Wtf is dark matter?

[Xamonas Chegwé]

Nobody knows much about dark matter.

There are vastly differing degrees of not knowing.

Stephen Hawking would honestly and humbly claim to know very little about dark matter and not to understand its nature. However, he knows far more about regular matter, regular energy and their interactions than you or I could possibly know if we studied 12 hours a day for the rest of our lives! He is therefore able to adorn his lack of knowledge with educated guesses regarding the nature of dark matter that completely dwarf your lack of knowledge and understanding of the subject and make it resemble that of a mouse looking at a crossword.

[jamest]

Given the gravitational nature of dark matter, it should not have a homogenous distribution across the universe. Just like visible matter, it should clump together as something akin to 'dark galaxies', full of large dark bodies structurally similar to visible stars and planets.

That depends entirely on the nature of dark matter

What I said is correct unless you want to have a physical model of the universe in which a form of matter has mass, impacts gravitationally upon spacetime, but is itself unaffected by these changes in spacetime. Which would be absurd.

, though I do so love the transition between total ignorance and complete authority within the space of a post or two on a topic that's taken me more than 20 years to get a minimal grasp on.

As I've just said to the other geezer, what I've written tonight is grounded on today's thinking. New thoughts. Thoughts which seek to make sense of certain premises within the model. You know me - a geezer who likes to make sense of everything.

You keep forgetting that the universe isn't actually required to pander to our puny intuitions, let alone intuitions as horribly puny as yours.

I beg your pardon? Every aspect of the physical model is borne of the mind... and is thus subject to the skepticism of other minds. Mine included.

For that reason, I would expect the velocities/speeds of visible stars within their galaxy to be variable and changeable (and not just those stars on the outer edges of galaxies).

You'd expect? You, who thinks that the fact that Einstein supplanted Newton demonstrates that the world doesn't exist?

Yes, I'm still awaiting my invite from Stockholm for that. I clearly need an agent. How much does yours charge?

The universe doesn't give a flying fuck about your expectations, and I, knowing you considerably better, care even less.

Don't be daft, or I'll start polishing the platter.

Also, unless there's some sort of unknown force (far greater than gravity - which would effectively nullify gravity in certain regions... so we'd be aware of it) preventing dark matter from clumping with visible matter, then the mass of all visible bodies should be comprised of 80+% of dark matter. Since our calculations of the mass of visible bodies ignores the presence of dark matter therein, and since our calculations using the mass of these visible bodies is extremely accurate, this in itself suffices to refute the existence of dark matter (as presently conceived).

Except that you've gotten the figures all wrong

The figures aren't essential. The principles behind what I've said are what the issue hinges upon.

there most certainly is a force greater than gravity, though it isn't unknown. And yes, it certainly does nullify the effects of gravity in certain regions, because it's considerably stronger and, where it operates, it so totally dominates the environment as to render gravity largely irrelevant, which is why you can pick up a paperclip with an ordinary household magnet, despite the fact that the gravitational attraction of an entire planet is fighting you.

Don't waste your time with irrelevancies. Not on me, anyway.

If dark matter doesn't interact with any of those forces (hint; it definitely doesn't interact with the electromagnetic force, which is why we can't see it), then we would expect to see it dominate where those forces are minimal.

Any matter/mass with gravitational affects impacts upon (interacts with) the electromagnetic force. That's why light bends (changes path) when passing a star, for instance. It's also why light cannot escape a black hole.

If there's dark matter out there, we should actually be able to observe its effect upon the light of/from the visible universe.

[klr]

You're UK based, aren't you, James? Did you happen to watch the Horizon program about DM a few nights back? If not, catch it on iPlayer. It presents a lot of the evidence in layman's terms.

And fitting ones theories to observed facts about the universe is not "desperate". It's the very basis of science. It's why Einstein's theory of gravity supplanted Newton's. Why we no longer think that the planets circle the Earth on mysterious "spheres" that cause their erratic movement. And why we no longer sacrifice virgins to volcano gods.

I'm recording the repeat of this right now.

But I need to catch up on the "Stargazing ..." programs first, amongst other things.

[jamest]

Nobody knows much about dark matter.

There are vastly differing degrees of not knowing.

Stephen Hawking would honestly and humbly claim to know very little about dark matter and not to understand its nature. However, he knows far more about regular matter, regular energy and their interactions than you or I could possibly know if we studied 12 hours a day for the rest of our lives! He is therefore able to adorn his lack of knowledge with educated guesses regarding the nature of dark matter that completely dwarf your lack of knowledge and understanding of the subject and make it resemble that of a mouse looking at a crossword.

