Episode 100: Unsolved Problems in Science

Evidence

The existence of dark matter is supported by compelling evidence from various astronomical observations. James Fodor explains that the unexpected rotational speeds of spiral galaxies suggest the presence of unseen mass, as stars at the edges rotate at similar speeds to those near the center, defying expectations based on visible matter alone 1. Additionally, gravitational lensing, a phenomenon where light from distant galaxies is bent by massive objects, reveals a mass deficiency in galaxy clusters, indicating more mass than what is visible 2.

We can see how much mass is there by the amount of bending of light. And we can see how much light there is by looking at the x-ray emissions.

--- James Fodor

These observations collectively point to the existence of dark matter, a mysterious form of matter that interacts with gravity but not electromagnetic radiation.

   

Candidates

The identity of dark matter remains one of the most intriguing mysteries in physics. James Fodor discusses potential candidates, including weakly interacting massive particles (WIMPs), which are hypothesized to be massive yet non-interactive with known forces except gravity 3. Another possibility is massive compact halo objects (MACHOs), which include non-luminous bodies like primordial black holes and unassociated planets 4.

It's thought that machos cannot account for the overwhelming majority of dark matter just because basically, there couldn't be enough of them for us to not see at least some of them.

--- James Fodor

While WIMPs are the leading hypothesis, the true nature of dark matter remains elusive, highlighting the complexity and depth of this unsolved problem.