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Messages - Virex

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4861
DF General Discussion / Re: Cleaning fluid?
« on: February 28, 2009, 04:50:31 pm »
Quote from: Protactinium on February 28, 2009, 09:53:00 am
If it's corrosive, it's pretty good at removing caked grime in small, diluted quantities (and should burn and destroy in large and concentrated amounts).

Only problem is that alcohol isn't nearly as corrosive as most cleaning agents. It's mainly used because it's capable of dissolving a large number of substances that don't disolve in watter (many oil-based substances and fats for example, though you won't be able to disolve the more resilliant types of oil-based products. For that you'd need aceton, or something like octane), and because it's good for disinfecting things.

4862
Roll To Dodge / Re: Penguinofhonor's RTD ROUND 2 Turn 31 AN UPDATE (AGAIN)
« on: February 28, 2009, 04:07:04 pm »
Quote from: Sean Mirrsen on February 28, 2009, 02:39:50 pm
Well, he IS doing fusion. Hydrogen does turn into helium when fused. So neutrons or no neutrons, you fuse hydrogen - you get helium. Can I propose not turning another topic into a fruitless physics discussion? ;)

But physics can be fun! Just imagine what would happen to him if he tries to channel enough energy to cause nuclear fusion. Instant living lightbulb! :D

4863
Creative Projects / Re: Realistic Space Travel
« on: February 28, 2009, 04:03:50 pm »
Quote from: Sean Mirrsen on February 28, 2009, 03:24:52 pm
No, mainiac, I'm talking about the large-scale interstellar travel. It's a lot easier to carve a colony out of a chunk of rock and move that chunk of rock than construct a ship the size of the chunk of rock and have it move. And I'm not talking about "most practical" or "most feasible", but "best". There is no better way to travel in space than on the planet you're inhabiting. Setting it up to be able to travel is another thing entirely, and I did say non-newtonian engines. By the time the sun's about to go blow on us, we just might have a technologically feasible way to take our planet off its orbit and fly away into the wild green yonder.

Moving the earth (or even mars, altough it´s half as large) would be impractical, since you're dragging around an ungodly amount of dead weight. Basicly, you only want to have the bare neceseties, like beams for structural integrety, a surface to mount things on and shielding to keep air in and nasty radiation out. Everything else you'd be dragging around is just stuff that's not helping but does need acceleration. Therefor it'd be Many Many Many times easier to carve a ship out of an asteroid then to move a planet, but then you're not realy talking about a planetship anymore. (of course I could go off in a tangent and say a Dysonsphere would be even more efficient, but we´re already too far away from our current reality'. Of course if you´re also using the excess mass as fuell it´d be another thing entirely, but then you´d need to make sure that the extra mass and extra thrust scale apropriately.

One thing to take into acoutn when talking about a moving colony is that it´s in the end an open system. There´s no way you can cheat thermodynamics, so you´ll always have the problem that you´re generating entropy at quite a fast rate. On earth that is compensated by work delivered in the form of radiation energy (mainly light and infrared), but once you leave our solar system, you'll need to take some sort of energy with you instead. You proposed brining a replacement sun. I'd keep things a bit smaller, but nuclear fusion is certanly an option, especialy when using a large-scale electromagnetic "scoop" to suck in hydrogen attoms from the surrounding space. But another option would be to prefabricate and store enough energy to get to the next star and recharge there. Tests have shown that thermal energy stored in molten salt only decreases with 1% per year, and that's with our current methodes to keep something adiabatic. presumably, you'd get a bonus if packing in large volumes (less contact area relative to the energy stored), and isolation would also improve. Storing electrical energy would be harder though, but perhaps it can be stored in the form of chemical energy. Superconducting coils would also be an option, but current desing only go up in the terrajoule range (which is practicaly nothing compared to our current anual energy usage), and they have a loss of aproximately 40% over longer periods of time, and are only desinged for a few days of operation. They're a lot more efficient then batteries though ;)

