Members Login
Username 
 
Password 
    Remember Me  
NUCLEARSPACE MESSAGE BOARD (ACTIVE) -> SCIENCE FICTION & NUCLEAR POWER -> The Speed of Light: How Fast Can We Go?/autodynam
Post Info TOPIC: The Speed of Light: How Fast Can We Go?/autodynam
Kevin J Waldroup

Date:
The Speed of Light: How Fast Can We Go?/autodynam
Permalink  

The Speed of Light: How Fast Can We Go?
Scott Ratliff
Kristopher Kimball
Garrett Heraty

* Introduction
* Problems with High Speed Travel

-speed
-fuel
-relativity
-time

* Theories: Propulsion Ideas

-Orion propulsion concept
-ion propulsion
-antimatter rockets
-laser sails

* Theories: Ideas to Get Around Relativity

-autodynamics
-worm holes
-warp drive

* Current Related Work

-Breakthrough Propulsion Physics Program
-X-34 Project
-AIMstar Project

* Conclusion
* Glossary
* References


Introduction

"If Science and Politics never mixed, we'd be colonizing other planets by now." -Anonymous

"For I dipped into the Future, far as human eye could see; saw the vision of the world, and all the wonder that would be." -Alfred Lord Tennyson, 1842

"Mankind will not remain on Earth forever, but in its quest for light and space will at first timidly penetrate beyond the confines of the atmosphere, and later will conquer for itself all the space near the Sun."
- Konstantin E. Tsiolkovsky

"There are things that are known and things that are unknown; in between is exploration."
-Anonymous

The depths of outer space has long been a mystery. From the casual observer who gazes into a clear night sky and beholds the majesty of a shooting star, to the experienced astronomer trying to determine the makeup of a star millions of light years away, the universe intrigues all. What secrets does it hold? Does life exist outside of our solar system, and if so, what is it like? Imagine all that could be learned visiting other solar systems, and even other galaxies. Our galaxy, the Milky Way, alone contains over 200 billion stars and has a diameter upwards of 100,000 light years.






This means that light, energy which to us seemingly travels instantaneously, takes 100 centuries to cross it. Comparatively, it takes light 2.3 million years to travel to the next closest galaxy. Obviously, if we are to explore even a comparatively short distance beyond our solar system, great travel speeds must be reached.
Alpha Centauri, the closest star outside the sun, is 4.35 light years away. Even traveling at 37,000 miles per hour, the speed at which the NASA Voyager left our solar system, it would take 78,842 plus years to reach it. Obviously not a feasible travel time. So are there ways to make space exploration possible? Is there a limit to how fast humans can travel? What happens when an object approaches the speed of light (299.792458 megameters per second)? Our objectives are to explain these questions, and the theories surrounding them.



Problems with High Speed Travel

There are many problems that arise from interstellar space travel. The most obvious would be getting someplace in a reasonable time. As stated in the introduction, using current technology, it would take far too long for travel outside the solar system to be feasible. For example, using a chemical engine like those used in space shuttles, a trip to the nearest star beyond the sun within 900 years would take a greater mass of fuel than the mass of the entire universe. Even with a fission rocket, the same trip would take over one billion supertanker sized propellant tanks. Therefore, a breakthrough in propulsion methods must be made.
However, things aren't quite that simple. Even if these speed and propulsion barriers are overcome, Einstein's theory of relativity introduces a whole new set of problems. According to this theory, the speed of light is nature's speed limit. That is, nothing can possibly move faster than the speed of light. The problem arises from Einstein's famous equation, E=mc2 ; as an object accelerates, its kinetic energy (E) increases, and because the speed of light (c) is constant, the mass of the object (m) would increase. Therefore, as an object approaches the speed of light, the object would approach an infinite mass. So to accelerate an object to superluminal speeds, an infinite amount of energy would be required.
Einstein also came up with the theory that time is not absolute. The idea is that the passage of time is dependent on the frame of reference. This concept is demonstrated by the famous "twin paradox." This thought experiment involves two twins, one who stays on earth and one who embarks on a high speed journey into space. The theory is that the traveling twin will come back to earth to be younger than his twin. If, for example, one twin travels through space at three fifths light speed for eight years from his point of view, ten years would have actually passed for the twin on earth, making him two years older than his traveling twin. This effect becomes even greater as speeds are increased. In other words, the faster one travels, the slower time passes until the speed of light is reached at which point time theoretically stops all together.
This theory does have experimental support. An experiment was done in which two synchronized atomic clocks were used. One was placed at a location near the equator, and the other was placed at the north pole. It turned out that the atomic clock at the equator after a period of time was noticed to be running slightly slower than its counterpart at the north pole. According to relativity, this result is due to the rotation of the earth being faster at the equator than at the north pole. This slowing of time due to increased speed becomes a problem in space travel because, even if we found a way to explore space at speeds near light and minimize travel time, the passengers would return to a futuristic world and still have the problem of lost time. So what can be done to get around these problems?



Theories : Propulsion Ideas

Scientists have come up with several viable theoretical solutions to the problem of speed. While none of them will solve the problems posed by relativity, they are a step toward further technologies. One such idea is using nuclear bombs for propulsion. The theory is simple: drop bombs behind a spacecraft and "ride the waves" (so to speak). The spacecraft would have large shock absorbers at the base of the ship. This is known as the Orion concept of propulsion.
One alternative to chemical propulsion that is already in use is ion propulsion. NASA's Deep Space One probe, launched October 24, 1998, is propelled by using electricity from solar panels to remove electrons from Xenon atoms. These ions are then expelled at 30 km/s, providing the craft's propulsion. The impulse provided by this method is about ten times that of a chemical engine, although the thrust is much lower. This means that, although an ion engine accelerates slower than a chemical engine, its maximum speed and fuel efficiency are much higher. This method is useful for more efficient travel in the near solar system. As the sun becomes more distant, however, the solar panels of the craft will not be able to absorb the necessary solar energy to ionize the atoms. Plans to explore the outer solar system involve accelerating the craft in the inner solar system, and allowing it to coast to the outer solar system. If such a system is ever to be used for further exploration, a more reliable power source is needed for the ionization.
Another alternative that has been proposed to chemical propellant is antimatter. It is known that every particle has a corresponding antiparticle. This antiparticle is identical to the particle, but with an opposite charge. When the two particles meet, they are converted into energy and some particle by-products. This process is called annihilation. Physicists are currently working on methods of storing antimatter particles, especially antiprotons, for use as a power source for spacecraft. In the simplest method of antimatter propulsion, the antimatter is essentially used as a heat source. Matter/antimatter reactions would heat a tungsten core which heats hydrogen as it flows through and then out of a rocket nozzle. This design is actually based on the solid core fission reactor, in which nuclear reactions are used to heat water and make something that is, in effect, an extremely efficient steam engine. A more complicated plan is to use magnetic coils to direct the particles created by the annihilation of protons and antiprotons to provide thrust. The first plan would provide an impulse of 800-1000 seconds, more than twice that of the space shuttle. The second would provide an impulse of 10,000,000 million seconds, but with a much lower thrust. Currently, plans are in the works for a 400 ton spacecraft that could travel to Mars and back in four months, with a one month stay on the surface, using only a few billionths of a gram of antimatter. This is much more efficient than current chemical propulsion, and removes the need for large propellant tanks. Essentially, the largest barrier to using antimatter as a propellant is its price. Currently, one milligram of antimatter would cost nearly one hundred billion dollars to produce. Until antimatter is more readily available, this technology will be difficult to implement.
Another possible technology that could improve the efficiency of space travel is the use of "laser sails." These rely on the principle that light has momentum. Because of this, when light strikes an object, a slight force is applied. If enough light is concentrated on a very large area, this force becomes great enough to be used for propulsion. A recent design proposal involved shining a 10 million gigawatt laser through a thousand kilometer lens onto a thousand kilometer sail. This system could send a thousand ton spacecraft with crew to Alpha Centauri within 10 years. The downside to this system is the massive scale of each of its components. There are numerous problems involved in making very large lenses, and this program requires a thousand kilometer lens. Also, the 10 million gigawatt laser presents a problem. Currently, only about one ten thousandth of that amount of power is used on the entire planet. A revised plan uses a 10 gigawatt microwave laser (which is only 1/100th of the current total power consumption of the planet), and rather than a huge, manned craft, it uses an array of sensors built into 16 grams of wire spread into a 1 kilometer frame. This system would take about twenty years to reach Alpha Centauri.



