In Star Trek (2009), when Kirk and Hikaru Sulu are falling from the drill, at the last moment Ensign Chekov locks on them and is able to transport them inside the ship.

By the time they were transported, they have gained a lot of momentum due to free fall, but when they are inside the ship they just experienced a mild thud.

  • Where did that much amount of momentum go?
  • Does momentum conservation not apply to Teleportation in the Star Trek Universe?

As far as i know from the game 'Portal', momentum was being conserved there. link

  • A better contrary example to Star Trek transporters than the portal gun would be teleportation in Larry Niven's known space, which generally conserves both kinetic and potential energy but more advanced larger devices can absorb energy to make longer distance travel possible. Commented Sep 18, 2017 at 1:36
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    "Momentum, a function of mass and velocity, is conserved between portals. In layman's terms, speedy thing goes in, speedy thing comes out." - GLaDOS Commented Sep 18, 2017 at 10:30

7 Answers 7


Does momentum conservation not apply to transporter operation in the Star Trek Universe? From what we have been shown, apparently not.

Given the transporters already violate so many of our current laws of physics including:

  • mass-to-energy conversion and back again,
  • quantum data storage and information manipulation,
  • not to mention manipulation of subspace to move the matter stream from one location to another,
  • the manipulation of an aspect of matter as simple as momentum from a falling object should be relatively easy to reduce a percentage of that in transport, possibly bleeding it off into subspace at the completion of the transport and reconstruction cycle.

Okay, it's not so simple but let's reverse engineer it and see if we can make it make sense...

What we know

The Law of Conservation of Momentum does indicate that within a closed system, momentum is conserved.

  • Two Starfleet officers are plunging to the deaths on the planet below.
  • As such, the closed system is composed of the officers, the planet and their momentum gained in freefall.
  • The conservation takes place when the potential energy of their fall is converted to kinetic energy upon landing, creating a nice cloud of dust, some heat from impact, and the squashing of all of their bones and organs to a nice jelly.

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Did anyone else think this was a bad idea?


  • Add a transporter beam which adds energy to this closed system, converts matter into energy and dematerializes the matter into a subspace confinement beam and then stores that stream of matter as a signal in a pattern buffer and biofilter.


  • Not at all. So any momentum the matter has after it is reconstituted should be able to be manipulated as just another variable in the transporter resequencing, meaning it can be modified or even removed if necessary.

  • I mention this because we have seen the transporter grab fighter pilots from the seats of their moving planes coming right at the Enterprise. (Tomorrow is Yesterday - TOS, Episode 1x21)

  • We have also seen the crew of the Galileo 7 being transported back to the Enterprise as the shuttlecraft they were on was re-entering the planet's atmosphere. (The Galileo Seven - TOS, Episode 1x13)

  • For that matter, anytime anyone is transported to any other location, there is almost always a movement differential that must be accounted for. Ships in orbit transporting anyone to the ground have to account for the rotational energy of the planet. I doubt seriously orbiting ships are forced to match course and speed to compensate for planetary rotation...

  • If momentum was conserved, they would splat against the wall of the transporter room upon reintegration, so it must be possible to treat momentum as just another variable to be manipulated mid-transport.

As to the Portal Gun

The level of technological sophistication between the transporter and the portal gun is the same level of difference between a bonfire and a tokamak reactor.

  • The portal gun opened a dimensional rift between two locations able to be bridged almost like a stable wormhole between two points.

  • Since the wormhole generated is still just an open doorway from one location to the next, all the gravitational, physical and energy requirements are unchanged from one side of the portal to the other, things falling between the two locations for example maintain their momentum and trajectory.

  • This means all normal physical rules apply since the only variation in the physics is the doorway between the two locations in space-time. A fall from a great height through one portal in the floor, while another is placed on a nearby wall will transform the energy of the fall into a corresponding distance value depending on the speed of exit from the wall portal.

  • There is no conversion of matter or energy, nor is any form of computational interface involved. Anything moving between the two boundaries is unchanged in any way. These two technologies are vastly different in their physics and their interaction with physical matter.

The Portal Gun simply allows matter to be moved from one location to another without any change in the state of that matter. The transporter is able to affect the state, position, relationship, momentum and energy condition of the transported material reconstituting the matter from an intermediate energy state.

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    Counter-example: The gun Ezri used in one episode of DS9 when trying to find a killer
    – Izkata
    Commented Aug 11, 2013 at 15:08
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    Don't believe mass to energy / energy to mass conversion violates the current laws of physics. Excellent answer though and, as you point out, many areas for discussion around 'transport'.
    – Stan
    Commented Aug 11, 2013 at 19:53
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    Also, the biofilters show the ability to alter the pattern as they alter it filtering out known contagions.
    – ewanm89
    Commented Aug 11, 2013 at 20:31
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    Keep in mind, most people dramatically misunderstand what those conservation laws mean. They don't mean "mass/energy/momentum is not allowed to change". They mean that the sum total across the entire system must match before/after. All the transporter has to do is convert the momentum into something else (like heat energy, which happens in nature all the time) to avoid violating those laws.
    – KutuluMike
    Commented Aug 12, 2013 at 20:46
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    My thought would be that the process of "locking on" to a transportation target involves setting the transporter to use a reference frame in which the target doesn't have any (or much) momentum.
    – David Z
    Commented Aug 16, 2013 at 1:24

The Aperture Science Gun and Star Trek teleportation have fundamentally different mechanics.

The portals created by the Aperture Science Gun allow objects to physically move from one location to another without transversing the space between these locations.