4864
Creative Projects / Re: Realistic Space Travel
« on: February 28, 2009, 02:54:06 pm »
Quote from: Sean Mirrsen on February 28, 2009, 02:23:28 pm
There exists a [ /quote ] tag on the forum. :)
Dully noted
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Has anyone tried to polarize sound? For example, in water?
How would you go about measuring the polarity of a sound wave? And what would you try to polarise in the first place? as far as we know, sound waves are formed by causing a medium to oscilate, and I have a hard time imagining how an oscilating medium could be polarised.
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I did not observe light in any meaningful way, but why exactly two ocillating fields? Can you point me to something that sheds some, uh, light on this? I doubt anyone actually observed the light's structure, only its effects. What effects require the twin-field structure to be possible?
I'm not quite sure, but I think it follows from Maxwell's equations. As in, the equations don't make sense if light isn't an electromagnetic radiation and the electric and magnetic field arn't perpendicular. But as to why it is this way, I don't know. You might want to study quantumelectrodynamics, or maybe even string theory to understand it.

4865
Roll To Dodge / Re: Penguinofhonor's RTD ROUND 2 Turn 31 AN UPDATE (AGAIN)
« on: February 28, 2009, 02:35:25 pm »
Quote from: Sean Mirrsen on February 28, 2009, 09:50:33 am
What do you want to get, H4O2, or He2S?

Can't get He2S like that, since you're a few neutrons short ;)

4866
Roll To Dodge / Re: Psyco Jelly's RTD
« on: February 28, 2009, 02:19:47 pm »
Quote from: Zasit Alebath on February 28, 2009, 02:03:45 pm
since NUKE9.13 and Digital Hellhound are busy wrestling, i attempt to open a door

There is only 1 door ;)

Anyway, I'll wait to see what happens with the door. In the mean time, I try to force the spikes on my glove to change shape and move around. I try to play a small game of chess against myself this way.

4867
Creative Projects / Re: Realistic Space Travel
« on: February 28, 2009, 02:11:07 pm »
Quote from: Sean Mirrsen on February 27, 2009, 08:16:25 pm
Isn't a gravitational redshift essentially the same as being slowed down? If you were to imagine a soundwave going through water past a pipe that sucks water in, the part of the wave going against the current would become dragged-out and increase in length. I'm not sure if such experiments were ever made (with pipe and sound), but it seems logical at first glance.
The analogy to sound is usualy flawed, mainly because the two aren't the same kind of wave. Sound is an oscilating medium, vibrations in a carrier substance. Light consists of two oscilating fields. They behave in similar ways when things like interference are concerned, since that has litle to do with the carier substance. But when it comes to interactions with the surrounding media thigns start to differ.

In this case I thought that a part of the potential energy that light has is converted into "light energy", which means a change of colour, and thus you get a blueshift when light's comming from an area with high gravity towards an area with low gravity. The other way around means "light energy" is converted into potential energy, and thus you get a redshift. Or at least I'd like to think it works like that, since the potential energy light has due to gravity has to go somewhere...

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I wonder if it's possible to attain supersonic speeds underwater without supercavitation?
Maybe a near-frictionless surface would work? A polarisable liquid, like watter, could also be magnetised and consequently aligned to reduce friction, or at least I think it's possible in theory. You'd need an ungodly powerfull magnet though.

