anti Dark Matter?

[notFritzArgelander]

Sorry I'm late to the party. Is the reason for energy density always being positive a result of the photon being its own anti particle? Or am I confusing this with something else?

It's a complicated something else that can have many answers. I'll sketch a few. First let's leave GR and QM out of it.

In classical physics the requirement is that the energy must be bounded from below for stability reasons. If the energy is not bounded from below one can always extract energy by reconfiguring the system in a lower and lower energy state. Then, since only differences in energy have physical significance, one is free to add a constant and redefine the energy scale so that the energy density in some reference state is zero. So one is free to define the zero of potential energy of a baseball at the surface of the Earth as zero or as zero if it is at an infinite separation.

In QM the vacuum state is taken to have zero energy by convention. There is a long history of hemming and hawing here starting with Dirac's negative energy states for his equation for the electron and continuing on through the Casimir effect. In the Casimir effect you can produce a highly localized negative energy density space between two parallel conducting plates. Essentially the parallel plates cut off modes of vibration of the vacuum EM field because of the boundary conditions at the plates. With fewer modes the energy is lowered with respect to the vacuum.

It's when we hit GR that we get the positivity requirement (with exceptions allowed locally like for the Casimir effect). There are several lines of reasoning.

1) The stress-energy-momentum tensor must have positive eigenvalues for physical matter and fields. There is a long Wikipedia article that explains this well with an example of perfect fluids. It is located at

https://en.wikipedia.org/wiki/Energy_co ... ect_fluids

The result is more general than perfect fluids which leads us to....

2) Hawking's chronology protection conjecture. Exotic matter (negative density) implies closed timeline curves and non causal physics. https://journals.aps.org/prd/abstract/1 ... evD.46.603

[GCoyote]

Hawking covered the second point in one of his books so my simple primate brain is okay with that one. However I get hives as soon as people start doing math with tensors so I will have to return to that one when I have a net positive caffeine balance.

Thanks as always!

[notFritzArgelander]

Hawking covered the second point in one of his books so my simple primate brain is okay with that one. However I get hives as soon as people start doing math with tensors so I will have to return to that one when I have a net positive caffeine balance.

Thanks as always!

Here’s a physical argument that is equivalent to the math. In a local Lorentz frame the stress energy momentum tensor is diagonal with mass density in the time and pressure in the space components. Consider dust which has zero pressure. That leaves the mass density which must be positive. It’s a special case but can be generalized to other kinds of matter.

[chasmanian]

It's nice, but I'm surprised she is still willing to believe in the DAMA results.

thank you nFA.

the book and video are a few years old, maybe she's changed her mind now.

[notFritzArgelander]

It's nice, but I'm surprised she is still willing to believe in the DAMA results.

thank you nFA.

the book and video are a few years old, maybe she's changed her mind now.

AH! that might explain it.

[chasmanian]

you rock nFA!!

[chasmanian]

nFA,
Happy St, Patrick's Day!!

I am thinking about energy. comparing types.

regular mass energy (making up 5% of the observable universe), tells space how to curve.

Dark Energy (making up 70% of the observable universe), creates new space (and that space is observable).

the most extreme version of regular mass energy curving space, creates a BH (which encloses an unobservable space).

thats quite a difference. one energy creates more observable space, the other creates unobservable space.

the next thing I was thinking about is vacuum.

could there be a relationship between vacuum BH's and the Dark Energy vacuum energy?

here are a couple links to Schwarzchild stuff with the word vacuum:

https://en.wikipedia.org/wiki/Schwarzschild_metric

https://en.wikipedia.org/wiki/Derivatio ... d_solution

most grateful for any thoughts,
Charlie

[notFritzArgelander]

nFA,
Happy St, Patrick's Day!!

Many pints o'the day to ye too!

I am thinking about energy. comparing types.

regular mass energy (making up 5% of the observable universe), tells space how to curve.

But not just regular matter tells space how to curve. Any matter or energy curves spacetime in its vicinity.

Dark Energy (making up 70% of the observable universe), creates new space (and that space is observable).

Except for those parts that are too far away corresponding to a look back time equal to the universe's age.....

the most extreme version of regular mass energy curving space, creates a BH (which encloses an unobservable space).

thats quite a difference. one energy creates more observable space, the other creates unobservable space.

