The World According to Physics
Jim Al-Khalili
Having read it
★★★★☆
A good read, with a few somewhat mind-bending (especially given I’m not a scientist!) realities, but all well-explained to engage enthusiasts like me about what physics has achieved, what it is exploring and discovering.
Its approach is also clear and makes for an accessible understanding of serious physics knowledge that intrigues and educates about the science and its associated fields.
A good passage
That our universe is expanding has been knowledge for almost a century. Astronomers observed the light from distant galaxies to be stretched towards the red end of the electromagnetic spectrum (or, redshifted), indicating that these galaxies are moving away from us. In fact, the further away galaxies are, the greater the redshift of their light and so the faster they must be moving. However, seeing galaxies receding in every direction does not mean that we occupy a privileged position in the centre of the universe. Rather, it means that all galaxies are moving away from each other, because the space between them is stretching. Note that this expansion does not apply within clusters of galaxies, like our Local Group: the Milky Way, Andromeda, and a handful of smaller galaxies, which are close enough to each other to be gravitationally bound and thus able to resist the expansion of space.
A second good passage
Think for a moment about why, if you slam your hand down on a solid table, it doesn’t pass straight through. You might regard this as trivial: surely it is because both your hand and the table are made of solid stuff. But don’t forget that down at the level of atoms, matter is mostly empty space – diffuse clouds of electrons surrounding a tiny nucleus – and so there should be plenty of room for the atoms that make up your hand to easily pass through the atoms of the table without any physical matter coming into contact. The reason they don’t is because of the electromagnetic force between the electrons in the atoms of your hand and the electrons in the atoms of the table, repelling each other and providing the resistance we experience as solidity. However, if your hand were made of dark matter, then it would pass straight through as though the table weren’t there – the gravitational force between them being too weak to have much effect.
A third good passage
Maybe an AI of our invention will emerge as the next Newton or Einstein, and we may have to accept that our puny human brains are just not smart enough to figure out the ultimate nature of reality on our own.9