Since it was so late in the day, most of the students were not attending to their projects. One of the Honorable Mention projects was attended by its investigator, a young man from one of the Plano High Schools who had studied Compton Scattering using a UV light source and a Strontium-90 beta emitting source. Many other projects spanned a space of topics, including the best storage conditions for popcorn (a freezer, not a pantry), wind conditions at a local school (for a turbine), a cellular-automata model for H1N1 spread with and without vaccination, the lead content of lipstick, and a hundred other studies.

Jodi and I were impressed with the breadth and quality of these studies. While we both wish we’d been able to meet more students, we were still happy to have time to spend a beautiful evening witnessing the future of science in this country.

[1] http://www.dallassciencefair.org/

Share this post with your friends

No related posts.

Related posts brought to you by Yet Another Related Posts Plugin.

Share this post with your friends

No related posts.

Related posts brought to you by Yet Another Related Posts Plugin.

What does all of this mean? We think of waves and particles as distinct things. Of particles, we ask: where are you, where are you going, when will you get there? Of waves, we ask: how often do you repeat in space and in time, what is your maximum amplitude, where are you zero, and how spread out are you? At first, putting these two phenomena together seems impossible. But then you start to think about “relevant dimensions,” and then you start to cease to see distinctions between the two.

What are “relevant dimensions?” The textbook I am using, Harris’s “Modern Physics,” handles this quite well: simply put, these are the relative sizes scatterer and the scatteree. If an electron is to scatter off of atoms spaced far apart, the relevant dimensions are large compared to the electron; if the spacing of the atoms is extremely close, then perhaps the dimensions are small compared to the electron.

Harris gives a nice analogy, which I modified a bit for my class. Imagine taking a boat out to the middle of a lake, then laying down in the boat (so you can’t see the water around you) and staring up at the sky. Somewhere far across the lake, at a construction site, a crane drops a large concrete or steel structure. What happens?

If the structure hits the beach and then rolls into the water, the waves it creates can have wavelengths that are meters long. The waves travel across the lake and reach your boat. Your boat is not that big, so the waves begin to raise, then lower, the boat. You would report that the boat experienced wave motion – the dimensions of the wave are much larger than the boat, so the boat only responds to a small part of the overall wave, rising and falling as the wave passes.

But what if the crane drops the structure straight into the water? Then the energy goes into one short, sharp wave. Its wavelength may be half-a-meter or less. When it reaches your boat, what happens? Rather than the boat responding to some small part of the wave, the whole of the wave strikes the boat at almost the same time. All that energy is deposited into the boat at nearly the same time. What do you report? You are likely to think another boat has hit you, or that you have drifted into a rock. You would report a “particle collision”.

The relevant dimensions – the wavelength compared to the boat – affect the interpretation of the event. Particle-like behavior manifests when the wavelength is short compared to the dimensions of the object, and wave-like behavior is apparent when the wavelength is long compared to the dimensions of the object.

But for matter, what is “waving”? If electrons, protons, atoms, etc. are waves – what is waving? The answer was not originally arrived at easily, and to this day nobody is sure if there is a better answer. But the answer that works is PROBABILITY. The particle itself is not oscillating or wiggling or vibrating. Rather, its associated wave is one of probability amplitude – in one place in space or time, the wave amplitude is lower, so the chance of finding the particle there is small, while in another the amplitude is large, making the chance of finding the particle there high. To see the particle, you have to measure it, and when you measure it the particle nature manifests (to find it, you have to detect it, and to detect it, you either have to bounce something off of it or make it bounce off something). Until the measurement is made, you only know where the particle is likely to be or not be.

This is among the hardest things in physics to accept. You accept it only because it works – it makes predictions that time after time have born out. The probability wave interpretation of matter tells us not only why atoms work the way they do, why electrons can be used to measure subatomic structure, and why transistors and diodes work, but gives us a means to explore new possibilities regarding the nature of reality.

Is the wave nature of matter true? Is it right? Those are difficult words for a physicist. Certainly, experiments don’t (yet) suggest otherwise. But perhaps one day we’ll find a better explanation, a bigger explanation, that makes this seem more sensible to us. Until then, I am excited that my class gets to explore the wave nature of matter, and I am excited that I get to teach it.

Homework, anyone?

Share this post with your friends

No related posts.

Related posts brought to you by Yet Another Related Posts Plugin.

