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View Full Version : The Bending and Warping of Space/time: Will we eventually do it?



ASTRO BOY
2013-Jan-11, 11:39 PM
My thoughts are along the lines of whatever is allowed by the laws of physics and GR, and given time, it is possible.
I'll include BH's and WH's in this also as both are examples of critical space/time warpages and curvature.

I found the following which aligns with my thoughts on the matter........

from:
http://www.astronomynow.com/news/n1205/29starship/

Kelvin Long is an aerospace engineer and physicist, as well as the founder of Project Icarus - a design study for an interstellar starship - and is Chief Editor of the Journal of the British Interplanetary Society. In addition, as part of Project Icarus, he is involved in the 100 Year Starship Project. As such, he's the perfect author to write Deep Space Propulsion, a new book that details the technologies necessary to take us to the stars. Astronomy Now spoke to him about his vision for the future.


some important extracts from the lengthy questions and answers article..........

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
"Keep an eye on nanotechnology developments as an example to watch out for. It's a game changer.

I'm also interested in the competing methodologies of SpaceX and Reaction Engines. Both companies have exciting ideas that could alter the possibilities."


"Otherwise, I love warp drive schemes. They may be pure conjecture right now but if nature figured out how to bend space then so can we, in time. In the early Universe space underwent an inflationary expansion period. In a black hole space collapses. This expansion and collapse of space is essentially how warp drive works and we can see this mathematically in Einstein's field equations of General Relativity."



" What the BIS needs to do for the future is to keep the vision alive. This is difficult with the backdrop of a retreating space programme and a struggling world economy but, as long as someone is pointing the way, our species will always have a direction to go and no matter the problems here on Earth, we can get there eventually. Optimism and hope before the vastness of the void is the only way we can make that journey towards another star and find our second home."
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>



He certainly appears to be a man of vision and Imagination....
He is not only doing what Newton claimed, that is standing on the shoulders of giants to see as far as he does, he appears to be standing on tippy toes.

I commend him for his insightfullness.

kevin1981
2013-Jan-12, 04:47 PM
I do not know a lot about it but from what i do know, most professional scientists think it is very unlikely because it will require vast amounts of energy. At the moment we are miles away from that sort of technology.

ASTRO BOY
2013-Jan-12, 07:55 PM
I do not know a lot about it but from what i do know, most professional scientists think it is very unlikely because it will require vast amounts of energy. At the moment we are miles away from that sort of technology.



Probably correct and as I mentioned we are probably a millenia or two away from that sort of technology, and yes it is hard for anyone including scientists to envisage such awe inspiring technology, but then again, no astronomical/cosmological goals are going to be easy.
To be thinking about this sort of stuff is a start though.

Thanatos
2013-Jan-12, 08:59 PM
The known laws of nature suggest interstellar travel is both too slow and expensive to be practical. We need to learn more about the laws [or discover new ones] to circumvent these restrictions.

ASTRO BOY
2013-Jan-12, 09:45 PM
The known laws of nature suggest interstellar travel is both too slow and expensive to be practical. We need to learn more about the laws [or discover new ones] to circumvent these restrictions.

Agreed....
We could also be interpreting our observations incorrectly. We once thought that time and space were absolute and unchanging.
We were wrong.......

ASTRO BOY
2013-Jan-12, 09:52 PM
As mentioned by the aerospace engineer and physicist, Kelvin Long, one of the disciplines that I think will facilitate greatly stellar travel in the future is "Nanotechnology".......

Van Rijn
2013-Jan-12, 10:01 PM
Probably correct and as I mentioned we are probably a millenia or two away from that sort of technology,


It's not just a matter of technology, but of science. It is not established that these "warp drive" ideas are physically possible. For instance:

The unphysical nature of "Warp Drive" (http://arxiv.org/abs/gr-qc/9702026)

If it isn't physically possible, it doesn't matter how advanced your technology is.


To be thinking about this sort of stuff is a start though.

It's a start if there is something that can be started. What's really important is to see if there is anything that can be tested. Until you can test, you can only speculate. And if you can test, don't be surprised if you don't get the result you'd like. (That happens a lot.)

ASTRO BOY
2013-Jan-12, 10:42 PM
It's not just a matter of technology, but of science. It is not established that these "warp drive" ideas are physically possible. For instance:

The unphysical nature of "Warp Drive" (http://arxiv.org/abs/gr-qc/9702026)

If it isn't physically possible, it doesn't matter how advanced your technology is.



It's a start if there is something that can be started. What's really important is to see if there is anything that can be tested. Until you can test, you can only speculate. And if you can test, don't be surprised if you don't get the result you'd like. (That happens a lot.)



While I agree with what you have said, again [1] it is not against the laws of physics and GR...[2]It will probably require "new physics" to achieve...[3] It has not been demonstrated that warp drives are impossible either.

As clearly outlined in the OP, I commend Kevin for his thoughts and Imagination on the concept.
It is only by starting to think about it, that we will be able to finally decide logically that it scientifically can or cannot be achieved, and secondly if we can ever achieve that technology.
Who knows, we may even come up with other means of achieving warp travel......as Kevin has said, pure conjecture at this time, but well worth considering in the course of time.

Markus Hanke
2013-Jan-13, 09:56 AM
It has not been demonstrated that warp drives are impossible either.

True, but in order for them to work you need exotic matter of some form. And currently there is no evidence that such matter exists in macroscopic quantities.
Another issue would be what exactly happens at the boundary between the "warp bubble" and normal space, particularly from the point of view of quantum field theory.

ASTRO BOY
2013-Jan-13, 07:04 PM
True, but in order for them to work you need exotic matter of some form. And currently there is no evidence that such matter exists in macroscopic quantities.
.


Non Baryonic DM?

Shaula
2013-Jan-13, 08:02 PM
Non Baryonic DM?
Nope, very different properties required.

ASTRO BOY
2013-Jan-13, 09:17 PM
Nope, very different properties required.

Do we know enough about non baryonic DM to be sure of that?

Shaula
2013-Jan-13, 09:47 PM
Do we know enough about non baryonic DM to be sure of that?
Non-baryonic dark matter is required to gravitate normally to explain the rotation curves we see. Exotic matter cannot, it has to have a repulsive effect either via negative mass or some other effect.

Delvo
2013-Jan-13, 09:57 PM
The fact that space-bending is mathematically non-impossible doesn't help if you don't have a specific mechanism to make it happen. The only one that's known, the gravity keeping you on the planet right now, requires lots of mass for even a weak effect and isn't useful. To actually do anything with it, some other cause for that effect would be needed. So, instead of just "space-bending is a real thing", how do you actually produce it without... the only thing that produces it? What object, made of what substances, will do it, under what conditions?

Jeff Root
2013-Jan-13, 10:07 PM
I wrote a reply to this thread several hours ago but didn't
do anything with it. Now I see that Delvo has said very
much the same as I did:

I haven't studied this subject one iota. But my ignorant
understanding is that warping spacetime by a large amount
requires a very large amount of energy. Concentrated
energy. The more concentrated, the better.

Mass is the most concentrated form of energy known, by far.

The energy in a mass equal to Earth's mass probably isn't
nearly enough to warp space sufficiently for interstellar
travel. More likely, the mass of thousands of suns is
needed.

Where are you going to get that mass from?

Mass has this little problem called "inertia".

-- Jeff, in Minneapolis

ASTRO BOY
2013-Jan-13, 10:10 PM
So, instead of just "space-bending is a real thing", how do you actually produce it without... the only thing that produces it? What object, made of what substances, will do it, under what conditions?


Well at this stage of our evolution we don't know.......But in a millennia or two? Who knows!
[There's also a non zero chance we may know next week]

caveman1917
2013-Jan-14, 02:12 PM
As has been said before, the problem isn't the amount of energy required (that's an engineering problem), the problem is that you require negative energy.

Jeff Root
2013-Jan-14, 06:13 PM
Is negative energy actually required or is that just
one way it might hypothetically be accomplished?

If it is required and there's no such thing as negative
energy, then we're done with the question, aren't we?

What is negative energy, in this context?

Why would negative energy be required or helpful?

-- Jeff, in Minneapolis

ASTRO BOY
2013-Jan-14, 07:01 PM
Is negative energy actually required or is that just
one way it might hypothetically be accomplished?



Bingo! :-)

caveman1917
2013-Jan-14, 11:46 PM
Is negative energy actually required or is that just
one way it might hypothetically be accomplished?

It is required.


If it is required and there's no such thing as negative
energy, then we're done with the question, aren't we?

Pretty much. Until there is actual evidence for the existence of negative energy (other than very small-scale effects such as the Casimir effect) the proposal is effectively science fiction.


What is negative energy, in this context?

Negative mass if that's easier to think about. Objects with a negative mass.


Why would negative energy be required or helpful?

You need to contract space in front of the bubble and expand it behind the bubble. The only way to do that is with a specific configuration of both positive and negative energy. It's the way mass affects spacetime.

Jerry
2013-Jan-15, 12:31 AM
Bingo! :-)
Heavier-than-air flying machines are impossible,"

Sigh. Kelvin is always misquoted. Thomson said that with the materials and technology available in 1895 - including steam power - manned flight was impossible; and he was almost correct. He was working with very heavy engines and low strength steel. The light new internal combustion engines were a deal-changer, and everyone knew it. Yet is still took years and exacting development of a remarkable new type of propeller to lift the Wright brothers.

