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Q & A: Why is dark matter dark?

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Most recent answer: 06/25/2013
if the dark matter particle heavier than electron for example why then its harder to detect? intuition tells - more massive - bigger size - easier to detect
- pavel (age 20)

First, I should say that we don't yet have any confidence in any particular theory of what dark matter is. Let's say for now that it is mainly some sort of particle.

The mass itself only enters into the gravitational interaction. Dark matter does interact gravitationally. It's precisely those effects that show us that it exists.

We detect most things by electromagnetic interactions. Particles with no electric charge or magnetic moment are usually hard to detect. Neutrinos, for example, are very hard to detect via their main interaction, the weak nuclear force. Neutrons aren't charged, but they interact by the strong (chromodynamic) nuclear force with protons, so it's not hard to detect them.  So if there happens to be a fairly massive particle that lacks electromagnetic and strong interactions, it would be hard to detect,

Mike W.


Another reason why dark matter particles, sometimes called WIMPs an anacronym for Weakly Interacting Massive Particles, are difficult to detect is that their presumed velocities are rather slow compared to the high energy particles in accelerators at CERN and Fermilab.   Most of the current experiments searching for wimps rely on measuring the recoil kinetic energy of a struck nucleus.   This is notoriously difficult because it's very, very small.  Many sources of background exist including naturally occuring radioactive nucleii,  penetrating cosmic ray muons, neutrinos, etc.   These experiments are carried out deep underground in order to reduce extraneous background radiation.   It's a hot topic in Physics these days, stay tuned

For more information on wimps, take a look at /wiki/Weakly_interacting_massive_particles.



(published on 06/25/2013)

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