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Compact Cosmos

45 44 TIMEANDLIGHTBUBBLES all that we see Our horizon,the limit of the visible, is a bubble expanding at the speed of light,about 186,000 miles per second. A lightyear is the distance light covers in a year,a little under 5.9 trillion miles and a convenient measure for the vastness of space. Light takes time to travel even at this incredible speed, so every glance can only peer into the past,and the more distant our gaze,the further back in time we see. Light from far quasars started off billions of years ago,back when the universe was if you believe in the big bang a sprightly youth. Much remains forever hidden,as illustrated by the boundaries of light cones opposite top. The theory of relativitylinksthe three dimensions of space and the one of time into a single fourdimensional entity, spacetime. We can imagine this as a stretchy sheet opposite center. Anything placed on it distorts its shapethe more massive the object,the greater the distortion,affecting both space andtime. It is this warping of space time that causes the pull of gravitational fields and the closely related tug we feel when in accelerated motion. Although we might not notice,everything is moving at the speed of light. We are hurtling through time at lightspeed even if sitting reading a book. If we start to move through space, our velocity through time slows to make the combined space and time velocities still equal to the speed of light. At our usual slow pace the effects are minimal,however the faster we go the more noticeable this curious give and take becomes opposite below.
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