Favourite faster than light technology

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Re: Favourite faster than light technology

Postby Pez Dispens3r » Sun Feb 13, 2011 1:10 pm UTC

HiFranc wrote:It workes by stretching/compressing the space that the craft is flying through to so that the local value of c is higher.

Normally methods that expand-contract space don't locally affect c. How does yours do so?
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Re: Favourite faster than light technology

Postby HiFranc » Sun Feb 13, 2011 2:53 pm UTC

Pez Dispens3r wrote:
HiFranc wrote:It workes by stretching/compressing the space that the craft is flying through to so that the local value of c is higher.

Normally methods that expand-contract space don't locally affect c. How does yours do so?


I was thinking of doing the stretching/compressing along the time axis.
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Re: Favourite faster than light technology

Postby charonme » Tue Mar 08, 2011 1:28 pm UTC

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Re: Favourite faster than light technology

Postby SlyReaper » Tue Mar 08, 2011 1:38 pm UTC

Time machine.

Go back to a few seconds after the big bang, move the machine a little bit to the right, and wind time forward again to the present day. You'll now be many light years from where you started, due to expansion of the universe.
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Re: Favourite faster than light technology

Postby Cobramaster » Thu Mar 10, 2011 4:29 am UTC

Also not die in the still very dense energy and mass you plopped down into.
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Re: Favourite faster than light technology

Postby zmatt » Fri Mar 11, 2011 2:35 pm UTC

I don't always travel faster than light. But when I do, I use the Alcubierre drive.
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Re: Favourite faster than light technology

Postby sikyon » Fri Mar 18, 2011 4:03 pm UTC

First you shrink the distance between you and your destination. The expansion and contraction of space is not limited to the speed of light, only movement through space is. So you find a way to locally shrink space between you and your destination, move to it and rexpand the space. Anything that gets in your way probably gets obliterated though.
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Re: Favourite faster than light technology

Postby nitePhyyre » Fri Mar 18, 2011 9:30 pm UTC

sikyon wrote:First you shrink the distance between you and your destination. The expansion and contraction of space is not limited to the speed of light, only movement through space is. So you find a way to locally shrink space between you and your destination, move to it and rexpand the space. Anything that gets in your way probably gets obliterated though.
This is called an 'Alcubierre drive'.
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Re: Favourite faster than light technology

Postby zmatt » Sun Mar 20, 2011 8:56 pm UTC

Also known as a warp drive to laymen. I think it's funny how Star Trek thought of it before physicists figured out it may be possible.
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Re: Favourite faster than light technology

Postby HiFranc » Sun Mar 20, 2011 9:43 pm UTC

zmatt wrote:Also known as a warp drive to laymen. I think it's funny how Star Trek thought of it before physicists figured out it may be possible.


Star Trek's Warp Drive is slightly different. It turns the fabric of space time into, essential, a wave and starships into high-tech surf boards. The idea is that, when surfing, your relative velocity to a point on the wave is less than you real speed and, as it's your relative velocity to space-time that is important, you get around the limitations of Relativity.
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Re: Favourite faster than light technology

Postby Idhan » Mon Mar 21, 2011 1:25 am UTC

Doesn't the Star Trek warp drive involve the use of subspace, which is somewhat different than the modification of regular 4D space-time used in the Alcubierre drive?
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Re: Favourite faster than light technology

Postby Cobramaster » Mon Mar 21, 2011 1:29 am UTC

Well that is what would happen in an Alculbierre Drive also, if you think of space as a flat membrane you compress and raise the region behind you and compress and raise the area ahead and ride the wave forwards.
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Re: Favourite faster than light technology

Postby Technical Ben » Mon Mar 21, 2011 9:48 am UTC

zmatt wrote:Also known as a warp drive to laymen. I think it's funny how Star Trek thought of it before physicists figured out it may be possible.

Saying it "may be possible" is like saying unicorns may be possible. ;)
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Re: Favourite faster than light technology

Postby Cobramaster » Mon Mar 21, 2011 11:50 pm UTC

Well as far as we can tell its not a question of if you could generate the field its just can you generate the energy required to do so.
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Re: Favourite faster than light technology

Postby zmatt » Tue Mar 22, 2011 8:37 pm UTC

And what process you would use to go about generating such field. As far as i can tell, theoretically it would work. it's just a question of how many centuries of technological progress do we need to make one.
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Re: Favourite faster than light technology

Postby Diadem » Wed Mar 23, 2011 12:34 am UTC

Cobramaster wrote:Well as far as we can tell its not a question of if you could generate the field its just can you generate the energy required to do so.

zmatt wrote:And what process you would use to go about generating such field. As far as i can tell, theoretically it would work. it's just a question of how many centuries of technological progress do we need to make one.

