How fast does time go, exactly? The answer can depend on who you are.

The screen flickers high and low, in bits and pieces. Some regions go dim for a while, only to brighten up again. The picture on display changes as well, a few bits at a time. Spaces here and there will fade away. They’ll be replaced by new, slightly different, images.

In spite of what it may sound like, this is not, in fact, a bad quality TV. In fact, it’s one of the latest high-definition screens. It has a 60Hz refresh rate. But even the best of screens display horrible visuals when seen through the eyes of a housefly.

Screens are designed for humans, who think much slower than flies. To them, the colours on the screen would look like a realistic, moving picture.

You can make out how slow humans are when they try to attack a fly. Their rolled-up newspaper glides slowly towards it, sending out a gust of compressed air before it. The fly feels the air on its sensitive hairs. It makes use of its eye to watch how the newspaper is approaching.

And by the time the newspaper hits, the fly is already far away.

How fast does time go by? The obvious answer is one second per second. Or one second per 9,192,631,770 vibrations of a cæsium atom, if you will.

But how fast does time seem to go by? Well, that can depend on what you’re doing and who you are. And, even more importantly, on what you are.

Whatever your species, your body is always doing things. It has to collect food from outside to give you energy and make you grow. It has to fix your injuries, and generally keep your system running. All these chemical reactions are collectively known as ‘metabolism’.

The faster your metabolism, the faster you will be. And you’ll likely evolve to perceive things faster too. Flies have a higher metabolic rate than humans. They can do everything faster, including calculating where the fly-swatter’s going to land.

But if flies are fast, then bacteria are even faster.

The Plasmodium flies through the blood and finds itself inside a new reservoir. Rich in food and nutrients, this is the perfect place to start breeding.

The blood makes its slow, plodding way up the artery, revealing new forks and veins and pathways on the side. The bacterium rides on, taking in all the sights, as it waits to find a suitable tissue. There, it will sink itself in and start to breed.

A long time later, this blood, too, will become unliveable. It’ll be filled with Coartem or Malarone or Mefloquine, and there’ll be hardly any place to hide. Maybe the whole system will collapse entirely, the blood flow stopping and drying out. Or maybe it’ll keep going right on, but becoming a more and more difficult place to live in.

Whatever happens, at that point, the options will be to either move out or die.

But the Plasmodium doesn’t worry about all those issues. They’re far in the future. Now, the blood is fresh, and whatever disasters may be waiting to happen, will be sorted out and dealt with by future generations.

To a bacterium, humans would seem really very slow. They’d be like trees: look at them, leave them, come back much later, and they might have moved a bit.

The speed of bacteria’s lives makes them useful for scientists, who can quickly grow many generations in a lab and see how the evolve. Of course, they do it to larger creatures too, including mice and fruit-flies.

These larger creatures have life-spans in terms of days or months. They probably see time a bit faster than us, but in the larger scale of things, the difference is tiny.

Not as much as, say, a tree.

The water flows through the drainpipe in leaps and bursts. It floods and drains, floods and drains, in a repeating cycle, but so quickly that it is, for all practical purposes, a continuous stream.

This is not some high-volume often-used multi-storey apartment drainage. It comes from a small household. But even a minimally-used drainpipe can seem like a continuous stream when heard through the roots of a guava tree.

As it makes its way to the water-source, humans are zipping about with their various activities. They dart in and out of the house multiple times a day, sometimes alighting briefly on a branch for just enough time to pluck off some fruit.

The tree reaches out to the pipe. It wraps its root round, feeling for an opening. It makes its way in through a hairline crack, expanding inside to block the flow, so that it can drink its fill.

Suddenly, it happens. Two humans tunnel in through the ground, and before the tree knows it, its root is gone, the ground sealed up, and the broken pipe replaced with a new one.

Oh, well. That didn’t take long. Time to reach out again.

Trees are the slowest-living creatures on the planet. Or are they?

Some years ago, scientists were studying a new kind of microbe. It lived deep down, thousands of metres under the ocean floor, where no man had ever looked before and no sunlight had ever reached.

These creatures lived on the tiny amount of nutrient that came with the soil. Instead of getting energy from plants or sunlight, they used ‘chemosynthesis’ — chemical reactions with sediments and rocks.

With such interesting creatures, it’s no surprise that scientists took them up to grow in the lab. What is surprising is what happened next: nothing.

The microbes didn’t grow.

Scientists tried every trick they had. They put in the optimum nutrients. They looked into the DNA to figure out the exact diet for the creatures. Nothing worked. And then, it hit them: there was nothing wrong with the methods they were using.

They just weren’t patient enough.

The microbe stays feeding under the bed of the ocean. Food is running low, so there haven’t been any divisions for a while. But patience always pays.

A meteorite strikes the Earth, triggering a chain of volcanic eruptions around the planet. Fresh soil gets drawn in by the raging sea, and sinks down over time to the feeding site.

The microbe tucks in. It is now full up, and is ready to start dividing. The Indian subcontinent breaks away from the Pangean landmass, and the shifting replenishes the food supply.

The supercontinent landmass breaks up. Most of it, along with the microbe, moves north. The Americas swing open like a jaw, freezing over for a few brief Ice Ages before thawing again.

Look carefully, now. You’ll see that the first step in the slow process of cell division has just about begun.

Why do we live at the speed we do? Why do we think in terms of nine-billion cæsium atom vibrations, rather than nine-thousand or nine-quadrillion?

All the life that we’re familiar with — which is to say, the ones that live near the surface — come into contact with a periodic clock: the Sun. They need to pay attention; they depend on sunlight for their food and warmth. So they’ve had to adapt to day and night, and to the changing seasons of the year.

But those deep subsurface microbes have never seen the Sun. There is no action, or cycles, or turbulence down there, except for he slow march of the continents. So why stick to a random, entirely arbitrary timescale? Instead, they’ve chosen one that’s more attuned to the long, slow nutrition they get.

Taken out by scientists, and fed with all the food they want, perhaps they’ll speed up a little. Perhaps they’ll reproduce in a hundred years, instead of a thousand.

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