José Manuel NievesSEGUIR Updated: Save Send news by mail electrónicoTu name *
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According to our daily experience, is the time only flows in one direction , which goes from the present to the future, and since a lot of physicists have tried to understand why. In general, the irreversibility of the time in the world around us is attributed to the fundamental laws of Physics. But it turns out that these laws are symmetric in time, that is to say, that they work equally well forward, backwards.
quantum mechanics, in effect, has taught us that at least in theory, reverse the “arrow” of time is something possible , although apply that possibility to the everyday reality requires of scenarios wildly intricate and implausible. Situations that is very unlikely to occur spontaneously in Nature.
despite this, physicists have managed to demonstrate that, although time reversal is something exponentially unlikely in a natural environment, it is possible to design algorithms able to reverse the arrow of time to a previous state known or given, in the interior of a quantum computer. This version of the arrow of time reversed, however, is applicable only to quantum states known , and it would be the equivalent to rewinding a video to take you to an earlier moment of the film we are watching.
Now, a team of physicists from the united States and Russia has managed to go a step further. In an article recently published in “Nature Communications Physics”, A. V. Lebedev, V. M. Vinokur and his colleagues, americans have managed to develop a method to reverse the temporal evolution of a quantum state is unknown and arbitrary. The work will open new ways for the algorithms of the physical can “send” the temporal evolution of an arbitrary system backwards in time. For the moment, the work is theoretical, and is limited to describe the mathematical process of investment of time. The researchers did not carry out any practical experiment because quantum computers today are not yet sufficiently advanced.
What we understand by “time”
When we speak of the “arrow of time”, what we do in reality is to express the address that follows the evolution of events in connection with the second principle, or law, of Thermodynamics, according to which “the amount of entropy (or disorder) of the Universe tends to increase over time.” It is a principle irreversible, that is to say, that whatever we do, we cannot avoid that the Universe is becoming more disordered.
The second principle of Thermodynamics states that the heat exchange is what makes any system, from a living being to a galaxy, to evolve. And any evolution system dissipates energy, in the form of heat, to the environment, which makes it inevitably that entropy generally increases. To understand this concept, let’s think about a bathtub divided into two parts by a gate.
In a half there is cold water and the other hot water. If we open the gate, the water will be mixed, until the whole is exactly the same temperature, that is, in thermal equilibrium. When this happens, ceases the exchange of heat and, therefore, also the whole activity. The universe, for his part, is cold, but is peppered with galaxies, hot, formed by stars, planets… and for ourselves. But, just like in the case of the tub, there will come a time in all of the Universe reach thermal equilibrium , that is to say, its state of maximum entropy. When that happens, every activity, even the atomic, will cease forever, and the time, which is nothing more than a way of measuring that activity, will cease to exist.
An idea to reverse the time
In this research, physicists considered that energy dissipation constant and inevitable in any system in close relationship with the environment in which that system is located. is What they propose is to use a “reservoir thermodynamic” temperatures, finite as to form a “bath” of high entropy able to termalizar a quantum system because, by increasing or reducing experimentally and at will the thermal disordering (entropy) in the system.
unfortunately, the current quantum computers do not support the thermalization, which is the first step necessary for the reversal to be temporary. In theory, however, the presence of the thermal reservoir as mentioned above have made possible the preparation of consolidated high temperature heat in a quantum system alternative is located in another place but ruled by the same “hamiltonian” (operator that corresponds to the sum of kinetic energy and potential energies of each of the particles in the system). That allowed Lebedev and Vinokur devise mathematically an operator of evolution able to “go back” in time and invest, thus, the dynamic timeline of the quantum system.
An algorithm of temporary investment
The authors believe that in this way, it would be possible to develop an algorithm of inversion of universal time, able to “do running the time in reverse” and find out the state of any system at any time of its evolution.
The article, however, only describes the mathematical analysis of such a temporary investment, without specifying how they should be experiments. In fact, the computational complexity required to do this is outside the scope of current quantum computers, so that the practical demonstration of this work will require a major upgrade of these computers. To do this, Lebedev and his colleagues proposed a series of updates to concrete in the design of the current chips quantum (called qubits), to convert into “qubits thermal” able to tackle the task.
In their work, the scientists have also developed a formula to calculate the number of cycles that must be repeated to reverse the state of a given system to previous states in the past. That number, according to Lebedev and their colleagues, will depend on the complexity of the system that you want to reverse and how much you are supposed to that should go back to that system at the time.
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