Theories: Ideas to Get Around Relativity

One of the easiest ways to get around relativity is not to believe in it in the first place. Like all things in life, relativity is not without its doubters. One such doubter, Ricardo Carezani, has formulated a new theory - one that replaces the shortcomings and limitations surrounding Einstein's theory. It is called autodynamics. The main difference between the two is their derivations:

Special relativity is a special case within autodynamics and uses two reference points, as opposed to only one. In addition, autodynamics does not require the existence of a neutrino (the existence of which is debatable). For some relativity calculations, excess energy has to be explained by a neutrino. Autodynamic calculations require no such particle. Also, while special relativity does explain gravity, it does not provide a physical mechanism for it. Autodynamics does. The most interesting difference, however, is that autodynamics does not predict any natural speed limit. In other words, particles can travel as fast as the energy contained in them will allow. According to the theory, relativity does not apply to cases involving radioactive decay. Any particle could transform all of its mass into an energetic photon through a decay process, and travel at superluminal speeds.
Other ways to get around the problems posed by the theory of relativity deal with a concept known as spacetime. One may think of spacetime as a sort of rubber sheet which, when a massive object (such as a planet) is placed on it, it curves around the mass. Space is believed to behave in this same manner. This would be helpful to space travel because, if some way of bending spacetime was discovered, the distance between two points would be essentially shortened. It would be like if you had a piece of paper with two holes in it and, instead of drawing a line from hole to hole, you fold the paper until the two holes are aligned. This would essentially be a fancy way around relativity because theoretically you could travel at superluminal speeds by making a really long distance respectively short and then putting it back again, but, of course, relativity prohibits speeds faster than light.. While not much is known about the actual bending of space, it is the basis from which such theories as "worm holes" and "warp drives" are conceived.
A worm hole, if it truly did exist, would be a shortcut through space using huge amounts of energy or mass, like that of a black hole, to create a massive distortion in spacetime. Theoretically, a naturally occurring worm hole would consist of a rotating black hole connected to an equally rotating white hole in another part of the universe. Normally, something entering a black hole would have no chance of escaping the immense force of gravity due to the singularity and would be essentially torn apart. A worm hole, however, would eliminate the destructive nature of the singularity by being connected to the white hole. In other words, something entering a worm hole would be sucked in by the black hole, pass through the singularity, and be spit out again by the white hole in another part of the universe.
This theory does have many problems. For one, white holes may not even exist since they rely on the concept of negative mass (the existence of which is debatable), and, if a white hole did actually exist, who is to say it would actually connect with a black hole in another part of the universe? Furthermore, a worm hole could only remain open for a minute instant of time so that it would collapse before something entering would get a chance to pass through it. Even if one could get through it before it collapsed, he would most likely be fried by the radiation being sucked in from nearby stars. In conclusion, while worm hole transportation would allow space travel in a relatively short time, it is not exactly a feasible method of space travel.




Another idea based on the folding of spacetime is the "warp drive." This concept, which would produce propulsion without propellant, is based on controlling gravity so as to expand spacetime behind a ship (pushing the ship forward) and contracting spacetime in front of the ship (pulling it forward). A ring consisting of huge amounts of negative mass would have to be created and wrapped around the ship in order for this effect to occur. However, as stated in the problems with worm holes, the existence of negative mass is an unknown to science today. While classical physics leans heavily toward negative mass not existing, quantum mechanics says that it is at least possible for it to exist.



Current Related Work

NASA began a program in 1996 known as the Breakthrough Propulsion Physics Program. This program is designed to research and explore new possibilities with the hopes of one day finding the ultimate breakthroughs in space transportation. Long term goals of the program include discovering ways of propelling a spacecraft without propellant mass, traveling as fast as physical limits will allow, and creating new efficient energy production methods. NASA believes that if these three goals are achieved, they will allow human travel to other stellar systems. Since not much is known in science today regarding such topics, the program focuses more on the credibility of propulsion ideas (like the theories explained above) and working toward further advancements in science rather than further investigation to what is already known.
Breakthroughs more likely to occur in the near future are those relating to current space shuttle technology. One such project is NASA's X-34 spacecraft. The X-34 is referred to as a reusable launch vehicle and its intent is to demonstrate and test technology to be used on future spacecraft. These technologies include airplane-like features which will require minimal inspection and maintenance, reusable propellant tanks, an advanced health monitor system which can quickly repair problems, and automatic controls such as navigation, guidance, and landing systems. Launched out of the belly of an in flight L-101, the spacecraft should eventually be able to reach speeds of greater than Mach 8 using a 60,000 pound thrust version of the Fastrac LOX/kerosen engine. The object of the X-34 program is to demonstrate an ability to integrate new technologies easily as they become available in a low cost, low hassle aircraft.