No. No no no. It can not work. Not even in theory.

I'm willing to grant that 'requires 10 trillion times the energy content of the universe' is a mere engineering problem. But there are plenty of there theoretical problems with Alcubierre drives. One, you need exotic matter for it (this is physicist speak for 'particles that I made up and do not actually exist). Two, you need an Alcubierre drive to build an Alcubierre drive. Three, once started, an alcubierre spaceship could not stop or steer. People inside would be doomed to stay inside forever. Four, Hawking radiation would instantly destroy anyone inside the bubble as soon as the Alcubierre spaceship went FTL, and collapse the bubble. I could go on for a while. Alcubierre drives do not work. Not in practise, not in theory.

FTL is impossible. Theoretically impossible. And it will remain that way forever. Most people do not know this, but the term of choice physicists use to decribe the fact that nothing can travel faster than the speed of light. is 'causality'. And that is no figure of speech. Causality really does depend on FTL being impossible. Building an FTL drive would be equivalent to proving that 1 is 2.

I like SF. And I don't mind SF authors using FTL in their books. But please do not think for a second that it might actually be remotely possible.
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Re: Favourite faster than light technology

Postby zmatt » Wed Mar 23, 2011 12:26 pm UTC

Diadem wrote:
Cobramaster wrote:Well as far as we can tell its not a question of if you could generate the field its just can you generate the energy required to do so.

zmatt wrote:And what process you would use to go about generating such field. As far as i can tell, theoretically it would work. it's just a question of how many centuries of technological progress do we need to make one.

No. No no no. It can not work. Not even in theory.

I'm willing to grant that 'requires 10 trillion times the energy content of the universe' is a mere engineering problem. But there are plenty of there theoretical problems with Alcubierre drives. One, you need exotic matter for it (this is physicist speak for 'particles that I made up and do not actually exist). Two, you need an Alcubierre drive to build an Alcubierre drive. Three, once started, an alcubierre spaceship could not stop or steer. People inside would be doomed to stay inside forever. Four, Hawking radiation would instantly destroy anyone inside the bubble as soon as the Alcubierre spaceship went FTL, and collapse the bubble. I could go on for a while. Alcubierre drives do not work. Not in practise, not in theory.

FTL is impossible. Theoretically impossible. And it will remain that way forever. Most people do not know this, but the term of choice physicists use to decribe the fact that nothing can travel faster than the speed of light. is 'causality'. And that is no figure of speech. Causality really does depend on FTL being impossible. Building an FTL drive would be equivalent to proving that 1 is 2.

I like SF. And I don't mind SF authors using FTL in their books. But please do not think for a second that it might actually be remotely possible.


Columbus, the Wright brothers and Chuck Yeager would like to have a word with you.

I've read the wikipedia article as well on Alcubierre drives and I am familiar with the issues you are citing, but most of them are more conjecture than the drive itself and mostly involve physicists saying "well this may happen guys". Things like not being able to steer it for example, assuming that things would operate the same way within a bubble as they do in this office. In the 1930's physicists said that trying to break the speed of sound would have the same problem, you would approach infinite energy and the shockwave form the sonic boom, if you could get that fast would blow the plane to smithereens. In truth we simply had to find a different power plant and develop a different wing. I also think that any attempt to calculate the energy requirements are dubious at best because we have no idea how to bend spacetime, so if we don't know how to do it then how can we know how much energy it needs. That is akin to not knowing how a door knob works, so assuming that you have to ram doors down to go through them. Well it isn't practical guys, because the energy requirements would soon wear you down and you would be too tired.

I would leave the engineering to the engineers. One reason I have a hard time taking anything physicists say that lacks direct proof is because they have a history of saying really dumb things that are based entirely on math and mental problems. Breaking their own maxim about things happening much differently then what you expect in physicists. Just because the math says it can't be done is no indication that it can't I think. We have run into that scenario enough times at this point to know, that sometimes the math is just wrong.

