“Scientists have managed to ‘reverse’ time using a quantum computer” — No, that did not happen
On 13th March, a group of scientists from Moscow Institute of Physics and Technology, Argonne National Laboratory and ETH Zurich, published a paper in Scientific Reports titled — “Arrow of time and its reversal on the IBM quantum computer”.
This paper to led to a series of sensationalised headlines -
1) “Physicists appear to ‘Reverse time’ in a Quantum Computer”
2) “Physicists reverse time using quantum computer”
3) “Scientists have reversed time in a quantum computer”
4) “In a breakthrough study, physicists manage to ‘reverse time’ using a quantum computer”
The list is by no means comprehensive. If you go by the headlines only, there seems to be a momentous feat in Physics — cracking the problem of time travel and which brings us closer to making “Back to the Future” a reality.
The reality however is far more nuanced. No, physicists did not ‘travel’ back in time, nor did they made any particle do that.
The Arrow of Time
The “Arrow of Time” is a peculiar phenomenon in physics. The fundamental laws of nature are symmetric in time. What that means is, there’s no preferred direction in which time should be. In the mathematics of the fundamental laws of Physics —
Past can be the future and future can be the past.
In a simplistic example, consider the motion of Earth around the Sun. The Earth can go around the Sun in the clockwise direction as well as the anti-clockwise direction, without changing a thing in the dynamical equations of the solar system. It happens to move in one direction. If we were to reverse the motion of Earth around the Sun, no laws governing the solar system will be violated.
There is one major exception to this — The Second Law of Thermodynamics (SLOT), which roughly states that the entropy (a measure of disorder in the physical system) of a system always increases.
SLOT prohibits reversing time, because it will entail decreasing entropy. It’s the only law in Physics which encodes a preferred direction in evolution of dynamical systems.
Take for example, an egg falling on the floor. You release an egg from a height, onto the floor, it will be smashed on the floor. The egg falls on the floor and is spontaneously shattered into pieces. It does not, however, spontaneously become whole.
This what increasing entropy means — a system moves from order to disorder. Always. That’s the preferred direction of nature. As we get older, our cells deteriorate (degrade and disintegrate). We do not get younger. There is thus a preferred direction of a dynamical system (our body). Young gets Old.
This is what “Arrow of Time” is — a preferred direction in which the dynamical systems progresses. And the Second Law of Thermodynamics encapsulates this “forward” motion of time.
This is puzzling because, Thermodynamics is macroscopic manifestation of the laws of Statistical Physics. Statistical Physics, which describes the behavior of microscopic particles (atoms, molecules, electrons etc.), does not have a preferred direction for a dynamical system to evolve i.e. no Arrow of Time. There is still no compelling theory to explain this disagreement between microscopic Statistical Physics and macroscopic Thermodynamics.
One of the biggest hurdles for inventing a Time Machine would be the SLOT. Any Time Machine, will violate SLOT. A lot of the sensationalized news articles state the violation of SLOT. However, none of that happened, because, the physicists in the paper, did not reverse the arrow of time.
What actually happened in “Arrow of Time and Its Reversal on IBM Quantum Computer”
To quote from the paper —
“…demonstrated a backward time dynamics of an electron… on the IBM quantum computer”
What the physicists have accomplished in the experiment, is less of time travel to the past, and more of a ‘rewind’ of a video. Think of the Quantum Computer as your computer. And then think of rewinding a video that you are watching on your computer.
Sure, you can see a video of glass shattering on the floor in reverse, but it is not same as having the glass become whole again.
To clarify further, “they have designed a quantum algorithm” which does it. It is an algorithm designed to work on quantum computers and they have used IBM’s public quantum computer to do this (“…design a quantum algorithm that includes complex conjugations and thus reverses the quantum state…”). Hence in the title of the paper they have included “on IBM Quantum Computer”.
Although the paper has received a wide sensationalisation from the media, the result that described in the paper is ultimately a working quantum algorithm on a quantum computer.
It is useful, but is not a ‘reality-shattering’ result.
The reason I am speaking about this is because of the deleterious effect sensationalisation of nuanced scientific research has on the lay populace. Use of ‘quantum computer’ (Know more about Quantum Computers here) in the headlines, would confuse the lay audience, to whom these headlines further pushed the notion that the physicists have achieved time travel into the past. This makes the public (who ultimately fund the expensive scientific projects), into believing that science is too obscure and ‘weird’ for them to understand.
For more like this, Listen to the Podcast — Data, Tech and The Universe
To stay informed about all things Data, Tech and about the Universe, follow us on Instagram and Facebook.
