Speed of light difference in the speeds of photons of different energies, confirming that Lorentz invariance is verified at least down to the scale of the Planck length ("l" = ≈ ) divided by 1.2. In a medium, light usually does not propagate at a speed equal to "c"; further, different types of light wave will travel at different speeds. The speed at which the individual crests and troughs of a plane wave (a wave filling the whole space, with only one frequency) propagate is called the phase velocity "v". An actual physical signal with a finite extent (a pulse of light) travels
In the Light of What We Know when the true pleasure of a work of fiction is its gravitational pull upon us?” In a 4,000-word review for "The New Yorker", the critic James Wood described Rahman as “a deep and subtle storyteller,” and praised the novel as “astonishingly achieved…Isn’t this kind of thinking—worldly and personal, abstract and concrete, essayistic and dramatic—exactly what the novel is for? How it justifies itself as a form?…"In the Light of What We Know" is what Salman Rushdie once called an ‘everything novel.’ It is wide-armed, hospitable, disputatious, worldly, cerebral. Ideas and provocations abound on every page.” Australian literary critic Louise Adler