Skip to main content
57 votes

Why is it ok for people to be saying that dark matter makes up x amount of the universe when we don't know what it is?

Ultimately, the presence of invisible mass is the most straightforward explanation for what we're seeing. We're aware that we could be wrong, but if we are, we're wrong about some of the fundamentals ...
Darth Pseudonym's user avatar
34 votes

Why doesn't dark matter clump strongly in the center of galaxies, since it doesn't feel either radiation pressure or the Pauli exclusion effect?

The reason is the fact that dark matter is non collisional. The dark matter particles interact only gravitationally, they feel no pressure, right, but they also feel no drag! No drag, no friction, ...
Prallax's user avatar
  • 4,431
31 votes
Accepted

Can there be planets, stars and galaxies made of dark matter or antimatter?

Dark matter galaxies are possible but very speculative. On a theoretical level, they are hard to form because dark matter interacts only gravitationally (see Anders Sandberg's answer), which makes it ...
Allure's user avatar
  • 4,684
29 votes
Accepted

How are we observing the newly discovered "dark galaxy" J0613+52, if it has no stars and is so far away from other galaxies?

The low surface brightness survey at the GBT is looking for H(I) emission, i.e. emission from neutral hydrogen atoms (for example see O'Neil 2023). The most obvious signature they use is the 21 cm ...
ProfRob's user avatar
  • 155k
28 votes

Can there be planets, stars and galaxies made of dark matter or antimatter?

Probably not. Dark matter should really be called "transparent matter" since it does not interact with light. This has an important consequence: it is hard for dark matter - whatever it is - ...
Anders Sandberg's user avatar
28 votes
Accepted

How would "dark matter", subject only to gravity, behave?

What you describe is the standard paradigm in cosmological physics, so it has been studied extensively. The basic consequence of dark matter not having significant nongravitational interactions is ...
Sten's user avatar
  • 4,753
27 votes
Accepted

Does the recent news of "ten times more galaxies" imply that there is correspondingly less dark matter?

All Conselice et al. (2016) appear to suggest is that when you look at something like the Hubble deep field, there are many faint (and presumably low mass) galaxies that are not seen. This has ...
ProfRob's user avatar
  • 155k
26 votes
Accepted

If dark matter bends light, how do we know the stuff in the sky is where we think it is?

The local dark matter density is actually quite tiny, on the order of $\rho\sim10^{-19}\text{ g/cm}^3$ (see e.g. Bovy & Tremaine (2012)). This means that there is roughly $0.001$-$0.01M_{\odot}$ ...
HDE 226868's user avatar
  • 37.1k
26 votes

Why is it ok for people to be saying that dark matter makes up x amount of the universe when we don't know what it is?

Let me use an analogy as an example of being able to say something about a thing we never see. I can fairly confidently say that Zinn exist. Why can I say that? I'...
slebetman's user avatar
  • 369
25 votes

Is Dark Matter possible if there is dynamical friction?

Dynamical friction is considered in the study of dark matter. The timescale for dynamical friction to cause a significant loss of kinetic energy is roughly $$\tau \sim \frac{10^{5}}{\sqrt3 \ln \Lambda}...
ProfRob's user avatar
  • 155k
24 votes
Accepted

Could dark matter be wrong?

Multiple theories and hypotheses have been proposed as an alternative to dark matter (DM). The most popular are, arguably, MOND (MOdified Newtonian Dynamics):A term for various theories where the ...
pela's user avatar
  • 38.7k
20 votes

Why is it ok for people to be saying that dark matter makes up x amount of the universe when we don't know what it is?

"Is there something wrong with the way I'm thinking about this?" Fundamentally, yes, but it's a matter of the philosophy of science as much as the science itself. The question makes the ...
ScienceSnake's user avatar
  • 1,048
19 votes

What is the estimated density of the dark matter?

The average density of dark matter over the entire universe is estimated to be $2.2 \times 10^{-27}$ kg/m$^3$ (sometimes quoted in the odd units of $1.2 \times 10^{-6}$ GeV/cm$^3$ or the more ...
ProfRob's user avatar
  • 155k
18 votes

How can dark matter be observed?

The purple is a "weak lensing" map. To quote from the original authors: WEAK LENSING MASS RECONSTRUCTION OF THE INTERACTING CLUSTER 1E0657-558: DIRECT EVIDENCE FOR THE EXISTENCE OF DARK ...
James K's user avatar
  • 125k
16 votes
Accepted

Is normal matter always accompanied by dark matter and vice versa?

