When a speaker brings a tangle of garden hoses, a bottle of water, and a towel to the podium, you know it’s going to be a fun talk. Computer scientist Harry Buhrman of the Centrum Wiksunde & Informatica in Amsterdam recently visited Singapore to help celebrate the fourth anniversary of the Centre for Quantum Technologies. He and his props gave quantum cryptography a whole new dimension--literally. Instead of encrypting a message or authenticating someone’s identity, Buhrman posed a deceptively simple question: Can someone be sure you are where you say you are?

Figure 1

Figure 2

Position verification isn’t just of interest to spouses who wonder about all those late nights at the office. It would tighten up secure communications channels and make it possible to send Mission Impossible-style messages that could be read only if someone visited a certain location (like geocaching puzzles). For fundamental physicists, the procedure raises an important question about the operational meaning of space. If you cannot confirm, even in principle, whether something is at a given location, does the concept of location have any objective meaning? In fact, the scenario Buhrman laid out bore a spooky resemblance to the holographic principle in quantum gravity.

Imagine trying to confirm your position in one dimension, along a straight line (Figure 1). A verifier can use the procedure of Einstein synchronization: send you a signal, to which you reply, and measure the round-trip time in order to gauge the distance between the two of you. It is the maximum distance; you might be closer, given the delays that could arise in the process. To narrow down your location, a second verifier on the opposite side of you also sends a signal that you must reply to. This technique goes by the name of distance bounding.

It’s easy to game the system, however (Figure 2). Two comrades intercept the signals, wait a short while (to simulate the travel time to your purported position), and reply on your behalf. Now you don’t need to be where you claim to be. With your friends covering for you, you can safely leave the office and have your affair.

(Images courtesy of Harry Buhrman.)

More nefarious scheming in the second part of this post, where things get quantum...

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A secure cryptography can be a numerical entanglement without quantum device.

I think that is possible a quantum entanglement simulation without quantum device using a simulation of a wave function, in common between transmitter and receiver.

A wave function can be transformed in a infinite binary code in two computers, then it is possible an equal string generator in the receiver and transmitter (common wave function with some sync emission): it is necessary an infinity of binary string to obtain a secure code (I think that is possible to take the not integer part of the real number like digit-the starting point must be the first one in the string); I think an hypothetical polynomial equation, with integer parameters and real solution (transformed in binary string), with infinite binary string like solution, or some real number obtained like pi using some simple equation, or some fractal generators (random generators).

It is necessary a transmission function (wave function modification) using a binary function (infinite random string common in receiver and transmitter) in receiver and transmission (I think an extension of OR, AND and XOR function) that transform the channel in a bidirectional channel: it is necessary to use the string to exchange the order of all the possible different outputs using the infinite transmission function like exchange function (one output of the function with a single input wave function and a single data transmission, and a measure function that change ever).

It seem that this method is perfect for a bidirectional streaming, and it seem that many cryptographic analytic method are included in this numerical method.

It is only a theoretical method, and I have not evaluated now all the system complexity.

Saluti

Domenico

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The link to Einstein synchronization led me to not just what I consider ridiculous efforts to discuss conceptuality of synchrony from the view point of SR instead of questioning the latter. I also found a rather poor but perhaps nonetheless helpful translation of Poincaré's 1898 paper La mesure du temps.

It can be considered as a guide to many mistakes that are still affecting physics.

Eckard

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Eckard

I hope you are not attribute the 'many mistakes' to Poincare. I agree ha made as many as anybody, but his logic seems so far not to have been falsified;

1897; "Whoever speaks of absolute space uses a word devoid of meaning." and; 1898 'Mesure du Temps'; “We do not have a direct intuition for simultaneity, just as little as for the equality of two periods. If we believe to have this intuition, it is an illusion. We helped ourselves with certain rules, which we usually use without giving us account over it [...] We choose these rules therefore, not because they are true, but because they are the most convenient."

1905; Academy of Sciences Paris 5 June; "...the space revealed to us by our senses is absolutely different from the space of geometry." and;

"what one may call the local time... as demanded by the relativity principle the observer cannot know whether he is at rest or in absolute motion."

Surely light also cannot 'know' of any state of motion of any local field with respect to any other when not interacting. Is any other logic possible?

It may seem that this can both prove the SR postulates AND allow 'Local Reality', consistent with Stokes and Shtyrkov. Light simply changes speed to local c on arrival and interaction with matter, as found in Chandrasekhara Raman's 1930 Noble winning paper. Is there any evidence inconsistent with this?

Best wishes

Peter

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Eckard

I interpret Poincare as Georgina's thesis. Sure he was groping in the dark, as they all were then including Lorentz, and I don't understand the quotes you give, but consider this scenario, which demonstrates the point that apparent (as all we can see is the apparent) elapsed time is not directly objectively measurable except in very unique and almost impossible circumstances;

Take a lightship emitting flashes at three second intervals. These are observed by three people. They will all measure different time intervals!

This is because one is on a ship receding, one on a plane approaching and one at rest on the shore. Yes it is simple, although the one on the shore may confuse, but not only may the lightship be adrift, but a strong wind will either reduce or dilate the period as n=1.0003 for air is a constant.

The point, and one of which Poincare was considering, is that also in a vacuum in space, any relative motion between emitter and observer changes the observed (i.e. measured) interval.

In the end it was Einstein who copied much but ignored some important parts of Poincare's hypothesese in 'painting himself round the room and into the corner' with SR.

I suggest simultaneity is however apparently always simply calculable with the correct data, including distance, relative motion in any medium and the n of the medium, by using c. Spectroscopy assists.

Peter

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