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Hi, I am a layman when it comes to physics.
Can you explain to me what is dark matter?
What do we know about it?
How far are we from proving its existence?


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Dark matter, as the name implies, is a type of matter. It's thought to be responsible for much of the mass in the universe.

It's thought that it makes up ~27% of all matter in the universe. Because it doesn't give off radiation of any sort, we can't use our current instruments to detect it. So, the only way we can tell it's there is by the way it affects other things. Mainly related to gravity.


I wouldn't dare post this in 4chan /sci/ but this is lainchan so I will.
Dark matter is known to interact (with normal matter) through gravity and nothing else. (afaik)
If there exist parallel universes and they can only interact through gravity (a big if). Then maybe the mass/gravity anomaly that we see in galaxies is the result of multiple parallel galaxies interacting gravitationally.

I don't know.. maybe. It's nice to think about parallel universes.


> I wouldn't dare post this in 4chan /sci/ but ...
Why not ???


because some seething nerd with severe retardation will jump in and ruin the conversation. The equivalent of a weeaboo but for science.

god I hate 4chan.


I think it is weakly interacting as well. I'm not sure about the strong interaction. The only thing I'm sure about is that it doesn't interact through the electromagnetic interaction (hence "dark"). In other words the only long range interaction is through gravity.

>How far are we from proving its existence?
That's kind of the wrong question. We know that there has to be some extra mass to explain certain phenomena, we just don't know what it is. I guess it's also possible that we just don't understand gravity as well as we think we do, and its nature changes at large distances.

I'm no astrophysicist though.


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There are many darks...

Dark Matter
Dark Energy
Dark Flow

Dark matter is an unidentified type of matter comprising approximately 27% of the mass and energy in the observable universe.

Dark energy is an unknown form of energy which is hypothesized to permeate all of space, tending to accelerate the expansion of the universe. Dark energy contributes 68.3% of the total energy in the present-day observable universe.

Dark flow is an astrophysical term describing a possible non-random component of the peculiar velocity of galaxy clusters. The actual measured velocity is the sum of the velocity predicted by Hubble's Law plus a possible small and unexplained (or dark) velocity flowing in a common direction.

Or you might want to expand on; Dark Fluid

Dark fluid is an alternative theory to both dark matter and dark energy and attempts to explain both phenomena in a single framework.

Dark fluid proposes that dark matter and dark energy are not separate physical phenomena as previously thought, nor do they have separate origins, but that they are strongly linked together and can be considered as two facets of a same fluid. At galactic scales, the dark fluid behaves like dark matter, and at larger scales its behavior becomes similar to the dark energy one. Our current observations within the scales of the Earth and the Solar System are currently insufficient to explain the gravitational effects observed at these larger scales.

Sorry for the Wiki dump - copypasta wadayagonnado...


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Further to this There are several experiments to detect Dark matter.


Thing is dark matter does interact but only very very very very little/occasionally... Its a class of matter called WIMPS.

Weakly Interacting Massive ParticleS


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There's discrepancy in stars' velocities and distribution of visible mass in our galaxy wrt gravitation force as if there is some extra unaccounted mass. That extra mass was called dark matter.
BTW how does one account for black holes or is their contribution infinitesimal?


Black holes have well defined masses/energies, so their contribution would be worked out as for any other star.


But how does one see a black hole? It's black on black background.


You can see effects that it causes, such as the bending of light.


Here's a wikipedia page with nice pictures https://en.wikipedia.org/wiki/Einstein_ring


don't quote me on this but i don't think it's actually #000000 (black) but actually just devoid of any color because it consumes any/all the matter and energy it comes across. what you can observe is the so called "hawking radiation" that is caused by virtual particles (essentially a pair of particles that constantly pop into existence in the vacuum of space and then nearly-instantaneously annihilate themselves by colliding with their anti-particle pair) being torn from their complementary anti-particle when popping into existence near the event horizon, in effect producing some observable phenomena.


A little bit of history first:
Beginning of 20th century every celestial body in our solar system are well defined and their orbits match the theory (newtonian dynamics, graity) except for some anomalies in Neptume and Uranus orbits'.
Scientific then theorized another planet or big asteroid might be at the periphery of our SS and they were right Pluton was then dicovered in 1930.

Now some years later while observing galaxys movements they again found anomalies, big ones. And they theorized the _dark matter_, an undentified type of matter that has a mass and is difficult to observe directly. We can only observe it's effects on light waves


Pretty sure Pluto's mass is way too small to have a noticeable effect on Neptune's orbit.


And yet, Pluto's existence was predicted from perturbations in the orbits of Uranus and Neptune before it was observed.
Look up Planet X.


