So, what does science say about Santa Claus?

Reality begins in each person's mind – and with Santa Claus, the logic couldn't be any different. "No one has ever really seen Santa Claus, but I believe that if there are people who believe in Santa Claus, it's because Santa Claus is also a reality for those people," replies Pedro Almeida, professor in the Physics Department at the Faculty of Sciences of the University of Lisbon (CIÊNCIAS ULisboa) and a self-confessed admirer of Santa Claus.

Throughout history, there has been no shortage of theses, dissertations, or even mere suggestions of phenomena that science guarantees exist even when they are not perceptible. In the case of Santa Claus, the question is somewhat the opposite: even the most dedicated scientist may be reluctant to dismantle the magic that, every year, captivates hundreds of millions of people who believe in a seemingly visible character whose existence no one can prove. Faced with this scenario, we decided to invite four researchers from the Faculty of Sciences of the University of Lisbon to reveal how Santa Claus could be explained in the light of scientific thought. Cristina Catita, Marília Antunes, Pedro Almeida, and Rui Agostinho are the four researchers from Ciências ULisboa who accepted the challenge.

Does Santa Claus really exist or not?

Just look at reality to realize that the question lends itself to confusion: any child can say that Santa Claus exists, although (almost) all adults deny it. Conversely, every year you see Santa Clauses in shopping malls and festive events that nobody recognizes as corresponding to the "real" Santa Claus. Perhaps it's not the easiest topic to start Christmas Eve with, but the incongruity between the existence and non-existence of Santa Claus could even benefit from an explanation from the discipline that studies the curious behaviors of particles. It's true that, on a macro scale, objects can follow other logics, but it's still an alternative for those seeking inspiration.

“In quantum mechanics, there is the principle of superposition, which indicates that a particle can be in different states simultaneously. According to this principle, it would already be possible to believe that Santa Claus exists and does not exist simultaneously. It is true that it doesn't help answer whether Santa Claus exists or not, but it certainly helps explain the magic that surrounds this famous character!”, replies Pedro Almeida, professor in the Department of Physics.

Within Physics, it's still possible to find other disciplines that can potentially get our neurons working when studying Santa Claus's supposed ability to travel the entire globe in tiny fractions of time. "To reach so many houses around midnight, Santa Claus would have to travel at speeds close to the speed of light, enough to circle the planet almost 10 times in a second… but in that case, he would start changing color," explains Pedro Almeida.

The professor at CIÊNCIAS ULisboa recalls that, due to the high speed at which he allegedly has to travel, Santa Claus is distinguished by the color blue when he arrives at a location to deliver presents, but quickly reverts to red when he is stopped and preparing to leave for another location. "This change in color perception is due to the so-called Doppler effect, which alters the perception of the colors of an object at high speed compared to someone who is stationary," concludes the researcher from CIÊNCIAS ULisboa.

If Santa Claus exists, then why has he never been "caught" by telescopes?

The question directly relates to some of today's space observation instruments. And curiously enough, proximity may not be sufficient for a clear observation of the famous bearded man and his reindeer sleigh. "If you could make an observation with the Very Large Telescope (VLT) in Chile, and Santa Claus were passing overhead but below the limit of commercial flights (less than 10 kilometers altitude), we would only capture a very blurry image, because the VLT was designed to focus only on infinity. It's a matter of distance," explains Rui Agostinho, professor in the Department of Physics and former director of the Lisbon Astronomical Observatory (Observatório Astronómico de Lisboa - OAL).

The focus on infinity, which limits the observation of objects that may be less than 10 kilometers away, would not prevent the most popular of all sleighs from being captured at a greater distance – and there may be those who admit that Santa Claus, for reasons that science does not explain, can indeed survive outside the Earth's atmosphere and may even stroll on the Moon. But even in this case, there is no guarantee that the VLT can provide images with the necessary sharpness.

Rui Agostinho points out that the images produced by the VLT today have extraordinary resolutions, but their minimum units are squares with sides of 47 meters for objects on the lunar surface. The telescope allows combining several of these "squares" to, in a logic similar to the pixels of photographic cameras, produce images that reveal much larger objects. Now, this pixel, which corresponds to a width of 47 meters on the Moon, will only contain the total brightness of the objects that are there, without being able to distinguish one from another. "The VLT would only allow us to clearly observe Santa Claus and his sleigh on the surface of the Moon if they had dimensions much larger than these squares with sides of 47 meters," explains Rui Agostinho.

