h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Traveller in Time riding by on a wave
"Just explain me what a Soliton is.

Perhaps I will get the idea too. "

A soliton is a special type of wave - it can be a water wave, or an electrical impulse.

If you drop a stone in a pond, you get ripples, which are waves, but they get wider and diminish as they get further away from the stone you dropped. That's how waves usually behave, in water, as in electricity, as in other things that carry waves.

Solitons don't diminish, or change shape, or slow down, though. So they're special.

Hope that helps - it's a long while since I wrote this entry, or studied solitons seriously, and I'm not sure I can explain any better...

Traveller in Time not any bit enlightened
"What you discribe, as in the entry, is just a normal wave.

Except for the part 'Solitons don't diminish, or change shape, or slow down, though. So they're special'

But that is where I fail in the entry as well, something is not special just by saying so.

Normal waves do not diminish, or change shape either. That is if you elimiate friction and changes in the transporting medium.

'Russel' follows an ordinary wave in the canal. That is any wave within a channel will propagate that way. The wave will be spreading wide, bounce against the walls and the reflections will enforce the original wavie in its path. Nothing special with it.

In the entry you suggest sound does not have solitons. Why?, if they are possible in water and electrical, there is no reason they should not be possible in sound.

'Severn Bore which travels 21 miles' and then it fades like any other wave ?

Sorry, this does not give any light in what a Soliton can be . . . if they exist . "

No, I have described a soliton, but evidently not well enough for you to distinguish it from a normal wave.

Solitons *do* exist; I'm sorry that my descriptions aren't good enough to help you understand this well known but (mathematically at least) highly complex phenomenon.

Maybe someone on SEx may be able to help you?

Traveller in Time formulating a Question
"Good idea "

Solitons occur when their is a balance between the disperion effects (caused by the superposition of internal waves with different phase velocities) and some sort of restricting force. The restricing force is seen at the beach when a wave approaches the shore. The water gets shallower causing resistance against the wave. This causes the wave to mount itself which is the point at which surfers 'ride the wave'. Eventually the wave becomes unstable and breaks. The restricting force may be anything so long as it opposes the wave (the Severn bore is restricted by a narrowing of the estuary).

A useful analogy is one of a running race. A group of runners set off as a bunch, shortly the faster runners move to the front and the slower runners to the back causing the group to disperse. Should a hurdle be placed at the front of the race the leaders would have to slow down to clear the obstacle thus bunching up the pack. If the bunching was equal to the spreading then the runners would run the race as a pack.

Hope that helps. O and there is nothing in the theory to stop solitons existing is sound waves. The main application of solitons is fibre optics as the pulse can travel vast distances without loss.