String theory seems to suggest that this isn’t quite the end of the story, rather just a blurry view of the real universe. String theory suggests that there exists a small particle that physicists call the graviton that communicates the force, just like the strong force has the gluon to communicate between quarks (called a force carrier). String theorists believe that gravity is not a very weak force, as is now the general thought, but that its strength is lessened because it is spread over more than just our dimension, and that parallel universes exist. These gravitons are thought to travel between these folds of parallel universes, and they are expected to travel at the speed of light and to be massless (only massless particles can travel at the speed of light, a consequence of relativity).
As a side note, you may wonder why presently the force of gravity is considered a weak force. It governs the motion of the planets and stars, so at first thought it seems like it should be a very strong force. But consider how a balloon that you rub on your hair is able to lift your hair against the gravitational force of the earth that is pulling down on your hair. When you rub a balloon on your head, some of the electrons are “rubbed off” on your hair and transferred to a localized region (balloons are insulators, so any charge you transfer sticks right where you put it) on the balloon, and it’s a relatively few number of electrons. Just a few electrons can attract the now positively-charged hair on your head (by rubbing electrons off your hair you have taken away negative charge, which leaves an unbalanced positive charge), and lift it very easily, despite the pull of Earth’s gravity. Gravity, therefore, must be a very weak force as compared to the strong force of electromagnetism. But perhaps string theorists are on to something if the gravitational force’s force carriers, gravitons, are spread out over more than one universe (parallel universe); then it would appear weak.
Applications
Black Holes
You have probably heard the term black hole and wondered exactly what it is. First, a black hole is not really a hole, a term first coined by John Wheeler in 1969. He called it a hole because it appears as a black, featureless area in space.
So then, what is a black hole? Physicists think that a black hole is formed when a large star (a few times larger than our Sun) runs out of the fuel that maintains it, and because it’s so large, its own gravitational force pulls it into a dense area of matter that is small, but very massive. Recall from our discussion of general relativity that celestial bodies, such as stars and planets, distort and stretch the fabric of space-time, like giant bowling balls on a rubber sheet. This distortion of space-time affects the path of light, whether it’s light that may be traveling by, or light emitted by the star actually causing the distortion. Note that the gravitational force only “pulls” on objects with mass, like planets and stars and particles. Light has no mass, so gravity does not “pull” on light. However, the actual path on which it is traveling is affected, so the gravitation force does affect the path of light, just not by directly pulling on it. Scientists believe that when a large star collapses its mass becomes distributed over a very small volume (it’s very dense).This collapse greatly distorts the fabric of space-time, so much so that light cannot escape its distortion. For example, for a space shuttle to escape orbiting our Earth, it has to go a certain speed. This speed is called the escape velocity. The larger the gravitational pull, the faster the object must go to escape its pull (or the distortion of space-time). Think about it this way: When you go around a bend in your car, if you go slowly enough, it’s easy to maintain circular motion. However, if you speed up, there is a certain speed that will cause you to break free from the frictional force keeping you circling and you will slide off tangentially. The difference with orbits is that the force causing the circular motion (or centripetal motion) is not friction (like it is with your car). Instead it’s the gravitational force (or the warping of space-time by Earth’s large mass). A collapsed star is very massive and creates such a gravitational force (or distorts space-time so much) that the path of light turns right back in toward the center. Its path can’t overcome the warping of space-time. Because light is the universe’s speed limit, nothing else can even come close to escaping the space-time warping from the collapsed star. Thus, a collapsed star is called a black hole, as nothing can escape it, not even light (Whitlock, “Gravity”). (Recall that to see something you need to detect light bouncing off of it.)
Dark Matter
Physicists have taken pictures of distant interacting bodies (like a grouping of stars), and after some calculations, have surprisingly discovered that there isn’t enough matter there to cause such an interaction. In this case interaction means gravitational pull or orbiting. How can these stars be grouped when the mathematics doesn’t seem to add up? Scientists are now conjecturing that there is matter that exists that does not reflect light, or perhaps reflects just a very small amount of light, so that it cannot be detected. They have called it dark matter. The term dark matter does not infer that it is dangerous or bad, or that it’s like black holes. Instead the term dark matter means that very little light reflects, if any, so it appears dark, or undetectable, or it would be if it were not for the fact that the gravitational forces are not adding up correctly (another example of learning about something’s existence without really being able to “see” it).
