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What Travels Faster Than What?


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#1 Qfwfq

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Posted 23 September 2011 - 09:24 AM

The neutrino has been caught at speeding! No, it won't have to pay a fine, even going to jail isn't enough, not even the DP, no, it's far far more serious than that. They say it is going faster than light!!!!!!

http://arxiv.org/pdf/1109.4897v1

Of course, folks are wildly drawing conclusions. Some say this means Einstein was wrong... or, at least, not perfectly right. Others say he was right, it only means that time travel is possible. What do you say?

I say it would mean people ought to finally get out of the habit of calling [imath]c[/imath] "the speed of light", or even "the speed of light in vacuo", or even "the speed of EM radiation in vacuo", because, as I often so feebly try to remind folks, [imath]c[/imath] is a much more general and, especially, more fundamental thing than that.

So, is the neutrino going faster than the photon? Or is it just that the photon isn't going quite as fast as the neutrino? What I mean is that maybe this breakthrough only shows that light isn't quite the best empirical tool for determining [imath]c[/imath] with. :shrug:

Edited by Qfwfq, 25 September 2011 - 02:42 PM.
dumb typos


#2 JMJones0424

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Posted 23 September 2011 - 11:31 AM

One of my favorite blogs is Starts With a Bang. I appreciate the author's ability to explain complicated concepts in a way that I can understand.

Besides raising doubt on the accuracy of their spatial measurements (60 nanoseconds at c is 18 meters), Ethan Siegel raises the following point-

Now, something fishy and possibly very interesting is going on, and there will certainly be scientists weighing in with new analysis in the coming weeks. But in all the excitement of this group declaring that they observe neutrinos moving faster than the speed of light, don't forget what we've already observed to much greater precision! And be skeptical of this result, and of the interpretation that neutrinos are moving faster than light, until we know more.


He uses data from neutrino detection from Supernova 1987A to refute this groups claims that neutrinos travel faster than c.
http://scienceblogs....claim_requi.php

#3 Qfwfq

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Posted 24 September 2011 - 11:55 AM

First clarification: the OPERA group itself is being very cautious, the made the announcement now that they really can't find any fault with their method and analyisis, they made it mainly to put it up for scrutiny by anybody sufficiently competent. I think Ethan Siegel would do better to check their details than to scoff at them so easily.

Second clarification: My point was in the sense that, even if it gets fully confirmed, we should be judicious in drawing conclusions.

Besides raising doubt on the accuracy of their spatial measurements (60 nanoseconds at c is 18 meters), Ethan Siegel raises the following point

It took me a bit to find where he raises this particular doubt and I'm not sure he has diligently examined their paper (my link above). Anyway it had occured to me to calculate the same thing and to ask how precise and reliable their measurements of distance are, I found the answers by the time I looked through their paper and saw some of the webcast yesterday. Their distance measurements are very precise indeed, accurate to 20cm which is quite amazing, and it's an ongoing measurement in which the changes through these years can be seen in the data (despite being less than the nominal accuracy). Their technique defeats Siegel's objection about effects of the atmosphere on EM propagation (and note that they are not comparing with photons sent directly between the same two places). They discuss their analysis in details concerning the production of the beam and the statistics. I think Siegel ought to have looked through these things carefully before all too easily criticizing.

He uses data from neutrino detection from Supernova 1987A to refute this groups claims that neutrinos travel faster than c.
http://scienceblogs....claim_requi.php

This does appear conflicting with the OPERA results, providing those 23 events were from the supernova. It certainly is a puzzle because I don't get the impression that the OPERA group made mistakes as coarse as Siegel implies.

#4 Fluxus

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Posted 24 September 2011 - 01:08 PM

FWIW, I don't think Siegel is definitively saying "don't you believe it." He's just saying it conflicts with what he regards as more accurate results, and to be skeptical of this claim until or unless its results are verified. He also does acknowledge that OPERA took "great care" with this measurement

#5 LaurieAG

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Posted 24 September 2011 - 11:47 PM

Hi Qfwfq,

The neutrino has been caught at speeding! No, it won't have to pay a fine, even going to jail isn't enough, not even the DP, no, it's far far more serious than that. They say it is going faster than light!!!!!!


