hi, I'mZayaan Syed

Physics

Inflation, without the equations

If you point a microwave telescope at any part of the sky, you see the same faint glow. It is light released about 380,000 years after the Big Bang, and its temperature is the same in every direction to about one part in a hundred thousand.

That is stranger than it sounds. Two patches of sky on opposite sides of us are so far apart that, in the simplest version of the Big Bang, light never had time to travel between them. Nothing could have evened them out. They should not match, and yet they do. This is called the horizon problem.

There is a second puzzle. Space on large scales is very close to flat, which in the standard picture requires the early universe to have been tuned to an almost impossible degree. This is the flatness problem.

In 1980 Alan Guth proposed an answer. Suppose that in a tiny fraction of the first second, roughly 10⁻³⁶ to 10⁻³² seconds after the start, the universe expanded far faster than it does now. In that instant every distance grew by a factor of at least 10²⁶. A region small enough to have settled to one temperature was stretched to become everything we can see. That explains the matching temperature. Stretching anything that much also makes it look flat, the way the Earth looks flat from where you stand.

What could drive that kind of expansion? The usual answer is a field, called the inflaton, filling space. While the field holds a lot of energy, gravity effectively pushes instead of pulls. The field slowly rolls down toward lower energy, the way a ball rolls down a gentle slope, and inflation lasts as long as the roll does. When it reaches the bottom, its energy turns into the hot soup of particles that the ordinary Big Bang story starts from.

The part I find most surprising is what happens to quantum fluctuations. Even during inflation, the field jitters slightly from place to place. Inflation stretches those jitters to astronomical size. Where the field was slightly denser, matter later collected a little more, and over hundreds of millions of years gravity pulled those regions into galaxies. So the universe is uniform on large scales because of the stretching, and uneven on small scales because of the jitters. The same idea explains both.

It also makes predictions. It predicts the pattern of the tiny temperature differences in the microwave glow, and satellite measurements match it closely. It predicts that the differences should be slightly stronger on large scales than on small ones, and they are.

Some things are still open. Nobody knows what the inflaton actually is. Inflation should also have produced gravitational waves, which would leave a faint twist in the polarisation of the microwave glow. Experiments are looking for it and have not found it yet. Until they do, inflation is the best explanation we have rather than a settled fact.

That is what draws me to it. An idea about a fraction of a second that no one will ever observe directly still makes predictions you can check against the sky.

Books

On Stoner, and lives that look small from outside

Stoner tells you on its first page that its main character will not be remembered. William Stoner teaches English at the University of Missouri for most of his life. His colleagues do not think much of him, and his students forget him. John Williams then spends the whole novel showing you that this life was worth writing about anyway.

Stoner grows up on a poor farm and is sent to university to study agriculture. In a required English class, his professor reads a Shakespeare sonnet and asks him what it means. He cannot answer. Something changes in him in that moment, and he quietly switches to literature without telling his parents. It is one of the best scenes I have read about finding the thing you want to do. Nothing dramatic happens. He just cannot go back.

After that, most of what happens to him is disappointing. His marriage to Edith is cold from the start. A feud with a colleague, Hollis Lomax, blocks his career for decades. He falls in love with Katherine Driscoll, a younger teacher, and gives her up so that the scandal will not end her career. His relationship with his daughter slips away from him. Written down like this, it sounds like a sad book. It is, but that is not how it feels to read.

The reason is the writing. Williams never asks you to pity Stoner, and Stoner never pities himself. The sentences are plain and steady, and the book moves at the pace of an ordinary life. You notice how much Stoner loves his work, how carefully he teaches, and how he keeps going without complaint. Near the end, ill and alone, he asks himself what he had expected from life. The book does not give an easy answer, and I think that is why it works.

What stays with me is the gap between how a life looks from outside and how it is lived from inside. From outside, Stoner is a minor professor with a failed marriage. From inside, he spent forty years doing something he loved, and he did it honestly. The novel does not say which view is the true one. It just shows you both.

It also made me think about why anyone studies anything. Stoner does not choose literature because it will make him successful. He chooses it because once he has seen it he cannot look away. I think most people who end up loving a subject start that way, before they have any reason to.

The book sold very little when it came out in 1965, and was rediscovered about forty years later. It is now read all over the world. I like that a novel about a forgotten man nearly ended up forgotten itself, and then didn't.

Music

Why a guitar string sounds the way it does

When you pluck a guitar string, it does not vibrate in one simple way. It vibrates in many ways at once, and what you hear is the mixture.

A string is fixed at both ends, at the nut and the bridge. The simplest way it can vibrate is as one long arc, moving up and down in the middle. That gives the note you hear, called the fundamental. But the string can also vibrate in two halves moving in opposite directions, with a still point in the middle. That produces a note at twice the frequency. It can vibrate in three parts, four parts, and so on. These are the harmonics, at two, three, four times the fundamental frequency, and a real pluck sets off many of them together.

The fundamental itself depends on three things: the length of the string, how tight it is, and how heavy it is. Shorter, tighter or lighter strings vibrate faster and sound higher. This is why pressing a fret raises the note. You shorten the part of the string that is free to vibrate. It is also why the low E string is the thickest.

The mixture of harmonics is what makes a sound recognisable. A guitar and a piano can play exactly the same note, with the same fundamental, and you still hear the difference immediately. Each has its own balance of harmonics. That balance is called timbre.

Where you pluck changes the balance. If you pluck exactly at the middle of the string, you cannot excite any harmonic that needs a still point there, so the second, fourth and sixth harmonics mostly disappear and the sound is round and soft. Plucking near the bridge excites many more high harmonics, and the sound becomes bright and sharp. You can hear this yourself by playing the same note over the soundhole and then right next to the bridge.

On an electric guitar there is one more step. The pickups are small magnets wrapped in wire, sitting under the strings. A vibrating steel string disturbs the magnetic field, and that produces a small electrical signal. Each pickup only "hears" the string at its own position. A pickup near the neck sits closer to the middle of the string and picks up more of the low harmonics, so it sounds warm. A pickup near the bridge picks up more of the high ones, so it sounds thin and cutting. Switching between them is one of the simplest ways to change your sound without touching the amplifier.

I find it satisfying that something I do every day without thinking has such a clean explanation. Choosing where to pick, or which pickup to use, is really choosing which harmonics you want. Knowing that has made me listen more carefully when I play.