The Western Lines

July 26, 2007

A Seemingly Stupid Question: What did the Big Bang Sound Like?

Everyone has heard of the Big Bang , which occurred some 14 billion years ago when a kernel of energy smaller than a proton exploded and gave rise to the whole shebang of existence. The extreme heat generated by that explosion exists today as the 3 K microwave background radiation that permeates the whole of the Cosmos. But, in my teaching experience some variation of the following questions always seems to crop up: Did the Big Bang really go BANG, as in KABOOM? And if so what did it sound like? Personally, I always thought these questions were rather stupid and would proceed to remind the offending student of some very salient facts from pervious lessons.

Well we all know from high school physics that sound waves cannot travel through a vacuum and need a medium such as a solid, liquid, or gas to carry them. We are also taught that sound waves are generated by vibrations that give rise to changes in the density of a medium known as rarefactions and compressions. Such waves can only be generated and travel within a material medium. So in a vacuum it’s basically impossible to hear anything. If you have trouble remembering this basic fact, just remember the old adage from the motion picture Alien – “In space no one can hear you scream.”

True enough but, it turns out though that the early universe wasn’t a vacuum. The primordial cosmos was in fact filled with hydrogen and ionized gas and these provided the medium through which the birth cry of the universe was allowed to travel. So these questions are not so stupid after all.

Well one fine day, physicist John G. Cramer of the University of Washington was confronted with the very same questions from the mother of an eleven year old who was doing a science project concerning the Big Bang. His initial impulse was to answer “NO” and perhaps proceed to answer in the way I outlined above. But, this query tickled his curiosity and he proceeded in a way that separates great minds from mere high school physics teachers and actually tackled the problem head on.

Using data from BOOMERanG, a balloon-borne cryogenic microwave telescope experiment that flew at an altitude of about 24 miles over the Antarctic and a space mission the Wilkinson Microwave Anisotropy Probe (WMAP) he was able to calculate and recreate in a computer simulation the sound wave generated during the first 760 thousand years of the universe. He then proceeded to correlated this data so that the sound intensity varies to match the cosmic microwave background as it changed during this epoch of cosmic history and obtained the necessary parameters of just how such a sound wave would propagate given the physical properties of the universe at that time. The frequency of the sound wave generated was too far below the range of human hearing to be perceived by the human ear. But, Cramer in his simulation boosted the frequency within the range of human hearing and produced an actually audio recording. The story of how and why Cramer decided to tackle the problem is a fascinating one and I highly recommend it to any teacher who was ever confronted by a seemingly stupid question.


1 Comment »

  1. That sure sounds eerie. NASA releases sounds from their Saturn missions a while ago which also sound spooky. me of the music in old science fiction movies.taRalph

    Comment by Ralph Buttigieg — July 29, 2007 @ 8:11 pm | Reply

RSS feed for comments on this post. TrackBack URI

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: