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the same for a fixed observer as for an observer who has a uniform motion of |
translation relative to him, so that we have not, nor can we possibly have, any |
mmeans of discerning whether or not we are carried along in such a motion.” |
When this idea descended upon the world, it caused a great stir among |
philosophers, particularly the “cocktail-party philosophers,” who say, “Oh, it is |
very simple: Einstein's theory says all is relativel” In fact, a surprisingly large |
number oŸ philosophers, not only those found at cocktail parties (but rather than |
embarrass them, we shall Just call them “cocktail-party philosophers”), will say, |
“That all is relative is a consequence of Einstein, and it has profound infuences |
on our ideas.” In addition, they say “lt has been demonstrated in physics that |
phenomena depend upon your frame of reference.” We hear that a great deal, |
but ï is dificult to ñnd out what it means. Probably the frames of reference |
that were originally referred to were the coordinate systems which we use in the |
analysis of the theory of relativity. So the fact that “things depend upon your |
frame of reference” is supposed to have had a profound efect on modern thought. |
One might well wonder why, because, after all, that things depend upon one”s |
point oŸ view is so simple an idea that it certainly cannot have been necessary to |
go to all the trouble of the physical relativity theory in order to discover it. That |
what one sees depends upon his tame of reference is certainly known to anybody |
who walks around, because he sees an approaching pedestrian first from the |
tront and then from the back; there is nothing deeper in most of the philosophy |
--- Trang 304 --- |
which is said to have come from the theory of relativity than the remark that “A |
person looks diferent from the front than from the back.” 'Phe old story about |
the elephant that several blind men describe in different ways is another example, |
perhaps, of the theory of relativity from the philosopher”s point of view. |
But certainly there must be deeper things in the theory of relativity than |
Just this simple remark that “Á person looks điferent rom the front than from |
the back.” Of course relativity is deeper than this, because +0e cøn rmmauke deftnife |
prediclions tuïth dt. It certainly would be rather remarkable if we could predict |
the behavior of nature from such a simple observation alone. |
'There is another school of philosophers who feel very uncomfortable about the |
theory of relativity, which asserts that we cannot determine our absolute velocity |
without looking at something outside, and who would say, “lt is obvious that |
one cannot measure his velocity without looking outside. It is self-evident that it |
1s mmeaningless to talk about the velocity of a thing without looking outside; the |
physieists are rather stupid for having thought otherwise, but ït has Just dawned on |
them that this is the case. If only we philosophers had realized what the problems |
were that the physicists had, we could have decided immediately by brainwork |
that it is impossible to tell how fast one is moving without looking outside, and |
we could have made an enormous contribution ©o physics.” 'These philosophers |
are always with us, struggling in the periphery $o try to tell us something, but |
they never really understand the subtleties and depths of the problem. |
Our inability to detect absolute motion is a result of ezperiment‡ and not a |
result of plain thought, as we can easily illustrate. In the fñrst place, Newton |
believed that it was true that one could not $ell how fast he is going If he 1s |
moving with uniform velocity in a straight line. In fact, Newton frst stated |
the principle of relativity, and one quotation made in the last chapter was a |
statement of Newtons. Why then did the philosophers not make all this fuss |
about “all is relative,” or whatever, in Newton's time? Because it was not until |
Maxwells theory of electrodynamics was developed that there were physical laws |
that suggested that one couldd measure his velocity without looking outside; soon |
1ÿ was found ezperimenfallu that one could noi. |
Now, 7s it absolutely, defñnitely, philosophically øœ=ecessøar that one should |
not be able $o tell how fast he is moving without looking outside? One of the |
consequences of relativity was the development of a philosophy which said, “You |
can only define what you can measurel Sinece it is self-evident that one cannot |
measure a velocity without seeing what he is measuring it relative to, therefore |
1t 1s clear that there is no rmeønzng to absolute velocity. 'he physicists should |
--- Trang 305 --- |
have realized that they can talk only about what they can measure.” But tha£ |
¡s the tphole problem: whether or not one can define absolute velocity is the |
same as the problem of whether or not one can defect ïn an ezpertữment, without |
looking outside, whether he is moving. In other words, whether or not a thing |
1s measurable is not something to be decided ø pz7or¿ by thought alone, but |
something that can be decided only by experiment. Given the fact that the |
velocity of light is 186,000 mi/sec, one will ñnd few philosophers who will calmly |
state that it is selEevident that if light goes 186,000 mi/sec inside a car, and |
the car is going 100,000 mi/sec, that the light also goes 186,000 mi/sec past an |
observer on the ground. That is a shocking fact to them; the very ones who claïim |
1E is obvious ñnd, when you give them a specifc fact, that it is not obvious. |
Finally, there is even a philosophy which says that one cannot detect ønw |
motion except by looking outside. It is simply not true in physics. True, one |
cannot perceive a wn⁄form motion in a strøigh# line, but 1f the whole room were |
rotating we would certainly know it, for everybody would be thrown to the wall— |
there would be all kinds of “centrifugal” efects. That the earth is turning on its |
axis can be determined without looking at the stars, by means of the so-called |
Foucault pendulum, for example. 'Therefore it is not true that “all is relative”; it |
is only wniform 0elocitu that cannot be detected without looking outside. Uniform |
rotation about a fxed axis cơn be. When this is told to a philosopher, he is very |
upset that he did not really understand it, because to him 1% seems Impossible |
that one should be able to determine rotation about an axis without looking |
outside. If the philosopher is good enough, after some time he may come back |
and say, “I understand. We really do not have such a thing as absolute rotation; |
we are really rotating relatiue to the stars, you see. And so some infuence exerted |
by the stars on the object must cause the centrifugal force.” |
Now, for all we know, that is true; we have no way, at the present time, of |
telling whether there would have been centrifugal force if there were no stars and |
nebulae around. We have not been able to do the experiment of removing all the |
nebulae and then measuring our rotation, so we simply do not know. We must |
admit that the philosopher may be right. He comes back, therefore, in delight and |
says, “lt is absolutely necessary that the world ultimately turn out to be this way: |
absolute rotation means nothing; it is only rela#zue to the nebulae.” Then we say to |
him, “ Nou, my friend, is it or is it not obvious that uniform velocity in a straight |
line, relate to the nebulae should produce no efects inside a car?” Now that the |
motion is no longer absolute, but is a motion relatibe to the nebulae, it becomes |
a mysterious question, and a question that can be answered only by experiment. |
--- Trang 306 --- |
'What, then, are the philosophiec inÑuences of the theory of relativity? If we |
limit ourselves to infuences in the sense of t0ha‡ kứnd oƒ neu tdeas ơnd suggestions |
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