Speed of light and dark matter

[Dale]

You can measure speed of anything more than that of light theoreticly or practically.

So do I correctly understand that you rescind your comment of post 3? If not, then you still need to post a valid reference supporting it. Neither the textbook nor the Wikipedia article made any comment supporting your post 3.

But I don't see it anyway simply when nothing can move faster than light then how can I measure it.

Agreed, but the point is that it is a limit on the physics, not a limit on the measuring devices. I.e. we don't measure anything going faster than c because we haven't found anything that goes faster than c, not because our devices are incapable of measuring speeds faster than c.

 

[Aadrish]

i have a question
why light waves are transverse waves?
as transverse waves are mechanical waves so these require a medium to propagate. while light don't require any material

 

[Dale]

i have a question
why light waves are transverse waves?
as transverse waves are mechanical waves so these require a medium to propagate. while light don't require any material

The defining feature of transverse waves is that they can be polarized, whereas longitudinal waves cannot.

 

[krash661]

there was an experiment from the ISS in the last couple of weeks that may help with this,
ALPHA MAGNETIC SPECTROMETER RESULTS
nasa.gov

Recent results from the AMS experiment
cern webcast

Potential Dark Matter Discovery a Win for Space Station Science
space.com

there are also these articles,

Homing in on Dark Matter
Three potential detections from deep underground could be from dark matter particles.
sky and telescope magazine

Researchers see potential hints of dark matter; gamma-ray flare up is cosmic coincidence
IOP-institute of physics

 

[Parlyne]

i have a question
why light waves are transverse waves?
as transverse waves are mechanical waves so these require a medium to propagate. while light don't require any material

Your mistake seems to be in the presumption that all transverse waves must be mechanical. But, there's no reason for such a presumption. As DaleSpam points out, transverseness implies polarizability; and, I'll just add that the dynamics of the electromagnetic field require that, in the absence of sources (that is charges or currents), the electric and magnetic fields must be mutually perpendicular and also perpendicular to the direction of energy transport (as determined from the extremely well-named Poynting vector).

 

[Parlyne]

there was an experiment from the ISS in the last couple of weeks that may help with this,
ALPHA MAGNETIC SPECTROMETER RESULTS
nasa.gov

Recent results from the AMS experiment
cern webcast

Potential Dark Matter Discovery a Win for Space Station Science
space.com

there are also these articles,

Homing in on Dark Matter
Three potential detections from deep underground could be from dark matter particles.
sky and telescope magazine

Researchers see potential hints of dark matter; gamma-ray flare up is cosmic coincidence
IOP-institute of physics

Despite the significant hype, the AMS results in no way point to dark matter any more than previous data about the same phenomenon had. The positron excess under discussion was actually first noted about 5 years ago by the PAMELA experiment; and, there was a flurry of papers at the time discussing the possible natures of dark matter models that could explain such a result. However, as was known then, the excess may well be the result of totally unrelated astrophysical processes, such as pulsars. And, because of the presence of galactic magnetic fields, the positrons can't be particularly reliably traced back to their source (or sources), meaning that we can't directly test whether they originate at the center of the galaxy (as a dark matter signal must) or from other more local sources. AMS has put out far more detailed and more precise data. However, at least as yet, the data shows no features that we're already present in the PAMELA data. Therefore, any attribution to dark matter is, at best, premature.

 

[krash661]

the best info is that nasa.gov and cern.

those were the actual releases.
i'm trying to find a written version of the actual release, but it's not as easy as i thought.

in that release there were questions and comments/answers that pertain to the tittle of this topic.

I'm trying to find it now.

 

[Bill_K]

The AMS paper is here.

 

[krash661]

Despite the significant hype, the AMS results in no way point to dark matter any more than previous data about the same phenomenon had. The positron excess under discussion was actually first noted about 5 years ago by the PAMELA experiment; and, there was a flurry of papers at the time discussing the possible natures of dark matter models that could explain such a result. However, as was known then, the excess may well be the result of totally unrelated astrophysical processes, such as pulsars. And, because of the presence of galactic magnetic fields, the positrons can't be particularly reliably traced back to their source (or sources), meaning that we can't directly test whether they originate at the center of the galaxy (as a dark matter signal must) or from other more local sources. AMS has put out far more detailed and more precise data. However, at least as yet, the data shows no features that we're already present in the PAMELA data. Therefore, any attribution to dark matter is, at best, premature.

just so i understand,

are you saying it was a waste of time and resources and useless ?

edit-

so the problem is finding the source of dark matter ?

edit 2 -

" We already were confident that there is an unknown source of positrons above 10 GeV. ",
is this what you are referring to ?
it was followed with this comment,

" What we wanted to know from AMS was whether the effect continues at even higher energy, well above 100-200 GeV, and whether their more detailed observations would give us insight into whether this increase is due to a new astronomical effect or a new particle physics phenomenon. "

 

[ZapperZ]

the best info is that nasa.gov and cern.

those were the actual releases.
i'm trying to find a written version of the actual release, but it's not as easy as i thought.

in that release there were questions and comments/answers that pertain to the tittle of this topic.

I'm trying to find it now.

