Dark matter really due to stars having some charge?

[PAllen]

Dark matter really due to stars having some charge??

I have an acquaintance who has a physics doctorate who argued the (to me) novel idea that dark matter doesn't really exist; that a plausible explanation of the observations suggesting it is that stars are sufficiently not exactly electrically neutral (and they deviate in both + and - direction) as to generate anomalous attraction, accounting for galactic stability.

At first I thought this idea had to be absurd on its face, but some quick research turned up that it is not necessarily well established how close to neutral stars are, and that plasma processes could maintain some deviation from neutrality for very long time periods. I am still very suspicious of this idea (this person has some other unusual ideas: based on his thesis from many years ago, he still insists that no realistic collapse process in GR could lead to a black hole; despite Penrose-Hawking results; and not relying on quantum arguments that do, indeed, suggest that actual black holes may not form).

What can people here say about whether and how such an explanation of galactic stability could be ruled out?

 

[DaveC426913]

I have an acquaintance who has a physics doctorate who argued the (to me) novel idea that dark matter doesn't really exist; that a plausible explanation of the observations suggesting it is that stars are sufficiently not exactly electrically neutral (and they deviate in both + and - direction) as to generate anomalous attraction, accounting for galactic stability.

At first I thought this idea had to be absurd on its face, but some quick research turned up that it is not necessarily well established how close to neutral stars are, and that plasma processes could maintain some deviation from neutrality for very long time periods. I am still very suspicious of this idea (this person has some other unusual ideas: based on his thesis from many years ago, he still insists that no realistic collapse process in GR could lead to a black hole; despite Penrose-Hawking results; and not relying on quantum arguments that do, indeed, suggest that actual black holes may not form).

What can people here say about whether and how such an explanation of galactic stability could be ruled out?

There are several independent types of observations of dark matter, not just the galactic rotation anomaly.

Have your friend look up the "bullet nebula".

 

[Andrew Mason]

There are several independent types of observations of dark matter, not just the galactic rotation anomaly.

Have your friend look up the "bullet nebula".

To be fair, these are not observations of dark matter. They are observations that are consistent with the presence of dark matter. The motion of the planets as measured in Ptolemy's time was consistent with Ptolemy's theory of nested spheres. But that does not mean the spheres were observed.

AM

 

[bcrowell]

This sounds like some variation on the electric universe kookery.

http://www.badastronomy.com/bad/misc/mccanney/index.html
http://www.tim-thompson.com/electric-sun.html

If the sun has a large electric charge, we should observe its effects on the positive and negative components of the solar wind.

 

[DaveC426913]

To be fair, these are not observations of dark matter. They are observations that are consistent with the presence of dark matter. The motion of the planets as measured in Ptolemy's time was consistent with Ptolemy's theory of nested spheres. But that does not mean the spheres were observed.

AM

True.

 

[Vanadium 50]

It does sound like electric universe kookery.

I don't think this is worth considering without at least a toy model of charged stars that quantitatively reproduced the observed dynamics. Once there is that, the next question is whether this is consistent with charge limits from the Stark effect in stellar spectra.

 

[twofish-quant]

I have an acquaintance who has a physics doctorate who argued the (to me) novel idea that dark matter doesn't really exist; that a plausible explanation of the observations suggesting it is that stars are sufficiently not exactly electrically neutral (and they deviate in both + and - direction) as to generate anomalous attraction, accounting for galactic stability.

Just because someone has a Ph.D. doesn't mean that they can't be a crackpot.

It is very, very hard to get an electrically charges object in space. Something with positive charges will quickly attract negative charges and end up neutral. Also something that is charged is very obvious from their spectrum.

At first I thought this idea had to be absurd on its face, but some quick research turned up that it is not necessarily well established how close to neutral stars are, and that plasma processes could maintain some deviation from neutrality for very long time periods.

