Are Superluminal Neutrinos Possible?

reply to post by Arbitrageur


I have yet to grasp it fully, and I need to read it some more times and let it sink in a bit more. My initial thoughts on it is that it only means that superluminal communication between two transceivers that have a different velocity is not possible, but between two transceivers with equal velocity it does not seem to cause any violation.

reply to post by Aim64C

I've been going far, far too easy on you guys.

No, you've been evading questions, creating straw man arguments and attempting to play semantic games. I've been hoping that you would reflect on some of the points that have been raised so that you can clarify your understanding of Relativity. I've been quite civil about it, despite your condescending attitude, too.

Relativity is absolute, is it not? Therefor - when I attach a clock to myself, and run away from you, and return. Who has the slower clock?

This is the sort of thing I'm talking about. Relativity isn't "absolute," it's relative. You would not even pose this question if you actually understood the concept of "frame of reference."

It's a trick question. Relativity is absolute. From my frame of reference, you were moving away from me - not the other way around. The two frames of reference cannot be reconciled unless a third frame of reference is called into account.

It is not a trick question, it is a sloppily constructed form of the "twin paradox." Let us assume that as you walk away from me, I remain at rest with respect to our surroundings. I just stand there, not moving relative to the house, the trees, the entire planet Earth. This is my inertial frame of reference. Granted, we're all whizzing through space in every which direction at once from some frames of reference, but me and my buddy the Earth form one single frame of reference so long as I don't go anywhere with respect to it. You, on the other hand, are using your legs to accelerate the entire mass of the Earth, everything on it and, arguably, the entire universe away from you... in your personal frame of reference. The Earth and I have aged at the same speed because we share the same frame of reference. You have not aged at the same speed because you have been off in your own frame of reference. No additional frame of reference is required. I'll leave you to work through the details.

This, however, creates two possible interpretations for the speed of light. Which collapses relativity and forms an absolute reference.

Even if you got the above correct, which you didn't, this is a complete non sequitur.

I'll give you a little bit to digest that.

Chewed up, spit out. Now you work through what I've posted.

Originally posted by -PLB-
I have yet to grasp it fully, and I need to read it some more times and let it sink in a bit more. My initial thoughts on it is that it only means that superluminal communication between two transceivers that have a different velocity is not possible, but between two transceivers with equal velocity it does not seem to cause any violation.

Your statement "equal velocity" is imprecise as a physical description, as it lacks direction.

If you say "two tranceivers in the same inertial frame of reference" meaning both the same velocity and the same direction, then you have to specify if those two transceivers have access to another inertial reference frame. If they do, then you still have a problem with causality. If their reference frame is somehow isolated and they don't have access to an outside inertial reference frame, then it is hard for me to see how this could result in the bomb going off before the detonator is pressed, and the source I linked you to says it's not a problem:

www.theculture.org...

Figure 3 First superluminal transmission. Alice transmits from event P and the signal is instantaneously received by Bob at event Q. Alice and Bob are at rest relative to each other.

By itself, this single use of the ansible doesn’t create a causality violation. If Bob transmits a signal back towards Alice using a conventional light-speed transmitter, she receives it a later time than when she signalled to Bob. Even if Bob re-transmits with his ansible, Alice receives the reply just a little after she sent out her signal. The problems arise when we bring another inertial frame into play.

So if you meant "same velocity in the same direction, without any access to another inertial reference frame", then you're right, no problem.

Originally posted by Arbitrageur
Your statement "equal velocity" is imprecise as a physical description, as it lacks direction.

English not being my native language, I still think you are not correct here. Velocity is a vector (so including direction) whereas speed is a scalar (with no direction).

If you say "two tranceivers in the same inertial frame of reference" meaning both the same velocity and the same direction, then you have to specify if those two transceivers have access to another inertial reference frame.

