Discussion
Can someone explain the MOND theory in terms that are simple enough for me to understand?
I recently had a conversation with an astronomer. I suggested that if Newton's Law of Gravitation was modified by the addition of a very small negative number, then we wouldn't need dark matter, or dark energy.
Newton said that F= G*(m1*m2)/r^2.
What if F= G*((m1*m2)/(r^2))-x where x doesn't have any real effect until r is about 50 million light years?
My astronomer freind said that this sounded a bit like MOND theory... but he wasn't clued up on MOND. My efforts at researching MOND (wikipedia) have not revealed much. Can anybody help?
Don
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I recently had a conversation with an astronomer. I suggested that if Newton's Law of Gravitation was modified by the addition of a very small negative number, then we wouldn't need dark matter, or dark energy.
Newton said that F= G*(m1*m2)/r^2.
What if F= G*((m1*m2)/(r^2))-x where x doesn't have any real effect until r is about 50 million light years?
My astronomer freind said that this sounded a bit like MOND theory... but he wasn't clued up on MOND. My efforts at researching MOND (wikipedia) have not revealed much. Can anybody help?
Don
--
http://en.wikipedia.org/wiki/Modified_Newtonian_dy...
You seriously couldn't find that? I googled "MOND" and it was the first thing.
You seriously couldn't find that? I googled "MOND" and it was the first thing.
davepoth said:
http://en.wikipedia.org/wiki/Modified_Newtonian_dy...
You seriously couldn't find that? I googled "MOND" and it was the first thing.
I did read that page.You seriously couldn't find that? I googled "MOND" and it was the first thing.
I didn't understand it.
If you could explain it in terms that a thicky like me could understand, then I would be grateful.
TIA
Don
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don4l said:
I did read that page.
I didn't understand it.
If you could explain it in terms that a thicky like me could understand, then I would be grateful.
TIA
Don
--
The basic idea (and after reading the article once, I'm simplifying this to such an extent that it's probably wrong) is that the Newtonian numbers don't add up properly. A spiral arm galaxy, like our own, shouldn't exist by his numbers because the further away from the centre of the galaxy something is, the slower it should orbit (the same way the planets work in our solar system). That would hold true if gravity was a constant.I didn't understand it.
If you could explain it in terms that a thicky like me could understand, then I would be grateful.
TIA
Don
--
What actually happens is that after a certain distance away from the galactic core the observed velocities of the stars stay the same. Dark Matter explains this by effectively being heavy stuff that we can't see; like when a magnet is used underneath a table to move things around.
MOND explains it by saying that gravity isn't a constant, but rather that it fluctuates according to an unknown function μ; and some proponents of MOND seem to think that μ could be dark matter anyway.
MOND can therefore be seen as more of an empirical observation, much like the apple falling from the tree.
don4l said:
Can someone explain the MOND theory in terms that are simple enough for me to understand?
Why bother?It is wrong so in the final analysis there is little or no point wasting time learning about a fudge.
The MOND hypo comes really from the fact that although cold dark matter was part of GR it was not elaborated upon in sufficient clarity to gain a foothold in public imagination.
MONDs present high profile is a relic of our lack of understanding of the Pioneer anomaly and those that hold the entire MOND idea close are usually Astronomers who are faced with constant observational persuasion.
MOND is dead.
Leave it be and let it be consigned to history.
davepoth said:
The basic idea (and after reading the article once, I'm simplifying this to such an extent that it's probably wrong) is that the Newtonian numbers don't add up properly. A spiral arm galaxy, like our own, shouldn't exist by his numbers because the further away from the centre of the galaxy something is, the slower it should orbit (the same way the planets work in our solar system). That would hold true if gravity was a constant.
What actually happens is that after a certain distance away from the galactic core the observed velocities of the stars stay the same. Dark Matter explains this by effectively being heavy stuff that we can't see; like when a magnet is used underneath a table to move things around.
MOND explains it by saying that gravity isn't a constant, but rather that it fluctuates according to an unknown function μ; and some proponents of MOND seem to think that μ could be dark matter anyway.
MOND can therefore be seen as more of an empirical observation, much like the apple falling from the tree.
Thanks. I now understand why I couldn't make sense of the Wikipedia article. I missed that pesky unknown function.What actually happens is that after a certain distance away from the galactic core the observed velocities of the stars stay the same. Dark Matter explains this by effectively being heavy stuff that we can't see; like when a magnet is used underneath a table to move things around.
