Heliosheath

[Vadrosaul]

http://science.nasa.gov/headlines/y2006/21sep_voyager.htm

 

What does the solar wind speed being a lot slower than expected mean exactly?

 

I'm not going to imagine I know much about this subject, but my brother brought it up and I know a lot of members here have interest in the astronomical topics.

 

Plus this is an opportunity for any number of Star Trek puns

[Komag]

I guess it means we won't be able to solar-sail to Alpha Centauri, drats!

[Dram]

Well basically it means that the sheath would not be as effective as originally thought, from what I gather, which means less acceleration gained from the solar wind. That's one future method of space travel down the plug then

[demagogue]

I have to ask myself: is my life is really any better off knowing that this thing even exists?

 

 

 

And the answer to that is question is "Yes. Yes, it is."

[Ishtvan]

They only said it's slower in that particular area as you go really far away. I don't think anyone was thinking of using solar wind for interstellar travel since it would drop off in intensity too much when you get outside the solar system. Doesn't mean we still can't use it for travel within the solar system.

 

I don't really know what it's saying though. I don't get anything from the "water faucet" analogy, unless they are saying that it's like diffusion that's driven by a concentration gradient, and there's not as much concentration gradient to drive it when you get out to the edges, but I'm not sure if that's what they mean.

[OrbWeaver]

I don't really know what it's saying though. I don't get anything from the "water faucet" analogy, unless they are saying that it's like diffusion that's driven by a concentration gradient, and there's not as much concentration gradient to drive it when you get out to the edges, but I'm not sure if that's what they mean.

 

I guess it just refers to matter which is expelled outwards at less than the required escape velocity - there will be a point where this matter loses its outward momentum and forms a boundary of some sort.

[demagogue]

I think the idea is ... it's not just that the rays run out of momentum at that distance (after being continually slowed by solar gravity). It's that they all run out of momentum all together, at about the same distance.

 

So there will be interference effects; the rays won't just slow down, but will start getting bounced around by other slowing rays, and the faster ones will get bunched up by the slower rays holding them in and bouncing them back, where they'll hit incoming rays and things get bounced around further.

 

So, the point is, you get a little sluggish, semi-turbulent pool of rays bouncing around in this zone, the wind gets *thickened*... rather than the rays just slowing down and dissapating and the wind getting *thinned*, which would happen if there were much fewer of them. It's the "pooling" of the rays that's the important point, it seems, not just the fact that they slow down after a while.

Edited October 6, 2006 by demagogue

[Order of the Hammer Bureaucrat]

It's hard to believe this 'jumping around' hypothesis. As far as I understand rays can't just slow down and start reflecting off of each other. When I was 7 years old I wondered what will happen if I make a box or a sphere perfectly encrusted with perfect mirrors on the inside and put an electriscal light-bulb glowing in the centre. I stopped wondering now, but I still don't know.

[Ishtvan]

I don't think we're really talking about photons here, but rather the charged(?) particles that make up "solar wind" like electrons, protons and atoms, which do have mass.

 

I wondered what will happen if I make a box or a sphere perfectly encrusted with perfect mirrors on the inside and put an electriscal light-bulb glowing in the centre. I stopped wondering now, but I still don't know.

 

That would be like a source inside a resonant cavity. Photons are bosons so they can theoretically be packed with infinite density (the exclusion principle doesn't apply to bosons). In reality, we can't make a perfect resonant cavity with 100% reflection and no loss. Probably the worst loss would be when they bounced back into the original lightbulb, since that obviously can't be 100% reflective since light has to get out of the bulb, and light has time reversal symmetry so it has to be able to get back in, and then might get absorbed somewhere.

 

Realistically it would probably come to some steady state intensity inside where the loss has balanced out the generation, or it might break down in some way first (like the intensity would build up enough to destroy the light bulb or one of the mirrors). Also as intensity built up a lot you would start to see nonlinear effects at the mirrors, like frequency conversion to some frequency that is not contained by the resonator.

 

If you replaced a light bulb with a current source and filled the resonator with a gain medium, you'd get a laser, and in simple terms that will also come to a sort of steady state where all additional energy you put in exits out of one of the mirrors.

[sparhawk]

Is the bulb powered by an outside cable? In that case the box would heat up and maybe explode or melts at some time, or it can give off enough heat that this does not happen, but then th energey is still radiating outside. In the case of a battery driven bulb, it would most likely also heat up, but it might happen that it dissipates over time and of course the battery will run out at some time either.

[Order of the Hammer Bureaucrat]

Since then I've played with lasers. But back then I had more of an 1880's mind. I played with tin cans, copper tubes, and copper wire, (asking my grandpa to drill) pretending to create some gizmos, and I was awed when my uncle showed me how to build an electromagnet. What I obsessed with until I was 9 years old is building chemical batteries.