Arthur Eddington was a British astronomer, mathematician, and physicist in the 20th century. He developed an interesting physics question in 1927 that remains unsolved to this day. It is called the arrow of time problem.
Time appears to be inherently directional: the past is fixed and immutable, accessible only through memory or written documentation; the future, on the other hand, is not necessarily fixed, and, while we can perhaps predict it to some extent, we have no firm evidence or proof of it. We find it difficult to believe that this growth could go any other path. The arrow of time, or the one-way direction or asymmetry of time, is what gives us the sensation of time passing, of our going through distinct moments. The consistent and unique direction connected with the apparent inevitable movement of time towards the future is the arrow of time.
In Eddington’s own words, ‘Let us draw an arrow arbitrarily. If as we follow the arrow we find more and more of the random element in the state of the world, then the arrow is pointing towards the future if the random element decreases the arrow points towards the past. That is the only distinction known to physics. This follows at once if our fundamental contention is admitted that the introduction of randomness is the only thing which cannot be undone. I shall use the phrase time’s arrow to express this one-way property of time which has no analogue in space.’
He also gave three main points about the arrow, which are as follows: Consciousness is acutely aware of it. Our reasoning faculty also insists on it, claiming that reversing the arrow would make the external world unintelligible. It only appears in physical science when it is used to study the organization of a group of individuals, meaning it is only observed in entropy.
There are different types of arrows. The first is the thermodynamic arrow of time. The second law of thermodynamics provides the thermodynamic arrow of time, which states that entropy tends to grow with time in an isolated system. As entropy is a measure of microscopic disorder, the second rule means that time is asymmetrical in relation to the degree of order in an isolated system: as time passes, the system gets statistically more disordered. Although measuring entropy does not correctly measure time, this imbalance can be utilized empirically to discriminate between the future and the past.
Next, we have the cosmological arrow of time. The cosmological arrow of time indicates the expansion of the universe. It could be related to the thermodynamic arrow, which indicates that the cosmos is approaching a heat death as the amount of usable energy decreases.
The radiative arrow of time is another arrow. Waves propagate outward from their source, despite the fact that the wave equations can allow both convergent and radiative wave solutions. This arrow has been reversed in carefully worked experiments that produced convergent waves, implying that it is related to the thermodynamic arrow in that meeting the requirements to produce a convergent wave takes more order than meeting the conditions to produce a radiative wave.
The causal arrow of time is a very intuitive arrow that we can all understand in this classical world. The causal event occurs before the event it causes or effects. As a result, causation is inextricably linked to the arrow of time. Controlling the future or causing something to happen establishes correlations between the doer and the effect. Thus the cause-and-effect relationship is a result of the thermodynamic arrow of time, which is a result of the second law of thermodynamics.
Some theorists, like Stephen Hawking, have predicted the direction of the arrow of time on what is known as the weak anthropic principle, which states that the laws of physics are as they are only to allow the development of sentient, inquiring entities such as ourselves. It is not that the universe is in some way structured to allow human existence, but rather that we only find ourselves in such a universe because it is as it is, despite the fact that the cosmos could have easily evolved differently with different laws. Thus, according to Hawking, a strong thermodynamic arrow of time is an essential prerequisite for sentient life as we know it to develop.
Writer: Golda Abs
Editors: Rana Alqahtani/Lamar Albukhari
1- “The Arrow of Time.” Exactly What Is Time? www.exactlywhatistime.com/physics-of-time/the-arrow-of-time/.
2- Callender, Craig. “Thermodynamic Asymmetry in Time.” Stanford Encyclopedia of Philosophy, Stanford University, 8 June 2021, plato.stanford.edu/entries/time-thermo/.
3- Hänggi, Peter. “Entropy.” Entropy | Special Issue: Arrow of Time, www.mdpi.com/journal/entropy/special_issues/arrow_of_time.
4- The Arrow of Time, http://www.informationphilosopher.com/problems/arrow_of_time/.