Still in the dark about dark matter

Dec 06, 2011 By Amina Khan

Dark matter, the mysterious stuff thought to make up about 80 percent of matter in the universe, has become even more inscrutable.

Scientists have been trying for decades to better understand and detect the nature of dark matter, which could help them figure out how galaxies first formed.

"We don't know much about dark matter," said Stefan Funk, a particle at Stanford University.

Unlike the in the universe, dark matter can't be seen and it's exceptionally hard to detect. It moves slowly, carries little energy and interacts very little with the stuff around it. But scientists do know that when a piece of dark matter is destroyed, the resulting burst includes a stream of high-energy particles.

These particles can be made of ordinary matter - protons, neutrons, electrons and their building blocks - and also of their antimatter counterparts. Antimatter was plentiful in the , but it's now exceedingly rare and is created only by strange processes - such as, theoretically, the destruction of dark matter in space or in man-made .

So scientists on the hunt for evidence of dark matter look for - the antimatter analog of electrons - in high-energy bursts of particles known as cosmic rays. If you find a positron, the thinking goes, you know that at some point there probably was dark matter.

Physicists don't know how big can be. But they think that the amount of energy carried by a positron is limited by the mass of its dark matter source.

Scientists figured they could find a cutoff point for the maximum size of a dark matter particle relatively quickly. But recent results from the Russian-European spacecraft known as PAMELA found that the abundance of positrons relative to electrons given off by at up to 100 gigaelectron volts never fell off - much to the surprise of physicists.

Some scientists questioned the findings. But now Funk and his colleagues at Stanford appear to have confirmed those results in a study that has been submitted to Physical Review Letters.

Researchers on the Stanford team used the Fermi Gamma-ray Space Telescope to look for particles at even higher energy levels. Since the orbiting telescope does not have a magnet on board, researchers used the Earth's magnetic field to separate positrons, which have a positive charge, from electrons, which have a negative charge.

Once again, they found that, even at energy levels as high as 200 gigaelectron volts - twice what PAMELA had been able to search - the share of positrons simply kept rising.

The cutoff point, then, proves elusive - and thus, so does the maximum mass of dark matter particles.

Michael Peskin, a theoretical particle physicist at Stanford who was not involved in the study, said there are two possible explanations. Either the cutoff point exists at a higher energy level than the scientists were able to search, a sign that that particles are more massive than some models had predicted - or it means that, no matter what energy levels physicists look at, they will not see a cutoff, which could mean that positrons are coming from other sources, like supernovae or pulsars.

In that case, looking for antimatter particles like positrons may not be a reliable way to search for signs of dark matter's presence. To find out, Funk said he may shift his search to positrons at energy levels of up 1,000 gigaelectron volts.

Until scientists settle the question by looking at higher energy ranges, Peskin said, "both of these ideas are still in play."

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Turritopsis
1 / 5 (8) Dec 06, 2011
A few billion supernova remnants within the Milky Way galaxy would be sufficient mass to explain the Dark Matter mystery.

The superstars preceding the stars of today were far more massive than their successors.

After going supernova and blowing off most of themselves into space to form next generation stellar nurseries, these monster blackholes could still be greater than 1000 solar masses. The upper limit of mass for these earlier generation stars leads back to the originating big bang.

No blackhole within the universe can exceed the mass of the universe.

Dark Matter may be dead stars. Simply put Dark Matter could be all of the dead matter of the universe. Dead stars. Dead atoms.
Turritopsis
2 / 5 (8) Dec 06, 2011
Blackholes translate their energy to the virtual particle pairs around them (Hawking Radiation).

The blackholes evaporate with this process of particle creation, Hawking states. One particle is swallowed by the blackhole while the other escapes its antiparticle and escapes its annihilation.

"But scientists do know that when a piece of dark matter is destroyed, the resulting burst includes a stream of high-energy particles." - article

I think "know" may be a tad presumptuous here. Suspect is better suited. The current physical models mathematically allow for this process. It may be true, but it is not a known.
Turritopsis
2.5 / 5 (8) Dec 06, 2011
No model can prove this. Reality can. You can mathematically prove the theory but that is based on the model used to prove it. Disprove the efficacy of the model and the mathematical proofs based upon the model are out the window. Models and math are useful tools, but they have their limits.

The only way to "know" what happens when Dark Matter is destroyed is to isolate it and destroy it.
EverythingsJustATheory
4.3 / 5 (11) Dec 06, 2011
Dark Matter may be dead stars. Simply put Dark Matter could be all of the dead matter of the universe. Dead stars. Dead atoms.