Not quite, the issue is with the calculated neutrino speed which is less than the speed of light. The experimental difference compared with some astronomical observations means the observed neutrino's are coming in about 4 years too late. This is an application issue not a theory issue.

The CERN team have been very thorough to date and their results are consistent so if there is an error all results will share the same error.

The total time elapsed from the moment photons reach the photocathode, a trigger is issued by the ROC analogue frontend chip, and the trigger arrives at the FPGA, where it is time-stamped, was determined to be (50.2 ± 2.3) ns.


The kicker signal is just used as a pre-trigger and as an arbitrary time origin. The measurement of the TOFv is based instead on the BCT waveforms, which are tagged with respect to the UTC.


The UTC time stamp is based on the kicker signal and the TOFv does not appear to have the 50.2 ± 2.3 ns added to the OPERA waveform UTC timestamp at the end. It's a pity Fig 2 doesn't show the actual point where the kicker signal is collected.

The arrival time distribution of the photons to the photocathode and the time walk due to the discriminator threshold in the analogue frontend chip as a function of the signal pulse height were accurately parameterized in laboratory measurements and included in the detector simulation.


Several checks were performed by comparing data and simulated events, as far as the earliest TT hit timing is concerned. Data and simulations agree within the Monte Carlo systematic uncertainty of 3 ns for both the time difference between the earliest and the following hits, and for the difference between the earliest hit and the average hit timing of muon tracks.


If the detector simulation has the same error and the FPGA lag has been paramterised (included in the calcs) instead of being used as an end UTC time stamp adjustment you would get a consistent error.

#6 Qfwfq

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Posted 25 September 2011 - 01:47 PM

FWIW, I don't think Siegel is definitively saying "don't you believe it." He's just saying it conflicts with what he regards as more accurate results, and to be skeptical of this claim until or unless its results are verified. He also does acknowledge that OPERA took "great care" with this measurement

Not quite.

I was talking about some of his specific arguments against the claim, which suggest he hadn't properly read/understood their paper before addressing the matter.

#7 Fluxus

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Posted 25 September 2011 - 11:56 PM

Not quite. I was talking about some of his specific arguments against the claim, which suggest he hadn't properly read/understood their paper before addressing the matter.

I agree that I don't see much of an indication that he pored over the article in the 20 minutes between the announcement and when he started writing it. :D

However, the only specific refutation I see there is that the OPERA results directly conflict with the Supernova evidence. My understanding is that if OPERA's measurement of the neutrino's speed is in fact correct, then the neutrinos released by the supernova should have shown up 4 years before the photons got here. Instead, it was just a few hours, which is easily explained without suggesting that neutrinos are faster than light.

I.e. I don't think it's his goal to provide a highly specific explanation of the flaw in OPERA's data; that's going to take weeks -- if not months, given how thorough OPERA reviewed their data. He's just saying that he's siding with the current belief that nothing can travel faster than c, no matter what data OPERA happened to produce.

#8 quantumtopology

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Posted 26 September 2011 - 08:30 AM

First clarification: the OPERA group itself is being very cautious, the made the announcement now that they really can't find any fault with their method and analyisis, they made it mainly to put it up for scrutiny by anybody sufficiently competent. I think Ethan Siegel would do better to check their details than to scoff at them so easily.

Second clarification: My point was in the sense that, even if it gets fully confirmed, we should be judicious in drawing conclusions.

Hi Qfwfq, I agree with you, even if the results are confirmed we should be careful with the interpretation, the media and some scientists are drawing all kind of absurd conclusions. IMO questioning relativity is the last option not the first, because the implications would deny almost a century of very accurate experiments.
Apparently serious researchers are looking at the fit between the pulses sent from the CERN and the detections at Gran Sasso, and some assumptions like the 10 microseconds lapse pulses from CERN having the same event probability at the detection end, are being questioned.
On the other hand certainly before declaring relativity and thus practically all of modern physiscs dead we should also reexamine assumptions about the nature of neutrinos, a particle that has had some exotic features from its theorizing by Pauli and posterior indirect detection.
Some speculate that maybe some of the detected signals may not be coming from the CERN, being local instead, related to the vacuum energy fluctuations.
There's a lot to be done before though, like replicating the results by another team.