It would be an interesting exercise to truly disprove Kelvin - to use materials and technology available in 1895.

Jeff Root
2013-Jan-15, 05:19 AM
Thanks, caveman! Nice, clear, concise explanations.




What is negative energy, in this context?
Negative mass if that's easier to think about.
Objects with a negative mass.
Ah-ha. I haven't explained my pet hypothesis in full
anywhere, but one of its central features is a version
of negative mass, so I can cozy up to the notion.
But which kind of negative mass? In what sense is
it "negative"? Is it negative gravitational mass, or
negative inertial mass, or both? My pet hypothesis
predicts the existence of negative gravitational mass,
but does not allow negative inertial mass. I make a
very small change in the interpretation of the Principle
of Equivalence which has rather large consequences.

I don't see, though, how that could lead to contracting
and un-contracting space. I'm guessing that what you
are talking about requires negative inertial mass.



You need to contract space in front of the bubble and
expand it behind the bubble. The only way to do that
is with a specific configuration of both positive and
negative energy. It's the way mass affects spacetime.
What if I only contract the space in front of the bubble
but don't bother to expand it again behind the bubble?

-- Jeff, in Minneapolis

Marakai
2013-Jan-15, 08:22 AM
Sigh. Kelvin is always misquoted. Thomson said that with the materials and technology available in 1895 - including steam power - manned flight was impossible; and he was almost correct. He was working with very heavy engines and low strength steel. The light new internal combustion engines were a deal-changer, and everyone knew it. Yet is still took years and exacting development of a remarkable new type of propeller to lift the Wright brothers.


Just for clarification: was the attitude indeed that "HTA flight is impossible with current technology" or was it "HTA flight is impossible" because the attitude was that the current technology was as good as it would get ("everything has been invented and discovered") and according to that there was never going to be an aeroplane?

The former would have at least been open-minded and should possibly guide us regarding quasi-FTL travel. That said, if it requires super-civilisation status to produce the energy for inter-stellar spaceflight, which is the pre-requisite for becoming a super-civilisation in the first place, we're in strife.

There's your solution to Fermi's Paradox: a bug in the algorithm of the universe. All civilisations will become asteroid fodder before they can acquire the energy to get off their rock to acquire the energy that they need to get off their rock.

They used to make us buy a case of beer for our fellow programmers if we coded an infinite loop...

Definitely a bug, not a feature! :D

Marakai
2013-Jan-15, 08:25 AM
What if I only contract the space in front of the bubble
but don't bother to expand it again behind the bubble?

-- Jeff, in Minneapolis

Cue Alan Dean Foster's KK drive from his Humanx scifi series!

Always thought it was one of the more imaginative designs, because it wasn't afraid to think through that it would result in pretty ugly spacecraft (a football with a plumber's helper stuck in front? oh, the glamour! :) ). That said it always sounded a bit like the old "pulling yourself out of a swamp by your own hair" trick, but if there were a possibility in line with Jeff's question, could it work? Disregarding the energy requirements.

Van Rijn
2013-Jan-15, 09:06 AM
Just for clarification: was the attitude indeed that "HTA flight is impossible with current technology" or was it "HTA flight is impossible" because the attitude was that the current technology was as good as it would get ("everything has been invented and discovered") and according to that there was never going to be an aeroplane?


There's apparently no primary source for the "impossible" statement. It appears to be a misquote.

He apparently did say "The air-ship, on the plan of those built by Santos-Dumont, is a delusion and a snare. A gas balloon, paddled around by oars, is an old idea, and can never be of any practical use. Some day, no doubt, some one will invent a flying machine that one will be able to navigate without having to have a balloon attachment. But the day is a long way off when we shall see human beings soaring around like birds."



The former would have at least been open-minded and should possibly guide us regarding quasi-FTL travel.


It's actually a very different issue, since the concern with HTA flight was not if it could be done (there were obvious examples that showed it to be physically possible), but if it was technologically feasible.

FTL travel has definitely not been established as being physically possible.



That said, if it requires super-civilisation status to produce the energy for inter-stellar spaceflight, which is the pre-requisite for becoming a super-civilisation in the first place, we're in strife.

There's your solution to Fermi's Paradox: a bug in the algorithm of the universe. All civilisations will become asteroid fodder before they can acquire the energy to get off their rock to acquire the energy that they need to get off their rock.


I don't understand this argument. We can already get off the planet. We don't need FTL (or sub-light "warp" drives, for that matter) to do that.

Marakai
2013-Jan-15, 10:07 AM
He apparently did say "The air-ship, on the plan of those built by Santos-Dumont, is a delusion and a snare. A gas balloon, paddled around by oars, is an old idea, and can never be of any practical use. Some day, no doubt, some one will invent a flying machine that one will be able to navigate without having to have a balloon attachment. But the day is a long way off when we shall see human beings soaring around like birds."


Ah, daresay absolutely technically correct if said that way, especially if the combustion engine hadn't come around when it did.





I don't understand this argument. We can already get off the planet. We don't need FTL (or sub-light "warp" drives, for that matter) to do that.

Yes, but where to? At this moment we can't even seriously envision "generation ships" or anything sub-light to get to other stars. Our solar system is a pretty dismal place (I'm a bah-humbugger when it comes to terra-forming overall - only Minnesotans and Siberians would think Mars a nice place to live. :p My "plan" to choose the much nicer because warmer Venus was shot down (probably by Minnesotans!) ;) ).

We probably can't assign statistical probabilities to discoveries and breakthroughs, so I don't know if it's valid to say that a global cataclysm of some kind is more likely than us finding a way to have a significant, feasible human population survive off Earth with a technological civilisation that can continue to "bootstrap itself to the stars" so to speak.

Maybe somewhere out there is a lucky species that has 30 planets in the habitable zone, Serenity/Firely style. Not us.

caveman1917
2013-Jan-15, 11:05 AM
Ah-ha. I haven't explained my pet hypothesis in full
anywhere, but one of its central features is a version
of negative mass, so I can cozy up to the notion.
But which kind of negative mass? In what sense is
it "negative"? Is it negative gravitational mass, or
negative inertial mass, or both? My pet hypothesis
predicts the existence of negative gravitational mass,
but does not allow negative inertial mass. I make a
very small change in the interpretation of the Principle
of Equivalence which has rather large consequences.

I don't see, though, how that could lead to contracting
and un-contracting space. I'm guessing that what you
are talking about requires negative inertial mass.

It is both. GR is based on the postulate that they are the same, and the alcubierre drive is expressed in terms of GR (it is a solution to the GR field equations). So in this context they are necessarily the same thing. I have no idea what will happen if you let go of that postulate, however you will not have GR anymore, so you'd basically have to come up with a new theory to replace GR as a whole and then see what is possible within that new theory.


What if I only contract the space in front of the bubble
but don't bother to expand it again behind the bubble?

Good question, and one that would require quite a bit of calculation. If you look at the Alcubierre metric you see that it corresponds to a local "disturbance" in an otherwise unaffected global spacetime (which is taken to be flat). So if you steer clear of big gravitational fields you're good to go. If you however only contract space in front of the bubble but don't expand it at the back you're creating a global disturbance. You're literally pulling a far-away galaxy closer to where you are. My guess is that this will turn out to be inconsistent.

Paul Beardsley
2013-Jan-15, 03:22 PM
There's apparently no primary source for the "impossible" statement. It appears to be a misquote.

He apparently did say "The air-ship, on the plan of those built by Santos-Dumont, is a delusion and a snare. A gas balloon, paddled around by oars, is an old idea, and can never be of any practical use. Some day, no doubt, some one will invent a flying machine that one will be able to navigate without having to have a balloon attachment. But the day is a long way off when we shall see human beings soaring around like birds."

In restrospect, this should not be surprising.

I think the real danger of the (mis)quote - especially when it's used as a sig - is that it portrays science as rather fuzzy, and encourages people to cherry-pick: If a scientist tells you something you want to hear, take it at face value, but if a scientist tells you something you don't want to hear, don't worry, he'll turn out to be wrong and we'll all laugh at him one day.

Of course science isn't like that.


It's actually a very different issue, since the concern with HTA flight was not if it could be done (there were obvious examples that showed it to be physically possible), but if it was technologically feasible.

FTL travel has definitely not been established as being physically possible.

Indeed. Lord Kelvin observed birds in flight. We have not observed tachyons in flight.

Jeff Root
2013-Jan-15, 06:38 PM
My pet hypothesis predicts the existence of negative
gravitational mass, but does not allow negative inertial
mass. I make a very small change in the interpretation
of the Principle of Equivalence which has rather large
consequences.
... I have no idea what will happen if you let go of that
postulate, however you will not have GR anymore, so
you'd basically have to come up with a new theory to
replace GR as a whole and then see what is possible
within that new theory.
You have said that to me before but it really isn't true.
I'm not suggesting any change to GR whatever, only a
small change in what is meant by "equivalence", which
results in changes to GR predictions that apply only to
conditions which have never been observed because
they are beyond our current technical ability to create.

To expand on that last little bit, since I think it is
relevant to the original question of the thread and
maybe even the side issue of whether Thomson's
comment on flight can be applied to the progress
of science... GR makes predictions about the interiors
of black holes which have never been observed, and
both SR and GR made predictions about phenomenae
which had not been observed but have subsequently
been observed. I am positing that there is a domain
of applicability of GR for which no observations yet
exist, that will require a change in the meaning of
the Principle of Equivalence to interpret correctly,
but which doesn't involve any change to GR.

