Ductile fracture. The propagation of a ductile crack involves substantial plastic flow and ductile fracture usually gives a characteristic rough fracture surface.Fracture occurs by a process known as microvoid coalescence. First, plastic strain causes small microvoids to form in the material, most often at sites of inclusions.he propagation of a ductile crack involves substantial plastic flow and ductile fracture usually gives a characteristic rough fracture surface.
An illustration of the space-time curvature caused by Earth. Space-time is a mathematical model that joins space and time into a single idea called a continuum. This four-dimensional continuum is known as Minkowski space. Combining these two ideas helped cosmology to understand how the universe works on the big level (e.g. galaxies) and small level (e.g. atoms).
Time travel. Time travel is the concept of movement (such as by a human) between certain points in time, analogous to movement between different points in space, typically using a hypothetical device known as a time machine, in the form of a vehicle or of a portal connecting distant points in time.