A machine to send objects into the past is not the cleanest modern evidence with regard to the physical reality of time travel. It is a laboratory illusion which causes waves to act as though part of their past has been rewound since the limit which they reach is in time, not space.
In normal optics, a place is a surface at which a wave is reflected. The mirror is a moment in the new experiments. Investigators design a medium whose offers a discontinuity and uniformity in all domains, such that an incident signal encounters a temporal interface. In that case, a section of the message will come out as the mirror image of it psychologically its spatial structure intact, but reversed. This has been shown with electromagnetic signals in switched metamaterial transmission lines, and has a twist in engineering: the interface can maintain broadband frequency translation, an effect that does not occur with a simple spatial mirror.
The concept is received differently when it is not part of electronics. Another group of experiments carried out the time-boundary behavior in mechanics by a beam with piezoelectric patches attached to time varying circuits. When the elastic waves come in contact with such time-modulated boundary, it is broken into components which are reflected and refracted, which is a temporal analog of the Snell law. This is important to engineers, since vibrations can be a common nuisance and a common signal: given the ability to build time interfaces into the structure, then the same physics that re-wrinds a waveform in a cable can then be applied to re-reform packets of vibration in solids without either repositioning a wall or adding mass, or modifying the geometry of the beam.
The time travel of that laboratory also follows the daily principle that brings about the effects precedes the cause. The reverse of the history of its propagation is the wave, yet the experiment does not convey any information to a previous observer, nor does it exceed the speed limit of relativity. Practically, modern physics already considers time to be a matter which can be engineered around just not through contradiction. It was demonstrated a long time ago, by portable atomic clocks, that at that time flights with cesium clocks showed consistent gains and losses with ground-based clocks, and this effect was explained by special and general relativity; the best known example is the 1971 round-the-world atomic clock flights. The same principle is now implemented in infrastructure: GPS needs to continuously compensate the relativistic effects as satellite clocks move at 38 microseconds per day faster than on-the-ground clocks when acceleration and motion are factored in as explained in the overview of precision clock tests at NIST.
The more far-reaching meaning of time-interface experiments is that they are a revelation of a symmetry concealed by everyday life. A large number of fundamental wave equations can be time-reversible, but macroscopic experience is not, in large part because entropy and uncontrolled interactions wipe out the minute details in which a process can be run backward. The principle of temporal mirrors consists in isolating a well-prepared wave and then introducing a fast global change of parameter the equivalent of a new control knob known as when. That knob does not disavow thermodynamics, but can focus, translate or restructure a signal in manners that are not easily replicated using purely spatial components.
In the meantime, even the science-fiction variant of the time travel is more a mathematical question. General relativity has solutions (loops of worldlines around on themselves) called closed timelike curve, but they are not laboratory apparatus and they are not solved in nature with causality puzzles which physics has not solved. Current engineering edge is less grand, more operational: to know how to cause fields and vibrations bounce back not off surfaces but off moments, allowing time to be made a design dimension not just in sensing but also in communications and signal processing.