E=mc^2 has done more than destroy cities or create new political entanglements. Converting mass to energy, as through the annihilation of matter and anti-matter in the PET scan, saves lives. Nuclear power created a new industry, a new way to generate electricity, and new challenges both in engineering and politics.

But E=mc^2 is only one half of a greater story. The general equation relating energy, mass, AND motion is E^2 = (mc^2)^2 + (pc)^2 – that second part encodes the effect of motion on energy. Just as this equation is interesting when nothing is moving (p=0), it’s interesting when there is no mass (m=0).

No mass means all of a body’s energy arises from its motion. Without motion, it does not exist. E = pc is the beginning of something greater, though at first that may not be terribly obvious. This equation, the forgotten fraternal twin of E=mc^2, carries with it an important requirement: if you are going to have no mass, you must move at the speed of light. This revelation teaches us something about light itself – that regardless of its other properties, it has no mass-energy. It is all movement, yet it transmits inertia from one place to another.

The fact that E=pc requires mass-less things to move at the speed of light arises from a mathematical necessity; due to the definition of momentum, p, in relativity, the only way that a mass-less object can do anything but not exist at all is that it must move at the speed of light.

However, that’s all this equation can tell us. The mathematical requirement that E=pc means the object moves at the speed of light leaves us with an otherwise undefined equation; that’s because p depends on both the mass (which is zero) and a function of velocity that returns infinity when the speed is that of light. This zero and this infinity compete to keep energy from being trivially zero, but in doing so give us no further insight into light.

The parallel revolution of quantum physics and the discretization of energy in radiation was needed to make progress on light itself. Quantum physics gives us the framework to describe the energy and momentum of light, in terms that are definite.

E=pc is often forgotten in all the excitement about the benefits, powers, and geopolitics of E=mc^2. Yet, E=pc is a gateway into the very nature of light. Light is so fundamental to life, and interactions among the living, that it is no less important than matter. In the study of E=pc, and the nature of radiation, we eventually come full circle on the relationship between energy and matter. That’s a story for another time. For now, let’s just quietly adore E=pc.

Share this post with your friends

Related posts:

1. A tale of two fermions Last year, when the rise of the bottomonium began, I...
2. More sweet, sweet collider physics on Mythbusters As I’ve probably hinted with my previous post on baseball...

Related posts brought to you by Yet Another Related Posts Plugin.

Such an implementation exists, in general, for JavaScript – this makes it portable to any major modern browser platform. As a review, LATEX [1]  is a type-setting language; like a printing press, it correctly places and kerns fonts and allows you to quickly and beautifully format mathematical equations.LATEX is available for every major computing platform. jsMath [2] is a JavaScript implementation of the parsers in LATEX and renders mathematics in native fonts. This is dissimilar from other implementations of LATEX on the web, where instead of fonts, GIF images are created for the equation. For a big document, this means loading dozens, or hundreds, or images. jsMath avoids this completely.

The missing piece: a plugin for TiddlyWiki, so that you can use jsMath in your electronic logbook. That plugin is achieved via the Tiddler “Plugin: jsMath” by Bob McElrath [3]. Here is my own personal recipe for installing jsMath and the Tiddler plugin.

1. As of the writing of this entry, I am using TiddlyWiki 2.5.3 and jsMath 3.6c (the latest public release versions of each). I downloaded them from the sites linked in this post.
2. I began by installing jsMath in the same directory where my top-level logbook .html file is located. I unpacked the jsMath ZIP archive, which automatically creates a jsMath subdirectory. The top-level logbook .html will look for jsMath in this way when the plugin is installed.
3. I installed the TrueType Fonts recommended by the jsMath site (see http://www.math.union.edu/~dpvc/jsMath/download/jsMath-fonts.html). For me, they had to be unpacked into the .fonts/ subdirectory in my home directory. Your needs may vary. Basically, your browser has to have access to these fonts.
4. I then added a new Tiddler to my logbook. I titled it “Plugin: jsMath”, and into it I copied the code on Bob’s webpage. I added the tag “systemConfig” to the tiddler, so that it is executed and loaded as a plugin to the logbook.
5. Installation complete! I then added LATEX code into my journal tiddlers (e.g. $\gamma \to e^+ e^-$) and it rendered beautifully

A few words of caution, before you get ahead of yourself. Please read the jsMath website information on defining new symbols. It’s not as straight-forward as experienced LATEX users would like it to be, but once you learn the syntax it gets to be a cut-and-paste operation. Second, if you’re using a remote server to host your wiki you are on your own; I don’t know what expectations the code will have for the location of the jsMath code (on the server, on your local machine, or both?). I know that the current implementation of the plugin does some text parsing and looks in the current directory for jsMath – you may have to edit this to make it work when your wiki is on a remote server.

