Dark matter and Dark energy

[sol invictus]

They will not be coming down any time soon, though he did admit if you go with the long view, gravity will bring them all back down to earth. Not keep them in orbit.

That's probably true, but not because of gravity alone (at least if we ignore general relativity). If you had two masses orbiting each other, and no non-gravitational forces acting, they would orbit forever. In order for the satellite to come back to earth you need some other force - either a third gravitating body or some kind of friction (maybe due to traces of atmosphere).

 

[DHamilton]

Uh, no. You're simply wrong. The fact that there is an additional Lorentz force doesn't make Coulomb attraction/repulsion go away.

I'm not simply wrong. You're simply delusional or absurdly uninformed about real data with respect to the existence of Coulombic forces between fundamental charged particles. You're operating not from data but from textbooks that teach about that which has never been observed to be true.

Oh, but Coulomb repulsion still most certainly applies. Consider electrons traveling in a copper wire. In the frame of the copper nuclei, the electrons still experience Coulomb repulsion, but they ALSO experience a Lorentz force from the magnetic field they generate. That additional force doesn't mean that the Coulomb repulsion is any less real. And if you look at the reference frame in which the electrons are stationary (no Lorentz force), you'll find that the positively charged nuclei have become Lorenz-contracted. The electrons still experience Coulomb repulsion from each other, but in their reference frame, the protons have a higher charge density, and so the Coulomb attraction of the wire becomes larger than the Coulomb repulsion of other electrons.

The problem here is that you don't know the difference between what has been observed and measured with respect to that which is purely theoretical and as such it is not possible to have a rational conversation with you.

You can calculate the force in either a stationary or a moving reference frame. The components (Coulomb repulsion and Lorentz force attraction) vary with speed, but the Coulomb repulsion never goes away - in fact, it will increase if they're side-by-side, because the electric field of a single moving charge gets compressed along the direction of motion. The total force between two like charges travelling parallel is therefore ALWAYS repulsive. I've DONE the calculation, on this very message board in fact. I suggest you check it out:
http://www.internationalskeptics.com/forums/showthread.php?postid=2472242#post2472242

You need to pay careful attention here... your calculations do not constitute either physical fact nor data. GIGO.

Uh, no. Dig through those calculations I did. If you can understand them, then maybe we can talk. But right now, what you're saying isn't even coherent.

How ridiculous is your contrived condescending 'Uh, no.' Do you even have a clue? It seems not.

It has been my experience that "the Truth"^TM is rarely actually true.

Now please ... carefully apply that 'experience' to your own brand of calculated 'Truth'.

 

[DHamilton]

.
Like two people sitting still on a moving train.

Amazing.. someone is actually paying attention... yes... so a single charged particle sitting still in your reference frame will not have emerging from its location ∇ X H vector fields that would be related to its motion because in your frame there is no ∂E/∂t (change of E with respect to change in time)

But in the rest frames of very many particles in the universe there would be. And it is through the intersection of the vector field that produce the conditions that dictate the motions of the particles...

DHamiltion

 

[Belz...]

You're displaying the properties of a tendiously dense person.

Yes, and you're displaying the properties of a condescending prick.

First, your question was how did I know these things... and so I answered that question and showed you the path that I used to discover these things...

The "path" ? What you said, basically, is that you thought it over and over and over and found an answer completely within the realm of your subjective mind. How is that rational ?

My question "how do YOU know these things" was meant to mean "how do YOU know these things and THEY don't ?", so I clarified it later on.

then you modified the question to asked how come these "brainy scientists" don't know all this and I answered that question also but it seems that you simply refuse to read or grasp the response.

Then explain it to me in a way that even a "tendiously" dense person could understand.

People who are locked into a mode of thinking that there is a an absolute spatial frame that particles can be at rest with respect to can't possible get this. That is even likely why when I answer the question you still are unaware that I did answer your question. ... and I'm not arguing... I'm making some claims... you need to keep up... and right now you've not showed that you can.

That's because making claims is one thing, but showing that you know what you're talking about is another.

I see no reason to think that the scientific community is "locked" into a mode of thinking that is incompatible with reality until you show us evidence that you are correct and that they are wrong.

You could gain worldwide fame this way, and with all the publicity and money you'd make, you could fund whatever charity you prefer.

So, impress me.

 

[Belz...]

Just a question, Hamilton: I assume you have a PhD or something similar. What's your field ?

 

[robinson]

That's probably true, but not because of gravity alone (at least if we ignore general relativity).

You may be confused. All satellites in orbit will return to earth, none of them are going to orbit forever. Gravity is pulling them back down. As I said, the timeline may seem very long to us, but to the Earth's sense of time, (if there were such a thing), they are all just object sent up very high, and they are all on their way back down.

Gravity doesn't produce an orbit, it causes things to fall. Nothing we have sent up is going to stay in orbit. If it isn't on it's way elsewhere, it is on its way back down.