Another current project being done by researchers at Penn State University is one which hopes to speed space travel. This project, called AIMstar (Antimatter Initiated Microfusion for Pre-cursor Interstellar Missions) can propel spacecraft more efficiently than any current technologies. The process used, called antiproton-catalyzed microfission/fusion(ACMF), could supply an impulse of about 10,000 seconds, and a thrust of 100kN. While an antimatter propulsion system would be more efficient and powerful, current methods of producing antimatter are too limited in the quantity that can be produced. The actual procedure was developed by researchers at CERN, Switzerland. It involves annihilating antiprotons on uranium nuclei, causing fission of the uranium. By introducing fusion reactants, the energy is increased even further. Certain problems with traditional fusion techniques arose during the planning of this project. Traditional fusion research usually uses the Hydrogen isotopes Deuterium and Tritium. However, with this method, large amounts of shielding are required because of the radioactive Tritium, which could damage the engine and payload. This makes the craft excessively heavy which increases the thrust requirements. To avoid this problem, Helium 3 is used in place of Tritium. The project is expected to "deliver a scientific payload to 10,000 astronomical units (approximately the distance from earth to the Oort Cloud) in 50 years."

Antimatter Propulsion Engine






Conclusion

So, will any of the above mentioned theories and ideas actually lead to a breakthrough in the world of space exploration? We believe so. Certainly some of them sound intriguing. Perhaps a combination of a few of the ideas presented here and the addition of new theories will combine to form a path leading to the technological advancements required. We have already come a long way. The Wright Brothers first flight traveled at 7 miles per hour. Today, our spacecraft can reach speeds upwards of 40,000 miles per hour, an increase of 6000 fold. Another increase of the same magnitude would produce speeds of better than one third the speed of light.
Traveling at light speed has long been a dream of man. Realizing this dream would open the door to a new "world" of knowledge. Science is well on its way to accomplishing this. The projects proposed above are all promising, but require more research and funding. The most important aspect is that scientists keep an open mind. What is true today, may not be true tomorrow. An example of this is the discovery of quantum mechanics. When it was first introduced (and still today), people had a hard time coming to grips with replacing classical physics with a new set of ideas. It is this type of atypical thinking that needs to be applied to space travel. What if at superluminal speeds physical laws change yet again, requiring the problem of faster than light travel to be approached from a completely different direction. We have the ideas to take us there, we just need experimental data to prove their feasibility. Nothing is incorrect until proven so. Some day the space and resources present on the earth will be exhausted. Will we have the ability to travel to a distance planet to meet the increasing needs of humanity? Only time will tell.



References

http://monet.physik.unibas.ch/~schatzer/space-time.html

http://www.lerc.nasa.gov/Other_Groups/PAO/warp.htm

http://mentock.home.mindspring.com/twins.htm

http://lifeintheuniverse.com/speedofl.html

http://www.autodynamics.org

http://cfpa.berkeley.edu/BHfaq.html#q1

http://seds.lpl.arizona.edu/messier/more/mw.html

http://bang.lanl.gov/solarsys/eng/solarsys.htm

http://www.parascope.com/en/antimatr.htm

http://www.cern.ch/Press/Releases96/PR01.96EAntiHydrogen.html

http://antimatter.phys.psu.edu/

http://wwwssl.msfc.nasa.gov/newhome/headlines/msad12nov97_1.htm

http://nmp.jpl.nasa.gov/ds1/

http://www.lerc.nasa.gov/WWW/bpp/

http://stp.msfc.nasa.gov/

http://www.cem.msu.edu/~cem181h/projects/98/lightspeed/group.htm



__________________
GoogleNaut

Date:
RE: The Speed of Light: How Fast Can We Go?/autod
Permalink  

I can tell that you are a person who likes to do their homework!

I have read, and studied (and don't understand quite a lot) of Miguel Alcubierre's "Warp Drive within General Relativity." What is so stunning about this work is that it points at some very intruiging ideas: that the space-time metric--the ruler (measuring stick as it were) for measuring distances and time seperations--can actually be engineered into a desired configuration, given sufficient conditions.

Basically, if I understand his work at all, is that if a suitable arrangement of matter-energy could be configured with enough energy density, then a bubble of space-time could be formed which mimics, in some ways, the inflationary universe just fractions of a second after the Big Bang. The FTL aspects of the Alcubierre Warp Metric come from this bubble self propogating itself through normal space time. This is somehow accomplished by causing space to contract in front of the vessel (by applying a large positive energy density to the front) and having it simultaneously expand in the back (by applying a large negative energy energy density to the rear.) Summing over the volumes occupied by the two fields and integrating for total energy results in a net-zero energy expenditure (which because of the almost impossibly high energy densities involved is a great relief, because the half-integral energy is about the equivalent of a Solar Mass in mass-energy!) Anything caught inside the nearly flat spacetime (a ship) within the Bubble will be carried along. This is analagous to Frame-Dragging, a General Relativistic Effect usually attributable to rotating black holes. Impossible levels of acceleration could be achieved without the occupants feeling a thing (provided they don't stray too close to the tortured shell of spacetime which surrounds their vessel!)

Supposedly, the Alcubierre Warp Metric allows speeds which are only limited by the speed of 'inflation,' however fast that could be. It could be hundreds, thousands or millions of c, who knows?

I came away with the idea that basically the concept of metric engineering--the process of modifying the spacetime continuum even to a limited extent for a desired purpose was possible atleast in principal. Whether this allows a Star Trek like propulsion system--I don't know. But it certainly is interesting how it works!

Another notion that I came away with was that if such a device was possible, then another device should be equally possible--one in which the shell is engineered to implode! A spec of matter caught inside might undergoe gravitational collapse. Now why do that? Well, imagine what you could do with a 1 milligram black hole. Hawking radiation will cause it to evaporate in a tiny fraction of a second--emitting a torrent of gamma-rays and showers of neutral pions. Basically, you could use anykind of matter you wanted: water, sand, regolith, garbage, hydrogen, whatever, and get intense flashes of gamma-rays back--which incidentally just happen to be easily absorbed by water. That 1 milligram black hole should release very close to the equivalent of 20 tons of TNT worth of gamma-rays. This is the heat equivalent of about 730 gallons of gasoline. Generating one pulse every ten seconds could run a conventional steam turbogenerator power plant capable of generating 3000MW of electricity!

So even if it's a long shot, it could be worth the effort to develop 'Metric Engineering.'
Unfortunately the mass-energy densities involved are huge--this makes it extremely difficult to do anything that affects gravity (which of course is why a planet the size of earth has to have the mass it does to achieve the grav field at its surface!)

There is another possibility: looking at the smallest scales of the quantum vacuum. There the fields are strong enough, the complexities wild enough, and the environment weird enough that such things as metric engineering might be possibile.






