What's key is that during the entire process, the photon did not enter the channel between sender and receiver: As long as the photon passes through the channel, it will be absorbed by the ensemble if the control atom is in the ground state – but if the atom is in the Rydberg state, the photon will be absorbed by the detector. In this way, an unknown quantum state can be transferred between two distant participants without any physical particles traveling between them.
http://phys.org/news/2015-03-quantum-scheme-states-transmitting-physical.htmlQuoteWhat's key is that during the entire process, the photon did not enter the channel between sender and receiver: As long as the photon passes through the channel, it will be absorbed by the ensemble if the control atom is in the ground state – but if the atom is in the Rydberg state, the photon will be absorbed by the detector. In this way, an unknown quantum state can be transferred between two distant participants without any physical particles traveling between them.It looks to me like it says you can send information without sending particles or energy the classical way. So far all quantum communications had to have a classical component and it meant that no information exchange could actually take place faster than FTL. But this seems to say that is not needed. But it also looks like they take pains to say (at least twice) that it applies to unknown information or an unknown state... So i am confused about whether this is FTL communications or not. What are they saying?
This has always bugged me. Wouldn't the time paradox not matter, because the second observer could not communicate any information about the time paradox he witnessed back to the first observer before the paradox happens in the first observer's frame of reference?
Wouldn't the time paradox not matter, because the second observer could not communicate any information about the time paradox he witnessed back to the first observer before the paradox happens in the first observer's frame of reference?
As soon as information can exceed c, then causality of some events changes in the view of some observers. They will not agree on whether A caused B or B caused A, something that was well-defined before. Because of this you can get a set of observers that see sequentially that A causes B, B causes C, and C causes A. That's a problem.
Quote from: ddunham on 04/03/2015 09:28 pmAs soon as information can exceed c, then causality of some events changes in the view of some observers. They will not agree on whether A caused B or B caused A, something that was well-defined before. Because of this you can get a set of observers that see sequentially that A causes B, B causes C, and C causes A. That's a problem.Why is that a problem?Who cares if two observers disagree about what they see? That happens all the time now and we all continue to exist.
Because if you have an ansible that can transmit information faster than light, you can send information back into your past light cone, something that all observers will agree on, and you get things like grandfather paradoxes.
Sure. But it is useful to point out that the consequences of even the slightest form of FTL effect are very drastic - it'd imply that the universe would be strongly acausal. For example, if you could use entanglement to transmit information, you could mess with events in billion-year old faraway stars or galaxies just by looking at them.At some point the consequences become so strong that you'd have to start wondering why we haven't seen any time travellers from the future.
Sure. But it is useful to point out that the consequences of even the slightest form of FTL effect are very drastic -
Quote from: Nilof on 04/04/2015 02:50 pmSure. But it is useful to point out that the consequences of even the slightest form of FTL effect are very drastic -Anyone who thinks they can live with it should at least attempt to decipher this new world and explain it to us. What sort of world is it where one observer at one velocity sees a man dying from a poisoned kool-aid while his phone rings beside him, while another observer at a different velocity sees him answer his phone and pour out the poison?
Manyworlds interpretation would.
Furthermore physicists will evoke time travel when convenient. Feynman and wheeler posited advanced waves and retarded waves traveling into the future and the past to solve certain otherwise intractible problems.
I think we are in trouble if our scientific analysis consists of "This violates some fudged principle created to make physicists feel better about the universe on philosophical grounds."There is absolutely no evidence of which I am aware that any of these postulates about preserving order have any basis in physical facts let alone that they are universally true.
EDIT: Unless i am mistaken any relativistic travel allows time travel