Space & astronomy · the experiment
Hunt down the fifth force
A galaxy seen edge-on, inside its dark matter halo. Set a force that pulls only on the halo, watch the disk bend, and recover the article's limit.
1 · Pull the halo
Beginner
A fifth force pulls the halo downwards, but not the stars. What shape does the disk take, seen edge-on?
Check it, with a cup greatly exaggerated to be visible. Raise the force to the cosmological bounds, between 4.8 and 5.4 × 10⁻³ of gravity.
2 · Tighten the limit
Intermediate
At the cosmological bounds, around 5 × 10⁻³, the disk curls to a certain depth. At the article's conservative limit, what happens to the cup?
Check it: bring the force down to the largest value the article still allows, counting every doubt. The dotted line keeps the cup of the cosmological bounds.
3 · Flatten the halo's core
Expert
Imagine a halo that held the outer stars as firmly as the central ones. With the same force, what would the test see?
4 · What the test measures
Expert
A model where the force was strong in the young Universe but has since vanished. What does the disk limit say about it?
Force hunted down
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