Dark matter and Dark energy

[Lynx2174]

I've never found anyone who actually knows the answer to my question. I'm not talking about just the energy of matter, but the Gravitational energy + EM energy of a volume of empty space.

Just the energy from one cosmic ray can be quite a lot. What is the energy of all the EM in a cubic meter of space?

You won't find an answer because your question is meaningless. You may as well be asking "How big is a box" without saying anything about parameters.

Now if you'd include WHERE this cubic meter of space is, then you can probably get an answer out of a fourmite more astronomically inclined than I.

There's a big difference between the energy contained in a cubic meter of space inside our solar system and one in the interstellar medium.

So no matter how powerful a magnetic field is, it is considered charge neutral?

Of course. A magnetic field is the result of a moving charge. It itself is not a charge at all. You may notice that magnets still don't attract stationary charged pieces of nonmagnetic material, and that charged items don't attract magnets any more than they attract neutrally charged non-magnetic things of similar composition.

Magnetic fields have a direction, and a magnitude. Their units are newton seconds per coulomb meter.

You may as well ask what is the mass of the acceleration of gravity somewhere.

 

[sol invictus]

They are ? Link ?

http://www.ps.uci.edu/~superk/
http://en.wikipedia.org/wiki/Neutrino

How do they manage to travel so fast and to avoid almost all interactions if they're massive ?

They travel fast because their mass is much smaller than the mass of all the other elementary particles. Hence when neutrinos are produced they typically have far more energy than mass, meaning they're ultra-relativistic.

As for interactions, that has nothing to do with mass (other than gravitational interactions, and those are extremely weak).

 

[sol invictus]

So no matter how powerful a magnetic field is, it is considered charge neutral?

I don't understand your question, but magnetic fields are not created by charge - they are created by currents.

Imagine a loop of copper wire, which contains exactly as many electrons as protons. If the electrons flow around the loop with some average velocity, the net charge is remains zero, but there will be a magnetic field generated by the current.

Magnetic fields are sourced by charge-neutral currents and by electric fields that change with time, not by charge densities.

 

[BeAChooser]

One thing to remember is that we evolved in this universe, and therefore our brains are relatively well-suited for understanding the rules it operates by (which appear to be formal logic and mathematics).

Actually, the brains of most people do not appear well suited to using formal logic or mathematics. And dark matter, dark energy and gnomish objects like black holes certainly played no obvious role in the evolution of our brains. But electricity did.

The computer you are using is good evidence we've succeeded pretty well so far

A computer is an object that owes it's existence to electromagnetism and particle theories that we have actually been able to observe and experiment with here on earth. Unlike dark matter, dark energy and gnomish objects like black holes.

and the methods of science and logic have so far shown no signs of ceasing to be useful.

I present the same challenge to you that I did to the others. Name a product developed from a fundamental physics theory (akin to Maxwell's laws or quantum mechanics) that was first formulated in the last 30 years or so ... the time when Big Bang cosmology and string theory began to dominate the mainstream. I think a fair case can be made that everything we now use (and some of it is truly amazing) stems from understanding of the fundamental physical laws gained more than 30 years ago.

Dark matter is not necessarily anything exotic. We can only directly see things that glow, like stars. We can infer the existence of other things (like dust clouds) by how they absorb the light from stars, even when we can't see them directly.

All told, dust clouds, plasma clouds (let's not forget them ), stellar remnants, brown dwarfs, dim red giants, and even particles we KNOW exist and that might have mass (such neutrinos) can only account for about 10-15 percent of the missing mass. So the rest does consist of "exotic" stuff.

And then there are little problems like this cropping up, making Big Bang's problem even bigger ...

http://www.sciencedaily.com/releases/2007/11/071102152248.htm "Big Chunk Of The Universe Is Missing -- Again, ScienceDaily (Nov. 5, 2007) ... snip ... The University of Alabama in Huntsville (UAH). The new calculations might leave the mass of the universe as much as ten to 20 percent lighter than previously calculated. The same UAH group that found what was theorized to be a significant fraction of the "missing mass" that binds together the universe has discovered that some x-rays thought to come from intergalactic clouds of "warm" gas are instead probably caused by lightweight electrons. ... snip ... "A significant portion of what we thought was missing mass turns out to be these 'relativistic' electrons." Traveling at almost the speed of light (and therefore "relativistic"), these feather weight electrons collide with photons from the cosmic microwave background. Energy from the collisions converts the photons from low-energy microwaves to high-energy x-rays."

Say ... what's this about huge clouds of free electrons in space? Doesn't electric current have something to do with free electrons? Don't the EU theorists postulate the existence of huge clouds of free electrons?