If it is dead matter, and as heavy as you assert, almost all would reside inside our current matter (visible) galaxy, because heavier things tend to migrate inwards. However, in order to have a galaxy whose angular velocities are independent of the radial distance from the center of the galaxy, a large amount of mass must be present outside the visible shell, hence the rationale for dark matter, whose halos extend much further out than the visible boundaries of galaxies.

I'm not stating that dark matter exists, because I don't know. But to me it currently offers the best explanation for the observations.
Turritopsis
1 / 5 (4) Dec 06, 2011
Stars are heavy too. Why don't they migrate to the galactic centre? These blackholes would be kept in galactic orbit by the same process keeping the "visible" stars from crashing into the galactic centre.

Thats on the heavy side.

Now to the galactic perimeter. Nobody defined the "visible" galactic edge as the outer galactic edge. The milky way galaxy radius could be 2 or 3 or more times greater than it appears visibly. Most Dark Matter could still be found in these galactic "halos".
Turritopsis
1 / 5 (5) Dec 06, 2011
The blackholes could be found not only within the visible galaxy but also in the non-visible regions of the galaxy as well (the galactic halo).

EverythingsJustATheory
4 / 5 (4) Dec 06, 2011
Yes, but would most of the mass be present outside the visible galaxy? That is what is needed in order to explain the constant angular velocity with respect to radial distance. More mass would need to be present outside the visible region than inside.
Pyle
3.1 / 5 (8) Dec 06, 2011
Wow, there is some really terrible stuff in that article.
Unlike the visible matter in the universe, dark matter can't be seen and it's exceptionally hard to detect.
Sort of. It's thought to be the cause of the majority of gravitational lensing we observe, but EM-wise, yes, hard to detect.
It moves slowly, carries little energy and interacts very little with the stuff around it. But scientists do know that when a piece of dark matter is destroyed, the resulting burst includes a stream of high-energy particles.
Nonsense and speculation. Moves slowly? Little energy? Interacts very little? Maybe electromagnetically. Not very well worded there.

The other article on this research : http://www.physor...rk.html, was better, but I like the added bit about energy levels in this article. The comment thread so far is lacking.

@Turri, enough pontifi-masturbatation. Your fact based commentary is better than your fantasy. Dial it back.
that_guy
3.4 / 5 (8) Dec 06, 2011
@pyle - It's only easy to detect, if the lensing is indeed caused by 'dark matter'

Perhaps I could offer these corrections for the article. "Dark matter PARTICLES are exceptionally hard to detect." or "Dark matter signals are terribly hard to verify"

I like the first correction best.

Perhaps the astronomers are looking too light. Perhaps the DM particles have a mass of a Kilo? Which weighs more, a Kilo of Dark Matter, or a Kilo of feathers?

While I dont agree with everything turri says, I think that a lot of people are frustrated that DM theory is based on a lot of other theories (Which are unlikely to all be correct) and observations that are ambiguous at best. The only solid 'proof' we have is the fact that there doesn't *seem* to be enough mass accounted for (by far) - yet DM tends to correlate very closely with the placement of baryonic matter - you don't 'find DM' in empty space.

Just saying that even if DM is correct, I wouldn't call skepticism unjustified.
Noumenon
4.8 / 5 (57) Dec 06, 2011
Dark Matter may be dead stars. Simply put Dark Matter could be all of the dead matter of the universe. Dead stars. Dead atoms.


What is meant here by "Dead stars. Dead atoms"? If you don't mean blackholes, then realize that even cold regular matter gives off electromagnetic radiation, and so can be detected and is taken into account already.
Pyle
3.1 / 5 (7) Dec 06, 2011
Noomie, not really on the "gives off EM radiation" part. We can't see lots of cold baryonic matter and our estimates have just recently shown quite wild variations. But, back to the heart of this article, as you said, all of that is taken into account (just not the way you said.) Look at me all semanticky.

@thatguy: Turri's ramblings about "heavy side, dead" stuff is just silliness. He varies rather wildly between being very technically correct, to throwing wild stuff out there like this.

