mysterious force slows pioneer spacecraft

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mysterious force slows pioneer spacecraft

Postby elite4koga » Wed Oct 06, 2010 3:13 am UTC

A few weeks ago I read this story
http://www.telegraph.co.uk/science/space/1384420/Mysterious-force-holds-back-Nasa-probe-in-deep-space.html
Essentially some new force, or at least a new component of gravity, has been discovered.

I find this intriguing and wanted to know what you (smart people who know more about physics and astronomy than me)
think about this.

if it is a new force it should be called "the force" for the lols.

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Re: mysterious force slows pioneer spacecraft

Postby sardia » Wed Oct 06, 2010 3:47 am UTC

Come on dark energy...Of course, I have no idea what I'm talking about, since I don't think dark energy works like that.

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Re: mysterious force slows pioneer spacecraft

Postby BlackSails » Wed Oct 06, 2010 3:55 am UTC

Odds are it is something completely mundane and boring.

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Re: mysterious force slows pioneer spacecraft

Postby CorruptUser » Wed Oct 06, 2010 4:08 am UTC

Well, the most interesting phrase in science is not "Eureka!" but "That's odd..."

I forget who said that first, but regardless, even if the explanation is boring we need to find it.

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Re: mysterious force slows pioneer spacecraft

Postby fjafjan » Wed Oct 06, 2010 5:06 am UTC

Considering the current theories about Dark Matter (and dark energy) the existence of a 'new force' or some such thing would be entirely on par. I mean at some point, hopefully, Dark Matter will be stop being "this thing we don't know what it is so we call it dark" and start being something.
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Re: mysterious force slows pioneer spacecraft

Postby SummerGlauFan » Wed Oct 06, 2010 5:21 am UTC

fjafjan wrote:Considering the current theories about Dark Matter (and dark energy) the existence of a 'new force' or some such thing would be entirely on par. I mean at some point, hopefully, Dark Matter will be stop being "this thing we don't know what it is so we call it dark" and start being something.


I thought dark matter didn't interact with normal matter, with the exception of still generating gravity.
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Re: mysterious force slows pioneer spacecraft

Postby sardia » Wed Oct 06, 2010 5:54 am UTC

SummerGlauFan wrote:
fjafjan wrote:Considering the current theories about Dark Matter (and dark energy) the existence of a 'new force' or some such thing would be entirely on par. I mean at some point, hopefully, Dark Matter will be stop being "this thing we don't know what it is so we call it dark" and start being something.


I thought dark matter didn't interact with normal matter, with the exception of still generating gravity.

Dark Energy is the opposite of gravity since it repels matter, not attracts. It still a stupid explanation though.

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Re: mysterious force slows pioneer spacecraft

Postby SummerGlauFan » Wed Oct 06, 2010 6:18 am UTC

Clearly the probe really got snagged on the very edge of a tractor beam. What's all this nonsense about dark matter? ;)
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Re: mysterious force slows pioneer spacecraft

Postby SlyReaper » Wed Oct 06, 2010 6:37 am UTC

So it's a force that stays constant with distance? I'm sure it will turn out to be something mundane, but in the meantime I'm going to hazard a guess at divine intervention. Clearly, the Gods do not wish filthy human technology to spread beyond our solar system.
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Re: mysterious force slows pioneer spacecraft

Postby Shivahn » Wed Oct 06, 2010 6:42 am UTC

SlyReaper wrote:So it's a force that stays constant with distance? I'm sure it will turn out to be something mundane, but in the meantime I'm going to hazard a guess at divine intervention. Clearly, the Gods do not wish filthy human technology to spread beyond our solar system.


Man, we sent the gods nude pics. They should love Pioneer.

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Re: mysterious force slows pioneer spacecraft

Postby Zamfir » Wed Oct 06, 2010 6:45 am UTC

Shivahn wrote:
SlyReaper wrote:So it's a force that stays constant with distance? I'm sure it will turn out to be something mundane, but in the meantime I'm going to hazard a guess at divine intervention. Clearly, the Gods do not wish filthy human technology to spread beyond our solar system.


Man, we sent the gods nude pics. They should love Pioneer.

