Ep 38. The Arrow of Time and How to Reverse It

The Arrow of Time and How to Reverse It is the 38th episode in the 2020 season of PBS Space Time, an educational show about astronomy and physics. In this episode, the host begins by discussing the concept of the arrow of time, which is the idea that time flows in a specific direction and that events always happen in a particular sequence. The arrow of time is linked to the second law of thermodynamics, which states that the entropy (or disorder) of a closed system always increases over time.

The host then explores a few thought experiments that demonstrate the arrow of time, such as a video of a pendulum swinging and then reversing its motion, which looks strange and unexpected because it goes against the arrow of time. He also discusses the concept of a time-reversed mirror, which would be a device that reflects everything that passes in front of it but in reverse order, indicating the absence of the arrow of time.

However, physicists have found a way to reverse the arrow of time in isolated systems by exploiting the laws of quantum mechanics. The host explains that a quantum computer can simulate a system that is time-symmetric, meaning that it would look the same if run forwards or backwards in time. By studying these simulations, scientists can learn how to precisely manipulate quantum states to reverse the arrow of time within the system.

The host also explains that this has practical implications beyond just theoretical physics. For example, if we could control the arrow of time in a closed system, we could effectively time-travel within it. Additionally, in the field of quantum computing, reversing the arrow of time could enhance the speed and efficiency of certain processes.

Throughout the episode, the host uses clear and concise language to explain complex concepts, making it accessible to viewers without advanced physics degrees. He also includes helpful visual aids, such as diagrams and animations, to illustrate his points and enhance viewers' understanding.

In conclusion, The Arrow of Time and How to Reverse It is a fascinating episode of PBS Space Time that explores a mind-bending concept while remaining grounded in scientific reality. It's an excellent watch for anyone interested in physics, astronomy, or the mysteries of time itself.