Speed of light and dark matter

Click For Summary

Discussion Overview

The discussion revolves around the concept of the speed of light as a universal speed limit and its implications for dark matter. Participants explore the reasons behind this speed limit, its relation to the properties of spacetime, and the challenges in measuring speeds at relativistic levels.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that the speed of light is a universal speed limit because it would require infinite energy to accelerate any mass to that speed, as per relativity theory.
  • Others argue that the speed of light is a limit because no measurement of speed can exceed it, although this claim is challenged by a participant who suggests that synchronized clocks can measure speeds greater than light.
  • A participant explains that the speed limit is a property of spacetime geometry, indicating that light's masslessness is a key factor in this relationship.
  • Some participants discuss the complexities of measuring speed at relativistic speeds, emphasizing the need to account for time dilation and frame of reference.
  • There are differing views on the implications of clock synchronization, with some asserting that synchronization is lost at relativistic speeds while others maintain that it can be preserved under certain conditions.
  • A participant presents a thought experiment involving observers and a bullet to illustrate the challenges of measuring speeds close to the speed of light.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the nature of the speed limit and the implications for measurement at relativistic speeds. The discussion remains unresolved, with no consensus reached on several key points.

Contextual Notes

Limitations include the dependence on definitions of synchronization and relativistic effects, as well as unresolved mathematical considerations regarding speed measurements in different frames of reference.

  • #61
krash661 said:
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.
 
Physics news on Phys.org
  • #62
ZapperZ said:
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.
 
  • #63
Parlyne said:
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.
 
  • #64
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.
 
  • #66
Bill_K said:
We just had a recent thread on mirror matter.

thanks.
 
  • #67
krash661 said:
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.
 
  • #68
ravikannaujiya said:
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.
 
  • #69
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.
 
  • #70
ash64449 said:
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?
 
  • #71
ghwellsjr said:
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...
 

Similar threads

High School How does Einstein's equation work? Why do we need to square c?
  • · Replies 18 ·
Replies
18
Views
2K
Undergrad Time dilation and the human body
  • · Replies 11 ·
Replies
11
Views
2K
Undergrad Conventionality of the One-Way Speed of Light
  • · Replies 6 ·
Replies
6
Views
2K
Undergrad Speed of light one more time
  • · Replies 5 ·
Replies
5
Views
1K
Undergrad Explanation for Galaxy Rotation Curves
  • · Replies 12 ·
Replies
12
Views
2K
Undergrad Has anyone measured the speed of light in one direction?
  • · Replies 45 ·
2
Replies
45
Views
7K
Undergrad Is the concept of a one-way speed of light meaningful and measurable?
  • · Replies 25 ·
Replies
25
Views
5K
High School Light Speed in Vacuum: Does It Reach Cosmic Limit?
  • · Replies 12 ·
Replies
12
Views
3K
Undergrad Relative Speed of Light Between Objects
  • · Replies 3 ·
Replies
3
Views
2K
High School Why does it require an infinite amount of energy to reach the speed of light?
  • · Replies 130 ·
5
Replies
130
Views
16K