We lack the precision to say that there aren't regions where there is matter without dark matter or vice-versa. But what is clear is that the ratio of dark matter to normal matter, which is (or needs ...
ProfRob's user avatar
  • 155k
16 votes
Accepted

Latest cosmological parameters

Cosmological parameters are measured in a variety of ways, and their values will depend on which measurements you trust the most. The paper you link to (Planck Collaboration et al. 2016) with the 2015 ...
pela's user avatar
  • 38.7k
16 votes

Why is it ok for people to be saying that dark matter makes up x amount of the universe when we don't know what it is?

This is a slightly more technical answer that should nonetheless illustrate the concepts. Wind back the clock to 1845. You are an astronomer of that period, and you are familiar with Newton's Laws, ...
Allure's user avatar
  • 4,684
15 votes
Accepted

Scientific evidence against CMB originating from “Oort Soup”?

The idea that belts or spheres of dust might be responsible for (some) microwave emission is not crazy. Indeed we know that dust does emit microwaves and indeed, the contribution of such dust has to ...
ProfRob's user avatar
  • 155k
15 votes
Accepted

Is there more dark matter than we previously thought?

Probably nothing changes Several reasons for this: The study actually asserts (last paragraph of main text) that: The IMF variation also calls for an extensive revision of star formation rates and ...
Allure's user avatar
  • 4,684
15 votes
Accepted

Is the amount of dark matter the same as you look back through time (further away from earth)?

Unclear, but the operational assumption is that the amount of dark matter does not change. Modern cosmology is based on the Friedmann equations, for which the energy density of matter, $\Omega_m$, is ...
Allure's user avatar
  • 4,684
15 votes

Why is it ok for people to be saying that dark matter makes up x amount of the universe when we don't know what it is?

We've extensively studied dark matter properties using the effects of its gravity. It's no different than the Sun, really. We've only know what the Sun is made of and where it gets its energy from for ...
John Doty's user avatar
  • 2,307
14 votes
Accepted

How can the (in my eyes quite ridiculous) conjecture of Sheldrake be disproven?

Firstly, thank you for your leveled and clear explanation of Sheldrake's essay. I agree with you that it is quite ridiculous to make such a bold claim when there is such little support for it even for ...
Daddy Kropotkin's user avatar
13 votes

Conventional matter to dark matter ratio, outside of galaxies

Let me see if I can answer at least some of this. Yes, there is dark matter between galaxies. This is demonstrated by the fact that in galaxy groups and clusters, you need more dark matter than is ...
Peter Erwin's user avatar
  • 17.2k
13 votes
Accepted

Are black holes expected to contain the same ratio of dark matter to regular matter as the rest of the universe?

(Short answer: No, scroll to the last point.) It is irrelevant to an external observer whether the matter that fell into the black hole was dark matter or baryonic, by the no hair theorem. The only ...
user25972's user avatar
  • 459
13 votes
Accepted

Why aren't neutron stars full of dark matter?

Yes, neutron stars might actually accumulate weakly interacting dark matter and this allows some observational constraints on its nature. Basically, the temperature and continued existence of neutron ...
Anders Sandberg's user avatar
13 votes

How can the (in my eyes quite ridiculous) conjecture of Sheldrake be disproven?

To be fair, Sheldrake credits Greg Matloff (2015) for this "dark matter is really the motions of 'volitional stars'" idea. It's easy enough to show this won't work (I mean, aside from all ...
Peter Erwin's user avatar
  • 17.2k
13 votes
Accepted

Could we detect dark matter by black holes gaining unexplained mass?

The accretion rate is far too small to make much difference to Galactic black holes, but how could this be distinguished from the accretion of normal, baryonic matter in any case? In fact it is easier ...
ProfRob's user avatar
  • 155k
11 votes

Is Anti-Dark Matter a thing?

Yes, it is a thing. Weakly Interacting Massive Particles (aka WIMPS) are thought to come in matter and anti-matter forms and have a self-annihilation cross-section in order to produce the "correct" ...
ProfRob's user avatar
  • 155k
11 votes
Accepted

Why "Dark matter" is still considered?

I'm going to answer this question, not because I believe you want a thoughtful, coherent answer, but rather for others who may come across this question and look at the propaganda you've posted. I don'...
zephyr's user avatar
  • 15k
11 votes
Accepted

Could not slow neutrinos orbit galaxies and clusters, thus comprising a large component of even COLD dark matter?

These neutrinos would have to be really cold. The cosmic neutrino background is at 1.9K, and they are considered hot dark matter, because they would have been highly relativistic at the epoch of ...
ProfRob's user avatar
  • 155k

Only top scored, non community-wiki answers of a minimum length are eligible