Help


from Wikipedia
« »  
To illustrate further, consider the question: " Does our Universe rotate?
" To answer, we might attempt to explain the shape of the Milky Way galaxy using the laws of physics.
( Other observations might be more definitive ( that is, provide larger discrepancies or less measurement uncertainty ), like the anisotropy of the microwave background radiation or Big Bang nucleosynthesis.
) Just how flat the disc of the Milky Way is depends on its rate of rotation in an inertial frame of reference.
If we attribute its apparent rate of rotation entirely to rotation in an inertial frame, a different " flatness " is predicted than if we suppose part of this rotation actually is due to rotation of the Universe and should not be included in the rotation of the galaxy itself.
Based upon the laws of physics, a model is set up in which one parameter is the rate of rotation of the Universe.
If the laws of physics agree more accurately with observations in a model with rotation than without it, we are inclined to select the best-fit value for rotation, subject to all other pertinent experimental observations.
If no value of the rotation parameter is successful and theory is not within observational error, a modification of physical law is considered.
( For example, dark matter is invoked to explain the galactic rotation curve.
) So far, observations show any rotation of the Universe is very slow ( no faster than once every 60 · 10 < sup > 12 </ sup > years ( 10 < sup >− 13 </ sup > rad / yr )), and debate persists over whether there is any rotation.
However, if rotation were found, interpretation of observations in a frame tied to the Universe would have to be corrected for the fictitious forces inherent in such rotation.
Evidently, such an approach adopts the view that " an inertial frame of reference is one where our laws of physics apply " ( or need the least modification ).

1.898 seconds.