“Even today, more than eighty years after Oort's bold guess, we still don't have a clue what this dark matter is made of. We know it exists. We know where it is. We have maps of its presence within and around galaxies throughout the universe. We even have stringent constraints on what it is not, but we have no clue what it is. And yes, its presence is overwhelming: for every one kilogram of ordinary matter made out of neutrons and protons and electrons, there are five kilograms of dark matter, made out of who-knows-what.” MatterUniverseMapsOverwhelmingClueGalaxyPresenceKnowConstraintsWhatElectronsExistDark MatterGalaxiesMapWhereNeutronsGuessExistsProtonsOort Book:The Universe in Your Hand: A Journey Through Space, Time, and Beyond Source: The Universe in Your Hand: A Journey Through Space, Time, and Beyond
“A clock that is moving through space at a very fast speed does not tick at the same rate as a slow-moving watch gently attached to your wrist as you stroll on a tropical beach. The idea of a universal time - a godlike clock that could somehow sit outside our universe and measure, in one go, the movement of everything in it, how its evolution unfolds, how old it is and all that - does not exist.” AgeMovingUniverseSpaceMovementEvolutionUniversalRateSpeedBeachClockEverythingOldTickExistGodlikeFastOutsideMeasureSlowStrollUnfolds Book:The Universe in Your Hand: A Journey Through Space, Time, and Beyond Source: The Universe in Your Hand: A Journey Through Space, Time, and Beyond