What is the weather?
Well, we all know what time is, we live in time,
it is a primitive concept that we all know.
Yet it is very difficult to describe, to give
an exact definition of the time.
This was also known by St. Augustine, who wrote precisely:
“What is time, then? If nobody asks me I know it well: but if I wanted to
give an explanation to those who ask me, I do not know. “
We could define time as the one that allows us to see the flow
of events from the past to the future, through the present.
Here, there is therefore a kind of arrow of time, we could say,
a symmetry in the passage of time, as in the three spatial dimensions
we can safely go back and forth, left and right
up and down, while the weather … we have to go forward.
On the other hand we all are born, grow up, grow old and die,
always in this direction.
And we experience it in everyday life, for example if we see a movie
like this, as if by magic there is a person who takes pieces of banana
and with a knife “zac, zac, oplà!”, he magically reconstructs a banana
how it was starting.
Or see this other movie, where there are some exultant people,
who applaud because they see this cloud of smoke and dust from which,
as if by magic, two skyscrapers are born.
Here, these two movies are strange, they are bizarre.
We understand immediately that there is a trick, the trick is soon said:
we are seeing the video backwards, back in time, because
the macroscopic phenomena of our daily life take place only in one direction
they are irreversible, in the sense that they are seen in the opposite direction
It’s weird, weird, it never happens.
Here … so this is essentially the heart of the concept
of the second principle of thermodynamics, which says that
“The entropy of the universe always increases.”
Now, it is difficult to explain what the concept of entropy is;
without being perfectly rigorous, entropy could be associated with it
to the concept of disorder.
For example, if we take this matrix of blue and yellow cards, and mix them
in a chaotic way, we mix them, we mix them …
at some point we will reach a configuration like this one
on the right, where the cards are in bulk.
If now we continue to mix and mix them, sooner or later we ask:
“We will return to the starting situation where all the blue tiles
are they on the left and the yellow tiles on the right? “
The answer is no. Time flows only in this direction,
towards the scattering, towards disorder, or rather,
it is not impossible to return to the starting condition;
it is possible but it is simply highly unlikely.
Here, this is the concept of entropy; the increase in entropy explains to us
the increase in disorder, then explains this unidirectionality
of the arrow of time.
I remember when, maybe I was in high school, they explained to me
for the first time what entropy was, I tried to use it as an excuse
for my mother who complained that my room was untidy, I said:
“Eh, it’s not my fault, it’s the entropy that increases the universe”.
But it’s an excuse that did not work, obviously.
So then, if the entropy of the universe is always destined to grow,
then we understand that in the end the death of the universe will be by entropy,
that is, it will be what is called the thermal death of the universe,
where all the matter and energy will be spread out in a homogeneous way,
so there will be no more transformation possible,
and therefore life will no longer be possible.
Here, but … what is life then?
Shrödinger, Nobel Prize in Physics, one of the fathers of quantum mechanics,
in his 1944 book, What is life, What is life,
he said that life is nourished by negative entropy, what does it mean?
It means that a living being not only fights the nefarious effects
of the increase in entropy, which would lead to premature death,
but it even does the opposite, works against entropy to create order,
to create structures, information.
In fact if we cut our body is able to restore the wound
and restore the fabrics.
Twenty years later, in 1964, NASA asked a group of researchers
to seek life on Mars or other planets, and then one of these
James Lovelock, he wondered:
“What can we do to recognize life on another planet?”
A life maybe different from ours, not based on carbon;
we do not expect to see people with two arms and two legs like us,
So what is the answer he gave?
Well, to look for life we must look for islands of low entropy.
This is perhaps the most general definition of life:
life is organization, it is information, it is complex structures, that is, low entropy
However, this does not contradict the second principle of thermodynamics,
because you can also create an island of low entropy, provided that
the decrease in entropy that occurs at a certain point,
in a certain moment of time, it is more than balanced
from the increase in entropy of the world around.
So then, if we go back to the example I was doing before
of my bedroom when I was little, I could put myself to fold clothes
order them, stack them well inside the closet but doing this I have to struggle,
it takes me some time, in the end maybe I’m sweaty,
and then I cool down by exchanging my heat with the environment,
and then the air molecules are stirred because it increases the heat,
and this agitation is entropy, it is an increase in disorder,
and this increase in disorder proves that it is greater than the order
that I put in folded clothes.
So nothing can be done, the entropy of the universe by force
it must always increase.
And therefore also the concept of recycling of the things we use
in every day it is certainly fundamental, but it is not the last answer.
In fact, by recycling, however, there is a need to take the substances, to remodel them,
and then you spend work, effort, and in any case the budget of entropy
it is against us, that is, we can not fight against the increase in entropy.
And therefore the true answer to slow down the death of our planet
it is that of, even before recycling, it is to consume little, in fact.
But we have not yet said why entropy increases.
To explain why entropy increases we can return to our example
blue cards all on the left and yellow all on the right.
Now let’s see a movie, here on the left, where each frame is exchanged
order two cards, randomly, you take two random cards and exchange them.
We see that disorder is slowly increasing;
now let’s make the movie go much faster, 32 times faster than before,
and we see that it quickly mixes, and we see that we climb in the right-hand corner
towards a definitive 50% situation.
Here on the right, this graph represents the percentage of yellow cards
that are on the left.