And here's the missing mass the UAH researchers originally theorized ...

http://www.sciencedaily.com/releases/2005/02/050205074635.htm "Astronomers Find Part Of Universe’s Missing Matter, ScienceDaily (Feb. 7, 2005) ... snip ... Scientists have located a sizeable chunk of the universe that seemed to be missing since back when the stars first formed. It’s floating in super-hot rivers of gas, invisible to the naked eye, surrounding galaxies like our own."

The interesting thing is that the "gas" is described as "rivers of gas" and as being a "100 times hotter than the sun". There is even a Chandra photo in the above link of these "rivers". And you know what? They look a lot like plasma in the form of interacting Birkeland currents. You don't suppose that's a lot more logical than assuming these are relativistic hitting the CMB radiation (the latest explanation from the mainstream), do you? By the way, did you ever find the missing cluster shadows on the CMB?

And we can infer the existence of dark matter, and something about its properties, from the way galaxies orbit and rotate

Only if we ignore various peer-reviewed papers by well credential scientists and engineers that were published in well respected technical journals.

we have seen dark matter directly via gravitational lensing around a particular galaxy cluster.

False. Dark matter was only INFERRED in that case. That colorful picture of supposed dark matter that the mainstream published with their announcement of discovery does not *show* dark matter. It shows emissions that might be due to other causes. The computer model that they used to *prove* dark matter is the cause ASSUMED many things that may not be true (like red shift always equates to distance) and IGNORED many others (like electromagnetism, for instance). So that is what NASA believes SHOULD be there. Garbage in, garbage out?

I think the case is closed on the existence of DM

Well you'd certainly like it to be. Is that called job security?

They have determined that, if Einstein was correct, there must be a large amount of matter which doesn't emit or absorb light, and some kind of dark energy. Those are the most conservative possibilities - they don't involve anything really new.

That's one of the funniest statements you've made yet, sol. That truly deserves one of my famous ROTFLOL!s.

 

[arthwollipot]

They are ? Link ?

How do they manage to travel so fast and to avoid almost all interactions if they're massive ?

http://www.ps.uci.edu/~superk/
http://en.wikipedia.org/wiki/Neutrino



They travel fast because their mass is much smaller than the mass of all the other elementary particles. Hence when neutrinos are produced they typically have far more energy than mass, meaning they're ultra-relativistic.

As for interactions, that has nothing to do with mass (other than gravitational interactions, and those are extremely weak).

To elaborate for lay readers, it has been known for some time that the sun only emits about a third of the number of neutrinos that our calculations said that it should emit. There are three types of neutrinos - the electron neutrino, the tau neutrino and the muon neutrino. It was previously thought that they were all massless particles, like the photon. This would mean that they travelled at the speed of light, and would interact only very rarely with other particles.

However, one answer to the question about why we see only about a third of the neutrinos from the sun that we should see was that the neutrinos were changing en route from one type to another. This would only be possible if the neutrinos had mass. It didn't have to be much mass, it just had to be non-zero.

To cut a long story short (too late), it was found that this was exactly what was happening. The neutrinos were changing into other types, which means that they must have a nonzero mass.

 

[Belz...]

But there are electrons in the core, because the core, like the rest of the sun, is close to charge neutral. Electrons in the core aren't bound to nuclei, but they're definitely there.

That's true. Actually, I have no idea why I said that, because I knew that already! Silly Belz... !

 

[Belz...]

If many high redshift quasars and high redshift galaxies turn out to be rather close objects instead of objects at the extreme edges of the universe, then all the calculations that have been done so far with regards to dark energy get tossed out the window.

Key word: if.

Besides, Quasars MAY be objects that are a lot closer than we think. Of course, that'd mean that their light has run across the universe at least once and back at us, again.

 

[Belz...]

http://www.ps.uci.edu/~superk/
http://en.wikipedia.org/wiki/Neutrino



They travel fast because their mass is much smaller than the mass of all the other elementary particles. Hence when neutrinos are produced they typically have far more energy than mass, meaning they're ultra-relativistic.

As for interactions, that has nothing to do with mass (other than gravitational interactions, and those are extremely weak).

Right.

Well, by "massive" did you mean "has a mass" or "has LOTS of mass" ?

 

[Cuddles]

That really isn't accurate, unless your definition of "nearby" extends out to millions (in the case of individual stars) or billions (in the case of galaxies) of light years. The light we capture from them -- via relatively "ordinary" optical means -- can be analyzed and interpreted, revealing a great deal of information about the stars that produced them. Thus their reality is directly observable, not inferred or theoretical.

Nope. To start with, the Milky Way is only about a hundred thousand light years at its widest, and we can't see most of the stars even with various bits of equpiment. The universe itself is only around 13 billion years old, and we haven't seen anywhere near the oldest parts yet. This is exactly the point Sol was making. We can't see these things without a whole pile of equipment and interpretation. You accept them because they have become common knowledge, not because there is anything intrinsically more "common sense" about them or because they are more directly observed.