As far as "unlikely to all be correct", Yup! But I still like Moffat's MOG. Fully relativistic theory that has been refined to remove the arbitrary fitting parameters that are so often (and justifiably) criticized in MOND. It theorizes a fifth force, so that is problematic, but I find it more palatable than a bunch of dark stuff causing curvature but leaving no other trace.
that_guy
4.3 / 5 (9) Dec 06, 2011
Consider this:

Scientists have recently shown that 'virtual' particle pairs can be seperated and made real.

http://www.physor...uum.html

You cannot create energy/matter out of nothing, so then, the fabric of space must be subject to conservation of energy.

If the vacuum of space is subject to conservation of energy, then there must be an equivalence to matter and energy, an equation similar to the matter/energy equivalence, e=mc squared.

We do not have that equation. i believe this is why einstein waffled on the cosmological constant at the end of his life - he only had part of the equation, and hadn't figured out how space itself related to matter.

This is also why i think the notion that 'dark energy' will expand space ad infinum is deeply flawed. It violates conservation of energy.

I believe that we are missing a fundamental property of space itself, and until we figure it out, dark matter/energy or MOG are merely band-aids...
Pyle
2.6 / 5 (7) Dec 06, 2011
Hmmmm, couple of points.

First, creating light from the vacuum is hardly what they did. They pushed a bunch of energy in and got virtual photon pairs to "realize". When a virtual pair is made "real" it borrows the energy from the environment. It doesn't come from nowhere. e=mc2 is absolutely in play.

Regarding dark energy. Yeah, we are obviously missing something. However, that doesn't mean that dark matter or MOG would be a Band-aid. Just because he didn't know quantum mechanics didn't make Newton's laws Band-aids. It was an approximation that was relevant within certain limits. Same with a host of other theories that fall apart at various scales.

Einstein didn't have all the data. He didn't like the cosmological constant because he didn't have data to support it. It was just something that worked in the math. Turned out to be spot on it seems.

GR allows singularities, inifinities, and closed time-like loops. It ain't perfect. MOG looks like an improvement to me.
Pyle
3.4 / 5 (5) Dec 06, 2011
Something from your earlier comment:
yet DM tends to correlate very closely with the placement of baryonic matter - you don't 'find DM' in empty space.

Actually we do see lensing where we don't see sufficient (if any) baryonic matter tied to it. More on point, we have a great example in our backyard demonstrating a higher DM to M ratio (Segue 1):

http://www.physor...ess.html

And check this out:
http://www.univer...-matter/
StarGazer2011
1.8 / 5 (5) Dec 06, 2011
What if gravity isnt the only force interacting at the scale of galaxies and galaxtic clusters?
My memory of physics is that a moving charge creates an electric field, which creates a magnetic field, and that ions are a moving charge. Then we consider that a lot of the mass of a galaxy is ionised gas (plasma) which is moving. Perhaps combining Newton with Maxwell would give some insight?
that_guy
3.8 / 5 (5) Dec 06, 2011
"when a virtual pair is realized, it borrows the energy from the environment."

Which environment? If they were made entirely from input energy, then they wouldn't be virtual particles. They would be explanable as photon emissions. They get their energy (SIC) from vacuum fluctuations, minus any energy imparted on them by the process.

The virtual particles do not come from "standard" energy/matter - They come from the very fabric of space - This is not disputed. Space has a specific finite mass/energy to it.

I see your point regarding newton. Although you could argue that to some sense it was a band-aid for lack of understanding the equation underneath it. But the difference between Newton and these issues are that newton had an understanding on some level of the cause, whereas our current theories are more like modeling it after the fact. Both DM and MOG have been adjusted until the data fits.
StarGazer2011
1 / 5 (4) Dec 06, 2011
@Noumenon
"even cold regular matter gives off electromagnetic radiation, and so can be detected and is taken into account already. "
umm no, thats a bizzare statement to claim that our estimates of baryonic matter are exact, we are talking about GALAXIES of the stuff. Maybe you should go into climate *snigger* 'science' they like that sort of arrogance.
that_guy
3.6 / 5 (5) Dec 06, 2011
Something from your earlier comment:
yet DM tends to correlate very closely with the placement of baryonic matter - you don't 'find DM' in empty space.

Actually we do see lensing where we don't see sufficient (if any) baryonic matter tied to it. More on point, we have a great example in our backyard demonstrating a higher DM to M ratio (Segue 1):

on segue 1, the DM correlates with...segue 1. albeight I'll give you that the extreme ratio of "DM" to matter is of note.

The second article is interesting but inconsequential to my statement. I said that all DM is associated with matter, not the other way around. "DM" around dwarf galaxies far away could easily get lost in the signal of DM Halo of the parent gal.