Theoretically yes, but you can't do it en mass over the whole galaxy with just a modern telescope. And hawking radiation is way below any achievable sensitivity.


No, this is from the Wiki page on Planet X:

"Clyde Tombaugh's discovery of Pluto in 1930 appeared to validate Lowell's hypothesis, and Pluto was officially named the ninth planet. In 1978, Pluto was conclusively determined to be too small for its gravity to affect the giant planets, resulting in a brief search for a tenth planet. The search was largely abandoned in the early 1990s, when a study of measurements made by the Voyager 2 spacecraft found that the irregularities observed in Uranus's orbit were due to a slight overestimation of Neptune's mass."

Also, original estimates for the mass of Planet X were 7 to 12 earth masses*; Pluto's mass is far below that, so you really can't say it's existence was predicted since they never actually found what they were looking for. And Pluto's mass makes it far to small to have major effects on Neptune's orbit.

*From http://www.vanderbilt.edu/AnS/physics/astrocourses/ast201/pluto_tombaugh.html


I know what dark matter is made of.


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The reason why people think that there is dark matter is very simple actually. You are probably aware that the stars in a galaxy revolve around the centre of that galaxy. Based on what we know about physics, we would expect that the stars far away from the galactic center move slower than the stars closer to the galactic center, as illustrated in the picture by the lower curve. However, our observations show that the reality follows the upper curve. Now if we assume that there is such a thing as dark matter, and we give it a certain distribution, then we can predict that the upper curve is the correct one, using what we already know about gravitation and stuff like that.

It is difficult (for me) to say how far we are from proving the existence of dark matter. There are numerous experiments running, but none of them have found conclusive results, merely encouraging results.

We don't know what dark matter is made of (if it even exists), but there are a number of candidates: WIMPs (weakly-interacting massive particles), neutrinos, and axions, and probably some more. What we do know is that, if it exists, it interacts only very little with "ordinary" matter.

If you are interested in reading more about dark matter and dark energy, I would advice you to search for the NASA website, this page https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy might be a good starting point. If you have access to a university, I would recommend you to borrow or download (but only if you can get it for free) the book Introduction to Particle and Astroparticle Physics, by De Angelis and Pimenta. It discusses dark matter and a lot of other topics.


Dark matter and quantum mechanical waves is a croc of soykaf. I am positive in two centuries these theories will be disposed of, and laughed at. Modern physics is a joke.


Got any justification for that opinion, or do you just not like dark matter?


QM is the most well-tested theory in existence. You'd better have some pretty intense evidence to suggest that it's false.


This just sounds like "I don't get it, so it's not real". There is incredible rigour put on physicists and the specific claims that get made are very strong. I'd argue further, but you've not given any specific examples of what you think is incorrect, so it's hard to make counterclaims.


To me dark matter is the largest indicator general relativity needs a giant upgrade, or it should be thrown out. Of course the people that argue this are ridiculed like hell because it hurts the people who have an deep attachment to magic particles. Physics has turned into an elitist religion. There are alternative theories to explain why galaxies behave that way.

Again this is the most preposterous comment I have to deal with, especially from "objective" scientists. According to what standards? You're just parroting soykaf and not providing an argument while demanding that I should. Go fuarrrk yourself. The QM wave evidence is extremely weak garbage inferred from the double slit experiment. Inferred. On the surface, how we describe this phenomenon should signal to physicists this sensationalized bullsoykaf is as weak and pathetique as the luminiferous aether, which was argued with "rigor" by respected scientists like Cauchy that everyone ball sucked. The key point is this is weakly inferred. I will stick by dear Newton and his particles.

Another asshole. Anyone with a respectful brain would realize just how pointless this comment is. I don't have difficulty reading science.

Overall, the way these theories are defended like its the undeniable truth and "you just don't understand God" makes me more certain you people are going to crash hard. I hope it happens in my lifetime. The ridicule is worse than the ridicule on climate change deniers which is funny, because I consider that evidence more well tested and less weakly inferred.


You make random general claims that you have surface knowledge of and then dismiss everyone who questions you with insults. I don't think they're the "assholes". Weak evidence works if the counter-evidence, or evidence for other ideas is even weaker. There are no truths in science.


Good one. Everyone can see past the last two comments I responded to and their insults to intelligence, and hypocrisy. Insults are allowed when ethics are violated. You fall short in attempt to further construe me as improper or wrong.

My claims arent random, nor did I claim to have surface knowledge. I have read the experiments. Try to have some of the formal intellectual courtesy youre telling me to have. Since this is an imageboard I'm not going to gear my argumrnt up to mathematics and write a 5 hour presentations. Like I said, it should be apparent to anyone with a brain the nonsense of QM should signal the initial inference to be probable trash. The alternative theories are just as good.