The sharpness of the images could be greatly improved if the observation were made using the Event Horizon Telescope, which combines several radio telescopes scattered across the planet to produce images of distant celestial objects with resolutions that, on the Moon, would be based on squares with sides of 3.5 meters. It wouldn't be unreasonable to believe that Santa's sleigh is more than 3.5 meters long, but the truth is that no one has ever claimed a single observation of the mythical gift-giver with the Event Horizon Telescope – possibly because neither Santa Claus nor reindeer emit radio frequencies.

Rui Agostinho also admits, with a considerable dose of irony, that astronomers may not have embarked on this type of mission "because they always have limited observation periods when they are at the telescope," leading them to pursue other, more scientific challenges. But the researcher also recalls that Santa Claus never made an appearance on missions that involved using probes continuously orbiting the Moon to make detailed mappings of the surface, with resolutions of 0.5 meters.

“This type of mapping allowed us to observe all the equipment left on the Moon by the Apollo missions, but there’s no news of Santa Claus,” says Rui Agostinho. “Of course, we can assume that Santa Claus, when he’s on the Moon, lives underground to protect himself from meteorites, radiation, or the lack of an atmosphere, but this is a hypothesis that has not yet been possible to disprove or confirm,” adds the astronomer.

How does Santa Claus find his way to all the chimneys?

With millions of presents and dreams in his saddlebag, the operational aspect ceases to be a detail. Without a map, Santa Claus probably won't be able to find a way to deliver presents. On the other hand, if he is equipped with the latest mapping and navigation technologies, he becomes a case study in the field of logistics: “Eventually, Santa Claus doesn't use magic, but he uses the best of geospatial engineering. If we consider the distribution of presents as a spatial optimization challenge, then we might be led to believe that Santa Claus – or at least one of his reindeer! – is using one of the most advanced navigation systems currently available,” explains Cristina Catita, professor in the Department of Earth and Energy Sciences and researcher at the Instituto Dom Luiz (IDL).

Determining the most efficient routes for delivering presents to millions of homes will always be a significant computational challenge, but at least it's known that, if he exists, Santa Claus can take advantage of precise coordinates that allow him to locate chimneys and doors of each house. Nowadays, it's already possible to obtain high-resolution satellite images, paving the way for cartography with centimeter-level resolution.

“In reality, Santa Claus doesn't even need to know where all the houses that will receive presents are located. He just has to use systems that allow for precise navigation on our planet!” concludes Cristina Catita.

What if Santa Claus has the flu? Will he infect the rest of the planet?

It's not yet clear what healthcare system Santa Claus uses, but it is known that the famous character will have to deal with different epidemiological risks as he interacts with the rest of the population.

“If he really exists and if he really has the flu, then there’s a chance that Santa Claus could leave the virus in the various houses he visits,” explains Marília Antunes, professor in the Department of Mathematical Sciences and coordinator of the Centre for Statistics and Applications (CEAUL). “On the other hand, there’s also a question that arises: if he’s not infected and goes to a place where someone is sick, Santa Claus himself then runs the risk of becoming infected,” adds the researcher.

Clinics, hospitals, and medical offices tend to focus on individualized clinical records, but in Statistics, the study tends to focus more on the collective. "It's difficult to make estimates for just one person because they depend heavily on individual behavior, but we can get an idea of ​​the overall risk of a neighborhood, a city, or a region from data that reveals how a particular contagion is evolving," emphasizes Marília Antunes.

It is also the behavioral patterns of the population that allow us to have a perspective on the effects produced by different public health measures. Marília Antunes uses a well-known example: those who are vaccinated benefit from a lower probability of infection, but this more encouraging scenario should not be confused with the absence of contagion risk for an entire group, which may even include several people who have not been vaccinated.

“The risk of contagion is different in vaccinated groups and in groups that do not get vaccinated because the exposures to viral loads are different. Therefore, groups with higher vaccination rates will, in principle, have less viral exposure and, probably, fewer cases of influenza,” emphasizes Marília Antunes.

Although statistics may have limitations in accurately predicting an individual's behavior, they are particularly useful in revealing to each citizen the geographical and temporal spread of an epidemic. “Using statistical techniques, it becomes possible to quantify the risk of contagion in a given location based on the number of detected infections and the data provided by health services,” explains Marília Antunes.

Worldwide, tools provided by governmental and scientific entities already exist that present contagion estimates for different regions based on notifications collected in real time. Marília Antunes highlights the importance of these estimates, but also reminds us that predictions should never lose sight of the quality and quantity of the information collected.

"It may happen that not all cases of infection are reported by patients or even known to hospital authorities, but statistics also has tools that already allow for predictions taking this type of bias into account," concludes the researcher in the field of statistics.

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