## mysterious force slows pioneer spacecraft

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Technical Ben
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### Re: mysterious force slows pioneer spacecraft

Cool that's the same Phil that does (or use to do more so) "Bad Astronomy" to shoot down crack pots and plain wrong people*.
Also, dark matter/energy are not "magic explanations". They are mealy names for an observation. If I say air exists in the gap between solid objects, I'm giving a definition, to the gap between solid objects. You cannot see the air, but there is defiantly something there.
Dark matter and dark energy have been observed and defined. Can we explain them yet? No, but we can "see" them and their effects.

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Wnderer
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### Re: mysterious force slows pioneer spacecraft

Hey this works just like my inflated balloon theory of gravity. You know those rubber sheet gravity models, where you put a big ball in the middle and it warps the sheet. Make the rubber sheet a huge balloon, so when the ball stretches the sheet the pressure in the balloon causes the rubber sheet to expand elsewhere. If two objects are close enough together pressure the bubble increase their attraction. If they are far enough apart the pressure bubble repels them. Now where's my Nobel Prize?

Me321
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### Re: mysterious force slows pioneer spacecraft

Wnderer wrote:Hey this works just like my inflated balloon theory of gravity. You know those rubber sheet gravity models, where you put a big ball in the middle and it warps the sheet. Make the rubber sheet a huge balloon, so when the ball stretches the sheet the pressure in the balloon causes the rubber sheet to expand elsewhere. If two objects are close enough together pressure the bubble increase their attraction. If they are far enough apart the pressure bubble repels them. Now where's my Nobel Prize?

You better write a paper on this before someone else take the idea.

Duban
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### Re: mysterious force slows pioneer spacecraft

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).

Spoilered for somewhat off-topic response to the stupidity of the Conservapedia writer:

Yeah I'm pretty dark matter is supposed to imply an exotic form of matter. The earth isn't "Dark" nor are neutron stars. Every single atom on this planet has an electromagnetic charge. They affect electromagnetic waves as they vibrate, absorb, and reflect light. Even neutrons can be measured as they are made of components that interact through the electromagnetic force.

"Dark Matter" still has mass and corresponding gravity but isn't affected by EM forces. It doesn't block light, create light, and it doesn't even interact with normal matter normally. The reason your hand doesn't pass through the keyboard you're typing on is the electromagnetic force. Of course it's this property that makes it so illusive. We can't see it, we can't touch it, we can't even see it interacting with normal matter. We just see gravity that can't be explained by normal matter.

At least that's my understanding of Dark Matter.
Last edited by Duban on Sun Oct 10, 2010 7:38 pm UTC, edited 1 time in total.
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BlackSails
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### Re: mysterious force slows pioneer spacecraft

Duban wrote:We can't see it, we can't touch it, we can't even see it interacting with normal matter.

Actually, there are a number of experiments running right now whose goal is exactly that.

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### Re: mysterious force slows pioneer spacecraft

Duban wrote:Yeah I'm pretty dark matter is supposed to be an exotic form of matter. The earth isn't "Dark" nor are neutron stars. Every single atom on this planet has an electromagnetic charge. They affect electromagnetic waves as they vibrate, absorb, and reflect light. Even neutrons can be measured as they are made of components that interact through the electromagnetic force.

Why do so many non-physicists always seem to think they know more about physics than the actual physicists? You know, even typing in 'dark matter' in wikipedia would immidiately show that you are wrong.

Like I said in my previous post. Dark matter is any matter that gives off no or very little electromagnetic radiation (eg: light). Exoplanets, neutron stars, black holes, they all count. It's just that we can not explain the amount of dark matter needed in terms of these, there must be much more dark matter than can just be explained by baronic (ie: made up out of atoms) dark matter. So there must be a lot of non-baryonic dark matter. These are not necessarily exotic. Neutrinos for example are one component of the dark matter content of the universe. But neutrinos do not add up to enough mass either. So we probably need exotic forms of matter to explain the amount of dark matter that we think is out there. But that is not what the term 'dark matter' means.
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Spambot5546
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### Re: mysterious force slows pioneer spacecraft

Duban wrote:Yeah I'm pretty dark matter is supposed to be an exotic form of matter. The earth isn't "Dark" nor are neutron stars. Every single atom on this planet has an electromagnetic charge. They affect electromagnetic waves as they vibrate, absorb, and reflect light. Even neutrons can be measured as they are made of components that interact through the electromagnetic force.