MOND explains it by saying that gravity isn't a constant, but rather that it fluctuates according to an unknown function μ; and some proponents of MOND seem to think that μ could be dark matter anyway.
MOND can therefore be seen as more of an empirical observation, much like the apple falling from the tree.
Gene, I won't give up on MOND, (or any other theory) until a lot more evidence comes along. There is, after all, sod all evidence for dark matter or dark energy. I'm quite content with the fact that I do not know the answers.
Don
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don4l said:
Gene, I won't give up on MOND, (or any other theory) until a lot more evidence comes along. There is, after all, sod all evidence for dark matter or dark energy. I'm quite content with the fact that I do not know the answers.
Evidence?.. hmmmm.There is no evidence that allows MOND into the standard model, zero, nothing, zilch.
Yet almost every day there is further evidence of the presence of cold dark matter and its rightful place in our model.
Like most people that want answers you may be confusing 'existence' (which is irrefutable) with understanding what exactly 'it' is (which we don't, well not exactly enough for closure)... we may not fully understand its lack of interaction but that does not mean it isn't there.
It is your life, you waste it away in whatever way you like... my guess if you weighed the number of papers that have confirmed the existence of CDM or DE then they'd amount to over a hundred tons, probably ten times as much... if you then weighed the papers proving MOND to have a place in the standard model it would amount to... about... zero, not one ounce or gram of it.
Evidence of existence precedes explanation, we have more than enough evidence, we are a little tardy on the fulsome explanation.
Have fun with MOND...
Gene Vincent said:
Evidence?.. hmmmm.
There is no evidence that allows MOND into the standard model, zero, nothing, zilch.
Yet almost every day there is further evidence of the presence of cold dark matter and its rightful place in our model.
Like most people that want answers you may be confusing 'existence' (which is irrefutable) with understanding what exactly 'it' is (which we don't, well not exactly enough for closure)... we may not fully understand its lack of interaction but that does not mean it isn't there.
It is your life, you waste it away in whatever way you like... my guess if you weighed the number of papers that have confirmed the existence of CDM or DE then they'd amount to over a hundred tons, probably ten times as much... if you then weighed the papers proving MOND to have a place in the standard model it would amount to... about... zero, not one ounce or gram of it.
Evidence of existence precedes explanation, we have more than enough evidence, we are a little tardy on the fulsome explanation.
Have fun with MOND...
Science fail. Just because everyone says it's true, doesn't mean it's true. The Sun doesn't spin around the earth, for example. That was held to be true by many; Galileo was imprisoned for life for being a believer in Heliocentrism. I expect you would have belittled him too.There is no evidence that allows MOND into the standard model, zero, nothing, zilch.
Yet almost every day there is further evidence of the presence of cold dark matter and its rightful place in our model.
Like most people that want answers you may be confusing 'existence' (which is irrefutable) with understanding what exactly 'it' is (which we don't, well not exactly enough for closure)... we may not fully understand its lack of interaction but that does not mean it isn't there.
It is your life, you waste it away in whatever way you like... my guess if you weighed the number of papers that have confirmed the existence of CDM or DE then they'd amount to over a hundred tons, probably ten times as much... if you then weighed the papers proving MOND to have a place in the standard model it would amount to... about... zero, not one ounce or gram of it.
Evidence of existence precedes explanation, we have more than enough evidence, we are a little tardy on the fulsome explanation.
Have fun with MOND...
There is, as far as I am aware at least, one paper from 2006 on the Bullet Cluster that claims to be direct proof of dark matter. That has been refuted by the guy who came up with MOND.
As I pointed out in a previous thread, it's generally a bad idea to reject theories out of hand just because they're considered heretical.
Edited by davepoth on Sunday 21st October 16:27
davepoth said:
Gene Vincent said:
Evidence?.. hmmmm.
There is no evidence that allows MOND into the standard model, zero, nothing, zilch.
Yet almost every day there is further evidence of the presence of cold dark matter and its rightful place in our model.
Like most people that want answers you may be confusing 'existence' (which is irrefutable) with understanding what exactly 'it' is (which we don't, well not exactly enough for closure)... we may not fully understand its lack of interaction but that does not mean it isn't there.