 

[sol invictus]

Gravity doesn't produce an orbit, it causes things to fall. Nothing we have sent up is going to stay in orbit. If it isn't on it's way elsewhere, it is on its way back down.

OK, that's what I thought you were saying. You're incorrect.

An inverse square law allows stable elliptical orbits. Stable means they don't change over time - each revolution is identical to the one before. For a satellite in such an orbit to fall to earth, some force other than Newtonian gravity must act on it.

Of course in reality gravity does not quite obey an inverse square law even for the ideal two-body problem and there so there are no truly stable orbits, but let's stick with Newton for now.

 

[Belz...]

Gravity doesn't produce an orbit, it causes things to fall.

No, gravity DOES produce an orbit, unless you have some other mechanism that can do that. Objects can be "captured" into orbit by gravity alone.

Nothing we have sent up is going to stay in orbit. If it isn't on it's way elsewhere, it is on its way back down.

Actually, orbits can also become larger and larger untile something reaches escapes velocity.

 

[ben m]

You may be confused. All satellites in orbit will return to earth, none of them are going to orbit forever. Gravity is pulling them back down. As I said, the timeline may seem very long to us, but to the Earth's sense of time, (if there were such a thing), they are all just object sent up very high, and they are all on their way back down.

Gravity doesn't produce an orbit, it causes things to fall. Nothing we have sent up is going to stay in orbit. If it isn't on it's way elsewhere, it is on its way back down.

Sorry, Robinson, you're making a very common mistake. Gravity exerts a force which makes objects accelerate towards one another. Due to conservation of momentum, though, it does not result in things simply "falling down", it results in absolutely stable elliptical orbits. (Remember that a circle is a special case of an ellipse, and thus a perfectly reasonable orbit shape.) When you drop a hammer onto your foot, what you're really doing is launching the hammer onto a highly-eccentric elliptical orbit "around" the earth---but your foot gets in the way. This is totally standard undergrad-level physics; see Halliday, Resnick, & Walker for an outline, or Marion and Thornton for some very general proofs.

Satellites can migrate away from perfect orbits due to effects in addition to two-body gravity: friction with the Earth's atmosphere, additional gravitational pulls from the Moon, radiation pressure from the Sun, etc.

And in General Relativity, orbiting bodies lose a little energy through gravitational radiation, but I suspect that this isn't what you're talking about.

 

[Cuddles]

A pair of charge particles that are at rest with respect to each other are prosecuting parallel paths with respect to the motion of many other particles in the universe. Of course, if your brain is locked into the concept of an absolute space... which is the case with most people...then you and other people, including those 'brainy' scientists you mention wouldn't think of it.

Of course, those brainy scientists thought of that well over a century ago, and that is in fact the foundation of relativity. Unfortunately for you, it doesn't have the consequences you imagine.

Just a question, Hamilton: I assume you have a PhD or something similar. What's your field ?

It's generally a little tricky for someone who can't understand basic GCSE physics to get a PhD.

 

[Ziggurat]

You may be confused. All satellites in orbit will return to earth, none of them are going to orbit forever.

That's because (as hinted in previous answers) gravity is not the only force involved. Even in orbit, there is in fact still a slight air resistance. It's VERY small for something in high earth orbit, but it's far from negligible in low earth orbit.

 

[Reality Check]

All satellites in orbit will return to earth, none of them are going to orbit forever. Gravity is pulling them back down.

Robinson, another way to look at this is to remember that the planets are satellites of the sun. Over 4 billion years and gravity has not pulled us into the sun yet !

 

[Cuddles]

OK, forget all the nonsense and lets get back to the subjects of dark matter and energy. Ladies and gentlemen, I bring you possibly the funniest article ever to grace the pages of New Scientist. Simulations have shown that many MOND theories, including the most popular one and the many other theories based on the same mathematics, have the rather serious problem that black holes would pop up all over the place all the time. Since the Earth still exists, it's a fair bet that these theories aren't correct. However, all is not lost, since one HongSheng Zhao has a solution.

Not so amusing so far, but wait for the punchline:

He and his colleagues have constructed a MOND theory based on a "dark fluid" made up of dark matter and dark energy

Yes, that's right. In order to support MOND, the whole point of which is to eliminate the need for dark matter and energy, they do in fact have to introduce both dark matter and energy. If there were any questions remaining about the viability of MOND, I think this pretty much answers them.

 

[sol invictus]

Yes, that's right. In order to support MOND, the whole point of which is to eliminate the need for dark matter and energy, they do in fact have to introduce both dark matter and energy. If there were any questions remaining about the viability of MOND, I think this pretty much answers them.

MOND never explained dark energy - only dark matter. And of the effects caused by DM, it only explained rotation curves (although in fairness it did a very good job with those - better than DM, really). It was never a complete theory - more like an ansatz - and so you couldn't really apply it to things like acoustic peaks in the CMB spectrum.

