Your computer or phone likely runs with a clock speed on the order of around 1 GHz (gigahertz) or faster (the iPhone’s A8 processor runs at 1.1 GHz). That means that there are one billion pulses per second controlling instructions inside it. This equals one pulse every nanosecond, which is just one billionth of a second.
One nanosecond compared to one second is the same as one second compared to 32 years. Every second there are as many pulses of instructions in your phone as there are seconds over the span of 32 years. Many computers run faster than this. My Intel i7 processor runs at around 3.5 GHz, so, we multiply the 32 years by 3.5, getting as many pulses per second as there are seconds in 112 years.
We can use this information to begin to understand large distances. In one nanosecond, light can travel just short of 30cm, the length of a standard school ruler. So this distance is 1 lightnanosecond. If we scale that up to one full second, a billion times more time, that light can now travel almost 299,792 km. 1 lightsecond.
How many seconds are there in a year? Let’s work it out: There are 60 seconds in a minute, 60 minutes in an hour, 24 hours in a day, and 365.25 days in a year (the .25 is to account for a leap day every four years). We multiply all those factors together to get 60×60×24×365.25 = 31,557,600 seconds in a year. That’s 31 million, 557 thousand and 600 seconds.
In astronomical terms, we talk about lightyears as one base unit of distance. One year is 31,557,600 times longer than one second, so one lightyear is 31,557,600 times further than one lightsecond. So we multiply: 299,792 km × 31,557,600 = 9,460,716,019,200 km. That’s 9 trillion, 460 billion, 716 million, 19 thousand and 200 kilometers!
Now, in the world of astronomy, we’re dealing with distances so big that those 200 km at the very end of that figure really don’t make much of a difference either way. Actually, what we really care about is only the first few digits, which leads to the scientific notation of numbers. We write one lightyear as being equal to 9.641 × 10^12 km. This means that we take the first part, 9.641, and move that decimal point twelve places to the right, adding zeros as we go, like this: 9 641 000 000 000. But rather than writing these things out all the time, astronomers use the lightyear as a unit by itself (the same as we use meters or kilometers), so we write 1 ly.
Now 1 ly is a long way compared to what we normally see and experience in our day-to-day lives, but really it’s not all that far when you look at star systems, let alone the whole galaxy. In fact, the very nearest star system to us (Alpha Centauri) is a little more than 4 lightyears away. This is a three-star system, with two stars orbiting each other close together, and a third star much further out, taking more than 500 000 years to orbit the other two.
But Alpha Centauri is just our nextdoor neighbour. Even if we go out to a distance of 10 lightyears, we’re still just strolling around the cul de sac with 9 star systems that close by. Our whole street might be out to 15 ly around us, which includes about 45 star systems, and our suburb might encompass 50 ly in any direction, with around 1400 star systems.
50 lightyears is a long way in human terms, but when we consider the Milky Way, our galaxy, we’re still only just scratching the surface. In fact, the centre of the galaxy, which is occupied by a supermassive black hole, is around 25,000 lightyears away from us here on Earth. The whole disc of our spiral galaxy is more than 100,000 lightyears across, with hundreds of billions of stars contained within it. Hundreds. Of billions.
We’ve certainly shot past the point of numbers that I can actually comprehend, and possibly you too, but why stop there? Our galaxy is not the only galaxy in the universe. In fact, we are part of a group of galaxies local to us which has the creative name of the Local Group. The Local Group comprises more than 50 individual galaxies, and the Milky Way is the second biggest of these. The biggest, the Andromeda Galaxy, is 2.5 million lightyears away from us. If we wanted to write that out in kilometres, we’re looking at something like 23 650 000 000 000 000 000 km, much more easily written as 2.365 × 10^19 km, or 2.5 Mly (the M stands for mega-, and like megabytes in a computer means a factor of one million).
Until recently, we thought that in the entire universe, there might be hundreds of billions of galaxies, each containing billions, or hundreds of billions, or trillions of stars themselves. Last year, a study was published that suggests that we actually underestimated the number of galaxies by a factor of 10 or so, which means that our current estimate is that there are at least a trillion galaxies in the universe. That’s 1 000 000 000 galaxies, each with about 100 000 000 stars.
In the last couple of decades, astronomers have confirmed the existence of planets around other stars – extrasolar planets, or exoplanets – something that was assumed to be true for centuries but not proven until 1995. Since then, thousands of exoplanets have been discovered (as of this month, 3,667 confirmed), and looking at the regularity of these across different types of stars in different parts of the sky, it is suspected that every star in our galaxy has at least one planet.
We even suspect that one out of every five stars like our Sun has an Earth-sized planet in its habitable zone, where liquid water is stable on the surface of the planet, conditions that we suspect may be conducive to the development of life.
Considering all of this; the magnificent scale of the universe around us, the unimaginable number of possible worlds around an unimaginable number of other suns, and that’s in just one galaxy out of an unimaginable number of other galaxies. Over the span of billions of years, with billions more to come, the universe is constantly surprising and awe-inspring.
And we’re down here arguing about who should be allowed to marry each other, and whether some people should be allowed to kneel when a particular song is sung. Go figure.