Please don't make this type of "citation". You are not providing other members the proper information for them to look it up if they don't know what is going on.

Either you point to the EXACT source, or use the proper format that is used to cite a publication.

In case you missed an earlier post, there is a source for you to not only read a report on this result, but to actually download the exact PRL paper for free from the PRL website.

http://physics.aps.org/articles/v6/40

So one gets to actually hear this from the horse's mouth itself, rather than through some 2nd or 3rd hand news.

Zz.

 

[Parlyne]

just so i understand,

are you saying it was a waste of time and resources and useless ?

Not at all. I'm just saying that the reporting of this result as evidence for dark matter is not a responsible representation of the data. I happen to think the AMS is an awesome experiment; and, I was actually quite excited when the shuttle mission was added in order to deliver it. Furthermore, I take no issues with the actual data or the work being done with it. And, as more data is collected, it may actually be able to help answer the question of the source of the positron excess - both by extending our knowledge about it to higher energy and by looking for directional dependence.

so the problem is finding the source of dark matter ?

No, it's finding the source of the excess positrons. It certainly could be that they come from dark matter annihilation; but, they could also come from astrophysical processes that nothing to do with dark matter.

" We already were confident that there is an unknown source of positrons above 10 GeV. ",
is this what you are referring to ?
it was followed with this comment,

" What we wanted to know from AMS was whether the effect continues at even higher energy, well above 100-200 GeV, and whether their more detailed observations would give us insight into whether this increase is due to a new astronomical effect or a new particle physics phenomenon. "

I'm not sure exactly what you're quoting; but, it seems to get at the basics of the issue.

 

[krash661]

Please don't make this type of "citation". You are not providing other members the proper information for them to look it up if they don't know what is going on.

Either you point to the EXACT source, or use the proper format that is used to cite a publication.

In case you missed an earlier post, there is a source for you to not only read a report on this result, but to actually download the exact PRL paper for free from the PRL website.

http://physics.aps.org/articles/v6/40

So one gets to actually hear this from the horse's mouth itself, rather than through some 2nd or 3rd hand news.

Zz.

I can not provide sources.
and also the comment you quoted was me doing just that.
i believe it says,

" those were the actual releases.
i'm trying to find a written version of the actual release, but it's not as easy as i thought. ",

and then the actual paper was provided after that comment of mine..

pay attention here.

edit-
and also what you posted is not the actual release.

 

[krash661]

Not at all. I'm just saying that the reporting of this result as evidence for dark matter is not a responsible representation of the data. I happen to think the AMS is an awesome experiment; and, I was actually quite excited when the shuttle mission was added in order to deliver it. Furthermore, I take no issues with the actual data or the work being done with it. And, as more data is collected, it may actually be able to help answer the question of the source of the positron excess - both by extending our knowledge about it to higher energy and by looking for directional dependence.



No, it's finding the source of the excess positrons. It certainly could be that they come from dark matter annihilation; but, they could also come from astrophysical processes that nothing to do with dark matter.



I'm not sure exactly what you're quoting; but, it seems to get at the basics of the issue.

Interesting,
ok, i understand.

 

[krash661]

interesting,

I'm on the cornell university site,
on it there is a very short paper, actual there are a couple of them,
it's titled,

cosmology with mirror dark matter
From: Paolo Ciarcelluti

there is also

Does mirror matter exist?
From: Robert Foot
which dates back to 2002

does anyone know/understand about this and have thought's on it.
this is the first i ever heard about this.

i do not know how to give you a resource without posting links.

 

[Bill_K]

We just had a recent thread on mirror matter.

 

[krash661]

We just had a recent thread on mirror matter.

thanks.

 

[ZapperZ]

I can not provide sources.
and also the comment you quoted was me doing just that.
i believe it says,

" those were the actual releases.
i'm trying to find a written version of the actual release, but it's not as easy as i thought. ",

and then the actual paper was provided after that comment of mine..

pay attention here.

edit-
and also what you posted is not the actual release.

I have no idea what you just said here.

Link that Bill_K gave is exactly the link that is provided in the article that I pointed to. So how is this not "the actual release"? It is the SOURCE! The article I cited contains the link to that very same paper! I thought providing a link to the APS Physics article might be easier for someone without an extensive background in this field to understand what that paper is all about.

Please note that when you cite arXiv articles (assuming that this is what you mean when you said that you are on the "Cornell university site"), you should provide the article number!

Zz.

 

[San K]

the speed of light is a universal speed limit because no one could measure the speed of anything more than that of light, not even of the light.

we can measure speed faster than the speed of light. for example, as other posts have said above, by having two clocks some distance apart.

as another example:

quantum entanglement has been measured to be at (the) least 10,000 times faster than the speed of light.

 

[ash64449]

yes.we can measure if particles go faster than speed of light.particles whould create cherenkov radiation if it moved faster than speed of light.

 

[ghwellsjr]

yes.we can measure if particles go faster than speed of light.particles whould create cherenkov radiation if it moved faster than speed of light.

How does that help measure the speed of a particle going faster than light?

 

[ash64449]

How does that help measure the speed of a particle going faster than light?

not like that.. I said we can identify whether particles are moving faster than light if we see that radiation...