Arithmetic is based on assumptions about the
nature of numbers, based on observations of real,
physical things. Yet introducing the concepts of
negative numbers and imaginary numbers did not
require new theories of arithmetic. They instead
required new understanding of what numbers are,
and arithmetic became able to produce results
that it previously could not.

-- Jeff, in Minneapolis

ASTRO BOY
2013-Jan-15, 07:51 PM
Sigh. Kelvin is always misquoted. Thomson said that with the materials and technology available in 1895 - including steam power - manned flight was impossible; and he was almost correct. He was working with very heavy engines and low strength steel. The light new internal combustion engines were a deal-changer, and everyone knew it. Yet is still took years and exacting development of a remarkable new type of propeller to lift the Wright brothers.

It would be an interesting exercise to truly disprove Kelvin - to use materials and technology available in 1895.


Misquoted????...Possibly but I'm pretty sure he wasn't predicting manned flight in any circumstances, considering he was supposed to have made the statement in 1895 only a decade before it became part of human history.
And of course we have many more examples.
see........
http://www.null-hypothesis.co.uk/science/strange-but-true/item/invention_failure_never_work_disaster

ASTRO BOY
2013-Jan-15, 07:59 PM
FTL travel has definitely not been established as being physically possible.




No it hasn't.....but it has also not been shown that it is physically impossible either.
Could be a whole new discipline of physics that needs to be unearthed to achieve it.

ASTRO BOY
2013-Jan-15, 08:12 PM
think the real danger of the (mis)quote - especially when it's used as a sig - is that it portrays science as rather fuzzy, and encourages people to cherry-pick: If a scientist tells you something you want to hear, take it at face value, but if a scientist tells you something you don't want to hear, don't worry, he'll turn out to be wrong and we'll all laugh at him one day.

Of course science isn't like that.




Firstly signatures are in the main personal scientific beliefs. Mine is just one of many that I picked and certainly illustrates my scientific beliefs based on available data etc.
Again there are many examples of science and scientists that appear to be constrained by the beliefs of the day.
The greatest of them all Einstein also managed to fit into that category with his "established belief of the day" that the Universe was static, when even his own equations were telling him different.
His greatness though stems from his humility in the fact that he finally recognised it as his "greatest blunder".

The belief that space and time were absolute throughout the Universe was an accepted law of physics that was shown to be wrong by the same man.

Marakai
2013-Jan-15, 08:50 PM
Firstly signatures are in the main personal scientific beliefs. Mine is just one of many that I picked and certainly illustrates my scientific beliefs based on available data etc.

[...]

"Heavier-than-air flying machines are impossible,"

-- Lord Kelvin, president Royal Society, 1895.


Sorry, you can really wind your way around this however you want, but when you put quotes around something together with an attribution it is considered a *literal* quote. Unless you add (paraphrased) or some other qualifier. Of course you can also quote literally yet out of context, which is what media and politicians like to do. ;)

I think we've pretty much established that LK did *not* say or write this statement as you quote it. It not mis-attributed, not even quoted out of context: at best it's a paraphrase and should be marked as such. Or retracted as being a quote.

Or, as Wikipedia likes to put it: "citation needed". :)

ASTRO BOY
2013-Jan-15, 09:33 PM
Sorry, you can really wind your way around this however you want, but when you put quotes around something together with an attribution it is considered a *literal* quote. Unless you add (paraphrased) or some other qualifier. Of course you can also quote literally yet out of context, which is what media and politicians like to do. ;)

I think we've pretty much established that LK did *not* say or write this statement as you quote it. It not mis-attributed, not even quoted out of context: at best it's a paraphrase and should be marked as such. Or retracted as being a quote.

Or, as Wikipedia likes to put it: "citation needed". :)



Interesting, but as I tried to point out, using that sig was to illustrate a point re the never ending progress advancements and so far unlimited nature of science and what the future may hold.

I did find the following from Wiki on Lord Kelvin:


http://en.wikipedia.org/wiki/William_Thomson,_1st_Baron_Kelvin


Pronouncements later proven to be false

Like many scientists, he did make some mistakes in predicting the future of technology.
Circa 1896, Lord Kelvin was initially sceptical of X-rays, and regarded their announcement as a hoax.[55] However, this was before he saw Röntgen's evidence, after which he accepted the idea, and even had his own hand X-rayed in May 1896.[56]
His forecast for practical aviation was negative. In 1896 he refused an invitation to join the Aeronautical Society, writing that "I have not the smallest molecule of faith in aerial navigation other than ballooning or of expectation of good results from any of the trials we hear of."[57] And in a 1902 newspaper interview he predicted that "No balloon and no aeroplane will ever be practically successful."[58]
The statement "There is nothing new to be discovered in physics now. All that remains is more and more precise measurement" is given in a number of sources, but without citation. It is reputed to be Kelvin's remark made in an address to the British Association for the Advancement of Science (1900). It is often found quoted without any footnote giving the source.[59] However, another author reports in a footnote that his search to document the quote failed to find any direct evidence supporting it.[60] Very similar statements have been attributed to other physicists contemporary to Kelvin.[61][62]
In 1898, Kelvin predicted that only 400 years of oxygen supply remained on the planet, due to the rate of burning combustibles.[63][64] In his calculation, Kelvin assumed that photosynthesis was the only source of free oxygen; he did not know all of the components of the oxygen cycle. He could not even have known all of the sources of photosynthesis: for example the cyanobacterium Prochlorococcus—which accounts for more than half of marine photosynthesis—was not discovered until 1986.
[edit]Eponyms
:::::::::::::::::::::::::::::::::::::::::::::::::: ::::::::::::::::::::::

Paul Beardsley
2013-Jan-15, 11:21 PM
No it hasn't.....but it has also not been shown that it is physically impossible either.

It hasn't?


Could be a whole new discipline of physics that needs to be unearthed to achieve it.

A perfect illustration of my earlier point. Unless I've missed something, FTL generally is regarded as physically impossible. But if we ignore that and wish really hard, perhaps it will turn out to be possible. After all, Kelvin was wrong about aeroplanes, so perhaps physicists are wrong about FTL.

kamaz
2013-Jan-16, 12:22 AM
The unphysical nature of "Warp Drive" (http://arxiv.org/abs/gr-qc/9702026)


That paper is from 1997, and some progress has been made since. NASA now considers the concept feasible, and is building an experiment to demonstrate the distortion effect.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110015936_2011016932.pdf
http://io9.com/5963263/how-nasa-will-build-its-very-first-warp-drive


As mentioned by the aerospace engineer and physicist, Kelvin Long, one of the disciplines that I think will facilitate greatly stellar travel in the future is "Nanotechnology".......

Particularly true with respect to warp drive.

Warp drive as envisioned by Harold White (above) stores energy in capacitors, and nanotech is believed to enable some really nice capacitors...

ASTRO BOY
2013-Jan-16, 12:49 AM
It hasn't?



A perfect illustration of my earlier point. Unless I've missed something, FTL generally is regarded as physically impossible. But if we ignore that and wish really hard, perhaps it will turn out to be possible. After all, Kelvin was wrong about aeroplanes, so perhaps physicists are wrong about FTL.



It's certainly impossible at this stage of our evolution and science but so was a lot of scenarios once upon a time.
Things could well change in a year, or decade or a millenia.

As Kelvin Long the aerospace engineer and physicist and also founder of project Icarus says in the OP........
" "Otherwise, I love warp drive schemes. They may be pure conjecture right now but if nature figured out how to bend space then so can we, in time. In the early Universe space underwent an inflationary expansion period. In a black hole space collapses. This expansion and collapse of space is essentially how warp drive works and we can see this mathematically in Einstein's field equations of General Relativity."

What the BIS needs to do for the future is to keep the vision alive. This is difficult with the backdrop of a retreating space programme and a struggling world economy but, as long as someone is pointing the way, our species will always have a direction to go and no matter the problems here on Earth, we can get there eventually. Optimism and hope before the vastness of the void is the only way we can make that journey towards another star and find our second home."

I just support the innovativeness and Imagination and the inevitable progress that stems from such qualities.

caveman1917
2013-Jan-16, 01:53 AM
You have said that to me before but it really isn't true.
I'm not suggesting any change to GR whatever, only a
small change in what is meant by "equivalence", which
results in changes to GR predictions that apply only to
conditions which have never been observed because
they are beyond our current technical ability to create.

Then what exactly is that small change in the meaning of equivalence?

Van Rijn
2013-Jan-16, 01:54 AM
That paper is from 1997, and some progress has been made since.


There have been other ideas since 1997. It isn't clear there has been any progress.



NASA now considers the concept feasible, and is building an experiment to demonstrate the distortion effect.


No, White thinks he has come up with something testable, which is the purpose of the experiment. Feasibility has not been established.

caveman1917
2013-Jan-16, 02:00 AM
That paper is from 1997, and some progress has been made since.

No essential progress though. It doesn't really matter if you need a solar mass of negative energy or only a gram of it until you can actually produce it at all.


NASA now considers the concept feasible, and is building an experiment to demonstrate the distortion effect.

