1. Time/Fatalism
Week 05

2. In today’s lecture… Recap 3 theories of time Hirsute
In today’s lecture…
Recap
3 theories of time
Hirsute
The Time Traveler’s Wife
Fatalism
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3. Recap The nature of time Newton, Kant and Einstein Time travel
Recap
The nature of time
Newton, Kant and Einstein
Time travel
Time travel paradoxes
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4. 3 theories of time 1. Eternalism (永恆論) 2. Presentism (現在論)
3 theories of time
1. Eternalism (永恆論)
2. Presentism (現在論)
3. Parallel universes (平行宇宙論)
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5.
3 theories of time
‘Eternalism’ – also known as ‘four-dimensionalism’ or ‘block universe theory – is the view that time is the fourth dimension, i.e. there is no difference between time and the other 3 spatial dimensions (length, width and height), and together they form the ‘block universe’ or four-dimensional ‘space-time block’.
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6.
3 theories of time
In the Newtonian universe, it was supposed that there was no connection between space and time. A ‘block universe’ (or ‘space-time block’), as postulated (提出) by Albert Einstein in his theories of relativity, is a four-dimensional structure in which space and time and inseparably connected.
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7.
3 theories of time
According to eternalism, all events are fixed and determined (既定的、注定的). The universe is one immutable (不變的), four-dimensional ‘space-time block’.
All objects and events – past, present, future – can be seen as in different fixed positions on the space-time block.
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8.
3 theories of time
As such, ‘the past’, ‘the present’ and ‘the future’ are just different parts or locations on the space-time block.
All objects and events – past, present, future – are equally real. Past and future objects and events are just as real as currently existing ones.
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9.
3 theories of time
The space-time block is like a movie on a videotape, and our experience of time is like that of watching a movie – although the whole movie is already there on the tape, we can only see it one frame at a time.
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10.
3 theories of time
From the standpoint of eternalism, the appearance (表象) of time passing or flowing is not real (i.e. not an objective fact).
There is no objective flow of time. The passage of time is a subjective illusion (假象) – it is because of our mental structure that we see time as flowing.
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11.
3 theories of time
According to eternalism, we know more about the past than the future, but this is not because the future is not real. The future is already there, fixed and determined. We cannot know the future simply because of the limitation of the human consciousness – our minds cannot see into the future.
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12.
3 theories of time
If time really is the fourth dimension, it should be possible to moving along the axis of time in either direction (like movement along the 3 spatial dimensions). In other words, it should be theoretically possible to travel either forward or backward in time.
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13.
3 theories of time
Thus, if eternalism is true, time travel is possible – it is theoretically possible to travel either to the past or to the future.
However, a time traveler cannot change the past nor the future because all events in the block universe are fixed and determined.
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14.
3 theories of time
Why does time always move (or seem to move) only in one direction?
Is there any real difference between the past, the present and the future?
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15.
3 theories of time
Opponents (反對者) to eternalism argue that unlike the 3 spatial dimensions (where movement in either direction is possible), some events are irreversible (不可逆轉的) and happen only in one direction in time.
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16.
3 theories of time
For example, you can burn a piece of paper to ashes, but you cannot turn the ashes back into a piece of paper.
Similarly, glasses fall and break all the time, but shards of glass do not put themselves back together and fly up on tables.
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17.
3 theories of time
The fact that time has a direction is called ‘time’s arrow’; for example: [1] some processes and events are irreversible; [2] causes always precede (先於) their effects; [3] we have memories of the past, but not the future; and [4] we cannot change the past, but our actions can affect the future.
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18.
3 theories of time
Another theory of time is called ‘presentism’, and it can be regarded as the common sense view of time.
According to presentism, as time passes, the moment that was once the present becomes part of the past; and part of the future, in turn, becomes the new present.
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19.
3 theories of time
The main argument of presentism is that reality is always changing. Time flows when events change from being future, to being present, to being past.
The past has gone. The future has yet to come into being. The past and future are both unreal. Only present objects, events and experiences are real.
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20.
3 theories of time
One of the implications (含義) of presentism is that time travel is impossible. Since only the present is real, there is no future or past to travel to.
The main problem with presentism is that it is in conflict with (有抵觸) currently accepted scientific theories, especially the special theory of relativity.
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21.
3 theories of time
The third theory of time is called ‘parallel universes’. As its name suggests, the theory states that reality consists of an infinite number of parallel universes.