__________________
Ashley

Date:
RE: The Speed of Light: How Fast Can We Go?/autodynam
Permalink  

Don't remember the link, (or possibly paper source) right off hand, tho it might be on NASA's "Warp Drive When" page, but the 'Alcubierre Drive' turned out (when they developed more math and better techniques) to be a stasis field.  It is essentially useless (except possibly as a weapon) since time ceases to exist inside it, and nothing outside (other than maybe a trip through a blackhole or megagiant star (is that the right name for the ones that are giant compared to supergiants?)) can affect the stuff inside it, while the stuff inside it no longer has acess to time.  It does aparently work tho, pretty well infact.  And they can be fast, depends on initial (unassisted) velocity, and total energy differential.  Initial velocity also decides direction of travel, since the pilot has been paradoxed.  Talk about losing your past, those guys would have no future! lol


I just thought of something, interstellar morse code!  Nothing (almost) can stop it!  Just make bunches of tiny probes that just have the bare minimum equipment to take flight, and send them one after another.  To decode, just mark down dots and dashes. lol



__________________
GoogleNaut

Date:
RE: The Speed of Light: How Fast Can We Go?/autod
Permalink  

The program you refer to is called the Breakthrough Propulsion Physics Program, a little known program which was a small branch of NASA run by Marc Millis of the Glenn Research Center. It can be found at:

http://www.grc.nasa.gov/WWW/bpp/

The program has the goal of nothing less than to legitimately attempt to find, quantify, and exploit any loopholes in the laws of physics allowing for 'anomalous' propulsive methods. By anomalous I mean propulsion systems that do not necessarily rely upon rockets to generate forces and/or actions. The goals of the program were to devlop--if possible--fundamentally new methods for generating and using energy; creating motion without expending propellant; or drastically reducing propellant to generate a desired motion. Also, if possible, the program was interested in identifying or creating methods of communication that circumvented the 'usual' laws of physics forbidding information transmission at faster-than-light speeds.

I believe this program has been cancelled, though it did identify some intriguing possibilities which really ought to be followed up.

__________________
Ashley

Date:
RE: The Speed of Light: How Fast Can We Go?/autodynam
Permalink  

Thanks.  It has been a while since I looked at that site.  Tho that's the first place I remember hearing about Orion.  I have read Footfall, but that was somtime later.  I just realized that I first saw that site 5 years ago.


I'm all for Orion, or any other method of getting to space that isn't to destructive.  Ironic, calling nukes non- (or at least minimally) destructive. lol


I also find the points that www.ssi.org and www.permanent.com make are valid.  We aren't going to suceed if we try to push one item by itself.  Sure, something like Orion could launch lots of cargo.  But unless we have uses worked out and in (or very close to) production, we are unlikely to get any takers.  What might be interesting would be if an equipment list, orbital flight plan, and logistics assesment was made, showing what would actually be necessary for something useful.  (read 'profitable to the stockholders')


That could be something like a science expedition, but they are unlikely to get the political clout (or money) necessary.  It could be something like an exploration voyage. Which would (hopefully) interest the public, but still would leave funds fluctuating at the whims of the politicians.  It could be a colonization effort, but that would possibly be the most pollitically troublesome.  (Save the other planet's (non- or barely- existent) environments! lol)  Or asteroid mining, which would be resisted by the businesses involved in mining.  (until it is actually done, at which point they try to beat (or beat up) the competion)  But a mission designed with several of these as sub-missions, might have a chance, (if all the technology and equipment can be shown to be readily available) since the temporary fall of one point, wont kill the whole thing.  And if necessary, the equipment will be around and can be sent the hard way, at which point we can show this plan and say 'we had it al ready, but...'



__________________
saurabh

Date:
Permalink  

we can travel at the max, with the speed of light 3,00,000Km/s(approx)
so far NASA has achived a 10 Mach speed
the speed of photon in the free space.
We can achive much more than that if we think of some new dimension
Who Knows what could be speed in that dimension. Searcing of the new dimension could be really interesting area in the field of sccience.
I beinng a student of computer Science Could think it possible in the graphics.

__________________
Ashley

Date:
lightspeed barrier/ sound barrier
Permalink  

According to NASA's 'breakthrough propulsion physics' (BPP) and 'warp drive when?' pages, there are a few ways already known that would allow "ftl" travel.  Of course they entail amounts of energy larger than we are capable of producing in the near future, exotic matter, negative energy (an actual technical term for what you get when you run anti-matter through the mass-energy formula), or result in an unbreakable stasis field.  So they are essentially useless, but as technicallities, it is possible to go "faster than light".  It is even theoretically possible to be at exactly the speed of light, assuming that you have access to an infinite amount of energy.  Tho if you achieve lightspeed exactly, you would have infinite mass, infinite volume, and time would have stopped, so you couldn't do anything.


Also, the speed of light is a limit, tho since the calculations are in some of the more advanced maths, it is possible for the limit to exist.  And it is possible to travel faster than lightspeed, tho getting past the c barrier is a problem.  Just remember not to turn your engines off while you're travelling ftl, or it might become rather hard to stop.  The graph of energy vs velocity is mirrored about the speed of light, so above c it takes more energy to slow down to c, and if you quit applying energy, you will continue to accellerate.  There is the question tho of whether something travelling ftl in realspace would still be going forward in time, or whether that is also mirrored.  Tho both of those states would explain the lack of tachyons in our searches.



__________________
GoogleNaut

Date:
RE: The Speed of Light: How Fast Can We Go?/autod
Permalink  

One of the main staples of NASA's BPP was addressing energy requirements for things like Miguel Alcubierre's "Warp Drive" metric--which is a mathematical description of a particular spacetime generated from a large concentration of negative energy density and positive energy density. A negative energy density is different from thinking about antimatter. Antimatter and matter, when they come into contact with each, annihilate and release energy in accordance to Einstein's famous formula E=MC^2. The M represents the total mass annihilated--thus this is the some of both the anti-matter's mass and matters' mass. Antimatter is a positive energy density--it would have a positive gravitation associated with it.

A negative energy density is a different animal altogether. Annihilating a positive mass with an equal 'amount' of negative mass yields....nothing.

A negative mass would have 'negative' gravitation--a planet sized chunk of negative mass would attract more negative mass to it, but would repel positive energy mass.

Here's the really bizarre thing--and it has been argued for various reasons as to why we don't observe negative mass--positive mass gravitationally attracts negative mass. It is this bizarre assymetry which leads to a very strange situation: if one were to construct a device wherein a negative mass was physically attached by a massless frame to a positive mass, then the positive mass would attract the negative mass, and the negative mass would repel the positive mass in exactly the same direct!
This would lead to a situation wherein the system would spontaneously accelerate in the direction of the positive mass. Now as long as these masses are small, the system's acceleration is vanishingly small, if the masses are large then so is the acceleration!

Alcubierre took advantage of this idea, but in a slightly different way. In classical physics it is possible to show that the gravity field anywhere inside a spherically symmetric shell of matter is zero. What this means is that for an arbitrarily massive shell of matter, the spacetime contained within that shell is approximately flat, regardless if that shell is 10 cm of aluminum, or 100 cm of neutronium!

Now what Alcubierre did (in my humble opinion is sheer genius on his part!) was to make the forward half of the shell a positive mass, and the rear half of the shell a negative mass. By increasing the energy densities until it began to approach the density of a black hole, very strong fields are set up. The forward half of the shell begins to collapse spacetime, while the rear half of the shell begins to expand it...the result, stressed spacetime slopes down from the rear to the front. The shell will accelerate, carried along by a space time distortion. Depending upon the amount of mass in each shell, conceivably accelerations of millions of g's could be possible.