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edit: IP, yes I am aware of differences in molecular structure being the deciding factor in whether or not a material absorbs or reflects light. The difference in speed isn't due to light bouncing around the molecules though, as the wiki article on Cherenkov radiation seems to state (likening it to a train that travels with many stops).
Well, as far as I know, the reason light's slower has to do with it interacting with electrons, which absorb the light and consequently re-emit it. There's a small delay between the absorbion and the emmiting though, causing light to "lag"  a bit and thus it's macroscopical speed is lower then c.
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Also gravity does seem to affect EM fields. What with black holes being strong enough to pull apart most of the waveforms that pass near, including and not limited to, light.
Are you certain that this isn't a side-effect of light (And all other waveforms) having impulse? Also, remember that black holes can create very powerfull magnetic fields, due to the acceleration of charged particles around it.
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And what does gravity have to do with space-time? While I can understand speed, motion through the space part of space-time, being able to affect the time flow, how can what essentially amounts to a force field affect space-time?
As far as I know, gravity causes a deviation from euclidian geometry to everything it can affect. Since the geometry of space contains the 3 dimenstions of motion and time, time also starts to behave in a non-euclidian way. And don't ask me exactly what happens, because I don't know.
What I'm interested in is if magnetic forces can cause a similar deviation from euclidian geometry for charged particles.

4868
Roll To Dodge / Re: RTD: Unfettered Fate (Turn one is up, actions for turn two needed.)
« on: February 28, 2009, 01:39:55 pm »
A body? I am not sure I ought to take a corporal form after what happened to my former body.
That's not to say I ought to remain like this...

I try to tap directly into the energy stream and alter it's direction of movement.

Riding the storms like ever before...

4869
Creative Projects / Re: Realistic Space Travel
« on: February 27, 2009, 08:08:25 pm »
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Anyway, getting back on topic:
About light sail form of propulsion, with a laser as a propellant - just imagine that, you build this thing somewhere in space and expect it to operate continously for 100 years(yes it's just a made up number), which is hardly possible, considering the amount of energy that it has to convert and transfer. So you'd have to send maintenance and/or fuel(if it's not solar-powered)
That's why your ship should be solar-powerd, though a nuclear battery could also run for long enough. Any other supplies could be made by efficient recycling, probably involving tricks like geneticly modified yeast and bacteria. Also, brining a large part of the population in stasis or a similar state might help.

As for the propulsion, I'd only use the laser in the early stages, since after a decade, the ship will be too far away for the laser to work realy efficiently.
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to keep it going for all this time, or else the precious spaceship loses thrust - which might be especially bad if it's decelerating.
In interstellar space, a solar sail would only decelerate if it's closer to a star in front of it then any star behind it. At first it won't be noticalbe, untill you get close, at which point you want to slow down, or else you'll overshoot the star system. So this can be fixed by propper planning.

Also, you could use a radiation coating to supply thrust. Basicly, it's radiating in all directions, but because you're catching the radiation going in one direction, the radiation pressure isn't canceling itself out anymore and you get a net thrust.

If it'd be slowing down due to another reason, then you've missed something. And that'd be a pretty big miss for a well-prepared mission to a relatively close planet. Also, if the sail's causing drag, you could always fold it up again ;)
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Now look at the human political and economical history, and imagine that you tell those colonists to get on the ship and count on people back home to spend resources to keep them alive. There might be more important things to do, you know. Like wars, or economic crisises, or disasters or whatnot.
Only if you're assuming the people have to stay ready for the full 100 years. It'd be more realistic to pack everything up in the 30 years prior to the mission, and launch everything in a short window of time. Because when the ship's gone, there's probably no way to resupply it, unless you'd like to wonder off to wormholes or something.

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My point is, as much as it's a feasible idea from the physics point of view, it seems too vulnerable to social situation on Earth.
Anyone has anything to say in it's defense, or should we cross it out of our "realistic space travel" options?

I wouldn't cross it out yet, since I think that the problems are smaller then the problems of a nuclear or chemical rocket. It has all the same problems, but it needs many times more fuell.