I don't follow you. Why can't two transceivers in one inertial frame of reference have different velocities (direction and speed)? Maybe this is just a matter of confusion over the definition of the terms, but I think its important to be in agreement on that. I will respond to the rest later (when we are clear on definitions).

Originally posted by -PLB-
I don't follow you. Why can't two transceivers in one inertial frame of reference have different velocities (direction and speed)? Maybe this is just a matter of confusion over the definition of the terms, but I think its important to be in agreement on that. I will respond to the rest later (when we are clear on definitions).

OK you're right that velocity does imply direction if you are using the term as a physicist and not as a layperson.

But if two transceivers have different velocity vectors, are they not by definition in different inertial reference frames?

reply to post by Arbitrageur


Velocity being a vector, it includes both speed and direction. The definition of a reference frame, then, of course, is a system with a unique velocity.
But, velocity is relative. As you mentioned earlier, the closest we come to having a preferred reference frame is the CMB, and that only appears to work because it's large and exceptionally uniform. In reality, it's no better than any other frame of reference.

I noticed the use of the word "philosophical" earlier, in reference to time. This is why physicists tend to work mathematically. In physics, both time and space are described in terms of a single generalized metric, x, and this metric is locally affected by relative velocity (as measured by an observer). This is all to ensure that causality is preserved and that the speed of light is constant according to all reference frames (the former being a consequence of the latter, which, itself, is required for light to exist, as I have explained several times).

An observer will always consider himself to be at rest. In the real world, when we drive, for example, we might say that we are moving at 80 km/h relative to the road, but, as a matter of convention, this isn't the case in Relativity. Instead, we consider that the road is moving -80 km/h relative to us. Then, the metric is locally affected for the road according to the road's velocity as we measure it. Different observers may measure different velocities, and, so, the road's metric will be affected differently in each case. This all according to each observer.

Causality is not really what we're worried about here. It's the constancy of the speed of light. Causality just happens to generally follow from this.

And now, finally, my point: this is why different velocities demand different reference frames. Velocity is what determines the transform of the metric, so any unique velocity is a unique frame of reference.

Originally posted by DJW001
It is not a trick question, it is a sloppily constructed form of the "twin paradox."

That's right, it's not really even a paradox though it's been called the "twin paradox".

If you use the cosmic microwave background which I mentioned earlier as a reference, it becomes apparent that the person on Earth has been moving at a relatively consistent velocity relative to the CMB, while the twin who left Earth and came back at relativistic speeds accelerated, then decelerated, turned around, accelerated, and decelerated again to arrive back at Earth, all of which could be measured against the CMB. The person on Earth would have detected no such reversal of direction relative to the CMB so it's quite asymmetrical and not symmetrical as the "paradox" misunderstanding seems to posit.

I don't think you even have to refer to the CMB to show there's no paradox, but referring to the CMB makes it easier to me.

reply to post by Arbitrageur


It seems to me an inertial frame of reference can be chosen arbitrarily. The way you observe the movement of objects depends on the chosen frame. But whatever frame you choose, all the same objects will be in it.

You can of course choose a frame of reference equal to the movement of an object (as long as its velocity is constant), but other objects still exist in that frame of reference, though not necessarily with a velocity of 0 of course.

At least, thats how I have always interpreted it.

reply to post by -PLB-


Yes.

reply to post by -PLB-

Fair enough.
But to clarify what it takes to eliminate the causality problem, the two transceivers can't be in relative motion, regardless of your reference frame. They have to be at rest with respect to each other, meaning they could have the same velocity vector with respect to the CMB for example; otherwise, you can demonstrate the causality problem with FTL if they are in relative motion.

reply to post by -PLB-


Generally, you choose a reference frame "attached" to the observer, ensuring that the observer is always at rest. The problems start when you have more than one observer, in which case you get more than one "right" answer, such as in the so-called Twin Paradox. It's not really a paradox, it's just a matter of "he says, she says."

reply to post by CLPrime


In particle physics, it's also common to use "CMS", the center-of-mass system. Doesn't really always map onto an observer.