The Alcubierre drive to me seems to be a very clever way to get around a big problem. And the future of human civilization in part depends on whether or not it or something like it is impossible. Radiation is an engineering problem, controlability is an engineering problem. Knowing that we can do it, well that gives us a reason to try. And hell even if we hadn't thought of it, we probably would try anyways. And people who try have a habit of proving PhDs wrong.
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Re: Favourite faster than light technology

Postby Technical Ben » Wed Mar 23, 2011 1:11 pm UTC

Cobramaster wrote:Well as far as we can tell its not a question of if you could generate the field its just can you generate the energy required to do so.

Um. AFAIK there is nothing that can bend space in that way, even with the energy.
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Oh, zmatt. It's not an engineering problem. And example would be accelerating to light speed = infinite energy. Infinite. No amount of engendering can compensate for that. To go faster needs greater than infinite energy.
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Re: Favourite faster than light technology

Postby MrConor » Wed Mar 23, 2011 1:31 pm UTC

zmatt wrote:I would leave the engineering to the engineers. One reason I have a hard time taking anything physicists say that lacks direct proof is because they have a history of saying really dumb things that are based entirely on math and mental problems. Breaking their own maxim about things happening much differently then what you expect in physicists. Just because the math says it can't be done is no indication that it can't I think. We have run into that scenario enough times at this point to know, that sometimes the math is just wrong.


Ironically...

Wikipedia wrote:The Alcubierre drive, also known as the Alcubierre metric, is a speculative mathematical model of a spacetime exhibiting features reminiscent of the fictional "warp drive" from Star Trek, which can travel "faster than light", although not in a local sense.
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Re: Favourite faster than light technology

Postby Diadem » Wed Mar 23, 2011 2:00 pm UTC

zmatt wrote:Columbus, the Wright brothers and Chuck Yeager would like to have a word with you.

Columbus actually was wrong. Just very lucky. Noone ever claimed that was the Wright Brothers did was theoretically impossible. Would be strange too, since we've been flying since 1783. Noone ever claimed that faster-than-sound was theoreticaly impossible either.

In the 1930's physicists said that trying to break the speed of sound would have the same problem, you would approach infinite energy and the shockwave form the sonic boom, if you could get that fast would blow the plane to smithereens. In truth we simply had to find a different power plant and develop a different wing.

They said that going faster-than-sound would create a shockwave that would destroy the plane. They were right. We had to design a new kind of plane to be able to do it. But no scientist ever claimed that faster than sound would be impossible. You're strawmanning.

I also think that any attempt to calculate the energy requirements are dubious at best because we have no idea how to bend spacetime, so if we don't know how to do it then how can we know how much energy it needs. That is akin to not knowing how a door knob works, so assuming that you have to ram doors down to go through them. Well it isn't practical guys, because the energy requirements would soon wear you down and you would be too tired.

Fine. You still need matter with a negative energy content (hint: No such matter exists) and break causality (hint: This is impossible). You may want to let the latter point sink in a bit more. Any form of FTL travel breaks causality.

I would leave the engineering to the engineers. One reason I have a hard time taking anything physicists say that lacks direct proof

There is direct proof. You just chose to ignore it.

is because they have a history of saying really dumb things that are based entirely on math and mental problems.

So give me an example. I'm sure you can find examples of individual scientists claiming something very dumb. But you are going against one of the most fundamental scientific understandings of our time. Show me one example of a major scientific theory which the majority of scientists thought irrefutible that was proven to be wrong.
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Re: Favourite faster than light technology

Postby zmatt » Wed Mar 23, 2011 2:44 pm UTC

Diadem wrote:Columbus actually was wrong. Just very lucky. Noone ever claimed that was the Wright Brothers did was theoretically impossible. Would be strange too, since we've been flying since 1783. Noone ever claimed that faster-than-sound was theoreticaly impossible either.


The fact he was wrong is beside the point, the fact that he tried anyways is my point. And no a lot of people did in fact say super sonic flight was impossible. There are court martial transcripts from the 1920's (or was it 30's) where Mitchell predicted and was right that we would have supersonic and intercontinental flight, and the "experts" the Army Air Corps brought said he was nuts.

Diadem wrote:They said that going faster-than-sound would create a shockwave that would destroy the plane. They were right. We had to design a new kind of plane to be able to do it. But no scientist ever claimed that faster than sound would be impossible. You're strawmanning.


