“See you tomorrow!” is probably a phrase you have at least heard once in your life and perhaps makes you smile a little wider than usual. In our day-to-day conversation, we throw around words related to stages of time like tomorrow, yesterday, and two years ago. These words, however, imply that their users and recipients are under one frame of time; that is, the present.
As much as we like their convenience and are often unbothered with the effects that these words carry, they in fact are incompatible with the reality of the concept of time.
Before Einstein, our understanding of time is that time is absolute. Meaning, there is as if the universe had a giant “master clock,” one that resembles that of Mozart’s metronome. One that keeps on ticking since the world started, ends when the universe ends, and is, more importantly, absolute regardless of where we are.
Is our former understanding of time flawed? Is it incompatible with the activities that we frequently do? Does it break any laws of nature?
The answer is: it certainly does. That’s where Einstein’s theory of Relativity kicks in. It takes quite a bit to understand the bigger picture of Relativity, but I’ll try my best to break these down into digestible pieces.
Curvature of Space-Time
Firstly, the concept of space and time being two entirely different properties are incorrect. Space and time live in one “fabric,” the fabric of space-time. If the fabric bends, both space and time bend accordingly and are inseparable. Such bending happens when there’s mass and a significant amount of mass bends the fabric quite largely. Take a peek at this video for better visualization of this concept.
For example, imagine the Sun. The Sun’s mass is about 2 times 10 to the power of 30 kilograms. That’s 2 with 30 zeroes trailing it. For comparison, the Sun weighs about 333,000 Earths – that’s a lot of weight to carry.
Because of how heavy it is, the Sun bends the fabric of space-time. As a consequence, it sort of creates a bent-pathway causing surrounding planetary objects to orbit. This distortion of space-time is indeed the explanation behind gravity, which we have understood semi-incorrectly since the days of Newton.
Previously, Newton has established that there is a gravitational force between two masses, which attracts one another and explains the orbital mechanics of the planets around us. However, one question that remained unanswered was how did the gravitational force work? Do they take time to attract the two objects together? Was there a magnet-like attraction event that occurred?
You see, there were flaws in Newton’s gravitational theory, although it did predict some planetary movements to a certain degree of accuracy. Nonetheless, Einstein’s framework came into the frame and gave a clearer description of the reality of space-time. Oh, and by the way, that was General Relativity, the second of Einstein’s Relativity-paper series.
Relativity of Time
Afterwards, do remember that the bending of space means the bending of time. What General Relativity has shown us is that time is that it can bend, but it hasn’t necessarily proved that time is not absolute. A more precise counter-proof to the absoluteness of time was annihilated first in Einstein’s earlier paper regarding Special Relativity.
This paper absolutely crushed our understanding of time. It proposes that time is not absolute and there isn’t an absolute present, so to say. Two events can happen simultaneously to one observer and yet happen separately to another, depending on their speeds.
My favourite thought experiment on this concept is called Einstein’s train. Imagine Bob is on a speeding train, while Alice is overlooking while standing at a platform. Then, two lightning strikes happened at the same time, one behind the train, and one in front of the train.
In Alice’s perspective, she sees the two events as simultaneous events. Lightning one occurred at the same time as Lightning two. However, in Bob’s perspective, he will observe the lightning in front of the train, in the direction where his train is speeding to, occurs first and then separately the lightning behind him.
Why so? Because to be able to observe the lightning happen with his eyes, light waves have to travel to Bob’s eyes. This process does not happen instantaneously and takes time – despite being very negligible. Nevertheless, since he is travelling towards the lightning in front of the train, those light waves will reach his eyes earlier, than the ones from the lightning behind him.
So then, what does this imply? Well, in Alice’s frame of reference, both events are simultaneous. Yet for the case of Bob, one happened before the other. When the two meets later on, wouldn’t this incompatibility make no sense?
The idea of the past and present is no longer a frame-independent concept. It is hence relative to the observer’s frame of reference. And worse, there is no “real” or “absolute” frame of reference, which, if it had existed, would be conveniently in line with what we presumably intended when we say today, tomorrow, or now.
Reasonably, the philosophy of time has long existed before the days of Einstein and Newton. One popular, contemporary understanding of time is called A-Theory, which divides events according to their pastness, presentness, and futurity. These properties are not only intrinsic and indivisible, they are what paved the way into our naive understanding of past, present, and future.
A-Theory was established by John McTaggart Ellis McTaggart, an English metaphysician, in his article called The Unreality of Time. In it, McTaggart argues that time is not real and that he discussed time through what he called “A-series” and the “B-series.”
In his book Philosophy 101, Paul Kleinman described A-series as the “series of positions which runs from the far past through the near past to the present, and then from the present through the near future to the far future, or conversely.”
Further, Kleinman explained that what McTaggart meant by “series of positions” was positions in time:
Events are positioned in the past if they have already happened; they are positioned in the present if they are happening now; and they are positioned in the future if they have not yet occurred. The property of being in the past, the present, or the future is temporary, not permanent property. For example, when it had not yet happened, the event of landing on the moon was in the future; when it was occurring, it was in the present; and now it is in the past.
Since we do experience different events occurring in different phases of time, we thus utilize the use of tensed sentences or A-sentences. Klein added that we often use tensed-keywords to describe events according to when they happen.
An event in the future will take place; an event in the present is taking place; and an event in the past has taken place
You see, we humans have taken such A-sentences or tensed-sentences very dearly to our understanding of reality. According to Klein, “A-theory combines presentism and non-reductionism,” where presentism implies that “nothing exists other than what presently exists” and that non-reductionism “corresponds to a fundamental and ineliminable feature of reality”.
Can A-Theory be Compatible with Special Relativity?
These tensed sentences, according to non-reductionism, have bled into our naive comprehension of time, as much as it is incompatible with the correct understanding of time via Special Relativity.
Indeed, as there isn’t an absolute, real frame of reference when we’re dealing with time, A-theory and tensed-sentences are in huge danger. Since Special Relativity has been proven to be accurate, “presentism becomes a frame-dependent matter,” said Klein. What you may say is tomorrow, could be someone else’s yesterday, or even their present.
Like Klein clarified in his book, A-theorists have tried to reconcile these two contrasting frameworks. On one end, several philosophers argue that Special Relativity remains an empirical theory and hence should not be used to assess metaphysical claims. As a consequence, Klein wrote that “current Physics does not completely rule out absolute simultaneity; it just cannot currently conceive it.”
On the other end, other A-theorists objected that “the relativity of simultaneity is itself only an apparent effect. Whether two events are observed simultaneously is one thing; whether they take place simultaneously is another.” That said, whether or not Special Relativity is true shouldn’t bother our usage of tensed sentences, since they do not interfere with our present observance.
Given what we have discussed here, humans have yet to understand much of what modern physics brings to the table, let alone incorporating these complex ideas into our day-to-day conversations.
I have to say, the naive usage of A-sentences is merely for convenience’s sake, in my opinion. As long as our activities do not involve high-speed movements – like that of riding a beam of light – the past, present, and future should relatively be the same with our conversation partner.
If you were Einstein though, your understanding of time would be closer to what your very own theory imposes. In a letter of condolence to the family of his friend Michele Besso, Einstein wrote:
Now he has departed from this strange world a little ahead of me. That means nothing. For us believing physicists the distinction between past, present, and future only has the meaning of an illusion, though a persistent one.
One month and three days after the passing of his friend, Einstein too, departed from this strange world on 18 April 1955.
Featured Image by Nicolas Poussin, Public domain, via Wikimedia Commons.