But the dark energy by creating the space that is observable also creates unobservable distant reaches....

the next thing I was thinking about is vacuum.

could there be a relationship between vacuum BH's and the Dark Energy vacuum energy?

i don't see one except for "in the dark all cats are black sense". in a local Lorentz reference or inertial frame all vacuums look alike.

here are a couple links to Schwarzchild stuff with the word vacuum:

https://en.wikipedia.org/wiki/Schwarzschild_metric

https://en.wikipedia.org/wiki/Derivatio ... d_solution

most grateful for any thoughts,
Charlie

so we got that bit about vacuum BHs settled then?

[chasmanian]

"But not just regular matter tells space how to curve. Any matter or energy curves spacetime in its vicinity."

I thought of another question.
lets think about Dark Matter.
it also tells space how to curve.
could there be an e=mc^2 version for DM?
(I may have asked you before, but I forget.)
if yes, it would be, well how about we call it DM energy (not to be confused with the DE thats causing the accelerating expansion of the universe).

"so we got that bit about vacuum BHs settled then?"

I think yes.

thank you for your excellent generous reply to all of this.
peace and joy and pints,
Charlie

[notFritzArgelander]

"But not just regular matter tells space how to curve. Any matter or energy curves spacetime in its vicinity."

I thought of another question.
lets think about Dark Matter.
it also tells space how to curve.
could there be an e=mc^2 version for DM?
(I may have asked you before, but I forget.)
if yes, it would be, well how about we call it DM energy (not to be confused with the DE thats causing the accelerating expansion of the universe).

"so we got that bit about vacuum BHs settled then?"

I think yes.

thank you for your excellent generous reply to all of this.
peace and joy and pints,
Charlie

yeah, the E =mc^2 works for anything with a nonzero rest mass, including DM. i think that the context prevents confusion. Speaking of confusion.... there is a chance that there is a Dark Energy particle.

Here's an article....

https://www.symmetrymagazine.org/articl ... y-particle

So far I see no reason to want such an idea except that QFT requires a field for every particle and vice versa.

[chasmanian]

thank you nFA.
awesome.

the article says DE particles could be produced by the Sun. wow.

and the article is from 2016. any idea on how the search is going currently?

[chasmanian]

also, think about this.

I'm assuming that the article is saying that all stars could produce DE.

now think about the stars that turn into BH's.

where does the DE go when that happens?

no idea.

also, interesting that the object (star), that was producing the particles causing the expansion of space,
turns into something (a BH), that is kind of the opposite:
the most tightly bound, curved space, contracted gravitational object that we know of.

[notFritzArgelander]

thank you nFA.
awesome.

the article says DE particles could be produced by the Sun. wow.

and the article is from 2016. any idea on how the search is going currently?

It’s not going anywhere quickly. I don’t think that the idea is particularly good and only mention it as a possibility.

[notFritzArgelander]

also, think about this.

I'm assuming that the article is saying that all stars could produce DE.

now think about the stars that turn into BH's.

where does the DE go when that happens?

no idea.

also, interesting that the object (star), that was producing the particles causing the expansion of space,
turns into something (a BH), that is kind of the opposite:
the most tightly bound, curved space, contracted gravitational object that we know of.

It’s amusing. I don’t know what the production mechanism is. Perhaps I should look into it? Anyway since you raise the question, the value of the Hubble constant would change when the stars go out.

[notFritzArgelander]

Two points to this post.....

1) On the original topic, anti DM, most theories of DM assume that like the photon, the DM particle is its own anti particle.

2) On the chameleon particle corresponding to DE:

Wikipedia has a summary which let's me understand the physics better than the Symmetry piece, https://en.wikipedia.org/wiki/Chameleon_particle


S&T has a good article on an experiment to look for DE in the lab (IF it's a particle)
https://skyandtelescope.org/astronomy-n ... 824201523/

and a live science piece.
https://www.livescience.com/65919-chame ... maybe.html

So far no detections. I prefer the cosmological constant idea (because it agrees with current data) and I have no idea specifically what the articles mention as its "problems". I think that the main problem is that folks who approach cosmology from a QFT biased perspective think that a new particle is necessary. Coming from a bias in favor of GR (or ECSK) rather than QFT a cosmological constant with no corresponding particle seems like a natural byproduct of a future quantum gravity. No particle required.

[chasmanian]

thank you very much again for all you posted nFA.

I appreciate your keen insights and brilliant thoughts on all of this.

I let my imagination go for a bit today, thinking about
the concept of the possibility of DE particles.

if somehow it turns out that there are DE particles,
and they have non zero mass, they will convert
via e=mc^2.

and perhaps there would be antimatter DE particles.

and I wondered how DE particles would interact with DM particles.

its fun to wonder.

