Datasets:
vnpthack
/
vnpt_data

Dataset card Data Studio Files
xet
 Community
1
text
stringlengths
0
6.73k
straightforward manner. There is an analog of this to computing machines and
computfing elements, in that they also have a lot of lines, and they have some
kind of element, analogous, perhaps, to the synapse, or connection oŸ one nerve
to another. 'Phis is a very interesting subject which we have not the time to
discuss further——the relationship between thinking and computing machines. lt
must be appreciated, of course, that this subject will tell us very little about the
real complexities of ordinary human behavior. All human beings are so diferent.
It will be a long time before we get there. We must start much further back. If
we could even fñgure out how a đoøg works, we would have gone pretty far. Dogs
are easier to understand, but nobody yet knows how dogs work.
3-7 How did it get that way?
In order for physics to be useful to other selences in a #heoretical way, other
than in the invention of instruments, the science in question must supply to the
--- Trang 83 ---
physicist a description of the object in a physicist's language. They can say “why
does a frog jump?,” and the physicist cannot answer. T they tell hm what a frog
1s, that there are so many molecules, there is a nerve here, etc., that is diferent.
Tf they will tell us, more or less, what the earth or the stars are like, then we
can figure it out. In order for physical theory to be of any use, we must know
where the atoms are located. In order to understand the chemistry, we must
know exactly what atoms are present, for otherwise we cannot analyze it. That
1s but one limitation, of course.
'There is another kinđ of problem in the sister seiences which does not exist in
physics; we might call it, for lack of a better term, the historical question. How
dịd it get that way? IÝ we understand all about biology, we will want to know how
all the things which are on the earth got there. There is the theory of evolution,
an important part of biology. In geology, we not only want to know how the
mmountains are forming, but how the entire earth was formed in the beginning,
the origin of the solar system, etc. 'That, of course, leads us to want to know
what kind of matter there was in the world. How did the stars evolve? What
were 0he initial conditions? “That is the problem of astronomical history. A great
deal has been found out about the formation of stars, the formation of elements
from which we were made, and even a little about the origin of the universe.
There is no historical question being studied in physics at the present time.
W© do not have a question, “Here are the laws of physics, how did they get that
way?” We do not imagine, at the moment, that the laws of physics are somehow
changing with time, that they were diferent in the past than they are a% present.
Of course they may be, and the moment we ñnd they øre, the historical question
of physics will be wrapped up with the rest of the history of the universe, and then
the physicist will be talking about the same problems as astronomers, geologists,
and biologists.
Finally, there is a physical problem that is commmon to many fields, that is very
old, and that has not been solved. It is not the problem of nding new fundamental
particles, but something left over from a long time ago—over a hundred years.
Nobody in physics has really been able to analyze it mathematically satisfactorily
in spite of its importance to the sister sciences. Ït is the analysis of c#rculafing or
turbulent ffưids. TÝ we watch the evolution of a star, there comes a point where we
can deduce that it is goïing to start convection, and thereafter we can no longer
deduce what should happen. AÁ few million years later the star explodes, but we
cannot fñgure out the reason. We cannot analyze the weather. We do not know
the patterns of motions that there should be inside the earth. The simplest form
--- Trang 84 ---
of the problem is to take a pipe that is very long and push water through i% at
high speed. We ask: to push a given amount of water through that pipe, how
much pressure is needed? No one can analyze it from first principles and the
properties of water. If the water ows very slowly, or if we use a thick goo like
honey, then we can do it nicely. You will ñnd that in your textbook. What we
really cannot do is deal with actual, wet water running through a pipe. That is
the central problem which we ought to solve some day, and we have not.
A poet once said, “The whole universe is in a glass of wine” We will probably
never know in what sense he meant that, for poets do not write to be understood.
But it is true that if we look at a glass of wine closely enough we see the
entire universe. 'There are the things of physics: the twisting liquid which
evaporates depending on the wind and weather, the refections in the glass, and
our imagination adds the atoms. 'Phe glass is a distillation of the earth”s rocks,
and in its composition we see the secrets of the universe's age, and the evolution
Of stars. What strange array of chemicals are in the wine? How did they come
to be? 'Phere are the ferments, the enzymes, the substrates, and the products.
There in wine is found the great generalization: all life is fermentation. Nobody
can discover the chemistry of wine without discovering, as did Louis Pasteur, the
cause of much disease. How vivid is the claret, pressing its existence into the
consciousness that watches it! TỶ our small minds, for some convenience, divide
this glass of wine, this universe, into parts—physics, biology, geology, astronomy,
psychology, and so on—remember that nature does not know itl So let us put
it all back together, not forgetting ultimately what it is for. Let it give us one
more fñinal pleasure: drink it and forget it all
--- Trang 85 ---
(©ortsor-'terffore œŸ F rt©r'JgJ/
4-1 What is energy?
In this chapter, we begin our more detailed study of the diferent aspects of
physics, having fñnished our description of things in general. To ilustrate the
ideas and the kind of reasoning that might be used in theoretical physics, we shall
now examine one of the most basic laws of physics, the conservation of energy.
There is a fact, or if you wish, a ia, governing all natural phenomena that
are known to date. There is no known exception to this law—it is exact so far as
we know. 'Phe law is called the conseruation oƒ energ. It states that there is
a certain quantity, which we call energy, that does not change In the manifold
changes which nature undergoes. hat is a most abstract idea, because 1W is a
mathematical principle; 1% says that there is a numerical quantity which does
not change when something happens. Ït is not a description of a mechanism, or
anything concrete; it is just a strange fact that we can calculate some number and
when we fnish watching nature go through her tricks and calculate the number
again, it is the same. (Something like the bishop on a red square, and after a
number of moves—details unknown——it is still on some red square. ÏIt is a law of
this nature.) Since it is an abstract idea, we shall illustrate the meaning of it by
an analogy.
TImagine a child, perhaps “Dennis the Menace,” who has blocks which are
absolutely indestructible, and cannot be divided into pieces. Each is the same
as the other. Let us suppose that he has 28 blocks. His mother puts him with
his 28 blocks into a room at the beginning of the day. At the end of the day,