Now what about the occupants inside the shell? Surely no one could survive million g accelerations?

Well as long as the shell is spherically symmetric, the space time is flat and the occupants will feel nothing but free fall.

What about conservation of momentum, speed of light limit, and everything else that implies limits on how fast we can go? Well, the stressed space existing between the shells of mass and negative mass approximate the conditions of the very early universe called inflation. The universe is thought to have expanded from a point to several light-years in diameter in an almost unbelievably brief amount of time: something around one Planck time unit (say 10^-35 seconds, that's a decimal point followed by thirty-five zeros and then a 1) This is an indication that space-time expanded at many times the speed of light (something like 10^43 times the speed of light, just for round numbers!) So presumably Aclubierre's warp-metric could propagate at some comfortable fraction of that: Personally I think a million times the speed of light is worth trying for (guffaw here!)

As for conservation of momentum and the like, well if I understand Alcubierre's paper at all I suspect that it is basically that since the massive shells of positive mass and negative mass are equal and opposite, their mass sums to zero if combined. Then this just leaves the ship with its associated crew, cargo and paying passengers. During hyper fast travel (O.K., let's just call it In Warp!) the ship is embedded in a self-propagating spacetime (i.e., Warp Bubble...?) The ship is not moving relative to the shells, so its relative kinetic energy is....ZERO.

How can this be? Well this is one of those extremely bizzare things--and it is one of the many arguments of why Alcubierre's metric can't possibly exist. Because it's like getting a free lunch--you can travel arbitrarily fast, and it doesn't cost you 'anything' energy wise. This means a ship could conceivably accelerate at millions of g's for a short duration, shut down it's drive and stop on a 'dime' after traveling several light-years.

Of course, this all depends on one's ability to procure a method for generating large negative energy densities. Quantum mechanics suggests that small negative energy densities are possible, in fact certain electron devices require negative energy densities to function: such as Josephson Field-Effect Transistors, commonly used in low temperature superconducting quantum interference detectors (SQuIDs,) some are also used in Analog to Digital Converters. But this is far and away from the ability to accumulate nearly stellar mass negative energy densities.

Perhaps by a subtle manipulation of the quantum vacuum, energy could be 'borrowed' for a brief moment and moved to another spot. This would create the required conditions of a large negative (depleted) energy region and a large positive (accumulated) energy region nearby. As long as all of the borrowed energy was 'paid back' then, possibly, Alcubierre's idea could work. But as you may already know, a 'theoretical possibility' is a long way from a practical prototype. Still, it's an idea worth researching. Which is why the BPP program exists.

Thanks for the fun question!


__________________
Ashley

Date:
RE: The Speed of Light: How Fast Can We Go?/autodynam
Permalink  

What it said on the BPP site was that an alcubierre drive does require massive amounts of energy to start it up, and the startup energy never quite gets recovered.  The reason for that is the same one that makes the alcubierre drive worthless even tho it would work, and that is simply that the 'boundary' between realspace and the space inside the alcubierre warp acts as a stasis field.  Instantaneously upon activation of the alcubierre warp, time ceases to exist as a meaningful concept inside the warp, so the pilot can't turn it off, and there is considerable argument as to whether even flying it (by setting up the course ahead of time) into a supermasive star or blackhole would be able to affect it from the outside.  (and either of those two methods would destroy the ship anyways) And nothing else could survive the journey through that boundary of tortured space.

__________________
GoogleNaut

Date:
RE: The Speed of Light: How Fast Can We Go?/autod
Permalink  

Well, I don't know about the 'stasis' effect. Atleast according to the math it would seem that time ought to flow pretty much like it does in normal space time, because the spacetime within the shell of distorted space time is flat. Only very near the inside surface of the shell does spacetime seriously misbehave--this is the origin of the so called tidal effect.

Agreed on the recovery of energy--all reversebile systems are enslaved to entropy--and there is no reason to think that an Alcubierre warp-metric is any different there. And of course, when blithely 'throwing around' stellar sized massess, any even small inefficiencies are likely to be Earth or Jupiter-mass in magnitude.

And yes, there are some fascinating papers out there which bring up the 'controlability' aspect of the Alcubierre metric. It would seem to behave much like a Soliton--which is great until you want to turn it off!

Interesting side note about controllability: aircraft are not engineered to be completely stable. They are engineered to have controlled instability. Why? Because an aircraft that is completely stable in flight is not controllable!

Direct application of the Alcubierre metric doesn't seem possible. However, what I came away with when I first studied the paper was the fantastic possibility that something like it could result in FTL travel, and that was the most startling implication of all.

__________________
Ashley

Date:
RE: The Speed of Light: How Fast Can We Go?/autodynam
Permalink  

I, unfortunately, definitely can't do the math.  I'm having trouble even just with calculus. And I need to learn orbital mechanics. lol


The stasis effect is supposed to be because of the shell, one of the things it does is mess up the difference between space and time.  It is supposed to make it so that inside the shell you have space, without time.  Thus no one inside the shell can do anything.  Time isn't just slowed down on passing the shell, it doesn't even manage to make the journey, and so ceases to exist inside the shell.  I'm still trying to see whether that makes any of the more dangerous temporal paradoxes, or if not being able to interact (its also supposedly a barrier to light) solves those problems.  It has been a while since I looked at the site seriously, or took the time to go rereading all the articles, so I may be miss-remembering, but thats what I've got.  (Maybe I should put that back on the to do list.  Even the encyclopedia gets boring after a half dozen passes.)



__________________
GoogleNaut

Date:
RE: The Speed of Light: How Fast Can We Go?/autod
Permalink  

Well, in allhonesty, I can't do much of the math either. I can crank out some of the calculus, but the tensors and differential geometry are beyond my abilities (dang it!)

I'm not sure where you heard of the "Stasis" effect, related to the Alcubierre metric. I definately got the impression that relativistic effects play little or no role near the center of the shell because the space-time is flat and does not move relative to the shell. However, conceivably if the mass of the shells became so large that a spherical discontinuity resulted (as in some kind of bizarre black-hole...) then possibly. But everything I've ever read about it points to a definate flow of time, very similar in all respects to classical (otherwise known as flat, Euclidean or non-relativistic) space-time. Perhaps I am the one missing something--which in all honesty could be...this is pretty far out stuff! I doubt that there are much more than several thousand people in the entire world who have a really good handle on the mathematics necessary to compute space-time metrics anyhow. Unfortunately, I'm not one of them!

__________________
Ashley

Date:
RE: The Speed of Light: How Fast Can We Go?/autodynam
Permalink  

Oh, and whatever this may look like, I didn't care much about the outcome, I was just enjoying the mental stimulation provided by the argument.