On the left initially everything was blue, so we start from scratch,
and slowly increases increases until rightly at the end
more or less statistically, the law of large numbers, we will have half tesserae
left and half right, 50%.
This final scenario is what we could call, in fact,
the end of the universe, the one I first called thermal death
of the universe, where everything has scattered and from there you can not move anymore.
But if we look carefully, we make a magnifying glass,
we see that in this region, in reality, 50% is only the average,
in reality it is a dynamic process, the order grows and decreases around 50%.
So if this were the trend of entropy not of these small cards,
but of the whole universe, and find us here for example,
at the point of minimum, we would see that entropy would increase both by going to the right
that is, forward in time, in the future, both going left,
that is back in time, in the past.
And so we would say that there is no single meaning, time can flow
in both directions, there is no arrow of time.
Even more, if we lived instead in this instant of indicated time
by the red arrow, that is on the apex, then we would say that not only
there is no arrow of time, because in both directions,
the past and the future, entropy has the same character, but moreover we would say
that the second principle of thermodynamics is wrong because
the future, or the past, however, leads us to a decrease in entropy
not an increase.
So we understand that we are not living in this scenario, we are
rather living in the initial events, in a still young universe,
still ordered: the man is here.
If we look to the future we see an increase in entropy,
if we look at the past we see a decrease in entropy, so there is one
arrow of time, time can only flow in a certain direction,
and so the real question now is to understand the reason for the starting point.
Because at first everything was ordered, like our cards,
all blue on one side, all yellow on the other?
Well, we know that at the beginning of the universe there was the Big Bang.
The Big Bang, all matter was all concentrated in a small region,
as big as the tip of my thumb, so at temperatures
very high and at very high pressures.
Now, how did the universe make all the matter stand out,
energy, in such a small space?
Well, we can think of a suitcase. If we want to put a lot
of things inside our suitcase, we put them in bulk,
there will not be much inside the suitcase, right?
If instead we want to make ourselves many clothes and objects, what should we do?
We’ll have to take some time, calmly fold the clothes well,
use every little space and organize everything well.
Here, for the Big bang is the same thing: to be able to keep everything in one space
so small, the universe had to be very neat primordial instants
And at this point we are asking, what is really the last question
that cosmologists are doing to us right now?
Cosmologists are trying to understand the origin of the universe, because the universe
at the beginning it was so neat. I tell you right away that the answer does not exist,
we do not know yet, it is more than 50 years that we work, what is the real reason
so at first everything was so neat, low entropy.
There are several scenarios, and I’ll give you a list of possible scenarios,
I leave you to choose which one you think is, according to you the most reasonable.
The first scenario is an answer that in reality is not an answer,
the first scenario says: “It’s like that, and that’s it, you have to accept it without asking questions.”
But we understand well that the intelligent human being asks himself these questions, he wants,
he demands an answer, he wants to understand why, if there is something particular,
not by chance, there must have been something underneath.
And indeed someone, according to scenario, thinks this
is the truest and most profound scientific evidence of the existence of God,
or call it what you want, of a superior body that has wanted and could
create the universe so ordered at the beginning
and now we are 14 billion years later to observe what is happening.
Or there are other theories, a theory I like to call it
the tireless monkey theorem, I do not know if you know the tireless monkey,
it’s a monkey that you put in front of a typewriter, a keyboard
and this will accidentally crush the keys without knowing how to write.
If you are tireless, then you have an infinite time ahead of you,
and I would also say an infinite number of sheets available,
here, sooner or later, by chance, will even manage to write the Divine Comedy.
Here, applied to the Big Bang we could say that the universe is so big
and has so much time, the universe is in no hurry, that sooner or later
simply by randomly mixing those fluctuations of cards we have seen
they will arrange by chance in a completely ordered manner, which is the Big Bang.
And from there we have evolved into what we see today;
only that this fluctuation that leads by chance to such a high order
it is indeed unlikely, but truly improbable
so much so that this theory today is practically not accredited by any scientist.
Another scenario is more likely, therefore the fourth
what is called Boltzmann’s brain, which is a bit of a paradox,
and he says, rather than creating the Big Bang that requires an incredible order,
of a very high fluctuation, it is more likely than at this time
in the universe there exists only a sentient mind, a mind that could
be yours right now, and everything else is it?
Nothing, a fiction, generated by our subconscious.
There is only a self-conscious mind, we have already seen this in many films,
for example in the Matrix, where we say that what we see, reality
in fact it is not true but it is a fiction of our subconscious,
a projection of our brain.
Here then are other scenarios, such as the multiverse.
The multiverse is a dirty word that means that there is no universe;
in contrast to the universe there are many universes, parallel universes, therefore
the Big Bang is not really the beginning of anything, but it’s a point inside
of a larger mother universe, perhaps where thermal equilibrium has been achieved,
where there is no arrow of time, and simply within these
parallel universes we create what we know, which is the Big Bang.
There are very many, many other scenarios that could occur,
and could be the real answer, just think that recently
we know that the universe we know in reality is only 5% of everything,
that is, 90% of the matter and energy of the universe is actually made
of dark matter and dark energy, and we still do not know how they work
Here it could be that in the future, studying the dark energy better
and dark matter is possible to give a definitive explanation of why
the universe started from the Big Bang so ordered, and then explain what it is
actually entropy, because entropy always increases
then explain what time is, what is the arrow of time,
and ultimately, what is life. Thank you.
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