Do We Live in a Black Hole?


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Consider the size of the universe.  You might have read in the popular science literature that the universe has a radius of about 10 (or 20) billion light years.  The size of our observable universe is based on Hubble's Law.  Hubble's law represents the expansion velocity of the universe as:

v=H0r

Where v is the expansion velocity of the universe at a distance r, and H0is Hubble's constant.   Now, since nothing can go faster than the speed of light, we can estimate the age of the universe by looking at our formula and noticing that v increases as r increases.  Or we can deduce that r cannot be large enough to bring v to a value greater than the speed of light.  In other words:

r=c/H0

Gives this as the maximum observable size of the universe.   This works out to be anywhere from 10 to 20 billion light years in radius (see also "How Old is the Universe")   If we run time backwards with this fixed radius, then, matter would  expand until it filled this volume.  A meter, then gets much closer to the size of the universe...  In  loose terms, then the size of the universe "ruler" at the time of the "big-bang" would be the same as a material ruler.    Furthermore, the evidence we've collected over the last 30 years or so indicate that the the "big-bang" might have been a hot "big-bang".  So, our initial conditions for the big-bang involve a very large, very hot "sphere"   of primordial stuff.  Now, if we run time forwards, we can kind of visualize the beginning of our universe as a very rapid collapse (the inverse of "Inflation").  A similar kind of event happens when a star (hot ,spherical, massive, dense...) becomes so dense and massive it collapses in on itself and forms that mysterious black hole.  Here's an interesting question to explore... "Did our universe begin as a star that underwent a gravitational collapse?"  I.e., do we live in a black hole? (See also "Is the big bang a black-hole?" for the other side.)

 

10/24/98           Copyright, 1997Jack Martinelli   

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