[notFritzArgelander]

thank you very much again for all you posted nFA.

I appreciate your keen insights and brilliant thoughts on all of this.

I let my imagination go for a bit today, thinking about
the concept of the possibility of DE particles.

if somehow it turns out that there are DE particles,
and they have non zero mass, they will convert
via e=mc^2.

and perhaps there would be antimatter DE particles.

and I wondered how DE particles would interact with DM particles.

its fun to wonder.

you are too kind. if i were really brilliant i would be doing this stuff. as it is i can only appreciate it as a somewhat competent amateur.....

models for DE particles seem to favor a new fifth force of Nature as described in the links above. models for DM particles favor the usual weak interaction in the Standard Model or an axion modification of electromagnetism and the strong force. so most commonly there is no interaction between DE and DM.

in all models the simplest idea is that the particles are their own anti particle. so looking for photons from self annihilation via Einstein's formula provides a test.

[chasmanian]

thank you nFA.

you are humble and you are kind and gracious.

perhaps brilliance is relative.

and you shine much brighter than most that I have known.

thank you for your generosity.

peace and joy and all good things, :)
Charlie

[chasmanian]

nFA,

I am wondering about some more things.
would you please tell me what you think about them?

imagine we have a very large scale. its so big, that we can put the entire Observable Universe on it, and weigh it.

would would it show us?
would regular matter weigh 5%, and DM 25%, and DE 70%?

next, is DM everywhere?
and if yes, is it in our bodies, and does it then make up a percentage of our body weight?

and would you please help me to understand this?

I thought it says on wikipedia, that the expansion of the Universe,
is only happening out beyond gravitationally bound objects,
up to the size of galaxy clusters.

https://en.wikipedia.org/wiki/Expansion_of_the_universe

this is super not clear to me either.

"Metric expansion is a key feature of Big Bang cosmology, is modeled mathematically with the Friedmann–Lemaître–Robertson–Walker metric and is a generic property of the universe we inhabit. However, the model is valid only on large scales (roughly the scale of galaxy clusters and above), because gravity binds matter together strongly enough that metric expansion cannot be observed on a smaller scale at this time. As such, the only galaxies receding from one another as a result of metric expansion are those separated by cosmologically relevant scales larger than the length scales associated with the gravitational collapse that are possible in the age of the universe given the matter density and average expansion rate. To paraphrase, the metric is forecasted to eventually begin to outpace the gravity that bodies require to remain bound together, meaning all but the most local bound groups will recede."

[notFritzArgelander]

nFA,

I am wondering about some more things.
would you please tell me what you think about them?

imagine we have a very large scale. its so big, that we can put the entire Observable Universe on it, and weigh it.

would would it show us?
would regular matter weigh 5%, and DM 25%, and DE 70%?

Yessirree and Bob's your uncle.

next, is DM everywhere?
and if yes, is it in our bodies, and does it then make up a percentage of our body weight?

A tiny percentage since the normal matter hangs together via chemical bonding. The DM is just passing by like the CMB and the cosmic neutrino background.

and would you please help me to understand this?

I thought it says on wikipedia, that the expansion of the Universe,
is only happening out beyond gravitationally bound objects,
up to the size of galaxy clusters.

https://en.wikipedia.org/wiki/Expansion_of_the_universe

this is super not clear to me either.

"Metric expansion is a key feature of Big Bang cosmology, is modeled mathematically with the Friedmann–Lemaître–Robertson–Walker metric and is a generic property of the universe we inhabit. However, the model is valid only on large scales (roughly the scale of galaxy clusters and above), because gravity binds matter together strongly enough that metric expansion cannot be observed on a smaller scale at this time. As such, the only galaxies receding from one another as a result of metric expansion are those separated by cosmologically relevant scales larger than the length scales associated with the gravitational collapse that are possible in the age of the universe given the matter density and average expansion rate. To paraphrase, the metric is forecasted to eventually begin to outpace the gravity that bodies require to remain bound together, meaning all but the most local bound groups will recede."

i think that whoever wrote that is confused, slightly, or is not expressing the situation adequately. the metric expansion of the FLRW is happening everywhere. local clumps of matter can cause local deviations from expansion that retard it. the metric expansion is accelerating due to DE so that less bound clusters will stop holding together and only the tighter clusters remain. does that help?