"Light Barrier" bothers me

[Anthony]

Originally posted by Space Cadet:
Actually, that's not what he said. He said things that have not been found either:
1) Do not exist

or

2) Have not been discovered yet

While this is true, it can easily be exaggerated. For every hypothetical which turns out to be true, there are a very large number which turn out not to be true. 'Maybe tachyons exist' is about as solid a basis for calculation as 'maybe the Easter Bunny exists'.

How do you know that causality and the light barrier are natural laws?

We know the light barrier is a natural law because we've seen it in action: no object with a nonzero rest mass has ever been seen to reach or exceed lightspeed, no matter how much we push. As for causality, we don't certainly know that it exists, but the consequences of it not being true are quite severe.

 

[Space Cadet]

Causality might be local instead of universal, that's what I'm getting at. Is causality is local, then it would be possible to "go back in time" and cause changes to history without affecting your own local history. One interpretation of wave/partical duality is that there are a number of different worldlines for a single particle that also make up a wave. Within a narrow frame of reference different paths of the electron keep on splitting of with the most probably direction of the electron being the path of the wave. The universe keeps on splitting up into many different copies each instant and we perceive onlyone universe with one direction that the electron travels in, but their are many other realities where the electron travels in a different direction. before reality splits in each instant, all possible paths of the electron are represented in a probability wave. If such is the case then causality is not a problem.

As for the light barrier, just because a barrier exists doesn't mean there is nothing on the other side.

 

[Space Cadet]

Originally posted by Heretic Keklas Rekobah:
A "better" FTL communications system would be one that actually works.

Tachyons do not exist. Therefore, Tachyon-based FTL comms do not exist.

That is a rather God-like denial.

Originally posted by Heretic Keklas Rekobah:
Your entire concept simply will not work!

Face it, Space-C, you're up against real degreed professionals who know more about this subject than you do. Any "handwave" fantasy you might try will be seen through and debunked almost immediately.

But how much do you know about this subject? Isn't it possible that you yourself do not know everything? Science Fiction is allowing to the possibilities that you do not know about. What you seem to be saying is that if you don't know everything about physics, you might as well be playing Star Wars. If you typ to make the science a little more believable, you'll have scientists trying to debunk you and telling you to go back to Star Wars, or even worse SpellJammer. So are you saying we all should be playing Spelljammer?

Originally posted by Heretic Keklas Rekobah:
Suggestion: Admit that you have minimal knowledge of physics, and move on. Either that, or apply some of that imagination to writing fiction; including Traveller adventures.

What's more plausible Jump Drives or Tachyons?
How about reactionless maneuver drives or tachyon drives? At least a tachyon drive is a reaction drive while a maneuver drive is reactionless.

Originally posted by Heretic Keklas Rekobah:
With a fantasy life like yours, you could really succeed as an SF author, as long as you do not take yourself so seriously.

As long as my knowledge is greater than the readers, he can't tell the difference. Now with a mass audience that watches Star Wars and Star Trek, they aren't going to quibble about whether Tachyons are possible.

 

[TheEngineer]

Hi !

I really like SC's question, whats more plausible

For jump drives and tachyons, I would note, that if jumpdrives could be somehow related to wormholes, at least both variants have in common, that they are spin-offs or solutions of regular and frequently used physical equotions.
Behind many of similar spin-offs lies the highly philisophical question, if mathematics itself is a representations of nature in whole, or just a tool to humbly model some aspects of it.
So, there are quite a few people out there, who are so very happy about any solution of a complex math/physics problem, that they optimistically take it as a hint for something real....

I would not step to say, that one is more plausible than another one.
And again the general hint: discussion the realism of fictional things is usually not productive.

Anyway I have to admit, that playing around with tachyons and black holes is a bit out my range

Regards,

TE

 

[Anthony]

Originally posted by Space Cadet:
What's more plausible Jump Drives or Tachyons?
How about reactionless maneuver drives or tachyon drives? At least a tachyon drive is a reaction drive while a maneuver drive is reactionless.

There is no meaningful difference in plausibility between jump drives, tachyons, and reactionless drives.

 

[Space Cadet]

Einstein's equations allow for Tachyons, there is nothing in them that allow for a reactionless drive. There being no reason to include Tachyons in your current model of the Universe is not proof of their nonexistance. The lack of their detection is not proof of their non-existance either. Remember 90% of the mass in the Universe goes undetected, this is known as dark matter. How can you be sure that a portion of this dark matter is not tachyons? There is evidence for dark matter, many stars in the Milky Way rotate too fast for the visible mass in the Galaxy to hold them in orbit, also if you assume non-luminous non-dark matter, there'd have to be enough of it to obscure vision of the more distance stars to a degree that is not evident. Dark matter interacts with normal matter only gravitationally, so perhaps there are tachyons except that they are all dark in relation to normal matter. Again Science fiction allows for these possibilities, if you discount them all, you have no science fiction and no Traveller.