#9 Qfwfq

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Posted 26 September 2011 - 11:06 AM

...in the 20 minutes between the announcement and when he started writing it.

Exactly. He started receiving questions from his fans and he gave knee-jerk replies. Not so scientific of him. :naughty:

However, the only specific refutation I see there is that the OPERA results directly conflict with the Supernova evidence. My understanding is that if OPERA's measurement of the neutrino's speed is in fact correct, then the neutrinos released by the supernova should have shown up 4 years before the photons got here. Instead, it was just a few hours, which is easily explained without suggesting that neutrinos are faster than light.

I have already mildly suggested that there is a slight assumption in this, however plausible it may be. After that, another thought occurred to me but it would be a more complicated thing to work out and I'm not sure how worthy it is. In short, you never know.

He's just saying that he's siding with the current belief that nothing can travel faster than c

Actually, that's my belief too. If you got my point, you'd be aware of it but, instead, you are committing the same thing I was guarding against.

I have long been pointing out that we should not identify [imath]c[/imath] with "the speed of light" but instead regard it as something much more fundamental... and there you go and do it yet again! :lol:

#10 JMJones0424

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Posted 26 September 2011 - 04:18 PM

I may be inadvertently taking the track of this thread off of your intended course Q, if so I apologize. Please move my posts to another thread if you feel the need. Hypography is my only source for trying to flesh out an understanding of what is going on, so I appreciate your critique of Ethan Siegel's blog. Keeping in mind the (lack of) education of your audience (me)...

What I mean is that maybe this breakthrough only shows that light isn't quite the best empirical tool for determining [imath]c[/imath] with. :shrug:


Are you suggesting that the value of c could be greater than we currently measure it to be using light? If so, wouldn't a higher value of c mess up mass/energy equations for very low mass, high energy particles in colliders, or are we not able to accurately measure these things well enough to provide an alternative source for the value of c? If photons in a near perfect vacuum travel slower than c at enough magnitude that neutrinos, while still being slower than c, actually travel faster than photons, would this not mean that photons must have mass?

#11 Qfwfq

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Posted 27 September 2011 - 04:40 AM

Don't worry JM, you're a great member and I apprecieate your calling attention to Siegel's blog, I appreciate him having called attention to the supernova event, I just put in my critique of his overly hasty response. :)

Are you suggesting that the value of c could be greater than we currently measure it to be using light?

Yes, if no flaw is found in these results I would regard this as the most plausible line of investigation.

If so, wouldn't a higher value of c mess up mass/energy equations for very low mass, high energy particles in colliders, or are we not able to accurately measure these things well enough to provide an alternative source for the value of c?

Agreed, and I was thinking the same myself. I don't possess all the detailed existing data and it might be quite an undertaking to check the compatibility, unless too many blatant contradictions come in at the onset, but it is possible that all could be sorted out in the end (including the supernova, perhaps with implications about GR).

One point I've been pondering is whether an electrically charged particle ought to be subject to the same effect as I conjecture for the photon (perhaps according to charge-mass ratio) if it is a matter of vacuum polarizability. Such aspects would be novel territory, if there is anything to the OPERA results.

One thing I stress is that both refuting SR and speculating time travel are the last conclusions to draw.

#12 quantumtopology

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Posted 27 September 2011 - 04:49 AM

I have next to zero knowledge about particle physics, so this may be a dumb question, do they have a baseline number of neutrino detection events when the accelerator is off? I would bet that count should be really low if they only obtain 15000 with the beam on, but I'm curious about this specific figure.
Thanks

#13 CraigD

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Posted 27 September 2011 - 07:29 AM

The neutrino has been caught at speeding! No, it won't have to pay a fine, even going to jail isn't enough, not even the DP, no, it's far far more serious than that. They say it is going faster than light!!!!!!

