Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: matthewh on 10/06/2019 17:04:32
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James listened to our Why Does Dark Matter Matter podcast and wanted to know:
Has anyone considered the possibility that dark matter could be particles traveling faster than light?
Let us know what can be said about the question at hand!
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Since we invoke dark matter to supply the missing mass - and hence gravity - in the Universe, then they cannot be travelling faster than light because that would require infinite energy.
So, based on my understanding, no, I don't think Dark Matter particles are moving faster than light and I suspect that others will also have dismissed that notion, but do please put me right everyone, if I'm barking up the wrong tree...
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There is a theoretical possibility in Einstein's relativity that hypothetical "Tachyons" could exist: particles travelling faster than the speed of light (c) could keep travelling faster than c. But as Chris says, we know of no way that they could get up to c, let alone beyond it.
See: https://en.wikipedia.org/wiki/Tachyon
Currently, the favorite flavor of Dark Matter is called "Cold Dark Matter".
- "Cold" refers to the speed of the individual particles
- In this case, the hypothetical Dark Matter particles would be travelling slow enough that they can be captured in the gravitational field of a galaxy, orbiting around the center of the galaxy in a spherical "Halo"
- This means that they can form the "Dark Matter Halo" that is suggested by galaxy rotation curves, the stability of galactic disks, clumping of galaxy clusters and gravitational lensing
There are other hypothesised forms of Dark Matter, including "Hot Dark Matter", which would have velocities high enough to exceed a galaxy's escape velocity, travelling through the intergalactic void. However, computer studies suggest that this would not form the galactic structures we see today.
So it seems that Dark Matter must be travelling less than the escape velocity of the Milky Way (550km/sec), so it can't be travelling faster than c (300,000 km/sec).
See: https://en.wikipedia.org/wiki/Cold_dark_matter
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Some things I have never known before. Until coming to know from all of you
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This recent episode of the Naked Scientists might help to shed a little light on the Dark Matter conundrum. We interviewed two dark matter authorities, Katherine Freese, who is searching for WIMPs, one dark matter candidate particle, and Gray Rybka who is part of the project looking for Axions, another theoretical manifestation of dark matter. It's an interesting programme:
https://www.thenakedscientists.com/podcasts/naked-scientists-podcast/why-does-dark-matter-matter