I searched at www.aiaa.org for "alcubierre" and got this page of results.
http://www.aiaa.org/content.cfm?pageid=406&lquery=Alcubierre%20AND%20V%5FSource%3D1&sort=Score,Desc&a=1&n=200&ms=1


Selecting this one brought up a paper that discusses the validity of the alcubierre drive. (this paper claims it is possible, but takes too much energy to be feasible, unfortunately I'm not a member and can only see the first page unless I pay)
http://pdf.aiaa.org/preview/CDReadyMJPC2003_775/PV2003_4677.pdf 
Warp Drives: How and When?
B. Cassenti, Pratt and Whitney, East Hartford, CT; H. Ringermacher, Kronotran Enterprises LLC, Delanson, NY
AIAA-2003-4677
39th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Huntsville, Alabama, July 20-23, 2003


I also searched on google's gov and mil site search (to hopefully weed out a few of the more questionable pages)
http://www.google.com/unclesam?hl=en&lr=&q=alcubierre+warp


Here are some of the results.
http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=20493411
http://www.grc.nasa.gov/WWW/bpp/TM-97-206241.htm  not specifically about alcubierre, but it does pertain to the thread topic
http://thomas.loc.gov/cgi-bin/query/z?r105:E25SE8-209: lol



__________________
GoogleNaut

Date:
RE: The Speed of Light: How Fast Can We Go?/autod
Permalink  

Agreed. A very stimulating exchange. I hope someday that Miguel Alcubierre's ideas pan out. Humanity could certainly use the shortcut!



__________________
kevin J waldroup


Newbie

Status: Offline
Posts: 4
Date:
RE: The Speed of Light: How Fast Can We Go?/autodynam
Permalink  

bmup


__________________
United States Deep Space Force Interplanetary FF Gross Mass 4,000 tons Exhaust Velocity 39,000 m/s Diameter 41 m Height 61 m Interplanetary DD Gross Mass 8,000 tons Exhaust Velocity 78,000 m/s Diameter 50 m Height 80 m
Andrew


Senior Member

Status: Offline
Posts: 199
Date:
Permalink  

Here is a site that contains "alternative views" regarding space drives: http://www.npl.washington.edu/AV/av_index_sub.html#8

__________________
John


Senior Member

Status: Offline
Posts: 366
Date:
Permalink  

That link has a lot of John G. Cramers Analog articles, which are always interesting. The whole top of space drives that beyond known physical principles (BKPP) have been a major obsession of my life and the main motivation of my studies in physics and math. Ive vacillated between optimism and pessimism on the subject. A lot of focus has been on Einsteins Special Theory of Relativity as the big obstacle to interstellar travel because of the speed of light limit. However, without E=mc^2 we could even hope to go at 100 km/sec let alone 300,000 km/sec (relative to the frame of reference of the launch point of course).

There are two major types of BKPP propulsion systems to consider. First some sort of propellant free drive that will allow acceleration with out ejecting reaction mass. This type of spacecraft would still be subjected to relativistic mechanics. It would allow easy transit form Earth to orbit or even to anywhere in the solar system. However this BKPP would seem to violate conservation of momentum.

The second type of BKPP drive is the FTL drive itself. The have been many ideas in SF on this. Jumps through "subspace" or "hyperspace" travel through wormholes, and "warp drives" such as in Star Trek and James Blishs "Spindizzy". The latter type of drive has been given some scientific credibility with Alcubierres Warp Drive solution to General Relativity (GR). In a way all of these concepts are related. GR is a theory that explains gravity and views the structure of the cosmos at large as a curved surface. The mathematics involve allows one to understand geometry based on the surface alone and without considering the underlying embedding space. However, the fact that these surfaces can be viewed as lower dimensional objects that can exist in a hyperspace is also clear mathematically. However, physicists and philosophers of science will mostly argue that this underlying embedding space will have no meaning. If you infer its existence from the math one can see that the dynamics of the hypersurface that we think of as space-time we can see that motion in the underlying hyperspace does allow motion faster then light just as SF as assumed. So all of these FTL drives listed above are all different slants on the same underlying concept.

Also, it seems to me that one might even be able to use the Alcubierre Drive to achieve the first BKPP objective. This is no requirement that one move it faster than light. In a lower power mode it might move along at sublight speeds. The real problem with this is that the only known way to generate a gravitational field is involves mass (more correctly mass, energy, and pressure) and the coupling constant is very small. There is no practical way to deploy the amounts of energy (negative energy) required by the coupling constant. The question that is raised is what knew discovery in physics might make this drive possible? One though is that it could turn out in a "quantum gravity" theory that the small gravitational coupling that we experience is a ground state interaction and that a higher state interaction could be stimulated in some unknown way so that large local curvature effects required by the Alcubierre Drive might be achieved. A step in science and technology analogous from go to the laser from the light bulb.

-- Edited by John at 18:41, 2007-04-14

__________________
GoogleNaut


Guru

Status: Offline
Posts: 606
Date:
Permalink  

Just as a side note, I once thought of a way to use the Alcubierre effect (if that's the right term for it) to create a spherically symmetric imploding wave. If this kind of collapsing metric could be made, then it may infact be possible to place a small bit of matter in a shell that collapses: eventually (as long as it is coherent enough) the shell may collapse to the Chandraseker Limit where gravitational collapse will take over: i.e., a tiny black hole is produced. If the implosion takes a miligram of matter along for the ride and becomes a microblack hole, then Hawking Radiation ought to evaporate the black hole in a tiny fraction of a second. This could be a pathway to circumvent nucleonics all together, and create a matter conversion powersource that can convert any matter into showers of energetic particles and gamma rays.

Very exciting stuff indeed. A new power source than can use any matter as fuel will be worth its weight platinum!



-- Edited by GoogleNaut at 03:14, 2007-04-15

__________________
Andrew


Senior Member

Status: Offline
Posts: 199
Date:
Permalink  

So, I gather the artificial gravity may be a required standard to create a FTL drive?

Some more links:
http://www.npl.washington.edu/AV/altvw99.html
http://omnis.if.ufrj.br/~mbr/warp/
http://www.geocities.com/zcphysicsms/

Hein's Unified theory may also look interesting:
http://www.heim-theory.com/Contents/contents.html

__________________
GoogleNaut


Guru

Status: Offline
Posts: 606
Date:
Permalink  

I don't know. I think that the 'artificial gravity' may be a more or less an artifact, or by product, of the 'metric engineering' to create the conditions necessary for the Alcubierre warp to happen.

Of course, it's all moot if you can't create the necessarily large negative energy densities--that's the trick with these things.

Of course, the quantum vacuum may have, hidden away inside at the slightly sub nanometer scale, a way of creating large negative energy densities. But if I knew how to do that, then creating repulsive or 'anti' gravity fields would be a trivial matter.



