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What is the speed of the Earth?

  1. May 5, 2012 #1

    I would like to know if it is possible to measure the current speed of the earth relative to the point of big bang?
  2. jcsd
  3. May 5, 2012 #2


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    There was NO "point" of the big bang. It happened everywhere, so no, that question has no answer.

    The speed of the earth HAS been measured against the CMB, but I don't recall what the speed is..
  4. May 5, 2012 #3


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    Solar system speed relative to the CMB is about 370 km/s
  5. May 5, 2012 #4


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    Phinds and Chronos gave you good answers already. I'll repeat with more detail in case you want a longer answer.

    Expansion is a uniform pattern of increasing distances. It is not "away from" any point in space that we can point to and it has no unique direction. So it is not like ordinary motion which has some direction and where you are going somewhere.

    So your question is not about expansion. It is about our small random motion relative to the absolute reference defined by the CMB.
    Things have small random motions relative to the universal rest.
    In the case of the solar system we are traveling roughly 370 km/s in the direction that is marked in the sky by the constellation Leo.

    What is the CMB? It's a soup of ancient light that dates from around 380,000 years after start of expansion. That's when the cloud of hot gas cooled enough to allow light to run free and the glow of that gas was released to travel essentially forever. The ancient light comes equally from all directions (or very nearly, within 1/1000 of one percent). And it is the same thermal mix of wavelengths in all directions. It's uniformity reflects the uniformity of the original cloud of hot gas which is it the glow from.

    That hot gas which was uniformly everywhere is our stationary reference for what we mean by being "at rest". So being at rest means being at rest with respect to the soup of ancient light.

    In the case of the solar system we know we are moving in the direction of Leo because there is a Doppler hotspot in the ancient light in that direction. the frequency of the light is about 1/10 of one percent higher in that direction. Slightly more, but roughly that much higher. The light is said to be that much "hotter" in the direction ahead of us, and that much colder at the point directly behind us. A Doppler effect. The light itself is uniform and evenly distributed thru space, as far as we can tell, only our own motion thru the soup of light shortens the wavelengths coming from directly ahead and lengthens the wavelengths coming from directly behind.

    Things have these small random motions relative to universe-rest because after the cloud cooled enough it began to condense into lumps, by its own gravity. And as the lumps formed randomly they began to FALL TOWARDS each other, and sail past, and adopt orbits around each other, and so on. A lumpy wispy structure developed.
    So pretty much all the objects we see have some random individual motion, typically a few hundred km/second. In no particular preferred direction overall. Only what is locally dictated by local gravity, orbits etc.
    Last edited: May 5, 2012
  6. May 6, 2012 #5

    It seems that you are asking how fast the earth is moving relative to The Location where the Big Bang took place. Correct? In that case the answere would be no for the reasons explained by the previous poster. It requires we pinpoint exactly where the BB took place and it seems from our subjective perspective that it took place everywhere.
    Last edited: May 6, 2012
  7. May 6, 2012 #6


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    Nonsense. There is nothing subjective about it. Read some cosmology.
  8. May 6, 2012 #7
    It took place 'everywhere' according to any observer anywhere in the universe. There is
    nothing anymore 'subjective' about our perspective than any other.....there are no special 'frames of reference' in relativity. That would be a place to read to learn more.
  9. May 8, 2012 #8
    Everything that you just said I said I didn't say. Please refrain from constantly attributing things to me that I did not say. Ask me instead of jumping to conclusions. For example, where did I express the idiotic idea that our perspecvtive of the universe is more subjective than any other? Can you show me? Of course not. English is your native tongue correct? Then all other essential things being OK, my clear statements should NOT be posing this problem.
    Last edited: May 8, 2012
  10. May 8, 2012 #9


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    I absolutely agree that your statement was clear. You said unambiguously, as I bolded above, that our perspective is subject, which is incorrect. Read your own posts before you attack others for correcting them.
  11. May 8, 2012 #10
    1. I am not attacking you.

    2. Your response isn't a correction. It is a crass misrepresentation.

    3. A perusal of what the meaning of the term "subjectivity" and how it clearly relates to special relativity would prove beneficial.

    4. Insisting that I mean what you understand I said instead of what I clearly said is illogical and not conducive to discussion.

    If a person says that from his perceptual perspective things are subjective, it merely means exactly that. That he perceives things subjectively. Claiming that the person meant that his perspective is drastically different from all others is a conclusion which requires a premise that is missing in that statement.

    However, saying that all perspectives are equal is definitely unscientrific and illogical and requires a faulty assumption. The assumption that all perceiving creatures in the universe must be neurolgically hardwired identically. Obviously that isn't the case. How do we know? Well, because right here on earth we have a vast variety of neural hardwiring that causes each creature to see his own universe subjectively.

    Need I go into fine details?
    Last edited: May 8, 2012
  12. May 8, 2012 #11


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    Yes, you do. It would help if you defined "subjective" for us and explained why you chose to use it there instead of nothing. But perhaps flipping it over would allow us to cut to the chase: what would an objective view show?
  13. May 12, 2012 #12
    You're right that we view things subjectively, but the Big Bang did not occur in existing space, rather it caused space to expand, so it is only subjective to our current understanding of physics. Unless the Big Bang model changes, then all present knowledge points to the Big Bang happening literally everywhere from a non-subjective view.

    edit: I feel like this argument is going to start turning into an existential one
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