussion we need to enumerate the fundamental particles**

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## The Nucleus and the Atom

_**The Nucleus and the Atom**_

**Nowadays we know the nucleus to be made of protons and neutrons**
**And the protons and neutrons of quarks!**
**So that a complete picture of the atom would include quarks and electrons.**

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## Scale

**Let’s just take a small detour to consider the scale of the atom**
**In fact the tiny electrons and quarks have no observed structure and are for all intents and purposes fundamental.**

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## The Standard Model

**The crowning achievement of particle physics is a model that describes all particles and particle interactions. The model includes:**
**6 quarks (those little fellows in the nucleus) and their antiparticles.**
**6 leptons (of which the electron is an example) and their antiparticles**
**4 force carrier particles (of which the photon is an example)**
_**All known matter is composed of composites of quarks and leptons which interact by exchanging force carriers.**_

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## The Quarks*

**There are three pairs                         of quarks.**
**The up and down are                          the constituents of                        protons = uud and                       neutrons = udd, and make up most matter.**
**The other particles are produced in energetic subatomic collisions from cosmic rays or in accelerators like Fermilab (where they are also studied.)**

- *The name comes from James’s Joyce’s *Finnegan’s Wake*,
- “Three quarks for Muster Mark!”

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## Leptons*

_**Leptons***_

**Leptons are generally lighter particles and are most readily observed in radioactive decays.**
**The best example is neutron decay into a proton, an **_**electron**_**, and a **_**neutrino**_**:**

- *Greek for “small mass”

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## Periodic Table of Fundamental Particles

**Add Antiparticles**
**Families reflect**
**increasing mass and**
**a theoretical**
**organization**
**u, d, e are “normal**
**matter”.**
**Because of the charge**
**quarks, electrons, **
**muons, and  tau’s**
**participate in EM**

** ****-****1**

**+2/3**

**-****1/3**

**0**

- Mass 

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## The Weak Force

**Radioactivity, in particular the neutron decay we discussed earlier, is actually a manifestation of the weak force**
**At the quark level, a down quark in the neutron decays into an up quark, by emitting a W boson.**
_**The heavy W boson is the carrier of the weak force.**_

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## The Weak Force (continued)

_**The Weak Force (continued)**_

**Since the W is very heavy (80 times the proton itself), it takes a long time for quantum fluctuations to gather the where-with-all to support the decay.  Thus a “weak” decay.**
**Finally the W itself decays into leptons **

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## The Weak Force (continued)

**The decay                    is a manifestation of the weak force**
**The weak force involves interactions between the quarks and leptons**
**In this case through the exchange of the carrier W. **
_**There are three weak carriers W**__**+**__**,W**__**-**__**, and Z**__**0**_**  Discovered 1983.**

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## A Brief, First, Consolidation

_**A Brief, First, Consolidation**_

**We’ve enumerated two fundamental forces.**
**Electromagnetism which occurs between charged particles and is carried by the photon, ******
**Weak force which occurs between quarks and leptons and is mediated by the intermediate vector bosons, W****+****,W****-****, and Z****0****.**

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## The Problem of the Nucleus

**Why doesn’t the nucleus - full of positive protons that repel one another and neutral neutrons - blow itself apart?**
**Gravity doesn’t work since it’s much too weak compared to electromagnetism.**
**There must be yet another force around!**

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## The Color Charge

**Well it turns out quarks have another quantum number or charge called “color charge”.**
**The force between these color charges is extremely strong.**
_**Two quarks interact by exchanging the strong carrier dubbed the “gluon”**_
**Gluons themselves have                     color charges**

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## The Color Charge (continued)

**There are three color charges named: “red”, “green” and “blue”. **
**These names are mathematical identifiers and have nothing to do with visible colors.**
**Quarks are bound in a particle, like the proton, by madly exchanging gluons  and forming a binding color field:**

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## The Color Charge (continued)

**Free quarks cannot be observed because of this strong field**
**If two quarks a pulled away from one another the field breaks into a new pair of quarks:**

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## The Color Charge (continued)

**Now back to the nucleus!**
**The residual strong field between the protons and neutrons overwhelms the repulsive electromagnetic force and holds the whole thing together**

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## A Second Consolidation

**The weak force occurs between quarks and leptons and is mediated by the massive intermediate vector bosons W****+****,W****-****, and Z****0**** **
**The electromagnetic force occurs between electrically charged particles and is mediated by the massless photon.**
**The strong force occurs between color charged particles and is mediated by the massless gluon.**

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## Gravity

_**Gravity**_

**Although a deep understanding of gravity has been around the longest it is not understood at the carrier level.**
**The **_**graviton**_** has not been discovered.**
**Still since this is a very weak force the Standard Model works very well in the absence of a full description  **

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## We could stop here but.....

**We could stop here but.....**

**Explained by complete theory**

**10****-37**** weaker**
**than EM**

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## A Few of the Unsolved Questions

**Can the forces be fully unified?**
**How do particles get mass?**
**How does gravity fit into all of this?**

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## The Electroweak Unification

**Remember that quarks and leptons interact through the weak force?**
**Note the quarks, leptons, and bosons all carry charge so they can also interact electromagnetically.  This is a big clue!**
**It turns formally (or mathematically) that electromagnetism and the weak force are manifestations of the same                    underlying force: the              electroweak force.**

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## Grand Unified Theories(GUTs) 

**	****At very   high   energies                       all interactions merge to                         a single                        strength. **

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## The Higgs Particle

**The electroweak unification postulates the existence of the Higgs Particle, H.**
**This particle or field interacts with all other particles to impart mass.**
**The experimental program at Fermilab in Illinois and the Large Hadron Collider in Europe are dedicated to the search for this particle.**
**It’s discovery would be an achievement of the highest order – reaching an understanding of the origins of mass! **

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## An Accelerator

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## A Detector

**International**
**50-100 institutions**
**500-1000 physicists**
**10 year lifecycles**
**$100M **
**Barn-sized**

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## Slide 35

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## Beyond the Standard Model

**The desire to explain gravity and unify it with the other forces has led to the ideas of Supersymmetry (SUSY) and Extra Dimensions (to name just two!)**
**In SUSY every particle and force carrier has a massive partner. Squarks, slectrons...**
**Since they are massive they’ve not been produced in current machines. The discovery requires more energetic               accelerators – something                  which the community is                 enthusiastically pursuing.**

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## Extra Dimensions

**Amazingly enough an 11 dimensional world (time, 3-D, 7 very small less than 1mm in size) can accommodate a fully unified theory!**
**Only gravity can communicate to the other dimensions and so it’s “strength” is diluted in ours. That is, the graviton can spread it’s influence among all 10 spatial dimensions.**
**Experiments are underway searching for signals of these dimensions.**

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## The “other”

**The “other”**
** ****dimensions**

**“****Our World”**

**q**

**graviton**

**Think of our world and the other dimensions **
**	****	****	****	****as just 2-d planes...**

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## In Conclusion

**The four fundamental forces: gravity, weak, electromagnetism, and strong**
**All but gravity explained by the Standard Model of particle physics**
**Theory and experiment give tantalizing hints of full unification!**

- Four Fundamental Forces