Antimatter
The term antimatter may sound mysterious, so let’s shine a little light on it. Antimatter was predicted before it was experimentally discovered by Paul Dirac, a theoretical physicist who was developing quantum mechanics. In his theory he predicted the existence of a particle that is the same mass as an electron, but has an opposite charge (positive). Later, this particle was called the positron. You might wonder what the difference is between the proton and the positron, because you already know that the proton has a positive charge. Protons are very large as compared to electrons. Positrons and electrons are the same mass, just opposite in charge. When charged particles move through a magnetic field, they spiral, and the direction of their spiral depends on their charge. Physicists saw evidence of particles spiraling in two different directions, implying opposite charges. However, the particles were the mass of an electron, thus showing the first evidence of antimatter. Now physicists have been able to produce antiparticles in particle accelerators (like at CERN in Switzerland), however, they never last very long as they are almost immediately annihilated by their corresponding particle (matter and antimatter annihilate each other). For example, if an anti electron (positron) is produced, it will be annihilated by an electron in very little time. Scientists at CERN have been able to produce antimatter (an atom made of antiparticles); they created an anti hydrogen atom by causing a positron to orbit an antiproton. Again, it was short-lived, as it was annihilated by the prevalent electrons and protons we have. It is predicted by quantum mechanics that the creation and annihilation of matter and antimatter happens frequently, but is so fast we cannot detect it, and because the particles annihilate each other, conservation laws are not violated (they end up canceling each other out). This is an application of the Heisenberg uncertainty principle, which we have not discussed.
We could continue to discuss and delve deeper into what all this means, all this unintuitive physics, and the implications for how we view our universe, and you should continue thinking and reading about our universe, but for now let’s leave with a summary quote from a notable thinker.
“I know that this defies the law of gravity, but, you see, I never studied law.” (Bugs Bunny)
References / Further Reading
“Double Slit Experiment.” Wikipedia: The Free Encyclopedia. 23 Jan 2009. http://en.wikipedia.org/wiki/Double-slit_experiment
Einstein, Albert. “Ideas and Opinions, based on Mein Weltbild.” Ed. Carl Seelig, New York: Bonzana Books, 1954. pp. 8–11.
Einstein, Albert. “Letter to Heinrich Zangger.” 20 May 1912. CPEA, Vol 5 Doc. 398.
Feynman, Richard. “QED: The Strange Theory of Light and Matter.”
Alix G. Mautner Memorial Lectures. Princeton University Press. 1986.
Greene, Brian. The Elegant Universe. 2000.
Newton, Isaac. “Original Letter from Isaac Newton to Richard Bentley.” Newton Project. 25 Jan 2009. http://www.newtonproject.sussex.ac.uk/texts/viewtext.php?id=THEM00258&mode=normalized
Pogge, Richard W. “Real-World Relativity: The GPS Navigation System.” 15 Dec 2008. http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html
Smolin, Lee. The Trouble with Physics: The Rise of String Theory, The Fall of a Science, and What Comes Next. Boston: Houghton Mifflin, 2006.
Weidner and Sells. Elementary Modern Physics. Boston: Allyn and Bacon, 1980.
Whitlock, Laura. “Ask an Astrophysicist.” “How Gravity Effects Photons.” NASA Goddard Space Flight Center. 15 Dec 2008. http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/961102.html
Virginia Physics Standards of Learning
This chapter fulfills section PH.14 of the Virginia Physics Curriculum.
Chapter 7: Nanoscience
Tapas Kar. "Nanoscience", 21st Century Physics Flexbook.
Introduction
The little word, nano, has been rapidly insinuating itself into our consciousness because of its big potential. In the media, nano has captured headlines in television news channels and almost every technical and scientific journal. A number of instruments with nanometer-scale resolution made this possible. We are entering the era of nanoscience and nanotechnology—many remarkable mysteries lie ahead and several fascinating developments are forthcoming. The application of nanotechnology has enormous potential to greatly influence the world in which we live. From consumer goods, electronics, computers, information and biotechnology, to aerospace, defense, energy, environment, and medicine, all sectors of the economy are to be profoundly impacted by nanotechnology. Properties (chemical, electrical, mechanical, and optical) of materials used in these sectors changes significantly in nanoscale than their bulk form. Expected impact of nanotechnology on different sectors is illustrated in the following pie-chart, created by Lux Research—an independent research and advisory firm providing strategic advice and ongoing intelligence for emerging technologies.
Figure 7.1
Lux Research Pie Chart
Future of Nanoscience and Nanotechnology
In 2001-02, the National Science Foundation (NSF) predicted that nanotechnology will be a trillion global market within 10–15 years. In October 2004, Lux Research estimated market growth to trillion by 2014, and in July 2008 they predicted a growth to trillion by 2015, while already billion worth of nano-enabled products were produced in 2007. It is estimated that by 2015, the scientific and technical workforce needed in nanotechnology will be greater than two million.
The following figure shows a series of technology “curves.” They represent the general pattern of slow emergence of a nascent technology, followed by extremely rapid (exponential) growth, ending in a very slow growth or stagnation of the now maturing technology.
The figure shows these behaviors for cars replacing railroads for intercity transport (car growth was limited until the old horse and carriage dirt road infrastructure was replaced with roadways and cars became more reliable—growth exploded after that was accomplished). It also shows various stages of aircraft growth as the new aero technology and support infrastructure (encouraged by the government with the FAA and NACA) matured slowly at first, then grew exponentially. As of this writing (2009), nanotechnology is in its “late emerging stage” in a number of applications. The U.S. government sponsored a National Nanotechnology Initiative in 2000, which was aimed at supporting and encouraging early growth.