Actually it didn't. there is evidence that on more than one occasion late in WW2 planes in a dive approached or broke the sound barrier. The problem in practice was never disintegration, it was controlling the aircraft. The control surfaces reacted differently in trans-and supersonic conditions and when they were working on the Bell X-1 they have to design a new way to control pitch for this very reason.

Diadem wrote:Fine. You still need matter with a negative energy content (hint: No such matter exists) and break causality (hint: This is impossible). You may want to let the latter point sink in a bit more. Any form of FTL travel breaks causality.


I think you are missing my point. You are saying it's impossible don't talk about it. I'm saying we should because the benefits here far outweigh the negatives. And even if it can't be done, the technology fallout would be great. It certainly isn't something we could do today if it were possible. But as a long term goal for spaceflight it would be nice. Things like "mass" production of antimatter, more advanced spacecraft. A better understanding of the physics involved through experience. etc.

Diadem wrote:There is direct proof. You just chose to ignore it.


Oh so you have tried it? Cool. what happened when you tried to bend spacetime?

Diadem wrote:So give me an example. I'm sure you can find examples of individual scientists claiming something very dumb. But you are going against one of the most fundamental scientific understandings of our time. Show me one example of a major scientific theory which the majority of scientists thought irrefutible that was proven to be wrong.


You really don't know much about history do you? Off the top of my head, plate tectonics. For the longest time it was laughed at by the scientific community, the previous paradigm being thought of as irrefutable. It took awhile for it to be accepted. There are more, and if i can find the time or bothered to look them up for you i will. Point being we are all humans here and imperfect. We will let our arrogance get the best of us even if we try to hold true to the ideals of science nobody is perfect. That and personally I think the best way to find something out is to try. You really wont know is X is possible unless you try to do it. It is generally agreed that the biggest crutch to physics nowadays is our technology, and how it is lagging behind theory. If we were more advanced we could better test these things, like faster than light travel. Right now the best we can do in the real world is observe relativistic effects on small objects in particle accelerators. Its a start.
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Re: Favourite faster than light technology

Postby Robert'); DROP TABLE *; » Wed Mar 23, 2011 5:18 pm UTC

Diadem wrote:FTL is impossible. Theoretically impossible. And it will remain that way forever. Most people do not know this, but the term of choice physicists use to decribe the fact that nothing can travel faster than the speed of light. is 'causality'. And that is no figure of speech. Causality really does depend on FTL being impossible. Building an FTL drive would be equivalent to proving that 1 is 2.

AFAIK, causality depends on the non-existence of a flawless way to send signals FTL, which isn't the same thing as "no FTL ever." Einstein allows FTL mechanisms that work only in circumstances that don't cause a paradox.
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Re: Favourite faster than light technology

Postby Antimony-120 » Wed Mar 23, 2011 6:50 pm UTC

Robert'); DROP TABLE *; wrote:
Diadem wrote:FTL is impossible. Theoretically impossible. And it will remain that way forever. Most people do not know this, but the term of choice physicists use to decribe the fact that nothing can travel faster than the speed of light. is 'causality'. And that is no figure of speech. Causality really does depend on FTL being impossible. Building an FTL drive would be equivalent to proving that 1 is 2.

AFAIK, causality depends on the non-existence of a flawless way to send signals FTL, which isn't the same thing as "no FTL ever." Einstein allows FTL mechanisms that work only in circumstances that don't cause a paradox.


And, perhaps more importantly, GR is a local theory, which is to say that the restriction is that you can't go faster than the speed of light as measured by you. Various warp drives cause no problems for Causality, since they the local speed of light is never violated, even if the speed of light as measured by a distant observer is.

So give me an example. I'm sure you can find examples of individual scientists claiming something very dumb. But you are going against one of the most fundamental scientific understandings of our time. Show me one example of a major scientific theory which the majority of scientists thought irrefutible that was proven to be wrong.


F1,2 = -F2,1, also known as Newton's Third Law, violated by the magnetic force.
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Re: Favourite faster than light technology

Postby MrConor » Wed Mar 23, 2011 7:03 pm UTC

zmatt wrote:
Diadem wrote:Columbus actually was wrong. Just very lucky. Noone ever claimed that was the Wright Brothers did was theoretically impossible. Would be strange too, since we've been flying since 1783. Noone ever claimed that faster-than-sound was theoreticaly impossible either.