So far, this has been a positive experience. I can still use unicode/HTML short-cuts for things, as needed (e.g. γ → e^^+^^ e^^-^^, which gives you almost the same result as the example LATEX above). But, now for complex equations I have the power of LATEX at my fingertips. I’m even thinking of doing lecture notes for classes in this way, so that they can be instantly placed on the web.

[1] http://www.latex-project.org/

[2] http://www.math.union.edu/~dpvc/jsMath/

[3] http://bob.mcelrath.org/tiddlyjsmath-2.0.3.html

Share this post with your friends

Related posts:

1. Electronic Notebook Revisit: TiddlyWiki, meet Git This past week, I got my SMU-provided desktop PC. The...
2. Electronic Logbooks I’ve experimented over many years with electronic logbooks. I got...
3. sshfs – remote access for the terminal In the world of modern HEP computing, your data analysis...

Related posts brought to you by Yet Another Related Posts Plugin.

I attended the meeting not only to present some recent research activities, but to present my case for SMU membership in the collaboration. This case has been built up, in consultation with leadership in the collaboration, over the course of the last two months. It is with tremendous pleasure that I report that the case for membership was enthusiastically received, and SMU is now a new institutional member of the BaBar collaboration.

My participation is focused largely on contributions to the physics efforts of the collaboration: research, review, and publication. My goal is to also contribute simulated data, produced at SMU and distributed to the collaboration; this effort is already well underway and nearing complete success. Having established these milestones, my attention will be turning back to contributing to ATLAS through operational work. I’ll be at CERN in December, training for these efforts and learning from my experienced ATLAS colleagues. There are two blocks in my life right now, and I feel like a new kid on both of them.

While I have been a member of the BaBar Collaboration since 2000, I have always been so under the auspices of an established institution. Bringing a new institution into the collaboration is a novel experience for me, exciting and full of opportunity. I envision significant contributions being made by SMU undergraduates to the BaBar research effort. I see BaBar data serving as a direct means to engage students in independent research, to teach them modern research techniques, and to communicate the work and knowledge of particle physics. I see the immense dataset, in conjunction with the coming data from ATLAS, teaching us about all aspects of new physical phenomena: their properties visible only at the highest energies and their subtle effects visible only with the best precision, the most data. I see opportunity for SMU, and I am happy to be leading this effort.

Share this post with your friends

Related posts:

1. Post-doctoral research opportunity at SMU on the ATLAS experiment I am pleased to announce my very first search for...

Related posts brought to you by Yet Another Related Posts Plugin.

What do I mean by this? Let’s consider the human head. The distance between our two ears is about 22cm (about 8.5 inches). This distance means that sounds that are not originating from directly in front of us reach our two ears at different times. The human auditory system is capable of discerning sounds that are no more than 0.000660 seconds apart from one another – that’s 0.660 milliseconds (ms) [1]. The result of this ability to process signals which arrive more than 0.660 ms apart is that we can localize sound in space. This process, called “Duplex theory,” means that if sounds are closer than 0.660 ms then they cannot be localized; we lose the ability to distinguish the sounds, and they seem to arrive at the same time.

So, what does this have to do with the conductor of an orchestra? Let’s imagine a situation where the orchestra, full of spite for the primadonna conductor, decides to go completely democratic and tosses the tyrant out onto the street. “We can synchronize ourselves!” they proclaim, and they turn to the oboe player.

“Oboe player, sit in the middle of the orchestra pit and blow a series of tones in the tempo of the song! That way, we can listen for the tempo and mark the passage of time, so that we, too, can stay on time.”

This seems like a great idea. Sadly, the universe has conspired against this democratic process. Sound travels at about 300 m/s. As a result, it takes 0.033s, or 33ms, for sound to travel even the 10 meters from the center of the pit to the outermost players (assuming a 20m-diameter pit). The result is that a player on the outskirts of the pit hears the oboe’s beat 33ms after a player next to the oboe hears it. Players on the outside of the pit are 33ms LATE in playing their instrument.

