In theory, it is possible for matter to travel at extremely high speeds in space or a vacuum. However, achieving speeds of 1 million km/h (or 621,371 mph) would require overcoming numerous practical challenges and technological limitations.
The primary obstacle to achieving such high speeds is the enormous amount of energy required to accelerate an object to those velocities. As an object approaches the speed of light (299,792 km/s or 186,282 miles/s), its relativistic mass increases, and it becomes progressively more difficult to accelerate further. The energy required to propel an object to relativistic speeds becomes impractical with our current propulsion technologies.
Additionally, there are other significant factors to consider. Friction and air resistance, which are negligible in a vacuum, are absent. However, objects moving at such high speeds would encounter resistance from interstellar gas and dust, which could have detrimental effects. The energy released from collisions with even tiny particles could be immense.
Furthermore, ensuring the safety of any occupants or payload at such speeds would be extremely challenging. The human body, for example, is not designed to withstand the extreme accelerations and decelerations involved in traveling at such velocities. Developing advanced propulsion systems and protective measures would be necessary.
While it is theoretically possible to imagine objects traveling at such speeds in space, the practical realities and technological constraints make achieving them with our current understanding and capabilities highly improbable. Nonetheless, scientists and engineers continue to explore novel propulsion concepts and technologies that could push the boundaries of space travel in the future.