SPACE TRAVEL AND THE BENEFITS:

What does "perception of FTL travel" mean? Who is having this "perception"? The travler or some one on Earth? Is the perception different for "perceivers" at rest in different inertial frames? Or do they all agree the traveler is traveling at some less than light speed?

Sorry for so many questions, but I have no understanding of what you are speaking of / asserting.

Are you just saying that I can swing a laser beam rapidly in angle and the spot it makes on a very distant screen appears to be moving faster than C?

 

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I'm sure you know what I am saying.
If we had the advanced technology to warp/curve spacetime, and form a bubble of sorts around our craft. Obviously it is spacetime moving at "c"or FTL, with the craft taken along for the ride.
An Alcubierre Drive speculative scenario is an example.
Please don't go into your "cannot ever be done" routine, we have gone through that before, and I'm sticking to my claim, that any sufficiently advanced civilisation, could possibly achieve that which is not forbidden by the laws of physics and GR.

 

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I think I read that more clearly stated earlier and asked (with no reply) about the energy (actually power level) creating a warp that would make a 1G acceleration. I'm sure I asked if the entire out put of the sun would be enough?

Again I have no idea what you mean by "space time moving FTL" as space time is a reference frame that particles can move in staying within their current light cone.

I can accept the idea that gravity is a warp of space time and that probably energy can do that as well as mass so think what you must mean is that one in principle could make a warp and move it with your space carft so the space craft had a constant 1G acceleration, but that space craft will never go faster than C as it mass will keep increasing as C is approached.

 

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The Alcubierre drive or Alcubierre metric(referring to metric tensor) is a speculative idea based on a solution of Einstein's field equations in general relativity as proposed by theoretical physicist Miguel Alcubierre, by which a spacecraft could achieve faster-than-light travel if a configurable energy-density field lower than that of vacuum (i.e.negative mass) could be created. Rather than exceeding the speed of light within alocal reference frame, a spacecraft would traverse distances by contracting space in front of it and expanding space behind it, resulting in effective faster-than-light travel.

Objects cannot accelerate to the speed of light within normal spacetime; instead, the Alcubierre drive shifts space around an object so that the object would arrive at its destination faster than light would in normal space.[1] Although the metric proposed by Alcubierre is mathematically valid in that it is consistent with the Einstein field equations, it may not be physically meaningful or indicate that such a drive could be constructed. The proposed mechanism of the Alcubierre drive implies a negative energy density and therefore requires exotic matter, so if exotic matter with the correct properties does not exist then it could not be constructed. However, at the close of his original paper[2] Alcubierre argued (following an argument developed by physicists analyzing traversable wormholes[3][4]) that the Casimir vacuum between parallel plates could fulfill the negative-energy requirement for the Alcubierre drive. Another possible issue is that although the Alcubierre metric is consistent with general relativity, general relativity does not incorporate quantum mechanics, and some physicists have presented arguments to suggest that a theory of quantum gravity, which incorporates both theories, would eliminate those solutions in general relativity that allow for backwards time travel (see the chronology protection conjecture), of which the Alcubierre drive is one.

http://en.wikipedia.org/wiki/Alcubierre_drive
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The pessimist sees difficulty in every opportunity. The optimist sees the opportunity in every difficulty.
Winston Churchill:
But again, we've been through all that before, havn't we?

 

I don't believe that for one minute..

All extremely difficult, all beyond anything we can do today, all maybe centuries away, but all being worked on as we speak, by many companies lead by reputable individuals, and all possible under the laws of physics and GR.

 

thanks for this link. Its figure makes it clear what you are speaking of and lists many of the reason why making that FTL bubble is impossible, despite such a warped space being a valid solution to GR equations. - I'll quote a nine of the strongest soon.

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I.e. the warp down in space made by lots of exotic (not any known to exist) matter's "negative mass" does make a gravity pulling ahead the interior flat space, in which the rocket ship could sit. Likewise the "warp up" behind, made by normal mass I think. effectively pushes the interior flat space (and spaceship) forward.