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Re: mysterious force slows pioneer spacecraft

Postby SlyReaper » Wed Oct 06, 2010 6:48 am UTC

Odin disapproves of us sending smut to alien star systems.
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Re: mysterious force slows pioneer spacecraft

Postby Shivahn » Wed Oct 06, 2010 6:53 am UTC

Zamfir wrote:
Shivahn wrote:
SlyReaper wrote:So it's a force that stays constant with distance? I'm sure it will turn out to be something mundane, but in the meantime I'm going to hazard a guess at divine intervention. Clearly, the Gods do not wish filthy human technology to spread beyond our solar system.


Man, we sent the gods nude pics. They should love Pioneer.

Shivahn, the gods watch everyday when you are in the shower. Every single day. Also at other naked moments of your life.


Knowing the Greek gods, this does not surprise me.

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Re: mysterious force slows pioneer spacecraft

Postby bittyx » Wed Oct 06, 2010 6:59 am UTC

Has no one noticed that the article linked is more than 8 years old? The fun part is that the effect is still in the process of hypothesizing about it. There is more than one proposed explanation for this phenomenon (though, not one of them has yet been proven or anything), and you can find some info about it here - it's an interesting read!

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Re: mysterious force slows pioneer spacecraft

Postby Diadem » Wed Oct 06, 2010 11:33 am UTC

Yep this is a very old anomaly. I'm not aware of any recent developments either. As far as I know they still aren't entirely sure what to think of it.

The most interesting explanation by far is MOND, or Modified Newtonian Dynamics. It's a modification of the (classical non-relativistic) laws of mechanics that was originally introduced to explain the rotation of galaxies without having to use dark matter. MOND introduces an extra parameter that only becomes relevant at very very low accelerations, so we never notice it in day-to-day life. But it's relevant for the rotation of galaxies. At the price of merely one extra variable the entire concept of dark matter can be ditched, which is a major gain in simplicity, so the theory is attractive.

The very interesting thing is that it turns out that the observed deviation of the pioneer from what you would expect based on Newton, is exactly what MOND predicts. So a theory designed for problem A predicts exactly the right thing for an entirely unrelated problem. As evidence comes, you can't get any stronger than that.

The one problem with MOND is that it flat out contradicts GR. So, yeah...
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Re: mysterious force slows pioneer spacecraft

Postby gmalivuk » Wed Oct 06, 2010 1:30 pm UTC

Diadem wrote:At the price of merely one extra variable the entire concept of dark matter can be ditched
What about evidence from gravitational lensing?
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Re: mysterious force slows pioneer spacecraft

Postby SlyReaper » Wed Oct 06, 2010 1:44 pm UTC

Diadem wrote:The one problem with MOND is that it flat out contradicts GR. So, yeah...


Not to mention conservation of momentum (if I recall correctly), but there are refined theories (scalar tensor something vector whatnot) that correct for that.

gmalivuk wrote:
Diadem wrote:At the price of merely one extra variable the entire concept of dark matter can be ditched
What about evidence from gravitational lensing?


If my understanding is right (and that's a very very big if), gravitational lensing poses no contradiction to MOND.
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Re: mysterious force slows pioneer spacecraft

Postby Duban » Wed Oct 06, 2010 1:53 pm UTC

Diadem wrote:
The one problem with MOND is that it flat out contradicts GR. So, yeah...

GR == General Relativity?
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Re: mysterious force slows pioneer spacecraft

Postby Diadem » Wed Oct 06, 2010 2:51 pm UTC

Duban wrote:
Diadem wrote:
The one problem with MOND is that it flat out contradicts GR. So, yeah...

GR == General Relativity?

Yeah
GR = General Relativity
SR = Special Relativity
QM = Quantum Mechanics

That's the most important physical theories.
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Re: mysterious force slows pioneer spacecraft

Postby Paranoid__Android » Wed Oct 06, 2010 3:03 pm UTC

I read about this recently in a book, apparently everyone is still very confused.
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Re: mysterious force slows pioneer spacecraft

Postby SlyReaper » Wed Oct 06, 2010 8:24 pm UTC

I keep telling you, it's Odin expressing his displeasure at our sending pictures of naked Vitruvian Men into outer space.
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Re: mysterious force slows pioneer spacecraft

Postby Xeio » Wed Oct 06, 2010 9:46 pm UTC

Nah, when the gods were creating the solar system, they just got bored really fast and figured that nobody would ever leave, so they just threw up a fancy wallpaper for the rest. Now instead of fixing the problem they'll just make it impossible to leave.

