These phenomena have been documented observationally, experimentally, and theoretically. These predictions have not yet been tested either observationally or experimentally. Changes in physical constants are not meaningful if they result in an "observationally indistinguishable" universe. Distinguishing both theoretically and observationally between these alternatives is a subject of current research. All observationally stable odd-odd nuclides have nonzero integer spin. Selenium has six observationally stable or nearly stable isotopes, 26 radioactive isotopes, and 9 isomers. Tegmark claims that the hypothesis has no free parameters and is not observationally ruled out. Several other theories of massive star formation remain to be tested observationally. The presence of amorphous ice in molecular clouds has been observationally confirmed. That said, super-Earth magnetic fields are yet to be detected observationally. In the latter case, those particles are called "observationally stable". However, this can be observationally difficult due to variation in line strength. The detection of the CIB is both observationally and astrophysically very challenging. The Persian calendar begins each year at the northward equinox, observationally determined at Tehran. Observationally, it is typified by shell lesions on the scutes.