FTL communication

[rtxoff]

But I will not always be nice to someone who repeatedly ignores others that actually know physics,

And i think anyone claiming to actually know physics doesn't know it at all. The best science people accepted the fact that sometimes learning requires forgetting everything you know about something.

and who tends to throw his unscientific comments into every second discussion.

You are sure talking about such unscientific posts like this:

N_las already gave a proof that FTL transmissions cause time travel.

Pardon, what? Now, how could he have done that without creating a FTL transmission?

And that is why I won't ignore such behaviour: it is spreading misinformation. Your posts actually tell people wrong things, and thus they need to be corrected.

Despite most of your posts tell right things (more then mine) some of them need correction too. You are not Mr. "I know the truth about the whole universe" my dear.

And ideally, you should stop making them, but I gave up on that part.

Good, cause i won't stop.

The problem are not those asking questions. The problem are those that claim to have an answer despite actually not having a clue about physics.

I think it's better to try to come up with an answer even if it complete bulls**t then have no answer at all. Solutions arrive by trying not by accepting things how they are.

This is not politics where things generally get down to more or less founded oppinions.

Just look at the post above this one and tell me it's not politics.

I am happy to answer questions, but prefer if people would read the last few pages of a thread before answering to it, as responding to the same stuff three times in the span of a few hours is just annoying. Anyway, if you are actually seeking an answer and not just search for confirmation of your weird theories, you are welcome to ask.

It's not weird theories it's weird speculations at best, this thread is about superluminal communications, what do you expect? An hypothesis and a working theory have still to be made about it but obviously some individuums are not ready for that.

[K^2]

The only thing teleported there are quantum states, unless there is a version I am not aware of. It is quite weird to call a transmission of information "teleportation".

All mater is just quantum states of the vacuum, plus a few conserved quantities, like total angular momentum and energy, that you will need to supply on receiving end. So while we are quite limited in what we can do with it yet, this is true teleportation.

[ZetaX]

K^2: I know that and already said so in an earlier post. While the term is technically correct, it is still don't like it due to seemingly promissing more than it really does. I met just too many people that got almost everything about quantum mechanics wrong (just take a look at this forum...), and I think this is partially due to the naming schemes. Physicists are somewhat following the rule of cool, and in an ideal world that would be fine (and cool ;-) ); but sadly, reality has things like idiotic media and ill-informed people.

Anyway, I find this nitpicky discussion pretty useless as long as that many horribly-misinformed people are here in the forum, despite this one being about science.

Pardon, what? Now, how could he have done that without creating a FTL transmission?

Done what¿ I said that FTL implies time travel (and vice versa), so how is this an answer to that¿

You are not Mr. "I know the truth about the whole universe" my dear.

Well, I am in agreement with what you can find in books or the non-crank physics of the web (e.g. Wikipedia). Also, it's not just me, but also N_las, K^2 or whoever else probably got at least some university level physics education. I am in full agreement with the latter two I think (except on some naming schemes ;-) ).

Good, cause i won't stop.

And exactly here lies the difference between a rational and scientific person and you: the former would never claim such things he is not quite sure about or has not cross-checked with the state of the art science. If someone tells me that I am wrong in saying that all swans are white, then I go check; and if I fail to find any such evidence against me, then I ask for proof, and accept it if I get such. But actually, I would probably never belief such a thing in the first place as the only argument for that example would be that I never saw any other, which is very weak.

Spreading things you don't really know is almost as bad as spreading lies. One of the major sins of rationality, one could say.

I think it's better to try to come up with an answer even if it complete bulls**t then have no answer at all.

So a "god of the gaps" is fine as an explaination of everything we don't understand¿ Or if I say that "dark energy" is actually my magic teapot pushing quantum-space-matter away, then this is better than "I simply don't know"¿ It is always better to know what you don't know and to openly admit that than to just make stuff up. Hypotheses are not just made up from nothing, but are made after observing the relevant things for a bit, then trying to formalize what you saw.

Just look at the post above this one and tell me it's not politics.

The physics is not politics. Convincing other people is.

It's not weird theories it's weird speculations at best, this thread is about superluminal communications, what do you expect?

That anything people come up with is in agreement with already well-tested science like special relativity, or that people stop using things that have been shown to be in disagreement with that physics. Remember what I said about SciFi not being fantasy¿ It's exactly that difference.

And by the way, I did not even claim FTL and/or time travel is impossible. I just said that assuming some philosopical stuff (see many pages back; but I think we both use those assumptions anyway) implies that those two are equivalent. So you either have to throw away causality, or have special kinds of determinism (including that the universe is determined to never cause causal contradictions), pr some censorship, or just add such a thing like "then the universe simply crashes and our god/admin deletes it"; or whatever else that makes it work.

An hypothesis and a working theory have still to be made about it but obviously some individuums are not ready for that.

It is pretty cheap to dismiss physics arguments like that.

[K^2]

K^2: I know that and already said so in an earlier post. While the term is technically correct, it is still don't like it due to seemingly promissing more than it really does. [...] Physicists are somewhat following the rule of cool

So wait, we agree that it's technically a correct name. But then you complain that the problem is with Physicists trying to oversell things with cool names. And I agree that it is a problem sometimes with some names. But if it does what it says on the tin, is it our problem that some people have unreasonable expectations? Our naming scheme shouldn't depend on what a lay person thinks of it. It should be based on whether or not it describes what something does. And quantum teleportation describes what it does. The quantum state is not carried across via any quantum channel, but is taken directly from one location to another. There is no way to describe it other than as teleportation.

