by Andy Berger
As a teaching assistant for college freshman physics labs at OSU, I had a student ask me what being a physicist is like. “Do we just throw tennis balls against the wall, and see how they bounce back?” he asked. As silly as it may sound, the question was fair because that was essentially what we were having students do in their lab that week. Since we understand that motion well now, having been described more than 300 years ago by Isaac Newton, physics can appear stale and mundane. My student would be surprised to learn that even today there are many unanswered questions in physics. Unfortunately, we don’t always do a great job promoting what continues to make physics interesting.
As humans, we live in the “middle” of size scales at which the universe unfolds. The motion of a tennis ball – spanning a few meters – also lives in that realm. However, there is much to explore at extremely large and small size scales. The estimated diameter of the universe is about 1027 meters (1 with 27 zeros after it – a billion billion billion meters). Meanwhile, the diameter of an individual proton is 10-15 meters (1 with a decimal point and 15 zeros before it – a millionth of a billionth of a meter). So 1.8 meters – the average human height – is near the middle.
Much of the excitement in physics now is centered on what is happening at those extreme size scales. At huge sizes we ask the questions: is there life on other planets, how do stars form, what is dark matter? And at small sizes: how do 2 meters of DNA fold into a cell nucleus, what are the most fundamental particles of matter, how do collections of atoms interact to produce everyday phenomena like color and magnetism?
The smallest object observable to the unaided human eye is about 50 micrometers (1 micrometer is 10-6 meters, one millionth of a meter). This is pretty much the diameter of the average human hair (17-180 micrometers, depending on color). Things smaller than this all get lumped into a single category: “microscopic.” Take for example a cell and an atom. On the blackboard, at least when my grade school teacher drew them, they looked very similar to me.
As a result, it was embarrassingly late in my lifetime when I had the light-bulb moment realization that a cell is much bigger than an atom. Much, much bigger – at 5 micrometers across, a red blood cell is about 40,000 times bigger than a carbon atom. So if my teacher had drawn an atom on the blackboard (big enough for the entire classroom to see), a to-scale blood cell would be as big around as Interstate 270, the beltway around Columbus, OH.
My research brings me into very close contact with the objects at the small end of the size spectrum – sometimes smaller than 1 micrometer. Since our specialized microscopes can “see” nanometer-sized objects (1 billionth of a meter), perhaps we should instead call them nanoscopes. Nevertheless, the microscope that I work with doesn’t just see very small objects; it actually “sees” magnetism.
This is an image from my microscope of the 1s and 0s of a magnetic hard drive – the device we all use every day to store our documents, music, photos, etc. It is a false color image – magnetism doesn’t actually have a “color,” but I’ve assigned the North and South magnetic poles to red and blue. A single stripe is known as a bit. A bit is the smallest amount of information, and can be thought about like a light switch – on or off, 1 or 0. Eight bits are needed to store a single letter of the alphabet, and are known collectively as a byte. The miniature size of the bits allows us to store billions of bytes (literally, that’s a Gigabyte) on a device that can fit in your pocket (iPods, cell phones, etc.). I’ve shrunk the image down so that you can see, when compared to a human hair, a hard drive bit is very small.
Richard Feynman, a renowned physicist, famously said, “There’s plenty of room at the bottom.” By this, he meant that we can utilize the tiny size of atoms and small collections of atoms to do tremendous things. “Nanoscience” – a catch term and hot research topic that seeks to realize Feynman’s goal – is any science that takes place at the nanometer scale (one billionth of a meter).
Some of the best examples of how much “room” is down there – at small sizes – are biological systems. Consider DNA, which stores our genetic code using base pairs the same way a hard drive stores files using magnetic bits. Scientists have actually begun utilizing DNA as if it were a hard drive. Feynman suggested that nanoscience would enable the writing of the entire collection of books in the world, which he estimated to be 24 million volumes, in a space the size of the head of a pin. In a near-fulfilling of Feynman’s prophecy, George Church, a Harvard Professor of molecular genetics, encoded 20 million copies of his book into a DNA sequence, and dropped it onto a small slip of paper. The droplet of DNA isn’t actually visible in this grainy photo, but its position is at the center of the red circle. Plenty of room, indeed.
To my tennis-ball throwing student, it wasn’t obvious what made physics interesting and exciting anymore. We can easily and routinely watch a tennis ball fly through the air with our own unaided eyes. We cannot however manipulate DNA or observe the magnetic bits of a hard drive without specialized scientific instruments. “Hardly any scientific discoveries of the past century flowed from the direct application of our five senses. They flowed instead from the direct application of sense-transcendent mathematics and hardware.” (Neil deGrasse Tyson, Death By Black Hole, page 29) Through my graduate work in physics, I have had the chance to directly interact with this type of “hardware” – a microscope which can “see” magnetism at size scales comprised of merely hundreds to thousands of atoms. Studying physics allows me to truly grasp the variety of scales in which the events of our universe unfold. Every day I’m amazed at how much room there is to explore “at the bottom.”
About Andy Berger
I grew up in Mansfield, Ohio, received my undergraduate degree from Kenyon College in Gambier, Ohio, and am now finishing my fifth year of the physics PhD program at Ohio State. I am a condensed matter experimentalist with a focus on scanning probe microscopy, magnetism, and graphene. I never would’ve guessed that would be my “job description” when I was in high school. Away from the lab, I enjoy staying active – mostly through swimming, running, cycling, and soccer.