## Posts Tagged ‘complete course’

### The Complete Physics Course: Part 2: Scales of nature

Tuesday, June 5th, 2007

What’s the difference between the following two sentences?

Two billiard balls, rolling along a table, crash into each other.

Two planets, traveling through space, crash into each other.

The difference is the scale. Two billiard balls rolling into each other on a pool table may just be the highlight of a high schooler’s Saturday evening. Two asteroids striking each other, however, would certainly be catastrophic to life on either of those planets, or anything within range of the destruction.

It’s hard to believe, but physics works the same way, whether things are big or small. The two collisions described above follow the same laws of physics. The two collisions would never be EXACTLY identical, because the collision of any two objects is very complex. However, the laws of physics as we understand them are the exact same for the billiard balls as for the planets. In fact, the same rules apply to galaxies colliding as well as cars or bowling pins or bacteria.

Around 1900, something strange happened — this wasn’t true anymore. A series of then-unsolved problems led to the idea that maybe this wasn’t true. As the solutions to those problems trickled in, it became clear that for really small scales, things get weird. This is because, ultimately, of the theory of the atom. Atoms together create bulk material. But when you try to move around things as tiny as atoms, the forces between the atoms can change quite radically with the distance that separates them, and so the old rules no longer apply.

In physics there are really two different scales of distance which have their own rules. The larger distance scale comprises the world of more than a few atoms at a time. This is the “macroscopic” world. The branch of physics that seeks to describe the motion of macroscopic objects is called Newtonian mechanics, after Sir Isaac Newton. As far as we all knew in the late nineteenth-century, Newtonian mechanics was all there was. In the first few decades of the twentieth century, what became known as quantum mechanics sought to describe the motion of very small objects. Quantum mechanics has some pretty strange rules. Particles can only spin in certain units. You can’t exactly tell where anything really is and know how fast it’s going at the same time. Symmetries which seem to be obvious break down.

Fortunately, in 1900 the entire body of Newtonian mechanics didn’t have to be thrown out. Science is based on observation, and the realization that things got weird when distance scales were small didn’t change the observations on the scale of our everyday life. Quantum mechanics must always “reduce” to Newtonian mechanics as the distance scale increases. So, still one set of laws, just two different parts.

Thankfully there are only two different scales in nature. Due to the fairly limited size of the world’s particle accelerators, we can only observe down to about the proton’s scale (about 0.000000000000001 m, or 10-15 m). What if there are entirely new laws of physics at a scale one-trillionth of the size of a proton? We would have no idea. For now, our two sets of physical laws are presenting us with enough trouble as it is.

### The Complete Physics Course: Part 1: Observation

Monday, April 30th, 2007

Observation is one of the fundamental elements of the scientific method. In science we can’t say that an event happens until we see it happen. You might ask, “I can never see the wind, so how do I know it’s there?” Even an astute five-year-old can tell you that she knows the wind is there because she can feel its effects: the leaves of trees blow, the skin is made cool, and flags stand out straight.

Scientists construct models to understand how the world works. For the wind, we understand that the wind is caused by moving air. If we ever observe something in nature that indicates that the wind is not caused by moving air, then we’re in trouble. Either the observation must be discredited or the model must be changed so as to make the new information fit.

Science can be an exceptionally painful process for this reason. The entire product of some scientists’ work has been discarded as a result of the scientific method. However, because scientists’ goal is to seek an accurate description of nature, such a tragic end is a necessary one.

Particularly visionary scientists have predicted certain models before the data was present to back them up. Alfred Wegener presented the theory of continental drift, the idea that the Earth’s continents move, as early as 1911; the theory only gained widespread acceptance in the mid-1950s as data began to prove Wegener correct.

A very popular current topic in physics is that of string theory. String theory states that all matter as we know it is made up of tiny vibrating strings. String theory is interesting to think about, but given our current limits on observation, will likely not be directly observable in our lifetime. Currently we are able to “see” objects using particle accelerators to a resolution of about 10-15 meters — about the width of the proton. Some of these “strings” have lengths as low as 10-35 meters. Imagine being so far away that the entire United States, from coast to coast, looked like a single dot; then try to find a single proton comprising an atom in a hair shed by a dog in Lawrence, Kansas.

Many physicists consider string theory as an interesting possibility, but few are willing to elevate it to absolute scientific fact, merely because it is not directly measurable. When more observations can be gathered, the theory will gain more credibility and widespread acceptance.

I remind my students that as they study physics, the most important habit to gain is that of observation. Many of us drive to and from our jobs and schools every day without truly seeing anything around us. I encourage everyone to be more astute. Look for details you’ve never seen. Literally stop and smell the roses.

Observing the universe around you will not only help you to appreciate science, but you will see what a beautiful place this universe is.

### The Complete Physics Course: Introduction

Saturday, April 28th, 2007

I love teaching, and I love physics. Combining the two, I guess I’ve chosen the perfect career.

Physics is a subject that I believe becomes more beautiful as one studies it. Maybe I’m wrong, but it seems that other subjects become more confusing as the details and rudiments of practice interfere with one’s appreciation. For example, in addition to teaching physics I’m a performing musician. I sometimes wish I wasn’t, just because it must be a wonderful “ignorance” to be able to listen to a beautiful work of art and not analyze it.

I think physics goes in the other direction. The pieces are interesting, but when you look at all the topics together there’s a certain beauty that comes from all the pieces.

I’d like to use some space on this blog to present a straightforward physics course in installment form. This course is designed for everyone — students, teachers, parents, and the everyday person that hated their high school physics class and wants another shot at it. Overall, I want you to have some appreciation for the subject I love.

I don’t have a Ph.D. in physics and I never will (due to lack of time, not lack of ability). Some topics in this course may be a little rough around the edges, so please bear with me. I ensure that the information is as accurate as I can make it, and I count on your support.

Physics is about both the qualitative (describing phenomena) and quantitative (measuring phenomena). This is only natural — in our attempts to understand nature we often need to know how much of something there is or how much energy it has. In order to provide a model for measurements and relationships, physicists use formulas to express ideas. I’m going to use a couple formulas here and there, but don’t be frightened by them. I’m going to aim to use as few formulas as possible, and when I use a formula I’m going to explain every little bit about its use. If you’re not a math person, it’s really okay. A few physicists in history, most notably Michael Faraday, had trouble with mathematics.

I hope you enjoy the course. This is a great experiment for me and hopefully this will be a rewarding experience for you! The first installment is coming soon.