Well, that's what would happen if I created the universe anyway... :P

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Re: mysterious force slows pioneer spacecraft

Postby frezik » Wed Oct 06, 2010 10:27 pm UTC

Diadem wrote:At the price of merely one extra variable the entire concept of dark matter can be ditched, which is a major gain in simplicity, so the theory is attractive.


I've never really bought the Occam's Razor argument for MOND. Where Dark Matter says there's a weird form of matter that doesn't interact with normal matter except by gravity, MOND wants to stick an extra variable in a long-standing and experimentally well-established equation. I think Occam slit his wrists on this one.
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Re: mysterious force slows pioneer spacecraft

Postby Gelsamel » Thu Oct 07, 2010 1:18 am UTC

frezik wrote:
Diadem wrote:At the price of merely one extra variable the entire concept of dark matter can be ditched, which is a major gain in simplicity, so the theory is attractive.


I've never really bought the Occam's Razor argument for MOND. Where Dark Matter says there's a weird form of matter that doesn't interact with normal matter except by gravity, MOND wants to stick an extra variable in a long-standing and experimentally well-established equation. I think Occam slit his wrists on this one.


An extra variables in a long-standing experimentally well established equation, as well as GR having to be changed or being wrong? I think I'll take a form of matter that doesn't interact with certain gauge bosons over that.
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Re: mysterious force slows pioneer spacecraft

Postby Soralin » Thu Oct 07, 2010 1:29 am UTC

SlyReaper wrote:If my understanding is right (and that's a very very big if), gravitational lensing poses no contradiction to MOND.

I don't think he's referring to the existence of gravitational lensing in general, but instead, stuff like http://en.wikipedia.org/wiki/Bullet_Cluster

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Re: mysterious force slows pioneer spacecraft

Postby Minchandre » Thu Oct 07, 2010 2:10 am UTC

Soralin wrote:
SlyReaper wrote:If my understanding is right (and that's a very very big if), gravitational lensing poses no contradiction to MOND.

I don't think he's referring to the existence of gravitational lensing in general, but instead, stuff like http://en.wikipedia.org/wiki/Bullet_Cluster


...But the Bullet Cluster doesn't require Dark Matter if you allow the theory that the galaxies are very cold (as might be the case with older galaxies)

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Re: mysterious force slows pioneer spacecraft

Postby meatyochre » Thu Oct 07, 2010 3:37 am UTC

I was under the impression that the only thing we know about dark matter is that something must exist to balance some important equation somewhere or other. Because there isn't enough matter to account for the amount of gravitational force observed. But there isn't any way to test it because it can't be seen (hence the "dark" part).

I am guessing the need for dark matter will go away once our tools of measurement and equations improve. It's just a placeholder for a theory, is it not? (my physics instruction is limited to 2 semesters so please don't be too harsh if this is a big dumbitude on my part)
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Re: mysterious force slows pioneer spacecraft

Postby frezik » Thu Oct 07, 2010 4:15 am UTC

meatyochre wrote:I am guessing the need for dark matter will go away once our tools of measurement and equations improve.


That's what MOND is in a nutshell--there's a variable in Newton's old equation for gravity that we couldn't measure before because it's only noticeable on really, really big scales. That gets rid of the need for Dark Matter, but as noted above, is modifying an old equation really any better, simplicity-wise?

One of these theories might be right, or maybe it'll end up like the old wave/particle theories of light, where there's a yet-unknown third answer that will blow everyone's mind. For now, there's nothing to discount either theory. Which is great, because what else would Physicists have to argue about in bars?
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Re: mysterious force slows pioneer spacecraft

Postby fjafjan » Thu Oct 07, 2010 8:05 am UTC

SummerGlauFan wrote:
fjafjan wrote:Considering the current theories about Dark Matter (and dark energy) the existence of a 'new force' or some such thing would be entirely on par. I mean at some point, hopefully, Dark Matter will be stop being "this thing we don't know what it is so we call it dark" and start being something.


