The last line of the Conclusion chapter (which was actually
written first) reads: "For, with evident rhyme but
illusive reason, the Universe is what it is!", but what does this mean? It
means that the world around us clearly exhibits a pattern susceptible to
mathematical description, but seeking a rationale — a *how*, or *why*
— is quite different, and likely a futile subjective aspiration.

When Albert Einstein developed his theory of *special relativity*,
he showed that space and time could be treated in a mathematically orthogonal
fashion, and that this resulted in the laws of physics — crucially including
Maxwell's equations of *electromagnetism* — being the same for all
inertial observers. Hermann Minkowski reformulated his equations using a
coordinate system involving an imaginary time (following an idea previously
considered by Henri Poincaré) and showed that the equations of *relativity*
and *electromagnetism* both took on a much simpler and symmetrical form in
this *space-time continuum*.

The *block universe* is a view of reality in which
space and time are equally real and unchanging. The idea can be traced back to
the Greek philosopher Parmenides of Elas, from around the early fifth century
BCE. *Special relativity*, and particularly in its Minkowski space-time
form, is often considered a model for a *block universe*, and yet Einstein
used it to describe the kinematics of objects and observers in relative motion.
This is a problem because there can be no motion, nor change of any kind,
without a flowing time, and yet by treating time as a space-like dimension then
he had already removed that notion. It is easy to draw a world-line on a
space-time diagram and claim that it represents a series of linked events
charting a particle's progress through space-time, but there is no inherent succession,
no progression, nor any specific direction.

In 1926, Einstein met renowned French philosopher Henri-Louis
Bergson, and the pair began a heated debate over the nature of time. Bergson
was a great believer in the importance of experience, and criticised *relativity*
for it having distanced itself from experience and for it leading to
counter-intuitive consequences. *Relativity* made sound sense,
mathematically, but Einstein didn't try to explain the connection between
experience and his mathematics.

In 1927, English philosopher John M. E. McTaggart introduced
the concepts of A-series and B-series times, which roughly correspond,
respectively, to the subjective and objective times defined in this book.
McTaggart's terms are not used in order to avoid the accidental implication of
propositions that might be conflicting. McTaggart argued that A-series time was
contradictory, and yet necessary for any description of change. He tried to
define a C-series time that retained some connection to the sequencing that we
experience, rather than adopting the less palatable B-series, but the notion of
some ordered sequencing of discrete events or mental states was ill-founded. Not
only is there no true simultaneity in *special relativity*, but there is
no cosmic equivalent of *'now'*.

The more perdurant approach taken in the book is essentially
to posit that we exist in a true *block universe*, and that this explains the
appropriacy of mathematical description. In other words, the fact that all
change is relative means that the smooth and finite differences we observe
across time can be modelled by mathematics. But mathematics cannot fully capture
any aspect of our experience, including the passage of time, dynamical change,
causality, consciousness, etc. It is then necessary to deconstruct these aspects
in order to see how they can emerge within the *block universe*.

A notable casualty of the premise is *quantum theory*:
the prevailing probabilistic interpretation is invalid in a *block universe*,
and must be substituted with a more deterministic interpretation. The one put
forward actually gives a clearer picture of why *wave-function collapse*
(the so-called 'measurement problem') is deemed to be at odds with a *wave-function*
description, and demonstrates that the problem goes away in a *block universe*.

The book concludes that all of experience can be reconciled with
the *block universe*, in addition to *quantum mechanics* and the *second
law of thermodynamics*, but it has repercussions for the scope of
mathematics and the pursuit of knowledge in general.

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