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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
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
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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
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
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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
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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
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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
  • 4,674
11 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?

The presence of a third family of massive quarks was theoretically predicted in 1973, based on clues provided by other particle physics experiments. The bottom quark was discovered in 1975, but the ...
ProfRob's user avatar
  • 155k
7 votes

Can dark matter accumulate at Lagrange points?

If dark matter is dissipationless and only interacts gravitationally, then no it can't. How could it be brought to approximate rest$^1$ with respect to a Lagrangian point, its inertia would mean it ...
ProfRob's user avatar
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7 votes
Accepted

How can we measure the amount of Dark Matter in the universe to the level of a percent?

The most precise figures for the amount of dark matter in the universe arise from measurements of the cosmic microwave background and are supported by estimates of the primordial abundances of helium ...
ProfRob's user avatar
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7 votes

Is dark matter made from the particles that had charge but no mass in the early part of the Big Bang

Charged, massless particles would be a form of "hot" dark matter. i.e. A form of energy density that was relativistic at the epoch of structure formation and of course, still relativistic ...
ProfRob's user avatar
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6 votes
Accepted

Dark Matter's effect on galaxy structure

The dark matter isn't directly responsible for the rotation of the Galaxy - that is a consequence of the initial angular momentum (or the angular momentum it has accrued during its formation). Dark ...
ProfRob's user avatar
  • 155k
5 votes
Accepted

What is everything wrong with this theory of dark matter?

Sorry, but this is not correct. In the diagram, spacetime and hence the universe is the curved line. The sun, Earth, and any dark matter are not on spacetime, they are in it. Visualising spacetime as ...
James K's user avatar
  • 125k
5 votes

Has anyone observed dark matter? What could we see?

I’m not a dark matter expert, but I think we have to clarify some fact about it. First of all, the reason we called them dark matter is that they don’t interact with normal matters, photons, and ...
Greeddeer's user avatar
  • 101
5 votes

If w bosons can create dark matter neutrinos by decay, can they also create dark energy?

The W boson has a lifetime of $3\times 10^{−25}$ seconds. So any big bang W bosons will have long decayed. So they are not a dark energy source. Also, they produce "hot" relativistic decay ...
Anders Sandberg's user avatar
4 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?

Your question is a "wag the dog" one. Observations indicate that there is mass which is otherwise unaccounted for (and more specifically, 85% of the mass present in the universe). This is, ...
tripleee's user avatar
  • 167
4 votes

If a cluster of stars in dynamical equilibrium falls into a much larger blob of dark matter, will it get hotter and expand? Will it stop?

Yes, what you are proposing is essentially the accretion of dwarf galaxies/globular clusters onto larger bound objects. As the gravitationally bound cluster falls towards the more massive object, it ...
Tom Donlon's user avatar
4 votes

Is dark matter made from the particles that had charge but no mass in the early part of the Big Bang

No, because if "dark matter" had no mass, it wouldn't be dark matter anymore. Keep in mind dark matter needs to exert gravitational force, and massless particles do not exert gravitational ...
Allure's user avatar
  • 4,674
3 votes

The consequences and the mechanisms of a shift of the Earth away from the sun

Your idea of a planetary-mass black hole is on track. The real challenge here is that the black hole only gets one chance to change the orbit as it passes through the solar system. It would definitely ...
Mark Foskey's user avatar
  • 3,916
2 votes

Light/Dark energy/Dark matter

Light is a form of energy, and like other forms of energy (such as "mass") it has a gravitational effect. Two photons travelling in space will be attracted to each other by gravity. Of ...
James K's user avatar
  • 125k
2 votes

Does dark matter exist because as Einstein said the laws of physics should be the same inside and outside a black hole?

The simple answer is: no. The reason is that there is no mechanism preventing matter from speeding when falling into a black hole (it cannot move faster than light according to the local light cones, ...
Anders Sandberg's user avatar
2 votes
Accepted

Why is the dark matter component of MOND important in central regions?

MOND, in generally, does not show a need for dark matter in the central regions of galaxies. The central regions of galaxies outside of galaxy clusters, in contrast, are a problem for cold dark matter ...
ohwilleke's user avatar
  • 143
2 votes

Relating virial radius to virial mass of a dark matter halo

Yes, for any spherical-overdensity mass definition, halo mass and halo radius are uniquely related at fixed time.
Sten's user avatar
  • 4,753
1 vote

How is dark matter distributed within our solar system?

The DM halo of a galaxy is expected to have a smooth density profile: highest at the center, with density increasingly smoothly outward.[*] At the approximate radius of the Sun's orbit, the DM density ...
Peter Erwin's user avatar
  • 17.1k
1 vote

Why are WIMP dark matter particles, if Majorana-like, expected to annihilate upon contact? But not neutrinos?

Gluons actually annihilate, so do neutrinos, just more rarely than Neutralinos. Neutrinos, Gluons, WIMPS, Majorana particles are always neutral being a Truly Neutral Particle. These Majorana particles ...
Arjun's user avatar
  • 1,474
1 vote

How can Deep MOND regime apply inside a star?

Hi bit late to the party but I think there are two issues here. 1) How to deal with superpositions of small Newtonian gravitational accelerations and their conversion to the Milgromian expectation and ...
Mark Huisjes's user avatar
1 vote

The anomaly of spiral galaxies and the need for dark matter

Besides the fact that the central black holes really aren't all that massive compared to the galaxy, there is another more fundamental reason they can't explain the overly rapid revolution of the ...
Mark Foskey's user avatar
  • 3,916

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