theoretical physics as a subject of science 

dir 

theoretical physics sometimes is regarded as a subject of purely thinking. 
however this is not really true. nevertheless it is based on experiments, 
like any other scientific subject. 

science is a method to understand nature, the key point of this method is 
that experiment is the only way to verify if the understanding is correct 
or not. any understanding by definition involves certain logic (sometimes 
the logic is precise, that is mathematics). so it is very correct to say 

科学=逻辑＋实证. 

take quantum mechanics as an example. there is no any conflict between above 
statement and the establishment of quantum mechnics. without relevant 
experiments, no one could even imagine out the physics of quantum mechanics, 
no matter how free his/her idea is. new logic and concepts have been cooperated 
in the new theory, of course. but the above statement never insists on that the 
logic should be the one in the old theory. by the way, the physicists who 
proposed quantum mechanics were pretty aware that their new theory has to 
recover the classical physics in the area where the old physics had been 
verified experimentally. actually, this was their main working point. 

in fact, einstein established his general relativity in a similarily scientific 
way. the special relativity and newton's gravity physics are in conflict with 
each other. motivated by this problem, he went to the general relativity with 
an idea of the curved spacetime. what i mean here is that he didn't come to the 
general relativity from nothing, or from his free willing. 

it might be misleading to emphazise on idea freely invention. even scientist 
great like einstein, who failed in his effort to find an unified theory of 
gravitional interaction and electromagnetic interaction. such an unification 
is just his willing. 

it is well-known that based on the same experimental facts, scientists may 
propose different theories with possibly very different logic. there is no 
mechanical relations between experimental results and theories. scientists 
have enough freedom in this sense. again, it is new experiments which exclude 
wrong theories, pick out the (temperally) correct ones and may motivate new 
theories. 

finally i would say that physics is always driven by experimental facts, by 
real problem. it would be dangerous to think that progresses are by people's 
willing. the current elementary particle theories (for example, supersymmetry) 
are focus on the gauge hierarchy problem, the newest approach in gravity 
physics tries to solve the conflict between the general relativity and quantum 
mechanics (superstring). and the most recent studies in theoretical physics 
are based on the challenge imposed by new measurements for the cosmological 
constant. 


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