And this is still avoiding the point that Sol wasn't talking about stars at all, he was talking about gas and dust which just sits there without giving off any light at all. The only way we can tell it's there is either by it absorbing light, or by its gravity. Indirect observations all the way, just like dark matter.

Wasn't aware of massive neutrinos. Interesting, although not all that germane to my main points.

It's extremely germane to your point. You accept the existence of neutrinos, but not WIMPs. Neutrinos are WIMPs. They can't be the only WIMPs because they're not massive enough to account for all the extra mass, but they are an example of something you claim requires "suspension of common sense", despite the fact that we know they exist.

I wasn't appealing to authority, and frankly I think you damn well know it. I was just showing that I wasn't totally making stuff up as I went along. Spurious accusations of rhetorical malfeasance won't work either, sorry. (See? Two can play at that game.)

Sol is correct that there is no difference between "dark matter" and "Dark Matter". However, the stuff that we know exists is obviously less interesting than the stuff that is still a mystery, so the term "dark matter" is often used to mean "the dark matter that we don't understand yet", rather than "all the dark matter". The authorities you are appealing to are not contradiciting Sol, they are just simplifying things for the lay audience. As Sol said, this is a perfect example of the constant misunderstandings of laypeople. You confuse a simplification for TV interviews with them contradicting a more thourough explanation. Sadly, this sort of thing is all too common.

 

[edd]

I'm a little puzzled.

If I understand you right, mainstream theorists are claiming that the average density of the universe, including dark matter and dark energy, is the equivalent of one hydrogen atom per cubic meter. Since dark energy is supposed to be about three-fourths the total mass, that leaves a density of about 0.25 hydrogen atoms per cubic meter for everything else (even assuming we could see dark matter in a cubic meter sample of vacuum).

My calculations make the critical density about 5 protons/cubic metre, which with a 4% baryon density is about one hydrogen atom every four cubic metres. Total matter, including dark, would be 1.6 or so hydrogen atoms per cubic metre.

But this source (http://www.ccmr.cornell.edu/education/ask/index.html?quid=1026 ) states that "It is estimated the gaseous density between stars in the Milky Way to be ~0.1 to 1 atom/cm³ ... snip ... . For intergalactic voids, the density drop further to ~0.001 atom/cm³". That's a density of 1000 atoms per cubic meter.

Care to offer an explanation for this huge discrepancy? Or did I just do the math wrong again? Or is that 1000 atoms per cubic meter just the density in nearby intergalactic space? If so, then there must be some huge areas of the universe where there really is next to nothing. Perhaps those giant voids that have been discovered recently (and that are giving mainstream theorists so much trouble) provide the answer to my dilemma. Let's look:

Intergalactic could well mean between the galaxies in a grouping like a cluster, which we know is full of hot gas, outweighing the baryonic mass in the galaxies themselves, so it could be that they mean that kind of environment. That 1/1000 atoms per cubic centimetre is the same number given on the wikipedia intracluster medium page in fact, although I've not searched out a suitable estimate from a more reliable source so someone may want to spend a bit more time checking that.

http://www.acceleratingfuture.com/michael/blog/?p=69 "The Bootes Void ... snip ... is the largest known region of empty space in the observable universe. ... The void ... snip ... is about 2% the diameter of the entire observable universe (!) ... snip ... The Boötes void is probably the most perfect vacuum in the universe. Its density is somewhat less than that of the universe’s average, which is about one atom per cubic meter. The void’s density is certainly lower than that of typical intergalactic space, which is already extremely sparse."

But "somewhat less" than the universe's average is not going to solve the problem. Obviously, this region, even to be labeled a void, must have much less matter than most other regions. Which means the other regions must have substantially more than the universes average density. So I'm still left with a dilemma. Another way to look at it is that if intergalactic space has a density a 1000 times greater than the average density, then no more than 1/1000th of the volume of the universe can be that density, even if the rest is a perfect vacuum (which clearly isn't true based on the above). Something just doesn't make sense. You being such an expert on Big Bang cosmology ... perhaps you can clear this matter D) up, sol?

The universe is very strongly clustered up. It doesn't strike me as unreasonable that 1/1000th of the volume is what you'd call intergalactic, with a much higher density. It's 10% of the length scale after all.

 

[edd]

It's extremely germane to your point. You accept the existence of neutrinos, but not WIMPs. Neutrinos are WIMPs. They can't be the only WIMPs because they're not massive enough to account for all the extra mass, but they are an example of something you claim requires "suspension of common sense", despite the fact that we know they exist.