The Casimir effect has been known for a long time, it is a very small scale effect that creates a negative vacuum energy. And that small scale is its problem, it is not scalable since the effect is directly related to the size of the region it appears in.

caveman1917
2013-Jan-16, 02:11 AM
No, White thinks he has come up with something testable, which is the purpose of the experiment. Feasibility has not been established.

Indeed, he is merely testing whether a configuration of negative energy can actually produce a warp bubble field, which has theoretically been assumed as correct. In a sense he's testing the most basic assertion, that if you get negative energy then you get a warp bubble field. That still doesn't make any progress as to how to get that negative energy other than relying on the casimir effect as he is, which is not scalable to useful proportions.

caveman1917
2013-Jan-16, 02:14 AM
I don't really understand the focus on the warp bubble method. Even if you could get negative energy in decent amounts, the method still has many other problems. So why not go the wormhole route? After all, if you can get your hands on a good amount of negative energy you can use wormhole travel which doesn't come with that host of other problems to solve.

Jeff Root
2013-Jan-16, 03:50 AM
Then what exactly is that small change in the meaning
of equivalence?
Yeah... That's a little bit over the line into ATM territory.
I wanna stay outa there. I *think* I've said enough
about it in past posts for you to get the idea, since it is
awfully simple. In fact, it could just be a subset of the
ideas that the Alcubierre drive is based on. I don't know
enough about it. But if the Alcubierre metric depends on
or predicts some kind of negative mass, then my idea is
pretty likely to be a subset of Alcubierre's.

-- Jeff, in Minneapolis

Paul Beardsley
2013-Jan-16, 07:04 AM
It's certainly impossible at this stage of our evolution and science but so was a lot of scenarios once upon a time.
Things could well change in a year, or decade or a millenia.

This is just another reiteration of "Kelvin was wrong about aeroplanes, therefore anything we want to happen might happen."


I just support the innovativeness and Imagination and the inevitable progress that stems from such qualities.

"Inevitable progress" from funding projects that don't even have a theoretical basis?

Marakai
2013-Jan-16, 07:55 AM
His forecast for practical aviation was negative. In 1896 he refused an invitation to join the Aeronautical Society, writing that "I have not the smallest molecule of faith in aerial navigation other than ballooning or of expectation of good results from any of the trials we hear of."[57] And in a 1902 newspaper interview he predicted that "No balloon and no aeroplane will ever be practically successful."[58]



And you really don't see the difference from your misquote of him supposedly stating that HTA was impossible?

ASTRO BOY
2013-Jan-16, 08:13 AM
This is just another reiteration of "Kelvin was wrong about aeroplanes, therefore anything we want to happen might happen."


No, it's a reasonably common reiteration prevalent throughout history with many examples...And of course, it doesn't mean "anything we want to happen will"
Which makes your statement incorrect on two counts...[1] No one has said [other then you] that it applies to "anything we want to happen"... and [2] It has nothing to do with "wanting something to happen" and everything to do with the fact that FTL via space/time manipulation, is not forbidden by GR and the laws of physics.
And of course it is just one of the many exotic propulsion methods being looked at in research by the JPL. and I dare say other research establishments over the world.



"Inevitable progress" from funding projects that don't even have a theoretical basis?



Inevitable progress is inevitable...what more can I say.
I mean I really don't think we are going to go backwards or stagnate...although admittedly there is a non zero chance.

ASTRO BOY
2013-Jan-16, 08:19 AM
And you really don't see the difference from your misquote of him supposedly stating that HTA was impossible?

Answered in post 32. and 34.

caveman1917
2013-Jan-16, 08:38 AM
FTL via space/time manipulation, is not forbidden by GR and the laws of physics.

Many things are not forbidden by GR, that doesn't mean we expect them to exist. To give a few examples
-White holes.
-Closed timelike curves. Pretty much like being stuck in an infinite "time loop" as is sometimes done in science fiction.
-Naked singularities.
-Naked singularities that are constantly producing huge pink elephants.

None of the above even requires negative energy. Here are some when you allow negative energy just like the warp drive
-Bullets that travel back in time to kill you right before you shoot the gun.
-A device that travels back in time to stop the universe from ever existing in the first place.

Surely you have just as much faith in all of the above as you have in the warp drive?

Van Rijn
2013-Jan-16, 09:46 AM
Side issue, but I did want to respond to this -



Yes, but where to? At this moment we can't even seriously envision "generation ships" or anything sub-light to get to other stars. Our solar system is a pretty dismal place (I'm a bah-humbugger when it comes to terra-forming overall - only Minnesotans and Siberians would think Mars a nice place to live. :p My "plan" to choose the much nicer because warmer Venus was shot down (probably by Minnesotans!) ;) ).


I don't think it's dismal at all. There's lots of construction material in the solar system for space habitats. There's no need to focus on planets. Ultimately, planets are an extremely inefficient use of mass for habitation, since you can only use the surface.


Maybe somewhere out there is a lucky species that has 30 planets in the habitable zone, Serenity/Firely style. Not us.

That's trivial compared to what could be done with space habitats.

ASTRO BOY
2013-Jan-16, 09:59 AM
Many things are not forbidden by GR, that doesn't mean we expect them to exist. To give a few examples
-White holes.
-Closed timelike curves. Pretty much like being stuck in an infinite "time loop" as is sometimes done in science fiction.
-Naked singularities.
-Naked singularities that are constantly producing huge pink elephants.

None of the above even requires negative energy. Here are some when you allow negative energy just like the warp drive
-Bullets that travel back in time to kill you right before you shoot the gun.
-A device that travels back in time to stop the universe from ever existing in the first place.

Surely you have just as much faith in all of the above as you have in the warp drive?

Faith?...Who's talking about faith?
I'm just agreeing with Kelvin Long an aerospace engineer and physicist, and his statement thus......

"Otherwise, I love warp drive schemes. They may be pure conjecture right now but if nature figured out how to bend space then so can we, in time. In the early Universe space underwent an inflationary expansion period. In a black hole space collapses. This expansion and collapse of space is essentially how warp drive works and we can see this mathematically in Einstein's field equations of General Relativity."

What the BIS needs to do for the future is to keep the vision alive. This is difficult with the backdrop of a retreating space programme and a struggling world economy but, as long as someone is pointing the way, our species will always have a direction to go and no matter the problems here on Earth, we can get there eventually. Optimism and hope before the vastness of the void is the only way we can make that journey towards another star and find our second home."
frpm........http://www.astronomynow.com/news/n1205/29starship/


And I not only concur with his thoughts on the matter, but as I clearly said in the OP,
"He certainly appears to be a man of vision and Imagination....
He is not only doing what Newton claimed, that is standing on the shoulders of giants to see as far as he does, he appears to be standing on tippy toes.

I commend him for his insightfullness."


I see no reason to change my views now.

Nothing as yet says positively that space/time cannot be manipulated......Again, We have no way of knowing how we could do it at this time, and it is all conjecture, but given time, we may find out.
What distinguishes space/time manipulation from the other hypothetical scenarios you have listed, is of course, we do know that space/time can be manipulated and curved in the presence of mass.......as Kevin Long notes, "If nature can do it, why not us"


Again, I highly commend him on his insightfullness Imagination and innovativeness on this matter.
It's scientists and people like him who lead the way into new ventures and take us forward.

Marakai
2013-Jan-16, 10:39 AM
Side issue, but I did want to respond to this -



I don't think it's dismal at all. There's lots of construction material in the solar system for space habitats. There's no need to focus on planets. Ultimately, planets are an extremely inefficient use of mass for habitation, since you can only use the surface.



That's trivial compared to what could be done with space habitats.

Hmm, can't disagree with that. Hadn't thought of that option. Not that I think it's any likelier before we either collapse or get hit on the head figuratively speaking. But yeah, I'm pretty much a hopeless pessimist as to our options and future (no, I don't have kids).

caveman1917
2013-Jan-16, 12:05 PM
What distinguishes space/time manipulation from the other hypothetical scenarios you have listed, is of course, we do know that space/time can be manipulated and curved in the presence of mass.......as Kevin Long notes, "If nature can do it, why not us"

All of my hypothetical scenarios have been specifically chosen as valid solutions to the field equations. The same justification, with the same standard, as the warp drive. The latter two actually follow directly from assuming the existence of a warp drive. The former four are spacetime manipulations that have even less stringent requirements to do so than the warp drive. Given that you have rejected Paul's explanation that it has to do with wanting something to happen, but all with what is allowed by GR, there is no reason to prefer any one of those over any other.

ASTRO BOY
2013-Jan-16, 08:05 PM
All of my hypothetical scenarios have been specifically chosen as valid solutions to the field equations. The same justification, with the same standard, as the warp drive. The latter two actually follow directly from assuming the existence of a warp drive. The former four are spacetime manipulations that have even less stringent requirements to do so than the warp drive. Given that you have rejected Paul's explanation that it has to do with wanting something to happen, but all with what is allowed by GR, there is no reason to prefer any one of those over any other.



As I have said previously in referring to Kevin Long, we know that in certain circumstances space/time is twisted, curved and/or warped in the presence of mass....see GP-B data.
So the possibility exists that scientists in the course of time might be able to do the same...Difficult in the extreme but given the time, who knows?
The other artifacts you raise while being solutions of GR, are as yet unobserved.
And a point worth remembering regarding probably the most bizzare of the artifacts you have raised, [naked singularities] is that Stephen Hawking and Kip Thorne have shown they could exist in theory.

