### Re: Ulrick's (or some other spelling) conjecture

Date: Fri Aug 25 18:06:59 2006
Posted By: Bryan Dunne, Instructor, Astronomy, University of Illinois
Area of science: Physics
ID: 1156269822.Ph
Message:

For your question, it sounds like you have some of the common misconceptions about the Big Bang. There are many misconceptions about the Big Bang. First, most people (and many science videos) imagine it as a giant explosion. There was NO explosion! The Big Bang was not an explosion of matter and energy through space; rather, it is an expansion of space, and the expansion continues. The galaxies are just along for the ride.

Imagine putting several dots with a pen on a deflated balloon; the dots represent galaxies and the balloon is space. As you blow the balloon up, the dots get farther apart, but the dots aren't moving across the surface of the balloon. They are getting farther apart without having to move through space! The light emitted by the stars and gas that make up galaxies does move through space (the galaxies can move through space, of course, but at much slower speeds than light - less than 1% the speed of light).

A second common misconception is that people think that the Big Bang happened somewhere in space. Instead, the Big Bang was the beginning of everything in the Universe. That includes space and time, as well as matter and energy. The Big Bang happened everywhere, because everywhere was created at the Big Bang. But, at the time of the Big Bang, space was incredibly small - the size of the observable Universe (about 100,000 trillion trillion centimeters across now) was only a hundredth of a trillionth of a trillionth of a trillionth of a trillionth of a centimeter across at the moment of the Big Bang (actually, at the smallest theoretically measurable increment of time after time=0; this is known at a Planck time, its about a hundred millionth of a trillionth of a trillionth of a trillionth of a second).

Finally, the Universe cannot be both spherical and infinite. A spherical geometry of the Universe means that it is finite in size. If the Universe is infinite in size, its geometry is either 'flat' or 'saddle-shaped'. If the Universe is spherical, the reason we haven't seen "the night sky lit up from light coming around the other way" is that the Universe is finite in time, and the Universe is bigger than the speed of light * the age of the Universe, so we can't yet see all the Universe.

P.S. - I think you mean 'Olber's Paradox'.

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