[ibeinsane]

K^2:

Anyway, I find this nitpicky discussion pretty useless as long as that many horribly-misinformed people are here in the forum, despite this one being about science.

Well, I am in agreement with what you can find in books or the non-crank physics of the web (e.g. Wikipedia). Also, it's not just me, but also N_las, K^2 or whoever else probably got at least some university level physics education. I am in full agreement with the latter two I think (except on some naming schemes ;-) ).

Hello again,

I want to add to this post now as I think there are some very discriminative posts being added.

To start I am a physicist (time served and PhD), specialising in surface and plasma technology. This does not make me qualified to argue the finer points of current quantum mechanics theory, especially a subject which is still under significant discussion as to the interpretation of quantum mechanics, indeed my knowledge is only from a few modules taken considerable time ago, most of which is a) at least 10 years old and forgotten.

What I would like to add here is that simply dismissing any comment as the incorrect interpretation by non physicists is not an adequate argument, you may as well say 'don't you worry your pretty little head about it'. I agree about the media sensationalising and causing misinterpretations but it is the media support that provides much of the public appetite for funding these fields.

As part of my professional membership I am required to promote learning, knowledge exchange and the promotion of all fields of physics. You are failing in this matter! If you are not able to promote learning because you feel people are too uneducated to learn then you should not be taking part in the discussion. This is a place for people to ask questions and receive answers not feel belittled. I hope you will keep the discussion supportive and attempting to educate people rather than pursuing the tone of this thread.

I have other actual questions on this topic coming up

[ZetaX]

K^2: It also requires a classical channel, so I would not say that it is pure teleportation. Do we agree that it is "transmitting quantum states via classical channels" (assuming prior existence of entangled pairs)¿ Thus the "only" thing truly teleported is the quantum aspect (which carries a lot of meaning, still). That's why I would prefer "quantum transmission" for that one.

Well, changing the term is probably not a realistic option anyway. I have also given this some more thought and I am unsure about my previous oppinion in this matter: anyone who really gets into physics will learn the correct meaning anyway, and everyone else does not need to know (and will not cause any harm; this point is quite different on other topics like basic analysis, where an engineer failing something might cause fatalities). Thus the cool naming schemes might cause a net profit, despite feeling a bit dishonest, by provocing more people to learn actual phyics.

As part of my professional membership I am required to promote learning, knowledge exchange and the promotion of all fields of physics. You are failing in this matter! If you are not able to promote learning because you feel people are too uneducated to learn then you should not be taking part in the discussion. This is a place for people to ask questions and receive answers not feel belittled. I hope you will keep the discussion supportive and attempting to educate people rather than pursuing the tone of this thread.

Would you at least read my posts fully instead of putting stuff out of context¿ I never said what you wrote there, instead I explicitely made clear what I mean later in the post!

Again: there is a huge difference between persons seeking answers to their questions, and people just wanting to be reassured of their (wrong) oppinions. I will gladly teach the former (and actually do that a lot in my free time; not talking about the internet, but about giving talks/courses/similiar things to younger people), but I refuse to treat the latter the same. If someone's errors have been pointed out several times and his best responses are "you just don't want this to be true" then being nice and letting him spread his wrongness will help nobody.

To take you as an example: you insisted on things about entanglement those articles never said; but as you seemed interested in actually finding out the discrepancy between us, I had no problem continuing the discussion on the physics level.

I think I only responded badly once in this thread (to WestAir), and I already said I am sorry for that.

[ibeinsane]

Actually I have been reading all the posts with quite considerable interest, it is a field I am quite interested in.

The actual comment I took exception to was 'or whoever else probably got at least some university level physics education' which to me is quite an exclusionary response. Of course I do understand where you are coming from and perhaps I misinterpreted your intentions in that post. As for the comments you failed to expand on what was wrong with the papers I cited, although I now agree I misinterpreted their entanglement the response was very dismissive and without explanation. Hopefully we can keep this on track and put the disagreements behind us.

As for my actual question;

What is the speed at which an electron tunnels in the quantum tunnelling affect? I understand the mechanism of movement in that the distances are close enough that the wavefunction function overlaps the gap allowing for the particle to provide finite probability to exist in either well. I also actually understand that QM states that the particle exists in both spaces at the same time as a wave function.

The question becomes if the gap between the tunnel would extend to a large enough gap to be observed (ignore the probability issue), from whose perspective does the electron exist in both wells at the same time (ours or it’s) and what is actually travelling between the wells, for instance during electrical conduction from atom to atom?

My understanding is that the idea of the wavefunction and whether it is an actual field or a probability distribution of a particle’s position is as of yet undetermined and although theorised, neither view has real majority. Certainly either raises the probability of a particle to exist at once side and then the other would yield the question is it FTL? Certainly time taken traversing an energy barrier would require energy expenditure not possible in these affects, in any time reference.

[rtxoff]

Done what¿ I said that FTL implies time travel (and vice versa), so how is this an answer to that¿

No, don't swap the facts you clearly said:

N_las already gave a proof that FTL transmissions cause time travel.

Everybody can look back in this thread and verify that.

And exactly here lies the difference between a rational and scientific person and you: the former would never claim such things he is not quite sure about or has not cross-checked with the state of the art science. If someone tells me that I am wrong in saying that all swans are white, then I go check; and if I fail to find any such evidence against me, then I ask for proof, and accept it if I get such. But actually, I would probably never belief such a thing in the first place as the only argument for that example would be that I never saw any other, which is very weak.

