Archive for 2013

No kind of space ship can making banking turns in space. When an airplane makes a banking turn, it does so by deflecting off a cushion of air. The air redirects the plane’s momentum in a new direction. In space, there is essentially no air, so space ships cannot make banking turns. In order for a space ship to turn, it has to fire a rocket sideways to reorient itself, than fire its main engines to begin traveling in this new direction. But because there is no air to redirect its momentum, a space ship still has momentum in the original direction. The result is a graceful, slow, arching turn. In order to get rid of its original momentum, a space ship would have to fire rockets in the opposite direction that it was originally traveling. The bottom line is that banking turns are not possible in space. Dogfights between enemy craft are only possible in the atmosphere – not in space. Hollywood tends to distort this principle of physics in order to make space battles more exciting, as well as to appeal to viewers who are accustomed to watching aerial dogfights that became the stuff of legends during World War II.

Space ships turn by reorienting and then firing its engines in the desired direction.

A space ship turns by reorienting and then firing its engines in the desired direction as there is no air to bank off of. Public Domain Image, source: Christopher S. Baird.

Airplanes turn by banking off the air.

An airplane turns by banking off the air. The air simply redirects the momentum of the plane. For this reason, a plane can turn with its engines off. Public Domain Image, source: Christopher S. Baird.

How do space ships make artificial gravity?

Despite the fact that outer space is brimming with gravity, the lack of solid ground in space means that objects without thrust are in a continual state of free fall, and free fall feels just like zero gravity. To stop all objects in a space ship from floating around due to their free fall motion, you would need artifical gravity. In the conventional sense, artificial gravity connotes a system aboard a ship that makes all objects fall to the floor and be held there as if they were on earth’s surface, but still allows people to walk around freely. In this sense, straps my hold a weightless astronaut to the floor, but they would not quality as artificial gravity because they would not allow the astronaut to walk around. Similarly, magnetic belts would not quality as artificial gravity because objects that the astronaut releases would still float around.

The only physically possible way to create a force as strong as earth’s gravity that acts on all objects in a ship is through acceleration. Acceleration always creates inertial forces. Inertial forces such as the centrifugal force or Coriolis force are very real in the accelerating reference frame. They are not imaginary or fictional, but are simply non-fundamental in that they arise from the movement of the frame itself. If the acceleration is held constant and at the right value, the inertial force will behave identically to earth’s gravity and will, in fact, be equivalent to Earth’s gravity. This fact is actually a basic tenet of General Relativity. There are two kinds of accelerations, rotational and linear. A ship could achieve artificial gravity by rotating about its axis. To be practical, the radius of rotation would have to be quite large. Additionally, a ship could create artificial gravity by constantly accelerating forwards. Shows that portray artificial gravity without rotation or constant forward acceleration are simply non-physical. Incorrect artificial gravity is often used in movies because of budgeting concerns. It is very expensive to make actors sitting on earth look like space voyagers floating in a space ship, or alternatively, to construct a space ship that is constantly rotating.


The inertial force of a fast acceleration is inevitable.

Acceleration always creates inertial forces. When you slam on your car’s gas pedal, the rapid acceleration throws you back into your seat. The force you feel pushing you back is called an “inertial force”. Every time a frame of reference is accelerated, objects in that frame of reference experience an inertial force. The greater the acceleration, the greater the force. Fighter jets that accelerate at high rates contain pilots that have to be specially trained to handle the high inertial forces (known to them as “g”-force or pulling “g”s). If the acceleration is small enough, the inertial force my not be noticeable. But all practical vehicles have high enough accelerations for their inertial forces to be felt. The fact that acceleration always causes inertial forces is universal and fundamental. There is no way to use technology to cancel out inertial forces. In terms of entertainment, this means that every time a space ship in a show speeds up, the actors should be visibility pushed back into their chairs, or be knocked over if standing. Similarly, every time the ship slows down, the actors should lurch forwards. This particular principle of physics is easy to act out, cheap to implement, and adds more drama, not less. Shows that get this principle wrong do so simply out of incompetence.

Voyager I took 36 years to leave our solar system. Sp

Voyager I took 36 years to leave our solar system. Real space travel is very time consuming because nothing can go faster than light and everything is so far apart. Public Domain Image, source: NASA.

Nothing can travel faster than light. This is not a question of technology, but of fundamental physics. Special relativity tells us that nothing can travel faster than the speed of light in vacuum (671 million mph or 300 million meters per second). This limitation applies to baseballs, protons, space ships, and cell phone signals. No alien species, no matter how advanced, can travel faster than light. Universal physics forbids it. As objects approach the speed of light, they get harder and harder to accelerate further. It would take an infinite amount of energy to exactly reach the speed of light, let alone pass it. This fact is proven everyday in particle accelerators such as the Large Hadron Collider (LHC) built by CERN. The LHC currently accelerates very small bunches of protons to 99.999997% the speed of light (planning to reach 99.9999991% the speed of light by 2015). The LHC uses 800,000,000 kilowatt-hours of energy a year to get tiny bunches of protons up to these speeds. That’s as much energy as released by 30 plutonium-core nuclear bombs. All that energy is used to get a handful of hydrogen nuclei close to the speed of light. Movies and television shows that depict space ships traveling faster than light are portraying pure fiction. While nothing can travel faster than light, this limitation does not necessarily rule out rapid travel to the stars. Physics has not yet invalidated the concept of wormholes, which are shortcuts to other parts of the universe by curving spacetime. Shows that depict faster-than-light speeds are physically unrealistic, while those that accomplish interstellar travel through wormholes could be more realistic. Fiction writers and producers purposely break this law of physics to enable their heroes to travel to alien planets without taking thousands of years to do it. Sometimes authors work around this speed limitation by putting planets and stars unrealistically close, but doing so does not make the science more credible.


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