What does this mean? It means that the players on the outskirts of the pit become unsynchronised from their center-pit colleagues. Is this a bad thing? YES. Since the human ear is capable of hearing the difference between sounds that are at least 0.66ms apart, and the sounds from the inside and outside of the pit are 50 times further apart than that in time, the whole orchestra sounds like they’re playing out-of-time. The resulting cacophony will  surely cause ticket sales to plummet, and our democratic orchestra will go flat broke.

The conductor, on the other hand, standing in front of the orchestra, uses light, not sound, to synchronize the orchestra. Since light travels at about 300,000,000 m/s, it takes just 0.000067 ms for their hand gestures to be seen by players at the back of the pit, compared to those closest to the conductor. This means that players are just 0.000067 ms out-of-time with one another; this is vastly below the human ability to hear the difference between two sounds, saving the orchestra and insuring a flawless performance.

Before you cast out that tyrant of a conductor, remember this: the universe has conspired to make it necessary to use light, and not sound, to synchronise the orchestra. Instead of tossing the bum out on the street, remember that you need them more than you don’t. Or, at least, think about hiring a replacement.

[1] http://en.wikipedia.org/wiki/Interaural_time_difference

Share this post with your friends

Related posts:

1. Thunder and Lightning Sunday night, as we sat on the patio by the...

Related posts brought to you by Yet Another Related Posts Plugin.

The light and sound travel the same distance, d. The time the light requires to go from the storm to us is shorter than the time for the sound. The time for the light is t_l = d/c, where c is the speed of light (300,000,000 m/s). The time for sound is t_s = d/v_s, where v_s is the speed of sound (300 m/s). We are interested in the number of seconds between the sound and the light, so let’s compute the time difference using these formula:

t_s – t_l = d/v_s – d/c = d(1/v_s – 1/c)

We can rewrite the quantity (1/v_s – 1/c) = (1/300 – 1/300,000,000) = 1/300 (1-0.000001), which is (to a very good approximation) 1/300.

We arrive at our final relationship:

t_s – t_1 = d/300

where time is in seconds and distance is in meters. So, if we are sitting on our patio and we see the flash of lightning, and then 6 seconds later we hear the thunder, the storm is (6s * 300 m/s) = 1,800 m, or about 1.1 miles.

Share this post with your friends

Related posts:

1. Why the cosmos needs conductors The conductor of an orchestra is not for show. A...
2. More sweet, sweet collider physics on Mythbusters As I’ve probably hinted with my previous post on baseball...
3. E=pc E=mc^2 gets all the fame and press. That’s because this...

Related posts brought to you by Yet Another Related Posts Plugin.

A recent hearing in Congress, in the Senate Energy and Water Appropriations Subcommittee [1], revealed just how poorly we have listened to their messages. The heads of three research agencies, as well as a theoretical physicist from Harvard, gave testimony (and heard messages of their own) earlier this month. The Senate committee overseeing research in basic research seemed to know little about the value of things like particle physics. We have a problem . . . still.

I won’t repeat the article I referenced above, except to quote the statement about Rep. Daniel Lipinski’s ” . . . observation that research in these fields is expensive and that more needs to be done to better communicate its results.” When somebody has to say that out loud, what they’re trying to tell you is that we don’t know why we’re spending money on what y’all do.

We have a great story to tell, no less than the quest for fundamental knowledge about matter, energy, space and time. This story and its human core are no less interesting (and entertaining) than the stories of doctors and police, which are routinely over-documented on TV. Clearly, this story is not getting out there (though the beginning lies in things like “The Big Bang Theory” and “Numb3rs” TV shows). Primarily, scientists themselves are not taking enough time to speak to the public – on TV, in newspapers, on the web, on the radio – about their work. Once-a-week shows like “Science Friday” or “Quirks and Quarks” are not enough. Once-a-year Congressional efforts are not enough. Echo chambers like “Fermilab Today” and “SLAC Today” are not enough. We need more.

Start at home. Write a short newsletter about your work and send it to your family. Instead of that annoying seasonal letter to friends and family about the state of your life, talk about the state of your work. Write a short letter to your Members of Congress. Tell them about your work, in short declarative sentences. Be non-technical. Be entertaining. Be honest.

Reach out to your institution. Find ways to get non-scientists at your institution into colloquia. Lessen the echo chamber by creating avenues for simple public communication. For instance, a department newsletter mailed once or twice a year to alumni can have a great effect. At labs, find ways to get the staff engaged in the work of the lab. I’m talking administrators and H.R. people, machinists and welders.

