30  An  Epoch-Making  Discovery.        { ^J^^^l' 
philosophers  who  are  equipped  for  this  recondite  branch  of  human 
study. 
In  the  words  of  one  of  the  recent  interpreters  of  Einstein  to  the 
multitude  this  thought  is  expressed  as  follows :  "The  main 
philosophic  achievement  of  the  special  theory  of  relativity  is  prob- 
ably the  recognition  that  the  description  of  the  event,  which  is 
admittedly  only  perfect,  if  both  the  space  and  time  coordinates  are 
specified,  will  vary  according  to  the  relative  motion  of  the  observer ; 
that  it  is  impossible  to  say,  for  instance,  whether  the  interval  sep- 
arating two  events  is  so  many  centimeters  and  so  many  seconds,  but 
that  this  interval  may  be  split  up  into  length  and  time  in  different 
ways,  which  depend  upon  the  observer  who  is  describing  it."  * 
The  "general  theory  of  relativity"  concerns  itself  with  the 
broader  fields  of  human  speculation  and  endeavor.  This  is  much 
more  daring  and  less  easily  comprehended  without  a  knowledge  of 
higher  mathematics  and  there  are  those  among  the  physicists  and 
mathematicians  who  characterize  it  as  "Metaphysical  Mathe- 
matics" and  "Intellectual  Moonshine." 
The  fundamental  question,  "are  space  and  time  real?"  cannot 
be  answered  simply  and  categorically.  Space  and  time  for  human 
comprehension  and  appreciation  are  dependent  upon  the  existence 
of  things  which  lie  closer  to  our  senses. 
If  there  were  no  material  bodies  we  could  have  no  conception 
of  "space"  and  if  no  events  or  changes  took  place  "time"  would  be 
devoid  of  meaning.  The  world-old  question  as  to  what  constitutes 
reality  finds  the  answer  of  the  modern  physicist  eminently  satis- 
fying.  "Whatever  can  be  measured  is  real." 
Are  space  and  time  real?  Both  being  measurable  we  unhesi- 
tatingly reply  in  the  affirmative.  Yet  if  we  perform  the  imaginary 
experiment  of  the  celebrated  French  mathematician  Poincare  and 
"suppose  that  all  material  bodies  should  increase  over  night  one 
hundred  fold,"  we  should  be  unable  to  perceive  the  change,  for  all 
of  our  measurement  standards  and  units  would  have  changed  like- 
wise. We  should  still  call  an  inch  by  that  name  although  it  had 
increased  to  more  than  eight  feet.  How  can  we  argue  convincingly 
about  the  reality  of  space,  therefore,  except  as  a  relative  concept. 
So  in  the  same  way  our  time  determinations  become  as  closely 
associated  with  physical  bodies  as  our  ideas  of  space,  and  quantita- 
*  "Space  and  Time  in  Contemporary  Physics,"  by  Moritz  Schlick. 