But I will refine what I said - We do not see this type of acute "gravitational lensing" in random extragalactic void space - or if we do, we incorrectly attribute it to being a DM halo of known baryonic matter. Which is itself an interesting possibility.
Seeker2
1 / 5 (1) Dec 06, 2011
vacuum of space

I hate that term. Sounds like something between our ears. Maybe spacetime?
that_guy
4.2 / 5 (5) Dec 06, 2011
@seeker - whatever you like to call it. Perhaps the fabric of space without regard to traditional energy or baryonic matter?

So, I know this idea will put me in quack territory, but what about this idea (Just a thought experiment/conjecture):

We consider space to be a more or less flat surface with matter and DM on top of it. They stretch the fabric of space to make gravitational wells. This causes grav lensing, etc.

Now lets argue that maybe space itself isn't so flat. What if it is smoothish, but still varies? Maybe, in addition to the properties that Matter may impart to it, spacetime has it's own properties as well, independent of matter or DM, aside from the interaction of gravity.

what if space that has a low energy level creates something analagous to a gravity well - because there is less fabric of space per volume - entropically, energy, other space, matter would generally flow toward low energy space. it would mimic a gravitational lense.

Continued...
Seeker2
1 / 5 (3) Dec 06, 2011
This is also why i think the notion that 'dark energy' will expand space ad infinum is deeply flawed. It violates conservation of energy.

Yes this is black magic physics. It has its appeal, but I prefer something more plausible: More likely DE runs out as space expands and time passes (in both directions, BTW). DE is the stuff in spacetime that makes it boil with energy. Before inflation there was no matter or anti-matter, dark or not. It was all DE. As spacetime expanded its turbulence went into dark matter and some of this (about 15%) condensed into particle-antiparticle pairs. And when the DE runs out (into spacetime expansion) the collapsing phase begins. I like to think we live on borrowed space and time - we pay the piper in the end.

that_guy
3.7 / 5 (6) Dec 06, 2011
So that would, in this theory, potentially explain DM.

Now the higher energy space would have more fabric per volume. It would act like a bubble in the spacetime fabric. any baryonic matter would slide away from the high energy space, leaving voids. light wavelengths would become stretched, because they would be traveling through space that locally to the photon would appear to be expanding...

And that would account for the "dark energy."

@seeker2 - I don't subscribe to DE at all, but I suppose with my thought here, you could still come out to something analagous to your conclusion anyways.
that_guy
1 / 5 (1) Dec 06, 2011
error post
javjav
5 / 5 (1) Dec 06, 2011
Perhaps the DM particles have a mass of a Kilo?


It sounds weird. A 1Kg particle would be very easy to detect. If it decay it would do it as a nuclear bomb. If not, it would create a black hole and visible light will disappear into it.
StarGazer2011
2.4 / 5 (5) Dec 06, 2011
im prety sure someone would have looked into this, but could the apparent discrepancy between the speed of roatation of the halo stars and the core stars be a product of the relativistic effects of the cores greater gravity causing some sort of time dialation effect? So that the exterior appears to be moving at the same speed from our point of view but actually its a relativistic effect? I dont have the maths to work it out, but it could be refuted/demonstrated by observing the relative motion of stars in our galaxy and comparing features of the motion of those closer to the core than us to those further away. Just spitballing
Noumenon
4.8 / 5 (50) Dec 06, 2011
"when a virtual pair is realized, it borrows the energy from the environment."


Which environment? If they were made entirely from input energy, then they wouldn't be virtual particles. They would be explanable as photon emissions. They get their energy (SIC) from vacuum fluctuations, minus any energy imparted on them by the process.

The virtual particles do not come from "standard" energy/matter - They come from the very fabric of space - This is not disputed. Space has a specific finite mass/energy to it.


Consider Hawking radiation of a BH. The virtual pair is realized. The black hole mass decreases, and the rest of the universe gains mass (the escaped virtual particle), the net effect being that the BH radiates some of it's original mass/energy. QM.

Now, the energy from "the very fabric of space" is thought to be represented in the cosmological constant, which is a very small value wrt the volume of a galaxy. GR.
Seeker2
1 / 5 (1) Dec 06, 2011
Maybe, in addition to the properties that Matter may impart to it, spacetime has it's own properties as well, independent of matter or DM, aside from the interaction of gravity.

