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RECENT POSTS IN THIS TOPIC

amrit: on 1/26/10 at 6:53am UTC, wrote Universe is timeless, time is not part of space. Even with speed higher...

Constantin Leshan: on 9/30/09 at 11:00am UTC, wrote Dear Carlos Barcelo, Your essay contradicts to Hubble's law; outside of...

Helmut Hansen: on 9/30/09 at 4:35am UTC, wrote Dear Mr. Barcelo, Originally, I was preoccupied with philosophical...

Lawrence B. Crowell: on 9/30/09 at 2:02am UTC, wrote I read your paper last summer: S. Finazzi, S. Liberati, and C. Barcelo,...

J.C.N. Smith: on 9/30/09 at 0:01am UTC, wrote Gentlemen, Thank you for an interesting essay. You wrote, "The mainstream...

Uncle Al: on 9/29/09 at 20:13pm UTC, wrote The Scharnhorst effect allows an arbitrarily large lightspeed, arxiv:...

Stefano Finazzi: on 9/29/09 at 13:59pm UTC, wrote Essay Abstract The question of whether it is possible or not to...


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FQXi FORUM
November 25, 2017

CATEGORY: What's Ultimately Possible in Physics? Essay Contest (2009) [back]
TOPIC: On the impossibility of superluminal travel: the warp drive lesson by Carlos Barcelo, Stefano Finazzi, and Stefano Liberati [refresh]
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Author Stefano Finazzi wrote on Sep. 29, 2009 @ 13:59 GMT
Essay Abstract

The question of whether it is possible or not to surpass the speed of light is already centennial. The special theory of relativity took the existence of a speed limit as a principle, the light postulate, which has proven to be enormously predictive. Here we discuss some of its twists and turns when general relativity and quantum mechanics come into play. In particular, we discuss one of the most interesting proposals for faster than light travel: warp drives. Even if one succeeded in creating such spacetime structures, it would be still necessary to check whether they would survive to the switching on of quantum matter effects. Here, we show that the quantum back-reaction to warp-drive geometries, created out of an initially flat spacetime, inevitably lead to their destabilization whenever superluminal speeds are attained. We close this investigation speculating the possible significance of this further success of the speed of light postulate.

Author Bio

C. Barcelo did his PhD in IAA (Spain) and postdocs at Washington University in St. Louis (USA) and the ICG in Portsmouth (UK). He is currently deputy director of the IAA and works on gravitation theory. S. Finazzi did his master in SNS (Italy). He is currently a PhD student in SISSA (Italy) working on gravitation theory under the supervision of S. Liberati. S. Liberati did his PhD in SISSA (Italy) and postdoc at the University of Maryland (USA). He is currently a research professor at SISSA working on gravitation theory.

Download Essay PDF File




Uncle Al wrote on Sep. 29, 2009 @ 20:13 GMT
The Scharnhorst effect allows an arbitrarily large lightspeed, arxiv: gr-qc/010709, quant-ph/0010055.

Prohibition of massed body superluminal propagation arises from undefined division by zero in SR. The same prohibition disallows attainment of absolute zero in thermodynamics. However, negative temperatures kelvin are trivially obtained in lasing media, NMR, MRI imaging, EPR, phosphorescence, optical hole burning, adiabatic demagnetization of paramagnetic salts for refrigeration... A molecular beam of room temperature ammonia molecules passed through a hexapole cylindrical electrostatic field will have half its molecules emerge focused, with negative temperature kelvin. Directed into a low loss cavity, said stream will lase at 23.69 MHz. This tactic is universal, Chinese Phys. Lett. 23 344 (2006).

One imagines suitably scaled application of one or both strategies to superluminal propagation would empirically falsify your conclusion. The limit to physics is then not theory but instead plebeian bench work.

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J.C.N. Smith wrote on Sep. 30, 2009 @ 00:01 GMT
Gentlemen,

Thank you for an interesting essay.

You wrote, "The mainstream opinion in this respect is that generically the physics associated to GR plus QFT (the same theoretical framework we used in our investigation) is always able to avoid the formation of time machines. This is the so called Hawking's chronology protection conjecture [31]. Unfortunately, this conjecture is not yet proved . . . ."

