We don't want the aliens to think we're idiots

One morning this week little (no longer at all little) Philou asked me: 

'Dad, what's a parsec?'

Our conversations often begin like this, a subject coming out of the blue.

'It's a unit of distance', I said, delighted to have one of those increasingly rare moments with my children to show off my brilliance. 'A parsec is a few light years.'

This is the sort of topic I geek out on.

'You're wrong Dad, 'cos in Star Wars they use it to talk about time', he replied.

Well that can't be right. So we dug out the wikipedia article where it says plainly that a parsec is a unit of distance, and also that it's used incorrectly as a time unit in the first Star Wars film.

'So why do we need parsecs if we have light-years?', Philou continued.

'Well', I replied, 'if we were to meet aliens in a distant star system and tried to explain where we came from using light-years, they'd just think we were idiots!'

Imagine the conversation as humans encounter an alien on a faraway planet.

'We come in peace', our earthling spacemen might say.

'Cool! Where exactly do you come from?', the aliens might ask.

'Oh, a blue planet called Earth, a few light-years that way', we'd reply. 'You know, the distance light travels in a year'.

'The speed of light, gotcha', the aliens would say. 'That's a universal constant. But what's a year?'

Well that is indeed the killer question alright.

'A year is how how long it takes our planet Earth to orbit our sun. Well sort of, it actually takes a bit longer than that so every 4th year is 1/365th longer, called a leap year. But we don't use light-leap-years. Well actually we don't use years to measure light-years at all, we use metres per second. A metre is how far light travels in 1/1299792458th of a second. Seconds are 1/86400th of a day - a day is the time it takes our planet to rotate once on its axis. Well sort of, it actually takes a bit longer than that so we have leap seconds. So we've redefined a second as the ground state hyperfine transition frequency of the caesium-133 atom which in hertz is 9192631770 when...'

'Oh you guys are idiots!", interrupt the exasperated aliens. "How did you ever find your way here at all'.

And that's why we have parsecs. All our alien needs to understand is the concept of a circle and a little trigonometry, both probably understood by any intelligent life form, and then we can tell him how far away earth is in parsecs.

A parsec is the distance at which one astronomical unit subtends an angle of one arcsecond.

Like this:

How cool is that? (OK so there's teeny bit more complexity - see the parsec wikipedia article - but still!)

If you must know, a parsec is around 3.26 lightyears - but let's not go there again.

Janna Levin: science and stories

Last night my partner-in-life and I were at a performance of Beethoven's 5th symphony. “De de de daaah”, et cetera. Les Violons du Roy were conducted from the violin by Anthony Marwood  - it was brilliant, visceral. Seated 6 rows from the front we were immersed in the music, from the French horns on our left through the strings and woodwinds in front of us to the drums and trumpets on our right. At the end our hearts were pounding. The musicians gave everything, Marwood ripping in to his violin to the point of almost toppling over, the orchestra's concertmaster and first violin Pascale Giguère matching his performance whilst also somehow managing to turn the pages of Marwood's score every ten seconds.

Beethoven's 5th is a work of music and it's a story. Fate, that “de de de daaah”, dominates the opening but after a vigorous struggle it is ultimately overpowered in the last movement by reason and beauty. The story is told compellingly, there could be no better way of telling it than through this music.

I'm an engineer with a degree in mathematics - I am rational, a latecomer to the arts. There are several scientists whose work I follow quite closely, masters of reason but of story-telling too; it's their ability to combine these two aspects of humanity that makes their work so fascinating.  Janna Levin, for instance.

Janna Levin is an astrophysicist, professor of physics and astronomy at Columbia University. She's an expert on black holes, gravitational waves, and multi-dimensional space. Levin's web site is a treasure trove of fascinating ideas but the best way to approach her work is to listen to her telling a story, beginning with one that has relatively little to do with astrophysics: a story of her own love affair, of reason and music, laughter and ideas, as she told on NPR.

In 2011 she gave a TED talk on “The sounds the universe makes”, explaining the concept of gravitational waves through the metaphor of music. In 2016 gravitational waves became big news as their discovery was confirmed - but this talk by Levin from five years ago is still the best way of understanding them, especially if you like music and love a good story.