Unlike you Anthony, I believe there are degrees of plausibility. I think the existance of tachyons is more plausible than the existance of God for example. One can also create a Space Opera setting that's more plausible than Star Wars without having to eliminate FTL Drives and FTL communications, but for you it seems its either Spelljammer or superhard Einsteinian space that doesn't allow for anything we don't know about today.

I'd rate a plausibility scale as such

10: Einsteininan Space/Fission - no undiscovered laws of physics or unknown particles, practically this means travel to nearby stars takes thousands of years. Star ship crews are all alone in the universe. There are no for profit star ship operations. Star ships are sent out either by governments of very generous charitable institutions with alot of money. There is no suspended animation and fusion is practical only in stars, so starships use fission drives. Enough nuclear fuel is carried to power a generation ship for the entire duration of the journey. Zero growth birth policies are stricly enforced to prevent over population of the Ark ship.

9: Fusion becomes a practical source of energy, now instead of taking thousands of years, interstellar travel only takes centuries, still generation ships are called for, there is no suspended animation. Starships are still pretty much alone in the universe, those who have sent them can hardly expect to have the patience to support the mission for such long time horizons. Basically those who paid for the mission consider the investment to be a write off or a charitable work. The starship crews hyave dedicated themselves and their children to this mission and don't expect ever to go home. No private enterprise, no investors, and no banks will ever loan out money to such a long mission with enourmous time horizons.

8: Fusion with suspended animation: As above except suspended animation becomes available. Most scientists today say this will never happen reliably due to ice crystalization destroying cells. But in this universe the same crews at the launch of the mission are around at the end to see to its completion. Sleeper ships are smaller than Ark ships, they don't have to be as large as O'Neill colonies and are thus cheaper

7: Beamed Propulsion: A form of beamed propulsion becomes available with very precise targetting capabilities, this beam might be made of pellets, light, or mini light sails. This is a non-rocket form of propulsion so reaction mass is conserved. Travel times to the nearest stars are reduced to a matter of decades, the mission time does take up most of a human lifetime though.

6: Antimatter Propulsion: relatavistic velocities become available when large scale production of antimatter can cheaply be produced and stored in multi-staged rockets that can travel near the speed of light. Acceleration is low as its hard to get reaction chambers that can handle the radiation released from the energetic matter/antimatter reactions within the magnetic nossil.

5: Antimatter paired with one gee acceleration: most places withint 10,000 light years of Earth can be reached within one relativistic human lifetime without resort to suspended animation. Antimatter is dirt cheap and its hard to believe that a society that could command such huge energies hasn't destroyed itself in warfare or a terrorist act a long time ago.

4: Wormholes are created: paired with an antimatter rocket of a mass driver, they are accelerated to near the speed of light. Some form of negative energy is required to hold these wormholes open. Chronology protection is in effect, so wormholes can only be moved outward, if they are moved back in to be used as time machines they explode

3: Wormhole Time Machines: Wormholes can be used as time machines, they can't go back to a time before they are created as Einsteinian laws are still in effect, but their are many different universes and a different future is reached with each Wormhole that is sent out. Scientific advances are rather arbitrary as communication and equipment regualrly arrives from the future and its not clear who invented them as the future got their stuff from their own wormholes to the future. Scientists and engineers are out of work except at the very far end and futuremost end of the wormhole network. There is some universe in the very distant future that did all the inventing.

2: Wormholes, Warp Drives, and Time machines: In this universe time travel in our historical past is possible of course many timelines prevent the occurance of paradoxes.

1: ESP, telepathy, psionic powers, UFOs. Everything but magical spell casting is allowed.

0: Magic is allowed and has always been around, its just that a giant government conspiracy covers the whole thing up.

 

[Anthony]

Originally posted by Space Cadet:
Einstein's equations allow for Tachyons, there is nothing in them that allow for a reactionless drive.

Actually, there are various constructed metrics that allow for reactionless drives. They just involve impossible materials such as negative energy densities (negative energy densities are a convenient way to group impossibilities, because they're also necessary for just about all FTL drives, and for that matter tachyons are likely to have negative energy...).

