Can We Build a Real Lightsaber? The Science of Star Wars

In 1977, Star Wars introduced audiences to a galaxy far, far away, filled with aliens, space travel, and the iconic lightsaber, a glowing energy blade capable of deflecting blaster bolts and clashing with other sabers. But how much of this cinematic fantasy holds up to real-world science? In honour of this beloved franchise, we turn to the paper, 'On the Physical (Im)Possibility of Lightsabers' [1]. The authors investigate whether a lightsaber could exist.

What is a Lightsaber?

Lightsabers are 'blades of light.' Thus, for this technology to be possible to create, we would need to be capable of stopping and shaping light [1]. However, the trick is that light travels freely. The paper does explain that light can be slowed down when passing through certain materials, such as a cloud of cold atoms; however, stopping and shaping the light into a beam is much more complex [1].

Can We Shape Light into a Blade?

Experiments have shown that it's possible to manipulate light by creating “needles of light” using polarised beams [1].  

Polarised beams are light waves that vibrate in just one direction, which helps scientists’ control and focus the light more precisely for experiments or technologies like lasers.

This creates a narrow, dense shape, resembling a lightsaber [1]. However, it would only be about 1 millimetre long [1], hence, not even close to the full size of a lightsaber.

Could Two Lightsabers Clash?

Another challenge is that light does not naturally block or collide with itself, thus making it impossible for two lightsabers to clash like swords [1]. Nevertheless, this would be possible under certain conditions, such as trapping light inside a cloud of cold atoms within a tube or container [1]. This would allow particles to push and pull on each other, creating an illusion of solid beams [1]. However, requiring a container to hold this light would make it far different from the elegant weapon we see on screen.

How Would a Lightsaber Clash Feel?

Interestingly, if light could clash with each other, it wouldn’t feel like two metal swords colliding but would still feel surprisingly solid [1]. That’s because when photons (the particles of light) bounce off each other, they create a tiny push called radiation pressure [1]. This could slow down the blade or push it back, making it feel strangely solid [1].

However, the researchers had to simplify assumptions to ensure the previously mentioned scenarios would work. This included:

• Ensuring the beams were square [1],
• Crossing at 90 degrees in this space and [1],
• Polarised in the same direction [1].

While it does not realistically depict an intense fight, it does provide a glimpse into how a lightsaber duel might theoretically work.

Gamma-Ray Sabers

Surprisingly, in a process called light-by-light scattering, light can interact with other light when it’s at very high energies, especially in a type of light called gamma rays [1].

Gamma rays are a form of light produced by radioactive material or supernovas, but they are much more powerful than the light we can see.

If gamma-ray sabers were used as an alternative, they would clash like swords; however, they would be invisible and emit dangerous radiation, which is a far cry from what we see in the movies [1].

The paper delves deeply into the physics and mathematical reasoning behind their findings. If you are interested in looking at these formulas and the researcher’s hard work, go to their paper and look at Section 2 (their theoretical background) or the appendix.

Energy Demands: Powering a Lightsaber

Creating and maintaining a lightsaber would require unimaginable amounts of energy. The authors estimate that operating a lightsaber for one minute would use about one-tenth of the Sun’s energy output in a second [1], which would equal about 38,460,000,000,000,000,000,000,000 watts. For reference, it takes about 18,000 watts to power a house.

What could possibly power that?

·       Nuclear fusion is a process by which two light atomic nuclei combine to form a single heavier one while releasing massive amounts of energy. To sustain a lightsaber for one minute, you would need fusion fuel equal to ten times the mass of the Great Pyramid of Giza [1]. This pyramid weighs 5.75 million tonnes; thus, to power a lightsaber, you would need 57.5 million tonnes of fusion fuel.

·       Matter-antimatter annihilation: the process where a particle of matter and its corresponding antimatter particle collide, resulting in their mutual destruction and the release of significant energy. However, the required energy from this would go beyond our current technological capability [1].

The Weight Problem

If a lightsaber emitted such powerful beams, the recoil from its movement alone would be catastrophic, being as strong as up to 40 million times the thrust of a Saturn V rocket (Figure 1) [1]. Unless the saber is bolted down, it would be uncontrollable [1].

The Science of Fiction

While science shows that lightsabers remain firmly in the realm of fiction, exploring physics reveals just how extraordinary such a device would be. From energy demands and light interaction to radiation risks and uncontrollable nature, constructing a lightsaber would require a completely new understanding of light, matter, energy, and technology. However, perhaps as we develop scientifically, there may be a new hope for those who desire their very own lightsaber.

May the force be with you all.

 References

Reference paper: ‘“'On the Physical (Im)Possibility of Lightsabers'

1.        “Fillion-Gourdeau, F. and Gagnon, J.S., 2019. On the physical (im) possibility of lightsabers. European Journal of Physics, 40(5), p.055201.”