Editor's Note: On Aug. 24, 2021, a planned visit to Vietnam by U.S. Vice President Kamala Harris was delayed after "a report of a recent possible anomalous health incident" in Hanoi, according to a news release from the State Department, apparently referring to a suspected case of "Havana Syndrome."
A mysterious international dispute that threatens the recently thawed diplomatic relationship between the United States and Cuba came to light in a 10 August 2017 story first reported by the Associated Press. The report focused on what has come to be known as the "Havana Syndrome," a series of seemingly related illnesses suffered by American and Canadian diplomats serving in Cuba. The original reporting included what later appeared to be speculation from unnamed United States government officials that some form of heretofore unknown sonic weapon was to blame:
In the fall of 2016, a series of U.S. diplomats began suffering unexplained losses of hearing, according to officials with knowledge of the investigation into the case. Several of the diplomats were recent arrivals at the embassy, which reopened in 2015 as part of President Barack Obama’s reestablishment of diplomatic relations with Cuba.
Some of the U.S. diplomats’ symptoms were so severe that they were forced to cancel their tours early and return to the United States, officials said. After months of investigation, U.S. officials concluded that the diplomats had been attacked with an advanced sonic weapon that operated outside the range of audible sound and had been deployed either inside or outside their residences.
The U.S. State Department later walked back claims that they specifically had concluded a sonic weapon was at play, saying through a spokesperson that "we do not know who or what is causing these incidents". Secretary of State Rex Tillerson has described the incidents as "health attacks", and Cuba denies any involvement. As reported by the Associated Press on 18 September 2017, the range of symptoms is nonspecific and vague:
Of the 21 medically confirmed U.S. victims, some have permanent hearing loss or concussions, while others suffered nausea, headaches and ear-ringing. Some are struggling with concentration or common word recall, the AP has reported. Some victims felt vibrations or heard loud sounds mysteriously audible in only parts of rooms, leading investigators to consider a potential "sonic attack." Others heard nothing but later developed symptoms.
In sum, the symptoms (none of which are universal to all cases) that have been used in the defense of the claim that a "sonic weapon" was used are as follows:
- Hearing loss
- Nausea, Vertigo, Headaches, Ear-ringing
- Concentration and memory problems
- Brain swelling or "damage to the central nervous system"
- "A more serious illness that involved a blood disorder"
Additional clues into the nature of the attack, including the occurrence of an audible noise in some cases, were provided first by a 20 August 2017 CNN report, reporting that some diplomats heard "a deafeningly loud [but unidentified] sound similar to the buzzing created by insects or metal scraping across a floor". CBS News reported:
Some felt vibrations, and heard sounds — loud ringing or a high-pitch chirping similar to crickets or cicadas. Others heard the grinding noise.
The reports of screeching noises in some cases and no noise in most cases initially fed both government and media speculation that a "silent" audible device was most likely used (there are ranges of noise close to audible sound that can be heard by some but not others). The two options, then, would be an infrasonic device (below the audible frequency humans hear) or an ultrasonic device (above that range).
The debate about which brand of inaudible noise would be used generally boils down to this: infrasonic waves capable of affecting humans covertly would need to be extremely close to the victim or unrealistically large, and they would not be able to produce a targeted attack, instead affecting a larger and thus more indiscriminate area. Ultrasonic waves could be targeted, focused, and beamed from further away, but are unlikely to cause a bulk of the symptoms ascribed to them and unless the device was physically touching the victim.
Before diving into this research, two variables related to sound are necessary to understand what follows. These include the frequency of the noise — defined by the number of waves per unit of time — and also its power, determined by the amount of energy each wave carries. The former is reported in Hz or kHz, with infrasound including noise below 20 Hz, and ultrasound encompassing noise above 20 kHz (20,000 Hz). (The latter is reported in decibels or dB.)
Below, we detail the main research regarding the primary symptoms discussed in the reporting of the Cuban "health attacks", finding a.) that the evidence is fairly weak for both ultrasound and infrasound as the cause for a majority of the symptoms listed and b.) that none of the symptoms can be described entirely by either only infrasound or only ultrasound.
- Poorly explained by infrasound
- Not explained by ultrasound
The source most commonly cited in news reports suggesting that infrasound can cause hearing loss is a 2001 review conducted by the NIH, which stated (with heavy qualification) that research, while sparse, shows "physical damage to the ear or some loss of hearing has been found in humans and/or animals at levels above 140 dB". The 140 dB measurement is no minor omission of detail, as 140 dB infrasonic waves projected covertly at any distance are essentially impossible. The actual studies reviewed in this NIH document generally suggest the opposite: low-frequency, high-power noise will not cause hearing loss, temporary or otherwise, if below the considerably high energy of 150 dB.