Here in only the first paragraph are three reasons "why impossible"
" it may not be physically meaningful or indicate that such a drive could be constructed. The proposed mechanism of
(1)the Alcubierre drive implies a negative energy density and therefore requires exotic matter, so if exotic matter with the correct properties does not exist then it could not be constructed.
(2)However, at the close of his original paper Alcubierre argued ... that the Casimir vacuum between parallel plates could fulfill the negative-energy requirement for the Alcubierre drive.
{I comment on (2) at end of post.}
(3)Another possible issue is that ... Alcubierre metric .. does not incorporate quantum mechanics, and some physicists have presented arguments to suggest that a theory of quantum gravity, which incorporates both theories, would eliminate those solutions in general relativity that allow for backwards time travel, of which the Alcubierre drive is one."

Billy t notes: I think paddoboy has conceded that backwards travel in time is impossible - for many reasons, including killing your grand parents, so not even your parents exsit to give birth to you who went back in time and killed them.

(4) Enormous tidal forces, however, would be present near the edges of the flat-space volume because of the large space curvature there, but suitable specification of the metric would keep them very small within the volume occupied by the ship."

Billy t notes: But those huge gradients would rip apart the distribution of both negative mass in front and normal mass behind that are postulated to be able to make the steep front and aft warp of space. SUMMARY: You can't have your cake and eat it to.

(5) Alcubierre interpreted his "warp bubble" in terms of a contraction of space ahead of the bubble and an expansion behind, but this interpretation may be misleading because the contraction and expansion actually refers to the relative motion of nearby members of the family of ADM observers."

Billy T expands that impossibility in other words: SR's contraction of space is ONLY the way it looks the much slower moving inertial observe, not really a contraction of space time itself. For example, one observer may see a contraction by a factor of two and another observer, in different inertia frame, may see a contraction by factor o four. Space time does not contract at all and certainly not by millions of differ factors all at the same time.

(6) The need for exotic matter raises questions about whether one can distribute the matter in an initial spacetime that lacks a warp bubble in such a way that the bubble is created at a later time, although some physicists have proposed models of dynamical warp-drive spacetimes in which a warp bubble is formed in a previously flat space."

Billy T notes: I think problem here is negative mass has negative gravity - repels or disperses itself. So some physicists are suggesting it could be dispersed widely in flat space time before being needed, and given just the vectorially correct (and different) initial velocity and momentum to come together briefly before dispersing again, just ahead of the flat space with the space ship in it and thus made the highly warped space time just ahead of the flat space with space ship in it. Lots of luck doing that more than solar system dispersal of something that does not exist and giving each particle of exotic negative mass precisely the correct and unique velocity to later converge briefly just ahead of the flat space with space craft.

(7) generating a bubble in a previously flat space for a one-way FTL trip requires forcing the exotic matter to move at local faster-than-light speeds, something that would require the existence of tachyons"

Billy T notes: Note only is non-existent exotic negative mass matter required, but it must locally violate both SR and GR! (TFL a tachyons, which also are not know to exist) Tachyons become more massive as the slow down from faster than C and would be infinitely masses. Some physicsts, following paddoboy's: "if not forbidden they exist" ideas say that they can not interact with normal mass mainly because if they could, then changing the nature of the interaction at point A could send information to point B, FTL. (Also allowing killing of your grandparents before your parents were born, etc.)

(8) Krasnikov proposed that if tachyonic matter cannot be found or used, then a solution might be to arrange for masses along the path of the vessel to be set in motion in such a way that the required field was produced. But in this case, the Alcubierre drive vessel can only travel routes that, like a railroad, have first been equipped with the necessary infrastructure. ... For example, travelling to Vega (which is 25 light-years from Earth) requires arranging everything so that the bubble moving toward Vega with a superluminal velocity would appear; such arrangements will always take more than 25 years."

