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Plotting planetary movements through space

  1. Jul 8, 2012 #1
    From a retired thread I (roughly) quote the following:
    "To plot the path that a point on the Earth takes through space, you would need to calculate these movements:
    The Earth relative to the Sun.
    The Sun relative to the Galaxy centre.
    The Galaxy relative to the Local Group.
    The Local Group relative to the Super Cluster.
    The Supercluster relative to the Great Attractor."
    I was wondering - because of all of the various ways, directions and speeds at which any point on earth travels at the same time, would you say that each moment of a person's lifetime is spent at a unique point in space? Is there any literature on that subject? Also... how can an object (e.g, me) travel in so many different directions and speeds simultaneously?
  2. jcsd
  3. Jul 8, 2012 #2


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    One is covering vastly different scales.

    Note that looking at other stars in our galaxy, they appear as points of light. Looking at other galaxies which are tens or hundreds thousands of light years, they appear as fuzzy dots. The closest galaxy to the solar system is Canis Major Dwarf Galaxy at 25,000 light-years, and it is approximately 42,000 light-years from the Galactic Center of the Milky Way.

    The Milky Way is very large - http://heasarc.nasa.gov/docs/cosmic/milkyway_info.html

    "The Galactic Center is the rotational center of the Milky Way galaxy. It is located at a distance of 8.33±0.35 kpc (~27,000±1,000 ly) from the Earth" - http://en.wikipedia.org/wiki/Galactic_Center

    I doubt anyone has calculated the Earth's trajectory through space, since with respect to the universe, it doesn't change very much over our lifetimes.
  4. Jul 8, 2012 #3
    It doesn't. It travels in one direction and one speed, but to calculate it, you have to take into account "so many different directions and speeds simultaneously".
  5. Jul 9, 2012 #4
    OK, thanks. What about my initial question: "would you say that each moment of a person's lifetime is spent at a unique point in space?"
  6. Jul 9, 2012 #5


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    First you should understand that there is no concept of "motion through space" in an absolute sense. Without a physical object to observe, such as a star or the CMB, you have absolutely no way of determining if you are moving or not. Relative to everything else in the universe you are moving in every direction at every possible velocity. But that's ok, because motion is relative to something else, not to space.
  7. Jul 9, 2012 #6


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    I would say that every person has a unique worldline through spacetime that nothing else will ever reproduce.
  8. Jul 9, 2012 #7


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    Relative to the cosmic microwave background, and relative to the center of our galaxy, the solar system is moving with >200km/s through space. This is larger than our velocity within the solar system (the largest component here is the earth's orbit with ~30km/s). In these systems, we can never visit the same point twice.
  9. Jul 9, 2012 #8
    Excellent! This is fascinating stuff. I'm not a physicist - actually, physics was the only course in high school in which I ever failed a final exam (what can I say? It was the 70s). I'm not college educated, either, so some of the stuff you all are pointing me to won't ever make complete sense to me, but I enjoy the challenge of reading it anyway. The world line concept is pretty much what I've been imagining, I think. And it ties in with my thoughts that each moment of a life of an object (or person) takes place in unique spacetime. Given that our primary vectors are the rotation and revolution of the earth, I would guess that my world line would be a slightly distorted helix moving away from the center of our galaxy (with each stretched "circumference" representing a year) and with that helix's line formed by a much tighter helix (each circumference representing a day), the first nine months of which would perfectly overlap my mother's world line. I imagine my world line as looking like a kind of a spring within a spring. Am I interpreting this correctly?
  10. Jul 9, 2012 #9


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    I'd say you got the general idea Rakky. It's not quite as you are imagining it, but close enough I'd say.
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