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

In a wave (say, in the canal full of water), there are two major forces acting on the wave. First, every wave is made up of smaller waves of slightly different frequencies, each of which travels at a slightly different speed. This causes the smaller waves to spread out over time, as some are faster or slower than the others. Secondly, the bottom and sides of the canal would exert an inwards force on the wave. This is the same effect that makes a wave tall and narrow, and eventually break, when it comes up on the beach -- the wave pushes against the sand and has nowhere to go but up.

In some form, these two forces exist for any physical wave. When they exactly cancel each other out, the wave neither spreads out nor builds and collapses: it stays steady. That's a soliton.

I was aware that solitons have been discovered in practically every place that we've looked for them, including possibly in the functioning of nerve and muscle cells. However, I was not aware that solitons existed in the firing patterns of our nervous system, and I have doubts about any form of wave traveling at higher-than-normal speeds in that system. We react quickly when we burn ourselves because the signal to protect ourselves doesn't come from the brain, but from the spinal cord. We skip virtually all of the processing and thinking that normally goes on before we move, so we're safe from harm before we're even aware that we've hurt ourselves.

Could I ask where you got the information about solitons in emergency nervous system firing from?

[bows respectfully]

--Caledonian

The lecture I had on solitons 2 days before I felt moved to write the entry. There's the distinct possibilty my lecturer was wrong

Interesting... If you don't mind, I'll think I'll try to find a reference to this (and maybe to some other places where solitons are thought to exist). If you're willing, I could then post them here... or not.

Your article (as far as I know) is very accurate, but it's just that one little claim that strikes me as being odd.

Well, I'll let you know what I find out.

[bows respectfully]

--Caledonian

Thats a good idea, thanks. I should've researched more carefully, I guess... I don't remember if my lecturer had any evidence to support his claim since it all happened 23 weeks ago.

Nice post! r u studying physics?

How much time did it pass between submmiting this text and beeing aprooved?

oO oO oO oO

Well i wrote the original entry on 26th January, & I don't imagine I submitted it long after I wrote it... so about 22 weeks. I guess the subeditor took nearly the maximum amount of time allowed, & getting a graphic also slowed it down as well.
I've had about 8 other entries submitted and approved in the interim, they don't all take this long by any means. They don't usually...

Additional notes:

Although solitions are unusual in that their speed is proportional to their energy, this property is shared by many non-soliton waves as well. Think about it: the speed of sound in water is extremely fast (faster than the speed of sound in air), but the waves you make at the pool don't travel that fast. Waves that travel at speeds proportional to their energy actually travel MORE slowly, as a rule, than waves whose speed is determined only by the medium in which they travel.

Solitions in water travel much more slowly than the maximum wave speed, and solitons in general do not travel faster than non-soliton waves; in fact, it's often the other way around. Some solitions travel at the same (maximum) speed as other waves, but they're slightly unusual -- or at least, they're not encountered everyday in a form that we recognize as being waves. Photons may be solitons, for example...

[bows respectfully]

--Caledonian

Does the spectrum of a soliton have a specific form? If so, what does it look like?

[desperately tries to remember the tiny amount of information about solitons stored in brain]

I'm not absolutely certain about this, but I think that (in most mediums), only certain groupings of wavelengths can become solitons. It depends on the precise balance between the dispersing forces and cohesive forces... and that's determined by the physical medium the waves are moving through and the size of that medium (how deep the water is, for example), how much viscosity there is, etc.

Is that what your question is about? I'm not sure that I understood it...

[bows respectfully]

--Caledonian

I'm actually looking for a picture of the (or, more likely, 'a') soliton spectrum. Anyway, I did a search on it, and found the following http://www.lightlink.com/sergey/java/java/toda/index.html

If you let the applet run for a while the spectrum develops. It seems to consist of equaly spaced discrete frequencies. Probably an infinite number of them, but rapidly decreasing in amplitude.

I think the line nature of the spectrum has to do with the periodicity of the soliton being modeled ( i.e. it bounces off two fixed barriers and therefore repeats indefinitely.) A soliton launched into an infinitely long channel (such as the river version mentioned earlier in this thread) should have a continuous spectrum.

My more pressing thought is the comment about telecommunications; as I see it solitons exist where nonlinear actions and reactions occur, such as between particles. In the massless, particle-less world of electromagnetic radio waves (at least when passing through free space), is it possible to have a soliton? If so, do the conditions have to be extreme (i.e. very high flux, more than can be safely radiated) in order to create them? If so it is hard to see where solitons could participate in telecommunications.

A lot of telecommunications at the moment are electric pulses through copper wires. These are the movement of electrons, not radio waves, and I think they could be made to behave as solitons

In reply to the comment about wave velocity being related to the energy. The statement doesn't really make sense as the velocity at which you are moving is a componant of your total energy. But I know what you're getting at. The oddity about solitons is that the velocity is greater the greater the amplitude of the wave. So a big wave travels faster than a small wave. A sound wave with a greater amplitude travels at the same sound through a medium as a wave with a smaller amplitude. This is why it is thought that solitons could be the cause of nervous system reactions. If we do something daft a soliton may be formed to get a message to the brain asap to warn us of the danger. I don't think this is concrete but I have seen the idea floating around in several places.

Hope some of that is useful.