I think I read somewhere that it's impossible to create absolute zero velocity because there is always a reference point? what defines the reference?

I seen the comments here: https://www.quora.com/How-do-relative-velocity-and-absolute-velocity-differ however I still have questions...

for example:

2 ships race to get to the sun first:
Spaceship 1 is rocket propelled, travelling towards the sun at 1,000 mph,
Spaceship 2 is able to phase out of the earths, suns, and galaxies velocity and become completely still, the suns trajectory is in line with ship 2,
The sun is travelling around the galaxy at 550,000 mph

Everything is travelling except ship 2

ship 1 is governed by the predetermined velocities made by the galaxy, sun and earth, which will add/subtract from its own velocity at various stages.

ship 2 is exempt from those forces, yet the sun is the target, or should I say, ship 2 is the suns target? It is still, but the sun is moving towards it at 515,000 mph.

Which is the reference point:
the target (sun)
the object with most speed
the object with least speed
the observer watching?

  • $\begingroup$ If there's a better answer than mine (and there certainly might be) then closing as duplicate would be appropriate. $\endgroup$
    – uhoh
    Sep 5, 2019 at 22:31
  • $\begingroup$ In your example, you're picking the center of the Milky Way galaxy as your reference point to get your 515000 mph speed. $\endgroup$ Sep 6, 2019 at 0:17

1 Answer 1


Which is the reference point?

is not answerable because we are free to choose any point and velocity as a reference to calculate the position and velocity of an object. There isn't any universal reference point.

What defines the reference?

You do!

Some points are much more useful for certain types of calculations, but it's purely a personal choice.

I think I read somewhere that it's impossible to create absolute zero velocity because there is always a reference point?

So this is true, simply because there is no "standard" reference point. It's purely subjective, you always have to state your "with respect to" whenever using the word velocity.

You can read further about frame of reference, and discover that there is no absolute frame of reference. As long as there are no accelerations or rotations, all frames are equally valid. That gets in to the basis of the theory of relativity but that discussion is beyond the scope of the question (or at least my answer).

  • 2
    $\begingroup$ Exactly. The reason it's called relativity is that all motion is relative to any reference point you wish to pick. If there was an absolute reference point, we would call it absolutivity. $\endgroup$
    – DrSheldon
    Sep 6, 2019 at 0:15
  • 1
    $\begingroup$ What if Einstein had known about the CMB? $\endgroup$
    – amI
    Sep 6, 2019 at 6:19
  • 1
    $\begingroup$ @ami: The laws of physics are the same in a frame at rest with respect to the CMB as they are in any other frame: the CMB dipole just happens to be zero in that frame. $\endgroup$
    – user21103
    Sep 6, 2019 at 9:24

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