4870
Creative Projects / Re: Realistic Space Travel
« on: February 27, 2009, 07:03:53 pm »
Quote from: Yanlin on February 27, 2009, 05:15:58 pm
In theory, it IS possible to stop a beam of light with enough matter.
At the very least you could catch up to it with a car: http://www.hno.harvard.edu/gazette/1999/02.18/light.html

As for the nature of light, as far as we know, light exhibits the so-called wave/particle duality. We know this because light exhibits interference, which only works if it's a wave. But to explain the Photo-electric effect, one needs to assume that light is made up of particles (I'm citing wikipedia here, I know. However, I have seen both effects before, in experiments done in high school. So I assume I don't have to cite more reliable sources here)

A common misinterpretation of this is that light is a vibrating photon. In fact, it most certainly isn't. As far as we know, the wave-state of light consists of an electrical field and an electromagnetic field that's perpendicular to the electrical field. Both fields are perpendicular to the direction in which light travels, and they oscillate at the light's frequency. The polarisation of light is directly related to the orientation of these two fields, and as such a magnetic field can change the polarisation of light. A simple experiment regarding this effect, called the Faraday Rotation, is described here.
At the same time, light can be a particle. For the system between this effect, there are several proposed theories, but as far as I know, there isn't a universally accepted solution. Then again, I'm not a theoretical physicist.

Do note that the effects described aren't exclusive to light. Matter can exhibit these properties as well, in which case the associated wave is called a de Broglie wave, and these have been reported for electrons in de broglie's original experiment, described here. Also, electron microscopes use this property. You can read about the most common kind, the TEM, here. This paper gives an example of the practical use of a de broglie beam of sodium atoms, and this site describes an experiment that verifies that even blackballs, large football-like structures of carbon atoms, can act as a wave. And in the world of particles, those things are huge.

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This causes me to think. Light DOES experience drag. But some force is making it go forward. If that were true, then it would manage to accelerate far more than the speed of light. Maybe the drag at that speed, even in space, cause it to not be able to accelerate any more?
Light does experience drag indeed, which is why the speed of light in for example glass is about 2/3 of the speed of light in a perfect vacuum. this page gives a basic introduction to this concept, and explains how it is related to the refractive index of a substance. It also gives values for the refractive indices for several materials, which can be used to calculate the speed of light in these materials.

But you are indeed right, since space isn't a perfect vacuum, the speed of light is slightly lower then one'd expect. But I'd dare to say that this difference is to small to be measured.
Another interesting effect related to this is the existence of Cherenkov radiation.

I'm not quite sure, but I think that light can't be slowed down by gravity. Instead, it experiences gravitational redshift, which is explained here. I'm to tired to dig up a scientific article backing that up though...

4871
Creative Projects / Re: Realistic Space Travel
« on: February 27, 2009, 03:22:09 pm »
Quote from: Il Palazzo on February 27, 2009, 02:39:40 pm
Quote from: Sergius
I'm not so sure about this, but I believe that's a consequence of dilation and not actually lack of acceleration. From your POV, you keep accelerating at the same rate, so you ARE going "faster and faster", but from the external POV you seem to be accelerating less and less. Or is it the other way around? That's why as you approach C, the people inside the ship could perceive a trip to be (near) instant, while people outside will still think you still took 4 or more years to reach the nearest star.
Ah, yes, you seem to be on the right track, as far as I can tell. There's just one more problem that I can see there. Mainly, what if you don't have any "destination point" and you just keep accelerating?
From the POV of external observer, it's rather easy to deduce: the spaceship's mass increases, it accelerates ever more slowly and it's on-board time slows down(with complete "time-stop" as the unatainable limit - asymptotic approach).
But what about POV of the space ship? As you accelerate, the universe becomes smaller in the direction of your travel(lenght contraction), but with what exactly as a limit?
And what is there to stop you from accelerating beyond said limit?
You've also got to take time dilation into account. If I remember correctly, speed induced time dilation is symmetrical, which means that to th outside observer, the object slows down, but to the object, the outside observer slows down. So as you approach c, the world around you seems to grind to a halt.

