If you’re a science fiction fan, you’ve likely heard of the Romulan cloaking device, a fictional means of making a spaceship invisible. While the the device works by way of technobabble, the basic idea is that it transports electromagnetic radiation from one side of the cloaking field to the other. It makes for a very interesting plot device, effectively turning any spaceship with such a device into an intergalactic submarine.
In my upcoming sequel to First Command, I explore a similar idea… a hostile spacecraft that can’t be seen.
But hard science fiction fans tend to scoff at this notion. An invisible spacecraft is scientifically implausible. It can’t be done.
Why is that? And is there any way around it that doesn’t resort to techno-magic?
Black Body Radiation
With sufficient instrumentation, you should be able to see just about anything in space (provided there’s nothing in the way). This is because all objects with a temperature above absolute zero radiate energy. This energy is called black body radiation because it’s given off even if the object in question has no other means of generating or reflecting energy.
In this graph, I’ve generated a plot of specrta–intensity of the frequency of light radiated from an object at a given temperature. Each curve corresponds to a temperature encountered here on Earth. The coldest recorded natural temperature, for example was about -89.2°C (-128.6°F) recorded in July 21, 1983 in Antarctica. What the graph shows is that as temperature increases, so does the overall energy radiated (the area under the curve), and spectrum shifts to the right–toward higher frequencies. For terrestrial temperatures, these emissions are in the infrared section of the electromagnetic spectrum. When you get up to several thousand Kelvin in temperature, the emissions are visible light. Our sun, for example, has a surface temperature of 5778 K, and obviously is the source of our light here on Earth.
The reason we can see anything at all generally comes down to an imaging concept called contrast. Simply defined, contrast is the relative difference in signal intensity of an object from it’s background.
Space itself has a temperature: 2.7 K (−270.45 °C/−454.81 °F). It’s not absolute zero. But it is pretty close. This background is pretty much the same in any direction. No matter where you look, the only electromagnetic radiation (that’s not coming from an actual object like a star or a planet) is in the form of very low energy microwaves. It’s like setting the background in the image above to nearly pure white, and that makes even the light gray squares stand out even more.
So basically, any object with any thermal energy at all, even liquid nitrogen at 77 K, will stand out. Living humans give off infrared radiation. Stars give off visible light. Therefore any given spaceship will be visible (or at least detectable) to any other spaceship.
This means that even if you have a perfect ‘camera-screen-ship-in-between’ system like the Romulan cloaking device that will transmit light from back to front, you still have the radiation coming off of you due to your temperature to worry about.
So is there any way to hide a spaceship without resorting to techno-magic?
Samarium Nickel Oxide
Recent scientific work has discovered a very interesting property of NiSMO3, a crystalline oxide that can be made into an ultrathin film. In a 2019 paper from the University of Wisconsin-Madison, researchers showed that when samarium nickel oxide heats up, it undergoes a transition from an insulator to a metal. As it does, it’s emissivity (the tendency to emit thermal radiation) goes down. Over a relatively broad range of temperatures from about 105 °C to 135 °C, there is no change in thermal emission.
This fundamental property of matter appears to be circumvented!
In principle, objects could be covered with a thin layer of this substance to mask their infrared signature.
Of course making something that’s 135 °C look like it’s 105 °C is a lot different than making something that’s several thousand Kelvin look like 2.7 K. But in science fiction we’re allowed some leeway to extrapolate from existing science. There is certainly some potential here anyway.
Here’ a link to a video explaining samarium nickel oxide.
There are some other strategies to consider too in a game of intergalactic hide-and-seek..
Infrared radiation can be blocked. All you really need is some aluminum foil (a conductor). Of course you can’t just wrap your ship in aluminum because someone would still see the aluminum (or the heat coming off of it). But the point is that you can hide behind something that can be seen… a planet, a star, an asteroid, etc. Space is full with a whole lot of nothing, but people are usually most interested in the rare spots where stuff actually is. So hiding behind something is certainly an option.
Space is really big. When two ships are far apart, it takes time for light from one to reach the other. If a ship that’s ten light minutes away suddenly turns to attack you, you won’t actually see that happen for 10 minutes. That’s not invisibility proper, but it does give rise to some interesting strategic games if you’re writing suspenseful space combat.
Resolution limits what you can see a far distances. Just about every image produced with modern technologies is made up of pixels. A given pixel value corresponds to the average amount of light incident on it. An object that is further and further away is made up of fewer and fewer pixels until eventually it’s just averaged over a single pixel. Eventually you just don’t see it at all.
Hacks. Since we need technology to detect infrared light, there’s always a risk that technology can be corrupted. It’s not too much of a jump to imagine that specific objects could be artificially masked out of existence.
Invisibility in Space?
By it’s most proper definition: no. It’s not going to happen.
But there is some absolutely fascinating science that suggests it may not be as impossible as we may have first thought.
Get Your Nerd On…
If you want to nerd out for a moment, the relationship between the frequency of the emitted electromagnetic radiation, referred to as ν, and temperature T, is this bad boy right here…
In 1900, the German physicist Max Planck showed that this empirical formula describes the intensity of a segment of the light spectra emitted from an object of temperature T (in Kelvin) into a solid angle. For reference, h is Planck’s constant (4.1357 x 10-15 eV s), c is the speed of light (2.9979 x 108 m/s), and k is the Boltzmann constant (8.6173x 10-5 eV K-1). Here’s the like to the Wiki article for more information.