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Light travels at 300,000 kilometres per second (186,000 miles per second). In one second, a beam of light can travel SEVEN TIMES around the Earth. This table shows a number of distances to various objects expressed in terms of how long a beam of light takes to travel that distance.
<object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=9,0,28,0" width="920" height="518" title="scale"><param name="movie" value="/content/begin/cells/scale/Scale.swf" /><param name="FlashVars" value="mydate=2519" /><param name="quality" value="high" /><embed src="/content/begin/cells/scale/Scale.swf" quality="high" pluginspage="http://www.adobe.com/shockwave/download/download.cgi?P1_Prod_Version=ShockwaveFlash" type="application/x-shockwave-flash" width="920" height="518"></embed></object> Some cells are visible to the unaided eye The smallest objects that the unaided human eye can see are about 0.1 mm long.
The Elegant Universe: Part 3 PBS Airdate: November 4, 2003 NARRATOR: Now, on NOVA, take a thrill ride into a world stranger than science fiction, where you play the game by breaking some rules, where a new view of the universe pushes you beyond the limits of your wildest imagination. This is the world of "string theory," a way of describing every force and all matter from an atom to earth, to the end of the galaxies—from the birth of time to its final tick, in a single theory, a "Theory of Everything." Our guide to this brave new world is Brian Greene, the bestselling author and physicist. BRIAN GREENE (Columbia University) : And no matter how many times I come here, I never seem to get used to it.