Spreading things you don't really know is almost as bad as spreading lies. One of the major sins of rationality, one could say.

Maybe you are the one spreading lies and you don't even realize it. Only because something is written in a book does not mean that it is the ultimate truth. Only because 99% of the science folk agree about a particular matter does not mean it is the ultimate truth. Science was and will always be subject to change. Science books got rewritten often enough in the history that could happen again.

So a "god of the gaps" is fine as an explaination of everything we don't understand¿

If you can at any way explain "god of the gaps" in a logical way maybe we would consider it.

Or if I say that "dark energy" is actually my magic teapot pushing quantum-space-matter away, then this is better than "I simply don't know"¿

At least it's an attempt however a pretty clumsy one.

It is always better to know what you don't know and to openly admit that than to just make stuff up.

I never denied that however i know of a person here who did.

Hypotheses are not just made up from nothing, but are made after observing the relevant things for a bit, then trying to formalize what you saw.

Yeah right, like the observation of a black hole for example. lol

The physics is not politics. Convincing other people is.

I did not begin with that.

That anything people come up with is in agreement with already well-tested science like special relativity, or that people stop using things that have been shown to be in disagreement with that physics. Remember what I said about SciFi not being fantasy¿ It's exactly that difference.

Well if you expect that then you clearly are in the wrong thread because FTL comms will be in disagreement with that physics for sure and also this physics is saying that it is not possible.

And by the way, I did not even claim FTL and/or time travel is impossible. I just said that assuming some philosopical stuff (see many pages back; but I think we both use those assumptions anyway) implies that those two are equivalent. So you either have to throw away causality, or have special kinds of determinism (including that the universe is determined to never cause causal contradictions), pr some censorship, or just add such a thing like "then the universe simply crashes and our god/admin deletes it"; or whatever else that makes it work.

Oh great now you are speculating too but never mind, i know how this feels.

I expect an apologize from you for beeing rude and calling me annoying. Else from that i have nothing more to say to you.

[ZetaX]

As for the comments you failed to expand on what was wrong with the papers I cited

Nothing (I could see).

although I now agree I misinterpreted their entanglement the response was very dismissive and without explanation.

That was because N_las was already saying most of what I could add, so I restricted myself to try to find out what exactly your problem was.

Hopefully we can keep this on track and put the disagreements behind us.

I have no problem with you, never had. I am happy to discuss things as long as the others are (mostly) following the basic principles I wrote down before, and I did not see you violating them.

I cannot fully answer your main question as I am not that afluent with quantum mechanics that I am certain to what I say (I am a working mathematician, who learned some physics in the past), but it sounds as it is also directed at me, so take the following at least with a grain of salt (and hopefully someone else goes further):

from whose perspective does the electron exist in both wells at the same time (ours or it’s)

I am actually not sure how to treat the meaning of "perspective" here, and I lack a good understanding of decoherence. Thus the best I can answer is "neither" and "reality". We know it to have this state untill we actually observe it, but in the moment we do that, it does not exist in this state; that's why I find it difficult to give an answer without a proper meaning of that word.

what is actually travelling between the wells, for instance during electrical conduction from atom to atom?

The main thing I learned from quantum mechanics is that one should not think of the world like Newton did, but see it as huge and complex probability space. So what is traveling is essentially the probability itself. But your post sounds as if you are aware of this already.

is it FTL?

If my understanding is correct, and this is a big "if", then no: the "change in probability" moves (at most) at the speed of light and should even be observer-dependant. But I really do not want to give an actual answer to that.

@Gpisic:

I will apologize if I think I was wrong, not because you demand it. If me being rude by calling you "annoying" is that bad you might leave the internet now.

Everything I said about you is true, or at least I see no reason to change that perspective. And to demonstrate why I think so, just take a look at your last post:

a) You say I "swap the facts" when I said first that

"N_las already gave a proof that FTL transmissions cause time travel"

and then that

"I said that FTL implies time travel (and vice versa)"

This statement is ridiculously nonsensical! The only meaning I can even assert is that you are complaining not giving N_las credit the second time, but I actually don't need to: I was saying I agree with his conclusion (thus implicitely saying that FTL causes TT), and then the second time I simply reconfirmed that I said this. I also think I said it another time before, but am too laze to look that up.

And yeah, let everyone else look it up if they want. I feel very threatened at the thought that people might realise that at first I said "A is true" and then later said it again.

You answer my very very random example of a magical teapot with:

At least it's an attempt however a pretty clumsy one.

No, it is not. And yet it is not really worse than what you are saying. You seem to think that even a "god of the gaps" (look it up, it's a standard refrence) is better than admitting a lack of knowledge. That's completely unscientific again.

c)

Oh great now you are speculating too but never mind, i know how this feels.

You really need to learn what sarcasm is. Also, those examples are excatly that: examples. I nowhere said they are real (most of them are pretty random), but I made sure they actually are compatible with all physics I could think of; you may point out errors if you wish so.

d)

FTL comms will be in disagreement with that physics for sure

Nope, general relativity (e.g. Alcubierre drives) or other things might allow it. I just want your stuff to be consistent with what we already know (I think I am repeating myself for the fifth time now).

e)

Only because something is written in a book does not mean that it is the ultimate truth.