You don't seem to understand where I'm coming from. My newly formulated objections to there being dark matter are borne of the logical implications this conception has for the visible universe as a whole wrt the universal laws of gravity as we currently understand it. Thus, my objections do not hinge upon anything other than the principle of applying logic to matter conceived of as affecting and being affected by gravity on and by an equal measure.

In other words, mine is a philosophical objection, not a scientific one. As per usual (if you knew me).

[Xamonas Chegwé]

Nobody knows much about dark matter.

There are vastly differing degrees of not knowing.

Stephen Hawking would honestly and humbly claim to know very little about dark matter and not to understand its nature. However, he knows far more about regular matter, regular energy and their interactions than you or I could possibly know if we studied 12 hours a day for the rest of our lives! He is therefore able to adorn his lack of knowledge with educated guesses regarding the nature of dark matter that completely dwarf your lack of knowledge and understanding of the subject and make it resemble that of a mouse looking at a crossword.

You don't seem to understand where I'm coming from. My newly formulated objections to there being dark matter are borne of the logical implications this conception has for the visible universe as a whole wrt the universal laws of gravity as we currently understand it. Thus, my objections do not hinge upon anything

This is where you should have ended this sentence. You're welcome.

SOMETHING makes the stars in galaxies behave in a way that the current standard models of cosmology and particle physics cannot explain. Therefore, something beyond those current models exists. That "something" is called, for better or worse, Dark Matter.

For you to object to this means that you are either denying the behaviour that the term Dark Matter has been coined to explain, or that you are somehow claiming that that behaviour falls within the remit of our current models. Because, if that behaviour is behaving that way and it cannot be explained by the current standard models, that - whateverthefuckitis - is Dark Matter!

[jamest]

Nobody knows much about dark matter.

There are vastly differing degrees of not knowing.

Stephen Hawking would honestly and humbly claim to know very little about dark matter and not to understand its nature. However, he knows far more about regular matter, regular energy and their interactions than you or I could possibly know if we studied 12 hours a day for the rest of our lives! He is therefore able to adorn his lack of knowledge with educated guesses regarding the nature of dark matter that completely dwarf your lack of knowledge and understanding of the subject and make it resemble that of a mouse looking at a crossword.

You don't seem to understand where I'm coming from. My newly formulated objections to there being dark matter are borne of the logical implications this conception has for the visible universe as a whole wrt the universal laws of gravity as we currently understand it. Thus, my objections do not hinge upon anything

This is where you should have ended this sentence. You're welcome.

You know what you can do with that hat.

SOMETHING makes the stars in galaxies behave in a way that the current standard models of cosmology and particle physics cannot explain. Therefore, something beyond those current models exists. That "something" is called, for better or worse, Dark Matter.

The first two sentences are correct. The last sentence is either meaningless or, if it seeks to imply meaning, an assertion. Why not call it God? Because, of course, there are meaningful implications for doing so. In other words, don't imbue mysterious essences with loaded names.

For you to object to this means that you are either denying the behaviour that the term Dark Matter has been coined to explain, or that you are somehow claiming that that behaviour falls within the remit of our current models.

I've objected to the conception of 'dark matter' for reasons already stated... and which you have failed to address. Namely, in a nutshell, that the aforementioned conception has irrational [illogical] implications for the physical universe as we currently understand it.

Because, if that behaviour is behaving that way and it cannot be explained by the current standard models, that - whateverthefuckitis - is Dark Matter!

Well, I'm not so much complaining about the name, as the properties attributed to it. The name of anything or anyone is not important. Nuntius autem non important.

[hackenslash]

I have to be off now, so haven't time to address this post in detail just yet, but:

Any matter/mass with gravitational affects impacts upon (interacts with) the electromagnetic force.

No, it really doesn't.

That's why light bends (changes path) when passing a star,

No, it really isn't. Light only seems to bend. What's actually happening is that the light traverses geodesics. A geodesic is the shortest distance between two points. A straight line is a special case of a geodesic that applies to Euclidean space, but space isn't actually Euclidean, so geodesics tend to be curved, because the shortest distance between two points in curved space is a curve.

Gravity and electromagnetism do not interact. Light can be affected by gravity, but only to a negligible degree, because it has mass associated with it's motion. In other words, it's interacting gravitationally. This can be wholly discounted, though, and contributes nothing to gravitational lensing.

