S. Han et al. / Physica A 394 (2014) 99–109 101
2.2.2. Metropolis rule
As we mentioned above, the probability that an individual transmits a rumor to others is not constant. A rumor is a kind
of misinformation or disinformation and has always not been verified in the beginning of rumor propagation [14]. It is also
eye-catching so that people can easily believe it and irrationally spread it as soon as they hear it [15]. Therefore, the rumor
transmit probability is usually large in the beginning of rumor propagation. However, as time goes on, a rumor may be
officially refuted or swallowed by other information. People no longer believe it or gradually lose interest in it. The transmit
probability thus decreases. Based on these analyses, in our paper, we assume that the rumor transmit probability for an
individual is large at the beginning and then decreases gradually, and we apply a form of Metropolis rule to formulate this
probability. The Metropolis rule can be expressed as follows.
P =
1 if E(x
new
) < E(x
old
),
exp(−(E(x
new
) − E(x
old
))/T ) if E(x
new
) ≥ E(x
old
),
(2)
where P is the probability of making the transition from state x
old
to state x
new
, E(x) is the energy of state x, and T is the
current temperature of system [16]. The expression of Metropolis rule has two properties. Firstly, if E(x
new
) < E(x
old
), the
probability P is 1. Otherwise, the probability P is a value less than 1. Secondly, the probability P decreases with the decrease
of the temperature T , and in the simulated annealing algorithm, the temperature T is represented as a decreasing func-
tion called the annealing schedule, that guarantees the probability P remains in a large value at the initial stage and then
decreases gradually [17].
In our model, we use E(x) to indicate a rumor’s impact on an individual, and use T to indicate a rumor’s attraction which is
also defined as a decreasing function. Based on the property of the Metropolis rule, the transmit probability is in accordance
with the above assumption that it is a large value in the beginning of rumor propagation, and then decreases as the rumor’s
attraction fades away. The detailed rule design and explanation will be elaborated in Section 3.1.5.
3. Model of rumor propagation
In this section, we analyze rumor propagation from five aspects and propose a novel model to describe this phenomenon
based on the physical theory, called the Energy Model. We first detail the design mechanisms of the proposed model, and
then analyze its advantages compared with the traditional models.
3.1. Energy model
Motivated by the observations mentioned in Section 1, there are five aspects need to be studied in our model: the
characteristics of a rumor, the impact of a rumor on an individual, the accumulation of an individual’s energy, the impact of
a rumor on a network and the rules of rumor transmission.
3.1.1. The characteristics of a rumor
A rumor is often viewed as an unverified account or explanation of events spreading in a population and pertaining to an
object or issue in the public concern [14]. It is usually eye-catching and has not been verified in the beginning of the rumor’s
propagation so that it is very attractive to people when they first hear it [14,15]. In the meantime, most rumors have their
timelines, they will become extinct if they are officially refuted or swallowed by other information. Thus, as time goes on,
a rumor’s attention usually fades away gradually. Consequently, we think the attraction of a rumor to an individual is large
initially and then exhibits a downtrend.
Such characterization of a rumor is similar to annealing in physics. Referring to the simulated annealing schedules in a
simulated annealing algorithm [16], we could define a rumor’s attraction as
T (t) = T
0
/ lg(10 + t), (3)
where T
0
is the initial temperature and t is the time step. T
0
indicates a rumor’s initial attraction, that is, the larger the
value is, the more attractive the rumor is. According to the expression, the attraction of a rumor declines as the time step
goes on. In addition, to depict different rumors, the form of a rumor’s attraction expression could be various as long as it is
monotonously decreasing.
Note that, in our paper, we model the characteristics of a rumor from a microcosmic view. For example, individual A
accepts a rumor at time step t, the attraction of the rumor to individual A at time step t is a large value and it decreases in
the subsequent time steps. Individual A transmits the rumor to individual B at time step t + k, the attraction of the rumor
to individual B at time step t + k is a large value and then it decreases. In other words, the attraction of a rumor to different
people is asynchronous.
3.1.2. The impact of a rumor on an individual
In our model, considering a rumor brings effects to an individual similarly to how a substance absorbs thermal energy,
we introduce a heat energy calculation to analogize and formalize the impact of a rumor on an individual. Specifically, we