Let's not forget [despite the predictions of someone in the past claiming we now know all there is to know and just need to refine the concepts] that we still have a long way to go in knowing the true reality of the Universe we live in, and would need a validated QGT to extend that knowledge to explain in more detail the artifacts that you have raised.

ASTRO BOY
2013-Jan-16, 08:19 PM
Hmm, can't disagree with that. Hadn't thought of that option. Not that I think it's any likelier before we either collapse or get hit on the head figuratively speaking. But yeah, I'm pretty much a hopeless pessimist as to our options and future (no, I don't have kids).

I prefer to remain optimistic and positive given the "predictions" of some scientists in the past.

http://www.null-hypothesis.co.uk/science/strange-but-true/item/invention_failure_never_work_disaster

NEOWatcher
2013-Jan-16, 08:46 PM
I prefer to remain optimistic and positive given the "predictions" of some scientists in the past.

http://www.null-hypothesis.co.uk/science/strange-but-true/item/invention_failure_never_work_disaster
But those all deal with the feasibility of the prediction, not the physical possibility.

Selfsim
2013-Jan-16, 09:18 PM
It's actually a very different issue, since the concern with HTA flight was not if it could be done (there were obvious examples that showed it to be physically possible), but if it was technologically feasible.

FTL travel has definitely not been established as being physically possible.Beyond technologically possible, is what's practically possible.
The key distinction between the two, being task complexity for a given finite resource.

Ie: something can be demonstrated to be within a given technology's capability space, but when other technologies are called upon to 'scale it up' and make the overall 'scaled up' function stable, reliable, sustainable, (etc), task complexity, which is also constrained by physical law, can still render something to not be practically feasible.

Practical feasibility is not a universal 'given'.

It seems many arguments about what 'must be possible, given more development time', assume the sustainability of phenomena outlined by things like Moore's Law. (http://en.wikipedia.org/wiki/Moore%27s_law) 'Laws' such as Moore's however, are not necessarily temporally universal, nor are they necessarily applicable beyond the technology space they were derived from. Thus, they cannot be said to be valid into the far distant future. There are other things they presume to be in place, which may or may not be the case into the future.

caveman1917
2013-Jan-16, 09:21 PM
As I have said previously in referring to Kevin Long, we know that in certain circumstances space/time is twisted, curved and/or warped in the presence of mass....see GP-B data. So the possibility exists that scientists in the course of time might be able to do the same...Difficult in the extreme but given the time, who knows?

Again, the exact same standards with the exact same justification. Why do you have such a preference for one specific allowed spacetime over other specific allowed spacetimes (that don't even violate energy conditions) if not because you "want it to happen"?


The other artifacts you raise while being solutions of GR, are as yet unobserved.

They are as much observed as (macroscopic) warp bubbles - ie not observed at all. Unless you would like to point out an observation of a warp bubble? Moreso, we actually have an observation of a naked singularity, the big bang. The examples i gave even have more going for them than the warp bubble. A schwarzschild black hole that existed since the big bang is predicted to have a white hole exterior, and we observe black holes. A kerr black hole interior is predicted to have closed timelike curves, and we observe rotating black holes. The big bang itself is an observation of a naked singularity. And the last two examples follow directly from allowing a warp bubble.

ASTRO BOY
2013-Jan-16, 09:25 PM
But those all deal with the feasibility of the prediction, not the physical possibility.

Ummm, no.

ASTRO BOY
2013-Jan-16, 09:38 PM
Again, the exact same standards with the exact same justification. Why do you have such a preference for one specific allowed spacetime over other specific allowed spacetimes (that don't even violate energy conditions) if not because you "want it to happen"?
.




Not really sure what you are driving at.....Maybe you need to take it up with Kevin Long and JPL or other agencies studying the probability and possibilities of exotic propulsion methods.






They are as much observed as (macroscopic) warp bubbles - ie not observed at all. Unless you would like to point out an observation of a warp bubble? Moreso, we actually have an observation of a naked singularity, the big bang. The examples i gave even have more going for them than the warp bubble. A schwarzschild black hole that existed since the big bang is predicted to have a white hole exterior, and we observe black holes. A kerr black hole interior is predicted to have closed timelike curves, and we observe rotating black holes. The big bang itself is an observation of a naked singularity. And the last two examples follow directly from allowing a warp bubble.


We have strong evidence to support the BB but we have not observed it nor can we observe it.
We do observe space/time warpage/curvature and other manipulation. [see GP-B]
And for your edification, I'm in no way refuting any of the other artifacts.
They are all solutions to GR which I have stated, even offering the theoretical possibilities of the most bizzare of them from Hawking and Thorne.
You seem to be ignoring what I have said.

Jeff Root
2013-Jan-16, 10:50 PM
You seem to be ignoring what I have said.
From my perspective it looks more like you are either
ignoring or not understanding what caveman said.

He described several scenarios which are predicted
by various interpretations of GR but have little or no
observational evidence supporting them. The scenario
you champion has the least support and the strongest
observational evidence indicating that it just isn't so.
Large pink elephants, for example, have been observed.
Warp bubbles have not. Negative matter has not.
Negative energy of the kind that appears to be required
has not.

What *has* been observed is ordinary matter and energy
causing gravity. That is the evidence you are going on
about. The law of the conservation of mass-energy came
before GR, and it is important, too. It says that the total
mass-energy in a closed system remains constant. So if
some future engineers are going to create warp bubbles
with gravity equal to, say, Earth's gravity, they need to
obtain a quantity of energy equal to the energy of Earth's
mass. No technology can change that. If they need it
to be negative energy, and there is no such thing as
negative energy, then they are out of luck.

Some things are possible, while other things are not
possible. The most fundamental task of science is to
sort out which of those are which. Engineers can try
to do things whether they are known to be possible or
not. When they are not possible, the attempts fail.
Most engineers are guided by science to some degree,
which significantly reduces the number of failures.

The problem with your tagline is that it is apparently
a lie. As far as other researchers have been able to
discover, William Thomson, Lord Kelvin, never said
any such thing as you quote him saying.

-- Jeff, in Minneapolis

ASTRO BOY
2013-Jan-16, 11:29 PM
[QUOTE=Jeff Root;2098786
The problem with your tagline is that it is apparently
a lie. As far as other researchers have been able to
discover, William Thomson, Lord Kelvin, never said
any such thing as you quote him saying.

-- Jeff, in Minneapolis[/QUOTE]

He said similar conveying the same idea, and actually much much more short-sighted observations were made by him also, such as....

[1] "There is nothing new to be discovered in physics now, All that remains is more and more precise measurement."

[2] "X-rays will prove to be a hoax."

frpm:
http://zapatopi.net/kelvin/quotes/


So no, it is not a lie.

ASTRO BOY
2013-Jan-17, 12:03 AM
That paper is from 1997, and some progress has been made since. NASA now considers the concept feasible, and is building an experiment to demonstrate the distortion effect.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110015936_2011016932.pdf
http://io9.com/5963263/how-nasa-will-build-its-very-first-warp-drive



Particularly true with respect to warp drive.

Warp drive as envisioned by Harold White (above) stores energy in capacitors, and nanotech is believed to enable some really nice capacitors...



I have always believed "Nanotechnology" will alleviate a number of the problems encountered with space travel, and yes, JPL and other agencies are certainly looking at the idea and probability of warp drive and probably by many methods.
How it will be achieved and when I don't know, but it is nice to know that innovative scientists and agencies are at the coal face and looking and talking about the problems associated with it.

Again what I am doing is supporting such research knowing the chances of ever achieving it in the near future is probably slim.

"A journey of a thousand miles starts with a single footstep" [or words to that effect]
Confucious:

kamaz
2013-Jan-17, 01:09 AM
No, White thinks he has come up with something testable, which is the purpose of the experiment. Feasibility has not been established.

According to White, the main obstacle was that the energy investment was prohibitive. He thinks that he has found a way to reduce energy needed to managable levels.

Swift
2013-Jan-17, 05:34 PM
This section of the forum is for astronomy and space exploration questions with straightforward, generally accepted answers.

Questions that are likely to lead to extended discussion about the correct answer, or that have no clearcut correct answer, should be posted in the forum most appropriate to the topic of the question. If a question does lead to such discussion, it may be split off or moved entirely to a more appropriate forum by a moderator.
I'm not sure this thread ever had a "straightforward, generally accepted answer", but it certainly is now an "extended discussion". I've moved the thread from Q&A to S&T.

NEOWatcher
2013-Jan-17, 06:13 PM
Ummm, no.
Why do you say that?

Paul Beardsley
2013-Jan-17, 07:48 PM
He said similar conveying the same idea, and actually much much more short-sighted observations were made by him also, such as....

[1] "There is nothing new to be discovered in physics now, All that remains is more and more precise measurement."

[2] "X-rays will prove to be a hoax."

frpm:
http://zapatopi.net/kelvin/quotes/


So no, it is not a lie.

If you are quoting someone when you know they didn't say it (or at least have good reason to doubt that they said it), it is less than honest. So what if they said something similar? If someone is convicted of burglary, it would still be slander or libel to state that they are guilty of shoplifting if they have not been convicted of this similar crime.

ASTRO BOY
2013-Jan-17, 09:00 PM
Why do you say that?

Because in answer to your question thus, "But those all deal with the feasibility of the prediction, not the physical possibility", [1] I disagree and [2] the difference is rather pedantic.

