The origin of cosmic rays and their main sources are discussed, focusing on whether these particles primarily come from external sources outside our galaxy. Initially, the isotropy of cosmic rays observed on Earth suggests an external origin. However, some authors argue that this isotropy is a result of a magnetic field in interstellar space. The critical magnetic field strength required to deflect particles significantly is calculated, and it is found to be about $10^{18}$ gauss, which is much higher than the average interstellar field of about $10^{16}$ gauss. Despite this, some argue that the magnetic moment of the Sun might be exceptionally small, or that the connection between angular momentum and magnetic moment could lead to a higher interstellar magnetic field. However, the effects of a magnetic field as high as $10^{16}$ gauss are still negligible. The key inequality, $H^{2} \ll 4 \pi W$, where $H$ is the magnetic field strength and $W$ is the energy density of the cosmic rays, shows that the momentum density of the particle beam is much larger than the average momentum density of the electromagnetic field. This conclusion is supported by the conservation of momentum. Therefore, the main source of cosmic rays must be external to the galaxy, implying that the source must provide an energy density of $\sim 10^{-13}$ ergs per cm$^{3}$ in interstellar space.The origin of cosmic rays and their main sources are discussed, focusing on whether these particles primarily come from external sources outside our galaxy. Initially, the isotropy of cosmic rays observed on Earth suggests an external origin. However, some authors argue that this isotropy is a result of a magnetic field in interstellar space. The critical magnetic field strength required to deflect particles significantly is calculated, and it is found to be about $10^{18}$ gauss, which is much higher than the average interstellar field of about $10^{16}$ gauss. Despite this, some argue that the magnetic moment of the Sun might be exceptionally small, or that the connection between angular momentum and magnetic moment could lead to a higher interstellar magnetic field. However, the effects of a magnetic field as high as $10^{16}$ gauss are still negligible. The key inequality, $H^{2} \ll 4 \pi W$, where $H$ is the magnetic field strength and $W$ is the energy density of the cosmic rays, shows that the momentum density of the particle beam is much larger than the average momentum density of the electromagnetic field. This conclusion is supported by the conservation of momentum. Therefore, the main source of cosmic rays must be external to the galaxy, implying that the source must provide an energy density of $\sim 10^{-13}$ ergs per cm$^{3}$ in interstellar space.