36 Introduction 



brew ones. Few philosophers have been able to shake it off completely. 

 Scholasticism it should be noted is not at all a denial of the value of 

 observation and experiment but a tendency to exaggerate deductive 

 reasoning on a given experimental basis. The experimental basis of 

 mediaeval schoolmen was pitifully, ridiculously, small, but the main 

 point is this, that no matter how large that basis be its fertility and 

 eflScacy are limited. Deductive reasoning, even of the purest kind as 

 in mathematical physics, needs periodic checking by experimental 

 means, or else it may degenerate into fallacies or nonsense. 



Many of the discussions of modern astrophysics seem to be based on 

 an insufficient experimental basis; at any rate, their theoretical construc- 

 tions are so gigantic that the experimental basis seems infinitesimal. We 

 need more than a red-shift "^ of spectral lines to agree to the prodigious 

 theory of the expanding universe, and more than a beautiful system of 

 equations to accept as a reality canon Georges Lemaitre's ingenious 

 idea of a cosmic egg. Everybody who is not an astrophysicist would 

 require additional evidence, not one set of observations interpreted in 

 agreement with the theory of relativity, but convergent sets of different 

 kinds of observation. The old astronomical theories were not as adven- 

 turous; they could be tested in many ways. The gradual development 

 of celestial mechanics and the elaboration of appropriate tables made 

 continual tests possible. Every observatory was a testing ground and 

 every eclipse or transit, a new challenge. Do the astrophysicists not 

 need cross-examinations? One would think that they could not rest 

 until their grandiose ideas had been checked and counterchecked in 

 every possible manner, yet they proceed cheerfully from one audacious 

 structure to another which is more audacious still and so on. Happily, 

 they restrict their extrapolations to their own field and do not try to legis- 

 late for the microscopic human world. 



Metaphysicians are less restrained and tend to offer their conclusions 

 in the most general and peremptory form. In his discussion of Plato's 

 Republic the illustrious Kant remarked, "Nothing can be more mischie- 

 vous and more unworthy a philosopher than the vulgar appeal to what 

 is called adverse experience, which possibly might never have existed, 

 if at the proper time institutions had been framed according to those 



^ "Red-shift" is short for shift of spectral lines toward the red end of the 

 spectrum. According to the Doppler principle such a shift toward the longer wave 

 length side represents a moving away of the radiating object from the observer. 

 But is the red-shift really a velocity-shift, or does it bear another interpretation? 

 For discussion of these puzzling matters see Arthur Eddington: The expanding 

 universe (Cambridge University, 1933); Edwin Hubble: The realm of the nebulae 

 (Yale Press, New Haven 1936); The observational approach to cosmology (Claren- 

 don Press, Oxford 1937). Harlow Shapley: Galaxies (Philadelphia 1943). Both 

 Hubble and Shapley are cautious and uneasy; Sir Arthur is more reckless. My 

 criticism does not apply to them but only to astronomers who speak too glibly 

 of the expanding universe. See also the excellent paper of Percy W. Bridgman: 

 On the nature and the limitations of cosmical inquiries (Scientific Monthly 37, 

 385-97, 1933). 



