Forces of Nature Beyond Gravity and Electromagnetism
Biochemistry Major (College of Arts & Sciences)
Joshua Long (College of Arts & Sciences)
Our group conducts experimental searches for forces of nature beyond gravity and electromagnetism. We concentrate on forces which act over distance ranges less than one millimeter. There are 4 known fundamental forces of nature: gravity, electromagnetism, and the strong and weak nuclear forces. However, there could be additional forces of nature millions of times stronger than gravity acting over distances resolvable to the unaided eye, about which we have no information. Many theories that attempt to describe both gravity and the other fundamental forces make predictions of additional, sub-millimeter forces. Discovery of a correct "unified theory" has long been a ""holy grail" of fundamental physics. Furthermore, ordinary matter makes up only 5% of the known mass in the observable universe. Exotic, sub-millimeter forces could be mediated by "dark matter," the otherwise unknown quantity making up 27% of the mass, and "dark energy" the even more mysterious quantity thought to make up the remaining 68%. We are conducting several experiments using different techniques. All techniques involve very sensitive measurements of the force between two test objects; those measurements are then compared to the predictions from known physics to check for any deviation. We have several projects associated with each experiment. One project is to calculate the sensitivity of one experiment to newly-published theoretical spin-dependent forces. Another project is to design, construct, and test a magnetic calibration system for this experiment.
Technology or Computational Component
The search for forces beyond gravity and electromagnetism is an active area in theoretical physics as well as experimental physics; theoretical predictions of exotic forces continue to appear in the literature. These forces could depend on several properties of test objects involved, such as mass (like gravity), or charge (like electromagnetism). Another fundamental property of matter is spin, which can be thought of as intrinsic angular momentum. Most subatomic particles (including protons, neutrons, and electrons) have non-zero spin. A recent publication (February 2019) lists 9 new or revised predictions of exotic forces that depend on spin. Several of our experiments are designed to be sensitive to spin-dependent forces; and one project is to assess how sensitive these experiments will be to the new predictions. The new predictions show the theoretical form of the exotic forces between two point-like objects. This is the simplest possible configuration. The test objects in our experiments are extended objects, so the main step in the sensitivity calculation will be the integration of the point-like force over the specific test object geometry of our experiments. To this end, the student will learn a computer-based numerical integration technique, most likely the widely-used ""Monte Carlo method."" Some computer code already exists for this purpose, though it is written in an old (but relatively easy-to-learn) language; the student will be encouraged to update the code to a more modern platform, preferably based on the C++ language. Once the theoretical forces are calculated, the sensitivity of the experiments will be estimated by comparing the results of the calculation to the minimum resolvable forces, or "noise." Another project is to design, construct, and test a magnetic calibration system for one of our exotic short-range force experiments. This experiment is sensitive to forces that depend on spin, so the test objects have been designed to have a high degree of spin. In most materials it is the charged particles (electrons, protons, and constituents of neutrons) that spin; this moving charge leads to a large degree of magnetism. Our group has developed special materials which have a high degree of spin but which, under the right conditions, very low magnetism. This is important because magnetic forces could swamp out a signal of an exotic force. These special materials will be used as the test masses in one of our experiments. In order to verify that we have attained the conditions in which the magnetism has been minimized, we plan to build a system to drive the test masses magnetically: when this force is minimized (and ideally zero), we can infer that we have attained the ideal conditions. The calibration system will consist of a set of magnetic coils. The student working on this project will be expected to learn and use techniques of computer modeling, coil construction, basic electronics, and magnetic field measurement. The student will first complete a computer model of the magnetic coils (based on the work of a previous CEWiT student) using the very powerful and versatile technique of finite element analysis. Then the student will work with an engineer to produce a practical design of the coils. Depending on the details of the design, the student will either help build the coils in the lab or coordinate their fabrication by outside vendors (or both, if shared construction is appropriate). Time permitting, the student will connect the finished coils to the appropriate electronic devices (signal generation, amplifier if needed), make measurements of the magnetic fields generated, and compare the results to the computer model.