Unlike you Anthony, I believe there are degrees of plausibility. I think the existance of tachyons is more plausible than the existance of God for example.

There are degrees of plausibility. Below a certain point, however, it really doesn't matter.

 

[Space Cadet]

Originally posted by Anthony:
</font><blockquote>quote:</font><hr />Originally posted by Space Cadet:
Einstein's equations allow for Tachyons, there is nothing in them that allow for a reactionless drive.

Actually, there are various constructed metrics that allow for reactionless drives. They just involve impossible materials such as negative energy densities (negative energy densities are a convenient way to group impossibilities, because they're also necessary for just about all FTL drives, and for that matter tachyons are likely to have negative energy...).</font>[/QUOTE]If the energy of a vacuum averages zero, that does that mean?

If negative energy is impossible, it is also impossible for a black hole to shrink or to radiate Hawking radiation.

Its funny that I get all this modern physics/quantum mechanics and then I encounter these expert opinions that act as if all particles in the Universe are like billiard balls. For example, the simplest atom is a hydrogen atom, a classical interpretation of an atom is that of a nice round proton with a nice round electron in orbit around it.

Black hole shrinkage is based on the premise that space is filled with virtual partical pairs.

Funny how I take one implication of quantum mechanics only to have Anthony say, "no you can't do that!"

I say, "Well black holes can shrink."

and Anthony would probably say, "well blach holes are special, negative energy exists for them so they can shrink, but negative energy does not exist for you and I so we can make tachyons, or build time machines."

That is the problem with quantum physics or so it seems to me. When you study classical mechanics, you can apply it down the line consistantly and logically, but when you apply quantum mechanics, you have to ask an expert for each instance, and if he figures that if it is something "billiard ball partical obeying classical rules, cannot do, then it must be impossible."

It would seem that Traveller starships would not need fusion reactors or to fuel at gas giants, as they only have to extract negative energy from the vacuum while spewing out positive matter and energy as a waste product.

One can make a rather neat vacuum energy rocket this way.

Originally posted by Anthony:

</font><blockquote>quote:</font><hr />Unlike you Anthony, I believe there are degrees of plausibility. I think the existance of tachyons is more plausible than the existance of God for example.

There are degrees of plausibility. Below a certain point, however, it really doesn't matter. </font>[/QUOTE]The question is where is that point?
If I'm going to have time machines in my campaign, I'd like them to obey certain rules consistantly. By combining a wormhole with a warp drive, one can make a time machine. You'd need the Wormhole to anchor the time machine to a base reality whose history does not change, and you need the warp drive to exceed the speed of light. The warp bubble encloses one end of the wormhole, while the other end is left on Earth. The Warp drive creates a pseudo-motion that accelerates the ship beyond the speed of light, this would be equivalent to parts of the universe that are receding from us at faster than the speed of light due to spacial expansion. Because there is a red shift, there is still time dialation. The Warp ship can go out some distance and return to Earth some time before it left, then the chrononaut can step through the wormhole and explore Earth's past, or at least an alternate history of the past with time travellers in it. The flow of goods and people through the wormhole must roughly balance in both directions over time, otherwise the imbalances cause the wormhole to collapse. For instance if a time traveller is going to step into the past through a wormhole, it would be a good I deal to pump some water through pipes equivalent in mass to the time traveller back into the future. The limiting factor in such a time travel campaign is that wormholes aren't cheap to make.

 

[TheEngineer]

Hi !

Negative energy often is a synomym for kind of antimatter and is called negative because of the mathematical appearance as negative values in related formulas.
So, when talking about black holes and negative energy, its about particles and anti-particles.
The physical wonder of the event horizon is able to split a former virtual particle pair and kick one part into actual life.

Anyway, IMHO the hypothetical existance of things like tachyons, or even wormholes and other stuff , which is at least "scientifically" discussed is only one aspect.
The other aspect is to be able to use that in a practical way. Thats a job for fiction, but in a range where plausibility is not so significant

BTW, setting up a somehow controllable (for the referee) wormhole and time machine using universe, is perhaps quite a task

Regards,

TE

 

[Space Cadet]

You know in the old days when the World wasn't fully explored, there were areas on the map labeled "Terra Incognita" and it was in those places where the most fantastic tales could be woven. One example was Gullivers Travels by Jonathan Swift, In Gulliver's Travels, Jonathan Swift populates these areas with fantastic places and cultures, one is an island of little people standing 1 inch tall on an island of perfectly proportioned humans, animals and plants, effectively making Gulliver a giant by comparison to give you an example. Since during Gulliver's time, there were places labled "Terra Incognita" he had places to set his adventure that had some plausibility since no one had explored those area as of yet, it was an early form of science fiction.

