Monthly Archives: May 2017

On Aisle 42, Universe Components: One Will Make You Smaller

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Or

A Top-Down Search for the Strange Charm of Putting Up With Those Quarks at Bottom of the Universe

For part two of our universe-construction project, while the helium models dry, it’s time to delve into the depths of the sub-sub-atomic universe.

Consider those carefully-constructed model atoms.   Each contains protons, neutrons, and electrons.

As it turns out, with electrons, there are (so far as physics can determine at present) no smaller particles needed to build an electron.  Electrons are part of a group of  six elementary particles called leptons.  Some of these leptons–the neutrinos–were predicted to not even have any mass, but experiments have shown that while they are incredibly low-mass, neutrinos do have some mass.  Interestingly, these experiments leading to even more new developments in fundamental physics and the Standard Model theory.  Still, electrons are by far the most numerous leptons (at least in our corner of the multiverse.)

In our candy-based model, we have more than one proton crammed into in a nucleus.  Each of those protons has a positive charge, but we all know that objects with the same charge repel each other.  Why does the nucleus stay together?

In our model, of course, there is all that sticky candy.  But in the real atom, there is also something that, in its own way, makes protons stick together.  These other particles are one type of another class of matter, called mesons.  These strange, essential, particles are stable only inside the nucleus, where (like our sticky marshmallows) they act as a “glue” to hold protons and neutrons close together.

Given that extremely tiny leptons have been observed, as well as tiny mesons inside the nucleus, protons and neutrons may begin to seem too big to be elementary particles.  Sure enough, it turns out that protons and neutrons are also made of smaller particles.  And those mesons, too, are made of those same even-smaller particles.  And, while it took thirty years to search them all out, a total of six more fundamental particles (on top of the six leptons) have been found.  Most of the matter we know about only requires two of those particles–plus the electron–but modern physics predicted six, and sure enough, there are six of them.

Meet the QUARKS.  Their six kinds are: up, down, charm, strange, top, and bottom.  Each kind comes in a matter form and an antimatter form.

Intriguingly, the terminology for “kinds” of quarks is flavors. Other characteristics of quarks and leptons include color, another clue to the pleasure scientists find in these discoveries.   For now, we’ll experiment with the flavors of quarks.  Unlike real quarks, we will use macroscopic objects that also happen to taste sweet.

As usual, if you’re working with youngsters, begin by reassuring everyone that there will be plenty of time to eat their quarks later.  Each person gets one each of the six flavors of candy…quarks. Because the candies will be handled a lot during the first stage, tell them not to open the wrappers yet.   Observe the candies.  One side has the brand name on it, and the other side is plain.  If we put the candy name-side up, we’ll call it a quark, and if it has the plain side up, we’ll call it an antiquark.

Quark vs Antiquark

A meson is formed by pairs of one quark and one antiquark.  Give the group some time to see just how many combinations can be made of such pairs.  (A few special mesons combine two or three such pairs, in quark combinations.)

A Small Set of Mesons

This will take some cooperation–participants will want to get together and different groups will organize their tests differently.  Meanwhile, if you have access to a whiteboard or poster paper, you can sketch out a list of simple mesons shown below.  For smaller (or older) groups, you can also pass out copies of this grid and let everyone check off the combinations as they are discovered.

quark antiquark candy (name) candy (plain)
bottom eta b b pineapple pineapple
Upsilon b b pineapple pineapple
charmed eta c c purple purple
D+ c d purple peppermint
D0 c u purple red
J/Psi c c purple purple
Strange D c s purple green
Charmed B b c purple pineapple
Kaon0 d s peppermint green
B0 d b peppermint pineapple
Phi s s green green
Strange B s b green pineapple
pion u d red peppermint
kaon+ u s red green
B+ u b red pineapple
Charged rho u d red peppermint
Kaon*+ u s red green

What’s important from this exercise is realizing that all of these two-quark combinations can really happen.  Some of the mesons are the ones that help stick nuclei together.  Others are found in outer space, as cosmic rays.  Others are only found when scientists smash other particles together to find out what they are made of.  Recently, the last of the mesons described by this model was detected by an international team of physicists, using the Large Hadron Collider at CERN, in  Switzerland.  This prompted huge celebrations by physicists and the process inspired a documentary film about the search for the Higgs Boson, Particle Fever.

