Happy birthday, dear Sheldon

Penny: I cannot believe Christie let Howard into my apartment.
Sheldon: And I cannot believe people pay for horoscopes.
“The Dumpling Paradox” (Season 1, Episode 7)

Anyone else would simply have empathized with Penny; Sheldon prefers to mock her. And he does so by dredging up a topic that he’s already dismissed (on Day One of The Big Bang Theory) as “the mass cultural delusion that the Sun’s apparent position relative to arbitrarily defined constellations at the time of your birth somehow affects your personality.”1

Rather than get sucked into that time-worn argument, let’s just concede that the Sun, Moon, planets, and stars do in fact exert a certain influence on a person at the moment of his birth. That influence is a gravitational one, and compared to everything else that’s happening to that person at that moment (let alone to his mother) it’s fairly insignificant, but it’s there nevertheless.

An object’s gravitational pull is proportional to its mass and inversely proportional to the square of its distance away. Something twice as close or four times as massive pulls four times as strongly. That makes it possible to compare the pull from different objects using simple arithmetic.

For instance (and without getting too deeply into the anatomical nitty-gritty), perhaps we can agree that the material that makes up a typical mother weighs somewhere between 90 and 290 pounds, and that while she’s giving birth most of it is located within a few feet of her baby. We can do the math and find that a (let’s say) 90-pound woman an average distance of (let’s say) three feet from a baby exerts less than a billionth of the gravitational attraction on him that the Earth does. (In other words, whenever she’s leaning over him, he weighs a few billionths of a pound less.)

How does her gravitational pull compare to those exerted by the various heavenly bodies commonly found in horoscopes? All we need to do is to look up their masses and distances (let’s say at closest approach, for maximum effect) and perform the same calculation. The table below lists the usual suspects:

Horoscope-y Objects,
in Decreasing Order
of Gravitational Influence
on a Newborn Earthling

Earth exerts a pull that is 4 billion times the strength of Mom’s
Sun 2 million
Moon 13 thousand
Jupiter 120
Venus 73
Saturn 9
Mars 3
Mercury 1
Uranus 1/3
Neptune 1/8

The only things in this list that exert less of a gravitational pull on the neonate than his mommy does are Neptune, Uranus, and possibly Mercury. The strongest pulls come from the Earth, which keeps babe (and mother) from floating away; the Sun, which keeps the Earth from floating away; and the Moon, which can lift ocean water (creating the tides).

You might protest that a 90-pound mother three feet away from her baby is pretty lightweight and distant, and that her gravitational pull would be much stronger if she were larger and closer. But it turns out that even (say) a 290-pound mom at (say) half a foot from her baby pulls on him only as strongly as Jupiter does. The Earth, Sun, and Moon still far outpull her.

Could it be that what’s important, horoscope-wise, isn’t just the strength of each object’s gravitational pull but its direction? But then suppose the newborn happened to be (if we may say it this way) “pointing” in a somewhat different direction at the moment of birth? That would change his orientation with respect to everything around him. He might, for instance, wind up with Jupiter tugging on his ear instead of his elbow — and then there’s no telling which aspects of his personality and his fate would be altered as a result. Will he still grow up to inherit a large sum of money? Will he still be kind to children and small animals? Will 3 still be his lucky number?

In any case, what’s so funny about all this, and why is the Nerd laughing? Is it because he’s noticed that Penny mutters, “Typical Taurus,” at Sheldon in response to his rant about real-life astrology debunker Bertram Forer,2 yet on his birthday seven years later she murmurs, “I never would have pegged you for a Pisces”?3

No — undoubtedly her Taurus comment merely constitutes a mistaken guess at Sheldon’s birthdate. (Or at Forer’s — which would also be a mistake, since he was a Scorpio.)

So then why is the Nerd laughing?

It’s because for the past few minutes he’s been finding it increasingly difficult to resist making a series of “yo’ mama” jokes.


1. “Pilot” (Season 1, Episode 1)

2. “The Peanut Reaction” (Season 1, Episode 16)

3. “The Intimacy Acceleration” (Season 8, Episode 16)