Nebulae are an extremely common setting in works of Science Fiction, most often used
as an all-purpose obstacle, hiding place or decorative backdrop.
While often compelling from a narrative standpoint, these uses are almost always in conflict with
reality and I’d like to take a moment to explain exactly why in this short video.
The first concern is with the apparent ubiquity of nebulae in popular science fiction.
It often seems like the crew of the Enterprise or the Millennium Falcon can’t complete
even the shortest of journeys without passing or stumbling into a Nebula.
Putting aside the fact that ‘stumbling across’ anything at all on an interplanetary or interstellar
voyage is astronomically unlikely, the simple truth is that Nebulae are generally vast entities
containing thousands of Star Systems whose positions are well recorded even today.
While Nebulae are not uncommon on a Galactic Scale, there are extremely few that fall within
the boundaries of human spaceflight in most works of science fiction.
Small single-system nebulae like those often seen in Star Trek and Star Wars do exist in
reality, though in far less frequency.
These smaller objects are known as ‘Planetary Nebulae’ and are formed by low-mass stars
as they shed their outer layers near the end of stellar evolution.
One such example of this is the nearby Helix Nebula, which is approximately 5.7 Light Years
in Diameter.
While this is drastically smaller than a conventional nebula, it still covers a sizeable interstellar
region, and does not correlate with the many instances from Star Trek and Star Wars where
we have seen ships cross fully through a Nebula using sublight propulsion alone.
The smallest known Nebula in the night sky is NGC 7027, which is approximately 0.2 Light
Years or 12600 AU in Diameter, still far too large to traverse at sublight speeds in any
reasonable time.
One of the closest Nebulae to Earth is the Orion Nebula, located approximately 1,344
Light Years from our solar system.
The Nebula is around 24 Light Years in diameter, covering a vast region of space, and while
it may appear to be a thick cloud of gas and dust, the region is in fact incredibly diffuse,
as is in fact the case with all nebulae, which brings me to my next point concerning the
often inaccurately portrayed density of Nebulae.
Let’s compare the density of a nebula to the density of the atmosphere on earth for
example.
The average particulate density of air is 30 quintillion particles per cubic centimetre,
whereas for a nebula it’s closer to only a few thousand particles per cubic centimetre
which is functionally barely any different to a vacuum, and is in fact, still less dense
than any artificially created vacuum on earth.
So when we see the Enterprise enter the conveniently placed Mutara nebula in the Wrath of Khan
what we should see is essentially no change in velocity for the ship, as the forces due
to drag would still be negligible when compared to those from the normal interstellar medium.
What we see instead is the entire bridge crew throwing themselves forward as they penetrate
the seemingly concrete nebula wall.
That is except for kirk, who uncharacteristically seems to be the only one aware that they did
not just fly into a giant space pillow.
The final and perhaps most crucial point, is that a Nebula would not function as convenient
natural smokescreen to hide your starship from an encroaching Borg Cube or Imperial
Star Destroyer.
A ship that is able to detect life signatures onboard another ship through several layers
of hull plating should have absolutely no trouble detecting an enemy ship through small
traces of stellar dust.
Two ships engaged in combat within a nebula would be able to see and detect eachother
just as easily as anywhere else, they would simply be battling against a much prettier
backdrop.
So there you have it, Nebula are enormous, interstellar regions of diffuse gas, lightly
scattered around the galaxy, their locations are well known and iconic, and suggesting
that you quickly find one to hide within during a space battle would be akin to suggesting
that you quickly run to the Great Wall of China and hide behind that.