约翰·惠勒 （John Wheeler， 1911－2008）
It from bit. Otherwise put, every "it" — every particle, every ﬁeld of force, even the space-
time continuum itself — derives its function, its meaning, its very existence entirely —
even if in some contexts indirectly — from the apparatus-elicited answers to yes-or-no
questions, binary choices, bits.
"It from bit" symbolizes the idea that every item of the physical world has at bottom — a
very deep bottom, in most instances — an immaterial source and explanation; that
which we call reality arises in the last analysis from the posing of yes-or-no questions
and the registering of equipment-evoked responses; in short, that all things physical are
information-theoretic in origin and that this is a participatory universe.
1990年惠勒提出信息是物理学基⽯石的观点—“它来⾃自⽐比特”（it from bit）
! H. Weyl, Philosophy of Mathematics and Natural Science, !
Princeton University Press, Princeton, 1949. !
2003年：Joseph Gerver 构造了⼀一个⽜牛顿⼒力学⾥里的 4 体!
tions are sym-
stems in which
om one pair to
jump from one
k ∆k < ∞.
uns S1, S2 with
circles sun S2
sits the second
um and energy.
rch for special solutions of the 3 body problem.⼲⼴广义相对论⾥里的时空奇点—如⿊黑洞—已被⼲⼴广泛接受。
在⼀一类被称为 Malament-Hogarth 时空中，利⽤用相对论的时空奇性来实现外尔的想
d are examined on pp. 245–247 of . The Malament–Hogarth event is characterized
ation rO(τ−) = r−. Clearly, τ− is ﬁnite since γO reaches the inner horizon under the
−g(˙γO(τ), ˙γO(τ)) dτ =
dτ = τ− < ∞.
e of the physical computer is very simple. We may assume the initial data are
(0) = q (the observer γO and the computer γP start from the same point) and take
M to be a geodesic corresponding to a stable circular orbit in the equatorial plane
black hole. This implies sgn ˙rP (0) = 0, sgn ˙ϑP (0) = 0, QP = 0 and EP > 0, E2
P < 1.
culate the radius of the circular orbit of γP by Lemma 4.14.9 while the corresponding
mentum LP can be determined via Corollary 4.14.8 of  (the concrete values are
ing for us in this moment). Trivially, ∥γP ∥ = ∞.
angement shows that, since both γP and γO move along geodesics, their acceleration
y zero, i.e. remains bounded throughout their existence. A three-dimensional picture
hine is shown on Figure 1.
Figure 1. The three-dimensional picture of the device G = (γP , γO).
presenting a four-dimensional space-time diagram of G = (γP , γO) as well. Such
re called Penrose diagrams and show the whole development of the system.
G. Etesi, I. N´emeti: Black Holes and the Church–Turing Thesis
Future Null Infinity
Figure 2. The Penrose diagram picture of the device G = (γP , γO).
We can see that in the case of Kerr space-time the Malament–Hogarth event appear
when he touches the inner horizon of the Kerr black hole (in a ﬁnite proper time, of cou
it is well known  the inner horizon of the Kerr black hole is a Cauchy horizon f
observers showing that this space-time fails to be globally hyperbolic. Later we will
this is a general property of Malament–Hogarth space-times. Although after crossing t
horizon the predictability of the fate of γO breaks down, it seems he can avoid the en