And it was already ruled out experimentally by the bullet cluster observation. When that came along last year the MONDies proposed that well, maybe there was some DM around, but also some MONDiness! It's a great example of how unscientific scientists can be. Personally, I actually think that's a good thing, most of the time. Who knows - maybe they're actually right! Since no rational person thinks that's possible, I'm glad there are some irrational people around to keep working on it.

 

[Reality Check]

The following 2 links (probably already in this thread somewhere) describe observational proof of the existence of dark matter.
Separation of dark matter and galaxies in the IE 0657-56 galactic cluster
A dark matter smoke ring

 

[edd]

And it was already ruled out experimentally by the bullet cluster observation. When that came along last year the MONDies proposed that well, maybe there was some DM around, but also some MONDiness! It's a great example of how unscientific scientists can be. Personally, I actually think that's a good thing, most of the time. Who knows - maybe they're actually right! Since no rational person thinks that's possible, I'm glad there are some irrational people around to keep working on it.

I'm not sure that's entirely fair. The claim I remember was that you could still fit it if you had a fairly heavy neutrino - basically the sort of mass that you might expect to be ruled in or out in the not too distant future. To some extent that's not an unreasonable standpoint to take - allowing for parameters for particles we know exist to take on some value that's not been ruled out in order to explain the situation.

And MOND and its relations remain excellent scientific theories from the perspective of them being easily falsifiable. Well, maybe not classical MOND as, since you note, there's an awful lot of cosmology you can't do with it, but its relativistic relations, certainly.

 

[sol invictus]

I'm not sure that's entirely fair. The claim I remember was that you could still fit it if you had a fairly heavy neutrino - basically the sort of mass that you might expect to be ruled in or out in the not too distant future. To some extent that's not an unreasonable standpoint to take - allowing for parameters for particles we know exist to take on some value that's not been ruled out in order to explain the situation.

Neutrinos would need to be very heavy, to the point that they could account for a significant fraction of the missing mass and explain the bullet observation. I don't think that's possible given current constraints. But even if it is, once you admit there is a lot of dark matter out there, MOND becomes an additional exotic assumption which seems far less probable than simply adding a bit more dark matter to what is already known.

And MOND and its relations remain excellent scientific theories from the perspective of them being easily falsifiable. Well, maybe not classical MOND as, since you note, there's an awful lot of cosmology you can't do with it, but its relativistic relations, certainly.

The relativistic version I looked at - TeVeS - was very far from easily falsifiable. It doesn't just have new free parameters, but several entire free functions. And it looked highly unlikely to be internally consistent - almost certainly it's got ghost issues.

The way I see it, the single great virtue of MOND was that it could explain galactic rotation curves and the Tully-Fisher relation, all with one or two parameters. The minute you start adding a bunch more stuff you lose the only virtue that made it interesting to begin with, and DM becomes a much more appealing alternative.

 

[tableplay]

nice work kid

<snip>
Yes, that's right. In order to support MOND, the whole point of which is to eliminate the need for dark matter and energy, they do in fact have to introduce both dark matter and energy. If there were any questions remaining about the viability of MOND, I think this pretty much answers them.

Big congrats to the grad student who did the calculations showing this (that mini black holes would pop up everywhere given MOND). Hathaway:"You graduate, you get the job . . . ." (quote from real genius) ;-)

Cheers, tp.

 

[edd]

Neutrinos would need to be very heavy, to the point that they could account for a significant fraction of the missing mass and explain the bullet observation. I don't think that's possible given current constraints. But even if it is, once you admit there is a lot of dark matter out there, MOND becomes an additional exotic assumption which seems far less probable than simply adding a bit more dark matter to what is already known.

I've absolutely no argument with that, which is why I've always preferred dark matter myself.

 

[Cuddles]

Well, I've had a couple of replies from New Scientist and they say that the article was actually badly worded. What it should have said, rather than:

He and his colleagues have constructed a MOND theory based on a "dark fluid" made up of dark matter and dark energy

is instead:

He and his colleagues have constructed a MOND theory based on a "dark fluid" **that mimics the effects** of dark matter and dark energy.

They will be publishing a correction, presumably in the next issue, which should clear things up. As it stands, I'm not sure this really helps much, since it still involves adding some kind of dark something, no matter what you call it, along with all the original complications of MOND.

Looking at the actual paper, it basically seems to be talking about generalising relativity, dark matter and dark energy so that current theories are just special cases, in much the same way that string theory is a general theory which gives many different possible universes. It looks like there could be plenty of interesting theory involved but, like string theory, it remains to be seen whether any of it actually has anything to do with the real world. However, this is a bit out of my field, so if anyone else wants to take a look and tell me I'm being an idiot, feel free.