When I ran this project at BayCon in 2017, one of the young participants scanned the list above and said, “What about the top quark?”  Trust a science-fiction fan to spot an anomaly.  Indeed, none of the known mesons make use of the top quark, which is the most elusive one of all, and in some ways the most peculiar.  The top quark is extremely unstable–even more ephemeral than the strange, charm, and bottom quarks–and it requires a large particle accelerator to observe one. (Fermilab managed it first; now CERN‘s Large Hadron Collider holds the record.)  Even then, once produced, a top quark vanishes in 1/1,000,000,000,000,000,000,000,000th of a second.  The top quark is also amazingly massive, fueling the deep interest in the nature of mass itself, which many think is one of the functions of the Higgs boson, which itself has only recently been (tentatively) observed.  Scientists at CERN hope to use the relatively massive top quark as a test laboratory to verify their (provisional) Higgs boson observations.

Three-quark particles are called baryons–the most common of these are protons and neutrons.  The next step for our own quark exploration is to find the combination of up and down quarks that yields the proton and the one that forms a neutron.   Each person has 2 peppermint and 2 of one other color to play with. Each group can also pool resources (still keeping those candy wrappers on) to mix and match groups of three using only 2 colors of candy.

To sort out which of these combinations works requires one extra piece of information.  We know that an electron has a charge of -1, a proton has a charge of +1, and a neutron is neutral, with a charge of zero.   Another cool feature of quarks…and one of the hardest things their discoverers had to come to terms with…is that they have fractional charges.  Before quarks, everyone used to think of a charge…equal to the electric charge of an electron…as an indivisible thing.  Just like an atom.  But just as it has turned out that atoms aren’t indivisible, neither is charge.

Up quark’s charge:       +2/3

Down quark’s charge:   -1/3

So, with just a little arithmetic, we can find out which of our combinations makes a proton and which makes a neutron.  Here’s the cheat sheet:

uuu

2/3 + 2/3 + 2/3 = 2

Positive…but too much for a proton
ddd

(-1/3) + (-1/3) + (-1/3) = -1

Negative, so it can’t be a proton or a neutron.

Note:  it’s not an electron either–remember, an electron is already an elementary particle.

uud

or udu

or duu

2/3 + 2/3 + (-1/3) = 1

OK!  It’s a proton!
(Just a reminder…the order the quarks are listed in doesn’t matter.)
ddu

or dud

or udd

-1/3 + (-1/3) + 2/3 = 0

Yes!  We have discovered the neutron!

 

Aha, it’s a proton.

Aha, It’s a neutron!

So, the charge calculations show that protons and neutrons are made of two ups plus one down for a proton and two downs plus one up for a neutron.

It’s possible to have participants glue their protons and neutron quark groups together.  A dip on the water cup from the atomic marshmallow project will make a candy piece sticky.  However, these sticky messes will need to sit aside for a while to dry.  If your participants include young children, you might want to skip that possibility, as a glued-up stack of Life-Savers could be a choking hazard.

Speaking of glue, the same BayCon2017 participants also suggested some ideas for incorporating gluons into our model.  To cover the topic of quantum chromodynamics would be a fun challenge, but for the present, those lonely orange LifeSavers we’d set aside as those transient top quarks can be added between the red and white candies in our proton and neutron models to represent the color exchanges among the quarks.

So now we have established that everything in matter is made of tiny (and flavorful) points of dancing energy called quarks and leptons. How can we visualize the true relative sizes of these quarks, protons, nuclei, and atoms?

