Quotes from Brian Clegg

Newton's law of gravitation. That's all you need (with a spot of calculus to crunch the numbers) to work out how the Earth will orbit the Sun or how an apple will fall if you let it go at a certain height. The only trouble is that Newton had no idea how this gravity thing worked. His model was simply: 'There is an attraction between bits of stuff, and let's not bother about why.

The year 1992 should have been remembered as the 700th anniversary of the death of a man who changed the world. Yet the occasion passed without note. Few know of the remarkable achievements of someone who, more than any other, can be said to have invented science.

Think of a Mexican wave travelling around a stadium (a Mexican wave is a transverse wave as the cycle of the motion is up and down, while the wave travels at right angles to that direction, round the stadium). The medium here is the mass of spectators who bob up and down. But they stay in their seat positions

Transverse waves usually have to travel along the edge of the medium – for example, on the top of the water that the wave passes through. For a longitudinal wave, the regular cycle is in the same direction as the wave moves forward, not at right angles. The medium is repeatedly squashed up and relaxed like a concertina, so what travels through it is a pattern of compression and rarefaction.

When you speak to someone, your vocal cords start a compression wave in the air that spreads out from your mouth until those compressions and rarefactions reach the listener's ear. There, they vibrate the hair-like structures in the ear, producing the sensation of hearing. But the link between you and the listener is the longitudinal waves that pass through the air.

The remarkable Scottish physicist James Clerk Maxwell worked out in the early 1860s that light was an interaction between electricity and magnetism. And this meant that in principle, you could have an electric wave creating a magnetic wave, creating an electric wave and so on, hauling itself through empty space by its own bootstraps without any material medium required – it is the electromagnetic field that acts as the material.

Immensely simplified, quantum physics has two rules: Very small things don't have locations, we just have probabilities of where they are. The first rule only works if these very small things don't interact with their environment.

is uncertain' or that 'anything goes'. In fact, it is a clear mathematical statement. It reflects the way that different aspects of the physical world are intimately connected at the quantum level. Its best-known formulation is that the more accurately you know the position of a quantum particle, the less accurately you know its momentum.†† It is impossible to know both perfectly at the same time.

If you had a piece of neutron star about the size of a grape, it would weigh 100 million tonnes.

La teoría de cuerdas tiene un inconfundible regusto a la Grecia antigua, pues en lugar de ser deducida de las observaciones del universo que nos rodea, es una posibilidad surgida de la pura matemática y luego ajustada al mundo

silica (also known as sand).

Imagine we're in a spaceship moving steadily through space and we throw a ball across the ship from side to side. It will move in a straight line, because both the ball and the ship are moving forwards at the same speed. But if the ship accelerates, the ball's path will become curved, as the ship moves ahead more quickly. The straight line path has become curved from the viewpoint of the ship. Similarly, Einstein reasoned, a straight line path in space would be curved by gravity.

So, for instance, even though the Earth is travelling in a straight line through space, space itself is curved, so the planet orbits the bowling ball of the Sun. It is a simple, but astonishing observation. Planets move in straight lines. There really is no force pulling them into an orbit. It's just that the space their straight line path runs through gets twisted.