It's well established that stars are neutral. Plasmas have all sorts of microscopic deviation from neutrality, but at large scales, they end up neutral.

What can people here say about whether and how such an explanation of galactic stability could be ruled out?

The problem is that a configuration of electrically charged objects is not very stable. If you have a positive charge and a negative charge they will very, very quickly stick together.

 

[Chalnoth]

I have an acquaintance who has a physics doctorate who argued the (to me) novel idea that dark matter doesn't really exist; that a plausible explanation of the observations suggesting it is that stars are sufficiently not exactly electrically neutral (and they deviate in both + and - direction) as to generate anomalous attraction, accounting for galactic stability.

At first I thought this idea had to be absurd on its face, but some quick research turned up that it is not necessarily well established how close to neutral stars are, and that plasma processes could maintain some deviation from neutrality for very long time periods. I am still very suspicious of this idea (this person has some other unusual ideas: based on his thesis from many years ago, he still insists that no realistic collapse process in GR could lead to a black hole; despite Penrose-Hawking results; and not relying on quantum arguments that do, indeed, suggest that actual black holes may not form).

What can people here say about whether and how such an explanation of galactic stability could be ruled out?

Because electrons are lighter than protons, you can actually calculate, if you know the surface temperature, roughly what charge of the star actually is. I can guarantee that it won't be significant (because the electromagnetic force is some 10^40 or so times stronger than gravity).

That said, even if there was some electrostatic repulsion between stars, the fact of the matter is that the electric force has the exact same distance dependence as gravity, so that it wouldn't look like dark matter, but instead just a slight change in the gravitational constant G.

 

[BillSaltLake]

The statistics of the extra force vs. distance from center of galaxy is a problem. If the inner regions of a galaxy have stars that are a random mix of + and - excess charge, a star in the outer region will experience much less force than porportional to the number of stars inside.

 

[Chalnoth]

The statistics of the extra force vs. distance from center of galaxy is a problem. If the inner regions of a galaxy have stars that are a random mix of + and - excess charge, a star in the outer region will experience much less force than porportional to the number of stars inside.

Sure, but the strength of the electromagnetic force prevents this from happening to any significant degree.

 

[BillSaltLake]

Sure, but the strength of the electromagnetic force prevents this from happening to any significant degree.

Suppose we make a simple model in which each star has a small excess charge +Q or -Q, and the distribution is random like a coin flip. If two adjacent stars experience an additional force of kF_g where k<<1 and F_g is the typical gravitational attraction between 2 adjacent stars, then the extra force that a star will experience if it is in the outer part of the galaxy (orbiting N stars) is ~ (N)^-1/2kF_G, where F_G is the total gravitational pull of the N stars. This is weaker by factor (N)^-1/2.

 

[Drakkith]

Ok? What does your equations say? Nothing right now, as they don't have any numbers input into the variables. Put some numbers into that and get back to us.

 

[Chalnoth]

Suppose we make a simple model in which each star has a small excess charge +Q or -Q, and the distribution is random like a coin flip. If two adjacent stars experience an additional force of kF_g where k<<1 and F_g is the typical gravitational attraction between 2 adjacent stars, then the extra force that a star will experience if it is in the outer part of the galaxy (orbiting N stars) is ~ (N)^-1/2kF_G, where F_G is the total gravitational pull of the N stars. This is weaker by factor (N)^-1/2.

Yes, I am aware that this would cause a suppression of the force. My point is that EM is so strong that it simply will not allow such charge discrepancies to build up in the first place. I'd also be highly surprised if you could get a class of rotation curves out of this that looks like observed rotation curves.

And, of course, this idea cannot explain the signature of dark matter we see in the CMB.

P.S. Oh, and one other thing: stars are sitting in a diffuse plasma (the interstellar medium). Plasmas are conductive. If significant charges did start to build up between stars, we'd simply have current flow between them, long before the force between the stars became noticeable.

