Have physicists found out why the speed of light is exactly 186,282.3831 mile per second, and not any faster or slower? What constrains light, and all other EM radiation, to such a specific speed?
The very specific speed of light is its speed in a vacuum. The ratio of its speed through a vacuum to its speed through a different medium is called the refractive index of that medium. Some refractive indices are:
1.00 vacuum 1.0003 air 1.33 water
For most cases where light speed is used, the refractive index is ignored. We don't normally think in terms of light speed when considering things other than astronomical time and distance.
Hope this provides at least part of what you're after! ++++++++++++++++++++++++++++++++++++++++++++++++++ 06-21-02, 04:11 AM MrSensitive I recomend making a BIG pot of coffee (or Jolt cola) and popping a couple Vivarin for this one:
06-21-02, 10:14 AM Minnesota Coldfuse and Mrsensitive
Thanks for the attempt, but if you read my question carefully you will see that what I am asking is not the conditions in which light is measured or its constancy, but the underlying reason for its specific speed:
Why does light travel at the speed it does rather than at some other speed?
06-21-02, 11:53 AM coldfuse Click here for part of the answer, included in the last article on the page.
Here is another response to the same question in a Q&A format.
I don't think it's what you're after; nonetheless, the last category on this site addresses the issue.
Hope these help to some degree...'fuse
06-21-02, 12:12 PM gerry Asking why the speed of light is what it is, is similar to asking why the mass of a proton is what it is, or why the size of the smallest atomic particle known, the quark, is what it is. Why are these sizes and masses so specific? The simple answer is "that's just the way the Universe is". That answer is not good enough for me. I believe the answer lies in "Superstring Theory', which is now being supplemented or replaced by "M-Theory" and a "Theory of Everything". We don't have all the answers...yet.
06-21-02, 09:55 PM Minnesota Coldfuse and Gerry, thanks.
Evidently the answer is quite elusive. Just a note CF on the answer given by Eric Brindeau from your "Here" link. This is one of the worst answers to any question I have ever seen (I am not blaming you for suggesting it) To simply say, as he does, that in effect "It is because it is" is inane, and unworthy of publication.
06-21-02, 10:37 PM Byter
quote: At the 1983 Conference Generale des Poids et Mesures the following SI (Systeme International) definition of the meter was adopted:
The meter is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second. This defines the speed of light in vacuum to be exactly 299,792,458 m/s. This provides a very short answer to the question "Is c constant": Yes, c is constant by definition!
I know that really doesn't answer the question of why light at that & only that speed.
Further along in the same article they talk about the assumptions that went into the above. Maybe that will shed a little "LIGHT" onto the subject. (sorry couldn't resist)
Way over my head confused confused confused confused
Excellent question to make the brain itch. Regards mike B. (AKA Byter)
[This message was edited by Byter on 06-21-02 at 10:54 PM.]
[This message was edited by Byter on 06-21-02 at 10:55 PM.]
06-21-02, 11:49 PM coldfuse I thought that link was pretty much a crunch of bap as well. Some people like this sort of self-important, empty drivel and I should have remembered, from Answer Point, that you would not be one of them!
...'fuse wink
06-22-02, 05:59 PM TomGL2 As you probably know, the measured speed of light does not change regardless of the movement of the light source or the measuring equipment. That is, if you and the source were moving away from, or toward, each other, you measure the same velocity.
Because space and time conspire to keep C constant, then space and time are in some sense the same (even though we may measure one in metres and the other in seconds). And if they are the same, then there is a factor which converts one to the other.
So we multiply seconds of time by [something] to get metres of space, and this [something] must be expressed in metres/sec.
The [something] is of course C, at about 300,000,000 metres/sec, and it has that value because a finite amount of time is equivalent to a specific amount of space.
Other items: (1) There is considerable good evidence that the speed of light is decreasing. (2) An NEC Research Institute experiment appears to have caused about 2% of the length of a light pulse to exceed C. (3) Researchers at Harvard managed to slow light to about one MPH, by passing it through a Bose-Einstein condensate, which can exist only at close to absolute zero.
[This message was edited by TomGL2 on 06-22-02 at 06:14 PM.]
06-22-02, 08:27 PM Minnesota Tom
quote:Because space and time conspire to keep C constant, then space and time are in some sense the same (even though we may measure one in metres and the other in seconds). And if they are the same, then there is a factor which converts one to the other
I'm sorry Tom, but to say that the two "conspire" to keep the speed of light constant is meaningless. First, because it implies a willful act; secondly, even lacking any such collusion, there is no basis for positing such an operational basis; thirdly, it simply does not follow that space and time would be the same just because they "conspire to keep C constant." Your illustration that follows of converting space to time is, to put it mildly, not valid.
[This message was edited by Minnesota on 06-22-02 at 08:37 PM.]
06-22-02, 10:51 PM TomGL2 See the Scientific American article Why isn't the speed of light infinite?, which expands on my explanation. The authors are professors of physics at Boston's Northeastern University, so I feel the information can be taken as authoritative.
Minnesota, your rebuttal was not thought through. While I have not studied this subject for over a quarter century, I still recall a few fundamentals.
And the use of "conspire" was obviously intended figuratively -- I'm sure no one thought I was ascribing conciousness -- so you're being unnecessarily fastidious.
06-23-02, 02:23 AM Minnesota Tom
There is a great deal of difference between what you posted and what is said in your source, the Scientific American article. I think that if you reread both very carefully you will see where your paraphrasing has led you astray.
I threw in the first objection (conspiring as a willful act) only because it irks me when I see inanimate subjects unnecessarily anthropomorphized. My hope was that in making it a point you would see that not only does such usage fail to add anything to a discussion, but that it imbues the subject with a subtle, but erroneous character. No big deal--it's just a quirk of mine.
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