Ok particle matter/antimatter imparts a certain configuration to spacetime (one of its quantum states). This configuration means higher energy density for matter and lower for antimatter. Matter, particle or dark, is basically a differential configuration or energy density of spacetime. Spacetime may look flat but actually there are variations everywhere, particle or no, and they all average out to be flat, or so we think.
Actually it might be more kosher to say spacetime imparts its properties to matter. Same contents (energy density) only in different forms.
Noumenon
4.7 / 5 (50) Dec 06, 2011
@Noumenon
"even cold regular matter gives off electromagnetic radiation, and so can be detected and is taken into account already. "
umm no, thats a bizzare statement to claim that our estimates of baryonic matter are exact, we are talking about GALAXIES of the stuff. Maybe you should go into climate *snigger* 'science' they like that sort of arrogance.

Yes, I over estimated ability to detect that radiation. Hmmm, maybe I could go into AGW work. :)
Noumenon
4.8 / 5 (49) Dec 06, 2011
If the vacuum of space is subject to conservation of energy, then there must be an equivalence to matter and energy, an equation similar to the matter/energy equivalence, e=mc squared.

We do not have that equation. i believe this is why einstein waffled on the cosmological constant at the end of his life - he only had part of the equation, and hadn't figured out how space itself related to matter.

This is also why i think the notion that 'dark energy' will expand space ad infinum is deeply flawed. It violates conservation of energy.


That was what the cosmological constant term was for,.. to relate the fabric of space-time to mass-energy,... i.e. the more space the more of this "DE" there is . It does not violate conservation of energy.
Noumenon
4.8 / 5 (48) Dec 06, 2011
We do not have that equation. i believe this is why einstein waffled on the cosmological constant at the end of his life - he only had part of the equation, and hadn't figured out how space itself related to matter


Einstein was the one who came up with the notion of 'zero point energy' (1913), which may explain what the cosmological constant 'is'.
Noumenon
4.8 / 5 (49) Dec 06, 2011
.... In GR, pressure is also a component of the stress-energy tensor, and so, a source of gravitation. In quantum theory it is predicted that the pressure of the zero-point vacuum energy is always negative**. Is DE, zero point energy, which is the cosmological constant,... more space, more negative energy, more accelerated expansion,... ?

**so acts to reduce gravitation from positive energy sources across vast distances.
Seeker2
2 / 5 (4) Dec 06, 2011
...the more space the more of this "DE" there is . It does not violate conservation of energy.

So as space expands so does the dark energy with no violation of conservation of energy. When would this process stop? More black magic physics?
Noumenon
4.8 / 5 (50) Dec 06, 2011
...the more space the more of this "DE" there is . It does not violate conservation of energy.

So as space expands so does the dark energy with no violation of conservation of energy. When would this process stop? More black magic physics?

Yes, if the cosmological constant is vacuum energy, it is a function of space-time volume, so as the universe expands more space means more negative pressure (pressure being a source of gravity; flow of momentum) to counter the positive mass-energy source of gravitation, ever so slightly on cosmological distances (which is why energy of the "fabric of space" is not related to DM; totally different scale).

Einstein was a white man,.. but yes, he was magic.

Noumenon
4.8 / 5 (49) Dec 06, 2011
Is DE, zero point energy, which is the cosmological constant,... more space, more negative energy, more accelerated expansion,... ?


Oops, I mean, more negative pressure, not ' more negative energy'.

[Re, my above posts,... AFAIK]
Seeker2
1 / 5 (1) Dec 07, 2011
(pressure being a source of gravity;

I thought that would be anti-gravity. I thought gravity was a pulling force. I guess now we know.
Seeker2
1 / 5 (1) Dec 07, 2011
Is DE, zero point energy, which is the cosmological constant,... more space, more negative energy, more accelerated expansion,... ?

Oops, I mean, more negative pressure, not ' more negative energy'.

[Re, my above posts,... AFAIK]

So more negative pressure means more accelerated expansion. And that positive pressure is what keeps the earth in orbit.
I see.
rwinners
2.3 / 5 (3) Dec 07, 2011
""We don't know much about dark matter," said Stefan Funk, a particle astrophysicist at Stanford University."