I thought dark matter didn't interact with normal matter, with the exception of still generating gravity.

Right, but dark matter is basically just scientists saying "something is wrong. What if we invent "matter" that's spread out as to explain this? Let's call it Dark Matter because we can't imagine what else it would be.

Basically it's a theory that's going to fail and something better is going to replace it, but I have no idea what or when or how. I basically think of dark matter as a 'problem' with our current theories/measurements rather than a thing.
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Re: mysterious force slows pioneer spacecraft

Postby Carlington » Thu Oct 07, 2010 11:40 am UTC

So the position of the spacecraft, and therefore the speed and acceleration, were being measured by way of EM signals? Did we account for interference with the signal due to solar radiation? If so, did we consider that there could be a slight change in the magnitude of this interference due to the distance from the Sun? If the signal, travelling at c, presumably, was actually travelling at marginally above or below c for some part of its journey, wouldn't this affect our measurements?
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Re: mysterious force slows pioneer spacecraft

Postby gmalivuk » Thu Oct 07, 2010 11:52 am UTC

fjafjan wrote:Basically it's a theory that's going to fail and something better is going to replace it, but I have no idea what or when or how. I basically think of dark matter as a 'problem' with our current theories/measurements rather than a thing.
Except, there's increasing evidence that it actually is a thing.

Carlington (The Aussie) wrote:If the signal, travelling at c, presumably, was actually travelling at marginally above or below c for some part of its journey, wouldn't this affect our measurements?
How do you propose to make a signal travel marginally above the fastest possible speed?
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Re: mysterious force slows pioneer spacecraft

Postby Godskalken » Thu Oct 07, 2010 12:02 pm UTC

You guys are joking about this being due to an intervention by some god, but this is argument is in fact taken very seriously by some people. The people at conservapedia, who believe that all science must be flawed since it comes out of conspiring left-wing scientists (all scientists are leftist, by definition), have been paying a whole lot of attention to this so called "pioneer anomaly".

From http://conservapedia.com/Pioneer_anomaly :
creation scientist Dr. D. Russell Humphreys wrote:The only non-standard assumption I used was that the matter of the cosmos is limited in extent, with a fair amount of empty space beyond the matter—an assumption supported by the Bible. [...] The assumption I used violently contradicts the foundational assumption of the big bang, which says the universe has no centre and no edge. In that model, the fabric of space would not change. Consequently, the big bang model has been unable to explain the anomalous Pioneer acceleration.

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Re: mysterious force slows pioneer spacecraft

Postby Carlington » Thu Oct 07, 2010 12:30 pm UTC

Carlington (The Aussie) wrote:If the signal, travelling at c, presumably, was actually travelling at marginally above or below c for some part of its journey, wouldn't this affect our measurements?
How do you propose to make a signal travel marginally above the fastest possible speed?[/quote]

Suspension of disbelief?

Yeah, catastrophic thought failure on my part there. And below c would make it seem like it were too far away. Discount everything I have said here completely. I'm a crackpot.
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Re: mysterious force slows pioneer spacecraft

Postby Vieto » Thu Oct 07, 2010 12:40 pm UTC

creation scientist Dr. D. Russell Humphreys wrote:The only non-standard assumption I used was that the matter of the cosmos is limited in extent, with a fair amount of empty space beyond the matter—an assumption supported by the Bible. [...] The assumption I used violently contradicts the foundational assumption of the big bang, which says the universe has no centre and no edge. In that model, the fabric of space would not change. Consequently, the big bang model has been unable to explain the anomalous Pioneer acceleration.

It doesn't explain the dinosaurs either! Oh noes!

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Re: mysterious force slows pioneer spacecraft

Postby Diadem » Thu Oct 07, 2010 1:34 pm UTC

meatyochre wrote:I was under the impression that the only thing we know about dark matter is that something must exist to balance some important equation somewhere or other. Because there isn't enough matter to account for the amount of gravitational force observed. But there isn't any way to test it because it can't be seen (hence the "dark" part).