The idea that there is some class of particles that always travel faster than the speed of light is another "Terra Incognita", it enables certain stories to happen which otherwise could not happen if we were stuck with slower than light speeds. There is no reason to believe that there are tachyons, but the existance of such eases the telling of the story. Now we know that 90% of the Universe consists of dark matter that cannot be detected very easily, except perhaps by direct collisions with atomic nuclei or gravitational interaction. Tachyons might be a type of matter that we call "dark" because they are so hard to detect, that is our "Terra Incognita", we don't know that they are out there, but this is where they plausibly could be.

If we make the assumption that tachyons are a form of dark matter, we then get an idea of what a tachyon detector would look like, it would look similar to a detector for neutrinos, and neutrinos move very fast, often very close to the speed of light. You don't get Chekov Radiation when a Tachyon whizzes by because photons don't interact with them, at least the kind of photons we can detect. There might be another sort of photon out there that they do interact with, these would be called negative energy photons. Negative energy photons don't interact normally with ordinary matter; to a negative energy photon, ordinary matter such as protons, and electrons are dark, while tachyons interact with the dark photons or negative energy photons. Tachyons have counterparts to normal matter. there is a tachyon-electron which orbits a tachyon-proton in orbital shells in tachyon atoms. These atoms go right through normal matter at FTL speeds often without displacing a single atom. Atomic nuclei are very hard to hit, but every so often you have a collision which sets off the detector, so tachyon detectors would often be buried deep under ground, to remove the interferrence from cosmic rays and other types or radiation so tachyons can be detected, while a tachyon emmitter would be a sort of nuclear reactor/particle accelerator that engineers collision between atons, and some of the by products are neutrinos, and some of those neutrinos are of the Tachyon variety. The details of how to direct or emit tachyons are somewhat murky, but this would give some idea of how it would be done, and how it would be incorporated into a campaign universe.

 

[Anthony]

Originally posted by Space Cadet:
If the energy of a vacuum averages zero, that does that mean?

That it averages zero?

If negative energy is impossible, it is also impossible for a black hole to shrink or to radiate Hawking radiation.

Well, we haven't detected Hawking radiation, but Hawking radiation doesn't involves negative energy densities -- antimatter is not negative energy.

There are some reasonable arguments that certain things in Quantum Mechanics do resemble negative energy densities. So far, there doesn't seem to be any method of making use of that fact, though various people have tried to do things with Zero Point Energy.

 

[travlar]

Originally posted by Anthony:
</font><blockquote>quote:</font><hr />Originally posted by Space Cadet:
If the energy of a vacuum averages zero, that does that mean?

That it averages zero?</font>[/QUOTE]Which means that some of it has negative energy.

 

[Space Cadet]

Originally posted by Anthony:
</font><blockquote>quote:</font><hr />Originally posted by Space Cadet:
If the energy of a vacuum averages zero, that does that mean?

That it averages zero?

If negative energy is impossible, it is also impossible for a black hole to shrink or to radiate Hawking radiation.

Well, we haven't detected Hawking radiation, but Hawking radiation doesn't involves negative energy densities -- antimatter is not negative energy.

There are some reasonable arguments that certain things in Quantum Mechanics do resemble negative energy densities. So far, there doesn't seem to be any method of making use of that fact, though various people have tried to do things with Zero Point Energy. </font>[/QUOTE]I never said antimatter was a form of negative energy, someone else did. When antimatter comes in contact with matter, the result is alot of positive energy. Matter and antimatter are forms of congealed energy. Much like a solid is a state of matter, matter is a state of energy, it is just one state of energy, the other state is the photonic form that travels at the speed of light.

You say Hawking Radiation doesn't involve negative energy densities? Well if you start with the axiom that nothing can escape from the event horizin of a black hole, what's the only way to reduce its mass?