In fact, dark matter is a construct used to explain why current physics cannot explain space as we see it. The same applies to dark matter. They are arbitrary values inserted into mathematical formula for the purpose of proving a finding.
I don't want to argue the issue, but I do much prefer science which is based upon and proven by experimentation and qualitative results.
TimESimmons
1 / 5 (5) Dec 07, 2011
There is no Dark Matter. The universe contains a thin atmosphere of anti-gravity matter. The gravitational effects we are observing are due to a local reduction in density of anti-gravity matter. Its a double negative. Here's the evidence:-
http://www.presto...ndex.htm
Noumenon
4.8 / 5 (48) Dec 07, 2011

Is DE, zero point energy, which is the cosmological constant,... more space, more negative energy, more accelerated expansion,... ?

Oops, I mean, more negative pressure, not ' more negative energy'.

[Re, my above posts,... AFAIK]

So more negative pressure means more accelerated expansion. And that positive pressure is what keeps the earth in orbit.
I see.


No, positive pressure is not related to orbits. But it is the reason a BH must form for a given mass star > 1.5 suns (left over core - mass after explosion). When pressure is a component of the source of gravity at a certain point it becomes a run-away situation, and not even QM electron or neutron degeneracy can prevent the collapse to a black hole.
Seeker2
1 / 5 (1) Dec 07, 2011
When pressure is a component of the source of gravity at a certain point

So at what point does pressure become a component of the source of gravity?
Seeker2
1 / 5 (1) Dec 07, 2011
I do much prefer science which is based upon and proven by experimentation and qualitative results.

Proven? Here we go again.
Crazy_council
3.4 / 5 (5) Dec 07, 2011
Consider this:.........
You cannot create energy/matter out of nothing, so then, the fabric of space must be subject to conservation of energy.

If the vacuum of space is subject to conservation of energy, then there must be an equivalence to matter and energy, an equation similar to the matter/energy equivalence, e=mc squared.

We do not have that equation. i believe this is why einstein waffled on the cosmological constant at the end of his life -

This is also why i think the notion that 'dark energy' will expand space ad infinum is deeply flawed. It violates conservation of energy.

I believe that we are missing a fundamental property of space itself, and until we figure it out, dark matter/energy or MOG are merely band-aids...


That guy, i agree totally, i think the fabric of space has energy. You have explaind it much better than i have managed to.
Crazy_council
4.2 / 5 (5) Dec 07, 2011
I notice someone has voted me a one without commenting on why.

I am not blindly devoted to my theory, and i am open to any explination that does not require magic or god. what i beleive has not much to do with aether, and is more closely tide to strig theory

So why the 1 mark ?
Noumenon
4.8 / 5 (49) Dec 07, 2011
When pressure is a component of the source of gravity at a certain point ...

So at what point does pressure become a component of the source of gravity?


It is included in the stress-energy tensor of Einsteins field equations (which is what I mean by component, of the tensor), so it's always a source, if it's there physically in a given circumstance,.. like in collapsing stars and space-time on cosmological distances.
Noumenon
4.7 / 5 (54) Dec 07, 2011
I notice someone has voted me a one without commenting on why.

I am not blindly devoted to my theory, and i am open to any explination that does not require magic or god. what i beleive has not much to do with aether, and is more closely tide to strig theory

So why the 1 mark ?


It appears to be "orac", who never posts anything. It is probably some one with multiple screen names who is too intellectually cowardly to debate. Don't worry, the ratings are meaningless on account of such trolls.
Seeker2
1 / 5 (1) Dec 07, 2011
It is included in the stress-energy tensor of Einsteins field equations (which is what I mean by component, of the tensor), so it's always a source, if it's there physically in a given circumstance,.. like in collapsing stars and space-time on cosmological distances.

So pressure is always a source, as in a collapsing star. So when the apple falls on your head that causes pressure, and that now becomes part of the source. Also the pain becomes part of the source since it is caused by pressure. I understand now.
Noumenon
4.8 / 5 (51) Dec 07, 2011
It is included in the stress-energy tensor of Einsteins field equations (which is what I mean by component, of the tensor), so it's always a source, if it's there physically in a given circumstance,.. like in collapsing stars and space-time on cosmological distances.

So pressure is always a source, as in a collapsing star. So when the apple falls on your head that causes pressure, and that now becomes part of the source. Also the pain becomes part of the source since it is caused by pressure. I understand now.


Is this sarcasm of some sort. What is the point?

