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Universal movement

  1. May 30, 2005 #1
    First of all this is my first post on this forum, or any other forum of this type. I am extremely interested in cosmology, physics etc. on a personal knowledge level. I usually just read stuff on the web, but Im glad to have found a place where people actually actively talk about this.

    I wanted to ask a few questions I just recently came up with while reading random posts. How fast are we actually moving? I guess relative to the earth we aren't moving at all, but we are orbiting around the sun. How fast do we move on our orbit? Is our sun orbiting around something larger? if so do we orbit faster in one direction than the other? is that thing(if it exists) orbiting around something larger(is it possible that our entire galaxy is orbiting around something more massive and that thing is orbiting around something more massive etc)? Is there any way to actually stop moving completely? is anything NOT orbiting around something larger? if the entire universe was only composed of 2 atoms at opposite ends of the universe, would their gravitational pull effect eachother? if not replace one atom with a SMBH, then?

    I guess i'll see if anyone will answer those before I go on to other stuff.
  2. jcsd
  3. May 30, 2005 #2


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    The earth moves around the sun at about 30 kilometers per second and sun around the galaxy at about 220 kilometers per second. Relative to the cosmic microwave background, we move about 600 kilometers per second.

    The sun is moving around the center of the galaxy and the galaxy is moving with respect to the center of mass of the local group of galaxies, which is itself moving with respect to the Virgo supercluster of galaxies. The sun's motion could be called an "orbit", since it goes approximately in a circle. The motion of the galaxies isn't really an orbit in the traditional sense, but it is being caused by the gravity of the other galaxies.

    Motion is all relative, so if we stop moving completely from one point of view, we'll still be moving relative to another.

    Everything in the universe that we can see is being effected by gravity (if it weren't, we couldn't see it). The reason is that gravitational effects travel at the speed of light, so anything we can see is, at least, being perturbed by our gravity. There could be things that we can't see, but then we couldn't say anything about them.

    If those atoms were within each other's particle horizon, then yes they would. Same with the SMBH.
  4. May 30, 2005 #3


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    Welcome to these Forums Enkiadu!! Those are good questions, keep thinking about it and keep them coming!

    As SpaceTiger has said motion is all relative, however there is one frame of reference that might be seen to be more fundamental than the rest. The Cosmic Microwave Background has come from a time when the entire universe was filled with a hot gas. It was mainly hydrogen that was in the form of a plasma, the electrons were not bound to their protons and the universe was 'foggy'. When the universe cooled to about 3,000oK the electrons combined with these protons to form hydrogen gas and the universe became transparent. That 'surface of last scattering' is spread out all over the entire sky and we receive the radiation from it, the CMB, which is extremely isotropic and now is equivalent to radiation coming from a black body at just less than 3oK. However, we are moving relative to that surface, so it looks hotter in one direction than in the opposite.

    In fact we are moving at 370+/-10 kms./sec towards the constellations Leo and Crater. Note that this velocity is 0.1%c and quite large, in fact it is difficult to explain! (Another question for you: "Are we being pulled towards a 'Large Attractor'?")

    I hope this helps.

    Last edited: May 30, 2005
  5. May 30, 2005 #4


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    Yes, as far as I understand this value of the speed is derived directly from the measured Doppler shift of the CMB photons (see e.g. this). Also, I found several sources in internet claiming that the Milky Way is moving at 500 to 650 km/s wrt to the CMB in the direction of the constellation of Hydra (e.g. http://zebu.uoregon.edu/~imamura/209/mar31/cmbr.html [Broken]). To me this seams not to make sense due to the following reasoning.

    Assume that Leo and Hydra are actually the same direction in sky (they are very near in the sky). Thus, the speed of the earth wrt to the CMB, should be equal to the speed of the Milky Way wrt to the CMB + the speed of the earth inside the Milky Way. Lets say the first is 600 km/s. The second is about 220 km/s in the direction of the constellation of Lyra (the solar apex; e.g. http://www.cartage.org.lb/en/themes/Sciences/Astronomy/Thestars/stellarmotion/MotionoftheSun/MotionoftheSun.htm [Broken]). However, to obtain about 370 km/s for the measured speed in the CMB (the earth's speed) the direction of earth inside the Milky Way should be in the opposite direction to Leo, so that 370 km/s would be more or less the result of 600 - 220. But Lyra is not in the opposite direction than Leo.

    What is wrong (or missing)?
    Last edited by a moderator: May 2, 2017
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