Faster Than Light Travel

[ponderingturtle]

Er, no. FIrst of all,. there is definitely such velocity; we've even measured "things" (broadly defined) moving at faster than the speed of light.

And there's nothing wrong with a material object travelling faster than the speed of light. Such objects are called tachyons and they're a well-accepted concept in physics. The problem is that such objects can never travel slower than the speed of light; the c barrier cannot be crossed by any method.

This is discounting the problems that having anything travel faster than light means when you change reference frames. If anything is moving faster than light to some reference frame there are reference frames where it is moving infinitely fast, ariving at the same time as they left, and ones where it arives before it left thus breaking the infinity bearier and going even faster.

Now it is not meaningless to have two events seperated by something that would require going faster than light, but different people will be in disagreement over which happened first and what there seperation in time is, and they are all correct.

 

[Ziggurat]

I don't think the sound barrier was ever really seen as an upper limit on speed though. People just went a bit faster - there was no special breakthrough required. The crack of a whip is due to it exceeding the speed of sound.

Actually, it was a barrier. But it was always and only an engineering barrier. That problem wasn't getting that fast (as your examples prove), the problem was creating a plane which would be stable at those speeds since aerodynamics do change once you go supersonic.

 

[ponderingturtle]

Oh I should also point out that useing the right definitions, you can show that everything always moves at the speed of light. This requires you to factor in their rate of travel through time into their rate of travel through space, but it works, you always get C in the end.

 

[maccy]

If they are not breaking things down into hard sf, soft SF and space opera to name a few then they are not being very precise with scifi.

I have had debates about how invasive scifi in relative to fantasy, and it seems that scifi is much more invasive as adding a little scifi element makes a story scifi while adding in a bunch of fantasy elements does not make the story fantasy.

Yes and it's the story that ultimately matters - getting the science right doesn't necessarily make the story better. Focussing too much on the science can ruin the story. Making up pseudoscience and technobabble to give the impression you're talking about something real can also ruin it. The key difference, it seems to me, is that what you're trying to persuade the audience is:

science fiction: this world is essentially like ours but includes technology that allows things that we cannot currently do

fanatsy: this is an imaginary world with magical happenings

If you do doing science fiction, the amount of time you spend detailing or explaining the technology and the degree to which it fits into current science is purely a matter of taste.

There's a bit of fun here, it's called "If all stories were written like science fiction stories"

http://www.shrovetuesdayobserved.com/flight.html

 

[chracatoa]

BTW doesn't FTL travel imply time travel?

 

[ponderingturtle]

Yes and it's the story that ultimately matters - getting the science right doesn't necessarily make the story better. Focussing too much on the science can ruin the story. Making up pseudoscience and technobabble to give the impression you're talking about something real can also ruin it. The key difference, it seems to me, is that what you're trying to persuade the audience is:

science fiction: this world is essentially like ours but includes technology that allows things that we cannot currently do

fanatsy: this is an imaginary world with magical happenings

If you do doing science fiction, the amount of time you spend detailing or explaining the technology and the degree to which it fits into current science is purely a matter of taste.

There's a bit of fun here, it's called "If all stories were written like science fiction stories"

http://www.shrovetuesdayobserved.com/flight.html

The problem with this is that you are discounting the number of very good stories that are based strongly on science and its resolution, look at the I, Robot stories, those are all logic puzzles, real science can make a story much better than it would be otherwise.

Out of curriosity how would you classify say Dune or McAfferies Dragon books? Are they fantasy or scifi? They seem like fantasy with minimal trapings of science in them but always seem to get classed as science fiction.

The existance of a real world does not work, or Narnia would be scifi as it has at least as strong a basis on our world as those ones do.

 

[drkitten]

This is discounting the problems that having anything travel faster than light means when you change reference frames. If anything is moving faster than light to some reference frame there are reference frames where it is moving infinitely fast, ariving at the same time as they left, and ones where it arives before it left thus breaking the infinity bearier and going even faster.

Now it is not meaningless to have two events seperated by something that would require going faster than light, but different people will be in disagreement over which happened first and what there seperation in time is, and they are all correct.

SInce, as you point out, that's not really a problem -- it's just wierd, and Ghu knows that we've got enough wierd stuff already on modern physics -- I suppose you're right that I'm "discounting" it.

You don't even need to involve FTL travel to get that kind of pseudo-paradox. If I see two events happening "simultaneously" (the usual example is that I drop a long, horizontal board), two travellers flashing past at high speed in different directions will see the board drop at an angle, with one end hitting before the other. And, of course, they see opposite ends hitting first.

 

[Ziggurat]

BTW doesn't FTL travel imply time travel?

It does unless you can specify a prefered reference frame. But we can't, so yes, you're correct.

 

[Cuddles]

I'd say the question has been answered pretty well, but I'll just add a couple of things. Firstly, there is no limit to the speed a particle can travel, it is accelerating that is the problem. If something is traveling slower than light, it can never accelerate faster than it since, as you said, it's mass wold tend to infinity and so would require infinite energy. Likewise if it is traveling faster than light. There is no limit to the speed a particle is created travelling at, so photons can travel at c because they are created doing so, and tachyons do not violate any laws because they are created travelling faster than light (if they exist, that is).