Why do so many non-physicists always seem to think they know more about physics than the actual physicists? You know, even typing in 'dark matter' in wikipedia would immidiately show that you are wrong.

Like I said in my previous post. Dark matter is any matter that gives off no or very little electromagnetic radiation (eg: light). Exoplanets, neutron stars, black holes, they all count. It's just that we can not explain the amount of dark matter needed in terms of these, there must be much more dark matter than can just be explained by baronic (ie: made up out of atoms) dark matter. So there must be a lot of non-baryonic dark matter. These are not necessarily exotic. Neutrinos for example are one component of the dark matter content of the universe. But neutrinos do not add up to enough mass either. So we probably need exotic forms of matter to explain the amount of dark matter that we think is out there. But that is not what the term 'dark matter' means.

You're technically correct, but in the context it's pretty clear we're talking about non-baryonic dark matter, which is believed (according to that same wikipedia article) to make up the vast majority of the universe's dark matter. Seems a little over-the-top to jump down someone's throat over a slightly improper use of terminology, especially since when most people refer to dark matter they refer to it as distinct from normal matter, so it's no surprise the layman would conflate the two.
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elite4koga
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### Re: mysterious force slows pioneer spacecraft

How does dark matter explain the acceleration towards the sun (which is very small, so to those people suggesting that god / odin etc. are doing it to prevent us from reaching the wallpaper at the edge of the solar system: this force makes it fractionally harder to move away from the sun, doesn't prevent travel through deep space). People seem to have gone off topic from my original question is all. Have tests been done to see if this force acts to oppose motion like friction or is attractive like gravity? Also, conservapedia will rot your brain, it is a website devoted to opposing logical thinking and claiming science is biased (when by definition it is unbiased). Spock does not approve.

Samsoneffect
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### Re: mysterious force slows pioneer spacecraft

For fjafjan - In addition to gmal's post at the end of the first page with the link to Phil Plait's post, here is a post by Ethan Siegel explaining how he was convinced of Dark Matter over MOND, and how the dark matter model outperforms MOND in other areas like large-scale structure and galaxy cluster formation.
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SummerGlauFan
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### Re: mysterious force slows pioneer spacecraft

elite4koga wrote:How does dark matter explain the acceleration towards the sun (which is very small, so to those people suggesting that god / odin etc. are doing it to prevent us from reaching the wallpaper at the edge of the solar system: this force makes it fractionally harder to move away from the sun, doesn't prevent travel through deep space).

I simply think Dark Matter was proposed as a candidate for the slowing, possibly due to it's ability to generate gravity.

elite4loga wrote:People seem to have gone off topic from my original question is all. Have tests been done to see if this force acts to oppose motion like friction or is attractive like gravity?

Considering this is a newly-discovered phenomenon located outside our solar system, I doubt much in the way of testing has been done.

Although, this has gotten me thinking. Could pioneer simply be decelerating due to the sun's gravity? I don't think it's far enough away to be unaffected by the gravity well (there are comets further out than it, I believe). Or is the slowing too much to be related to the sun's gravitational pull?
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elite4koga
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### Re: mysterious force slows pioneer spacecraft

I simply think Dark Matter was proposed as a candidate for the slowing, possibly due to it's ability to generate gravity.

but having gravity doesn't explain why the acceleration is in the direction of the sun

Although, this has gotten me thinking. Could pioneer simply be decelerating due to the sun's gravity? I don't think it's far enough away to be unaffected by the gravity well (there are comets further out than it, I believe). Or is the slowing too much to be related to the sun's gravitational pull?

If you read the article you would know it says that the force of gravity was ruled out. the sun's gravity still affects objects in deep space but it is too weak to account for the force slowing pioneer. Also gravity decreases with distance and this force is constant so stray comets wont solve it either. Is it possible deep space is more dense because it is not stretched out by the suns gravity. I'm thinking like some sort of deep space resistance force similar to air resistance in effect.