Figure 7.2
Time frames of Development of Technology
What is Nano?
To understand nanoscience and nanotechnology, we have to first know what is nano? Nano means dwarf in Greek and it is a prefix in the metric scale.
Figure 7.3
Table 1. Metric Scale and Prefixes
Thus, a micrometer is one-millionth of a meter and a nanometer is one-billionth of a meter. Larger scales are easier to conceptualize than smaller scales. The following are some examples that provide a sense of scale (small) for milli-, micro-, and nanometer objects.
Understanding Size
Although in the United States the standard unit of length is foot, the meter is the standard unit of length used in many other countries. Let us first examine the relationship between a foot and a meter.
or
or
or
Online conversion calculator: http://www.onlineconversion.com/length_common.htm
How Small is One Millimeter (mm)?
The diameter of one dime is and the thickness is .
Figure 7.4
A CD or DVD is thinner than a dime. The diameter and thickness of a CD or DVD are and , respectively.
Figure 7.5
CD or DVD
We can see objects as small as millimeter —that is the limitation of the human eye. For example, the typical width of a human hair is .
Figure 7.6
Human hair
How Small is One Micrometer (µm)?
We need a microscope to see objects smaller than . The most widely used microscopes are optical microscopes, which use visible light to create a magnified image of an object. The best optical microscope can magnify objects about 1000 times.
How Small is the Smallest Thing You Can See Under a Microscope?
The smallest object that can be seen under a microscope is about.
Figure 7.7
If you could split a human hair into separate strands, each would be a micrometer wide.
How Small is One Nanometer (nm)?
One nanometer is
If you could split a human hair into separate strands, each would be a nanometer wide. In fact, human hairs grow by one nm every few seconds.
To see nanometer scale objects, we need an electron microscope, in which electrons are used instead of light, to see nanometer scale objects. An electron microscope can resolve objects about 1000 times smaller than an optical microscope, enabling magnifications of 1,000,000 times, without loss of detail.
Step-by-Step Magnification
Figure 7.8
Step-by-Step Magnification
Periodic Table and description of Elements: http://www.webelements.com/
Periodic Table and description of Elements: http://www.chemicool.com/
Periodic Table and description of Elements: http://www.lenntech.com/Periodic-chart.htm
So at the nanometer scale we see molecules (a combination of different atoms connected by bonds). For example, any form of water (ice, snow, water vapor) is a combination of two hydrogen atoms and one oxygen atom, where the oxygen-hydrogen distance is about .
Some Examples of Different Objects on the Nanoscale
Figure 7.9
Water molecule. Red and gray balls represents oxygen and hydrogen atoms, respectively.
Figure 7.10
Different Objects on the Nanoscale.
More examples of step-by-step magnification: http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/
Figure 7.11
How Small is a Nano?
Atoms and Molecules: the Building Blocks
Figure illustrates some examples that any material or object or thing (living or non-living) in this world is made from atoms. Size (radius) of atoms is about to . The human body is composed of several elements, such as carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, sulfur, calcium, iron, zinc, etc. Oxygen is the most abundant element (about %) in the body. The next one is carbon (%), followed by hydrogen (%), and then nitrogen (%). In fact, % of the mass of the human body is made up of the six elements oxygen , carbon , hydrogen , nitrogen , calcium , and phosphorus .
For a complete list of chemical elements found in the human body visit http://web2.iadfw.net/uthman/elements_of_body.html.
Nobel Prize winner Dr. Horst Störm
er said that the nanoscale is more interesting than the atomic scale because the nanoscale is the first point where we can assemble something—it's not until we start putting atoms together that we can make anything useful.
On the nanoscale, we can potentially assemble atoms together to make almost anything. For example, oxygen and hydrogen found in the human body is mostly as a component of water molecule. Carbon, hydrogen, and oxygen are integral components of all proteins, nucleic acids (DNA and RNA), carbohydrates, and fats. The combination of all of these molecules creates the living cells of the body.
What is Nanoscience and Nanotechnology?
The properties and functionalities of any living or non–living object come from its constituent molecule(s). Over millions of years, Mother Nature has perfected the science of manufacturing matter molecularly. Nanoscience is basically understanding science at the molecular scale. Nanoscience is both the discovery and study of novel phenomena at the nanoscale as well as the creation of new concepts to describe them.
Since the Stone Age (approximately million years ago), we have been using available materials around us to produce tools and devices for practical uses. New discoveries in science enabled us to create more application-oriented products, new devices, and electronic gadgets. Since the beginning of the 1980s, the world witnessed the development of microtechnology, a step toward miniaturization. Nanotechnology is the engineering of functional systems at the molecular scale (sizes between ). Nanotechnology is the fabrication, characterization, production, and application of man-made devices, and systems by controlled manipulation of size and shape at a small scale that produces devices and systems with novel and superior characteristics or properties.
CK-12 21st Century Physics: A Compilation of Contemporary and Emerging Technologies Page 16