In GR the source of gravitation is energy in whatever form, as you know,... pressure is the flow of momentum (in spacetime) and is an energy, so contributes as well as mass, ... except is normal circumstances it is to minute to amount to anything.

http://en.wikiped...nsor.svg
Seeker2
1 / 5 (1) Dec 07, 2011
In GR the source of gravitation is energy in whatever form

So energy in the form of heat would be gravitation? Just checking.
that_guy
3 / 5 (2) Dec 07, 2011
Perhaps the DM particles have a mass of a Kilo?


It sounds weird. A 1Kg particle would be very easy to detect. If it decay it would do it as a nuclear bomb. If not, it would create a black hole and visible light will disappear into it.

Haha, the assumption that a 1kg particle would be easy to detect or decay is very presumptuous...almost as presumptuous as the idea that a DM particle would weigh a Kilo.

Though the second conjecture you put out actually makes sense.

Perhaps this link will help you understand my statement a little better, javjav:

http://en.wikiped...ki/Humor

@the rest - interesting conversation
Pyle
3 / 5 (4) Dec 07, 2011
@that_guy:
Both DM and MOG have been adjusted until the data fits.

No. This statement is not true.

DM - fit by definition since the only way we know it might be there is based on our observations of its effects.

MOG - if we see mass via EM we can calculate what the gravitational effects will be and see if it matches our observations (so far it matches based on a very limited sample size).

Moreover, we can set initial conditions, run simulations with the MOG field equations and see if the outcome matches observations. This was done to "recreate" the Bullet Cluster using MOG. This is similar to the recent successful simulation of a spiral galaxy (Eris) that has been hailed as powerful confirmation of the DM theory. Nothing of the Eris scale has been done with MOG yet. Not enough interest in the theory. Until there is a major blow to DM, or some MOG prediction proves accurate there probably won't be sufficient resources devoted to developing it.
that_guy
1 / 5 (1) Dec 07, 2011
The original DM and MOG theories both had to be adjusted after the observational data or simulations did not match up correctly.

For example, WIMPs are the third or fourth major dark matter candidate. Neutrinos were proposed as a light mass DM particle, until they were ruled out due to insufficient aggregate mass.

The reason why DM is favored over MOG is because originally when they did simulations of universe formations, they found that some DM candidates produced a picture that more closely resembles our galaxies today than the contemporary version of MOG did at the time - Granted, MOG was just beginning to be developed at the time, whereas more work had been done with DM.

I'm not saying that there is anything wrong with MOG - I'm saying that it more a model built on top of observations, so by definition it has to be adjusted to make it fit. (Like some aspects of newtonian motion.)

continued
Noumenon
4.8 / 5 (51) Dec 07, 2011
In GR the source of gravitation is energy in whatever form

So energy in the form of heat would be gravitation? Just checking.


E=mc^2

Is there a point to your attitude? Just checking.
that_guy
1 / 5 (1) Dec 07, 2011
DM is an attempt to understand underneath. Ideally, if they were to get DM right (Assuming it is correct), they would be able to predict phenomena that hasn't been understood or noticed in advance. This hasn't really happened, although you could argue that the example of galaxy formation above may lend some support to that.

DM theory has predicted dark stars, measurable signals from DM annihilation, and other things, all inconclusive, unconfirmed, or having compelling alternative explanations.

MOG is more about getting the nuances of gravity correct on larger scales. It is proven not by making predictions as such, but more by being accurate to what we already see. It is an attempt at newtonian dynamics, vs DM's attempt at the theory of relativity.

But to say that they are not adjusted to fit the data...IE, to be 'correct' is at best a semantic argument.

But my point is, it is far more OK for MOG to be adjusted to fit the data than DM, which should predict.
that_guy
4.3 / 5 (6) Dec 07, 2011
In GR the source of gravitation is energy in whatever form

So energy in the form of heat would be gravitation? Just checking.


E=mc^2

Is there a point to your attitude? Just checking.

aha! I love this comment.

Noum is correct. Energy has gravity. However, it is normally discountable because it is exceeedingly exceedingly small. Consider that matter has gravity that is the speed of light squared times larger than the gravity of energy to give you perspective...
Pyle
2.7 / 5 (3) Dec 07, 2011
*Pyle beats dead horse*

@tg: Regarding MOG. Here, read this:
http://arxiv.org/abs/1101.1935

From this paper:
"we have demonstrated that cosmological observations do not trivially rule out MOG as a possible alternative to the standard LCDM model of cosmology."
Turritopsis
1.7 / 5 (6) Dec 07, 2011
Y'all are confused. The Big Bang happened two thousand years ago when God met Mary. Dark Matter is crossdimensional mass from heaven and hell. Both influence our spacetime and all is destined to crossover to one of the two. Dark Energy is the energy of the devil as he tries to drive us all apart. Gravity is the influence of God as he tries to bring us together.
that_guy
3 / 5 (2) Dec 07, 2011
*Pyle beats dead horse*

@tg: Regarding MOG. Here, read this:
http://arxiv.org/abs/1101.1935

From this paper:
"we have demonstrated that cosmological observations do not trivially rule out MOG as a possible alternative to the standard LCDM model of cosmology."