In addition, most sci-fi, including Star Trek, never violates these rules. The idea behind warp drives and the like is that they warp space-time in the local vicinity so that the spacecraft is travelling fairly slowly relative to the space it is contained in, but that space is itself moving. These are genuine solutions to the problem, but unfortunately need either exotic matter with negative mass (which is a theoretical idea only, although not neccesarily impossible), or mny time the energy contained in the universe. Wormholes are also really possible, and actually almost certainly exist, but in order to make them large enough and stable enough to pass through they also need silly amounts of energy or exotic matter. There is also debate over whether it could ever be possible to create wormholes, or if the techniques would only allow existing ones to be manipulated.

 

[Badly Shaved Monkey]

If it's a good story, it can require Leprechauns with matter transmitters for all I care.

Say it isn't so. My retirement plans were based entirely on a pot of gold discovery fund.

Damn that financial adviser with his little green hat, twinkling eyes and jaunty tin whistle.

 

[ponderingturtle]

In addition, most sci-fi, including Star Trek, never violates these rules. The idea behind warp drives and the like is that they warp space-time in the local vicinity so that the spacecraft is travelling fairly slowly relative to the space it is contained in, but that space is itself moving. These are genuine solutions to the problem, but unfortunately need either exotic matter with negative mass (which is a theoretical idea only, although not neccesarily impossible), or mny time the energy contained in the universe. Wormholes are also really possible, and actually almost certainly exist, but in order to make them large enough and stable enough to pass through they also need silly amounts of energy or exotic matter. There is also debate over whether it could ever be possible to create wormholes, or if the techniques would only allow existing ones to be manipulated.

That is a false concept, all you need to do is have two events your arival and your departure, if you apear to some observer to travel faster than light, then there are observers who saw you arive before you left.

What they are really doing is creating a universe with a prefered reference frame, and so relative to that is the important issue.

 

[alexi_drago]

And there's nothing wrong with a material object travelling faster than the speed of light. Such objects are called tachyons and they're a well-accepted concept in physics. The problem is that such objects can never travel slower than the speed of light; the c barrier cannot be crossed by any method.

I realise that was in answer to the statement that FTL velocities don't exist, I'm not arguing with your reply but it is my (limited) understanding that tachyons are purely theoretical and not related to any ideas that there are actually FTL particles. I'm just wondering about that as it doesn't seem clear either way in your reply.

 

[I less than three logic]

I realise that was in answer to the statement that FTL velocities don't exist, I'm not arguing with your reply but it is my (limited) understanding that tachyons are purely theoretical and not related to any ideas that there are actually FTL particles. I'm just wondering about that as it doesn't seem clear either way in your reply.

Perhaps I can help out here.

And there's nothing wrong with a material object travelling faster than the speed of light. Such objects are called tachyons and they're a well-accepted concept in physics. The problem is that such objects can never travel slower than the speed of light; the c barrier cannot be crossed by any method.

I don’t think DrK meant to imply tachyons actually existed anywhere beyond a conceptual notion.

 

[alexi_drago]

OK, thanks. I just thought that the word 'concept' could also be used to describe an idea that something is thought to be possible though not yet discovered or proven.

 

[fuelair]

Regarding wormholes, I only have the vaguest undertasnding of space-time and I cannot really understand how a clear metaphor involing folding a sheet of paper can be applied to space-time.

I understans that this is only a mathematical hypothesis, but can anybody suggest a good place to start for getting a hendle on the idea of wormholes?

There is good evidence that space folds under the effects of strong gravity and since paper also folds it is not perfect but is a reasonable analogy.

 

[I less than three logic]

OK, thanks. I just thought that the word 'concept' could also be used to describe an idea that something is thought to be possible though not yet discovered or proven.

Yes, but that is kind of what “purely theoretical” means as well. There isn’t anything to prove the existence of tachyons is impossible, they are consistent with relativity and physics in general as we currently understand it. As long as tachyons are unable to interact with slower-than-light matter/energy in anyway, causality is not broken, but that would also make detecting or proving their existence impossible as well. I suspect tachyons will probably remain as an unfalsifiable, yet theoretically possible concept. Fun for thinking about, but not really useful for anything.

 

[gentlehorse]

I’ve never liked fantasy. I get very put off by elves and dwarves and any sort of Middle-earth fantasy land. I can’t stand The Lord of the Rings.

I can't add much to what's been said about c, but old Russell needs a good swift kick. Then he'll understand.

 

[alexi_drago]

Yes, but that is kind of what “purely theoretical” means as well. There isn’t anything to prove the existence of tachyons is impossible, they are consistent with relativity and physics in general as we currently understand it. As long as tachyons are unable to interact with slower-than-light matter/energy in anyway, causality is not broken, but that would also make detecting or proving their existence impossible as well. I suspect tachyons will probably remain as an unfalsifiable, yet theoretically possible concept. Fun for thinking about, but not really useful for anything.

Ah OK, I was thinking of something along the lines of imaginary numbers or something where the properties of an FTL particle would be useful in some way even though no such thing was theorised to exist.

 

[phildonnia]

Wild-assed speculation begins here.

All arguments concerning the impossibility of matter moving faster than light seem to rely on the fact that matter can't be accelerated to the speed of light and beyond. I don't know what this says about hypothetical matter that might always have been moving faster than light.

Here's an intriguing thought: do faster-than-light inertial reference frames exist? If so, then I think it would appear in these that ordinary slower-than-light matter was moving faster than light. (must do the math sometime...)Since no inertial frame is to be preferred, it might be the case that all matter is already moving faster than light.

 

[jmercer]

Phildonnia - no. The limit is a "hard stop", not only for light, but for all types of energy. Matter doesn't even enter into the equation as matter.

One reason a black hole is "black" is because the gravity gradient is so steep that to escape it's grasp would require travelling (you guessed it!) faster than light.