Not so much that they're 'not massive enough to account for all the extra mass' but they're not massive enough to be 'cold dark matter' rather than warm or hot - essentially they whizz round the place too fast to stay still and help structure form. Something a little more sedate is necessary, and that would be a more massive particle.

 

[sol invictus]

Well, by "massive" did you mean "has a mass" or "has LOTS of mass" ?

"Has a mass".

 

[edd]

I've never found anyone who actually knows the answer to my question. I'm not talking about just the energy of matter, but the Gravitational energy + EM energy of a volume of empty space.

Just the energy from one cosmic ray can be quite a lot. What is the energy of all the EM in a cubic meter of space?

Radiation densities drop off as the fourth power of the size of the universe (compared to the third power for ordinary matter - as you'd expect scaling like the volume, and not at all for a cosmological constant which is, well, constant). So whereas this was a really important component of the universe when the universe was small, it rapidly lost out to the density in matter and more recently dark energy. But that's just what is now the CMB. The energy density in the CMB now is I think something like 1/20000th the critical density, or 800 times less than the matter density, if I've done my sums right.

To add up all the more recently emitted light you have to integrate up the background radiation from the microwave right up to gamma rays, which is a bit of a lengthy job. I'm also not so familiar with it but http://www.astro.ucla.edu/~wright/CIBR/ suggests you get something like 10% more energy going up through the IR to the optical. Also here gives numbers around 10 nW/m^2/sr, which I make about 1% of the CMB energy. X-rays and higher are important too, but according to http://universe.nasa.gov/press/1999/cw99_19.html again the CMB is dominant. So you're talking in the ballpark of a thousandth of the density of matter in the form of radiation today.

As to gravity... I'm not sure exactly how to interpret that question.

 

[robinson]

I don't understand your question, but magnetic fields are not created by charge - they are created by currents.

Magnetic fields are sourced by charge-neutral currents and by electric fields that change with time, not by charge densities.

So no matter how huge and powerful a magnetic field is, it is considered charge neutral? No matter what the source of the magnetic field is?

You won't find an answer because your question is meaningless. You may as well be asking "How big is a box" without saying anything about parameters.

I would love to know the answer for different regions of outer space.

What is the mass as well as the energy.

Say, between us and the sun. Between us and the moon. Out near the orbit of Jupiter.

One parsec out from the sun, both in and out of the ecliptic.

What is it between stars. Between Galaxies.

In the heart of a galaxy.

How much matter is there? How much energy?

I don't expect answers, because we don't know, I just wonder about it.

 

[Cuddles]

So no matter how huge and powerful a magnetic field is, it is considered charge neutral? No matter what the source of the magnetic field is?

Not "considered" neutral, it is neutral. Because it doesn't have an electric (or any other) charge. That's what neutral means.

 

[Belz...]

"Has a mass".

Ah! Well, that was a misunderstanding, then. I already knew they had some mass; or at least I was under the impression that the mainstream view was that they did.

 

[sol invictus]

So no matter how huge and powerful a magnetic field is, it is considered charge neutral? No matter what the source of the magnetic field is?

It's not "considered" anything - it just is. Fields themselves don't have electric charge. They are sourced by charges and currents, but as I explained above, magnetic fields are sourced by currents, not charge densities.

I would love to know the answer for different regions of outer space.

What is the mass as well as the energy.

Say, between us and the sun. Between us and the moon. Out near the orbit of Jupiter.

One parsec out from the sun, both in and out of the ecliptic.

What is it between stars. Between Galaxies.

In the heart of a galaxy.

How much matter is there? How much energy?

I don't expect answers, because we don't know, I just wonder about it.

Actually, we know the answers to most of those reasonably well. You can probably find them on the web, or if not then in astro papers.

 

[robinson]

Like I said, we don't know the answers. Somebody somewhere might have estimated the values, somewhere on the web. But nobody here knows the values.

But what about energy? Has anybody calculated the energy of a given amount of empty space?

 

[sol invictus]

Like I said, we don't know the answers. Somebody somewhere might have estimated the values, somewhere on the web. But nobody here knows the values.

OK, whatever you say.

But what about energy? Has anybody calculated the energy of a given amount of empty space?

I answered that in a previous post.

 

[robinson]

I answered that in a previous post.

Where? You mean this?

Yes, there's a formula, and it gives a completely wrong answer. Much, much, much too big. More or less, it says that the energy density of the vacuum should be of order the energy of the most energetic particle divided by the characteristic size of that particle cubed. So if protons were the most energetic particle in the world (they're not), the answer would be off by 10^45. In fact it's off by at least 10^60.

This is called the cosmological constant problem. Some have argued it's the most profound and difficult problem in modern physics, akin to the ultraviolet catastrophe of the early 20th century (which lead to the discovery of quantum mechanics).

Do you mean the answer is nobody knows?