I'll fuck the rest of your nonsense over when I have leisure.

[jamest]

That's why light bends (changes path) when passing a star,

No, it really isn't. Light only seems to bend. What's actually happening is that the light traverses geodesics. A geodesic is the shortest distance between two points. A straight line is a special case of a geodesic that applies to Euclidean space, but space isn't actually Euclidean, so geodesics tend to be curved, because the shortest distance between two points in curved space is a curve.

The point being that gravity causes that curve in space-time... and therefore impacts upon the velocity of the electromagnetic force.

Gravity and electromagnetism do not interact.

Anything which impacts upon the behaviour of something else is indicative of interaction between those things. Since gravity impacts upon the behaviour of light, you appear to be talking bollocks.

Light can be affected by gravity, but only to a negligible degree

The measure of gravity's effect upon light is irrelevant (notwithstanding your dismal failure to recognise the colossal impact of a black hole's gravitational effect upon light).

, because it has mass associated with it's motion. In other words, it's interacting gravitationally. This can be wholly discounted, though, and contributes nothing to gravitational lensing.

Wtf are you talking about? The issue at-hand is whether gravity and electromagnetism (light) interact. If they didn't, then light wouldn't bend around stars nor fail to escape from black holes. It's that fucking simple. This is what interaction essentially means: different/distinct things/forces being affected due to their combined presence. You seem to have some naive understanding of the term 'interact', whereby things don't interact unless they shag or talk.

I'll fuck the rest of your nonsense over when I have leisure.

I've just fucked-over the [logical] notion of dark matter. Which pretty-much destroys contemporary physics, or didn't you grasp that point? If you were a physicist and understood this, your leisure-time would hence be hell.

[JimC]

I'm especially keen to see a response to my previous post, since if DM exists then it should constitute 80+% of the mass of visible bodies.

How do you arrive at this bollocks? Not that it matters how you arrived at it, because it definitely is bollocks, and I've already explained why (though I'm not totally convinced you have the equipment to grasp it), but it will be interesting to see your 'working out', if it even deserves such an appellation.

Unless dark matter itself is unaffected by gravity (an absurd suggestion), and given that it constitutes 80+% of all matter, then why should we not expect bodies of matter to be comprised of 80+% dark matter and 20-% of visible matter?

Because, due to its many difference to other matter in responding to the other forces in the universe, it does not clump in the same way...

[Xamonas Chegwé]

SOMETHING makes the stars in galaxies behave in a way that the current standard models of cosmology and particle physics cannot explain. Therefore, something beyond those current models exists. That "something" is called, for better or worse, Dark Matter.

The first two sentences are correct. The last sentence is either meaningless or, if it seeks to imply meaning, an assertion. Why not call it God? Because, of course, there are meaningful implications for doing so. In other words, don't imbue mysterious essences with loaded names.

So your objection is simply to the name chosen to describe this phenomenon? Why didn't you say so? So let's call it Fnukrangl instead - a word with no semantic baggage. Better?

For you to object to this means that you are either denying the behaviour that the term Dark Matter has been coined to explain, or that you are somehow claiming that that behaviour falls within the remit of our current models.

I've objected to the conception of 'dark matter' for reasons already stated... and which you have failed to address. Namely, in a nutshell, that the aforementioned conception has irrational [illogical] implications for the physical universe as we currently understand it.

So, let me get this clear. You are objecting to a phrase that simply describes an addition to our current understanding that will allow it to explain currently unexplained phenomena because (you say) it will make the universe work illogically?

Did you pay ANY attention to anything that either myself of Hack said? Fnukrangl (once known as dark matter and before that, in select circles, as Big Elsie) is simply a placeholder for whatever is causing the massive disparity between the predicted orbital speeds of stars at the edge of a galaxy and their actual speeds. SOMETHING is causing that disparity and that something is referred to as Fnukrangl (or, in parts of Sweden, Blind Lettuce.)

Because, if that behaviour is behaving that way and it cannot be explained by the current standard models, that - whateverthefuckitis - is Dark Matter!

Well, I'm not so much complaining about the name, as the properties attributed to it. The name of anything or anyone is not important. Nuntius autem non important.

Correct. The name is not important. But its properties are simply this: IT FUCKING WELL MAKES THE UNIVERSE DO WHAT IT ACTUALLY DOES, INSTEAD OF WHAT WE THOUGHT IT WOULD DO!

