Why is the speed of light constant?

In summary: I'm still not sure about what you are asking here, but I guess you are asking why light travels at the speed it does. In summary, light travels at a constant speed because it is not matter and does not have to overcome friction to move. This question may seem philosophical, but it is actually a physical question that is still being studied and debated by scientists. The speed of light is a fundamental constant in the universe and plays a crucial role in many phenomena. Its value is determined by various factors, such as the size and frequency of atomic structures. Ultimately, the answer to why light travels at the speed it does lies in the laws of physics.
  • #71
PhanthomJay said:
The finite speed of light is not a philosophical speed. ...or maybe there will never be an answer),

Well, if the answer may never be known, it sounds philosophical to me -- though I must admit that the speed of philosophy is not well defined...

Thanks for the reply, happy new year!
 
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  • #72
Oldfart said:
PhanthomJay said:
The finite speed of light is not a philosophical speed. ...or maybe there will never be an answer),

Well, if the answer may never be known, it sounds philosophical to me --
you may be right
though I must admit that the speed of philosophy is not well defined...
I thought it was the same as the speed of time :wink::rofl:
Thanks for the reply, happy new year!
Same to you, thanks. I Read Hawking's last chapter just after Dick Clark's countdown. I'm told the million dollar ball dropped, but i guess i was not watching carefully, because I never saw the damn thing drop. Maybe it was one of those Vacuum Fluctuations...

Anyway, Hawking/Mladinow's book fell short of a masterpiece, but nevertheless, it is a MUST read that reflects the latest thinking on the the Universe on both the Quantum and Cosmological scales that one day will be merged, perhaps. It didn't really answer anything that I haven't already learned from the expert responders on the Cosmology forum ..they are second to none in my estimatiion...especially, but not limited to, Chalnoth, who must come from the Great Beyond somewhere.

I did learn , per my understanding, a few new things new, however, such as

-The nature of the Time Dimension in the very very very early stages of the Universe;
- The Sum of Histories leading to the multiverses (I've got a lot of work to due on this, however);
- the nature of Inelligent Life, and,
here's the biggy:
- The Theist may be Gravity...unless i misunderstood, which i probably did.

I'll be posting more questions to the Cosmologists here, on the Cosmology forum.
 
  • #73
PhanthomJay said:
So it is best to ask why this constant is what it is, rather than ask why the speed of light is what it is,

Excellent PhanthomJay! Just Excellent!

I’ll order that book NOW! I have http://en.wikipedia.org/wiki/The_Universe_in_a_Nutshell" [Broken] and it’s just wonderful + fantastic graphics!

Cover_Universe_in_a_nutshell.jpg



P.S. I also believe in Gravity. :wink:
 
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  • #74
P.S.2. It’s this one you’re reading, right?

http://en.wikipedia.org/wiki/The_Grand_Design_(book)" [Broken]

The_grand_design_book_cover.jpg
 
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  • #75
DevilsAvocado said:
P.S.2. It’s this one you’re reading, right?

http://en.wikipedia.org/wiki/The_Grand_Design_(book)" [Broken]

The_grand_design_book_cover.jpg
Yeah, that's the One!

I believe in Gravity, ---World without End...Amen!
 
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  • #76
Thanks!

Amen :wink:
 
  • #77
Well, I've been thinking about this. There are a bunch of dimensionless constants of the universe, like, for example, the fine structure constant &alpha; which has to do with the electromagnetic force, and involves the charge and mass of an electron. Another one is the gravitational coupling constant &alpha;<sub>G</sub> which has to do with the gravitational force, and involves the mass of an electron and the gravitational constant. I guess there are others, having to do with the other forces, weak, strong, etc. I always thought that if you had another universe where all the dimensionless constants were the same, you would not be able to detect that you were in a "different" universe. In other words, all the lengths, times, masses, etc. might be "different", but if you used the same procedures to define units of length, time, mass, etc., the numerical value of the fundamental constants (speed of light, Planck constant, mass of electron, electron charge, vacuum permittivity, gravitational constant, etc.) would all be the same. If they were not, you would be detecting that you were in a "different" universe.

But I can't get it to work. If you take three fundamental constants, electron mass (m), Planck constant (h) and speed of light (c), you can form a fundamental mass (m), a fundamental length (L=h/mc) which is the Compton wavelength, and a fundamental time (T=h/mc^2) which is 1 over the Compton frequency. If you go to a new universe, where the speed of light is c' (as measured by our present universe meter sticks and clocks) but all the dimensionless constants remain the same, then some or all of the fundamental constants will have to change their values in order to keep the dimensionless constants the same. That means that the Compton wavelength may change by some unknown factor due to the change in the speed of light, and the possible corresponding changes in the Planck constant and the mass of the electron required to keep the dimensionless constants the same. Suppose the values of h and m in the new universe are h' and m' as measured by our clocks and meter sticks. Then the new Compton wavelength will be L'=h'/m'c' and the new Compton time will be T'=h'/m'c'^2. The new speed of light will be measured as L'/T'=c', not c!. For example, if, in the new universe, the speed of light were cut in half, and h and m remained the same, and the dimensionless constants were kept constant by changing the vacuum permittivity and the gravitational constants, then all lengths would double in the new universe, but all times would quadruple. A meter stick would be twice as long, but a clock would click 4 times more slowly, and the numerical value of c would be half of what it is in our universe. It appears that the speed of light is something that must have its particular value in order for the universe to be what it is, and it is a valid question to ask why it has the value it does. Either that or I missed something...
 
  • #78
Rap said:
It appears that the speed of light is something that must have its particular value in order for the universe to be what it is, and it is a valid question to ask why it has the value it does. Either that or I missed something...
Thanks for the response! The most popular responses to the question regarding why the speed of light is what it is are:
1.) "It just is", and
2.) "Its the way we define the meter and second"

Neither one of these satisfies me...I think it's got something to do with Feynman's sum of histories...but what do I know about the quantum world...and If I read Hawking correctly, he's on his knees worshipping Gravity...

Thanks again.
 
  • #79
Number 1 is not very satisfying and 2 is wrong. My wrong (I think) idea was that if the speed of light changed, but every dimensionless constant stayed the same, you would not be able to tell that anything had changed, because other things would have to change to keep the dimensionless constants the same, and the dimensionless constants are what determines the physics of the universe. The meter stick would change, the second would change, and the numerical value of the speed of light in meters/sec would come out the same.
 
  • #80
I think I figured out where my argument went wrong: c' is the speed of light in the other universe as measured by us, not by them. So cancel that whole argument. I go back to my original argument. It makes no sense to ask how fast is light any more than it makes sense to ask how long is a meter, or how long is a second. The minute you answer that question, you have made reference to some other velocity, length, or time. So what you are really asking is why is that ratio what it is.
 

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