Poke a pin through a piece of paper and hold it up to the light, then pass it around, so everyone can see how tiny that hole is.   Think of that bright speck as an electron or a quark.  To be at the same scale, our helium nucleus would be about 3 feet across.  A handy meter-stick or yardstick will provide a sense of scale, but for drama, bring out a huge balloon (the 36-inch size).  It won’t be edible, but it will be fun to play with afterwards.  If that big old balloon is the tiny nucleus, then to build a whole helium atom we’d need a marshmallow about seven miles (ten kilometers) across!

So let’s check back on our atom model from the atomic marshmallow project.  It’s mostly nothing, just that airy, fluffy marshmallow.  Remember how thin the “shell” of the electron cloud is, and how surprisingly hard it is to notice the tiny nucleus once the two little protons and neutrons were placed inside.  Even so, in our model, the protons and neutrons are huge compared with the atom.  Imagine how fantastic the resulting candy treat would be–and how many people could enjoy it–if we’d tried to make this marshmallow atom model to scale.

On Aisle 42, Universe Components: The Atomic Marshmallow Project

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The Atomic Marshmallow Kit

Now that you have all of your supplies ready, it’s time to guide your group through the construction of a model atom.

Start by handing out the marshmallows and ice-cream topping pieces.  With younger participants, it can maintain focus if you mention that there are extra supplies for snacking on afterwards.

Start with the marshmallow.  Most of an atom is empty space.  And most of a marshmallow is nothing but air frothed into sugar.  So this marshmallow represents the “empty” space of an atom.  For older participants, you can encourage them to think of the sugar of the marshmallow as representing not only the energy that permeates what we call “empty” space but also the forces that hold the atom together.

For a very long time, the atom was believed to be more-or-less of uniform density, an amorphous mixture of tiny negative particles called electrons swirling around in a positively-charged “pudding.”  In 1911, Ernst Rutherford and his team completed a series of experiments that shocked the physics community by revealing that most of the mass of an atom is concentrated in a tiny, central nucleus containing all of the positive charge.  For our model, in honor of Rutherford, we’ll build a helium (He) atom, which has a nucleus containing two protons and two neutrons.  (Much of Rutherford’s research focused on the alpha particle–which happens to be exactly the same as a helium nucleus.)

Let your dark-colored candies be protons and your light-colored candies be neutrons.  (It doesn’t really matter, but textbooks often draw protons as dark dots and neutrons as white dots.)

Candy Pieces Ready To Become Nucleons

Two Neutrons Plus Two Protons

Using the wooden skewer or toothpick, drill a small hole in the side of the marshmallow.

Making a Pathway for the Nucleus

Now use the same toothpick or skewer to push those nucleons (a word which here means “candy pieces representing protons and neutrons”) into the center of the marshmallow.

One Down, Three To Go

 

At this point, we have a positively charged ion, because we haven’t added any electrons yet.  A helium atom needs two electrons, negatively-charged particles, to balance out the two positively-charged protons.  Once it was established that the positive charge is concentrated in the nucleus, where did researchers decide that the electrons belong?

This is a good time in the activity to stop lecturing and instead gather suggestions from the participants and sketch their ideas on a board if you have one, or to gather around some sketching paper for discussion purposes.  You can expect to see pictures that look much like a planetary system, because that’s the way the atom often (still!) is drawn in textbooks.  You might have a knowledgeable participant who’ll shout out something like, “Shells!  The electrons are in shells!” or “They’re in the Cloud!”  Regardless, during the discussion, build on these volunteered suggestions to reach a description of the electrons as whirling around the nucleus in a cloud, going so fast that you can’t really tell exactly where they are, only that you know roughly how far they are from the nucleus.

Our helium atom’s two electrons do indeed share an electron “shell”, a layer of electrons a known distance from the nucleus.  So let’s put a very thin, energetic, sparkly shell around our atom.

