Collisionless dark matter refers to particles that do not scatter or collide with each other, interacting primarily through gravity, as described by the Lambda Cold Dark Matter (LCDM) model. In contrast, self-interacting dark matter (SIDM) allows for interactions between dark matter particles, which can lead to different cosmic structures and dynamics. The discussion emphasizes the importance of understanding these distinctions to grasp dark matter's role in the universe. Clarifying these terms is crucial for advancing theories in cosmology. Overall, the differences between collisionless and self-interacting dark matter have significant implications for our understanding of the universe.
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Ranku
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When dark matter is called collisionless, does it only mean that they do not collide and scatter, or does it also mean that there is no other significant non-contact interaction?
That would be the LCDM theory of dark matter.
I would think collisionless means no physical scattering, no interaction whatsoever, except through gravity.
But let us have a second opinion before you send off.
Keep you finger on the keyboard.
There is also the SIDM - self interacting dark matter.
Partial solar eclipse from Twizel, South Isl., New Zealand ...
almost missed it due to cloud, didnt see max at 0710 NZST as it went back into cloud.
20250922, 0701NZST
Canon 6D II 70-200mm @200mm,
F4, 100th sec, 1600ISO
Makeshift solar filter made out of solar eclipse sunglasses
Today at about 4:30 am I saw the conjunction of Venus and Jupiter, where they were about the width of the full moon, or one half degree apart. Did anyone else see it?
Edit: The moon is 2,200 miles in diameter and at a distance of 240,000 miles. Thereby it subtends an angle in radians of 2,200/240,000=.01 (approximately). With pi radians being 180 degrees, one radian is 57.3 degrees, so that .01 radians is about .50 degrees (angle subtended by the moon). (.57 to be more exact, but with...
This thread is dedicated to the beauty and awesomeness of our Universe. If you feel like it, please share video clips and photos (or nice animations) of space and objects in space in this thread. Your posts, clips and photos may by all means include scientific information; that does not make it less beautiful to me (n.b. the posts must of course comply with the PF guidelines, i.e. regarding science, only mainstream science is allowed, fringe/pseudoscience is not allowed).
n.b. I start this...