BlackSails
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### Re: mysterious force slows pioneer spacecraft

elite4koga wrote:
I simply think Dark Matter was proposed as a candidate for the slowing, possibly due to it's ability to generate gravity.

but having gravity doesn't explain why the acceleration is in the direction of the sun

The sun could be surrounded by a dark matter halo, making its actual mass a tiny bit more than we think.

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### Re: mysterious force slows pioneer spacecraft

BlackSails wrote:
elite4koga wrote:
I simply think Dark Matter was proposed as a candidate for the slowing, possibly due to it's ability to generate gravity.
but having gravity doesn't explain why the acceleration is in the direction of the sun
The sun could be surrounded by a dark matter halo, making its actual mass a tiny bit more than we think.
Shouldn't we be able to detect that by way of the effects on planetary orbits, though? Unless you're suggesting a sort of spherical shell at some distance to the sun, outside the orbits of the planets, in which case Pioneer would have had anomalous acceleration outwards as it approached the shell, nothing much as it passed through, and now the unexplained force towards the sun.
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### Re: mysterious force slows pioneer spacecraft

Spambot5546 wrote:Seems a little over-the-top to jump down someone's throat over a slightly improper use of terminology

I didn't jump at1 his throat over proper use of terminology. I jumped at his throat because he insisted on it despite it being pointed out earlier in this threat that that terminology is wrong. Besides it's not entirely a matter of terminology either. While baronic sources of dark matter, such as black holes or brown dwarfs (collectively named MACHOs), look unlikely now, they were taken very seriously only a few years ago, and they haven't been entirely ruled out yet either. Also something like neutrinos can easily make up about 10% of dark matter, and again, measurements ruling them out as the major contribution are recent and not entirely certain yet. So it is not merely terminology.

1 The mental picture of jumping 'down' someone's throat is somewhat disturbing

elite4koga wrote:How does dark matter explain the acceleration towards the sun

It doesn't. The hypothesis of dark matter and the pioneer anomaly are unrelated. There is as of yet no explanation of the pioneer anomaly.

SummerGlauFan wrote:Although, this has gotten me thinking. Could pioneer simply be decelerating due to the sun's gravity? I don't think it's far enough away to be unaffected by the gravity well (there are comets further out than it, I believe). Or is the slowing too much to be related to the sun's gravitational pull?

Well, of course it's slowing due to the sun's gravitational pull. The puzzle is not that it is slowing, the puzzle is that it is slowing too much. They have taken into account the sun, all the other planets, even nearby stars, and it's still slowing too much. That's the anomaly. There's dozens of other sources that have been considered and rejected. Read up on it, it's an interesting story.

In all honesty, I have to wonder about your question. This is an effect that has been puzzling physicists for decades. You really think thousands of scientists would forget about something so obvious as the sun for so long?

BlackSails wrote:The sun could be surrounded by a dark matter halo, making its actual mass a tiny bit more than we think.

No. If it was, then this would show up in the orbits of all the planets as well, which it doesn't.
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Vaniver
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### Re: mysterious force slows pioneer spacecraft

I feel this image from the "dark matter" explanation needs to be reposted:

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ConMan
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### Re: mysterious force slows pioneer spacecraft

PhoenixEnigma wrote:Shouldn't we be able to detect that by way of the effects on planetary orbits, though? Unless you're suggesting a sort of spherical shell at some distance to the sun, outside the orbits of the planets, in which case Pioneer would have had anomalous acceleration outwards as it approached the shell, nothing much as it passed through, and now the unexplained force towards the sun.