__________________
John


Senior Member

Status: Offline
Posts: 366
Date:
Permalink  

There has been some recent ideas in string theory that it might be possible to have strings that are much longer than the Plank Length and that would result in the creation of microblack holes in the new CERN experiments. 

I don't see anyway to create the energies required for the Alcubrierre Drive based on known gravitational coupling with the Newtons constant.  That is just too weak for any humanly controllable amount of energy.  It could turn out that there are other modes of interaction that create gravitational effects that might be discovered in the process of developing a quantum gravity theory.  One possibililty would be some sort of short range massive gravitions that would complement long range massless gravitons that are responsible for classical gravitation.  This all a very long shot but it would take a big discovery to make this possible. 



__________________
GoogleNaut


Guru

Status: Offline
Posts: 606
Date:
Permalink  

Looking at the 'Zero Point' energy density--this is the ground state vacuum energy and is thought to be responsible for setting up things like Heisenberg Uncertainty Principle, entropy, absolute zero, and other basic thermodynamic phenomena--it is possible to do calculate transient energy densities that are astounding: depending upon how you do the sums over all 'modes' which are quantum vacuum electromagnetic vibrations, seemingly nonsensical results can be obtained like ending up with energy densities of 10^20 times the total mass of the universe crammed into a single cubic meter of free space, etc. But what is clear is that the quantum vacuum is extremely dynamic, and the energy density involved with this chaos sums very close to zero--otherwise the universe, everything we see, and we would not exist!


However, it may be possible to 'borrow' from this vacuum, for even a fraction of a second, a very large amount of mass-energy which also creates momentarily a very large negative mass energy. The simulataneous creation of both could in principle yield the large energy densities cited by Alcubierre. And if the Alcubierre warp need be coherent for only a fraction of a second to perform its faster-than-light magic, then perhaps we can still have our cake and eat it too as it were. By pulsing such a system it may be possible to travel great distances by borrowing energy density from the vacuum and paying it back in very short order.

Of course, this is all wild speculation. If I really knew how do to this, I think I would probably have a net worth greater than Bill Gates and the Walton Family combined!

Oh well, I guess I'll stick to my messy conjectures!



-- Edited by GoogleNaut at 18:46, 2007-04-16

__________________
Andrew


Senior Member

Status: Offline
Posts: 199
Date:
Permalink  

What about Dr. Van Der Broeck (must...resist...urge...no...too...strong... THE LIGHTSPEED BARON)
idea, of scaling down the whole Arcubierre to require far less amount of negative energy?
http://www.npl.washington.edu/AV/altvw99.html

And what is really negative energy?

__________________
John


Senior Member

Status: Offline
Posts: 366
Date:
Permalink  

Sounds like Dr. Who's Tardis! 

This is all quite speculative of course.  The Hein unified field theory was interesting too. 

__________________
GoogleNaut


Guru

Status: Offline
Posts: 606
Date:
Permalink  

I read Dr Van Der Broeck's paper and it is interesting. It seems if you can create a warp metric, then you can create one that is small on the outside and big on the inside. The particular metric mentioned had an exterior diameter about the size of a proton--if memory serves--but the interior diameter approached 200 m. This is almost like an "Alice in Wonderland" metric--but if you can bend spacetime to your will, then it certainly may be possible to make an inside out spacetime bubble.

Negative energy density is really weird, it is not antimatter. Matter and antimatter are both positive energy densities. The proof of this is that if one were to annhilate a chunk of matter with antimatter--the energy produced in the explosion is the twice the smaller of the masses annhilated times the speed of light squared. If the two chunks are exactly the same, then the energy produced will be exactly twice the mass-energy of one mass.

Negative energy density--whatever that is ultimately--is a different animal altogether. If a negative mass is annhilated with an equal amount of positive mass then you get--nothing. It dissappears completely.

Another strange, counter intuitive thing with negative mass density is what it does to Newton's Laws of Gravitation: it does weird things!

A negative energy mass will repel a positive energy mass, but the positive energy mass will attract the negative energy mass. Confused? Don't feel bad. It gets worse.

If one were to create a frame work that places a negative energy mass in close proximity to a positive energy mass, what would happen? Well if the two masses were ordinary matter, then nothing would happen. But if one mass is replaced with a negative energy mass, then something extraordinary can happen: the negative mass will create a force of opposite sense from the positive mass; it repels the positive mass. The positive mass creates an attractive force in the SAME direction as the negative mass' opposite sense force. A system composed of a negative mass and positive mass will experience an unbalanced force--and will accelerate in the direction of the negative mass. It has been argued that this very problem--a seemingly physical contradiction--as proof that negative masses cannot exist. However, atleast at small scales, quantum mechanics demands that there are negative masses. The proof of this is in the very function of JFET--Josephson Field Effect Transistors--which operate on the principle of quantum tunneling to function. Tunneling could not happen without the apparent existance of negative energy densities to cause the anhilation effect that physically transports electrons across a nonconductive barrier.

Anyways, what Miguel Alcubierre realized was that if you were to create a very large negative and positive energy density in close proximity to one another, such as in two joined hemispherical shells, then it may be possible to physically 'cutoff' or gravitationally isolate a region of spacetime, say 100 m across or so, and accelerate it at arbitarily large accelerations dependent only upon the magnitude of the energy density of the negative/positive mass shells. That since the sum of the masses of the negative and positive shells would sum to zero or very close to it, then this movement would be 'free' or nearly so.

And even now, this is still a very exciting proposition to me as I write this!


__________________
Andrew


Senior Member

Status: Offline
Posts: 199
Date:
Permalink  

And I understand that the problem lies in the fact that no one knows how to create negative energy?

And I seem to be developing the notion that negative energy would somehow allow reactionless drives. Am I correct?

__________________
John


Senior Member

Status: Offline
Posts: 366
Date:
Permalink  

Negative energy is really just being in a potential well.  I think the big problem is that the quantities of energy are some massive as to beyond our access.  (Unless you can to that minature one).   My question is does the classical gravitational constant represent then only mode of gravity in a quantum gravity theory.  It could be a ground/degenerate state and that if we could some how access a higher state were could generate gravitational effects that might rival strong forces like electromagnitism over short distances.  One idea is that there could in addition to massless spin-2 gravitons exist massive spin-1 gravitions that could act over short distances and that photons over the correst energy could have resonance with these particles at the right frequency and conditions.  We might call that vector graviton dominace in analogy vector meson dominace where photons of the right energy can interact as vector mesons.  There have been some experiences with superconductors that seemed to show an antigravity effect. This might be generated with easily available energies.

-- Edited by John at 06:58, 2007-04-17

__________________
Andrew


Senior Member

Status: Offline
Posts: 199
Date:
Permalink  

So superconducters might somehow give us artificial gravity? That's strange. :S And what are gravitons?

