 When the discussion of tachyons began to appear in physics in the 1960s, it was soon noticed that such particles according to some frames of reference were associated with negative energies going backwards in time. To understand how, consider the trajectory of the same tachyon in relation of three different reference frames, \(S, S^*\), and \(S^{**}\) in the Minkowski-space. Now assume that \(A\) is, in relation to \(S\), the emission of a tachyon at \(t_{1}\) and \(B\) is the absorption of the tachyon at \(t_{2}\). According to an observer in \(S, A\) will be earlier than \(B\) and the tachyon will carry positive energy forward in time. Nevertheless it is always possible to select a reference frame \(S^*\) in relation to which an observer will see \(A\) happen simultaneously with \(B\) and yet another reference frame \(S^{**}\) in relation to which an observer sees \(A\) happens at \(t_{2}^{**}\) whereas \(B\) happens at \(t_{1}^{**}\). According to the observer in \(S^{*}\), \(A\) will take place later than \(B\) and the tachyon carries negative energy backwards in time (See Figure 1).