Electromagnetism appears to have the potential to alter the fate of relativistic gravitational implosion. Coulomb forces, for example, can in principle prevent the ultimate collapse of charged matter to a singularity. Also, half a century ago, Melvin noted that magnetic forcelines do not collapse under their own gravity, no matter how strong the latter may be. Instead, magnetic fields seemed capable of stabilising themselves against gravitational self-contraction. Intrigued, Melvin wondered whether magnetism could also support against the realistic collapse of charged matter. Here, we look back into these issues by means of two complementary scenarios. The first reconsiders Melvin’s highly idealised ‘magnetic universe’ and reaches the same conclusion, namely that magnetic fields do not self-gravitate. The second is a realistic collapse scenario, like that of magnetised massive compact stars. Looking for answers to Melvin’s question, we find that magnetic fields do show a generic tendency to support against relativistic gravitational implosion. The magnetic effect in question involves the curvature of the host space, it grows stronger as the collapse progresses and the triggering agent is the field’s tension. In other words, the reason is the elasticity of the field lines and their inherent tendency to react against anything that distorts them from equilibrium. In this case, the distorting agent is the ever increasing curvature of the collapsing host space.

电磁学似乎有可能改变相对论引力内爆的命运。例如，库仑力原则上可以防止带电物质最终坍缩成奇点。此外，半个世纪前，梅尔文指出，磁力线不会在自身引力作用下坍塌，无论后者有多强。取而代之的是，磁场似乎能够稳定自身以抵抗重力的自收缩。出于好奇，梅尔文想知道磁性是否也可以支持带电物质的现实坍缩。在这里，我们通过两个互补的场景回顾这些问题。第一个重新考虑了梅尔文高度理想化的“磁性宇宙”并得出了相同的结论，即磁场不会自引力。第二个是现实的崩溃场景，就像磁化的大质量致密恒星一样。寻找梅尔文问题的答案，我们发现磁场确实显示出一种普遍的趋势来支持相对论引力内爆。所讨论的磁效应涉及宿主空间的曲率，它随着坍缩的进行而变得更强，触发因素是场的张力。换句话说，原因是场线的弹性以及它们对任何使它们偏离平衡的事物产生反应的内在倾向。在这种情况下，扭曲剂是不断增加的坍缩主体空间的曲率。所讨论的磁效应涉及宿主空间的曲率，它随着坍缩的进行而变得更强，触发因素是场的张力。换句话说，原因是场线的弹性以及它们对任何使它们偏离平衡的事物产生反应的内在倾向。在这种情况下，扭曲剂是不断增加的坍缩主体空间的曲率。所讨论的磁效应涉及宿主空间的曲率，它随着坍缩的进行而变得更强，触发因素是场的张力。换句话说，原因是场线的弹性以及它们对任何使它们偏离平衡的事物产生反应的内在倾向。在这种情况下，扭曲剂是不断增加的坍缩主体空间的曲率。