For another approach to demonstrating the impossibility of time travel, please see my essay, 'On the Impossibility of Time Travel,' which appears elsewhere among this collection of essays. Your thoughts and comments on the essay would, of course, be welcome. Thank you.

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Lawrence B. Crowell wrote on Sep. 30, 2009 @ 02:02 GMT
I read your paper last summer:

S. Finazzi, S. Liberati, and C. Barcelo, Phys. Rev. D79, 124017 (2009).

I did some related calculations with warp drives on AdS spacetime. I had this idea that your result in the paper above has implications for information preservation with BTZ black holes and AdS spacetimes. Maybe I will return to the idea to see if there is something which can be worked to completion.

Cheers LC

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Helmut Hansen wrote on Sep. 30, 2009 @ 04:35 GMT
Dear Mr. Barcelo,

Originally, I was preoccupied with philosophical questions, such as the question of the possibility of a scientific metaphysics, but this occupation has ushered me deeply into the territory of modern physics.

By investigating the question How do Space and Time have to be organized in the case of a transcendent foundation of the Universe I came across a geometrical structure which was of archetypal design. I looked very much like a MANDALA. This very beautiful geometrical structure can in fact be read as an extension of the Minkowski diagram.

The space-time-structure related to this archetypal space-time-picture has actually a special feature: The speed of 1/SQRT 2 (0.707 c) seems to be a bifurcation point. At this point the relativistic function splits into two branches. The first part of these two branches is the well-known relativistic function with the speed of light as the ultimate limiting speed. But the second part of the function leads into a branch which is still unknown. Its limiting speed is infinite. I am calling this second branch GOEDELs TRENCH.

If this second branch would really exist then the speed of 1/SQRT 2 (0.707 c) could possibly be a GATE to the stars, because it allows us to reach superluminal speeds by circumventing the lightbarrier.

Kind regards

H. Hansen

See attachment Do Space and Time have an Archetypal Design?

attachments: 1_Do_Space_and_Time_have_an_Archetypal_Design_Hansen_2007.pdf

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Constantin Zaharia Leshan wrote on Sep. 30, 2009 @ 11:00 GMT
Dear Carlos Barcelo,

Your essay contradicts to Hubble's law; outside of the Hubble's sphere the recession velocities of galaxies are greater than the speed of light. To save relativity, the physicists invented the fable as if these galaxies do not move; it is expansion of space-time only. Let's see the definition of motion: Motion - the act of changing location from one place to another. Since the superluminal galaxies changes their location concerning us, consequently it is the true MOTION. Yes, it is a FTL motion of an isolated bubble of space-time with galaxies. We cannot observe this FTL motion only because the speed of photons is limited by the speed of light c. However, the absence of direct observation of FTL motion is not a cause for the terror and persecution of FTL theories. Now all mainstream journals rejects FTL theories as ancient inquisition. In the same way inquisition pursued Bruno and Copernic because their theories contradict to official dogmas.

You wrote: In fact, not only the Alcubierre warp drive but also alternative \spacetime shortcuts", such as the Krasnikov tube [9, 10] or traversable wormholes [5],seem to require the same kind of exotic matter'

There are FTL methods that don't requires any kind of exotic matter, for example Hole teleportation. If universe has a limited volume, we can teleport matter by sending an object outside of universe. What would happen if we sent a body outside the Universe? Since zero-space is a point and where time as a property does not exist, therefore it can not contain a body and consequently this body will appear in the real universe at that same moment in time. With the distances between zero-space and any other point of universe being equal to zero, these holes can potentially exist in every point of universe. Theoretically, body A could appear at random in at point of in the Universe.

For FTL teleportation of matter we need the holes in space-time only, but not exotic matter. My essay explains how to create and detect holes in space-time.

Sincerely, Leshan

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amrit wrote on Jan. 26, 2010 @ 06:53 GMT
Universe is timeless, time is not part of space.

Even with speed higher of light speed no way to travel in time.

We can only travel in space.

Yours Amrit

attachments: TIMELESS_UNIVERSE.pdf

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