Ultrasonic sound is widely considered to be irrelevant to hearing loss. Another 2001 review by Jürgen Altmann, an acoustic weapons expert and physicist at Germany's Technische Universitaet Dortmund and who investigated the bulk of the literature up to that time, concluded that at ultrasound "the ear is essentially untouched" if levels are below 140 dB.
Fatigue, Headaches, Ringing Ears, Vertigo, and Nausea
- Not explained by infrasound
- Inconclusive evidence regarding ultrasound
Based on the reviews performed by both the NIH and by Altmann, there is no scientific consensus on fatigue, headaches, ringing ears, or vertigo as they apply to infrasonic noise. The only symptom in this category discussed as a possible result of infrasonic noise is nausea. Per the NIH:
There is no agreement about the biological activity of infrasound. Reported effects include [...] nausea, vomiting, and bowel spasm.
Altmann (and many others) argued that the gastrointestinal symptoms such as nausea, and bowel spasms in particular, while frequently reported in the press, have been overblown and cannot conclusively be tied to infrasonic sound:
The vertigo and nausea effects in the journalistic articles ascribed to intense infrasound cannot be confirmed. On the other hand, low [but still audible] frequencies of 50-100 Hz at 150 to 155 dB caused mild nausea.
Many of the above symptoms (headaches, ringing ears, nausea, and fatigue), however, were once referred to in the literature as "ultrasonic sickness". This suite of symptoms and their ties to ultrasonic noise was based on numerous reports from workers in proximity to a variety of ultrasonic devices or tools. Altmann has argued that this literature is hard to interpret as these environments contain significant audible sound, as well. A 2013 review of the effects of ultrasound on humans makes a similar argument:
Many studies confirmed the appearance of subjective symptoms of exposure to noise emitted by ultrasonic devices like dizziness, balance disturbances, tinnitus and fatigue. It is assumed that those symptoms result from the effect of noise on the vestibular system; however, further studies are necessary. [...]
According to the results of studies in the 1960s and 1970s, “audible” components of the noise spectrum are, above all, responsible for subjective symptoms among workers exposed to noise emitted by ultrasonic devices.
Concentration and memory problems
- Poorly explained by infrasound
- Poorly explained by ultrasound
There are few human studies addressing the neurological effects of infrasonic sound on cognition. Within those, a few single studies demonstrate a connection between infrasound and cognition on humans and animals. Overall, however, most research demonstrates no connection at all, and none have suggested permanent or persistent issues after exposure, as stated in the National Institutes of Health's 2001 review:
In several experiments to assess cognitive performance during exposure to infrasound [...] no reduction in performance was observed in the subjects. Sole exposure to infrasound at 10 to 15 Hz and 130 to 135 dB for 30 minutes also did not produce changes in autonomic nervous functions.
In terms of ultrasound, the 2013 review noted that many concentration issues could be associated with the symptoms of “ultrasonic sickness” without being directly caused by the noise itself:
It is worth mentioning that some subjective effects of exposure to ultrasonic noise such as fatigue, headache, discomfort or irritation may disturb human cognitive functions.
This body of research refers to the transient appearance of these symptoms when in direct contact with that sound, and makes no suggestion of prolonged memory problems like word recall. Outside of occupational studies that lack relevance to sonic weapon development and by their nature include audible sound as well, there is little evidence in humans to suggest that ultrasound can be the cause for permanent neurological damage.
Mild Traumatic Brain Injury
- Poorly explained by infrasound
- Not explained by ultrasound
Altmann, author of the 2001 review of acoustic weapons, told the Associated Press:
I know of no acoustic effect or device that could produce traumatic brain injury or concussion-like symptoms.
The only real mechanism for a damage to the internal organ system such as the brain would be through some sort of powerful internal vibration caused by the strong vibration of the sound waves themselves. Scientists agree that this would best be achieved by infrasound, but the evidence that such frequencies could actually make this happen is quite limited and derived almost entirely from studies on animals or anecdotal reports.
A 2009 review published in the journal Military Medicine notes that "remarkable properties have been attributed to infrasound, including the capacity to ‘debilitate people for hours and even days,’ with ‘pulsing in their internal organs and blurred vision, both of which can lead to …, in rare cases, death,'" but this review also highlights the reality that there are nearly no studies to back up such claims. In fact, studies performed as far back as 1978 and as recently as 2009 conclude that an infrasonic weapon used to harm major organ systems would be implausible — if not completely impossible.
In terms of ultrasound, it is essentially impossible for this kind of energy to penetrate into the human body without direct contact, as the waves dissipate rapidly through the air (and, it should be noted, pretty rapidly within the body as well). Responding to questions that ultrasonic waves could cause brain damage, Robin Cleveland, a professor of engineering science at the University of Oxford, told the Guardian he doesn’t buy it: “The sound would have to enter the brain tissue itself [...]. If there’s even a tiny bit of air between the sound and your body it doesn’t get through.”
