Is time a single block? Eternalism and the Andromeda paradox
We are used to thinking about the past as something stable and
immutable, and to the future as something that's somehow fluid and indefinite.
That's how it really is? According to the theory of relativity,
past present and future can't be separated and split in a precise way and absolute,
and this has some consequences on our interpretation of past, present and future.
Indeed, according to einstein, the future is real and fixed as much as the present and the past.
When we think about space, we don't have any problem visualizing it as something
that exists everywhere in the same way. We say that something is “here” in this
point of space and that another one is “there” in another point, but both things are equally real.
For what concerns time, we think about it in a completely different way.
Everything which we think is real is something that is existing NOW.
Past and future don't seem to exist in the same way in which objects exist
in different points of space. In terms of direct experience,
from our point of view, only the present exists and it's real.
Past and future are somehow out of our hands. We give the past an existence “more real” than
the future, because it has already happened and we can't change it.
Instead, the future seems indefinite, inexistent (until it happens).
However, as soon as we start thinking in a different way,
we realize that things are completely different.
Relativity changed our vision of the past future and present, and time.
Before the theory came out, we were thinking that the present was the same for everyone,
and even the way of dividing the time in the present, past and future was something on which
we all would agree: nobody would have had doubts about what was the future.
But in the relativity theory, this is no more true.
Simultaneity is not an absolute concept.
Two events can happen at the same time, but according to someone else an event can happen
before another one, and the chronological order of events could also be interchanged!
Even the way time flows is different according to different observers.
All of us move from past to future at a different pace.
This idea of time that comes out of relativity is a well known and proven one.
Relativity is one of the most experimented theories that we have,
and the result that events depend on reference frames has been proved many times.
We know for sure that there is no absolute distinction between past present and future.
Each of us has his own present which is different from all of the other people.
My present is not necessarily the same as another observer.
So, the concept of “now” becomes similar to the one of “here”.
In a nutshell, just as every point in space exists in the same way, also instants of time
have to be thought together. Space and time can be seen as a 4 dimensional
volume, a 4 dimensional block, in which all events are positioned and present together.
What we experience are some slices of this block, and every slice is a slice
of present which establishes a distinction between past and future, but the way the
block gets sliced is not absolute and common for everyone: it depends on the observer.
This vision of spacetime is quite different from the one a physician
would have had before Einstein, and it's also pretty counterintuitive.
Before Einstein, we thought that the present was common for everyone,
and the past was fixed and everybody was moving towards the future in the same way.
After Einstein, past present and future depend on the observer,
and they have to be placed on the same plane. This vision Is also called eternalism.
Every instant of time already exist, as every point of space, but it's just our point of
view that creates an illusion of a movement to past from future and an illusion of present.
Relativity merges space and time into a single fourth-dimensional structure known as spacetime.
We should think of time the same way we think of space; just as all of space exists outside of our
world and any point within space can be described by coordinates, all of time exists as well and any
events that have happened or will happen already exist, described by their own coordinates within
the universe. And the same way all coordinates in space are valid, all coordinates (or events) in
time are valid as well, meaning that there should be no such distinctions as “past”,
“present,” or “future”. The universe and life within it is not organic thing that’s constantly
changing and morphing. Instead, it’s like a video where the present moment is merely a frame
within that video. And that video, had we access to it, would reveal every event to ever take
place in our universe, from beginning to end. This cosmos is known as the “block universe”,
a place where change isn’t real and there’s nothing special about the present moment.
Considering this on a philosophical scale brings into question the idea of free will.
Let's take an example to make things clearer.
It is known as the Andromeda Paradox, invented by Roger Penrose.
Among other things, Penrose is famous to have won the Nobel Prize for physics because, in 1964,
he proposed critical mathematical tools to describe black holes. He showed that Einstein’s
general theory of relativity means the formation of black holes must be seen as a natural process
in the development of the universe. He was also able to describe black holes in detail:
at their farthest depths is a singularity where all known laws of nature dissolve.
Here's the real quote from him:
<<Two people pass each other on the street; and according to one of the two people,
an Andromedean space fleet has already set off on its journey,
while to the other, the decision as to whether or not the journey will actually take place has
not yet been made. How can there still be some uncertainty as to the outcome of that decision?
If to either person the decision has already been made, then surely there cannot be any uncertainty.
The launching of the space fleet is an inevitability. In fact, neither of the
people can yet know of the launching of the space fleet. They can know only later when
telescopic observations from Earth reveal that the fleet is indeed on its way. Then they can
hark back to that chance encounter, and conclude that at that time, according to one of them,
the decision lay in the uncertain future, while to the other, it lay in the certain past. Was
there then any uncertainty about that future? Or was the future of both people already "fixed"?>>
In short terms, the theory of relativity says that if a person is moving next to me, this person will
slice the spacetime differently from me, and events for him will not be the same as mine.
Also if people were walking towards the Andromeda Galaxy (or vice versa),
then events in this galaxy might be hours or even days advanced of the events on Andromeda for the
person walking in the other direction. So the decision to invade earth may have
already been taken. In the andromeda present, spaceships have already sailed
and they are coming towards earth. So, again: it could be that, even if
according to me the decision has to be taken, that decision has been already determined.
Of course from a practical point of view, we couldn't experience this decision now,
because we have to wait at least 2.5 million years (since andromeda's distance
from us is about 2.5 million years) before the invaders' information arrives here on earth.
All of this has important consequences on our concept of time.
We could also think of changing the point of view, as we were the aliens that wanted to
invade Andromeda, and we could see that the same reasoning can be applied to Andromeda inhabitants.
The "paradox" consists of two observers who are, from their conscious perspective,
in the same place and at the same instant having different sets of events
in their "present moment". The argument is not about what can be "seen";
it is purely about what events different observers consider to occur in the present.
Depending on the velocity and direction of Andromeda's observer has with respect to us,
for him, what we are saying now may happen in the future, or in the present, or in the past.
For example, you may have never been born, or you may have already died.,
according to his reference frame. This means that a different observer
could receive some information about you that you don't know yet.
So in a sense: some strangers may
know you better than you do. Isn't it amazing and...creepy at the same time?
Somewhere, Lost in spacetime, there is Galileo pointing his telescope towards Jupiter for the
first time, or maybe Einstein how is writing his brand new theory.,
And we can't say that those events don't exist, because they are in the past according to us, but
they could be happening in the present of another observer, and maybe in the future for some others.
Those events simply coexist. So why do we feel like time
is flowing from past to future? How can we distinguish past from present and future?
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It's because of entropy. The feeling of the flowing of
time depends on the way we make our memories and depends upon the fact
that even this process of memories formation goes in the direction of increasing entropy.
Entropy is one of the few quantities in the physical sciences that require a particular
direction for a time, sometimes called an arrow of time. As one goes "forward" in time, the second
law of thermodynamics says, the entropy of an isolated system can increase, but not decrease.
Thus, entropy measurement is a way of distinguishing the past from the future.
In thermodynamic systems that are not isolated, entropy can decrease with time,
for example living systems where local entropy is reduced at the expense of an
environmental increase (resulting in a net increase in entropy),
the formation of typical crystals, the workings of a refrigerator and within living organisms.
As Stephen Hawking said:
“The increase of disorder or entropy is what distinguishes the past from the future,
giving a direction to time.”
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