What I think you are really trying to object to, are the proposed mechanisms by which Fnukrangl achieves this effect. However, your profound ignorance of the topic leads you to repeatedly and tiresomely keep repeating that you object to the very concept of Fnukrangl itself. This is what makes you look so silly.

[JimC]

Yes. There has been much speculation by physicists as to what "dark mater" could be. Any such speculation is bounded by 2 key points:

1. It must explain the anomalous orbital behaviour of galaxies, for which current gravitational theory and the observed distribution of visible matter is not sufficient as an explanation.

2. It must account for its lack of visibility. If indeed it is a form of matter, then this implies low interaction with both ordinary matter and electromagnetic photons. If it involves additional forces, or a modification of existing laws of gravity, then the model must account for the fact that no such forces or modification has yet been observed by experiment locally.

Other than those constraints, all options are up for grabs...

[pErvinalia]

For you to object to this means that you are either denying the behaviour that the term Dark Matter has been coined to explain, or that you are somehow claiming that that behaviour falls within the remit of our current models.

I've objected to the conception of 'dark matter' for reasons already stated... and which you have failed to address. Namely, in a nutshell, that the aforementioned conception has irrational [illogical] implications for the physical universe as we currently understand it.

I.e. It could fall outside the remit of our current models, as xc just explained to you and you are both rebutting any agreeing. This is your problem, James , you get in this 'trees for the forest' tangle and can't bring yourself to properly read what people are writing.

[mistermack]

James, I can't claim to have followed every word of this discussion, or any great knowledge on the subject. But I'll just hazard a comment anyway.

You write that ''matter clumps together'' but are missing the fact that lots of matter doesn't clump together. It needs a certain density to start clumping, as in molecular clouds of gas and dust.
Even then, often nothing happens, till you get something like a supernova which blasts out energy in a shockwave and compresses local clouds enough that they can start to clump together.
If the temperature of the gas cloud isn't low enough, and the mass of the cloud isn't great enough, the gas cloud can just stay in balance for billions of years. The heat energy is enough to prevent a gravity collapse.

I would think that it's perfectly possible for dark matter to be so thinly distributed that it's not going to ever clump together, in time-frames of just a few billion years.

[jamest]

James, I can't claim to have followed every word of this discussion, or any great knowledge on the subject. But I'll just hazard a comment anyway.

You write that ''matter clumps together'' but are missing the fact that lots of matter doesn't clump together. It needs a certain density to start clumping, as in molecular clouds of gas and dust.
Even then, often nothing happens, till you get something like a supernova which blasts out energy in a shockwave and compresses local clouds enough that they can start to clump together.
If the temperature of the gas cloud isn't low enough, and the mass of the cloud isn't great enough, the gas cloud can just stay in balance for billions of years. The heat energy is enough to prevent a gravity collapse.

I would think that it's perfectly possible for dark matter to be so thinly distributed that it's not going to ever clump together, in time-frames of just a few billion years.

The problem with that is that there's more than four times the mass of dark matter relative to visible matter, yet visible matter has evidently clumped together. If the gravitational affect of visible matter sufficed to facilitate its clumping together, then there can be no good reason why dark matter should remain evenly distributed throughout.

[Xamonas Chegwé]

James, I can't claim to have followed every word of this discussion, or any great knowledge on the subject. But I'll just hazard a comment anyway.

You write that ''matter clumps together'' but are missing the fact that lots of matter doesn't clump together. It needs a certain density to start clumping, as in molecular clouds of gas and dust.
Even then, often nothing happens, till you get something like a supernova which blasts out energy in a shockwave and compresses local clouds enough that they can start to clump together.
If the temperature of the gas cloud isn't low enough, and the mass of the cloud isn't great enough, the gas cloud can just stay in balance for billions of years. The heat energy is enough to prevent a gravity collapse.

I would think that it's perfectly possible for dark matter to be so thinly distributed that it's not going to ever clump together, in time-frames of just a few billion years.

The problem with that is that there's more than four times the mass of dark matter relative to visible matter, yet visible matter has evidently clumped together. If the gravitational affect of visible matter sufficed to facilitate its clumping together, then there can be no good reason why dark matter should remain evenly distributed throughout.

You are assuming here that something that is not understood and with which we have no experience will (for some reason that you found in your arse) behave in exactly the same way as the matter with which we are familiar.

What part of "Nobody knows what it is or how it does what it does" don't you get?