The fact he was wrong is beside the point, the fact that he tried anyways is my point.


The Columbus point is an interesting one for you to bring up. He was completely wrong (he said the Earth was a lot smaller than people thought it was, and he could nip across the Atlantic and hit Japan)and he went on to prove himself completely wrong (the Earth was about as big as people thought it was, and he never got anywhere near Japan).

You were arguing that scientific consensus isn't always right, so you brought up an example of when the scientific consensus was right.

From Wikipedia:

Wikipedia wrote:In Columbus's time, the techniques of celestial navigation, which use the position of the Sun and the Stars in the sky, together with the understanding that the Earth is a sphere, were beginning to be widely used by mariners.

Where Columbus did differ from the view accepted by scholars in his day was in his estimate of the westward distance from Europe to Asia. Columbus's ideas in this regard were based on three factors: his low estimate of the size of the Earth, his high estimate of the size of the Eurasian landmass, and his belief that Japan and other inhabited islands lay far to the east of the coast of China. In all three of these issues Columbus was both wrong and at odds with the scholarly consensus of his day.


The idea that the world was round was nothing new when Columbus was setting out.
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Re: Favourite faster than light technology

Postby charonme » Wed Mar 23, 2011 7:13 pm UTC

Diadem wrote:FTL is impossible. Theoretically impossible. And it will remain that way forever.
Nothing can travel faster than the speed of light through space. Look up inflation. Things can move apart faster than the speed of light. A possibility of a useful practical FTL drive using this fact is another thing however.
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Re: Favourite faster than light technology

Postby zmatt » Thu Mar 24, 2011 1:20 am UTC

MrConor wrote:
The idea that the world was round was nothing new when Columbus was setting out.



Oh yeah, it's a great story and pretty interesting. the version most people are taught in school is watered down and often simply wrong. The idea people thought the world was flat and colombus was the one to show them how things really were is silly. Not to mention the vikings got to America much earlier, and the native Americans had to discover it first, although the land bridge theory seems to be less plausible now a days then when I was in public school.
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Going on to inflation (I forgot that even existed for a bit) does that idea throw a cog into the whole faster than light means infinite energy idea? I mean, if space expanded faster than light, and the universe isn't infinite, and we still have energy that hasn't completely fallen to entropy then it must not take infinite energy, at least to expand space faster than the speed of light. And when you can expand and contract space really fast, at the end of the day what's the difference?
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Re: Favourite faster than light technology

Postby Antimony-120 » Thu Mar 24, 2011 2:01 am UTC

[quote=]Going on to inflation (I forgot that even existed for a bit) does that idea throw a cog into the whole faster than light means infinite energy idea? I mean, if space expanded faster than light, and the universe isn't infinite, and we still have energy that hasn't completely fallen to entropy then it must not take infinite energy, at least to expand space faster than the speed of light. And when you can expand and contract space really fast, at the end of the day what's the difference?[/quote]

The reason going faster than light takes infinite energy is because of the good old E = ymc^2 (I'm using y for gamma because I don't want to use jsmath). This is the energy of a particle moving at reletivistic speeds, where: y = 1/sqrt(1-v^2/c^2). As v -> c, the square root goes to zero, and gamma goes to infinity (and therefore so does the energy).

But a particle sitting in space has v = 0, y = 1, and herefore E = mc^2, the rest energy of the particle. If space expands, that doesn't impart any more energy to the particle, since it's still not moving relative to the space around it. If someone ELSE were to try to measure the energy of a particle that was being expanded away from the observer at the speed of light, they would measure it as having infinite energy. But they wouldn't SEE the particle, since any signal sent from the particle would travel at the speed of light or less, and therefore be expanded away.

I'm handwaving a bunch of things here, including an implicit lorentz boost of c (which is one of those things that throws wobblies), but the basic concept is that, again, Relativity is a LOCAL theory, and there is always some neighbourhood around you where the velocity imparted by the expansion of space is less than c, so it doesn't have to cause problems.