I am guessing the need for dark matter will go away once our tools of measurement and equations improve. It's just a placeholder for a theory, is it not? (my physics instruction is limited to 2 semesters so please don't be too harsh if this is a big dumbitude on my part)

Well, no, not entirely. The name 'dark matter' sounds very fancy. But the concept is not so alien. You're standing on a giant ball of dark matter. Yep. The earth is dark matter - it doesn't give off light you see. We know there are plenty of dark objects out there. Exoplanets, brown dwarves, neutron stars, black holes, etc, etc. The 'dark matter problem' is not that there's dark matter out there, it's that there's so much out there. To explain the observed rotation of galaxies (as well as a few other things) you need 5 times as much dark matter as ordinary matter, and you also need a rather peculiar distribution of it - it needs to be concentrated mainly in the halo of galaxies instead of the centre as most visible matter is.

We can't really see exoplanets or black holes or such things totalling up to that much mass. So people have been looking at more exotic explanations, such as new elementary particles. And then we're going deep into theoretical and speculative physics. But the concept of dark matter in itself is mundane enough.

Perhaps you were thinking of 'Dark Energy'? Because dark energy really is a placeholder name. If you take the most general possible form of the Einstein equations, which are the equations governing general relativity, you get a constant in there that wasn't needed before (Just as x^2 and x^2 + 2 are both valid solutions to the question 'what is the integral of 2x'. You have an extra constant that you can take whatever value you want without changing the problem). Everthing we saw was explained without it just fine. In itself that's nothing strange. Integration always yields extra constants all over the place. If you can't explain physically why they should not be zero, you should ignore them.

If we take this constant non-zero than the universe will expand faster than it ought. And, lo and behold, recent measurements do show that the universe is expanding faster than it ought. So suddenly putting this constant in makes sense. But we still do not have any idea what it could be. It's a pretty mathematical number, but what is it, physically? We have no idea. So we call it 'dark energy'.
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Re: mysterious force slows pioneer spacecraft

Postby Carlington » Thu Oct 07, 2010 2:16 pm UTC

I actually "get" dark energy now. Good grief, man, be a lecturer or some such. Your talent for explanation is incredible.
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Re: mysterious force slows pioneer spacecraft

Postby SummerGlauFan » Thu Oct 07, 2010 9:33 pm UTC

fjafjan wrote:
SummerGlauFan wrote:
fjafjan wrote:Considering the current theories about Dark Matter (and dark energy) the existence of a 'new force' or some such thing would be entirely on par. I mean at some point, hopefully, Dark Matter will be stop being "this thing we don't know what it is so we call it dark" and start being something.


I thought dark matter didn't interact with normal matter, with the exception of still generating gravity.

Right, but dark matter is basically just scientists saying "something is wrong. What if we invent "matter" that's spread out as to explain this? Let's call it Dark Matter because we can't imagine what else it would be.

Basically it's a theory that's going to fail and something better is going to replace it, but I have no idea what or when or how. I basically think of dark matter as a 'problem' with our current theories/measurements rather than a thing.


While I know some theories about dark matter involve such things as as-yet-unknown black holes, nuetron stars, etc, isn't it true that we have seen gravitational lensing and other direct evidence of an as-yet-unknown exotic form of dark matter? I remember reading somewhere of scientists seeing gravitational lensing on a large scale in areas outside of galaxies while whatever was causing them remained invisible (it didn't even block the light from the galaxies in question).

Spoilered for somewhat off-topic response to the stupidity of the Conservapedia writer:
Spoiler:
creation scientist Dr. D. Russell Humphreys wrote: The only non-standard assumption I used was that the matter of the cosmos is limited in extent, with a fair amount of empty space beyond the matter—an assumption supported by the Bible. [...] The assumption I used violently contradicts the foundational assumption of the big bang, which says the universe has no centre and no edge. In that model, the fabric of space would not change. Consequently, the big bang model has been unable to explain the anomalous Pioneer acceleration.

Ok, where do I start? First, even IF the universe is not infinite (and btw the Bible makes no statements that it isn't, so Bible Reading Fail) why would that account for Pioneer slowing down? If the universe had an "edge*" it would be beyond what we can currently see of the Universe, which is more than 14 billion light years away, very, very far away from the edge of our system where the Pioneer probe currently is.

Second, so what if the Big Bang can't explain it? It's not the Answer to Everything, it's just a theory on how the universe got started.

