Are Superluminal Neutrinos Possible?, page 6
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reply posted on 4-1-2012 @ 09:58 PM by Arbitrageur
reply to post by CLPrime

We talked about that a little earlier in the thread, but this explains it a little more:

Superluminal communication
Superluminal communication is the term used to describe the hypothetical process by which one might send information at faster-than-light (FTL) speeds.

Some theories and experiments include:

* Group velocity > c experiments
* Evanescent wave coupling
* Tachyons
* Quantum non-locality

According to the currently accepted theory, three of those four phenomena do not produce superluminal communication, even though they may give that appearance under some conditions. As for tachyons, their existence remains hypothetical; even if their existence were to be proven, attempts to quantize them appear to indicate that they may not be used for superluminal communication, because experiments to produce or absorb tachyons cannot be fully controlled
That's my understanding too, and I've seen you explain group velocity >c isn't really superluminal.

Now here's the part talking about the causality question:

The no cloning theorem prevents superluminal communication via quantum cloning. However, this does not in itself prevent faster-than-light or superluminal communication, since it is not the only proposed method of such communication[1]. But, consider the EPR thought experiment, and suppose quantum states could be cloned. Alice could send bits to Bob in the following way:

If Alice wishes to transmit a '0', she measures the spin of her electron in the z direction, collapsing Bob's state to either |z+>B or |z->B. If Alice wishes to transmit a '1', she measures the spin of her electron in the x direction, collapsing Bob's state to either |x+>B or |x->B. Bob creates many copies of his electron's state, and measures the spin of each copy in the z direction. If Alice transmitted a '0', all his measurements will produce the same result; otherwise, his measurements will be split evenly between +1/2 and -1/2. This would allow Alice and Bob to communicate across space-like separations, potentially violating causality. But violation of causality is not sufficient as proof of no superluminal communication. So superluminal communication remains an open issue [2].
So there could be potential causality violations, but I agree this in itself doesn't mean that it's not possible.
edit on 4-1-2012 by Arbitrageur because: clarification



reply posted on 4-1-2012 @ 10:07 PM by CLPrime
reply to post by Arbitrageur


Definitely, if anything is ever found to violate causality, I bet it'll be a quantum effect. In fact, if neutrinos are found to be sporadically superluminal, I bet it'll be a quantum effect. Maybe a new quantum effect unique to neutrinos. That would keep me up at night.


reply posted on 4-1-2012 @ 10:48 PM by Aim64C
reply to post by DJW001


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.


*shakes head*

I understand both General Relativity and Special relativity perfectly.

The problem is that you think you do, but you only understand the dogmatic principles thereof.

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."


*sigh*

Relativity, as a concept, is absolute relativity. _Everything_ is relative.

Perhaps my choice of the term "absolute" was poor. Noted.

I just stand there, not moving relative to the house, the trees, the entire planet Earth.


You want to call in a separate frame of reference.

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.


But everything is relative. If you want to expand your frame of reference, that is fine. However, it doesn't resolve the twin paradox. From my frame of reference, the earth - and everything you draw into your single frame of reference, moved. Not me.

The distinction becomes even more difficult when dealing with orbital bodies and not terrestrial transportation.

Unless you call in an arbitrary third reference - the solution cannot be solved.

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.


But this is not the case, according to Relativity. You are the one who moved. Thus, it is you who should be moving slower. I did not.

Both frames of reference are equally valid in Relativity - but both cannot be correct.

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


*yawn* Check.

You're not dumb. You're just not thinking.



reply posted on 4-1-2012 @ 11:22 PM by Arbitrageur
Originally posted by Aim64C
But everything is relative. If you want to expand your frame of reference, that is fine. However, it doesn't resolve the twin paradox.
There is no twin paradox.

Read this to understand why:

The twin paradox: Is the symmetry of time dilation paradoxical?

From Jane's point of view, immediately after she has fired her engines, she begins receiving Joe's greetings more frequently. This does not surprise her: she has gone from travelling away from the sender of the greetings and is now travelling towards him.

Jane observes this change as soon as she turns around, which is for her the midpoint of her voyage. (She now receives blue shifted messages instead of red shifted ones. One could apply the same relativistic Doppler factor to the frequency of arrival of the messages.) Joe, on the other hand, doesn't start to receive messages at a higher frequency (blue shifted messages) until considerably after the midpoint between Jane's departure and arrival, simply because the effect of Jane's acceleration and changed reference frame takes a while to get to him: he doesn't see the high frequency arrival of messages until the arrival of the first message that Jane sends after she turns around.

This is a clear example of where the asymmetry of the twins appears. The causes of this asymmetry are the fact that Jane reverses direction and Joe does not, and the finite time that light takes to transmit this information to Joe means that Joe doesn't get the news immediately. Jane leaves one inertial frame and joins another, and she has the effect of that change immediately. Joe, on the other hand, doesn't notice the effects of Jane being in a different inertial frame until much later because she is a long way away from him when it happens. The asymmetry is as simple as that.
This doesn't even invoke a third reference frame to show the asymmetry.

