Our view of reality is severely limited. The reason for this is simple: we evolved on an African plain three million years ago. And so we have the senses necessary to survive on an African plain: eyes that can see far enough to spot a predator approaching, ears sensitive enough to hear a rustling in the long grass…
Those senses have revealed only an infinitesimal fraction of the world and provided us with a certain ‘common sense’. But, at every level, we’re deceived by our ape-like intuition. Most of nature is deeply hidden from us and the world isn’t what it seems.
So many things that seem obviously true are not. And here are just a few…
1. Earth is flat
Apart from the lumps and bumps of mountains, Earth certainly seems flat. But there are several clues that not only is it curved, but in fact it’s a large ball. For one thing, receding ships drop below the horizon before dwindling to a dot.
Also, during an eclipse of the Moon, when Earth passes between the Moon and the Sun, the shadow of Earth on the Moon is clearly curved.
Even stronger evidence that Earth is round came from the first circumnavigation of the world in a ship sailed by the Portuguese navigator Ferdinand Magellan. Though he was killed in the Philippines, the voyage was completed by the Basque navigator Juan Sebastián del Cano in 1521.
But, of course, the easiest way to see that Earth is a sphere is from space. And there’s no doubt that what the Apollo 8 astronauts photographed rising above the grey desolation of the Moon half a century ago was a sphere.
Measuring the size of Earth is a bit more difficult. But on a sphere, the mutual distances between four cities are different from what they would be on a flat surface (in fact, the American physicist Steven Weinberg, in his 1972 book, Gravitation and Cosmology, used JRR Tolkien’s distances to deduce that Middle Earth isn’t flat!). By this means, it’s possible to determine Earth’s magnitude from airline mileage tables and confirm that it’s a sphere.
The first estimate of the size of Earth, however, was made around 240 BC by Eratosthenes, chief librarian at the Museum of Alexandria. He knew that at midday on Midsummer’s Day, a vertical pillar at Syrene (modern-day Aswan) cast no shadow because the Sun was directly overhead, whereas one in Alexandria cast a shadow because the Sun was 7° from the vertical.
Knowing the distance between Syene and Alexandria, and using geometry, Eratosthenes deduced that Earth must be round with a circumference of about 40,000km (24,855 miles), which is remarkably close to the modern value.
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2. The stars turn around Earth
It seems patently obvious that the stars are wheeling around a stationary Earth rather than the stars are still and it’s Earth that’s turning. For one thing, it’s the way it looks. And for another thing, it’s the simplest explanation.
It’s much more complicated to believe that it’s the Earth that’s turning because that requires explaining how the planet can possibly be in motion without any of us noticing.
That conundrum was only explained by 17th-century Italian physicist Galileo Galilei. He realised that if you threw a ball on the deck of a ship moving at a constant speed, it would loop through the
air just as it would if you were stationary and standing on dry land.
If it wasn’t obvious you were on a ship, you might think you were stationary. Similarly, we can easily be hoodwinked into thinking that we’re stationary even though Earth’s surface is moving – at 1,670km/h (1,038mph) at the equator.
Evidence that Earth is turning came from the trajectories of long-range artillery. They’re deflected to the right (with respect to the direction of travel) in the northern hemisphere and to the left in the southern hemisphere.
This is because the ground beneath the projectiles moves at different speeds at different latitudes. For instance, a projectile travelling north from the equator constantly moves into latitudes where the speed of the ground is slower. From the ground, it therefore appears deflected eastward.
But proving that Earth is rotating still required the invention of the Foucault Pendulum – one of which swings at London’s Science Museum. It’s a simple device named after French physicist Léon Foucault, who, in Paris in 1851, came up with the idea of suspending an iron ball on a steel wire from the dome of the Panthéon.
The extremely long pendulum, free to swing any way it likes, appears to change its direction. In fact, it maintains its direction while Earth turns beneath it. Ultimately, however, the proof that Earth is spinning came from seeing the planet turning against the inky backdrop of space from the vantage point of Earth’s orbit.
3. Creatures are designed for their habitats
This seems obviously true. After all, we all know that sharks are the perfect ocean predators, pine trees are the perfect trees for snowy conditions and so on. As biologist Richard Dawkins says in his 1986 book, The Blind Watchmaker: “Biology is the study of complicated things that give the appearance of having been designed for a purpose.”
But no design is at play. It’s simply that ‘mutations’ of DNA, the molecule that in a loose sense transmits blueprints of an organism between generations, producing an enormous variety of different creatures.
The majority turn out to be unsuited for their environments and die of hunger before reproductive age. Only a minority are suited – or ‘naturally selected’, in the jargon – and leave offspring to further the process of adaptation to their environment.
Think of a machine that makes random keys. The vast majority don’t fit a particular lock. But one or two do. Would you say they have been ‘designed’ for the lock? No. Nevertheless, the illusion of design in the natural world is very powerful and, even now, creationists refuse to believe it’s an illusion.