*Even if the universe wasn't infinite (and tests suggest it is, but you know you can't trust them there libral scientists) it likely would not have an edge but would almost certainly "bend back into itself;" i.e. you throw a baseball and billions of trillions of years later it smacks you in the back of the head.** Thus there would be even less "reason" for the Pioneer to slow down.

**This is what I have gotten from a rudimentary physics education combing high school physics classes with the Science channel and the Science forum on these boards, so take it with a grain of salt. It's still more reliable than that kook.
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Re: mysterious force slows pioneer spacecraft

Postby fjafjan » Thu Oct 07, 2010 9:58 pm UTC

gmalivuk wrote:
fjafjan wrote:Basically it's a theory that's going to fail and something better is going to replace it, but I have no idea what or when or how. I basically think of dark matter as a 'problem' with our current theories/measurements rather than a thing.
Except, there's increasing evidence that it actually is a thing.

Well please tell me, astronomy is a hobby of mine and while I hardly read "all the papers" I havn't heard anything. So yeah, citation required
I mean yes there is evidence that our current model is wrong, and this is increasing. Explaining it by magic matter that for no good reason is exactly where we need it to be is not what I call a good explanation.
"How come the ball landed over there when your theory predicted it would land here?"
"Well .. we have this 'dark force' that just happens to be .. how far away did it land you say? Well this big. Oh wow it happened to match. We don't really now where we have this dark force so you better try again and I can tell you". => Not predictive.

SummerGlauFan wrote:While I know some theories about dark matter involve such things as as-yet-unknown black holes, nuetron stars, etc, isn't it true that we have seen gravitational lensing and other direct evidence of an as-yet-unknown exotic form of dark matter? I remember reading somewhere of scientists seeing gravitational lensing on a large scale in areas outside of galaxies while whatever was causing them remained invisible (it didn't even block the light from the galaxies in question).

I don't think black holes or Neutron stars could explain dark matter, it's matter that's supposed to be evenly distributed right at the edge of galaxies, unless you can find explanation why there would be very evenly distributed black holes and/or neutron stars throughout the galaxy...
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Re: mysterious force slows pioneer spacecraft

Postby Kain » Fri Oct 08, 2010 3:51 am UTC

fjafjan wrote:
SummerGlauFan wrote:While I know some theories about dark matter involve such things as as-yet-unknown black holes, nuetron stars, etc, isn't it true that we have seen gravitational lensing and other direct evidence of an as-yet-unknown exotic form of dark matter? I remember reading somewhere of scientists seeing gravitational lensing on a large scale in areas outside of galaxies while whatever was causing them remained invisible (it didn't even block the light from the galaxies in question).

I don't think black holes or Neutron stars could explain dark matter, it's matter that's supposed to be evenly distributed right at the edge of galaxies, unless you can find explanation why there would be very evenly distributed black holes and/or neutron stars throughout the galaxy...


This here pretty much requires me to send you on a brief journey to the mystical land of wikipedia, for the articles on Massive Compact Halo Objects and on Weakly Interacting Massive Particles. I wish I could explain more, but I am still only an undergrad in Astro, and most of our courses have been on photometry, general sciences, stellar structures, etc, not the more theoretical stuff... :(
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Re: mysterious force slows pioneer spacecraft

Postby gmalivuk » Fri Oct 08, 2010 5:28 am UTC

fjafjan wrote:
gmalivuk wrote:
fjafjan wrote:Basically it's a theory that's going to fail and something better is going to replace it, but I have no idea what or when or how. I basically think of dark matter as a 'problem' with our current theories/measurements rather than a thing.
Except, there's increasing evidence that it actually is a thing.
Well please tell me, astronomy is a hobby of mine and while I hardly read "all the papers" I havn't heard anything.
Define "anything". A ridiculously quick search brought me to this post from the beginning of 2007 by Phil Plait. And I don't know about you, but I think actually being able to map the stuff strongly suggests something a bit more than your ridiculous story about making some stuff up out of whole cloth to explain just one narrow set of observations. There are multiple lines of evidence for it (which even a cursory perusal of the Wikipedia article will tell you), and so any anti-dark-matter theory would have to explain all of that without positing the existence of matter we can't see.
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