 

[PAllen]

Thanks for all the discussion so far (and links, and hints to research Stark effect, etc.). It has been very helpful, and as I expected. It is not easy for someone with self-taught, uneven background to effectively debate someone with a Ph.D in the subject matter.

 

[BillSaltLake]

The conductivity of the plasma will of course reduce the charge effect. Even if a negative charged star (for example) blew away all the plasma in its vicinity so plasma couldn't conduct + charge directly to the star, the plasma would nonetheless surround the star with + charge, effectively shielding it from creating significant long-range electrostatic force. Also, the fact that the N^-1/2 effect doesn't match the rotation curves was my point.

 

[AstrophysicsX]

There are many theories that try to explain what dark matter really is. Have we even observed dark matter yet?

 

[Chalnoth]

There are many theories that try to explain what dark matter really is. Have we even observed dark matter yet?

We have not yet directly observed the particles that make up dark matter. However, our cosmological observations to date provide extremely strong support for the idea that dark matter is some sort of massive, weakly-interacting particle. Furthermore, the astrophysical properties of dark matter actually require it to be pretty hard to detect on Earth, so it isn't necessarily a problem at all that we haven't seen it in the lab yet.

 

[AstrophysicsX]

What kind of properties have we predicted?

 

[BillSaltLake]

I think DM acts something like iron marbles ~1cm diameter distributed fairly uniformly with one every ~billion cubic miles, except that iron marbles might be a little too interactive to match DM properties well.

 

[Manojg]

What about repulsive gravitational between matter and anti-matter?

Universe is expanding, may be due to repulsive force between matter and anti-matter. We do not see anti-matter because it is in other part of the expanding universe.

Although, it contradicts the general relativity but who knows until it is measured.(gravitational force between matter and anti-matter)

Just a thought.

 

[BillSaltLake]

I believe that decades ago, the first antimatter experiments were done in which the antimatter accelerated downward at the same rate as matter.

 

[DaveC426913]

Yes, gravitationally, antimatter behaves exactly the same as matter. Gravity is a purely attractive force between any form of matter (including antimatter); there is no repulsive counterpart.

 

[phinds]

There are many theories that try to explain what dark matter really is. Have we even observed dark matter yet?

Observations have been made which show conclusively that something exists that has gravitational effect but does not emit or reflect any known radiation. We call this "dark matter" because we don't know what it is, so no, it has never been observed directly but its presence and its effects are not questioned. As you say, WHAT it is is just conjecture at present.

 

[PAllen]

I think DM acts something like iron marbles ~1cm diameter distributed fairly uniformly with one every ~billion cubic miles, except that iron marbles might be a little too interactive to match DM properties well.

So we can say, early in the expansion of the universe, God lost his marbles, therefore we have dark matter.

 

[BillSaltLake]

Yep, maybe something like that happened, although a cloud of these marbles ~10 billion LY thick would be more opaque than what is observed. Maybe they're much bigger marbles (which would block less light than small marbles, given the same average density of "Dark Matter").

 

[George Jones]

I believe that decades ago, the first antimatter experiments were done in which the antimatter accelerated downward at the same rate as matter.

I don't think that this has been directly tested, and it doesn't look like this will happen in the near future.

http://meetings.aps.org/Meeting/APR10/Event/115638

 

[BillSaltLake]

Sorry. I thought it had been done with real positron beams. Turns out it's only been done indirectly with virtual positrons (mixed with virtual electrons).

 

[Chalnoth]

Yep, maybe something like that happened, although a cloud of these marbles ~10 billion LY thick would be more opaque than what is observed. Maybe they're much bigger marbles (which would block less light than small marbles, given the same average density of "Dark Matter").

Well, yes, this idea is known as a "Massive astrophysical compact halo object", or MACHO. The problem is that the CMB pretty conclusively rules this idea out, because such objects couldn't have existed in the hot plasma of our early universe, and yet we see the signature of the dark matter in the CMB clear as day.