Before setting up the shell supplies, pause to demonstrate the procedure.  If you’re working with younger students, you may need to stress that everyone will get their turn.  If the “mess” part of the activity is an issue, set up a protected area where the messy activity is OK and let the participants queue up to build their atoms in assembly-line fashion.

Each group needs a container with about a cup of water in it and another container with a packet of dry gelatin mix emptied into it.  (For fun, choose a gelatin color in keeping with whatever events are ongoing, or a local sports team’s colors…anything to drive interest.)

Dunk

To create the “electron shell” skewer the marshmallow firmly on the wooden stick, then very briefly dunk it into the water, then tap off any excess water into the water container.

and un-dunk.

Tapping off excess water is important, because otherwise the marshmallow can get soggy, which makes for a less-attractive candy atom.

Finally, gently swirl the damp marshmallow in the gelatin mix.

Adding the Electron Shell

Set the decorated marshmallows aside on a sheet of waxed paper or a plate.

Two Finished Helium Atoms

As time permits, participants can make other atoms…stuffing different numbers of protons or neutrons into marshmallows and adding a shell of electrons.

 

On Aisle 42, Universe Components: The Shopping List(s)

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As hinted in the previous post, for our universe-building project we’re doing two construction activities related to elementary particles.  So, we’ll have two “Lists of Requirements” this time around.  The model atoms use marshmallows, miniature candy chips, and gelatin mix.  You’ll need just one packet of mixed-flavor candies for even a fairly large group–in advance, you can separate out flavors into the amounts needed.  For sub-atomic particles, we’ll use multi-flavor candies, such as “Life-Savers”…we need six flavors, so you get to buy both peppermint and five-flavor mixtures.  Depending on your workspace, you may choose to have participants work in table groups of of 3-4 people or to set up supplies assembly-line style in a relatively mess-friendly zone.  The assembly-line method reduces the need for extra supplies, though these are quite inexpensive materials.  For pre-preparation, it helps to count out supplies for each participant–small paper cups are ideal and stack neatly once your supplies are set up.  Another helpful side item is a roll of waxed paper or a stack of paper plates for setting out the end-products while they dry or for taking them home.

One extra item, for your wrap-up, is highly recommended if your budget permits:  pick up one humongous balloon–the 36-inch diameter size, in any color or design that delights you.

The recommended quantities are generous, to allow for after-project treats.  Ice-cream sundaes, anyone?

 

The Atomic Marshmallow Project

Per person For a group of 10 For a group of 30
Standard size (not miniature) marshmallows

1

10

30

Miniature candies,  dark color*:  try candy “decors” or extra-tiny chocolate chip ice-cream topping mixture

2

1 package of mixed candies:  count out at least 20 dark-colored pieces

1 package of mixed candies:  count out at least 20 dark-colored pieces
Miniature candies:  light color*:  try candy “decors” or extra-tiny white candy chip ice-cream topping mixture 2

From the same packet of mixed-flavor candies:  count out at least 20 light-colored pieces

From the same packet of mixed-flavor candies: count out at least 60 light-colored pieces.

Gelatin mix

(choose a variety of fun, colorful flavors)

1 packet

(3-ounce size)

3 packets

(one per group of 3-4 people)

For groups:

8 packets

For an assembly line:

3 packets

Water

1 cup

3 cups

(one per group of 3-4 people)

For groups:

8 cups

For each assembly line:

1 cup

Wooden skewers (alternative: toothpicks) 1  10  30
10-16 ounce containers

(mugs, plastic cups, reused food containers)

2 6

For groups: 16

For each assembly line: 2

Small cups for sorting supplies 2 20 60

*   IMPORTANT NOTE:  If you’re tempted to use peanut-flavor candies, remember to be SURE to check in advance that none of the participants suffers from peanut allergy.  In its worst form, this allergy can trigger anaphylaxis merely through physical contact with peanut oils or proteins, but at the very least, peanut-sensitive people should not eat anything tagged “packed in same location as peanut-handling equipment” or “may contain nuts”.    There are lots of different candy chips to choose from; just be sure you end up with two different colors of “chips” for the protons and neutrons.