A convenient way to look at cross-sections and rates across different experiment -- if you have these for a particular CMS energy, they would apply to either setup.

reply to post by buddhasystem


In more complicated cases, yes...as a generalization of the center-of-momentum (what I described). We can't always define an observer, and we can't always define one observer, so it's often more convenient to define the frame relative to the mass of the system.

reply to post by Arbitrageur


Ok, looks like we are on the same page here. Being an engineer, I tend to look at practical applications. From that perspective, I see a bright future for superluminal communication, even when its only possible between transceivers that are at a fixed distance from each other.

Like I said, I have yet to grasp the full implications of special relativity, but just as a brainfart, can't there simply be a correction added to superluminal communication, making to satisfy SR, causality and FTL? I can imagine that when a delay is added as relative speeds between transceivers increases, causality problems are avoided. Or is SR making that impossible?

Its interesting stuff, I will take another look at it tomorrow.

Originally posted by -PLB-

I see a bright future for superluminal communication, even when its only possible between transceivers that are at a fixed distance from each other.

In Relativity, superluminal communication is never possible, even between transceivers a fixed distance apart. Unless you find a way to harness tachyons.

reply to post by -PLB-


reply to post by CLPrime


There have definitely been people thinking about how quantum entanglement might be used for superluminal communication. I would not be so bold as to say it's impossible, but of course it's never been demonstrated. If it's ever demonstrated, and I wouldn't rule out that possibility, we may find there are some limitations on the behavior such that causality isn't an issue.

I've seen claims of proof that FTL communication via quantum entanglement is not possible, but you get into the circular argument scenario again, which you mentioned previously, where the proofs are based on our existing understanding of physical laws, which may be incomplete or flawed in some way.

My personal position is that it's unknown if it's possible or not, and I'm skeptical of it until I see it demonstrated. The title of this article suggests FTL communication may have been demonstrated, but I don't think so, it's just another misleading title:

Scientists Measure Communication Between Quantum Entangled Atoms

It's clear there is quantum linkage, but it's not clear it qualifies as communication. But obviously you and I aren't the only people pondering this.

reply to post by Arbitrageur


Full Text

I'm too busy and tired to give it a very thorough read, but percursory examination seems OK.

reply to post by Arbitrageur


In the strictest sense, "superluminal" demands a relative velocity greater than the speed of light (according to our agreed definition of a reference frame). We could say that, because entanglement does not actually involve a superluminal velocity (where velocity demands motion), it is not truly a superluminal phenomenon, and, therefore, does not violate Relativity. As I said earlier in this thread, Quantum Mechanics is all probabilities. If we say that entanglement is superluminal, then electrons must also be superluminal, because their change in position is just as instantaneous.

ETA: that is, a velocity is continuous and deterministic, whereas entanglement (and all motion at the quantum scale) is discrete and probabilistic.

reply to post by buddhasystem

Thanks for the link.

I clicked that link and it locked up Firefox, does that happen to anybody else sometimes when opening pdf's?

It's been a week since I rebooted, so I rebooted, and then saved the file, and opened it Acrobat instead of in Firefox and it opens perfectly. I read the abstract and I didn't really see them making the "communication" claim in the abstract which appeared in the title of the article about the paper. I'll have to read the rest of it later.

reply to post by CLPrime

I think those are valid points. However, whatever you choose to call it, there can be causality implications if the quantum entanglement can actually "communicate" at faster than light.

reply to post by Arbitrageur


Fortunately, causality isn't exactly set in stone. And, even in the case of entanglement, causality is preserved, because the effect never precedes the cause. The issue is with the exchange of information extending beyond the event's light cone. This is only a problem if we assume that the information is being exchanged with some sort of classical particle or other continuous (that is, in the sense of unbroken linear) mechanism... if it's not, then there is really no issue. And, of course, it's not. So, there should be no issue.