Billy T comments: Are we assuming that the "infrastructure" stays in the required space location for years as it is "resting on turtles, all the way down"? So has no tendency to clump even though has gravitational mass mutually attracting various parts of it into clumps as it is initially "side by side" along the "railroad track" in space.

(9) Coule has argued that schemes, such as the one proposed by Alcubierre, are infeasible because matter placed en route of the intended path of a craft must be placed at superluminal speed—that constructing an Alcubierre drive requires an Alcubierre drive even if the metric that allows it is physically meaningful. Coule further argues that an analogous objection will apply to any proposed method of constructing an Alcubierre drive.[13]"

I'll stop here after only 9 reasons why this is warp drive is Star Trek science fiction. I.e. not only has paddoboy's "first batter" struck out, all his three batters of the first inning have too. Ironically by quotes from his own link, his 1st inning is over; However, if he wants a 2nd inning turn at bat, there are more than nine more ways his second inning would end still with not one batter reaching first base.

My comments on (2), as promised:
Casmir effect does make slightly less energy in space between closely spaced (mm or less) electrically conducting plates, but it is TOTAL USELESS for making even one billionth of the negative energy required to warp space as is Alcubiere's FTL drive idea. Casmir effect is due to fact space is filled with virtual EM waves of all frequencies, but those with wave lengths longer than the space between the Casmir plates are absent ("shorted out") between the plates. It is much like a metal microwave guide. Any frequency with wave length shorter than the internal circumference (or perimeter for rectangular cross section guide) will not propagate down the wave guide, but for example light waves will shine thru it just fine.

These virtual waves not only exist and give an energy density to space, but they make a "space pressure" too. That pressure in between the Casmir plates is slightly less than outside and with very sensitive detector of net force, it can be measured. One can think of the space between the Casmir plates as with negative pressure (compared to zero pressure outside). It is quite normal to think there is no pressure outside as it "pushes" equally in all directions so is not detectable - gets called "zero pressure" and that then leads to the false idea there is negative pressure between the plates - There is still positive pressure there, just less than outside.

I.e. even between the plates the energy density is positive, not negative as Alcubiere's FTL drive idea requires. Very poor (i.e. false) of him to suggest the Casmir effect shows even one billionth of the "negative energy density" his warp drive requires. - Not even the sign is correct! The energy density is reduced between the plates, but still positive.

 

Agreed.

Also agreed.

Now if you had a _very_ efficient neutron source, you could change that decay rate, and get much longer useful lives out of those RTG's.

 

Yes if you can get the neutron captured. I.e. increase the mass number by one while not changing the atomic number - same chemical, different Isotope. But again that is not modulating the original decay rate, but changing it to that of a different isotope of the same chemical element.

When I have time (see next post) I'll try to return and give an example of one atomic number with at lease five different isotopes. As I recall, if order them by increasing mass, the jumps in half lives help to understand what may be going on in the nucleus. At least in one case (by memory - a "magic number" case) inside that ordering there are some stable isotopes!

 

* I spent half an hour - a lot is new since I last looked into question of why some isotopes have the half lifes they do or are stable. Even "magic numbers" are changed from decades ago. Here is interesting article on that: http://www.scientificamerican.com/article/new-magic-number-atoms-discovered/
Be sure to read the comments too - some are the best part.

 

Wow!! What can I say!
Billy, I'm not sure why, but as in the time thread, you appear to be getting rather emotional about all of this.

In the meantime, despite your ever lengthening posts, my beliefs and reasonings remain as is.
Certain aspects of time and space remain as allowable by GR.
As such, they are not Impossible.
Any sufficiently advanced civilisation can achieve what at this time we may view as Impossible...that includes the manipulation of space time.

Remember pessimism never got humanity anywhere.
I remain optimistic of what mankind can achieve, given time.