Before this turns into a dumb philosophical conversation about truth and science, which science has, it is plain evident you assholes are on the high horse. This is really a waste of time.


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You're seeing through it perfectly.


>I have read the experiments. Try to have some of the formal intellectual courtesy youre telling me to have.
You're assuming that everyone here who doesn't think QM is a croc of soykaf hasn't actually read about it from a primary source?

If QM is clearly "nonsense", then get a peer-reviewed article published proving it and collect your Nobel prize. Or at least actually present a reasoned argument here, rather than just acting as if everyone else is an idiot.


I don't even know what your question means. You're continuously picking at things that don't exist in my argument.


>There are alternative theories to explain why galaxies behave that way.
Most of which are either not supported by research (like ones claiming that gravity just works differently) or just variations of the same (dark fluid, which combines dark energy and dark matter theories). If you have other ones, please present them here, I'd be genuinely interested in seeing them.

> The QM wave evidence is extremely weak garbage inferred from the double slit experiment

Just before I go into this, is your claim here that the particle-wave duality is not a thing, that everything is just a particle, or are you saying that there are things that are just one or the other?

>Another asshole

Not sure why you thought that had any relevance, but the purpose of that post was to ask _specific examples_ of what you think is incorrect and why it is so.

> insults to intelligence, and hypocrisy.
Well, I didn't give any counter proof in my post because there were no specific claims made and no proof was presented. It's hard to argue against something when it's not been made clear what it is and why you believe in it.

He is asking you why something that is apparently "obviously fake" is so widely accepted by scientists and used in practice.

You've made no specific claims against any specific case, but you just keep saying how stupid people are and how obvious it is. If it really is this obvious, just show us the proof and we'll shut up.


>There are alternative theories to explain why galaxies behave that way.

Working physicists would probably love to believe them too. Dark matter causes them lots of stress.

>According to what standards?

really fuarrrking strict ones. I'm telling you, QM is *the* most well-tested theory in existence. Nothing comes close, except maybe General Relativity and Conservation of Momentum.

>You're just parroting soykaf and not providing an argument while demanding that I should.

I could show you the fuarrrkng experiments. You could do most of them yourself if you're so skeptical.


it's basically the only reasonable explanation. You can "bend" photons around small objects too, in a way that exactly matches the expected wave interference pattern. But they also must be particles with individual energy a la photoelectric effect. I suggest you maybe actually learn physics before saying it's all bullsoykaf.

>The ridicule is worse than the ridicule on climate change deniers which is funny, because I consider that evidence more well tested and less weakly inferred.

then you're wrong. Climate science will never get close to the level of proof that exists for GR and QM.


>The alternative theories are just as good.

I know the OP is probably long gone, but what alternate theories are there? I know of de Broglie-Bohm theory, but according to the wikipedia entry it's been proved not mathematically equivalent (and hence wrong? Wikis not clear) earlier last year.


Well, pilot wave theories have less compatibility with special relativity, and it has failings in some experimental stuff, in my understanding. For a pilot wave theory to become accepted, we need some major additions to the current ones.


yes they are a bit random....

But just to play devils advocate and provide a real alternative for thought :)

Variable G me old chummers!
If gravity is not a constant over time or space then all the bets are off! - neither of which we can yet measure in enough detail for this to be completely off the table, i believe.


>If gravity is not a constant over time or space then all the bets are off!

Scientists have done a massive amount of research on what would have happened if that was the case, but from what we know, the universe could not exist as it is if that was the case, down to things like no Solar system and thus, no humans.

There's no good reason to consider variable G beyond this - if it really is variable, either the rest of physics needs a heavy re-working despite being heavily consistent and able to predict the future findings or the variations are insignificant enough to not be sufficient to explain dark matter and energy away.


And then there's this guy:

MOND - Modified Newtonian Dynamics


Correct me if I'm wrong, but gravity is distortions in a four dimensional sheet of space and time, right? How do we know that this is large amounts of unaccounted for mass, and not some force acting on time?


can you give me any reason to read that article? i find the praise of unverified hypothesis quite disgusting. journalism needs sanctions.


I'm not here to educate you


>on a science board
>not here to lean and help others learn
what are you even doing with your life.


'mass' is basically defined(in GR at least) as distortion in said spacetime, so the difference is just semantic.


i didn't ask for education. i asked for an argument. as if it's smart in being educated through journalist exhibition instead of the real MOND publications. your show and tell is soykaf.


It's pretty simple OP. If you apply basic centrepetal motion to galaxies you'd expect the matter near the outside to spinning far more slowly than it actually is (think of how mercury moves far faster than say jupiter - conservation of momentum). As physicists don't really have an explanation the leading theory is there is a bunch of unaccounted mass that makes up for this discrepancy.