Sufficient Supplies For Construction of Approximately 40 Model Atoms

The second project’s list is even easier, and doesn’t require a “mess zone”:

One Side Makes You Smaller

or

A Top-Down Search for the Strange Charm of Putting Up With Those Quarks at Bottom of the Universe

The counts of candies in a mixed bag of five-flavor candies is a bit random, so if buying for a group you may need to grab an extra bag, just in case you need it.  The package of sorting cups you purchased for the Atomic Marshmallow Project will have enough for you to sort supplies for this project as well.

Per person

Per 10 people

For 30-person group

Five-flavor Life-Savers candies

1 of each color,

a total of 5

50:

each gets 5 total, 1 of each color

(2 bags of individually-wrapped Life-Savers)

150:

each gets 5 total, 1 of each color

(6 bags of individually-wrapped Life-Savers)

1 extra piece of one of the five flavors

1

10

(There should be enough left over from the 2 bags you’ve purchased.)

30

(There should enough left over from the 6 bags you’ve purchased.)

Peppermint Life-Savers

2

20: each gets 2

(1 bag of individually-wrapped peppermints

60: each gets 2

(2 bags of individually-wrapped peppermints)

A Pile of Quarks, Ready for Construction of a Small Universe

On Aisle 42, Universe Components: Notes for Project Leaders

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I have a pair of projects to present this time–together, they are a sugar-based approach to understanding the building blocks of our universe.  The goal is to build up a sense of the scale and dynamic relationships among the smallest particles identified to date, and how they combine to form the stuff we call “matter”.  By the end of these activities, everyone participating should have a clearer picture of the following:

1. All of the matter in our universe is composed of just a few extremely basic and very tiny building blocks.  They’re called quarks and leptons.

2.These building blocks, in the right combinations, make the next-level construction materials.  The most common ones are electrons, protons, and neutrons.  But there are others, too.

3. Once you have electrons, protons, and neutrons, you can build elements.  Each element has particular physical and chemical properties–which arise from its unique physical composition of protons, electrons, and neutrons.

To make this activity fun (besides incorporating sweet treats), it helps to build into the presentation an element of discovery.  First, we come to terms with the fact that the familiar atom is not the smallest particle.  Second, we wrap our minds around the knowledge that even the tiny particles inside the atomic nucleus are made of even tinier ones.  Third, at the conclusion, it’s truly mind-expanding to try to envision each of these in true relative scale.

The atom is still a meaningful idea, so long as we adjust its definition to suit modern understanding.  The concept of the atom dates back over 2500 years, to Leucippus of Miletus and his more-famous student, Democritus.  They reasoned out that if you keep cutting a material, you’ll eventually reach a particle that cannot be divided further.  In Greek, the word “a” means “not” and “tomos” means cut, so when you call something an “atom,” you’re saying you can’t subdivide it.  However, even now that we know that the structures we call “atoms” can be broken open, we still use the term. For instance, we’ll talk about “an atom of iron” or “the carbon atom”.  But instead of defining the atom as “indivisible”, we now describe it as the smallest unit of a material that still retains those unique physical and chemical properties defined by its combination of electrons, protons, and neutrons.

In this project, we will build atoms from electrons, protons, and neutrons.  Energized by our constructions, we will discard our preconceptions about the structure of the universe and descend to the sub-sub atomic scale, where we will capture quarks and leptons, then build ourselves some protons and neutrons and electrons.  And then we will eat the lot:  atoms, quarks, protons and all. It’s elemental.

We’ll proceed in two parts:  “The Atomic Marshmallow Project” introduces the idea of atoms and their components, and “One Side Will Make You Smaller” takes us down into the realm of quarks.  As in our other science projects, we’ll include information to share with the participants as you go along. For those who would like to delve into more detail, you’ll find links to good sources with plenty of depth.

Everything You Need to Build A Universe

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