ASTRO BOY
2013-Jan-17, 09:05 PM
If you are quoting someone when you know they didn't say it (or at least have good reason to doubt that they said it), it is less than honest. So what if they said something similar? If someone is convicted of burglary, it would still be slander or libel to state that they are guilty of shoplifting if they have not been convicted of this similar crime.

The spirit of the quote is the message it conveys, and I remain unconvinced he did not say it.


And as I said previously, he said similar conveying the same idea, and actually much much more short-sighted observations were made by him also, such as....

[1] "There is nothing new to be discovered in physics now, All that remains is more and more precise measurement."

[2] "X-rays will prove to be a hoax."

http://zapatopi.net/kelvin/quotes/

ASTRO BOY
2013-Jan-17, 09:10 PM
And from Wiki.......

Pronouncements later proven to be false

Like many scientists, he did make some mistakes in predicting the future of technology.
Circa 1896, Lord Kelvin was initially sceptical of X-rays, and regarded their announcement as a hoax.[55] However, this was before he saw Röntgen's evidence, after which he accepted the idea, and even had his own hand X-rayed in May 1896.[56]
His forecast for practical aviation was negative. In 1896 he refused an invitation to join the Aeronautical Society, writing that "I have not the smallest molecule of faith in aerial navigation other than ballooning or of expectation of good results from any of the trials we hear of."[57] And in a 1902 newspaper interview he predicted that "No balloon and no aeroplane will ever be practically successful."[58]


http://en.wikipedia.org/wiki/William_Thomson,_1st_Baron_Kelvin#Pronouncements_l ater_proven_to_be_false

Paul Beardsley
2013-Jan-17, 09:55 PM
I remain unconvinced he did not say it.

Listen to yourself.

eburacum45
2013-Jan-17, 10:50 PM
He said similar conveying the same idea, and actually much much more short-sighted observations were made by him also, such as....

[1] "There is nothing new to be discovered in physics now, All that remains is more and more precise measurement."
This too is disputed;
see
http://en.wikiquote.org/wiki/William_Thomson,_1st_Baron_Kelvin

Disputed
There is nothing new to be discovered in physics now. All that remains is more and more precise measurement.

Although reportedly from an address to the British Association for the Advancement of Science (1900), the quote is only duplicated without citation to any primary source in various books, including Superstring : A theory of everything? (1988) by Paul Davies and Julian Brown; also in Rebuilding the Matrix : Science and Faith in the 21st Century (2003) by Denis Alexander. To be more credible, a source prior to the 1980s and close to 1900 is needed.
Confusion may be due to Michelson who made a similar quote whilst mentioning Lord Kelvin: In 1894, Albert A. Michelson remarked that in physics there were no more fundamental discoveries to be made. Quoting Lord Kelvin, he continued, “An eminent physicist remarked that the future truths of physical science are to be looked for in the sixth place of decimals.
So even this is not as clear-cut as one might think. I suggest that you should consider avoid attributing such statements to Kelvin without better evidence.

ASTRO BOY
2013-Jan-17, 11:12 PM
So even this is not as clear-cut as one might think. I suggest that you should consider avoid attributing such statements to Kelvin without better evidence.




Again, there are other more positive attributed quotes as well as my sig, to which I remain convinced of what he meant and the spirit of what he said....And they convey the same message and thoughts, which in itself is far more honest then "up in the air' statements.

The following seems to be conveying his thoughts quite admirably as far as I am concerned.

"His forecast for practical aviation was negative. In 1896 he refused an invitation to join the Aeronautical Society, writing that "I have not the smallest molecule of faith in aerial navigation other than ballooning or of expectation of good results from any of the trials we hear of."[57] And in a 1902 newspaper interview he predicted that "No balloon and no aeroplane will ever be practically successful."[58]"


http://en.wikipedia.org/wiki/William_Thomson,_1st_Baron_Kelvin#Pronouncements_l ater_proven_to_be_false
:::::::::::::::::::::::::::::::::::::::::::::::::: :::::::::::::::::::::::::::::::::::::::::::::::::: ::::::::::::::::::::::::::::::::::


Obviously a great man, and I do not detract from what services he has contributed to science.
But he did lack foresight, Imagination and modesty.
But this thread is not about my signature.
I'm sure if all signatures were given the third degree, we would find plenty of shortcomings.

Van Rijn
2013-Jan-18, 12:28 AM
According to White, the main obstacle was that the energy investment was prohibitive. He thinks that he has found a way to reduce energy needed to managable levels.

According to White, he has an idea he is planning to test. He has not established anything at this point.

Paul Beardsley
2013-Jan-18, 06:32 AM
I'm sure if all signatures were given the third degree, we would find plenty of shortcomings.

Yet another statement unsupported by evidence.

As far as I know, nobody else persists in quoting somebody on something they most likely didn't say.

ASTRO BOY
2013-Jan-18, 11:29 AM
Yet another statement unsupported by evidence.

As far as I know, nobody else persists in quoting somebody on something they most likely didn't say.


Like I said previously, The spirit of the quote is the message it conveys, and I remain convinced he did say it in line with the evidence.
And seriously I'm not that pedantic to examine the signatures of people....They impart a message the member wants to send and that's OK by me...each to there own.

eburacum45
2013-Jan-18, 11:52 AM
Well, to get back to the original subject of this thread; if some sort of space-warping is possible, and it allows some sort of faster-than-light travel, this makes the Fermi Paradox a bit more paradoxical. If we can expect aliens to be coming here at speeds faster than light, then we have to somehow explain why none of them have made contact with us yet; it is relatively easy to understand that advanced aliens might not want to travel tens or hundreds of light years just to make contact, but if they have FTL, then even the more distant onces might have a chance to get here.

Even if the closest civilisations decline to make contact for some reason, then there is always the possibility that a more distant civ could zip in and say hello, or colonise us, or wipe us out pre-emptively. This hasn't happened, so my gut feeling is that faster-than-light travel can't happen.

eburacum45
2013-Jan-18, 11:56 AM
The other thing that suggests that FTL might not be possible is the absence of time travellers. We've discussed this a few times in the past; it turns out that any kind of FTL travel in a relativistic universe opens the door to time travel in one way or another; we don't see people from the future either, so it seems likely that either FTL or relativity is unphysicial.

Jens
2013-Jan-18, 11:58 AM
About this whole discussion, I think considering the possibility and allocating some resources to research in this area is not a bad idea, because the basic research may lead to useful discoveries even if we never develop a warp drive. At the same time, like many others I find it improbable that such a think is physically possible.

Jeff Root
2013-Jan-18, 12:45 PM
There is a large enough range of different possible reasons
why we don't see ET visitors that I can't infer nonexistence
of warp drive from it alone. For example, warp drive might
work but still be terribly expensive. It might be FTL but not
infinitely fast, so that very long trips just don't make sense
when you can find anything you want closer to home.

I intend to argue in another thread, sometime soon,
against the idea that FTL is equivalent to time travel.
I think I understand the reasoning, and it looks flawed.
But I need to think on it more.

-- Jeff, in Minneapolis

caveman1917
2013-Jan-18, 12:47 PM
According to White, the main obstacle was that the energy investment was prohibitive. He thinks that he has found a way to reduce energy needed to managable levels.

It's still negative energy that's required though. He seems to leave out that important little qualifier. Using a toroidal capacitator to produce a dynamic casimir effect
1 does not scale up
2 may or may not produce a local negative energy vacuum. Apparently the casimir effect can be explained in terms of a relativistic van der waals force, not necessarily in terms of a negative vacuum expectation value for energy.
3 even if it is correctly descibed in terms of a negative energy vacuum, the capacitator is disjoint from the warp field it would produce. In other words the warp bubble is static, it isn't going anywhere

In any case, it is already assumed as a given that microscopic warp bubbles are possible using the casimir effect. In any theoretical exposition on the alcubierre metric it is assumed that his test will come out positive. This isn't some sort of breakthrough. His use of a toroidal configuration of negative mass is clever, but it doesn't solve any of the problems related to a warp drive.

ASTRO BOY
2013-Jan-18, 08:11 PM
Well, to get back to the original subject of this thread; if some sort of space-warping is possible, and it allows some sort of faster-than-light travel, this makes the Fermi Paradox a bit more paradoxical. If we can expect aliens to be coming here at speeds faster than light, then we have to somehow explain why none of them have made contact with us yet; it is relatively easy to understand that advanced aliens might not want to travel tens or hundreds of light years just to make contact, but if they have FTL, then even the more distant onces might have a chance to get here.

Even if the closest civilisations decline to make contact for some reason, then there is always the possibility that a more distant civ could zip in and say hello, or colonise us, or wipe us out pre-emptively. This hasn't happened, so my gut feeling is that faster-than-light travel can't happen.




Thanks for getting us back on track!
My view is that any Alien civilisation that has mastered FTL travel by whatever means, is a civilisation far ahead of us in science and technology.
I do try and believe that such intelligence will result in a common sense, non belligerent attitude, so I don't believe in what Hawking proposes.
Perhaps also they have a "Prime Directive" type of principal re non interference with races of basic technology such as us.
Just a thought.

ASTRO BOY
2013-Jan-18, 08:17 PM
The other thing that suggests that FTL might not be possible is the absence of time travellers. We've discussed this a few times in the past; it turns out that any kind of FTL travel in a relativistic universe opens the door to time travel in one way or another; we don't see people from the future either, so it seems likely that either FTL or relativity is unphysicial.