The reason there's a limit at c in the first place has to do with the fact that if you start to appraoch c, all kinds of things happen (time dilation, space contraction, mass increase) and those things cost energy, or more precicely, a larger part of the energy is converted into those changes instead of a change in speed. The amount of energy that goes into these changes aproaches 100% of the added energy as your speed approaches c. So you will continue accelerating, but at an ever slowing pace. There's no real hard limit, you're just losing more and more of the acceleration to unwanted side-effects.

4872
Roll To Dodge / Re: Psyco Jelly's RTD
« on: February 27, 2009, 02:28:01 pm »
I'll join

I walk up to the steel door and lay my hands on it. Focusing strongly, I try to comunicate with the internall structure of the door, and force it into forming a pair of spiked metal gloves.

4873
Creative Projects / Re: Sci fi ascii game brainstorming.
« on: February 27, 2009, 01:16:51 pm »
It's probably not movement itself that would give problems. Harder is the apropriate representation.

A good approximation to the location problem would be to divide the ship in a set of spheres, and give the center of the spheres a location vector relative to the ship's center (or another point of reference if that's easier). Then when the ship turns around a certain pivot point, you'd take the location vector of each of the component spheres relative to that pivot point and multiply it with a rotation matrix (note, this only works if matrix multiplications are supported. I don't know if they are). Then you'd translate all the resulting vectors back to location vectors relative to the ship's center and you're done (this means you can ssing things like speed and acceleration to the ship's center without having to change them whenever the ship turns). Collision checking would be done by checking if one of the spheres of one ship intersects with one of the spheres of another ship, which will be slightly harder. This can however be aproximated by reducing one of the spheres to a polygon, and check if any one of the points of that polygon is or will be inside the other sphere.

The problem will however be representing a rotated ship, since ASCII graphics don't realy like being rotated. Basicly, if you'd try to force the ship unto a large grid, like what happens in Dwarf Fortress, you'll horribly distrot everything. That means you'd need to use a small grid and find some way to get the ASCII characters to work with such a grid. But I assume you chose ASCII graphics to keep things simple, in which case this could be a less then desired option

4874
Creative Projects / Re: Realistic Space Travel
« on: February 27, 2009, 01:07:53 pm »
Quote from: Granite26 on February 27, 2009, 12:25:37 pm
Just to throw another wrench in the machine:  Is there any real reason to believe that light is traveling at the speed of light?  All we know is that light propagates at a certain rate relative to us, and everything kinda bends around so that the fastest rate anything can move is c.  It's already established that if you start chasing light, it's source will be redshifted.  That is, pushing light harder increases the energy, but does not APPEAR to make it faster

Exactly what do you mean? Experimental evidence that the speed of light is the same for all observers?

4875
Creative Projects / Re: Realistic Space Travel
« on: February 27, 2009, 11:58:25 am »
Quote from: Yanlin on February 27, 2009, 08:59:03 am
The nature of light and transfer of energy are NOT firmly established.

They are heavily theorized.

You can theorise about the nature of light all you want, but for the discussion at hand it's sufficient to say that there have been extensive measurements of the impulse conveyed by light to a particle (http://www.lpi.usra.edu/meetings/dust2005/pdf/4010.pdf) and to mirrors: (http://rspa.royalsocietypublishing.org/content/360/1702/347.full.pdf+html). Another study showed that it's possible to cancel out the thermal motion of a mirror by using a laser to generate radiation pressure: http://www.articlearchives.com/science-technology/physics-lasers/1652418-1.html, though I was not able to retrieve the original document of this study.

Now it's of course up to debate whether this means that light actually has mass. However, there's another kind of circumstantial evidence that points in that direction, namely that light is influenced by gravity. The most spectacular example of this is seen in the following paper: http://hubblesite.org/pubinfo/pdf/2008/04/pdf.pdf. This paper describes the discovery of a so called double einstein ring, in which light is bend twice to generate a very specific shape, which is described in this related article as a bulls-eye patern.

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