independent

Saturday 14 December 2019

Mind-boggling speeds of our vast space journey

Western Europe at night as seen from space
Western Europe at night as seen from space

Jim Hurley - Nature Trail

As you sit quietly reading these words it is difficult for you to believe that you are hurtling along at great speed in at least four different directions.

First, planet Earth is rotating, so you are spinning around in a daily circle. The speed of rotation varies with location; in Ireland it is about 1,180 kilometres per hour. From driving a car, or from being a passenger in one that is being driven, most people have an appreciation of what the 100km/h speed limit that applies on many main roads feels like. However, it is difficult to imagine travelling at over eleven times that speed.

Second, in addition to rotating around itself, planet Earth is orbiting the sun. 108,000km/h is the ballpark figure given for the speed we are going at on our annual trip around our nearest star on the journey that brings us the four seasons.

Thinking about the combined sensation of rotating and orbiting brings back a childhood memory.

One of the rides at the visiting summer carnival was a set of huge multi-coloured cups and saucers on a merry-go-round. Each cup had seating for about four people. Once the fee had been paid to the man with the shiny leather money bag on his hip and the warning to hold on tight had been issued and heeded, the cups began to spin around themselves as the whole tea set waltzed around the carousel.

Third, our entire solar system is but a tiny part of the Milky Way galaxy, a huge disk-like structure somewhat like a vinyl record. We are located about halfway between the centre of the disk and its outer edge and we are orbiting around the galactic centre at a speed of about 780,000km/h.

And fourth, the entire universe is expanding, so the Milky Way and all the other heavenly bodies are hurtling outwards at some unimaginable speed in a slow-motion explosion driven by that mysterious, theorised force called 'dark energy'.

An alternative and more modern view is that as you sit quietly reading these words you are not in fact hurtling along at great speed because since everything is moving you have no fixed reference point to tell you that you are in motion.

Since there is no fixed reference point, the interpretation in modern relativistic thinking is that nothing is moving; it is merely that the metric governing the size and geometry of spacetime itself is changing in scale.

Wexford People

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