Not quite, the issue is with the calculated neutrino speed which is less than the speed of light. The experimental difference compared with some astronomical observations means the observed neutrino's are coming in about 4 years too late. This is an application issue not a theory issue.

I think you’re misreading the “4 years late” mention, Laurie :Exclamati It states that, if the speed of neutrinos were what the CERN OPERA experiment findings suggest, the increase in neutrino detection rate that accompanied the 1987 detection of a supernova about 168000 ly distant (SN 1987A) should have been detected about 4 years too early, before the light from that event was detected, rather than the about 3 minutes early actually observed. This slight (about [imath]\frac{|v-c|}{c} = 2 \times 10^{-11}[/imath]) difference in detection time is, I think, due not to the neutrons traveling faster than c (exactly 299792458 m/s), but due to the light signal traveling slightly slower due to the slightly less than perfect vacuum of the interstellar medium.

According to everything I’ve read, such as this wikipedia article section, the speed of neutrinos in vacuum has be shown to be very nearly (within 0.0000001%, or one part in 109) exactly the same as the speed of light, c. Most theorists, I believe, expect the two speeds to be exactly equal. The OPERA findings show it to be 1.00002 c, that is faster by about 0.002% or one part in 105.

I think most physicists, including the OPERA ones, are betting at present that this finding is either a statistical fluke or a subtle mistake in the design or execution of the experiment. Unburdened as I am from the need to be so cautious, I’m just gonna take the result at face value and leap right into speculating how FTL neutrinos could be physically real:

The most obvious difference between SN 1987A lighspeed and OPERA’s FTL neutrinos are the medium through which they traveled. SN 1987A’s traveled mostly through the near complete vacuum of interstellar space, while OPERA’s traveled through roughly 1020 times denser dirt and rock, leading me to the vague suspicion that the OPERA neutrinos’ much greater interaction with massive particles is responsible for the difference in neutron speed.

I recall about 4 years ago another announcement of an apparently FTL signal by the University of Koblenz’s (DE) Gunter Nimtz and Alfons Stahlhofen (who’s original announcement dates back to at least early 2004), which we discussed in the threads FTL signaling through frustrated total internal reflection and We have broken speed of light. Summarizing, Nimtz and Stahlhofen’s results suggest that the small fraction of a light not reflected but instead passing through a pair of slightly separated glass prisms effectively traveled faster than c due to non-classical, quantum tunneling effects.

My hunch is that the OPERA neutrinos are doing something similar to N&S’s photons, tunneling many times due to interaction with all the dirt through which they pass, which functions as a partial “neutrino barrier” (while neutrinos interact only very weakly with matter like dirt, they do interact) similar to the photonic barriers N&S describe in such articles as this 22 Apr 2004 Popular Science one.

As in our 2007 threads, my intuition is that these FTL effects are physically real. If I’m right, the consequences are profound, as FTL signaling leads, inevitably it seems, to possible causality violations (Richard Baker’s http://www.thecultur...es/000089.html'>Sharp Blue: Relativity, FTL, and causality remains the best and prettiest explanation of this I’ve seen). “Cosmic censorship” of such effects appears to me to be the great engineering difficulty of actually making (artificially or via an accident of nature) a signaling-into-the-past device. In my vast leisure time ;) I’ll try to calculate some details, but it seems to me to involve accelerating planet or greater mass bodies to appreciable fractions of c, engineering far beyond the capability of our presently about type 0.72 civilization.

#14 Qfwfq

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Posted 27 September 2011 - 11:23 AM

do they have a baseline number of neutrino detection events when the accelerator is off?

Of course they see the difference between during and out of beam pulses. The real difficulty is the pulse duration which is necessarily greater than 60 ns so it took humonguous statistical analysis to come out with that kind of a precise determination.