 

At this time, going to the stars is just a dream. But many reputable people including the likes of Marc Millis, former expert at Glenn Labs on alternative propulsion physics, is working on that dream as we speak.....
http://www.grc.nasa.gov/WWW/bpp/MillisBio.html
One of those possible methodologies is via space warp technology.
As Marc explained, one way to look at this type of scenario is to imagine the way a toy boat reacts in a bath tub when you put some detergent behind it.
This has the effect of moving the boat forward because the detergent bubbles will expand the space behind the boat.
http://gizmodo.com/5247705/why-we-need-to-reach-the-stars-and-we-will
Yes, only an analogy but when we note and realise that our ventures into space are just beginning and still at the kindergarten stage, and our knowledge of the Universe/spacetime, although having advanced ten fold over the last century, is still rather basic to put it mildly, I find it incredibly naive to think that we are not going to go any further.
There are others of course, Mae Jemeson, physician and NASA astronaut, of the "100 Year Star Ship" Co.

These are people, smart people with vision.
And while Billy has impressive credentials and credentials he should be proud of, so too do the two I have mentioned.
Billy has raised many figures about why this cannot be done, and why that cannot be done, but those same figures are just as available to the likes of Marc Millis and Mae Jemison, who see it in a different light, and do not see it as prohibiting the possibilities of either warp travel or some other means.

The "otherwise" great Lord Kelvin saw no future in continuing mans quest to fly in machines as late as 1897.
Not much more needs to be said about that little faux pas and how such pessimism will almost always be shown to be wrong.
The same "otherwise"great man, had similar views about the discovery of X-Rays.

Any attempt to reach the stars, is going to be difficult and dangerous in the extreme. Any attempt to reach the stars is most probably not viable for the next 100 to 200 years, and certainly totally impossible at this time.
That doesn't mean that it can't be done. That doesn't mean that we stop all the efforts at this early time in that venture and throw in the towel. That doesn't mean we are going to forever stagnate on this little blue orb.
Given time, given optimistic visionaries like the two I have mentioned, the possibility of achieving it in one of many methodologies is always open and possible.

I can't as a lay person refute Billy's many figures and his lengthy posts of why it cannot be done, but I can and I do refute his incredibly naive, and pessimistic attitude to what will and what won't occur.

 

http://www.nasa.gov/sites/default/f...emming-from-Space-Exploration-2013-TAGGED.pdf

Conclusions:
Space exploration has produced an impressive record of benefits for humanity. This paper has distilled a body of evidence of such benefits into a few key observations about the capacity of future space exploration to contribute to innovation, culture and inspiration, and new means to address global challenges. Space exploration has driven scientific and technological innovation that benefits people around the globe every day. Sending humans and machines into space presents challenges that are overcome only by the utmost ingenuity; this leads to new knowledge and technical innovations that are used on Earth in ways that can be dramatic and unpredictable. Space exploration serves a cultural and inspirational purpose by fulfilling a deep need to understand the world, address questions about the origins of life and the nature of the Universe, and to expand the notion of what it means to be human. Because space exploration stimulates significant global investment and international partnerships, and because of its extremely challenging nature, demands the development of cutting edge technical capabilities, it provides unique opportunities to address some of the global challenges facing society today. When nations work together on challenging space missions, this promotes international cooperation beyond the realm of space. It aligns interests and forges relationships that further peace and stability on Earth. There is no activity on Earth that matches the unique challenges of space exploration. The first fifty years of space activity have generated benefits for people around the globe. This past record gives strong reason for confidence that renewed investments in space exploration will have similarly positive impacts for future generations.

 

Hi paddoboy. Well said. But I will say that with use of nanotechnology, interstellar travels can be a reality. Technology is so fast developing day to day that in the near future many problems in space travels can be eliminated.

 

I agree totally. I see nanotechnology as further creating material concepts that will be used to facilitate our eventual interstellar ventures.