It is your life, you waste it away in whatever way you like... my guess if you weighed the number of papers that have confirmed the existence of CDM or DE then they'd amount to over a hundred tons, probably ten times as much... if you then weighed the papers proving MOND to have a place in the standard model it would amount to... about... zero, not one ounce or gram of it.
Evidence of existence precedes explanation, we have more than enough evidence, we are a little tardy on the fulsome explanation.
Have fun with MOND...
Science fail.There is no evidence that allows MOND into the standard model, zero, nothing, zilch.
Yet almost every day there is further evidence of the presence of cold dark matter and its rightful place in our model.
Like most people that want answers you may be confusing 'existence' (which is irrefutable) with understanding what exactly 'it' is (which we don't, well not exactly enough for closure)... we may not fully understand its lack of interaction but that does not mean it isn't there.
It is your life, you waste it away in whatever way you like... my guess if you weighed the number of papers that have confirmed the existence of CDM or DE then they'd amount to over a hundred tons, probably ten times as much... if you then weighed the papers proving MOND to have a place in the standard model it would amount to... about... zero, not one ounce or gram of it.
Evidence of existence precedes explanation, we have more than enough evidence, we are a little tardy on the fulsome explanation.
Have fun with MOND...
I'm not in the least bit interested in what you or others think is the right 'attitude' to Scientific endeavour.
I deal with maths, MOND has no place in my world, it doesn't fit, it has no evidence and it has only an academic value as nothing more than a way to fudge things if we didn't have a proper explanation.
I'm a Mathematician, if it fits, it's used, if it doesn't it has no value at all for me.
MOND is valueless.
You added to your post so I'll address that also if I may.
[rant]
The tinkering with the maths that is MOND is all well and good... but we are, and more specifically, I am in the business of understanding this Cosmos, not just being able to perform accurate calculations of celestial mechanics whilst ignoring what is blindingly obvious to any 'relativist' worth his salt!
[/rant]
[rant]
The tinkering with the maths that is MOND is all well and good... but we are, and more specifically, I am in the business of understanding this Cosmos, not just being able to perform accurate calculations of celestial mechanics whilst ignoring what is blindingly obvious to any 'relativist' worth his salt!
[/rant]
Gene Vincent said:
don4l said:
Gene, I won't give up on MOND, (or any other theory) until a lot more evidence comes along. There is, after all, sod all evidence for dark matter or dark energy. I'm quite content with the fact that I do not know the answers.
Evidence?.. hmmmm.There is no evidence that allows MOND into the standard model, zero, nothing, zilch.
Yet almost every day there is further evidence of the presence of cold dark matter and its rightful place in our model.
Like most people that want answers you may be confusing 'existence' (which is irrefutable) with understanding what exactly 'it' is (which we don't, well not exactly enough for closure)... we may not fully understand its lack of interaction but that does not mean it isn't there.
It is your life, you waste it away in whatever way you like... my guess if you weighed the number of papers that have confirmed the existence of CDM or DE then they'd amount to over a hundred tons, probably ten times as much... if you then weighed the papers proving MOND to have a place in the standard model it would amount to... about... zero, not one ounce or gram of it.
Evidence of existence precedes explanation, we have more than enough evidence, we are a little tardy on the fulsome explanation.
Have fun with MOND...
Dark Matter was invented when scientists discovered that galaxies appeared to be spinning faster than existing theories predicted.
Dark Energy was invented when scientists discovered that the Universe appears to be expanding at an increasing rate.
They were both invented to prevent scientists from admitting that existing theories were wrong. Experts hate admitting that they simply "don't know".
Don
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don4l said:
Dark Matter was invented when scientists discovered that galaxies appeared to be spinning faster than existing theories predicted.
Dark Energy was invented when scientists discovered that the Universe appears to be expanding at an increasing rate.
No, the name was a relatively new invention, but its presence was acknowledged by Einstein and every subsequent theorist of any stature.Dark Energy was invented when scientists discovered that the Universe appears to be expanding at an increasing rate.
Again presence and the effect of that presence has does not always go hand-in-hand.
It's not new... 97 years this November...