I think you’re misreading the “4 years late” mention, Laurie

Actually Craig, he meant “4 years late” in comparison to 4 years earlier... :hihi:

Did you get my drift about time travel not necessarily being a consequent possibility?

#15 quantumtopology

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Posted 27 September 2011 - 01:30 PM

Unburdened as I am from the need to be so cautious, I’m just gonna take the result at face value and leap right into speculating how FTL neutrinos could be physically real:

The most obvious difference between SN 1987A lighspeed and OPERA’s FTL neutrinos are the medium through which they traveled. SN 1987A’s traveled mostly through the near complete vacuum of interstellar space, while OPERA’s traveled through roughly 1020 times denser dirt and rock, leading me to the vague suspicion that the OPERA neutrinos’ much greater interaction with massive particles is responsible for the difference in neutron speed.

I recall about 4 years ago another announcement of an apparently FTL signal by the University of Koblenz’s (DE) Gunter Nimtz and Alfons Stahlhofen (who’s original announcement dates back to at least early 2004), which we discussed in the threads FTL signaling through frustrated total internal reflection and We have broken speed of light. Summarizing, Nimtz and Stahlhofen’s results suggest that the small fraction of a light not reflected but instead passing through a pair of slightly separated glass prisms effectively traveled faster than c due to non-classical, quantum tunneling effects.

My hunch is that the OPERA neutrinos are doing something similar to N&S’s photons, tunneling many times due to interaction with all the dirt through which they pass, which functions as a partial “neutrino barrier” (while neutrinos interact only very weakly with matter like dirt, they do interact) similar to the photonic barriers N&S describe in such articles as this 22 Apr 2004 Popular Science one.

As in our 2007 threads, my intuition is that these FTL effects are physically real. If I’m right, the consequences are profound, as FTL signaling leads, inevitably it seems, to possible causality violations (Richard Baker’s http://www.thecultur...es/000089.html'>Sharp Blue: Relativity, FTL, and causality remains the best and prettiest explanation of this I’ve seen). “Cosmic censorship” of such effects appears to me to be the great engineering difficulty of actually making (artificially or via an accident of nature) a signaling-into-the-past device. In my vast leisure time ;) I’ll try to calculate some details, but it seems to me to involve accelerating planet or greater mass bodies to appreciable fractions of c, engineering far beyond the capability of our presently about type 0.72 civilization.

I find this point of view very interesting, the thing is if after all this turns out to be a quantum effect it wouldn't have such tremendous impact in relativity as the media and many scientists claim, what I mean is that we have always known that some "non-local" quantum effects seem to defy c as a limit, I'm thinking of the EPR experiments etc, the key point about all of them is that this "non-locality" can't be used to send information faster than light so relativity remains fine.
I think the same situation appear here in the way the neutrinos are detected, wich can only be in a statistical way, that is there's no way we can send a neutrino and be sure that one will be detected, we need to send zillions to recover a few of them.
All this of course provided it is not due to some error in the latency time claculation or some bias in the detected neutrinos wrt the pulse waveform.
Where I do see some new physics is in the fact that it is hard to see how neutrinos could have some mass from these results, it would look like at the very least they travel at lightspeed but this contradicts flavour oscillation. It's all really odd.

Of course they see the difference between during and out of beam pulses. The real difficulty is the pulse duration which is necessarily greater than 60 ns so it took humonguous statistical analysis to come out with that kind of a precise determination.

Ok, I see, thanks.

#16 CraigD

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Posted 29 September 2011 - 12:50 PM

Did you get my drift about time travel not necessarily being a consequent possibility?

I think I do, but to be sure, let me playback what I think you’re saying and implying:

Suppose the constant c, as it appears in the Lorentz term throughout special relativity, such as the time dilation formula [imath]t_s = t_f \sqrt{1-\left( \frac{v}{c}\right)^2}[/imath], is actually slightly greater than the observed speed of light in vacuum [imath]s_L = 299792458 \,\mbox{m/s}[/imath]. Let’s call this “true” constant [imath]c^*[/imath].

