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Why Time Always Marches Forward ?

Ray Cummings in his 1922 science fiction novel “The Girl inthe Golden Atom” wrote:  “Time is what keeps everything from happening at once,” and which tells us time’s purpose quite agreeably. But how does time prevents everything from happening simultaneously? What process pushes time forward, but not backwards? In a new study printed in the journal Physical Review Letters, a team of theoretical physicists re-examine the “Arrow of Time”, an idea that defines the persistent forward march of time, and focuses on a different view of looking at how time expresses itself over all universal levels.


Usually, time is defined by the “past hypothesis” that assumes that any specified system initiates in a low entropy condition and then, compelled by thermodynamics, its entropy rises. You think of it like: The past is low entropy state and the future is high entropy state, a theory recognized as thermodynamic time asymmetry. In our daily knowledge, we can find several patterns of increasing entropy, for example a gas filling an apartment or an ice cube melting. In these cases, an irretrievable rise in entropy (and hence disorder) is detected. If this concept is applied on a universal level, it is supposed that the Big Bang produced the cosmos in a low entropy state, i.e. a state of lowest entropy. With time, as the universe expanded and chilled, the entropy of this huge scale system has enlarged. Hence, as the hypothesis goes, time is essentially connected with the amount of entropy, or disorder, in our cosmos.

But there are more than a few complications with this concept.

Right after the Big Bang, many lines of observational proof point to a Big Bang situation that was a hot and tremendously chaotic mess of prehistoric particles. As the universe aged and chilled, gravity took over and prepared the universe well-ordered and more multifaceted, from the chilling clouds of gas, stars were made and planets developed from gravitational fall. Finally, organic chemistry turns out to be possible, giving growth to life and humans that speculate about time and space. On a Universal level, thus, “disorder” has efficiently decreased, not increased as the “past hypothesis” postulates.

This, argues co-investigator Flavio Mercati of the PerimeterInstitute (PI) for Theoretical Physics in Ontario, Canada, is a problem with how entropy is being measured.

As entropy is a physical quantity with dimensions (just like energy and temperature), there has to be an exterior reference frame so they can be measured against. Here is what Mercati told Discovery News “This can be done for subsystems of the universe because the rest of the universe sets these references for them, but the whole universe has, by definition, nothing exterior to it with respect to define these things,”.

So if it’s not entropy, what may possibly be driving universal time in a forward direction?
Complexity is a dimensionless quantity that, in its utmost straightforward form, defines how complex a system actually is. So, if one looks at our universe, complexity is openly connected with time; as time moves, the universe turn out to be more and more structured.

Mercati said “The question we seek to answer in our paper is: what set these systems in that very low-entropy state in first place? Our answer is: gravity, and its tendency to create order and structure (complexity) from chaos,”

To experiment this concept, Mercati and his coworkers made simple computer models to simulate particles in a toy universe. They establish that, no matter how the simulation was preceded, the universes’ complexity at all times increased, and not ever decreased, with time.

From the Big Bang, the universe started in its lowermost complexity state. Then and there, as the universe chilled to a state that gravity arose to take over, gases stamped together, stars made and galaxies developed. The universe turns out to be relentlessly more complex, and gravity is the driving force of this upsurge in complexity.

Mercati said“Every solution of the gravitational toy model we studied has this property of having somewhere in the middle a very homogeneous, chaotic and unstructured state, which looks very much like the plasma soup that constituted the universe at the time the Cosmic Microwave Background was created. Then in both time directions from that state gravity enhances the inhomogeneities and creates a lot of structure and order, in an irreversible way.”

As the universe ages, he added, the subsystems become isolated enough so that additional forces set up the circumstances for the ‘classical’ flow of time to direct in low-entropy subsystems. In these subsystems, for example regular life on Earth, entropy can hijack, generating a “thermodynamical arrow of time.”

Over Universal scales, our observation of time is determined by the endless growth of complexity, but in these subsystems, entropy rules.

Mercati in a PI press release said “The universe is a structure whose complexity is growing. The universe is made up of big galaxies separated by vast voids. In the distant past, they were more clumped together. Our conjecture is that our perception of time is the result of a law that determines an irreversible growth of complexity.”

The next stage in this study would be to look for observational indication, something Mercati and his group is working on. “…we don’t know yet whether there is any (observational) support, but we know what kind of experiments have a chance of testing our idea. These are cosmological observations.”

For the time being, he hasn’t shown what types of cosmological observations will be examined, only that they will detailed in an upcoming, and possibly fascinating, paper.

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