According to a recently published study, a group of physicists and computing scientists managed to "turned back the clock" on an IBM quantum computer, to a fraction of a second into the past. The report received immediate massive media coverage, intriguing academics and average citizen alike worldwide.
While some considered that the feat as the primer for future time travel technologies, many have doubts if we will ever see Marty McFly driving a space-time warping Delorean.
To look into this matter more carefully, let's dive into the nature of time, starting with another cultural reference. In his first popular science installment, A Brief History of Time, Stephen Hawking elaborated on the sequence of events that happens in our universe--the origin, expansion, and eventual fate. Hawking also touched upon what he called the "real time", which is how humans observe and experience time in a directional flow.
The flow of time is in one direction, from the past towards the future. This important property, known as the arrow of time or the asymmetry of time, was first developed in 1927 by the British astronomer Arthur Eddington. Still embedded with many unsolved questions, the arrow of time has been used a guiding mechanism in studying different components of our universe, from something as small as atoms and molecules, to large bodies such as planets and stars.
The arrow of time has a deep connection to another important doctrine in physics the second law of thermodynamics. According to this universally applicable proposition, in an isolated system, entropy (otherwise known as the level of disorder), tends to increase over time. Previously, many experiments managed to show matters exhibit "time-reversing" behavior. But in the end, scientists found no violation of the second law of thermodynamics, therefore the asymmetry of time was found not broken.
Entropy and the Arrow of Time (The Royal Institute)
However, the meaning of time has been under close scrutiny since the infancy of contemporary physics. With Albert Einstein's theories of relativity swept the world in the early 20th century, scientists turned the page on Issac Newton's classical mechanics and started to look at time very differently: it is no longer an independent (space and time are interwoven), unchanging (gravity and speed alter one's experience with time) parament of our universe.
Since Einstein, there has been an increasing amount of works that poked holes in how we perceive time. When working on a framework to reconcile quantum mechanics with relativity, renowned physicists John Wheeler and Bryce DeWitt developed an extraordinary equation that provides a possible framework for unifying relativity (which governs the large bodies) and quantum mechanics (which governs the microscopic world). While the Wheeler-DeWitt equation did provide a mathematical clue to unify the two theories, but in it time plays a conceptual conflicted role. It is as if this seemingly universal constant can simply remove itself from the mechanisms that operate our world, and everything will still hold.
Despite its elusive nature, scientists had never stopped pursuing projects that would lead us to a better understanding of time, such as ultra-precise measurement of time using atomic clocks, exploring the interplay of quantum entanglement and thermodynamics, and breaking time asymmetry using microwave signal circulator.
As scientists are piecing together a brand image of time with evidence collected from different lines of research, it is only human curiosity to speculate that time travel or manipulation of time would come true soon.
Timeless Time in the Quantum World (World Science Festival)