Space Cadet Reporting... How big is a light year?

Don't read this section if you are sane. It's complete and utter rubbish that was an appalling waste of time to write, let alone to read. If you're still with me, the foregoing is true, but you obviously don't care. This part of my account of the J2E is the continuation of my Starship fantasy that I began when I collected my new car from Cairns and drove it to Nirvana.
How big is a light year?
I ask because while it’s fun to tall tale about travelling at speeds impossible to comprehend across distances impossible to visualise, the universe really is veeeeeeeery big. One can hear scientists talking about the distance between galaxies and think one understands. The Milky Way, for example contains from 200-400 billion stars in a disc that is 100,000 light years in diameter. The nearest galaxy, Canis Major Dwarf Galaxy is 12.9 kiloparsecs away. That’s a little over 42,000 light years. Get it? Compared with the size of individual galaxies, neighbouring galaxies are pretty close. Yeah, right. The nearest star to the Sun is a mere 4 light years away. We understand figures like four, 42,000, and even 200 billion. The latter in dollar terms is about how much the Iraq war costs per day – just kidding of course, but when budgets are expressed in trillions, a figure like 200 billion is within our grasp. But apply that number, or even a number as small as 4, to light years, and we have to stop and think that ….

…a light year is the distance that light travels in one year.
Light travels 300,000 km/sec.
The circumference of the Earth is 40,000 km.
Light travels around the Earth 7.5 times in one second.
There are 31,557,600 seconds in one year.
In one year light travels 236,682,000 Earth circumferences.

To put that in terms of human experience, one of the most fundamental aspects of what it means to be human is that we walk. Doesn’t every animal? Yes, most, but not every animal has occupied every part of the Earth. Except for a few places, such as the Pacific Islands – and the Antarctic – human beings reached every part of the planet on foot. Our ancestors would not have walked to a neat schedule such as the work day. But the work day is also as fundamental to modern humans as walking – perhaps more. So for the purposes bringing a human perspective to the scale of a light year, consider how long it would take to walk one light year to a schedule that would be acheivable if we lived long enough – not just individually, but as a species.

Walking 8 hours a day (every day – no week ends) at 3.6 kilometres per hour (1 m/s) it would take 1389 days or aprox 3 years 10 months to walk one Earth circumferences. Let’s say 4 years to allow for 2 weeks annual leave. It would therefore take 946,728,000 years to walk one light year – in round terms a billion years.

That’s about how long multicellular life has existed on earth. But that’s hardly a human perspective. At three score years and ten it would take 13,524,686 human life times to walk one light year, or 33.3 million human generations (at 30 y/g). What about the lifetime of the human species? How long humans have been around depends on how humans are defined. It could therefore be up to 5,000,000 years. But let’s confine our consideration to the only kind of humans that exist today, ie modern humans – who, incidently were the only kind of humans to have occupied the whole earth on foot. At approximately 100,000 years, it would require the duration of human existence to be repeated 9,467 times to walk one light year.

And that’s just one light year. If you’re thinking of walking from one side of the milky way to the other, having walked for the whole duration of (modern) human existence a little short of ten thousand times, you will have 999,999 times that time and distance to go. Don’t do it. That’s what I always say.

What if we were to travel at 50,000 km per hour – the fastest speed achieved by any man made craft – that’s 13,889 metres per second (nearly 14 km – think of somewhere 14 km away, and imagine getting there in one second – beam me up Scottie!) Now we’re torquen! At that speed travelling one light year comes down from 13,524,686 human life spans to just 794. But that’s still almost 2300 generations – almost 70,000 years. Were we to set out now for the star nearest the sun, about four light years away, by the time we got one quarter of the distance, there’s a good chance we’d still be human. We were as we are now 70,000 years ago. But it would be almost 300,000 years before we got to Alpha Centori. What would we be then? Were we, 300,000 years ago, able to imagine what we would become over that time span? In the billion years it would take to walk just a quarter of the way to the Sun’s nearest neighbour, we might expect to go through evolutionary change on a scale matching the earliest multicelled animals on this planet, on their way to becoming us.

But let’s get back to familiar territory and consider something we can actually imagine – walking around the earth in great circles, starting on the equator, changing direction by one second each time. I did say imagine! It would take 1,296,000 circumnavigations of the earth to cover the whole globe, or 5,184,000 years. That’s about how long it has taken humans to evolve. It’s about 500 times the duration of modern human existence. Having walked thus we would have travelled 0.005 of a light year. We would have to do it again 200 times to travel one light year.

What would we have seen after almost two hundred meticulous surveys of the earth, each of which took about five million years? Well, that’s a subject for another time. But here’s a preview. We’d see the planet change its orientation is space many times. We’d watch as the one original landmass broke up into migrating fragments, some of which slide under others and disappear altogether, only to erupt through volcanic vents to form new types of landmass (granite continents) that “float” on the earlier type (basalt ocean floors). Life would have been in the water as single cells for a couple of billion years just enjoy being itself, and only fairly recently (about six hundred million years ago) started getting on with the job of becoming multi cellular; emitting oxygen into the atmosphere; and then dragging itself up onto land where mountains grow, though not as abundantly as plants that lay down the fossil fuels of the future in deep basins that are covered by eroding mountains; the planet freezes over several times killing off most of what is there; followed by renewed vigour of plant and animal life including the dinosaurs… and mountains continue to rise and fall as continents continue to merge and emerge; then come mammals and birds the likes of which you would not want to be down wind of, rapidly adapting to new opportunities as plants begin to flower a mere hundred million years ago; and in the final five million years, the meteoric rise of a species that for the last 100,000 years has gradually started learning to see and understand the grand story that reaches back much further than the billion years we’re talking about here – back to fifteen billion years of galactic evolution. And, if the theoretical physicists are right, perhaps back to infinite time in which parallel universes merge and emerge.

Who wouldn’t want to drive long distance when you can think thoughts like these … and know that you are actually present to the whole of the story – even the bits we may never know. Anyone need something delivered to Perth?