Tachyonic antitelephone

An anti telephone (also tachyon Anti telephone) is a hypothetical device that could be sent with the signals into his own past. It is based on a thought experiment Albert Einstein (1907 ), after which move faster than light signals propagating in accordance with the special theory of relativity backwards through time. Einstein ( 1910) described the in a conversation with Arnold Sommerfeld as a means to " telegraph in the past." A similar thought experiment was Richard Chace Tolman from (1917 ) discussed why it is also known as Tolman's paradox. A hypothetical device with which this could be accomplished has been described by Gregory Benford later as " anti Tachyon phone ". For tachyons are hypothetical superluminal particles.

Such " telegraphing to the past" means faster than light communication would, however, lead to causality violations, so it was Einstein, Tolman and unrated possible by the vast majority of physicists as practical. Also the associated tachyon theories are controversial.

Disposable example

Based on Einstein's thought experiment, Tolman looked at the following situation: Let there be given a distance L with end points A and B. A signal is then transmitted at the time A in the direction B with the speed, and there is at the time to. The flight time of the signal obtained with

Here, then, is the cause (event at A) before the sequence ( Event at B) instead. However, in an inertial reference frame, which moves relative to the speed to results in accordance with the Lorentz transformation, the flight time of the signal until the arrival at B with:

It can be seen that a negative is created by a suitable choice of V, when. In other words, the effect of B occurs before the source of A in this system. Einstein and Tolman pointed out that this result does not contain a logical contradiction, but it contradicts the totality of the experience, so that the impossibility of superluminal speeds is their view, sufficiently proved.

Zweiwegbeispiel

Things are more complicated contexts, if the following example is discussed: It is an inertial frame S 'is given, resting in the observer A, and S, rested in the B. B moves in the negative x - direction from the perspective of A. It is also assumed that both A and B have the same device, which superluminal signals can be sent in their respective inertial frames.

A sends a the time with superluminal velocity (measured in S ') propagating signal to B, the there at the time

Arrives. Here is the distance traveled by the signal until it reaches the them flying in the negative x direction B. At B now immediately the own transmitter is activated and sends a faster than light (measured in S) propagating signal to A. It must be remembered that the route is contracted in length, and that A runs away to the signal in the positive direction. This results in an arrival time of

In S ' on the other hand (cf. formula for the one-way example ) yields

Generally speaking, therefore, the total time is obtained up to the return to A

Again, results for that with a suitable choice arises from a negative, that is, A gets back the response before the original signal () was ever sent. Benford et al. wrote about such situations:

" The paradoxes of backward - through-the- time communications are well known. Suppose that A and B make the following agreement: A will send a message by three clock, but only if no message arrives here around a clock. Immediately after the news of A by two clock arrives at B, B sends a message, which reached A is a clock. The message exchange thus takes place only if he does not take place. This is a real paradox, a causal contradiction. "

They concluded that faster than light particles such as tachyons should not transmit signals.