Physics is often perceived as a science of complex and precise calculations, making possible any sorts of technical “miracles” in the midst of which we live. However, the basis of the discipline does not lie in these refinements, be they enabled by fancy mathematics or, today, by computer calculations, but in a small number of laws that should be rigorously applied; it also lies in the physicists' ability to distinguish the secondary from the essential and therefore to perform justified approximations. Strangely, some people often talk about “conspiracy theories” in order to denigrate some alternative interpretations of known events, even when the very existence of a conspiracy makes no doubt: this is for instance the case with 9/11 terrorist attacks in the USA, for which only the perpetrators, the motive and the technical means are questioned. As a correct argument cannot rely on improper vocabulary, we shall not impede ourselves with such demonizing and shall only show which “conspiracy theories” are compatible with physics laws and which ones are not, since even the official version belongs to them. A striking and well documented feature of 9/11 attacks in New York City is persisting fires in the World Trade Center ruins: the last one was extinguished only 100 days after the event. This simple fact is intriguing and needs explanation. Airborne or satellite infrared thermography measurements have been made, just after the event as well as weeks and months later, which allow to estimate surface temperature and corresponding areas, and the cooling characteristic time of the place. Cooling of a hot body in a colder environment occurs thanks to conduction, convection and radiation. In open air, thermal dissipative power due to free convection is easily obtained if one knows the heat transfer coefficient h, the temperature difference \Delta T and the area S of the corresponding surface. Taking into account only free convection, and performing only orders of magnitude calculations because of a lack of accurate data, it is possible to get a lower estimate of the total heat released at Ground Zero. For fundamental reasons (electrons energy levels in atoms, nucleons mass) any kind of chemical energy production involves a minimum amount of mass. Nuclear energy, involving the same mass but using nuclear bonding energy roughly 10^{6} larger, releases consequently about 10^{6} more energy per unit mass, or, for technical applications such as nuclear explosives which include a lot of matter not releasing any nuclear energy, still 10^{4} times more. Combining the minimum total heat estimate with the physical limits of chemical energy carriers, we can rule out any chemical energy as the source of heat released at Ground Zero and therefore consider nuclear energy explosives as the only available solution. For obvious reasons, only deep underground nuclear explosions could remain relatively unnoticed as such; therefore only the opportunistic use of a built-in nuclear demolition feature, designed at the same time as the World Trade Center itself, is a viable explanation. Some literature search about pacific use of nuclear explosives as envisaged in the 1960s (especially some books like The Constructive Uses of Nuclear Explosives by Teller et al., 1968) shows that such an idea, if surprising today, was not unthinkable in the context of the time. It comes out that any nuclear explosion in a bedrock produces a shock wave that turns this material into tiny pieces (the smaller ones being the closer to the “zero point”), then creates a plasma-filled cavity with extremely high pressures (\sim10^{14}\,\text{Pa}) and temperatures (\sim10^{7}\,\text{K}) which, after cooling, ends most of the time filled with rock debris falling from a “collapse chimney” located above the cavity. Depending on the energy released and on the depth of burial of the explosive, it is therefore possible to generate effects at ground level, first when the shock wave travels through the media (including on materials not usually considered as brittle, such as steel, because of the exceptionally steep shape of the wavefront), later when the cavity “roof” collapses and creates a rubble chimney, and finally during heat diffusion which lasts for months. It turns out that the physics community, having been too easily intimidated by arguments being not real ones, or being not a matter of physics (“likelihood” of a hypothesis...), has for too long, and with few exceptions, tacitly admitted interpretations of extremely important events that are merely pseudo-science, if not extravagant science-fiction. Would physicists have worked with academic rigour and starting from the most well established foundations of their science, such as the first and second laws of thermodynamics, and would have they added to a purely scientific work some retrospective critical look on their own enthusiasm - partly irrational - during the post-World War II era, they could have shown that not only the explanation of the destruction of 3 high-rise buildings in New York City on September 11, 2001 by underground nuclear explosions, given more than a decade ago by someone pretending to be a former soviet officer and nuclear weapons expert (Dimitri Khalezov), was not a crazy one, but that it was actually, with a few corrections, the only possible one.