Solving this problem will take years, maybe decades. But it’s clear that even though we’ve started a few things in the past decade, they’re not having an effect. These same questions about the value of our work were around 10 years ago, and from many of the same people and institutions. We’re not sinking in. We have to saturate. The only way to soak the public in science knowledge is to dump truckloads of it on top of them, and hope any of it filters into their lives.

[1] http://www.aip.org/fyi/2009/125.html

Share this post with your friends

Related posts:

1. Communication: Breakdown It’s been a number of years since I had to...
2. Messages for the Community This past week, three user organizations joined forces yet again...
3. 3 Days on Capitol Hill As a member of the SLUO executive committee and co-chair...

Related posts brought to you by Yet Another Related Posts Plugin.

I’ve been thinking about freeze out, a property of particles which is often exploited in order to make statements about dark matter. “Freeze out” is when a particle species is unable to interact with itself or other matter because either the probability of an interaction is very small or because the likelihood of running into other matter is very small, or both. One can think of freeze out in a very human way.

Let’s consider a social situation, in which you are invited to a party where you don’t know anybody (except maybe the host). Let’s also consider a parameter, your “social cross-section”, which simply is a measure of how willing you are to approach a complete stranger and begin, then sustain, a conversation.

At the beginning, the party is hot. People are densely packed, the music is loud and thumping, you’re walking around with a drink in your hand and bumping into complete strangers. If you have a high social cross-section, you’ll take every bump and jab as a chance to flash a smile and start a conversation. With a sufficiently high social cross-section, you’ll dance with people and even as the party cools off (time goes on, people leave, the music gets less interesting) you’ll continue to stick with party-goers and socialise. You’ll keep meeting up with people, running into them, dancing, forming small social cliques of equally interactive people. Even when the party is completely wound down, you’ll stick with the hard-core types, the most social – maybe even go and have an after-party somewhere else. A high social cross-section can overcome the cooling effect on the party, allowing people to stick together and form new relationships despite a thinning population density at the party.

Consider instead a person with a low social cross-section. They may be comfortable starting a conversation but not sustaining it past small-talk. They certainly don’t like to dance, unless they really get prodded into it. Maybe they really don’t even like to start conversations but they feel obliged to go to the party because of the host. So they go, and the party starts off real hot. They get bumped and jostled, drink spilling, and maybe they flash a smile and start a conversation. But the interactions are weak and rare, sustained in frequency only by the density of the people at the party. Eventually the party cools, people start leaving, high social cross-section folks are cliquing and grouping. The low cross-section people are off by themselves, tapping a foot by the side of the dance floor or standing by the buffet, but not forming new relationships.

This is dark matter, and this is how dark matter “freezes out” of interactions. When the party is hopping, it almost doesn’t matter what your cross-section is. You’re caught up in the fray, forced to interact by the sheer number density of party-goers. But as the party cools and the crowd thins, the inclination to interact remains the same but the opportunity drops precipitously. Now imagine a party where 85% of the party-goers left over when the cooling happens are low cross-section types. That’s our universe. High cross-section people are forced to clump and group in between the low cross-section types, forming little groups in this sea of non-interacting people. Welcome to our cosmos. Nerds rule!

Of course, the trick here is that it’s possible that the low cross-section types are only low on verbal and physical communication. Imagine a party where the low cross-section types are super-techy, and prefer to interact through social media. They’re standing around, mobile phones out and tapping away on their Facebook or Twitter streams, while the high cross-section people have phones put away and are gabbing and laughing and dancing. “This party is lame,” tweets one low cross-section type. “Let’s leave,” types another. “But the dip is good and the beer is free,” says a third. “Good call, let’s stay,” says a fourth. They are actually communicating all the time but the talkers are unaware, because they are not tapped into this social stream.

The promise of studying the dark sector, dark matter and all of its friends, is that we might tap into how they communicate with one another. Maybe every now and then one of the low cross-section types laughs at a Tweet, and a nearby high cross-section type hears them and asks, “What’s so funny?” “Oh, it’s just that my friend PwnN00bs1984 noticed that girl in the corner is so drunk she is mistaking some random guy for the guy she came in with.” “That IS funny,” says the high cross-section type, suddenly exposed to a whole conversation going on behind the scenes.

Let’s hope that eventually, we find a way to tap into the dark sector’s own little conversation. Maybe, then, we’ll figure out what 85% of these people are doing at this party.

Share this post with your friends

No related posts.

Related posts brought to you by Yet Another Related Posts Plugin.