If you wanted to use the CMB as a reference frame, I wouldn't say it's completely "arbitrary".


reply posted on 5-1-2012 @ 03:38 AM by -PLB-
reply to post by Aim64C


What you are doing wrong is that you choose the frame of reference incorrectly. A frame of reference is not allowed to change direction or accelerate. (Its not even allowed to rotate, making the earth an incorrect frame reference too) So when you have chosen a frame of reference, and then start walking, you will move in that frame. The frame does not follow the movement, that is simply not allowed.


reply posted on 5-1-2012 @ 09:30 AM by CLPrime
reply to post by -PLB-


A frame of reference can certainly move with an object. The Earth is a legitimate reference frame. That's the whole point of Relativity. You think the Earth is moving, but, if you were to ask the Earth, it might say it's not moving. Instead, it might claim that the Sun and the other planets are all moving around it, while it sits at rest.

Let's say you choose a frame of reference that you say is at rest. What do you say it's at rest relative to? The Sun? Well...the Sun is moving relative to the galaxy, so that won't work. How about the galaxy then? That won't work either, because the galaxy is moving relative to the Local Group. So, what about the Local Group? Wrong again...the Local Group is moving relative to the CMB. You see, the problem is, when you start saying that a frame of reference is at rest, you then have to define what it's at rest relative to. And every object you choose will always be moving relative to something else.

However, as I said, that's the whole point of Relativity. You can say that anything is at rest, and all you have to do is say that it's at rest relative to itself, and that everything else is moving around it.. The Earth, within the Earth's frame of reference, is at rest - everything else orbits and moves around it. This is a perfectly legitimate frame of reference. It's called co-moving. In the case of the Earth, it happens to be a non-inertial reference frame, because of the Earth's angular momentum and gravitational potential, but that's fine. That's what General Relativity is for.
edit on 5-1-2012 by CLPrime because: (no reason given)



reply posted on 5-1-2012 @ 10:15 AM by Arbitrageur
reply to post by buddhasystem

I was going to write a similar reply earlier. If I had to guess, it's probably more than 4, but still a very limited number of people who understand all the nuances. Then there are quite a few folks who have a general understanding.

I was reading a thread in physicsforums where several physics PhDs were happily explaining some relativity principles that were widely understood. When the discussion got into some of the finer nuances, the moderator had to ask one of the few people who really knows all the nuances to reply in the thread, because the invited guest specialized in relativity, which apparently isn't that common.

The reason I never posted the reply is I tried looking for the thread and wasn't able to find it in a reasonable amount of time, and I don't have time to keep looking for it, but I assure you I read it.

So yes, when someone claims to fully understand relativity and all the nuances it entails, I do believe that's a pretty bold claim which I'd find hard to swallow without some pretty good reason to believe it.
edit on 5-1-2012 by Arbitrageur because: clarification



reply posted on 5-1-2012 @ 10:39 AM by -PLB-
reply to post by CLPrime


I shall clarify, I am talking about an inertia frame of reference. Of course you can make up any non-inertia frame of reference you like, but then calculating time dilation gives wrong answers. And that was the context of Aim64C example.


reply posted on 5-1-2012 @ 11:01 AM by CLPrime
reply to post by -PLB-


Indeed. The issue with the Twin Paradox is the presence of a non-inertial reference frame. Within the framework of GR, the paradox is fully explained by the acceleration of the Earth-bound twin with respect to the travelling twin's reference frame. No matter which reference frame is used, the travelling twin comes back younger.


reply posted on 5-1-2012 @ 11:32 AM by buddhasystem
Originally posted by Arbitrageur
reply to post by buddhasystem

I was going to write a similar reply earlier. If I had to guess, it's probably more than 4, but still a very limited number of people who understand all the nuances. Then there are quite a few folks who have a general understanding.


To put things in perspective, I selected a different class in school. I knew I would not be able to give GR it's full due.
That GR class was taught by one of the gurus. Depending on who you asked, the number of gurus varied, and the lowest estimate I heard in rumors among people far worthier than me was 3. Three.


reply posted on 5-1-2012 @ 01:24 PM by Arbitrageur
reply to post by buddhasystem

The way I heard the story, Eddington knew of two people, and was still trying to find the third person!

The meeting of 6 November 1919 of the Royal Society also originated a myth that persists even today (though in a very much diluted version):' Only three persons in the world understand relativity'. Eddington explained the origin of this myth during the Christmas-recess conversation with which I began this account.

Sir J.J. Thomson, as President of the Royal Society at that time, concluded the meeting with the statement', I have to confess that no one has yet succeeded in stating in clear language what the theory of Einstein's really is'. And Eddington recalled that as the meeting was dispersing, Ludwig Silberstei (the author of one of the early books on relativity), came up to him and said,' Professor Eddington, you must be one of three persons in the world who understands general relativity'. On Eddington demuring to this statement, Silberstein responded, 'Don't be modest Eddington'. And Eddington's reply was, 'On the contrary, I am trying to think who the third person is!'
Source:
Verifying the Theory of Relativity
S. Chandrasekhar
Notes and Records of the Royal Society of London, Vol. 30, No. 2 (Jan., 1976), pp. 249-260
www.jstor.org...

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