Perhaps there is a built in prohibitive law with time travel, that sees the traveller unable to interfer or be seen by anyone in the present.
Perhaps the time traveller assumes ghostly formation.
Just another thought.

ASTRO BOY
2013-Jan-18, 08:25 PM
About this whole discussion, I think considering the possibility and allocating some resources to research in this area is not a bad idea, because the basic research may lead to useful discoveries even if we never develop a warp drive..



My thoughts exactly....It's all worthwhile science.









At the same time, like many others I find it improbable that such a think is physically possible.


Quite possibly true, but on this one, I remain a fence sitter.

eburacum45
2013-Jan-18, 10:02 PM
Thanks for getting us back on track!
My view is that any Alien civilisation that has mastered FTL travel by whatever means, is a civilisation far ahead of us in science and technology.
I do try and believe that such intelligence will result in a common sense, non belligerent attitude, so I don't believe in what Hawking proposes.
It seems likely to me that intelligent alien entities will be very varied, and variable; you can't rely on them to have anything resembling human common sense, or even to be reliable in any way.

Perhaps also they have a "Prime Directive" type of principal re non interference with races of basic technology such as us.
Some might- but others might not - and with FTL transportation we could be within reach of both types. In fact these diverse entities could be so different to each other that they are in conflict over various philosophical or territorial issues; easy FTL would make such conflicts possible, even inevitable.

On the other hand hard, expensive, almost-impossible FTL wouldn't really make much impact on the Fermi Paradox or on our chances of encountering aliens.

Van Rijn
2013-Jan-19, 01:09 AM
I intend to argue in another thread, sometime soon,
against the idea that FTL is equivalent to time travel.
I think I understand the reasoning, and it looks flawed.


Please do a search for previous threads. This subject has been discussed to death.

Jens
2013-Jan-19, 05:19 AM
I intend to argue in another thread, sometime soon,
against the idea that FTL is equivalent to time travel.
I think I understand the reasoning, and it looks flawed.
But I need to think on it more.

Please do! I have the same feeling but I can't quite figure it out.

Jeff Root
2013-Jan-19, 05:31 AM
I love you both!

Intuitively, time travel into the past just doesn't make
sense, so I rule out anything that implies it. But, like the
warp drive speculated on in this thread, GR supposedly
allows FTL in certain cases. Pretty non-useful cases, I'd
say, such as the interior of black holes and the expansion
of the Universe, but FTL nevertheless. That's just a hint
that FTL *might* not imply going back in time. I spent a
couple of hours last month thinking about it and wrote up
what I had so far, but I need to work on it more before I
can say I've got anything.

-- Jeff, in Minneapolis

Van Rijn
2013-Jan-19, 05:53 AM
Intuitively, time travel into the past just doesn't make
sense, so I rule out anything that implies it.


Argh. You're assuming there is just one past ("the past"). The issue arises in relativity because there is no single present that everyone can agree on, so also no single past or future. *IF* you have FTL communication or travel in space with relativity, you can have causality violations for some observers. The rule, as has been discussed many times is:


Causality, FTL, relativity. Pick any two. You can't have all three.

publius
2013-Jan-19, 06:07 AM
I just noticed this thread and I ought to be ashamed since I'm not paying attention to this stuff.

The question about causality and FTL, with FTL being defined (properly) as something moving along a space-like path is without question. It can violate it. As was just said, FTL, relativity, causality, pick any two.

In the context of "exotic spacetimes", such as the Alcubierre metric, the question comes down to does the spacetime allow closed time-like curves. That is, can a time-like path be closed (Note FTL as discussed in simple cases involving just Minkowski and SR involves closed world lines -- that's what destroys causality -- but such a closed path requires space-like sections -- in exotic spacetimes, such closed paths can be time-like, which is the problem).

I don't think Alcubierre admits closed time-like curves, but I'm not 100% sure.

Something that hasn't been proven, but would be very nice to prove is that any physically possible spacetime, one that could "really exist" would not allow such closed timelike curves. Such a condition would require more restrictions than the EFE itself.

Jeff Root
2013-Jan-19, 07:21 AM
Intuitively, time travel into the past just doesn't make
sense, so I rule out anything that implies it.
Argh. You're assuming there is just one past ("the past").
No, I'm not assuming that. I'm not assuming anything
at all about "the past". It might as well be "the pasta".



The issue arises in relativity because there is no single
present that everyone can agree on, so also no single
past or future.
I don't know what you mean by "single". I know that
my present is something you can't experience because
you aren't here. You can only observe my present after
the fact, when it is no longer anyone's present. And I
can't experience your present because I'm not there.
I can only observe your present after it is no longer
anyone's present. Essentially you are saying "time is
relative". Is that the point of your above sentence?
In other words, you are picking relativity from your
list of three choices below. So am I.



*IF* you have FTL communication or travel in space
with relativity, you can have causality violations for
some observers.
The snippet you quoted of me above was me choosing
causality from your list of three choices.

I'm saying you can't have causality violations,
meaning that if causality violations appear in my
predictions, I've made a mistake somewhere, and
my predictions must be wrong.

My statement was intended to be exactly the opposite
of "Argh." It was supposed to be "Ahhh, at least he's
not throwing out causality. That's a relief."



The rule, as has been discussed many times is:


Causality, FTL, relativity. Pick any two. You can't have all three.
Yes. That is exactly the rule that has been argued
for here with what appear to be flawed arguments
that I intend to argue against... sometime.

The fact that relative speeds can be FTL between
things which are cosmologically far apart or in
different places inside and outside a black hole
suggests that FTL really isn't incompatible with
relativity and causality.

-- Jeff, in Minneapolis

publius
2013-Jan-19, 08:58 AM
The fact that relative speeds can be FTL between
things which are cosmologically far apart or in
different places inside and outside a black hole
suggests that FTL really isn't incompatible with
relativity and causality.

-- Jeff, in Minneapolis

This is precisely the problem with using the phrase "faster than light". To be precise, what is meant by FTL is something following a space-like path through spacetime. In the realm of SR, Minkowski spacetime, such a space-like path means the coordinate speed is greater than the constant 'c'.

In curved spacetime, and eve non-inertial frames in flat spacetime, that is not the case, and time-like paths can resolve to coordinate speeds greater than the constant 'c'. This is the case with cosmological "superluminal" speeds. They are going faster than the constant 'c', but they are following time-like paths.

FTL means space-like to be precise, not greater than the constant 'c'.

Delvo
2013-Jan-19, 02:17 PM
I find it interesting that the discussion focuses on FTL effects of space-manipulation, but skips over non-FTL effects. The latter are more interesting to me because there's more hope of actually achieving them at some point. We now know that gravity, like electromagnetism, has a spin component, which affects objects in the gravitational field of an object with angular momentum. For a satellite orbiting the Earth, it's pretty weak despite the huge mass, because the rotation rate is slow and because a macroscopic object's total net angular momentum is only based on the whole object's movement because the spins of its constituent particles are random and cancel each other out. With faster rotation and/or aligned particle spins, like the way we get magnetism out of electricity only under the right conditions, the effect would depend less on mass.

This would not create a warp field and move a ship faster than light like in Star Trek. If it's close to anything in Star Trek, it would be the impulse engines (slower-than-light propulsion), artificial gravity, inertial dampers, and/or the pushing or pulling effects of tractor beams... or maybe a way of increasing or decreasing or neutralizing the power of an ambient gravitational field that you're already in. The best this could do for interstellar travel is allow constant acceleration below light-speed, cutting travel time to a few years to the nearest stars instead of millennia... and with relativity in effect, it would be less than that aboard the ship. But let's assume that it's too weak to ever use for space ship propulsion. There's still other cool stuff to do with it on smaller scales anyway. For example, it could not only accelerate objects or make accelerating those objects easier, but also allow the construction of zero-g laboratories on Earth so we don't have to keep flying to laboratories that do it with orbital freefall instead.

Unfortunately, it seems to require materials science that we can't do; the only suggestion I've seen for creating the necessary circumstances to get the effect out of usable amounts of mass & energy involved not only creating but also sustaining and manipulating a Bose-Einstien condensate. But we have at least created those before, so that puts us a lot closer to creating these simple push/pull/rotate forces than we are to creating warp fields.

caveman1917
2013-Jan-19, 04:32 PM
I just noticed this thread and I ought to be ashamed since I'm not paying attention to this stuff.

The question about causality and FTL, with FTL being defined (properly) as something moving along a space-like path is without question. It can violate it. As was just said, FTL, relativity, causality, pick any two.

In the context of "exotic spacetimes", such as the Alcubierre metric, the question comes down to does the spacetime allow closed time-like curves. That is, can a time-like path be closed (Note FTL as discussed in simple cases involving just Minkowski and SR involves closed world lines -- that's what destroys causality -- but such a closed path requires space-like sections -- in exotic spacetimes, such closed paths can be time-like, which is the problem).

I don't think Alcubierre admits closed time-like curves, but I'm not 100% sure.

Something that hasn't been proven, but would be very nice to prove is that any physically possible spacetime, one that could "really exist" would not allow such closed timelike curves. Such a condition would require more restrictions than the EFE itself.