Well, drop some negative energy of mass into it. Since nothing can be taken away, the only thing you can do is to add a negative. Where Hawking's theory loses me is why should a black hole attract more of the negative component of a virtual particle pair than the positive component? I would thing statistically there would be a 50% chance of the negative particle falling into the event horizion and a 50% chance of the positive particle doing the same. All and all with everything else being the same, the virtual particle pairs should not add or substract to a black hole's mass no matter how small the black hole is. I wonder, if Stephen Hawking is so smart, how could have overlooked the possibility that the pasitive component of a virtual particle pair might fall into the event horizion of a black hole leaving a negative mass/energy particle as real and having it radiated out as "negative Hawking" radiation. I think with 50% positive and 50% negative, the particles should just nullifie each other as they radiate away from the black hole leaving a net average radiation of zero. But I guess one is not supposed to think indipendently of these expert Physicists, since it can be assumed that they know much more than I do, so I take their word for it and resort to the agument from authority, "If Stephen Hawking says its so, it must be true." I remember my Modern Physics courses, alot of equations were thrown on the board, I was totally lost as I was just learning the fundamentals of Calculus at the time. Taking a bunch of course at the same time really did me a disservice. Common sense doesn't apply to Modern Physics, equations are just thrown on the board and its supposed to make sense. Well when you tell me that something can be both a particle and a wave and that a single photon can travel along two paths at once and cancel itself out in a dual slit experiment, it doesn't make much sense to me, but as experimental evidence seems to bear it out, I'm willing to give time travel my open minded consideration.

Take the double slit experiment, if a single photon can travel two paths at once, then one interpretation is that there are two universe so close together that they are indistinguaishable and that in once universe the photon takes one path and in the other universe the photon follows another path; as the tow universes are not far enough apart yet, the two versions of the same photon merge and cancel out. The photons hit the photo receptor along certain patters where the wave lengths of the single photons don't cancel in such places as their amplitudes aren't opposed. But there is just one photon going thorugh one slit at a time, their dispersal pattern should be random according to common sense as common sense implies that if only one photon travels at a time, their should be no other photon for it to cancel with except itself and how could it cancel itself? if there are many version of history and we only experience only one of an infinite variety of possible events, then there is no problem with casuality or time travel. the Universe is weird enough and a visitor from the future would only be just another drop in the bucket, although at large scales the Universe does seem to behave clasically.

 

[Space Cadet]

Just thought of something. If Tachyons exist, then a black hole might radiate tachyons if they are produced inside of it, everything else couldn't escape, but tachyons could since they can exceed the escape velocity of the black hole.

 

[veltyen]

Just thought of something. If Tachyons exist, then a black hole might radiate tachyons if they are produced inside of it, everything else couldn't escape, but tachyons could since they can exceed the escape velocity of the black hole.

Two things:

1: You don't need to have an escape velocity faster then the event horizon, you can tunnel your way out. In general you cannot escape coherently, but you can still escape.

2: The event horizon for tachyons would still exist, it would just be further into a black hole. A working tachyon telescope would be one way to reliably see slightly further into a black hole, but (probably) wouldn't be able to see the centre.

 

[TheEngineer]

As I ("someone else") said, "negative energy" is sometimes called that way, because mathemtical descriptions like Dirac theory brings some solutions with negative energy levels = the sign is negative. The energy is NOT negative.
The negative sign is physically interpretated as the representation of antimatter.

Take a look here:
http://en.wikipedia.org/wiki/Dirac_equation

 

[Anthony]

Originally posted by TheEngineer:
As I ("someone else") said, "negative energy" is sometimes called that way, because mathemtical descriptions like Dirac theory brings some solutions with negative energy levels = the sign is negative. The energy is NOT negative.

Um, no, 'negative energy density' does in fact mean negative energy. It's traditionally called Exotic Matter (that page also has a useful discussion of tachyons).

 

[TheEngineer]

Sorry, but this article appears a bit strange to me

The concepts are perhaps related, but while the explanations of "negative energy" in context of the Dirac equotions appear quite plausible to me, the things about hypothetical "negative energy densities" are still a bit vague (so are the articles).

I guess the "negative energy" I refered to is maybe different from the one you talk about.

 

[Space Cadet]

I think you are confusiong negative energy with negative electric charges, an antimatter hydrogen atom consists of an antiproton with a negative charge and a cloud of 1 positron with a positive charge. The term negative and positive charges are related to Franklin's experimentation with electricity, he supposed that electricity flowed in one direction in a circuit when it actually flowed in the opposite direction, because of that electrons were arbitrarilly assigned a "negative" charge.

 

[TheEngineer]

No,no,no

Its not about an electrical charge here.
Its just as described in my last wiki link.
Anti-particles are mathematically represented in the Dirac-equations as particles with negative energy.
Anyway the Dirac model describes anti particles via "missing" energy levels. Thats why the energy term is negative. In fact its about regular "positiv" energy here.

The "negative energy" or "negative energy density" you talk about, is indeed a completely different and highly hypothetical concept and comes along with exotic matter, warp drives and wormhole construction.
Now, thats not my business