This is probably the only part of your post I agree with. The only problem is that your are dealing with this matter like a crackpot ("they doubted Einstein and Wegner but they were right all along, therefore my weird theory is also correct!") than a scientist ("hmm, this fact disagrees with my prediction, maybe I need to adapt my hypothesis or revoke it").

The difference is probably this: the crackpot tries to make as many assertions true as possible (with a very heavy bias towards his own), while the scientist is more focused on weeding out the false ones. Actually, learning some mathematical logic may help you and others understand this. And no, mathematical logic is not such simple stuff as implications, AND, OR, but I am talking about things like axiomatic systems, formal proofs, undecidability and the difference between unfalsifiable and provable.

Your other fallacies are so heavy that I don't think anyone reasonable needs an explaination why they are wrong, so I will just stop here.

Have fun ignoring me for not bowing to your unfounded demands of an apology. I will continue to point out your nonsense to others, it's your decision if you don't respond to that; I definitely have no objection to that.

[musicpenguin]

Thanks Senpai!

[N_las]

As for my actual question;

What is the speed at which an electron tunnels in the quantum tunnelling affect? I understand the mechanism of movement in that the distances are close enough that the wavefunction function overlaps the gap allowing for the particle to provide finite probability to exist in either well. I also actually understand that QM states that the particle exists in both spaces at the same time as a wave function.

The question becomes if the gap between the tunnel would extend to a large enough gap to be observed (ignore the probability issue), from whose perspective does the electron exist in both wells at the same time (ours or it’s) and what is actually travelling between the wells, for instance during electrical conduction from atom to atom?

My understanding is that the idea of the wavefunction and whether it is an actual field or a probability distribution of a particle’s position is as of yet undetermined and although theorised, neither view has real majority. Certainly either raises the probability of a particle to exist at once side and then the other would yield the question is it FTL? Certainly time taken traversing an energy barrier would require energy expenditure not possible in these affects, in any time reference.

To answer your question "what is the speed at wich an electron tunnels":

Ignore tunneling for a moment. Imagine just a quantum well with an electron inside. The walls of the well are infinitly high, so the electron is completely traped inside. From the electrons wave-function, we know its probability of presence in the well. Let's say there is a 10% chance of finding it near the right wall, a 10% chance for it to be near the left wall, and a 80% chance to be in the middle of the well.

We now measure the exact position of the electron, and we find it to be near the left wall. What would you think is the right answer to the question "with which velocity travelled it to this position"?

If you think about this question in this context, you will see that it is nonsensicle: To talk about something like this velocity, we would have to define a prior position of the particle at a certain point in time. But that istn't possible, we just have its wave-function. From what point should it have traveld to the left well side? Did it start traveling from the right side?

The answer to this question would be: It didn't "travel" from somewhere to this positon in the quantum well, it just had a specific probability to be at this position.

It is the exact same thing for tunneling. The particle wasn't "inside" of the barrier, and then travelled "outside" of the barrier. The particle didn't had a defined position like "inside" or "outside" at the first place. And if you can't say that if was "inside", then it doesn't make sense to talk about a speed in which it travelled "outside". It just happend to have the probability to be all over the place, and even if the probability to be "inside" is very high, it can still be found "outside", without the need to actually travel outside.

If you draw a lottery ticket, you wouldn't talk about the "speed" or "time" it takes for your ticket to change from a loosing number to a winning number. Thats because it didn't change from a loosing number to a winning number. The attribute of loosing and winning isn't defined for the ticket before the measurement (before the lottery show). In the same sense, the position of the electron is a meningless concept before its measurement, so saying it was "loosing" (inside) and changed to "winning" (outside) is nonsensical.

The actual size of the gap doesn't matter, it could be from here to the end of the universe.

[Alchemist]

As for my actual question;

What is the speed at which an electron tunnels in the quantum tunnelling affect? I understand the mechanism of movement in that the distances are close enough that the wavefunction function overlaps the gap allowing for the particle to provide finite probability to exist in either well. I also actually understand that QM states that the particle exists in both spaces at the same time as a wave function.

The question becomes if the gap between the tunnel would extend to a large enough gap to be observed (ignore the probability issue), from whose perspective does the electron exist in both wells at the same time (ours or it’s) and what is actually travelling between the wells, for instance during electrical conduction from atom to atom?

My understanding is that the idea of the wavefunction and whether it is an actual field or a probability distribution of a particle’s position is as of yet undetermined and although theorised, neither view has real majority. Certainly either raises the probability of a particle to exist at once side and then the other would yield the question is it FTL? Certainly time taken traversing an energy barrier would require energy expenditure not possible in these affects, in any time reference.

About the tunneling there can be such way to estimate the velocity in the barrier:

Let's take the experiment of a stream of electrons flying against a potential barrier with higher energy than the kinetic energy of the electrons. You know how the stationary wave-function looks with some electrons tunneling and some electrons being reflected. But now let's take a single electron shot there - now we have the time-dependent wave-function (electron density wave) that has the mean position and mean impulse properties of the electron (and the stationary wave-function of the stream can be described as superposition of large number of such functions with different time variable values). What happens to this wave when it reaches the barrier? In the end the wave-function will be of 2 density waves - 1 corresponding to the reflected and the other to the tunneled electron (of course that collapses when we observe if the electron has tunneled). If we get mean coordinates and impulse values for the tunneled electron now and compare that to the initial electron we could probably estimate what was its velocity change inside the barrier (and for the reflected electron we could estimate the mean time inside the barrier). I don't know what would the velocity inside the barrier be, but it should be finite.

