Many people firmly believe that astrology is capable of predicting our destiny. And other people believe that astrology is a big hoax without any scientific basis. Today I am going to prove that both beliefs are wrong. So, can astrology work?

Every astronomer on the face of the Earth from time to time has to face the question: “Hey, what do you do again, astrology or astronomy?” So, to save you some time from now on, today at AltruPhysics I am going to try to resolve the confusion.

It turns out that for hundreds of years there was actually no difference between astrology and astronomy. In fact, important figures like Ptolemy, Galileo, Kepler or Brahe, some of whom we consider the fathers of astronomy today, believed in astrology. After all, they had no better scientific alternatives. But around the 17th century, the two began to diverge, and today they mean very different things.

To start with, astronomy with an “n” is the science that studies the composition and laws of the Universe, which includes areas such as cosmology, astrobiology, or astrophysics. So like, the things that I usually talk about on this channel… except today!

In the remainder of the episode I am going to talk about astrology with an “l”, which, summarising greatly, is a set of traditions and beliefs that seek to predict what happens to human beings on Earth by studying the positions of the stars. So how did these beliefs come to be?

How did astrology begin?

More than 2,500 years ago, in ancient Babylon, the first astrologers were observers who found patterns in the sky. They saw that those bright dots did not change randomly, but were repeated every night, and they gradually moved across the sky, night after night, until returning to the same place after a certain amount of time, which used to coincide with about 12 moons.

In other words, they discovered that the movements of stars that they saw in the sky were repeated year after year.

They also realized that what was happening on Earth changed with the same periodicity as the objects in the sky: There were hotter periods, and colder ones, seasons with more rain and others with less. And for each of those eras on Earth, the sky displayed a characteristic set of stars.

In other words, they discovered a correlation between the position of the stars in the sky, and the phenomena that happened on Earth.

And so they created models to be able to predict these phenomena on Earth based on the position of the stars. To do this, they drew easily recognizable figures in the sky which joined those bright dots: A lion, a crab, a scorpion, some fish, a bull… And, depending on which figure the sky showed at a certain time, the people of Babylon would be able to predict, for example, when the next harvest season, or date or pomegranate picking would be.

So far, astrology was not only very useful, but it fits in perfectly with modern science. You see, where the astrologers of that time went wrong was in assuming causality: Upon seeing this correlation between patterns in the sky and phenomena on Earth, they concluded that the stars caused these phenomena. In other words, they believed that the stars, whatever they were, had an influence on the world and on us.

So, by studying the sky, astrologers believed they could not only predict the arrival of the seasons of the year, but also conquests, defeats, plagues, and all our other sorrows and joys on Earth. And this is where astrology begins to diverge from modern science. But first let’s ask – to what extent is this scientifically possible?

Does astrology work?

In dating apps, one of the most important details in a person’s profile is their zodiac sign. But does it have any relevance? Should you worry if the other person is a Sagittarius or an Aquarius? Would we be able to predict, based on the position of the stars on the day you were born, if your date will go well tonight?

Fake dating app

For starters, the sky has changed since the zodiac signs were invented some 2,500 years ago. Partly because the stars are constantly moving, so they’ve been moving across the sky in random directions ever since. Although seen from Earth, their positions haven’t changed much to be fair, less than one degree on average.

But what is much more important is that the axis of rotation of the Earth has changed its orientation. So much so that your zodiac sign is no longer what you would have been assigned 2,500 years ago, but should be the one from the previous month.

In other words, if you were an Aquarius in ancient Babylon, it’s because the Sun passed through the constellation Aquarius the day you were born. But today, if you believe yourself to be an Aquarius, when you were born the Sun actually passed through the constellation of Capricorn. And if you were born in late November, like me, your sign isn’t really a Sagittarius, but a Scorpio, or even Ophiuchus, which you’ve probably never heard of since it’s not even a traditional zodiac sign.

