﻿648 
  Prof. 
  S. 
  B. 
  McLaren 
  on 
  a 
  

  

  experience 
  and 
  must 
  be 
  admitted 
  by 
  the 
  purest 
  empiricism. 
  

   This 
  I 
  hope 
  to 
  argue 
  at 
  greater 
  length 
  elsewhere, 
  here 
  I 
  must 
  

   be 
  content 
  to 
  assert 
  dogmatically. 
  The 
  universe 
  consists 
  of 
  

   u 
  instants 
  " 
  or 
  of 
  that 
  which 
  has 
  position 
  in 
  time 
  and 
  space. 
  

   With 
  Minkowski, 
  therefore, 
  we 
  represent 
  all 
  reality 
  as 
  in- 
  

   cluded 
  in 
  a 
  four-dimensional 
  manifold, 
  which 
  is 
  time 
  and 
  

   space 
  and 
  is 
  not 
  therefore 
  in 
  time 
  or 
  space. 
  But 
  neither 
  

   Minkowski 
  nor 
  any 
  sane 
  man 
  wishes 
  to 
  deny 
  the 
  psychological 
  

   distinction 
  between 
  space 
  and 
  time. 
  When 
  time 
  is 
  used 
  in 
  

   that 
  sense 
  it 
  is 
  evidently 
  nonsense 
  to 
  resolve 
  it 
  into 
  something- 
  

   else. 
  What 
  we 
  do 
  deny 
  is 
  the 
  view 
  that 
  time 
  and 
  space 
  are 
  

   distinct 
  physical 
  objects. 
  The 
  only 
  physical 
  reality 
  is 
  the 
  

   four 
  dimensional 
  manifold 
  of 
  space-time, 
  where 
  all 
  the 
  instants 
  

   we 
  become 
  aware 
  of 
  in 
  succession 
  exist 
  together. 
  

  

  Startling 
  as 
  Minkowski's 
  procedure 
  may 
  appear, 
  there 
  

   seems 
  no 
  doubt 
  that 
  it 
  is 
  dictated 
  by 
  a 
  very 
  common-sense 
  

   instinct. 
  The 
  least 
  innovating 
  of 
  physicists 
  will 
  be 
  loath 
  to 
  

   accept 
  the 
  view 
  that 
  time 
  is 
  a 
  physical 
  object 
  as 
  much 
  as 
  

   space 
  and 
  different 
  from 
  it. 
  And 
  Minkowski 
  satisfies 
  this 
  

   instinctive 
  feeling 
  b}^ 
  resolving 
  time 
  into 
  a 
  fourth 
  dimension 
  

   plus 
  what 
  he 
  can 
  only 
  perhaps 
  describe 
  as 
  a 
  psyschological 
  

   illusion, 
  at 
  all 
  events 
  not 
  a 
  real 
  object 
  for 
  the 
  physicist. 
  

  

  It 
  is 
  at 
  this 
  point 
  we 
  diverge 
  from 
  him. 
  He 
  too 
  uses 
  the 
  

   symbol 
  t 
  in 
  (23), 
  but 
  defines 
  it 
  in 
  terms 
  of 
  the 
  spatial 
  co- 
  

   ordinates. 
  With 
  us 
  it 
  is 
  an 
  independent 
  variable 
  described 
  

   as 
  the 
  " 
  absolute 
  time 
  " 
  of 
  the 
  unchanging 
  universe. 
  But 
  

   here 
  I 
  use 
  the 
  word 
  time 
  to 
  denote 
  a 
  logical 
  order 
  in 
  

   thought, 
  t 
  is 
  the 
  symbol 
  of 
  a 
  continuous 
  point 
  transformation. 
  

   If 
  any 
  instant 
  a 
  2 
  is 
  substituted 
  for 
  a^ 
  in 
  this 
  transformation, 
  

   then 
  there 
  is 
  a 
  third 
  instant 
  a 
  s 
  which 
  by 
  the 
  same 
  process 
  

   replaces 
  a 
  2 
  , 
  and 
  a 
  fourth 
  instant 
  a 
  4 
  succeeding 
  to 
  a 
  3 
  . 
  Thus 
  

   any 
  transformation 
  generates 
  a 
  continuous 
  succession 
  of 
  

   instants, 
  and 
  this 
  may 
  be 
  described 
  as 
  the 
  motion 
  of 
  a 
  

   material 
  point 
  a. 
  As 
  with 
  Hegel 
  matter 
  becomes 
  objectified 
  

   thought, 
  time 
  incarnates 
  a 
  logical 
  process. 
  

  

  Return 
  again 
  to 
  time 
  and 
  space 
  as 
  we 
  experience 
  them, 
  

   remembering 
  that 
  the 
  ordinary 
  time 
  variable 
  t 
  is 
  nothing 
  but 
  

   the 
  fourth 
  of 
  the 
  coordinates 
  defining 
  the 
  position 
  of 
  any 
  

   point 
  in 
  a 
  certain 
  four-dimensional 
  space. 
  How 
  far 
  then 
  

   can 
  it 
  be 
  said 
  with 
  significance 
  that 
  any 
  instant 
  is 
  " 
  before 
  '~ 
  

   or 
  " 
  after 
  " 
  any 
  other 
  instant. 
  

  

  As 
  Robb 
  has 
  insisted 
  (' 
  Time 
  and 
  Space/ 
  Cambridge, 
  

   1912), 
  the 
  only 
  meaning 
  to 
  be 
  attached 
  to 
  the 
  statement 
  

   " 
  the 
  instant 
  P 
  preceded 
  Q 
  " 
  depends 
  upon 
  a 
  theory 
  of 
  

   causation. 
  It 
  implies 
  that 
  a 
  cause 
  at 
  P 
  can 
  produce 
  an 
  

   effect 
  at 
  Q. 
  Now, 
  no 
  cause 
  at 
  P 
  can 
  influence 
  any 
  effect 
  

  

  