The theory was first proposed as an interpretation (解釋、解說) of quantum mechanics (量子力學), but the most common use of ‘parallel universes’ is in science fiction.
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22.
3 theories of time
According to one interpretation of quantum theory, when we make a choice between two or more options, it will result in the creation of two or more universes or ‘timelines’ – one for each option in a given choice – through a process called ‘branching’ (分枝).
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23.
3 theories of time
The parallel universes theory suggests that each of these parallel worlds is just as real as our own, and there is an alternative history for every possible outcome of every decision ever made.
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24.
3 theories of time
The parallel universes theory suggests that backward time travel would take a time traveler to a parallel universe in which the course of history would begin to diverge (出現分歧) at the very moment the time traveler arrives in the past.
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25.
3 theories of time
In other words, when a time traveler goes back to the past, the universe splits (分叉) at that moment into two parallel universes.
The time traveler’s attempt to change the past will give rise to an alternative universe with a different history (i.e. a new ‘timeline’).
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26.
3 theories of time
However, in the original universe, nothing has changed and everything remains the same.
Thus, if the parallel universe theory is true, the time traveler’s actions will not have any effects on the universe from which he came.
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27.
3 theories of time
Suppose a time traveler goes back in time to kill Hitler in order to prevent the World War II. His action will result in two parallel universes, one in which the war happened exactly as it did (the original universe), and an alternative universe where Hitler is killed (if he succeeds) and the war may not happen.
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28.
Think!
Which theory – eternalism, presntism, or parallel universes – offers the best explanation of the nature of time?
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29.
Think!
You should notice, first of all, that the 3 theories of time are in conflict or incompatible (不相容) with one another. It means they cannot all be true. But, of course, it is possible that they are all false.
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30.
Think!
The 3 different theories also provide different answers to paradoxes of time travels such as the grandfather paradox.
For example, from the standpoint of presentism, these paradoxes indicate that time travel, especially backward time travel, is logically impossible.
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31.
Think!
According to eternalism, all events are fixed and determined. Thus, although time travel may be possible, a time traveler may not be able to interact with objects and people of the past.
Even if he was able to interact with objects and people of the past, anything he did must have been part of known history.
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32.
Think!
The parallel universes theory suggests that backward time travel would cause the universe to branch off into two different timelines, creating a new universe with a different course of events. However, everything in the original universe (where the time traveler came from) would remain unaffected.
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33.
Think!
According to the parallel universes theory, because different timelines are completely separated from one another, actions and events that take place on one parallel universe do not have any effects on the others.
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34.
Think!
Thus, in one parallel universe a time traveler may kill his grandfather so that his family will cease to exist. But in the original universe, his grandfather continues to live to a ripe old age.
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35.
Think!
Suppose the parallel universes theory is true. If someone travels back in time, jumps into another universe and kills his grandfather. Is the person he kills really his grandfather?
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36.
Think!
Now we are going to watch a short video titled ‘Hirsute’. Pay attention to the puzzles and paradoxes involved in this film.
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37.
Think!
What exactly are the paradoxes involved in this time travel story?
Do you see why understanding the nature of time and solving the mystery of time travel becomes extremely important for the scientist when he sees a future version of himself commit suicide on a time travel journey?
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38.
Fatalism
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39.
Fatalism
Next week, we will consider a number of arguments related to fatalism (宿命論). For the time being, let us take a brief look at the meaning of fatalism.
Simply put, fatalism is the idea that whatever is going to happen is unavoidable (不能避免的).
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40.
Fatalism
In other words, fatalism is the view that if something is going to happen, it is going to happen. There is nothing we can do to change it.
A fatalist thinks that we have no control over what is going to happen in the future.
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41.
Fatalism
An ancient argument for fatalism is called the ‘idle argument’ (無用論). Here is an example:
[1] If it is fated (注定) for you to recover from your illness, then you will recover whether you call a doctor or not.
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42.
Fatalism
[2] Similarly, if you are fated not to recover from your illness, you will not recover even if you call a doctor.
[3] Therefore, whether you call a doctor or not does not make any difference.
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43.
Fatalism
Is there anything wrong with the reasoning of the idle argument?
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44.
Read!
Go to the course website, download and read the article titled ‘Aristotle and Fatalism’. (Some parts of the article may look difficult but we will look at related issues in next week’s lecture.)
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45. The Time Traveler’s Wife
The Time Traveler’s Wife
As you are watching the film, you should keep asking yourself whether or not the story is logical.
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