Does dark matter contribute to my body mass?

  • #1
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No I'm not a particularly big person with a weight issue.
Somebody asked me this question and I don't know the answer, but somebody here will.

OK, it's now accepted that dark matter is everywhere in the Universe, it tends to clump with regular matter because all matter is subject to gravity, but there is a lot more of it than the normal matter.
So, some proportion of my body mass will be due to dark matter.
If the dark matter wasn't there, would I weigh less according my bathroom scales?
 

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  • #2
phinds
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Dark matter does not really clump except on cosmological scales. Any dark matter passing through your body just keeps right on going as though you weren't there. Also, there is so little dark matter in our solar system that the amount in the volume of your body would be unmeasurable with current technology.
 
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  • #3
Janus
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To give you an idea of how little dark matter there is in the solar system in total, it is about the same as that of a small asteroid. This may seem strange considering there is more dark matter in the universe than "normal: matter, but this has to do with distribution.

Planets are dense. The solar system taken as a whole is much less dense even though the total mass of the solar system is more than any given planet. The solar system as a whole is denser than a given volume of our local stellar neighborhood, even thought the combined mass of all the stars in the local neighborhood is more than that of the solar system. The density of the galactic disk is greater than that of the dark matter halo, but since the DM halo fills a much, much larger volume, the total mass of the dark matter halo is greater than that of the galactic disk.

It is the electromagnetic interaction of normal matter along with gravity that causes it to clump up like it does, and it is the lack of this electromagnetic interaction that keeps DM from clumping as densely.
 
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  • #4
JMz
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Planets are dense. The solar system taken as a whole is much less dense even though the total mass of the solar system is more than any given planet. The solar system as a whole is denser than a given volume of our local stellar neighborhood, even thought the combined mass of all the stars in the local neighborhood is more than that of the solar system. The density of the galactic disk is greater than that of the dark matter halo, but since the DM halo fills a much, much larger volume, the total mass of the dark matter halo is greater than that of the galactic disk.
Indeed, in that whole hierarchy, normal matter apparently has greater density than DM at every level, until the last one, the (outer) halo.
 
  • #5
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Even if there was a tonne of dark matter around, it wouldn't affect a measurement of your mass. It is just floating straight through you. If I push you, I will not feel the dark matter contributing to your inertia since it will just stay where it is while you move, since it is essentially not coupled to you at all. Likewise, it will not push down on the scales, since it goes straight through your body and straight through the scales. There is also no bouyant force or any such thing generated by it, since you are not displacing any dark matter. The only way it will change the measurement is by there being loads of dark matter collected in the Earth, which makes the effective gravitational mass of the Earth bigger. Then gravity on Earth will be a little bigger and you will register a larger weight on the scales as a result. Of course we would also have calibrated our scales to take this into account, so the marking on your scales would just have "10 kg" written in a slightly different position.
 
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