I would like to stress however that there are many thought experiments in this area that are quite interesting, and much of the handwaving I'm doing is hiding the more interesting aspects in an effort to give a simple answer to the question. If you want some more thought about it, I recommend thinking about what would happen to the signals of objects moving away from us if the expansion of space was slowing down. Those signals would then be able to reach us, but those are the signals I said were being cosmically censored because they showed things moving faster than c. So can they reach us if the expansion slows? Do they still show things as having gone faster than c? How could this relate to a shrinking black hole?
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Re: Favourite faster than light technology

Postby MrConor » Thu Mar 24, 2011 12:50 pm UTC

Speaking as a total layman, I would have thought it obvious that space would expand faster than the speed of light. If you have two particles moving in opposite directions at the speed of light, the distance between them is going to grow at a faster rate than the speed they're actually moving. That still wouldn't mean that anything could move faster than the speed of light, of course.

However, as I said, I don't really know much about physics. So if I've failed physics forever and space does not work that way, please enlighten me as to where I've gone wrong.
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Re: Favourite faster than light technology

Postby Diadem » Thu Mar 24, 2011 1:34 pm UTC

zmatt wrote:I think you are missing my point. You are saying it's impossible don't talk about it. I'm saying we should because the benefits here far outweigh the negatives. And even if it can't be done, the technology fallout would be great. It certainly isn't something we could do today if it were possible. But as a long term goal for spaceflight it would be nice. Things like "mass" production of antimatter, more advanced spacecraft. A better understanding of the physics involved through experience. etc.

I never said any such thing. I just said to be realistic. It's still a very interesting avenue of exploration because it can teach us more about the nature of spacetime. You know, scientists actually do research in FTL travel, even though they know it is impossible, for exactly that reason. Take this guy Alcubierre for example, ever heard of him?

What you are suggesting is deceiving yourself though. That's never a good thing in science.


zmatt wrote:
Diadem wrote:There is direct proof. You just chose to ignore it.

Oh so you have tried it? Cool. what happened when you tried to bend spacetime?

Ask your mother, she's the expert. But seriouslyk, GR has been independently confirmed in at least half a dozen different ways. It's pretty thoroughly proven by now.

zmatt wrote:
Diadem wrote:So give me an example. I'm sure you can find examples of individual scientists claiming something very dumb. But you are going against one of the most fundamental scientific understandings of our time. Show me one example of a major scientific theory which the majority of scientists thought irrefutible that was proven to be wrong.

You really don't know much about history do you? Off the top of my head, plate tectonics. For the longest time it was laughed at by the scientific community, the previous paradigm being thought of as irrefutable. It took awhile for it to be accepted.

You know throwing around ad hominem attacks is not going to make you look more sympathetic. Besides it was perfectly predictable you were going to come up with this example. It's pretty much the default example of a paradigm shift. However I did not ask you for a major scientific theory that took a while to be accepted, I asked for one that was proven wrong. Neither is your example particularly good. Continental drift in some form or another had been discussed since the early 19th century. And it's not people did not see the merits of the hypothesis, but the problem was that noone was ever able to give a plausible mechanism for it until the 1960s. Plate tectonics replaces the earlier idea of continental drift, that was very similar except that plate tectonics provided a plausible mechanism. Either way though, it is in no way an example of what I asked for.

Point being we are all humans here and imperfect. We will let our arrogance get the best of us even if we try to hold true to the ideals of science nobody is perfect. That and personally I think the best way to find something out is to try. You really wont know is X is possible unless you try to do it.

That's a nice sentiment. But it is also wrong. I know with perfect certainty that I can not walk on the surface of the sun. I have never tried it, nor has anyone I know, but I still know this with absolute certainty.

In general laymen tend to underestimate how much scientists know. That's not surprising, because scientists are always talking and thinking about things they do now know. That's the nature of science. Once you know something you move on. But unfortunately this leads to the impression with the general public that science is always in flux and always uncertain. That's simply not true. There are a lot of things we simply know. With certainty.

Right now the best we can do in the real world is observe relativistic effects on small objects in particle accelerators. Its a start.

Not true at all. We can measure perihelion precessions of planets, we can measure the gravitational bending of light and the gravitational redshift of light. We can measure time dilation both due to velocity and a gravitational field. We have observed gravitational lensing, we have measured geodetic precession. We are very close to measuring the Lense-Thirring effect, and very close to measuring gravitational waves. And that's just for GR. I'm not as well versed in QFT but I'm sure a similar list can be compiled for it.