The teleportation technology used by Star Trek involves scanning you, destroying your body, and using the resultant energy to email the scan to a 3D flesh printer, where it prints you out again based on the scan.

Any attempt to figure out the effects of one of these technologies based on the other will be largely futile.


Definitely not. If it did, then even people standing still on the surface of a planet being transported to the ship would be hurled at high speed in some direction if the ship transporting them up was not moving perfectly in the direction of the planet's orbit. This would clearly be highly impractical, so it must have been designed to account for this.

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    Besides, transport is not instantaneous, which is why it requires a "transporter lock" first and foremost before transport can begin. This means the transporter beam is always locked to the position of the object. Unlike a static portal that you must move through, the transporter beam constantly has the transport target as its frame of reference, so the momentum of the target would be zero relative to the transporter beam. Commented Aug 12, 2013 at 3:50
  • To add some numbers to this good answer... The International Space Station orbits the Earth at about 17,000mph. That's how fast someone would splat against the transporter room wall if momentum was conserved during transport.
    – Ghedipunk
    Commented Oct 10, 2018 at 20:11

I think that it's simpler than that-- the transporter effectively scans each atom of your body, deletes the original, then recreates it on the transporter pad. Hence Bones's comment about preferring a shuttle in one of the later movies.

As such, there's no need to conserve momentum- you're creating a new copy, effectively from scratch.

So why did they fall when they hit the pad? Because the computer didn't reorient them to be standing- they were left in their original horizontal state, but they had to be above the pad to not intersect with it.

So when they hit the pad, it wasn't the result of momentum being conserved, but rather that they were "rebuilt" 2 feet above the pad, then fell and hit it.

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    So... are they carbon copies like in The Prestigue? Their bodies die everytime, but thanks to some high-level math, they get reborn? Creepy.
    – Jersey
    Commented Aug 12, 2013 at 14:45
  • The actual matter is transformed and transported. It's a bit sentimental though. It's not possible to replicate living things, not even on a transporter pad.
    – Lodewijk
    Commented Sep 1, 2013 at 23:57
  • If this were true, then every starship and space station comes with a high-throughput cloning facility. Just run multiple copies while the pattern is in the transporter buffer and you now have an army of Datas.
    – Ellesedil
    Commented Sep 18, 2017 at 23:33
  • @Jersey: I always thought The Prestige as well as Think Like a Dinosaur were very good explorations of transporter technology and the broader question of whether uploading one's mind to an artificial body would not be what most people had in mind when they stepped into a transporter or paid for immortality. If someone said, "You successfully transported; You don't mind if we disintegrate you since a perfect copy exists? Do you mind?" I sure would mind...
    – releseabe
    Commented Sep 26, 2023 at 22:19


Transporters are not portals, they dematerialize, move, then rematerialize people. Lots of moving involved. Not inherently safe stuff. Relative motion is negated otherwise many more problems would be had.


It seems to depend on circumstance (and frankly, the needs of the story). The DS9 episode "Field of Fire" involves an assassin and his use of a rifle equipped with a micro transporter. The idea is that the shooter can fire the weapon from a discrete location, the bullet is de-materialized as it exits the muzzle and re-materialized where it can "come out of nowhere" to strike its target. This would require the transporter to conserve momentum. However, I think the bullet could be re-materialized onto a path not parallel to that from which it was fired, so momentum isn't actually conserved, but "adjusted" as needed.

Anyway, as already covered in different answers, transporters seem to routinely confer and remove momentum such as when beaming between orbiting ship and planet surface.


I posit that transporters do capture all the energy of each atom of the object being transported--including momentum, but that the Heisenberg compensators can be set to remove (or retain) momentum of the whole object. Mass/energy must be conserved, but so too must momentum. Since the "closed system" includes energy added by the transporters themselves, it stands to reason that the transporters can remove momentum from a moving object that has been transported.

Atoms (and their constituent electrons) have kinetic energy, which means they have tiny tiny momentum. EM waves also have momentum. Wave/particle duality and other "complimentary variables" (such as the three axis of spin) must be accurately recreated upon rematerialization. That's probably the main function of the Heisenberg compensators. (E.g., if none of your atoms had motion, you'd be frozen!)

Assuming that the macro-level momentum of the object is "carried" by the atoms comprising that object, it stands to reason that the transporter can negate or "compensate" for the motion of that object relative to the transporter pad. As @Thaddeus Howze and @Eric B pointed out their answers, a person standing on Earth is already moving 67,000 mph around the sun. So, unless your starship is moving in the exact same speed and direction... "uh, clean up in the transporter room."

The TR-116 gun, as @Itzkata brilliantly points out, simply preserves momentum.

  • There are some pretty bold statements here. Can you offer any actual evidence that this is the case?
    – Valorum
    Commented Oct 10, 2018 at 20:06
  • Hmm. I'm less concerned about how the transporters work in real life (top tip, they don't) and more concerned that you've not addressed how you know the things you say that you know. What are you basing your answer on?
    – Valorum
    Commented Oct 10, 2018 at 20:23
  • I don't really care about the (fake) science. I'm more concerned about how you know the things you know. Did you see them in the show or read them in one of the in-universe factbooks?
    – Valorum
    Commented Oct 10, 2018 at 21:22
  • I am just reasoning from the TR-116. I also thought about inertial dampeners, which attenuate the momentum of people and objects within a ship.
    – Xplodotron
    Commented Oct 10, 2018 at 22:28

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