Hmm. I'm not sure how well Gauss' Law extends to GR, but under Newtonian gravitation the gravitational field around a spherically symmetrical system is proportional to the mass inside the surrounding sphere at that radius - meaning that inside a spherical shell the gravitational pull is zero, and outside the shell it's the same as if the mass of the shell were concentrated at the centre.
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Duban
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### Re: mysterious force slows pioneer spacecraft

ConMan wrote:Hmm. I'm not sure how well Gauss' Law extends to GR, but under Newtonian gravitation the gravitational field around a spherically symmetrical system is proportional to the mass inside the surrounding sphere at that radius - meaning that inside a spherical shell the gravitational pull is zero, and outside the shell it's the same as if the mass of the shell were concentrated at the centre.

nm, i misunderstood what you were saying.
Last edited by Duban on Mon Oct 11, 2010 3:52 am UTC, edited 1 time in total.
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Vaniver
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### Re: mysterious force slows pioneer spacecraft

Duban wrote:That assumes the location you're measuring gravity in is outside the sphere of matter. For an object inside the sphere of matter the mass outside of your section of the sphere is going to pull you back out. Let’s say you were in the middle of the earth, would gravity still pull you to the center? No, the force would pull you in all directions equally because the mass of the earth is spread in all directions equally.
This description doesn't sound right.

If the Earth were a hollow shell of uniform density, and you were anywhere inside that shell, there would not be a gravitational force on you. If the Earth were a full sphere whose density depended only on radius, and you were anywhere inside that sphere, the gravitational force on you would point towards the center of the Earth, and would depend only on the mass closer to the center than your position.

You can find a description of both situations here. I suspect the results are not materially different in GR, but do not know for sure.
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SummerGlauFan
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### Re: mysterious force slows pioneer spacecraft

elite4koga wrote:but having gravity doesn't explain why the acceleration is in the direction of the sun

Poppycock. A difficult-to-detect mass generating gravity would only slow down the probe if the probe were headed away from it; i.e., it could be in the direction of the Sun. If the source was not pulling in the direction of the Sun, we would see the probe being pulled in that general direction.

elite4koga wrote:
Although, this has gotten me thinking. Could pioneer simply be decelerating due to the sun's gravity? I don't think it's far enough away to be unaffected by the gravity well (there are comets further out than it, I believe). Or is the slowing too much to be related to the sun's gravitational pull?

If you read the article you would know it says that the force of gravity was ruled out. the sun's gravity still affects objects in deep space but it is too weak to account for the force slowing pioneer. Also gravity decreases with distance and this force is constant so stray comets wont solve it either. Is it possible deep space is more dense because it is not stretched out by the suns gravity. I'm thinking like some sort of deep space resistance force similar to air resistance in effect.

Sorry, I forgot about that part of the article (this was posted awhile ago, after all).

In all honesty, I have to wonder about your question. This is an effect that has been puzzling physicists for decades. You really think thousands of scientists would forget about something so obvious as the sun for so long?

You'd be surprised how often that happens, actually. It's a fair question, but more reading has cleared this up.
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### Re: mysterious force slows pioneer spacecraft

PhoenixEnigma wrote:Unless you're suggesting a sort of spherical shell at some distance to the sun, outside the orbits of the planets, in which case Pioneer would have had anomalous acceleration outwards as it approached the shell, nothing much as it passed through, and now the unexplained force towards the sun.
No, there'd be nothing at all until after it passed through. (As others have already said, there'd be zero gravitational effect from a spherically symmetric distribution of matter surrounding us.)
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### Re: mysterious force slows pioneer spacecraft

gmalivuk wrote:
PhoenixEnigma wrote:Unless you're suggesting a sort of spherical shell at some distance to the sun, outside the orbits of the planets, in which case Pioneer would have had anomalous acceleration outwards as it approached the shell, nothing much as it passed through, and now the unexplained force towards the sun.
No, there'd be nothing at all until after it passed through. (As others have already said, there'd be zero gravitational effect from a spherically symmetric distribution of matter surrounding us.)
Yeah, physics fail day for me here.

We can still determine that any shell would need to lie either inside mercury's orbit (and be meaningless to this discussion), or outside whatever the most distant thing orbiting the sun that we've made highly accurate studies of. If it were, say, between Jupiter and Saturn, I'd imagine we'd have noticed the effects of an effectively more massive Sun than anticipated on the orbits of the outer planets.

Of course, it's not like we haven't seen strange anomalies closer to home, either, so I guess it is still possible.
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