The only thing we do not know is quantum gravity. But there is not a single plausible generalization of GR or QFT that allows FTL. Nor could there be, because it would violate both GR and QFT in fundamental ways.
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Re: Favourite faster than light technology

Postby Diadem » Thu Mar 24, 2011 1:44 pm UTC

MrConor wrote:Speaking as a total layman, I would have thought it obvious that space would expand faster than the speed of light. If you have two particles moving in opposite directions at the speed of light, the distance between them is going to grow at a faster rate than the speed they're actually moving. That still wouldn't mean that anything could move faster than the speed of light, of course.

You're both right and wrong. If send one spaceship with almost the speed of light one way and one with the same speed in the opposite direction, and then measure the speed difference between those two, I will obviously measure a speed difference of (almost) 2c (c = speed of light). But I won't measure anything moving faster than c, both spaceships are happily moving at a sublight velocity. The speed difference between those two ships has no physical meaning (it can not facilitate information transfer).

If I were in that spaceship however, I would see the earth moving away with me with almost c, but I would not see the other spaceship move with more than c. This is because time flows differently for me. The result is that I see the second spaceship move away from me even faster than the earth, but still below c. That's the fundamental idea of relativity. Time and space depend on velocity. The faster you move the slower time goes for you, so that other fast moving objects will move slower relative to you. The math works out in such a way that nothing can ever move faster than the speed of light relative to you, no matter how you are moving yourself. The second fundamental part is that there is no difference between all these frames of reference. Physics works the same in all of them.

There are many good introductions to relativity on the internet. Isn't there one sticked on this very forum in the science subsection?
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Re: Favourite faster than light technology

Postby zmatt » Thu Mar 24, 2011 6:35 pm UTC

I can't believe you are still saying relativity doesn't allow for ftl. It obviously doesn't allow your velocity to exceed the speed of light, but that was never the argument behind something like an Alcubierre drive. The idea is that you in a sense bring your destination close to you so that the time it takes you to get form point a to b is shorter than it would take light in normal space. Every single relativity book I have ever read brings this up and aside from you I have never heard anyone dispute it. In fact things like gravitation lensing and directly observable distortions caused by massive objects lend credence to this. It's pretty obvious you can bend space time and can shorten the distance between two objects. As for negative energy, Hawking thinks it can exist and cites the Casimir effect. I don't know a lot about the specifics, quantum stuff is a total wtf to my head. But as far as I can tell nobody is saying that ftl is impossible, only extremely difficult and there is a lot we don't know given some interesting problems.



As for the rest of the stuff, it's pretty off topic, and I want to get this back on track. I think arguing the possibility of ftl still fits though.
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Re: Favourite faster than light technology

Postby Fobs » Wed May 18, 2011 8:34 am UTC

There is a way you can appear to go faster than light without breaking physics. What you do is slow down everybody's biological functions, including brain processes a few thousand times, or more or less. That way you can travel using conventional propulsion to a star and back, and very little apparent time will have passed as everyone now lives for millions of years, and the few decades the trip took is now insignificant. Of course this does create many other problems...
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Re: Favourite faster than light technology

Postby AvatarIII » Wed May 18, 2011 10:43 am UTC

Fobs wrote:There is a way you can appear to go faster than light without breaking physics. What you do is slow down everybody's biological functions, including brain processes a few thousand times, or more or less. That way you can travel using conventional propulsion to a star and back, and very little apparent time will have passed as everyone now lives for millions of years, and the few decades the trip took is now insignificant. Of course this does create many other problems...



by "everyones" do you mean including people not on the ship? because going near the speed of light will deal with the people on the ship due to relativistic effects of travelling at that speed.
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Re: Favourite faster than light technology

Postby Fobs » Wed May 18, 2011 2:36 pm UTC

Yeah, including people not on the ship. Basically, just change the human timescale, so that for us, the amount of time required for a ship to leave and return from an observers point of view becomes insignificant.
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Re: Favourite faster than light technology

Postby AvatarIII » Wed May 18, 2011 2:44 pm UTC

Fobs wrote:Yeah, including people not on the ship. Basically, just change the human timescale, so that for us, the amount of time required for a ship to leave and return from an observers point of view becomes insignificant.


i guess the main problem with that is, what about other sentient, or even non-sentient races? the life cycles of stars, and the reliabilility of the "timescale altering" technology, what if it didn't work on 0.00001% of the population or something or what if space travel became so common timescales just never returned to normal, and stars would be dying much faster relatively speaking etc.
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Re: Favourite faster than light technology

Postby Fobs » Wed May 18, 2011 3:54 pm UTC

AvatarIII wrote:
Fobs wrote:Yeah, including people not on the ship. Basically, just change the human timescale, so that for us, the amount of time required for a ship to leave and return from an observers point of view becomes insignificant.


i guess the main problem with that is, what about other sentient, or even non-sentient races? the life cycles of stars, and the reliabilility of the "timescale altering" technology, what if it didn't work on 0.00001% of the population or something or what if space travel became so common timescales just never returned to normal, and stars would be dying much faster relatively speaking etc.


