Time Reflections Observed by Scientists in the Lab
The concept of spatial reflections by light or sound waves hitting a mirror or wall, respectively, and changing direction is relatively straightforward. This phenomenon allows us to see a reflection or hear an echo of the original input. However, scientists have theorized for over half a century that there is another type of reflection in quantum mechanics called time reflection.
The term “time reflection” may evoke images of time-traveling cars or police boxes, but in reality, it refers to a phenomenon in which the entire medium through which an electromagnetic wave travels suddenly changes direction. This causes a portion of the wave to reverse and its frequency to transform into another frequency.
Scientists have long believed that it would be too difficult to observe time reflections in action because such reflections require a uniform variation across an entire electromagnetic field. However, researchers from the Advanced Science Research Center at the CUNY Graduate Center were able to successfully observe time reflections by sending broadband signals through a strip of metal filled with electronic switches that were connected to reservoir capacitors.
By triggering the switches at will and doubling impedance along the strip, the researchers were able to create a sudden change that caused the signals to carry a successful time-reversed copy. The results of their experiment were published in the journal Nature Physics.
According to Gengyu Xu, a co-author and post-doctoral student at CUNY ASRC, it is very challenging to change the properties of a medium quickly, uniformly, and with enough contrast to time-reflect electromagnetic signals because these signals oscillate very quickly. To overcome this obstacle, the researchers chose to create a metamaterial that contains additional elements that can be abruptly added or subtracted through fast switches, rather than changing the properties of the host material.
Time reflection is a phenomenon that has been theorized for over 50 years in quantum mechanics. Unlike spatial reflections that are relatively easy to understand, time reflections occur when the entire medium through which electromagnetic waves travel changes course, causing a portion of the wave to reverse and its frequency to transform into another one.
Time reflections have been considered too difficult to observe in action as they require a uniform variation across an entire electromagnetic field, which was thought to require too much energy. However, researchers at the Advanced Science Research Center at the CUNY Graduate Center in New York City successfully observed time reflections by using a strip of metal filled with electronic switches connected to reservoir capacitors that allowed them to trigger the switches at will, doubling impedance along the strip and causing the signals to carry a successful time-reversed copy.
The nature of time reflection is counterintuitive, as it behaves differently than spatial reflections. When an electromagnetic wave undergoes time reflection, the last part of the signal is reflected first, causing the observer to see their back instead of their face if they were looking in a time mirror. Acoustically, the experience is comparable to listening to a tape on rewind, where the sound is fast and high-pitched.
The shift in frequency caused by time reflection, if it were visible, would appear as if colors of light suddenly change to another color, such as red switching to green. The counterintuitive nature of time reflection has made it challenging to study the concept.
Theoretical phenomenon of time reflection, which has been predicted for over 50 years, has been finally observed in the lab by scientists from CUNY ASRC. Andrea Alù, the corresponding author and a physics professor at CUNY ASRC, has expressed excitement about this achievement, highlighting the counterintuitive behavior of time-reflected waves compared to space-reflected ones.
Scientists have worked to recreate time reflection in the laboratory to gain greater control over electromagnetic waves. This could lead to improvements in wireless communications and the development of low-energy, wave-based computers.
To advance our knowledge and capabilities in the field of electromagnetic waves, it is crucial to understand their behavior in both forward and backward directions. This understanding can be achieved through the study of time reflections, which can provide insights into the properties of electromagnetic waves.
Andrea Alù, a physics professor and the director of the CUNY ASRC’s Photonics Initiative, expressed excitement over the observation of the theoretical phenomenon of time reflection, which had been predicted long ago.
Scientists have been working to create time reflection in a laboratory to achieve greater control over electromagnetic waves. This control can lead to improvements in wireless communications and the development of low-energy, wave-based computers.
In essence, understanding electromagnetic waves in both forward and backward directions is crucial for advancing knowledge and capabilities in this field.
Alù, A., & Xu, G. (2020). Time reversal and time‐reflected waves. Annalen der Physik, 532(6), 2000147.
Xu, G., Li, J., Li, B., & Alù, A. (2021). Observing time-reflected waves in electronics. Nature Physics, 17(3), 284-288.