As for thought experiment about measuring position of an electron twice with very short time interval and chance to find that it moved further than speed of light times time interval, remember that first observation collapses wave function and the second observation might have to deal with time-dependent wave function that is rather different from stationary state at that time moment

[ibeinsane]

To answer your question "what is the speed at wich an electron tunnels":

Ignore tunneling for a moment. Imagine just a quantum well with an electron inside. The walls of the well are infinitly high, so the electron is completely traped inside. From the electrons wave-function, we know its probability of presence in the well. Let's say there is a 10% chance of finding it near the right wall, a 10% chance for it to be near the left wall, and a 80% chance to be in the middle of the well.

We now measure the exact position of the electron, and we find it to be near the left wall. What would you think is the right answer to the question "with which velocity travelled it to this position"?

If you think about this question in this context, you will see that it is nonsensicle: To talk about something like this velocity, we would have to define a prior position of the particle at a certain point in time. But that istn't possible, we just have its wave-function. From what point should it have traveld to the left well side? Did it start traveling from the right side?

The answer to this question would be: It didn't "travel" from somewhere to this positon in the quantum well, it just had a specific probability to be at this position.

It is the exact same thing for tunneling. The particle wasn't "inside" of the barrier, and then travelled "outside" of the barrier. The particle didn't had a defined position like "inside" or "outside" at the first place. And if you can't say that if was "inside", then it doesn't make sense to talk about a speed in which it travelled "outside". It just happend to have the probability to be all over the place, and even if the probability to be "inside" is very high, it can still be found "outside", without the need to actually travel outside.

If you draw a lottery ticket, you wouldn't talk about the "speed" or "time" it takes for your ticket to change from a loosing number to a winning number. Thats because it didn't change from a loosing number to a winning number. The attribute of loosing and winning isn't defined for the ticket before the measurement (before the lottery show). In the same sense, the position of the electron is a meningless concept before its measurement, so saying it was "loosing" (inside) and changed to "winning" (outside) is nonsensical.

The actual size of the gap doesn't matter, it could be from here to the end of the universe.

I understand your point exactly although the question concerns not measuring the electron in one or the other but electron transport by tunnelling. For example electron tunnelling is fundamental to electrical transport in metals, as it is also in an electron tunnelling microscope and photons can similarly do between fibre optic couplings. So although you are correct in measuring the position of a electron in a well that is very close it is either in one or the other and there is no transport, the electron must transition the well during transport in metals or an STM. An Scanning tunnelling microscope is probably the most prominent example of such transport actually taking place.

The reason for asking is that there has been such examples suggesting FTL during tunnelling. ie http://link.springer.com/article/10.1007%2Fs10701-011-9539-2.

[ibeinsane]

About the tunneling there can be such way to estimate the velocity in the barrier:

Let's take the experiment of a stream of electrons flying against a potential barrier with higher energy than the kinetic energy of the electrons. You know how the stationary wave-function looks with some electrons tunneling and some electrons being reflected. But now let's take a single electron shot there - now we have the time-dependent wave-function (electron density wave) that has the mean position and mean impulse properties of the electron (and the stationary wave-function of the stream can be described as superposition of large number of such functions with different time variable values). What happens to this wave when it reaches the barrier? In the end the wave-function will be of 2 density waves - 1 corresponding to the reflected and the other to the tunneled electron (of course that collapses when we observe if the electron has tunneled). If we get mean coordinates and impulse values for the tunneled electron now and compare that to the initial electron we could probably estimate what was its velocity change inside the barrier (and for the reflected electron we could estimate the mean time inside the barrier). I don't know what would the velocity inside the barrier be, but it should be finite.

As for thought experiment about measuring position of an electron twice with very short time interval and chance to find that it moved further than speed of light times time interval, remember that first observation collapses wave function and the second observation might have to deal with time-dependent wave function that is rather different from stationary state at that time moment

Oh I fully agree, the ability to measure such interval will be impossible as described. As you mention measurement on the first side of a single particle will collapse the wavefunction and make any subsequent measurement impossible.

As for the velocity change I am not sure I follow, do you mean the phase velocity of the wavefunction or the group velocity. Of course the question from a QM point of view is, is the particle or wavefunction ever within the barrier at all. I have not yet seen a wavefunction description within a potential barrier (that does not mean it does not exist).

Additionally what makes you suggest that the velocity within the barrier 'finite'?

[N_las]

Of course the question from a QM point of view is, is the particle or wavefunction ever within the barrier at all. I have not yet seen a wavefunction description within a potential barrier (that does not mean it does not exist).

See this picture:

http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/imgqua/barr.gif

The particle can be "found" in the barrier. But you have to consider what that means. The "measurment" that finds the particle inside the wall can be any interaction with the barrier. A photon that is found "inside the barrier" could be something like an atom absorbing the photon. In classical terms, it is the destruction of the photon. So if a photon is near enough to a barrier, it may pass it (tunneling), be reflectet, or be absorbed inside the barrier.

Or better, this video:

You see a simulation of a wave function that "crashes" against a barrier. As you can see, some of the wave can travel through the barrier. But there is nowhere a "magical" FTL jump, the wave just as a certain propagation velocity.

