What is the average mean density of outer space?

This answer is taken from the site of "The Physics Factbook", edited by Glenn Elert, and written by his students....

"The interstellar medium is mainly made of lone hydrogen atoms. They do not even exist as pairs as they do on earth. I mentioned before that space is filled with hydrogen atoms. The actual density of hydrogen as it exists in interstellar space is on the average of about 1 atom per cubic centimeter. In the extremes, as low as 0.1 atom per cubic centimeter has been found in the space between the spiral arms and as high as 1000 atoms per cubic centimeter are known to exist near the galactic core.

The interstellar medium also contains cosmic dust. These particles are much bigger than hydrogen atoms. However, there are far fewer particles of cosmic dust than there are hydrogen atoms in the same volume of space. It is estimated that cosmic dust is 1000 times less common than hydrogen atoms in the interstellar medium."

May I indulge myself in some speculation for a moment, please? But first, this from an article in "The New World Encyclopedia" to add more to our references:-

"Stars, planets, asteroids, and moons keep their atmospheres by gravitational attraction, and as such, atmospheres have no clearly delineated boundary: the density of atmospheric gas simply decreases with distance from the object. The Earth's atmospheric pressure drops to about 1 Pa at 100 kilometers (62 mi) of altitude, the Kármán line which is a common definition of the boundary with outer space. Beyond this line, isotropic gas pressure rapidly becomes insignificant when compared to radiation pressure from the sun and the dynamic pressure of the solar wind, so the definition of pressure becomes difficult to interpret. The thermosphere in this range has large gradients of pressure, temperature and composition, and varies greatly due to space weather. Astrophysicists prefer to use number density to describe these environments, in units of particles per cubic centimeter.

All of the observable universe is filled with large numbers of photons, the so-called cosmic background radiation, and quite likely a correspondingly large number of neutrinos. The current temperature of this radiation is about 3 K (−270.15 °C; −454.27 °F)."

Now, for my speculations, in which imagination takes over.... If we've got very thinly distributed atoms of hydrogen, along with one-thousandth that number of particles of space dust, bigger but farther between, along with large numbers of photons, assumed to be cosmic radiation background (residue of The Big Bang) then what?  Let's stuff all this back into our Time Machine, and set the dial back to "Big Bang Minus One Second".....

I'm looking at an alternate or parallel universe, in which there's a big thermonuclear device called a 'Hydrogen Bomb' and it's about to be detonated. We anticipate there will be a huge explosion, with immense expansion immediately following ignition, and the end products will be mostly pressure, heat, light, radiation leading to radioactive decay, and to a lesser extent, space dust caused by the vaporized casing of the device, assuming it is detonated as an "air burst" in atmosphere, rather than on or under ground.

Today's "Question Everything" is: "Haven't we seen this movie once or twice before?"  I seem to recall images of an island in a ocean completely disappearing while the device was being tested prior to completion of its development. Are we nothing but 'copycats'?