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That's my understanding too, and I've seen you explain group velocity >c isn't really superluminal.
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
* 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
So there could be potential causality violations, but I agree this in itself doesn't mean that it's not possible.
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. 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 .
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.
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."
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.
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.
Chewed up, spit out. Now you work through what I've posted.
There is no twin paradox.
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.
This doesn't even invoke a third reference frame to show the asymmetry.
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.
Originally posted by Aim64C
I understand both General Relativity and Special relativity perfectly.
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.
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!'