GV - you use the phrase "cold dark matter" (since you're last attempt to educate me in the dark arts of physics, excuse the pun, I've been trawling around trying to get a grip as best I can on Dark Matter / Dark Energy; curiosity on my part as I enjoy astronomy and like to have a simple understanding of as much as I can about the subject) and from what I've gleaned to explain the rotational speed of galaxies dark matter, assuming it exists, needs to be unformly spread throughout said galaxy rather than 'clumped' together in the centre as you'd expect; this requires dark matter to be hotter than originally thought? Am I reading out of date stuff or is your use of 'cold' relative?
pointedstarman said:
GV - you use the phrase "cold dark matter" (since you're last attempt to educate me in the dark arts of physics, excuse the pun, I've been trawling around trying to get a grip as best I can on Dark Matter / Dark Energy; curiosity on my part as I enjoy astronomy and like to have a simple understanding of as much as I can about the subject) and from what I've gleaned to explain the rotational speed of galaxies dark matter, assuming it exists, needs to be unformly spread throughout said galaxy rather than 'clumped' together in the centre as you'd expect; this requires dark matter to be hotter than originally thought? Am I reading out of date stuff or is your use of 'cold' relative?
We call it cold because it is not radiating its presence like normal matter, which gives off or reflects EMR to let us know it's there.Our only real of 'experience' of non-radiating material is that of things at absolute zero or extremely close to it, so we called it that for a while, the 'cold' bit is largely discarded now, but may have to return as we find out more, there may be at least two distinct forms of 'Dark Matter', one being simply inert but ambient in temp. and the other actually very cold indeed.
Wouldn't it be possible that it's not that cold but dark matter shares no property with 'normal' matter other than gravity and is simply emitting a form of radiation we're not aware of, i.e. not EM but something completely different that is not visible to us or detectable by any form of sensor we've built? Being completely hypothetical and extrapolating just for the sake of it, if there were an inteligent form of life made of dark matter and they we're looking out into the universe they may be scratching thier heads saying 'we know there's more matter/energy out there but we can't detect it yet...' (and no, I'm not into Von Daniken et al)
pointedstarman said:
Wouldn't it be possible that it's not that cold but dark matter shares no property with 'normal' matter other than gravity and is simply emitting a form of radiation we're not aware of, i.e. not EM but something completely different that is not visible to us or detectable by any form of sensor we've built? Being completely hypothetical and extrapolating just for the sake of it, if there were an inteligent form of life made of dark matter and they we're looking out into the universe they may be scratching thier heads saying 'we know there's more matter/energy out there but we can't detect it yet...' (and no, I'm not into Von Daniken et al)
Your idea is not at all outlandish, except possibly the idea of life being made of something so inert.
But in previous posts I have mentioned the (at present) strongest candidate for what DM/DE are and that is simply that parts or elements of this Cosmos have not fully interacted with all the Quantum Fields, this could be that one of the fields is 'flat lined' as far as probability is concerned, this would leave matter sort of 'nearly there' but not quite matter, this solution is quite attractive for various mathematical reasons but not very satisfactory for the same reasons. Why any field would do this is beyond present understanding.
My personal favourite is my own (of course) and it is much simpler, DM and DE may be just the result of matter that was left over from previous failed attempts to form a Cosmos and finally the right amount of Energy+eq was used up to allow this Cosmos to form, all previous attempts being too energetic and had no damper to coalesce things, DM and DE in this hypothesis allowed the Cosmos to form filaments that ran like huge rivers of energy rather than a flood.
The maths work well to do this, DM and DE seems to have many of the attributes of a spent item.
But yours might be right, we have looked for differing types of radiation, I can find 14 papers on that subject alone.
Gene Vincent said:
Evidence?.. hmmmm.
There is no evidence that allows MOND into the standard model, zero, nothing, zilch.
Yet almost every day there is further evidence of the presence of cold dark matter and its rightful place in our model.
Like most people that want answers you may be confusing 'existence' (which is irrefutable) with understanding what exactly 'it' is (which we don't, well not exactly enough for closure)... we may not fully understand its lack of interaction but that does not mean it isn't there.
It is your life, you waste it away in whatever way you like... my guess if you weighed the number of papers that have confirmed the existence of CDM or DE then they'd amount to over a hundred tons, probably ten times as much... if you then weighed the papers proving MOND to have a place in the standard model it would amount to... about... zero, not one ounce or gram of it.
Evidence of existence precedes explanation, we have more than enough evidence, we are a little tardy on the fulsome explanation.
Have fun with MOND...