“It’s almost as if the human brain were specifically designed to misunderstand Darwinism and find it hard to believe,” says Dawkins.
4. Your time is the same as someone else’s time
This seems obviously true. After all, we can synchronise clocks and, some time later, confirm that they’ve ticked along at the same rate.
However, time flies at the same rate everywhere only because we live in nature’s ultra-slow lane and in weak gravity. Were we travelling at close to the speed of light or in strong gravity, we would see something radically different.
Mysteriously, the Universe is constructed in such a way that the speed of light plays the role of infinite speed, so the speed appears the same to everyone. If everyone is to measure the same speed for light, then something must happen to their rulers and clocks, as speed is the distance something travels in an interval of time.
The thing that happens, as Einstein discovered in 1905, is that rulers shrink in the direction of motion and clocks slow down. Someone passing you close to the speed of light flattens like a pancake while appearing to be moving through treacle.
In short, the speed of light is the rock on which the Universe is founded, and space and time are but shifting sand.
And it’s not just high-speed travel that affects the flow of time. Anyone who moves under gravity is in fact moving through the valleys and hills of ‘warped space-time’. Because we didn’t realise this (it took Einstein in 1915 to do that), we invented a ‘force’ called gravity.
The simplest imaginable clock consists of a laser travelling parallel to the ground and bouncing back and forth between two mirrors, producing a ‘tick’ whenever the light hits a mirror.
Nearer to Earth, where gravity is stronger, space-time is more warped so the light must take a more curved path between the mirrors. Traversing such a path takes longer, revealing that time slows down in strong gravity.
5. The Moon is not falling
The Moon is in fact falling, though it took the genius of Isaac Newton to realise it. He imagined a cannon that fired a cannonball horizontally across the ground. Gravity would gradually curb its trajectory downwards and after say, a kilometre (just over half a mile) it would strike the ground.
Then Newton imagined an even bigger cannon and a cannonball that would travel say, 10km (six miles) before it hit the ground.
Finally, he envisioned a super-cannon that could fire a cannonball at 18,000km/h (11,185mph). In this case, the curvature of the Earth is crucially important. As fast as the cannonball falls, the surface of Earth curves away from it.
So, it never hits the ground. It falls forever – in a circle. And this is what the Moon is doing.
A related fact is that if something is in free fall, it feels no gravity, just as you would feel no gravity if you were in a lift and the cable snapped (until the safety mechanism cut in, of course).
And this is the case of astronauts on the International Space Station, where gravity is about 89 per cent of that on the ground. They experience ‘zero-g’ not because they’re beyond gravity, but because, like the Moon, they’re falling in the circle.
6. The stars are pinpricks in the celestial sphere
They certainly look that way. They don’t look like suns – unless they’re an astonishingly long way away. But, in fact, they are – although it was extremely hard to prove.
The key was to observe a nearby star from one side of Earth’s orbit and then, six months later, from the other side. Just as your finger observed from one eye and then the other shifts position, so too should a star.
It’s such a small effect, even for the nearest stars, that this shift, or ‘parallax’, was only first observed in 1838. German astronomer Friedrich Bessel found that the star 61 Cygni was 10 light-years away – more than 600,000 times farther away than the Sun.
The definitive proof that the stars are other suns actually came from studying their light. In 1835, French philosopher Auguste Comte declared: “Never, by any means, shall we be able to study the chemical composition or mineralogical structure of the stars.”
He was totally wrong. Nature has been kind to us. Each element emits light at characteristic colours, or wavelengths, which amounts to a fingerprint. In
the spectrum of the Sun – its light fanned out into the colours of the rainbow – such fingerprints manifest themselves as dark bands, much like supermarket barcodes. Lo and behold, the spectra of stars contain such dark bands.
7. We can know what the Universe is 'now'
You would think this is obviously true. But ‘now’ is a meaningless concept in the Universe.
The problem is that, while light is fast, the Universe is huge. As Douglas Adams wrote in The Hitchhiker’s Guide to the Galaxy: “Space is big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space.”
Consequently, light crawls like a snail across this cosmic vastness and, as it’s by means of light that we gain knowledge of the cosmos, we see everything as it was at an earlier time.
To understand what this means, imagine the speed of light was not 300,000km (186,400 miles) per second, but only 100m (328ft) per century. Depending on where you are in the world, 100m away you might see a street scene of 1924; just over a kilometre away you would see the Battle of Hastings mid-battle; 4.5km (2.8 miles) distant and near the horizon, you’ll see the pyramid of Khufu still being built.
In reality, when we look out into the Universe, we see the Moon as it was 1.25 seconds ago; the nearest big galaxy, Andromeda, as it was 2.5 million years ago; and the most distant galaxies as they were 13 billion years ago.
While we can’t know what the Universe is like now, telescopes show us its entire history, all the way back to the Big Bang.
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