this section, we also prove that its throat separates two regions where the curvature tensor goes to zero as we walk away from the throat, at least for certain values of one of the parameters presented in Wyman’s solution. In addition, the detailed analysis reveals that this throat cannot be traversed by humans, although it could be by something else that could last long enough. The results of this paper are summarized in Sec. \[1032014d\].

Traversable Wormholes {#29012014a}
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To describe a spherically symmetric wormhole, it is convenient to write the metric in the form $$ds^2=e^{2\Phi(R)}dt^2-dR^2/\left[1-b(R)/R \right]-R^2d\Omega^2, \label{10082013a}$$ where $b$ is known as the shape function and $\Phi$ as the redshift function [@citeulike:5196630]. The orthonormal basis of reference frame of static observers are given by $$e_{\hat{t}}=e^{-\Phi}\partial_t, \quad e_{\hat{R}}=(1-b/R)^{1/2}\partial_{R}, \quad e_{\hat{\theta}}=R^{-1}\partial_{\theta},\quad e_{\hat{\varphi}}=(r\sin\theta)^{-1}\partial_{\varphi}.\label{10082013b}$$

The functions $\Phi$ and $b$ must satisfy some conditions in order for the spacetime (\[10082013a\]) to have a wormhole that can be traversed by humans. A list with such conditions was given by Morris-Thorne in Ref. [@citeulike:5196630]. However, a more general definition of wormhole can be found in Ref. [@PhysRevD.56.4745]. The latter definition is much wider and include the former as a particular case, hence, we will stick to 