But other than that, constellations are totally arbitrary groupings of stars. They’re like perceptual art installations: Seen from a certain angle (ie from Earth), the stars seem to draw a pattern, but seen from any other angle, those stars aren’t even close to each other.

Leaving all that aside, for astrology to work and for us to be able to predict human behavior through the observation of the stars, at least two premises must be met:

  1. The stars exert some kind of observable influence on human beings.
  2. We have the ability to predict human behavior.

Let’s look at the first premise.

How do the stars influence our lives?

The star that has the greatest influence on our lives is, of course, the Sun, whose gravitational attraction keeps the Earth in its annual orbit. Secondly, the Moon also has an important gravitational influence and is the main cause of the tides.

In addition to gravity, life on Earth is also greatly affected by the radiation that reaches us directly from the Sun, and to a much lesser extent that which reaches us reflected from the Moon.

And this is the end of the list of relevant interactions between the stars and human life. The gravitational attraction, as well as the radiation that reaches us from the other planets and stars, are both much weaker.

But let’s dive in a little deeper. What would happen if the influence of other stars was comparable to that of the Moon and the Sun? Let’s hack the Milky Way.

Imagine we replaced Proxima Centauri, the closest star to Earth after the Sun, with TON 618, the largest supermassive black hole observed so far in the entire Universe (about 60 billion times more massive than the Sun).

Doing the math, the gravitational attraction that the Earth would feel towards that enormous beast would be similar to the attraction that the Earth feels towards the Sun. So we would have succeeded: we would have objects beyond the Solar System exerting an enormous influence on us. But would this help astrologers predict the outcome of your date tonight?

Rather the other way around.

The orbit of the Earth, the Moon and the Sun would be affected by the new attractor, which would affect the length of the day, the temperature, the atmosphere… and in fact the Earth would begin a chaotic trajectory through space (and all life would end in a terrible way, but that’s another story).

In other words, if the stars had a greater influence on the Earth, astrological predictions would not be easier, quite the contrary: Predicting the movement of the Earth, as well as our adventures on it, would be even more difficult.

And this brings us to the second premise of astrology, which is the most important.

Can we predict human behavior?

The main problem of astrology actually has nothing to do with the stars, but with ourselves: Predicting human behavior is just extremely complicated.

Let’s go back to tonight’s date. Suppose that you have already calculated the influence of the position of the stars on Earth, on your potential partner and on you. The stars are aligned for the date to be a success. And indeed, everything is going well… until a speck of dust makes your partner sneeze at the most inappropriate moment. Or a grain of rice during dinner makes you choke and wine comes out of your nose. Or just when you’re leaning in for your first kiss, a bird poops on your head and to hell with romance.

Suddenly, you realize that your zodiac sign is completely useless: Unless you can predict every speck of dust, every grain of rice, or the bowel movement of every bird in the city, you’re simply not going to be able to predict how tonight’s date will end.

In other words, the position of the stars, regardless of how much they influence us, will never provide enough information to make rigorous predictions about our earthly experiences.

So neither of the two premises of astrology seem to work. Then what do we do?

Time to turn the page

“Do you know what they call alternative medicine that’s been proven to work? Medicine.” So said Australian comedian Tim Minchin. Indeed, if you have a disease, you can turn to both alternative and modern medicine. And both options may work, but modern medicine, while not perfect, is much more likely to cure you.

Something similar occurs with astrology. As a source of entertainment, or to satisfy certain esoteric curiosities, it can be a good option. But if you need advice on important decisions in your life, remember that astrology simply does not work for these types of predictions. The position of the stars bears absolutely no relevance to your life. Astrological forecasts are simply no better than the ones you can get by tossing a coin, or rolling a dice, or asking your cat.

In conclusion, astrology was a very useful tool once upon a time. But its time passed several centuries ago. Today, astrology is ancient science, or protoscience, a “beta version.” So it really is time to install the update. It’s called astronomy, with an “n” for new.

Thank you for accompanying me here, and I hope to see you in the next episode of AltruPhysics…

…unless you’re a Pisces ascendant Gemini.