The Alcubierre spacetime doesn't admit CTC's but that's not where the causality violation comes from. The warp bubble is enclosed in an event horizon (which is why there are globally no CTC's), so if you want a signal to leave to warp bubble it will have to travel locally FTL at the edge of the bubble. This is what gets you causality violations. It is akin to forcing a signal to leave a black hole. To be precise, events inside the bubble and outside the bubble are space-like seperated.

eburacum45
2013-Jan-19, 05:36 PM
Even with relativity in the frame (so to speak) not all forms of FTL travel lead to causality reversals. As I've pointed out on this forum before, certain configurations of wormholes do lead to causality reversals, but others do not. I suspect that there might be a limited number of other forms of faster-than-light travel that are equally 'safe', such as instantaneous teleportation between sufficiently distant points - I suspect Jeff Root might have realised this.

Jeff Root
2013-Jan-19, 08:34 PM
What I have in mind is one particular argument that was
discussed here several months ago, involving teleportation
over moderate distances. I want to change some of the
assumptions of that argument. With the assumptions
used, the result definitely has an unacceptable problem
with causality. With less severe assumptions, I think the
problem will go away.

-- Jeff, in Minneapolis

Van Rijn
2013-Jan-19, 11:12 PM
I suspect that there might be a limited number of other forms of faster-than-light travel that are equally 'safe', such as instantaneous teleportation between sufficiently distant points - I suspect Jeff Root might have realised this.

Sure, if you go far enough that light can't get back, you don't have a causality problem, but unless there's some unknown exclusion preventing you from teleporting back at FTL velocity to (for example) Alpha Centauri after you teleported from Earth, the problem remains.

Van Rijn
2013-Jan-19, 11:24 PM
The fact that relative speeds can be FTL between
things which are cosmologically far apart or in
different places inside and outside a black hole
suggests that FTL really isn't incompatible with
relativity and causality.


That's not "FTL communication or travel in space" as I specified. There are (per the science) parts of the universe receding at FTL velocity, but it's causally disconnected. Nothing there is moving at FTL velocity in space.

Jeff Root
2013-Jan-20, 06:20 AM
The fact that relative speeds can be FTL between
things which are cosmologically far apart or in
different places inside and outside a black hole
suggests that FTL really isn't incompatible with
relativity and causality.
That's not "FTL communication or travel in space" as
I specified. There are (per the science) parts of the
universe receding at FTL velocity, but it's causally
disconnected. Nothing there is moving at FTL
velocity in space.
I *said* that those cases are "pretty non-useful".
They might be useful for throwing away garbage that
you want to be really sure will never come back, but
they aren't useful for communication or travel.
I don't think I suggested that they might be, and I
certainly didn't intend to suggest it. Just that the
restriction on FTL isn't absolute. I'd say it's relative.

-- Jeff, in Minneapolis

Jens
2013-Jan-20, 12:35 PM
Argh. You're assuming there is just one past ("the past"). The issue arises in relativity because there is no single present that everyone can agree on, so also no single past or future.

I have a fairly specific idea. I mean going back to a time where I can meet myself but at an earlier age, or where I can meet my own parents or grandparents. So for example, there would be two of me. Is it possible to use an Alcubiere drive to arrive back at the place where I was born to witness my own birth? That's what I mean by time travel.

eburacum45
2013-Jan-20, 01:23 PM
Sure, if you go far enough that light can't get back, you don't have a causality problem, but unless there's some unknown exclusion preventing you from teleporting back at FTL velocity to (for example) Alpha Centauri after you teleported from Earth, the problem remains.
Yes; that's why wormholes are sometimes safe. If you can only travel to and from certain safe locations in space that are outside each other's light cones, then wormholes would not permit time travel. To make instant teleportation safe then it must be constrained to only work when it takes you to a location outside the region where closed timelike curves can be formed, and vice versa.

caveman1917
2013-Jan-20, 01:43 PM
Yes; that's why wormholes are sometimes safe. If you can only travel to and from certain safe locations in space that are outside each other's light cones, then wormholes would not permit time travel. To make instant teleportation safe then it must be constrained to only work when it takes you to a location outside the region where closed timelike curves can be formed, and vice versa.

How do you propose nature would enforce such constraints? There is nothing in the laws of physics saying that, given that you could build a wormhole, that you can't build it anywhere you want.

What's worse, those constraints themselves must violate causality. If i open a wormhole to a star in andromeda, then from that exact moment there is a range around that star that cannot be used to open a wormhole back to a range around earth. However that constraint must be put in place immediately upon opening the first wormhole, even though everything else in that range is spacelike seperated from the wormhole at that point. Otherwise we could still get around it by having the opening of both wormholes be outside eachother's lightcones.

eburacum45
2013-Jan-20, 03:04 PM
The only constraint is that you can't open a wormhole mouth that opens in a region that is in the past light cone of its other mouth. If you do you form a CTC, which is forbidden. All other wormhole mouth pairs should be stable. Matt Visser suggested that opening a CTC wormhole would cause an infinite loop, where virtual particles would race round and round through the hole and cause it to collapse; this might be the natural phenomenon which prevents time travel.

caveman1917
2013-Jan-20, 06:36 PM
The only constraint is that you can't open a wormhole mouth that opens in a region that is in the past light cone of its other mouth.

In that case it is easy to violate causality. Open a wormhole from here to some star and another wormhole from that star back to here. Neither of them are opened in the past light cones of their other mouths, yet you can directly form a CTC. How would virtual particles increase by running through CTCs? A CTC is after all, by definition, a closed timelike curve such that any field must return to the same state it was in one "loop" ago.

eburacum45
2013-Jan-20, 11:11 PM
In that case it is easy to violate causality. Open a wormhole from here to some star and another wormhole from that star back to here. Neither of them are opened in the past light cones of their other mouths, yet you can directly form a CTC.

This is called a 'Roman Ring', (named after Tom Roman)
http://en.wikipedia.org/wiki/Roman_ring
and to quote Wikipedia
... some experts such as Matt Visser feel that there are reasons to think the semiclassical approach is unreliable here, and that a full theory of quantum gravity will likely uphold chronology protection.
I tend to agree. Either the universe prevents time travel or it allows it; a relatively simple trick like doubling-up wormholes shouldn't make something possible that a single wormhole won't allow.

caveman1917
2013-Jan-20, 11:48 PM
This is called a 'Roman Ring', (named after Tom Roman)
http://en.wikipedia.org/wiki/Roman_ring
and to quote Wikipedia
... some experts such as Matt Visser feel that there are reasons to think the semiclassical approach is unreliable here, and that a full theory of quantum gravity will likely uphold chronology protection.
I tend to agree. Either the universe prevents time travel or it allows it; a relatively simple trick like doubling-up wormholes shouldn't make something possible that a single wormhole won't allow.

That was my point in post 101. If the universe prevents the construction of a double wormhole but allows the construction of a single wormhole, that itself can be used to violate causality, because the restriction on constructing the second wormhole must take effect immediately (ie over a spacelike seperation) upon construction of the first wormhole. You could use that restriction itself to cause a CTC, which is the irony of it. But perhaps i didn't explain my point clearly.

Suppose you are at earth and i am at alpha centauri. We agree that i (say every second or so) open up and close again a wormhole to andromeda. You get to send me an instantaneous signal by opening a wormhole yourself to andromeda, because if the universe prevents the formation of a double wormhole that will mean that i am suddenly not able to open my own wormhole anymore. This way you get to send me a bit of information over a spacelike seperation. Extend that construction a little and we'll have effectively built a tachyon antitelephone system between earth and alpha centauri using our (in)ability to open wormholes to andromeda.

The only reasonable options here seem to be that either the universe doesn't allow wormholes (and related things such as teleportation) at all, or that you get to violate causality.

eburacum45
2013-Jan-21, 04:37 AM
The only reasonable options here seem to be that either the universe doesn't allow wormholes (and related things such as teleportation) at all, or that you get to violate causality.It seems that Visser disagrees. The thing that is forbidden is a closed timelike curve; it doesn't matter if that geodesic passes through one wormhole, or a million, it is still forbidden. There is a real difference between space-time that has got a CTC in it and spacetime that doesn't; a CTC is instantly infinite in duration, since you can pass through it in both directions an infinite number of times. There will be an unknown, perhaps infinite, number of acausal events occuring within that loop - I don't think a Roman ring would be safe to pass through, and the most likely result is that the ring collapses as soon as it starts to form.

eburacum45
2013-Jan-21, 04:47 AM
Incidentally I don't think it is possible to 'open and close' a Morris-Thorne wormhole in any meaningful way; as it is a topological flaw in spacetime it either exists or it doesn't. If you close it completely you can't open it again- the connection is lost. You can make it smaller so that no matter could get through- but that wouldn't stop massless particles.

caveman1917
2013-Jan-23, 12:26 AM
There is a real difference between space-time that has got a CTC in it and spacetime that doesn't; a CTC is instantly infinite in duration, since you can pass through it in both directions an infinite number of times.

That is the same thing as saying that a circle is infinitely long because you can go around it an infinite number of times.

However i do retract my previous statement on being able to pass information along spacelike intervals using the restriction. A cauchy horizon consists by definition of closed null curves so any effect that destroys it the moment it forms cannot be used the way i stated.

JCoyote
2013-Jan-23, 06:43 AM
I wish I had a solid way to consider Many Worlds against Relativistic causality violation; the bifurcation of universes is a pretty convenient way to remove causality violation in a chronology.