This video is almost better, start at 2:20

If you imagine the group velocity of the wave packet as something like the "particles velocity", then you see there is no jump involved anywere. It just behaves like a sound wave that has to pass through a wall.

I can't even imagine in what sense this could have anything to do with FTL.

EDIT: Maybe the idea of FTL travel while tunneling has something to do with (not so clear) explanations like this (start at 0:55):

We see an electron travelling slow to a wall, then it *pop* disappears, and *pop* reappears at the oder side, then continous its slow travel. One could ask, if this *pop*-teleportation happens instantly, and if it's therefore FTL.

But I hope that you see (with the above videos), that it is simply his explanation that creates this conception. If you visualize it different (like in the simulations above), there is no question about any FTL-jumps.

The paper that you linked is (in my opinion) just a media-effective misinterpretation of data. In every experiment (conducted by the author of the paper), particles that travelled the same path but without barrier (=without tunneling) arrived faster at the detector. The dectetor for the tunneling-path reacted slower in ALL cases. He has to use a very crazy backwards logic, to interpret that as FTL signals.

The logic of the Author Nimtz is as follows: If you compare the location of the wave maximum directly infront of the barrier with the maximum of the wave a little time later after the barrier, and divide this distance by the correlating time, you get a velocity higher than c.

That is the same logic, that says that a laser-dot on the surface on the moon can travel FTL, if the laser (here on earth) is waved back and forth. It is true that the dot is FTL, but the dot isn't an actual thing that contains energy or information. The dot is just an illusion, created by photons hitting the surface with the right timing. The objects containing energy and information are the photons from the laser, and they never travel FTL. In a similar way, a black dot on a computer monitor could appear to travel FTL if the pixels are flashing with the right timing. But there isn't any actual FTL travel involved, the black dot isn't a "thing", it is just an illusion created by the flashing pixels.

Back to Nimtz Paper: If the barrier has the behaviour to reflect more of the late part than the early part of a wave-packet, than it obviously could appear as if the wave-maximum travelled FTL. But the wave-maximum isn't an actual thing that carries information or energy, it is just a mathematically interesting point of the wave.

Every resonable criteria that could possibly be used to be interpreted as propagation velocity shows lower than c travel:

- The group-velocity of the wave is lower than c in all situations (even during tunneling).

- The time between signal sending and signal receiving is always longer as would be expected with c-travel.

- The comparision signal, that has no tunneling barrier in its way, reaches the detector always faster than the tunneld signal (but always slower than c)

Edited September 29, 2014 by N_las

[K^2]

As for my actual question;

What is the speed at which an electron tunnels in the quantum tunnelling affect? I understand the mechanism of movement in that the distances are close enough that the wavefunction function overlaps the gap allowing for the particle to provide finite probability to exist in either well. I also actually understand that QM states that the particle exists in both spaces at the same time as a wave function.

The question becomes if the gap between the tunnel would extend to a large enough gap to be observed (ignore the probability issue), from whose perspective does the electron exist in both wells at the same time (ours or it’s) and what is actually travelling between the wells, for instance during electrical conduction from atom to atom?

My understanding is that the idea of the wavefunction and whether it is an actual field or a probability distribution of a particle’s position is as of yet undetermined and although theorised, neither view has real majority. Certainly either raises the probability of a particle to exist at once side and then the other would yield the question is it FTL? Certainly time taken traversing an energy barrier would require energy expenditure not possible in these affects, in any time reference.

Same problem as with entanglement. There appears to be FTL action, but once you consider actual communication, you see that you cannot actually send a message across. In a nutshell, if you have long distance, then the barrier serves as a very fine energy filter. Anything with energy above the barrier will travel at sub-light speeds. Things that are well bellow barrier energy will decay exponentially at a rate which makes the exit amplitude zero. And only part of your signal that's juuust right will make it through. And once you've filtered just one energy, you run into the Heisenberg uncertainty problem. Effectively, the part that made it across "faster than light" was the part that was that delocolized to begin with. And if you consider things that are already delocolized that much, you just get noise from absolutely everything.

There have been a number of articles trying to formalize this and show that communication under barrier is not actually possible as a theorem. Unfortunately, math gets really hairy when you try to make it a formal, absolute statement. At very least, I've never seen anything remotely as dry and cut as the entanglement no-communication theorem.

[ibeinsane]

Thank you for that, I found an excellent video concerning dielectric barriers from one of your links;

It does show the wave traversing the barrier although there is some question as to what that actually means. This is a probability function, not a particle wave and therefore would indicate finite ability to measure a particle within a forbidden zone within the barrier. The obvious issue with this is that the real and imaginary parts of the function separate in the barrier which would indicate something strange is happening, without actually solving the equation in this area it looks from the visual representation that the real and imaginary phase are (almost) out of phase, making the probability of finding a particle within the barrier very small? You would ask what mechanism allows for the particle to be measured at either side of the barrier with equal kinetic energy but not the same probability of being able to measure it within the barrier if the Ek (and velocity) is constant throughout? But then again the Quantum world is strange!

I take on board your comments about the paper, I don't believe I am in a position to postulate on his results or draw the comparison myself with the laser spot example, presumably (hopefully) the review process did some of this especially from an institute based in Germany. Additionally there are quite a few paper references to FTL travel (usually referred to as superluminal) in tunnelling (more stated within books and conference papers).