Yeah, these are the sort of problems that I would see happening, along with things like gravity being unaltered, so everything seems to fall insanely fast. But you could increase the human lifespan and memory capacity, but still have us perceive things at the same rate. Although 1000 years will still feel like 1000 years.
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Re: Favourite faster than light technology

Postby idobox » Wed May 18, 2011 6:27 pm UTC

Fobs wrote:
AvatarIII wrote:
Fobs wrote:Yeah, including people not on the ship. Basically, just change the human timescale, so that for us, the amount of time required for a ship to leave and return from an observers point of view becomes insignificant.


i guess the main problem with that is, what about other sentient, or even non-sentient races? the life cycles of stars, and the reliabilility of the "timescale altering" technology, what if it didn't work on 0.00001% of the population or something or what if space travel became so common timescales just never returned to normal, and stars would be dying much faster relatively speaking etc.


Yeah, these are the sort of problems that I would see happening, along with things like gravity being unaltered, so everything seems to fall insanely fast. But you could increase the human lifespan and memory capacity, but still have us perceive things at the same rate. Although 1000 years will still feel like 1000 years.

The main problem is the time altering machine could not alter time everywhere at the same same time, there would be a bubble of slow time expanding at c.

The Alcubiere drive is a solution that works in GR making some assumptions. Particles with negative mass have never been observed, but there are theories that allow them, and there are a bunch of particles that have never been observed, but that are still considered very plausible, including the Higgs boson and supersymetrical particles. So the drive relies on theorical particles, okay, but not on pseudoscientific handwaving.
The real main issue is that you wouldn't be able to build one, even with negative mass at hand. To put it simply, we don't know a way to go from a universe with no Alcubiere drive to one with one.

About FTL and causality in general, we have to be very careful when we claim something is absolute. Before Einstein, we thought the mass of a particle to be a constant, and that there was only one global time frame. Relativity introduced a number of things that are counter intuitive, and predict things Newton forbade.
Who are we to say relativity is absolute, and can never be proved wrong? Maybe a theory of quantum gravity will allow local variations of c or even weirder, more unexpected behaviours.
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Re: Favourite faster than light technology

Postby Technical Ben » Wed May 18, 2011 8:07 pm UTC

I wonder if there are any FTL sci-fi stories where the spacecrafts time dilation is the only mitigating factor? You could only ever meet up with travellers via chance, or very accurate and advance predictions otherwise. Especially as everyone not travelling with you will have hundreds or thousands of years pass by.
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Re: Favourite faster than light technology

Postby zmatt » Thu May 19, 2011 1:46 pm UTC

idobox wrote:The real main issue is that you wouldn't be able to build one, even with negative mass at hand. To put it simply, we don't know a way to go from a universe with no Alcubiere drive to one with one.


I thought that there was already a rebuttal to that one.


Anyways I am confident that through some means be it warp drive, worm holes or something we haven't thought of yet we will break the arbitrary speed limit of the universe.
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Re: Favourite faster than light technology

Postby bigglesworth » Thu May 19, 2011 4:15 pm UTC

Cynical Idealist wrote:or make it so there's no real reason for manned spaceships (If you've got a fixed network of wormholes, why not put them on the planets and do your interstellar travel with trains? If you need microgravity manufacturing capabilities, put a wormhole endpoint somewhere in orbit and build a factory there. If you need to drag an endpoint of a wormhole with you to expand the network, why not use an unmanned probe?)
I'd like you to consider a wormhole device that (like the Star Wars hyperdrives, supposedly) cannot function too deep within a gravity well. Near Earth, they would have to be constructed at the Lagrangian points, for example. This then requires spacecraft to use and service them. It also makes a Moon base much more useful.
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