Talk:Krasnikov tube

message: I do not get what it is that violates causality in this example. Astronaughts go into one tube, and appear nearly instantaneuously on the other side. Then they go to the other and go back to earth. Its instantaneous but I see no causality violations.
:Instantaneous travel produces causality violations in relativity. There's an explanation in the WP article on special relativity.--76.93.42.50 (talk) 19:49, 7 May 2008 (UTC)
replies: text: I don't see how causality would be violated. Let's say that transit between two points (A and B) that are 3000 lightyears apart takes 5 minutes. A person traveling from point A to point B and back to point A takes 10 minutes to transit, not -6000 years. I can see that some frames of reference exist where the effect from a cause at point A would reach them after the effect at point B (Classic receiving a "battle won" message before receiving "under attack" example) but how does that violate causality? Observers at point C are causally removed from the situation. I understand that it takes a change in how we see time, but I just can't see how it violates causality in a destructive way.  —Preceding unsigned comment added by 173.17.139.28 (talk) 02:18, 9 March 2010 (UTC)
replies: text:  Causality could be violated because once the 2 tubes are in place, astronauts could witness an event 6000 years in Earth's future, go through the 2nd tube back to the distant star, then through the 1st tube to go back to Earth's present (6000 years before the event), and do something to prevent or alter the event.  — Preceding unsigned comment added by 82.232.149.24 (talk) 22:03, 11 September 2012 (UTC)
replies: text:  According to this, Krasnikov's tube is basicaly a time wormhole. --194.152.217.129 (talk) 15:01, 18 September 2012 (UTC)
thread_title: 2 Krasnikov Tubes

message: What prevents time travel or round-trip FTL in the situation where you have two parallel tubes pointing in opposite directions? --Christopher Thomas 20:03, 20 Jun 2005 (UTC)
replies: text: The "causality violations" section makes things much clearer, thanks. The only extra information that would be handy would be a "references" section with links to the papers by Krasnikov, Everett, and Roman. --Christopher Thomas 22:25, 22 Jun 2005 (UTC)
thread_title: Time travel via Krasnikov tubes

message: I note that large parts of this article are rather similar to this article:
http://www.npl.washington.edu/AV/altvw86.html
which was "Published in the September-1997 issue of Analog Science Fiction & Fact Magazine".
Is it republished with permission of the author? —The preceding unsigned comment was added by 137.222.10.57 (talk • contribs) .
:Speaking as John G. Cramer's daughter, I can say that there was no permission from the author. My mother, Pauline Cramer, wrote to me thio morning asking that I have the infringing sections removed. I will have a look later today. --Pleasantville (talk) 10:30, 16 September 2009 (UTC)
replies: text: I have added to the article a request for speedy deletion for copyright violation. If someone is able to rewrite the article without infringing on  Krasnikov Tube: A Subway to the Stars, by John G. Cramer, published in Analog (Sept, 1997), please do. --Pleasantville (talk) 10:38, 16 September 2009 (UTC)
thread_title: Potential copyright violation

message: "Sergei Krasnikov is a theoretical physicist at the Central Astronomical Observatory at Pulkovo in St. Petersburg, Russia. He identified what he saw as a critical flaw in Miguel Alcubierre's space warp proposal for space travel: if the space warp moves faster than the velocity of light, it cannot be controlled from inside. Krasnikov's analysis shows that at superluminal speeds the interior of the bubble is causally isolated from its surface and exterior. Photons cannot pass from the inside to the outside. Therefore, there would be no way of controlling the space warp—of stopping, starting or steering."
If you were to set up a track, of sorts, a series of devices strategically placed throughout space that could sustain and move the warp  bubble onward through space, which would allow an object to be moved through space at superluminal speeds to an intentional destination. This would mean we would first need to have reached the destination using conventional methods to deploy such devices, but at least it would make the trip much faster for future travelers. --Steakpirate 04:52, 27 April 2007 (UTC)
replies: text: The trouble that would arise is, what if the bubble's direction was even just slightly off?  Even if it were only off by a tenth of a degree, the ship would end up something like 71 billion kilometers off course over the distance from Earth to Alpha Centauri.  Would it be possible to steer the bubble from an outside device?  Even if it were so, you'd need quite a few of these devices along the "road" to your destination (or perhaps a large number of these devices orbitting the destination star at a distance of, say, 100 billion kilometers to catch arriving ships).  And what if something went wrong and the bubble were veered off the road completely?  It would end up flying through space forever, uncontrolled. Nik42 18:10, 12 May 2007 (UTC)
thread_title: Response to Warp Bubble Criticism

message: the math on the trip to daneb doesnt seem to work out. the wikipedia page on that star says its 3000 light years away, if the ship created a 2nd tube on the way back, wouldnt it take 6000 years? not 3200 some odd? Narmical 20:29, 24 May 2007 (UTC)
thread_title:  2 tubes 

message: The introductory paragraph speaks of superluminal travel, but the rest speaks of relativistic velocities. What is the case here? --Weissbaer (talk) 22:06, 26 September 2010 (UTC)
thread_title:  Contradiction 

message: I do not think the second reference "^ "Krasnikov Tube". The Arcana Wiki. 2010-03-08. Retrieved 2010-09-20." is an appropriate reference.  — Preceding unsigned comment added by Martin.hedin (talk • contribs) 23:48, 18 November 2013 (UTC)
thread_title:  Reference number 2 

message: On Quora Krasnikov gave as answer to the question of time travel that one can not use tubes in reverse order for time travel as the tubes can be only used by the same ship once:
Can the ship now return to Time B (2020) from "Time A (2016) plus a few minutes" using the tube just as quickly?
I think one should be more precise at this point. So, let's introduce space coordinates into our consideration. Then we have event 1 (the start: Earth, 2016), event 2 (the finish: Destination Star, 2020), and event 3 (the return: Earth, 2016 plus a few minutes). Then, I suppose, your question is: given there is a Krasnikov tube from event 2 to event 3 how soon one can reach Destination Star if one starts at event 3?
My answer: it will take the same 4 years (by the terrestrial clock), if the same ship is used. It is essential that the tube works only in one direction. Besides, in the simplest case by the moment the ship returns (event 3) the tube will have already "dissolved" (it is supposed to lie only between the Earth and the ship).
(full qu or a at https://www.quora.com/How-does-time-add-up-for-observers-outside-of-and-travelers-inside-of-a-Krasnikov-tube?__snids__=1525690532) 
As a variant on the Alcubierre drive (https://en.wikipedia.org/wiki/Alcubierre_drive or using another metric in looking for solutions of Einstein's GR equations, both find/need the existence of exotic matter or negative matter. More over the wikipedia article on the Alcubierre drive does mention Krasnikov tubes. 
Wouldn't it not be better to head these articles under a heading with alternative metrics which are also a mathematical correct solution to the Einstein equitations? For technical (how to build if-ever) arguments  one could propose to have reference to these type of articles. 
GerGroeneveld (talk) 10:26, 25 January 2016 (UTC)
thread_title:  Answer from the man himself: Krasnikov replying