The various experimental confirmations of relativity would be unaffected, because [imath]s_L - c^*[/imath] is smaller than these experiments’ precisions could detect, so the theoretical framework of modern physics isn’t much threatened.

An explanation of the slowness of light in vacuum is that, as when it’s slower in a medium with a non-zero index of refraction, such as air or glass, photons are interacting with something in the vacuum. Neutrinos, however, even when traveling through a dense medium such as the Earth, interact much less than photons, even in vacuum, so their speed is closer to [imath]c^*[/imath].

Since even neutrinos travel less than [imath]c^*[/imath], no scheme using them or any other particle can send a causality-destroying signal into the past.

Please let me know if I’m wrong or missing something important.

I find this point of view very interesting, the thing is if after all this turns out to be a quantum effect it wouldn't have such tremendous impact in relativity as the media and many scientists claim, what I mean is that we have always known that some "non-local" quantum effects seem to defy c as a limit, I'm thinking of the EPR experiments etc, the key point about all of them is that this "non-locality" can't be used to send information faster than light so relativity remains fine.

What the OPERA group is reporting is a phenomenon that could be used for genuine faster-than c signaling – in principle, a strong, very brief neutrino emitter could send information to a receiver before a light signal could, for a sufficiently large emitter-detector distance d, in less time than [imath]t=\frac{d}{c}[/imath]. Non-local quantum effect such as the measurement of complementary states of entangled particles at great distances from one another can’t be used for signaling, because it’s not possible to force either measurement to be a given state. In other words, such setups can “communicate” instantly, but can their signal must be “100% noise, 0% signal”, incapable of sending information. The recent OPERA result, and Nimtz Stahlhofen’s FTIR experiment’s result, don’t have this limitation. They could, in principle, send information.

The implications of this are tremendous. Either causality can, in principle, be violated, by information from the future being sent to the past, the theory that predicts that a FTL signal can do this, special relativity, is wrong, or something even weirder must be true.

Of course, the smart bets are, I think, still on the explanation that some as-yet unknown things are wrong with these experiments. As Qfwfq pointed out, some “humonguous statistical analysis” has to have been involved, not to mention a lot of possible points of consistent failure in the physical apparatus and its design. Personally, I’m hoping there’s not, and that causality violation is a real potential feature of physical reality. Considering the difficulty of building or finding anything realizing the effect on a macroscopic time scale, despite its profundity, this isn’t nearly as scary as prospect to me as the old, realized ones of the 1940s that showed the way to the creation of nuclear weapons. Even if time travel/signaling is shown to be in principle possible, “time wars” and the accidental destruction of all time and space will, I’m fairly certain, remain the stuff of scifi.

#17 quantumtopology

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Posted 29 September 2011 - 03:57 PM

What the OPERA group is reporting is a phenomenon that could be used for genuine faster-than c signaling – in principle, a strong, very brief neutrino emitter could send information to a receiver before a light signal could, for a sufficiently large emitter-detector distance d, in less time than [imath]t=\frac{d}{c}[/imath]. Non-local quantum effect such as the measurement of complementary states of entangled particles at great distances from one another can’t be used for signaling, because it’s not possible to force either measurement to be a given state. In other words, such setups can “communicate” instantly, but can their signal must be “100% noise, 0% signal”, incapable of sending information. The recent OPERA result, and Nimtz Stahlhofen’s FTIR experiment’s result, don’t have this limitation. They could, in principle, send information.

Don't you see as a limitation the fact that it is impossible to predict if an individual neutrino sent at one point will be detected at the other? I mean they needed 10^20 neutrinos to obtain 10^4 detection events after a few years. I would say this limits sending any information faster than light that differentiates itself from random noise no matter how strong the emitter is (and there's also energy limitations to that).
I'm not sure but I don't even think for instance Nimtz claims that his experiments defy causality, only that they show Lorentz violation, actually here http://arxiv.org/abs/physics/0009043 Nimtz claims causality is preserved. Certainly the closely related Scharnhorst effect in the words of Scharnhorst himself according to wikipedia argues that the effect can't be used to create causal paradoxes.