I have no disagreeance that a mature version of MOG may turn out to be more effective than DM/DE
Seeker2
1.8 / 5 (5) Dec 07, 2011
E=mc^2

Is there a point to your attitude? Just checking.

Is there a point to your answer? Sorry about the attitude.
Seeker2
1.8 / 5 (5) Dec 07, 2011
E=mc^2

Noum is correct. Energy has gravity.

Looks to me like mass has energy. Problem with cause and effect?
Seeker2
1 / 5 (2) Dec 07, 2011
Gravity is the influence of God as he tries to bring us together.

Yes, we can always hope.
vacuum-mechanics
1.8 / 5 (5) Dec 07, 2011
Consider this:

Scientists have recently shown that 'virtual' particle pairs can be seperated and made real.
...........
I believe that we are missing a fundamental property of space itself, and until we figure it out, dark matter/energy or MOG are merely band-aids...

May be vacuum is neither (empty) space that filled with virtual particles nor aether, instead it is vacuum medium which is the fabric structure of space-time itself. Together with gravity as its intrinsic property, then the conservation energy is preserved, also dark matter/energy problem could be easy solved!

Pease refer to Dark energy is in front of your eyes! below.

http://www.vacuum...id=14=en
Seeker2
2.3 / 5 (3) Dec 08, 2011
Gravity is the influence of God as he tries to bring us together.

Someone keeps telling me gravity is pressure. It's great to find someone who thinks gravity is a pulling force.
Seeker2
2.8 / 5 (5) Dec 08, 2011
A 1Kg particle would be very easy to detect. If it decay it would do it as a nuclear bomb.

I dunno about that but note if it met an equal amount of antimatter it would destroy the world.
vidyunmaya
1 / 5 (3) Dec 11, 2011
Sub: Spirit of Science at stake- needs change in concepts
SENSE Index-SENSITIVE INDEX-SUN SPOT DYNAMIC SPIRIT DRIVES PARTICLE FLOWS
http://www.scribd...72919866
Plasma Regulated Electromagnetic Phenomena in magnetic Field Environment
Cosmology needs best of brains trust.
Search: Vidyardhicosmology [dot] blogspot [dot] com
theon
1 / 5 (1) Dec 26, 2011
No mystery remains if one gives up the prejudice that dark matter should arise from WIMPs, elementary particles. The idea of galactic dark matter just being "missing" baryons locked up in Machos of earth mass is working fantastically, a Macho of 3 earth masses is approaching the black hole at Sagittarius A*, the center of the Galaxy. Cold dark matter performs so poorly in galaxies, that it can be considered as ruled out. Macho dark matter explains more and more new data, while they pose ongoing problems for cold dark matter. In galaxy clusters one would need neutrinos as dark matter particles. The Katrin experiment will test the relevant 1.5 eV mass.
Callippo
1 / 5 (2) Dec 26, 2011
IMO it's clear already, the gravity is the shielding effect of gravitational waves with massive bodies and the cold dark matter is the shielding effect this shielding with all other massive bodies. After then the hot dark matter will be the analogous effect caused with cold dark matter fluctuations. The people could be shadows of some galactic clusters, after then? Well, it's just working hypothesis in this moment.
Seeker2
1 / 5 (1) Dec 27, 2011
Now the higher energy space would have more fabric per volume.
I would say higher energy density spacetime has more energy per unit volume.

It would act like a bubble in the spacetime fabric.
I think antimatter acts like a bubble in spacetime since I think it has less energy density.

any baryonic matter would slide away from the high energy space, leaving voids.

I think matter has more energy density and searches spacetime for regions of similar density like an object dropped into a pool with less density than water at the bottom of the pool. Heavy objects collect on the bottom of the pool as matter eventually collects in black holes. Sort of like water going down the drain. You can even see it swirling around before it goes down the drain like the accretion disc accumulating around a black hole before its matter falls in.