__________________
GoogleNaut


Guru

Status: Offline
Posts: 606
Date:
Permalink  

I wish I was a bit more capable in the quantum physics aspects, but I think I have a pretty good grasp some of the concepts.

If gravity like inertia has its origins at the quantum vacuum field fluctuation level of things, then the ground state is set by the zero point energy of the interacting fields. Finding a way to suppress these fields reduces their mode density, which will also create a potential well that would appear as negative energy. In fact, it is only negative in the sense that compared to normal ground state it would be below that.

Gravity and inertia (which is proportional to mass) could then be viewed as a phenomelogical property. In this sense, gravity is no longer a true force, but is in a sense the result of induced dipole interactions: very similar in some ways to van der Waal's Forces in chemistry. In fact, it is thought by some that van der Waal's Forces are in fact Casimir Forces acting at a molecular level. And Casimir Forces have their origins in modesuppression of the quantum vacuum. They appear mathematically related.

Inertia can be described as a Lorentz Force interaction of ordinary matter charged particles interacting with the vacuum fields of zero-point 'sea' of interacting virtual charges. It's crazy to think that inertia may infact be intimately related to the vacuum--but that's kind of what the mathematics implies. Atleast, the tiny little bit that has soaked into my brain!

Gravity may be a phenomelogical weak interaction related to the polarizability of the quantum vacuum field dipoles (virtual charged particle pairs.) If you have more mass, then you naturally have more charges, and this relates directly to induced polarizability of the vacuum dipoles, which somehow indirectly couples with other nearby masses in a kind of extended van der Waal's interaction. I can't do the math--wish I could--but it is a very intruiging idea especially in the face of the Standard Model. Gravity has always been an orphaned force--it doesn't quite fit in with the other forces without creating ideas like Supersymmetry, Superstrings, etc. etc. How much would the whole works be simplified if gravity were not actually a real force, but a second order weak interaction of the electromagnetic force (a force that does fit in quite well,) somehow facilitated by the quantum vacuum zero-point field? If Gravity were not actually a unique force, but another second order long range electromagnetic force coupling charges facilitated by the quantum vacuum, then might not some simplification of the Standard Model result?

That is the 64 Trillion dollar question!

Here's another mind blowing idea: what if the whole concept of space-time and three spatial dimensions, and one non-reversible time dimension were phenomologicly the result of the dimensionless chaos of the zero-point field? Going a little further the one direction arrow of time can be nicely explained by the total chaos of the zero point field forming a kind of zero-point 'clock'--this also can nicely explain why there is such a thing as Entropy: it's not too hard to imagine that the chaos of the zero-point field 'leaks out,' and is amplified to influence macroscopic things like rusty Ford pickup trucks, leaky heart valves, and tired brains attempting to grasp the inner workings of the universe! It can even explain why things like Causality seem to be a hardwired prerequisite of the universe. Time is irreversible, because to travel 'back' to a previous time requires arranging the quantum vacuum field fluctuations to a previous 'configuration.' I won't say it's impossible, but it's got to be just about the next thing to impossible that there can be.

Superconductors: there was an interesting paper done a couple of years ago where it was proposed that superconductors may infact act as a gravity wave transducer. A gravity wave impinging on a superconductor will cause electrons in the Cooper pairs to jiggle--and this will induce either a current (if its a wire) or a transient voltage (if it is a plate) to form. These currents or voltages can be detected even at extremely low levels--so in principle atleast, superconductors could be used directly as gravity wave detectors. What makes it a transducer is the fact that inducing a current to flow in the superconducting wire, or voltage applied laterally across a superconducting plate, will cause electrons in Cooper pairs to flow. And this flow of charge, which has mass, will induce a gravity wave to form. Theoretically, one could thus create a gravity wave antenna by exciting a few kilometers of superconducting cable with a radio frequency source.

However, because the charges involved have so little mass, I would imagine that it is probably much easier to create a detector rather than a transmitter. Because the oscilating masses are so small, even a gigahertz transmitter will not transmit more than a few pico pico watts (10^-24 W) of gravitational radiation--of course this is just a WAG (Wild @$$&! Guess) on my part.

Refernces:

you have to buy this paper:

http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel1/20/3041/00092845.pdf?arnumber=92845

This one is free:

http://arxiv.org/PS_cache/gr-qc/pdf/0304/0304026v1.pdf

This is one of the original papers on the subject, also free:

http://arxiv.org/PS_cache/gr-qc/pdf/0204/0204012v3.pdf




-- Edited by GoogleNaut at 17:32, 2007-04-17

__________________
John


Senior Member

Status: Offline
Posts: 366
Date:
Permalink  

What is a graviton?  The gravition is the quanta of the gravitational field just like the photon is the quanta of the electromagnetic field.  The electromagnetic field is a vector field an my the math of quantum theory this results in it being a spin one particle. That is each photon has h/2pi units of angular momentum.  It also has h units of action (h=planck's constant = 6.77 E-27 erg-sec).  The gravitional field is a tensor field and its quanta has a spin or angular momentum of 2 h/2pi and an action of h.  Both of these particle are massless particles.  I hope that helped.

The reference to superconductivity is that some time back an experimenter thought they had found an antigravity effect involving a superconductor.  This remains a controversial result and was put forward as a hypothetical example.

What I was addressing above is that while long range "classical gravity" is due to the spin 2 graviton described above some attempts to create a quantum theory of gravity not only produce the standard graviton but also other particles such as a spin 1 particle.  Here is where I go a little more fiction than science.  What if such a spin 1 particle had a very small mass?  Short range forces such as the weak and strong force are transmitted by massive particles.  The basic strong interaction between nucleons is transmitted by the pi meson.  The greater the mass of an exchange particle the shorter it's effective range.  My though for this additional gravitational particle is that is has a very small but non-zero mass.  This would give it a macroscopic range but on that is still rather short.  The effects of this would ordinary be small so that it hasn't been discovered.  

There is a property of particles that if they have identical quantum numbers then they can interact as the other particle if the energy is about the mass of the second particle.  In this case a photon near the mass of my hypothetical spin 1 particle could interact  as it would, i.e. gravity like.  This could be the explaination of the superconductor levitation results.  If this exists (the is guess work at this point) we might learn to control gravity locally.  This effect might have a completely different coupling constant that spin 2 standard gravity. 

Now what Googlenaut is describing seems like either the Sakharov theory of gravity, an allusion to the Higg's field, or another  novel theory that i'd ran across.  I can't tell which.



-- Edited by John at 03:58, 2007-04-18

__________________
Page 1 of 1  sorted by
 
Quick Reply

Please log in to post quick replies.
NUCLEARSPACE MESSAGE BOARD (ACTIVE) -> SCIENCE FICTION & NUCLEAR POWER -> The Speed of Light: How Fast Can We Go?/autodynam
Tweet this page Post to Digg Post to Del.icio.us


Create your own FREE Forum
Report Abuse 		Powered by ActiveBoard