Air weighs 10,000 kg per m2 and other orbit myths debunked

Air weighs 10,000 kg per m2 and other orbit myths debunked

What if gravity didn't exist, and it were the magnetic fields of the Sun and the planets that kept everything spinning in place? The thesis circulates with enviable confidence: Newton's apple doesn't fall because of gravity, it falls pushed down by the 10,000 kilograms of air pressing on every square metre at sea level. The Sun would attract the planets the way a magnet attracts iron, and the seasons wouldn't come from the tilt of the axis but from whether Earth's magnetic pole matches the Sun's in sign. It's a pretty theory. And it's almost entirely false.

How much does the air above us actually weigh?

The starting calculation is correct: one cubic metre of air at 15 degrees and sea level weighs approximately 1.225 kilograms. If you stack the entire atmosphere at that constant density, you get a column about 8,163 metres high and, multiplying, roughly 10,000 kilograms per square metre. That equals one kilogram per square centimetre, which is exactly the everyday atmospheric pressure: one atmosphere, about 1,013 hectopascals.

The error isn't in the arithmetic, it's in the interpretation. Air weighs precisely because gravity pulls it downward. Without gravity, the atmosphere would escape into space. And that's exactly what happens on the Moon: it has plenty of mass, but too little gravity to hold onto a gaseous envelope. The Moon's lack of atmosphere doesn't prove that gravity doesn't exist; it proves the opposite.

Why does Mercury dismantle the magnetic hypothesis?

The most powerful argument against the theory isn't philosophical, it's orbital. The precession of Mercury's perihelion —that slow dance of the point closest to the Sun— only matches Einstein's general relativity, not any magnetic interaction. If planets were held up by field attraction, the numbers would be different.

Then there's the magnitude. The Sun's magnetic field, at Earth's distance, is measured in nanoteslas: thousands of times weaker than a fridge magnet. Venus has barely any magnetic field of its own and orbits quite happily. Earth's magnetosphere, moreover, acts like a cage: it encloses the planet's field and limits its outward interaction. The probability that this magnetic dialogue holds up an orbit is, quite simply, zero.

Do the seasons depend on distance from the Sun?

No. Earth passes through perihelion —the point closest to the Sun— in early January, in the middle of the northern hemisphere's winter, and through aphelion in early July, in the middle of summer. If the seasons came from proximity, both hemispheres would have summer at the same time. The real cause is the tilt of the axis, about 23.4 degrees: in June the north receives more direct sunlight and more hours of daylight, while the south is cold on the very same day.

The other leg of the theory, the Sun flipping its poles, also has a known explanation. The Sun's magnetic field changes polarity every eleven years, at each cycle maximum. It has peine dozens of times since records began. And its effect on the radiation reaching us is minimal: between the maximum and minimum of the cycle the difference is around 0.1%. Since the 1980s the Sun hasn't shone any brighter, if anything a little less, while the planet's temperature kept rising.

Magnetism doesn't explain the orbit, but the debate goes on

The conversation drifted into more creative territory: if we packed many solar systems into one point a black hole would form, the Sun changed polarity because millions of people started feeling colder, Einstein's formula is incomplete and missing a variable yet to be discovered. The ether also made an appearance, that old classic. And one ironic defence: the force that moves the planets is the force of love.

None of that has experimental backing. Newtonian physics and relativity keep describing the orbits with a precision no magnetic theory has matched. But the discussion leaves a useful datum: many people don't know why an apple falls or why it's hot in August. And that, more than a physics problem, is a science communication problem.