Thread: Dark Matter question

If there is a lot of dark matter in the universe, why doesn't it (apparently) affect us here? How did NASA manage to "thread the needle" with the voyager space probes without knowing about dark matter and it gravitational effects??

Do not forget that dark matter is hypothetical. There are many possible explanations for its seeming lack of effects:

1. You don't know that it has no effects. If you are immersed in dark matter, whatever effects it has are just a normal part of your existence. Also, do not confuse lack of awareness with lack of effects. If you were immersed in water at 37 °C, then you would not feel it. However, you would drown in it.
2. Dark matter is believed to range throughout the Universe. A galactic-size clump of it is small. No Earth-borne space probe has exited our solar system. Relative to the size of the Universe, this is nothing.
3. Dark matter may not be strongly interacting with normal matter. If it is composed of neutrinos, then it makes the residual molecules in a hard vacuum look like a brick wall. It hurts to punch your fist through a wall because both your fist and the wall are composed of fermions. No two fermions may occupy the same space at the same time. This is not true of bosons. If dark matter is composed of bosons, then it may be possible for it to pass through you without your knowledge.

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Originally Posted by MisterMe

If it is composed of neutrinos, then it makes the residual molecules in a hard vacuum look like a brick wall. It hurts to punch your fist through a wall because both your fist and the wall are composed of fermions. No two fermions may occupy the same space at the same time. This is not true of bosons. If dark matter is composed of bosons, then it may be possible for it to pass through you without your knowledge.

Could i bother you to explain a little more, the differences between fermions and bozons? this is cool stuff.

Bosons are objects with Spin-0, Spin-1, or Spin-2. In other words, they are objects with integral spin. Mesons have Spin-0. Photons have Spin-1. However, no material particle having Spin-1 has ever been found. This includes the long sought hypothetical Higgs Boson. The hypothetical graviton has Spin-2, but has never been found. Fermions are objects with Spin-1/2 or Spin-3/2. Leptons such as electrons and neutrinos have Spin-1/2. The hypothetical supersymmetric gravitino has Spin-3/2.

A collection of bosons has a symmetric wave function. This allows members of the collective to share quantum states. There is no exclusion principle for bosons. They may occupy the same space at the same time. A collection of fermions has an asymmetric wave function. If any two members of the collective share quantum states, then the wave function collapses. This is known as the Pauli Exclusion Principle. No two members of collective can share quantum states. Any attempt to occupy the same space at the same time results in a repulsive force.

Although no two fermions may share quantum states, two fermions may combine to form a boson. In the case of electrons, this bosonic combination is called a Cooper Pair. A Cooper Pair may share quantum states with other Cooper Pairs. This allows them to transport charge with zero resistance and, thus, are superconducting. A similar phenomenon occurs in helium below the -point. Superfluid helium is able to flow with zero resistance, appearing to assume perpetual motion. Each atom of the Bose-Einstein condensate is assumed to occupy the entire container. Bose-Einstein condensates in materials heavier than helium is an active area of research. But I digress.