Changing speed of light

  • #1
466
5
If the speed of light is changing, does this mean that the permattivity and/or permeability are dynamically changing quantities? are these "constants" derivable yet or are they still only experimentally measured quantities?
 

Answers and Replies

  • #2
mathman
Science Advisor
7,971
510
If the speed of light is changing, does this mean that the permattivity and/or permeability are dynamically changing quantities? are these "constants" derivable yet or are they still only experimentally measured quantities?

What makes you think the speed of light (in vacuum) is changing?
 
  • #3
Dale
Mentor
Insights Author
2020 Award
31,851
8,712
If the speed of light is changing, does this mean that the permattivity and/or permeability are dynamically changing quantities? are these "constants" derivable yet or are they still only experimentally measured quantities?
The speed of light, vacuum permettivity and vacuum permeability are all determined by the system of units. In natural units they are all equal to 1, and in CGS the vacuum permeability and permittivity do not even exist.

What you should really be asking is if the fine structure constant is derivable or only experimentally measured. That is a dimensionless number and so is independent of the system of units. It characterizes the physics rather than the units.

The answer is that the fine structure constant is experimentally measured, not yet derivable.
 
  • #4
CWatters
Science Advisor
Homework Helper
Gold Member
10,541
2,308
Has there been a follow up to..

http://www.newscientist.com/article...t-may-have-changed-recently.html#.U6_HJ2cU91M

Now, Lamoreaux, along with LANL colleague Justin Torgerson, has re-analysed the Oklo data using what he says are more realistic figures for the energy spectrum of the neutrons present in the reactor. The results have surprised him. Alpha, it seems, has decreased by more than 4.5 parts in 108 since Oklo was live (Physical Review D, vol 69, p121701).

That translates into a very small increase in the speed of light (assuming no change in the other constants that alpha depends on), but Lamoreaux's new analysis is so precise that he can rule out the possibility of zero change in the speed of light. "It's pretty exciting," he says.
 
  • #5
466
5
What makes you think the speed of light (in vacuum) is changing?

I just assumed he was referring to vacuum

The speed of light, vacuum permettivity and vacuum permeability are all determined by the system of units. In natural units they are all equal to 1, and in CGS the vacuum permeability and permittivity do not even exist.

what's CGS?
 
  • #7
67
8
the speed of light will be changed when the light goes from the vaccum into the media due to the change of the permability and permittivity. the speed of the light is related to these material properties by checking the wave equations in the medias.
 

Related Threads on Changing speed of light

  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
12
Views
2K
  • Last Post
Replies
3
Views
846
  • Last Post
Replies
6
Views
2K
  • Last Post
Replies
9
Views
1K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
10
Views
2K
  • Last Post
Replies
9
Views
2K
  • Last Post
Replies
20
Views
3K
  • Last Post
Replies
3
Views
616
Top