system
Given the following post, respond as if you're commenting on Reddit:
human
Theoretically, if you had a chunk of dark matter and put it on Earth, what would it look like?

Would it have a certain colour? Would it reflect light like a mirror? From my extremely limited knowledge, I think that dark matter is able to bend light due to its gravitational field. Does this mean that its ability to bend light depends on its mass? Using what we know so far, what would give the best visualisation of what dark matter looks like to the naked eye (which then poses the question, would we be able to see dark matter with the naked eye)?
gpt
The basic idea behind dark matter is that it's basically like normal matter, *but more boring*.

Matter interacts with other matter through the four fundamental forces: the weak and strong nuclear forces, gravity, and electromagnetism.

The nuclear forces hold atoms together and control nuclear fission and fusion and radioactive half-lifes and so on. This is hard to notice in our day-to-day lives because nuclear forces are so strong that atoms tend to be very stable: you don't get nuclear fission happening when you drop a banana. You do get a slow nuclear decay of some of  the potassium etc, but it's weak enough that you need special equipment to notice is.

Gravity on the other hand, is a very weak force. It has to add up over very large amounts of mass, which means it tends to be only really be significant on big scales, and tends to be fairly smooth and featureless. This is why galaxies end up with simple geometric shapes - spheroids, discs, etc. It's why gravity is close to uniform across the surface of Earth - it just pulls you towards Earth's centre from everywhere.

But the *electromagnetic* force is different. It's a strong force, and can be attractive or repulsive. This means you can build up really complex structures with molecular bonds, and even with intermolecular forces. Electromagnetic forces are how the ground holds you up, how the table stays in place, and even how your computer works. They allow a huge amount of complexity, enough complexity to produce life itself. Electromagnetism is the most important force for normal life (gravity is second place). Light is an electromagnetic force too. Sound is transmitted through electromagnetic interactions between nearby atoms. Touch, sight, and sound - all of our senses - are based on electromagnetism.

But not every particle interacts with all these forces! Neutrinos don't interact electromagnetically, for example. We have to detect them via nuclear reactions. Neutrinos can't form complex molecules, and you can't touch them, or see them. They just flow straight through things, occasionally having a nuclear reaction with an atom.

The idea of dark matter is that it's made of particles that are just like neutrinos, but more massive. So you can't see it or touch it. Gravity causes it to form big galaxy-sized blobs, but there's not a lot of complex structure - there's just blobs in blobs.

Dark matter also doesn't do anything special with gravity. A kilogram of dark matter has the same gravity as a kilogram of potatoes. So unless you have a huge amount of dark matter you wouldn't see light bending around a concentration of dark matter either. On a *galactic* scale we can start to see "gravitational lensing" though. But even for a whole galaxy, it's still considered "weak lensing". It's only when you get up to a whole *cluster* of galaxies that you get lensing that's strong enough to see with the naked eye.