You do come across as rather dogmatic Gene, I have to say.There is no evidence that allows MOND into the standard model, zero, nothing, zilch.
Yet almost every day there is further evidence of the presence of cold dark matter and its rightful place in our model.
Like most people that want answers you may be confusing 'existence' (which is irrefutable) with understanding what exactly 'it' is (which we don't, well not exactly enough for closure)... we may not fully understand its lack of interaction but that does not mean it isn't there.
It is your life, you waste it away in whatever way you like... my guess if you weighed the number of papers that have confirmed the existence of CDM or DE then they'd amount to over a hundred tons, probably ten times as much... if you then weighed the papers proving MOND to have a place in the standard model it would amount to... about... zero, not one ounce or gram of it.
Evidence of existence precedes explanation, we have more than enough evidence, we are a little tardy on the fulsome explanation.
Have fun with MOND...
I've never seen any evidence for the existance of dark matter. Plenty of observations which can be explained by the dark matter hypothesis. But that's not the same as evidence of its existance.
The Black Flash said:
Gene Vincent said:
Evidence?.. hmmmm.
There is no evidence that allows MOND into the standard model, zero, nothing, zilch.
Yet almost every day there is further evidence of the presence of cold dark matter and its rightful place in our model.
Like most people that want answers you may be confusing 'existence' (which is irrefutable) with understanding what exactly 'it' is (which we don't, well not exactly enough for closure)... we may not fully understand its lack of interaction but that does not mean it isn't there.
It is your life, you waste it away in whatever way you like... my guess if you weighed the number of papers that have confirmed the existence of CDM or DE then they'd amount to over a hundred tons, probably ten times as much... if you then weighed the papers proving MOND to have a place in the standard model it would amount to... about... zero, not one ounce or gram of it.
Evidence of existence precedes explanation, we have more than enough evidence, we are a little tardy on the fulsome explanation.
Have fun with MOND...
You do come across as rather dogmatic Gene, I have to say.There is no evidence that allows MOND into the standard model, zero, nothing, zilch.
Yet almost every day there is further evidence of the presence of cold dark matter and its rightful place in our model.
Like most people that want answers you may be confusing 'existence' (which is irrefutable) with understanding what exactly 'it' is (which we don't, well not exactly enough for closure)... we may not fully understand its lack of interaction but that does not mean it isn't there.
It is your life, you waste it away in whatever way you like... my guess if you weighed the number of papers that have confirmed the existence of CDM or DE then they'd amount to over a hundred tons, probably ten times as much... if you then weighed the papers proving MOND to have a place in the standard model it would amount to... about... zero, not one ounce or gram of it.
Evidence of existence precedes explanation, we have more than enough evidence, we are a little tardy on the fulsome explanation.
Have fun with MOND...
I've never seen any evidence for the existance of dark matter. Plenty of observations which can be explained by the dark matter hypothesis. But that's not the same as evidence of its existance.
http://arxiv.org/find/grp_physics/1/ti:+AND+matter...
I've read every one of those, some parts of them twice, I have tested them against proven maths results and some observations, they all failed... what would you have me do?
Stare longingly at the screen for another to eventually come along for me to test or in the mean time get on with something that actually works?
Is that good use of the taxes you pay for me to do this sort of thing?
Don't mistake my focus for dogma.
Gene Vincent said:
A quick check for alternatives to DM brought this in return...
http://arxiv.org/find/grp_physics/1/ti:+AND+matter...
I've read every one of those, some parts of them twice, I have tested them against proven maths results and some observations, they all failed... what would you have me do?
Stare longingly at the screen for another to eventually come along for me to test or in the mean time get on with something that actually works?
Is that good use of the taxes you pay for me to do this sort of thing?
Don't mistake my focus for dogma.
I said that you come across as dogmatic. I don't know if you are or not, but that's how it appears. "This is wrong, that is right, this model is right and will still be right in a thousand year's time".http://arxiv.org/find/grp_physics/1/ti:+AND+matter...
I've read every one of those, some parts of them twice, I have tested them against proven maths results and some observations, they all failed... what would you have me do?
Stare longingly at the screen for another to eventually come along for me to test or in the mean time get on with something that actually works?
Is that good use of the taxes you pay for me to do this sort of thing?
Don't mistake my focus for dogma.
You could well be correct, but it all sounds rather like hubris.
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