In this issue (page 243)1, Van Dyck and Chen report an electron-microscopy technique that draws on an analogy with the method used in astronomy for determining distances to galaxies. The technique allows high-resolution, three-dimensional information to be obtained about a sample using only one viewing direction.
A central observation in astronomy is that distant galaxies are moving away from us, and from each other, with a speed that is proportional to their distance from Earth. In other words, the farther away they are, the faster they are moving. Because the speeds of galaxies can be measured from the Doppler effect, which shifts the galaxies' light to the red end of the electromagnetic spectrum, their distances can be determined using the constant of proportionality between speed and distance, known as the Hubble constant2. This central observation, called Hubble's law, is crucial evidence for the now accepted view that the Universe originated in a Big Bang, as a tiny, unimaginably dense entity that has been expanding ever since. What's more, it provides astronomers with a neat way of determining the distances to objects, which would otherwise be impossible using only the objects' observed positions in the sky.