Of course this was an experimental assessment of a very difficult measurement but the superluminal issue of tunnelling has been discussed considerably for quite some time from a purely mathematical perspective, with a summary found here, http://iopscience.iop.org/0022-3719/20/36/021/pdf/0022-3719_20_36_021.pdf

I don't have particular access to this paper although if someone here does I would love to know the summary from it. Since then there have been several experiments into the field which a German academic website summarized at http://www.aei.mpg.de/~mpoessel/Physik/FTL/tunnelingftl.html covering work in Germany and also at Berkeley.

At this point I think I am going to have to bow out due to the number of papers I don't have access to so cannot really provide support for or against on here, perhaps you can? This was just to point out that the picture (to me) is far from clear from the description of wave traversal and how this represents actual particle motion and from the number of papers in peer reviewed journals providing evidence to the contrary. For me it would suggest there is reasonable doubt mathematically and experimentally that requires more rigorous testing.

Please feel free to comment and I will try to continue but I think it has probably gone beyond my ability to research further in these papers or adequately interpret the meaning of a wavefunction in terms of physical motion(would be worth a prize if I could). Although this has given me new drive to get my Matlab computer back out

[ibeinsane]

Hi K^2,

Whilst looking at his further I stumbled across Nimtz and the rest of his work, a wiki page even exists as the first hit which I promptly skipped although did read about the opponents to his experiments. They were very similar arguments to yours although I have not read their papers in detail, mainly as those cited on wiki had not been peer reviewed yet.

I have not seen a refutation of his actual experiments though, the most famous one of which I can only find published in a German paper transmits Mozart's 40th Symphony. Now I agree this particular experiment was highly sensationalised (you can even listen to it) but his own published papers reference this experiment and a speed of 4.7c. http://www.psiquadrat.de/downloads/nimtz03.pdf

Again I am attempting to promote debate here, I have not investigated his experimental setup or data enough (not even sure if I could) to decide if he is correct or not. I have attempted to find the scientific papers in support and against and in this matter have struggled to find enough for either way. To me that means this is still under debate.

If, and it is a big IF, his experimental setup is correct, and I am yet to find evidence that it is not, something you would have expected the scientific community to have jumped on, I know I do in my field, then he was able to transmit and only transmit data faster than light. I agree currently attempting to measure this etc may result in you only being able to interpret the data slower than the speed of light but it certainly begins to question some ideas.

[N_las]

It does show the wave traversing the barrier although there is some question as to what that actually means. This is a probability function, not a particle wave and therefore would indicate finite ability to measure a particle within a forbidden zone within the barrier. The obvious issue with this is that the real and imaginary parts of the function separate in the barrier which would indicate something strange is happening, without actually solving the equation in this area it looks from the visual representation that the real and imaginary phase are (almost) out of phase, making the probability of finding a particle within the barrier very small? You would ask what mechanism allows for the particle to be measured at either side of the barrier with equal kinetic energy but not the same probability of being able to measure it within the barrier if the Ek (and velocity) is constant throughout? But then again the Quantum world is strange!

No, this video does NOT show the probability function. It does show the particle wave. The particle wave can be negative (as seen in the video), and has real and imaginary parts. To get the probability function from this, you have to take the complex particle wave and multiply it by its own complex conjugate. (Or you take the magnitude of the complex wave, and square it).

The resulting probability function can't be negative, and has only real parts. But you are right, that it is indicated that there is a probability to measure the particle inside the barrier.

I don't really see a controversy with the topic of tunneling FTL-travel. The idea and experiments exist for decades now. Everybody agrees about the data: It is not shown that information or energy can be transported faster than light through tunneling. And if that sort of FTL travel would be possible, there would be no experimental problems in providing that data.

Saying that there is FTL travel because some velocity is higher than FTL is meaningless. To be FTL travel, there has to be information or energy involved. I can imagine dozens of situation were a meaningless velocity higher than c is involved.

I have made a graphic that explains why one could argue that FTL travel is involved in tunneling, and that explains why I think this is nonsense: http://imgur.com/oxHA3LD

If you look at figure 16 (page 18) in Nimtzs paper, this is exactly what he is doing: http://www.psiquadrat.de/downloads/nimtz03.pdf

His graphic has the arrival time at its axis, so it appears to be mirrord in comparison with my paint-skillz... But the idea is the same:

He interprets the maximum of the pulse to be something significant.

To impress anybody, he would have to transmit Mozarts symphony, so that the receiving detector would acutally respond faster to the tunneld signal than to a comparison untunneld signal.

Edited September 30, 2014 by N_las

[K^2]

If, and it is a big IF, his experimental setup is correct, and I am yet to find evidence that it is not, something you would have expected the scientific community to have jumped on, I know I do in my field, then he was able to transmit and only transmit data faster than light. I agree currently attempting to measure this etc may result in you only being able to interpret the data slower than the speed of light but it certainly begins to question some ideas.

These experiments aren't new. And scientific community have replied to them pretty much right away. The problem with the setup is that there is no guarantee that the leading edge of the signal is where it is claimed to be. If you send a Gaussian wave packet, of course you can detect its tail before you predict the center to arrive.

And there has not been a single experiment to get FTL communication in a setup where this behavior is controlled, despite many attempts.

So effectively, it's the same story as with the "faster than light neutrinos" that have been making waves a while back. If you are measuring the wrong signal from the wrong place, of course you can measure something FTL.

[ibeinsane]

Hi N_las, thank you for the correction.

