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Thread: Question about space time and dark matter.

  1. #1
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    Question about space time and dark matter.

    When we calculate the mass of the sun and planets, does the Newton's laws of gravitation and Einstein's equations of space-time take into account dark matter, I guess not since Newton didn't know about dark stuff, so does that mean there's isn't any dark matter in the solar system?
    Or it is included in the calculations then, dark matter is 27% and normal matter is 5% is the sun, earth and us mostly dark matter?

  2. #2
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    You can work in our solar system using Newton. Smallish errors like Mercury’s orbit are explained by Einstein but we postulate dark matter by observing distant galaxies which seem to have not enough mass to hold their outer stars. Then galaxies seem to be accelerating away from us and each other, requiring dark energy to model it. If dark matter exists, as it seems to do from observing things millions of light years away, then we can assume it is around us too but we cannot detect it on small scales. There are billions of stars in a galaxy and billions of galaxies. So the scale effect is really really big!
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

  3. #3
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    Quote Originally Posted by Damien Huxley View Post
    When we calculate the mass of the sun and planets, does the Newton's laws of gravitation and Einstein's equations of space-time take into account dark matter, I guess not since Newton didn't know about dark stuff, so does that mean there's isn't any dark matter in the solar system?
    Or it is included in the calculations then, dark matter is 27% and normal matter is 5% is the sun, earth and us mostly dark matter?
    There appears to be significantly more dark matter than normal matter in our galaxy as a whole (as you note, the ratio is about 5 to 1). But because dark matter does not interact appreciably except through gravity, it does not clump together the way normal matter does. So it's spread pretty thinly throughout space, while the Sun and planets are large local concentrations of normal matter, and dominate the dynamics of the solar system. If you work out the expected mass, you find that the total amount of dark matter in the solar system should be about the mass of one smallish asteroid (and spread out, not concentrated in one location), so not enough to measurably affect planetary orbits.
    Conserve energy. Commute with the Hamiltonian.

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