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 is the concept of movement (often by a human) between different points in time in a manner analogous to moving between different points in space, typically using a hypothetical device known as a time machine.harles Dickens ' 1843 book A Christmas Carol is considered by some to be one of the first depictions of time travel in both directions, as the main character, Ebenezer Scrooge, is transported to Christmases past, present and yet to come.