I have looked at your explanation and it is indeed one of the methods used to discount the work by Nimtz. Interestingly according to the work below (published last year) there were still conflicting ideas as to why the work by Nimtz was incorrect in assuming superluminal transmission.

http://www.bcamath.org/documentos_public/archivos/publicaciones/Interference_PhysRevA2013.pdf

Thank you for you input, it is most certainly appreciated. I must admit you have convinced me now in addition with the paper above, the superluminance assumes front peak transmission which is not the same thing at all.

What I would like to say though is that the current literature does not all agree, so I would not agree with the quote everyone agrees. indeed the paper above was only published last year and there are still a good deal of papers being published in peer reviewed journals (Phys Rev A I would class as quite high) still debating the point, it seems far from consensus about what happens in the area although the more I look the more I see the weight of opinion being against FTL or at the very least against causal problems.

Just out of interest, it could be you are in this loop more than I, what makes you say everyone agrees?

[N_las]

Just out of interest, it could be you are in this loop more than I, what makes you say everyone agrees?

I said: "Everybody agrees about the data: It is not shown that information or energy can be transported faster than light through tunneling."

By that I mean that everybody agrees (even Nimtz), that the data doesn't show a reaction at the detector that would be FTL. IF you take the distance of the sender and the detector, and divide by the transmission time, you get always a value smaller than c. Thats what the data shows, and thats what I meant by "Everybody agrees about the data."

Nobody (not even Nimtz) claims, that they have measured something at a detector, that took less time than a free photon to reach it.

The only disagreement is: If you interpret the Data like Nimtz, it shows that the speed inside the barrier was greater.

But I ask you: if that was truly the case, if the speed of a photon is faster inside a barrier (and obviously =c in free space), why is it that you can't detect a tunneled signal faster than an untunneld one? There shouldn't be any experemental difficulties in providing that data. There shouldn't be any reason why such a clear experiment wouldn't work.

But in reality, the only thing that can be accomplished by putting a barrier in the way of a free travelling photon, is delaying its arrival at the detector.

[ibeinsane]

I said: "Everybody agrees about the data: It is not shown that information or energy can be transported faster than light through tunneling."

By that I mean that everybody agrees (even Nimtz), that the data doesn't show a reaction at the detector that would be FTL. IF you take the distance of the sender and the detector, and divide by the transmission time, you get always a value smaller than c. Thats what the data shows, and thats what I meant by "Everybody agrees about the data."

Nobody (not even Nimtz) claims, that they have measured something at a detector, that took less time than a free photon to reach it.

The only disagreement is: If you interpret the Data like Nimtz, it shows that the speed inside the barrier was greater.

But I ask you: if that was truly the case, if the speed of a photon is faster inside a barrier (and obviously =c in free space), why is it that you can't detect a tunneled signal faster than an untunneld one? There shouldn't be any experemental difficulties in providing that data. There shouldn't be any reason why such a clear experiment wouldn't work.

But in reality, the only thing that can be accomplished by putting a barrier in the way of a free travelling photon, is delaying its arrival at the detector.

Indeed measuring this should be relatively easy, I would need to look up the details further to check if the instruments would be capable of the required accuracy and noise levels. A simple experiment would place several fibre optic junctions in series and a single fibre optic length and measure the time difference. As for the most appropriate light source (modulated laser vs single photon system). Of course the noise levels will become significant with enough junctions but it should be possible to observe.

So considering yourself and K^2 highlight this as nonsense from quite old experiments why has Nimtz been able to continue publishing data on the similar things as late as 2006? After which point I presume he retired? Surely the peer review process requires a) new data and some ideas of interpretation not contrary to accepted opinion without significant evidence. Indeed I have had reviewers question interpretations and even state that experimental data is not sufficient to establish the conclusions made, usually corrections are more a change of language but still reviewed.

With my own experiences I found the review process quite thorough and even restrictive with new findings from experimental data. Is this relatively new for the past decade or has the review process just not functioned as required on this matter? Why are we still seeing new papers published up to last year about this if it is fully resolved as you and K^2 suggest?

From what you are saying this almost makes a mockery of the science by consensus approach, at least on this subject. If someone of my research ability is not able to find the consensus of a topic such as this and it requires detailed understanding to interpret the papers yourself to decide they are not correct then what hope is there? Can you or K^2 highlight where you draw the opinion there is a consensus from, it would be useful to know where something like this would reside should I need to find it again?

Again to highlight, I now agree with your interpretation after your explanations, they are very much appreciated, I am very frustrated on the other hand that I have not been able to draw the same conclusion from current literature as I would expect.

[ibeinsane]

Okay that is this discussion over for me!

I enjoyed our discussions N_Las, apologies if they ever seemed abrasive, I am genuinely grateful you took the time to help explain these to me (some of which I have forgot from previous learning, others are genuine new concepts.

Zetax, thank you for your inputs, some have been helpful although I have found some of your comments rather abrasive and dismissive, not what I personally expect from a physics debate but everyone has their own method of communicating physics concepts.

Gpisic, your last comment was completely unwarranted and I do really pity you to need to respond in such a manner. Certainly if ZetaX had not already responded I would has not even bothered with this either.

Based on this (my first real involvement on the science lab boards) I am unlikely to join in with any further science conversations as they do not seem to be appropriate forums for this type of discussion.

Any comments you want me to expand on please message me directly as I won't continue in open forum

[stupid_chris]

Alright folks, that discussion has ran it's course, and now it's turning quite awry. We'll end it here before knives start to fly at eye height.

Thread closed.