How Scientifically Accurate Is Batman’s SONAR Machine In ‘The Dark Knight’?

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The machine is not scientifically accurate, as it would be impossible to build and the results would be inaccurate.

The Dark Knight isn’t just the best movie in Christopher Nolan’s trilogy, but the best Batman story ever told. Nolan’s characters, both written and portrayed, represent the most scintillating and well-polished pearls, whether it is Alfred’s dry wit and insightful anecdotes, the Joker’s obtrusive ecstasy and the unflinching needle of Batman’s moral compass. Nolan’s slow-boiling plot then strings these pearls together to make an exquisite necklace of the highest quality.

The dark knight bruce wayne and batman suit Christian Bale
The Dark Knight isn’t just the best movie in Christopher Nolan’s trilogy, but the best Batman story ever told. (Photo Credit: The Dark Knight (film) / Warner Bros. Pictures)

Nolan’s protagonists always find themselves in the congenial company of resourceful men who carry a delightful candor, whether it is Tesla in The Prestige, Arthur in Inception or Fox in the Batman trilogy. Fox regularly gifts military toys, that are otherwise rotting in his basement, to Batman, who uses them, more than often recklessly, to fight crime.

However, while the suitcase in Inception was obviously fictional (or we’ll find out), Batman’s utility belt and other tools were depicted to be quite realistic. However, did Nolan, who is appreciated for his meticulousness, compromise scientific accuracy to avoid any hindrance to his high-paced plot?

What Does The Machine Do?

Batman’s machine that operated on Fox’s concept of SONAR. (Photo Credit: The Dark Knight (film) / Warner Bros. Pictures)

Well… yes. Consider the triangulation machine Bruce Wayne developed to find out where the Joker was hiding by turning “every cell phone in Gotham into a microphone”. To understand what the machine does, let’s rewind to Fox’s meeting in Hong Kong, where he deliberately leaves behind a modified cell phone in a drawer in the building’s reception.

The device, which is another R&D project, sends out “a high-frequency pulse and records the response time for mapping an environment.” Wayne immediately realizes that it relies on SONAR, suggesting “it works like a –”… “A submarine, Mr. Wayne, like a submarine” interrupts Fox.

Is this technology realistic or is it just CSI-esque hogwash masquerading under technical jargon? Let’s first try to understand how the machine might work.

A representation of how SONAR works.

SONAR is a technology that uses ultra high-frequency sound waves to calculate the location of an object. A submarine sends these pulses in an object’s direction and determines its location by calculating the time taken by the pulse to be reflected and received by its receivers. Bats and dolphins also voice similar pulses and use echolocation to draw a map of their environment. Bats… of course!

So, basically, Bruce Wayne implemented echolocation by converting every cell phone into a high-frequency generator and developed a detailed map of the city. This is clear when Fox looks at the violent blue ripples on the grid of screens and wanly says “you took my SONAR concept and applied it to every phone in the city. Half the city feeding you SONAR, you can image all of Gotham.” Batman can now find the Joker using this map when he speaks anywhere “within the range of a cell phone”.

However, Fox despairingly calls it “unethical” and “dangerous” for the abuse of liberty and consent it entails. The Joker’s guile has forced even one of the most scrupulous of men to break the rules. Yet, of course, the good guys in Hollywood are forgiven, since their violations are always well intended, always for the sake of the greater good (sigh).

Also Read: What Is SONAR?

Why Can’t It Be Built?

Hardware Constraints

The only way Batman could accomplish this is by tweaking every individual citizen’s phone. However, even if Batman were to maliciously install a piece of software on every phone by some brilliant technological feat, implementing SONAR seems to be impossible.

The Joker’s location was disclosed when he spoke within the range of a cell phone. (Photo Credit: The Dark Knight (film) / Warner Bros. Pictures)

SONAR requires a transmitter that emanates high-frequency sound pulses in the MHz range. A cell phone’s speaker, its only component that can draw such a squeal, draws it at frequencies even less than 20Khz, frequencies that we perceive as sound. To implement echolocation, Batman would have to visit every house in Gotham and install a new piece of hardware on every single resident’s phone, which I’m guessing would be extremely tedious. The expense, however, we are sure, would not be an issue.

Even if Batman did run, glide and ride to every house and install a hardware patch on every citizens’ phone, his maps are bound to be erroneous. The energy of a sound wave dwindles with the square of the distance it travels, which means that the voice of a citizen speaking into his phone will clearly obscure the voice of the Joker traveling from a few meters away. Add to that the distortion of Batman’s results, exacerbated by background noise and obstructions attenuating the signals.

Quality Constraints

Furthermore, generating a 3D map of such clarity and high resolution in real-time, as depicted in the movie, is a ridiculous exaggeration. Batman’s system’s software and hardware would have to be incredibly powerful to achieve this, which, assuming the time frame of 2008 (when the movie was released), seems highly unlikely.

Batman using his high-resolution map to trackthe bad guys. (Photo Credit : The Dark Knight (film) / Warner Bros. Pictures)

Researchers at the Swiss Institute of Technology in Lausanne actually did successfully develop a similar mapping system that operates on SONAR. A speaker blasts high-frequency pulses and the receivers build a 3D map of a hall by detecting the pulses reflected off its walls. However, despite using a highly advanced algorithm and microphones boasting utmost acuity, the system still produces maps that are crude and inaccurate.

Also, the parameters’ resolution and attenuation share an inverse relationship. To achieve a higher resolution, Batman would have to use ultrahigh frequency pulses, however, ultrahigh frequency pulses are more likely to be attenuated by objects. On the other hand, low-frequency pulses will flow around objects, but cause the people in the map to appear like deformed blobs floating in space.

Also Read: 5 High-Tech Gadgets That Can Make You Batman!

An Alternative

What seems more feasible is RADAR, a technology that relies on electromagnetic radiation, rather than sound waves. RADAR uses microwaves and radio waves, electromagnetic radiation incessantly emitted by our smartphones, to call other phones and navigate. A software hack could allow Batman to use every phone as an obedient radio transmitter to develop his much-coveted map.

A RADAR dial.

That being said, achieving the resolution and accuracy depicted in the film is out of bounds for RADAR as well. Even a primitive map would require a large phone density, where each phone would have to be distributed uniformly in, which in the chaos caused by the Joker’s killing spree, could not have been achieved.

Further research could potentially substantiate Fox’s “nightmare”, but it does have lucrative applications in virtual reality and audio forensics as well. As for immoral surveillance, Fox echoed every citizen’s thoughts by admitting that it is “too much power for one person.” This was, of course, back when social media did not exist.

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References (click to expand)
  1. Sonar operates at much lower frequencies than Radar -
  2. Dark Knight: Sonar Phones?.
  3. This Technology From The Dark Knight Could Become Reality. Slate
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About the Author

Akash Peshin is an Electronic Engineer from the University of Mumbai, India and a science writer at ScienceABC. Enamored with science ever since discovering a picture book about Saturn at the age of 7, he believes that what fundamentally fuels this passion is his curiosity and appetite for wonder.