- Not enough information
Without knowing more than that a victim experienced "a more serious illness that involved a blood disorder" it is hard to confidently assess plausibility of this this kind of disease except to say that the reasons ultrasonic noise do not explain brain damage would likely hold for any illness that requires sound to penetrate into the body. According to the NIH, the most consistently reported effect of infrasonic noise (though the mechanisms remains unclear) seem to be changes in blood pressure and respiratory rate, which could perhaps be linked to other diseases indirectly. There is no existing evidence that links noise of any kind to the development of a blood disorder.
In the End, Neither Infrasound or Ultrasound Work as an Explanation
Taking even the most tenuous scientific research at face value, an ultrasonic device could be responsible for the transient occurrence of fatigue, headaches, ringing ears, vertigo, and nausea and (even more dubious) concentration and memory issues. Taking a similarly loose approach for infrasound, this kind of noise could cause hearing loss, nausea, and (most dubiously) some form of organ discomfort or damage. Neither can explain all of the symptoms.
Further, there is no real way to create a covert version of either device. F. Joseph Pompei, a former MIT researcher and current chief executive officer of a company that develops devices that focus sound into narrow, targeted beams, told us that a focused or controllable beam of 20Hz (infrasonic) sound would require an array of subwoofers "the size of a stadium".
Conversely, he told us, for an ultrasonic device to penetrate into the body at all, the victim would either have to be submerged in water or have the device in physical contact (both conditions would allow those waves to pass into the body without reflecting off it). This, as well, seems unlikely to be a covert choice for an attack.
"It sounds very appealing and interesting, but I find it hard to believe that there actually is such a device," John Oghalai, Chair of the Caruso Department of Otolaryngology – Head and Neck Surgery at the University of Southern California, told The Verge.
Collectively, the scientific research — which in many cases notes that anecdotal and inaccurate reports in newspapers have long obfuscated the actual science behind the plausibility of such a device — demonstrates that no single brand of sound could create the range of symptoms described by the victims of the Cuban health attacks, and even if they could, a covert device would be hard if not impossible to design. As such we rank the specific claim that an inaudible sonic device adequately explains the health attacks in Cuba as false.
On 1 September 2018, the New York Times reported on a theory the government is said to be considering as a cause of the health attacks on American and other diplomats in Cuba: focused beams of microwave energy that can cause both brain damage and the perception of noises when such noises do not exist. This effect, the Times reported, has been known to science since 1961 as the Frey effect or the microwave auditory effect. In a 2017 paper, electrical engineering professor James Lin suggested this phenomenon could explain the events in Havana:
Some readers may find it preposterous or astonishing that auditory perception of (or hearing) microwave pulses is possible. So let me explain. Studies have shown that the auditory phenomenon occurs at a microwave radiation specific-energy-absorption rate threshold of 1.6 W/g for a single 10-μs-wide pulse of microwaves aimed at the subject or subject’s head, for example. Most significantly, high-power microwave pulses may be covertly delivered remotely, so that only the intended target would perceive the sound in his or her own head ...
Depending on the intensity of the impinging microwave pulses, the level of induced sound pressure could be considerably above the threshold of auditory perception at the cochlea— approaching or exceeding levels of discomfort (including the reported headaches, ringing in the ears, nausea, and problems with balance or vertigo) and even causing potential tissue injury.
Douglas H. Smith, the lead author on a March 2018 paper about the Cuban health attacks and the director of the Center for Brain Injury and Repair at the University of Pennsylvania, said that “microwaves were now considered a main suspect.” The Times also cited “a secretive group of elite scientists that helps the federal government assess new threats to national security” assuggesting that the microwave theory is among those being considered. The weaponization of this technology, the Times reported, has been of interest to both the United States and the former Soviet Union.
The Cuban government, via a CNN interview with a member of the Cuban task force investigating the attacks, has pushed back against this theory, suggesting it belongs in the realm of science fiction and that it is inconsistent with the reported circumstances described by the victims:
"If you look at the alleged events, there have been reports that there are several people in a room with thick walls and thick windows and only one person was targeted. This is a kind of weapon that doesn't exist," said Dr. Mitchell Valdes-Sosa, a well-known neurologist who is part of the Cuban special task force investigating the alleged attacks. "It's science fiction, not science," he said.
"First, it was sonic weapons, now microwave. What's next, kryptonite?" the investigator said in an interview with CNN at his research center in Havana, referring to an earlier theory that sonic weapons emitting high-powered ultrasound waves could have caused the injuries.
We note an apparent conflict between reports of actual audio recordings of the attack that were published by the Associated Press in October 2017 and the general conclusion that the microwave auditory effects register only in the brains of the victims and not in a way that is detectable by traditional recording equipment. CNN reported that the Cuban government is currently working on a rebuttal to the microwave theory.