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Q: Speed of light - why? ( Answered ,   8 Comments )
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 Subject: Speed of light - why? Category: Science > Physics Asked by: eppy-ga List Price: \$10.00 Posted: 18 Mar 2006 05:03 PST Expires: 17 Apr 2006 06:03 PDT Question ID: 708752
 I was prompted to ask this question after reading Hedgie-GA's most informative answer the recent question 'Speed of light, why not?' I have now read all the referenced material, and have gained a high level overview of most areas from duality to 10 dimensional string theory. However, there no no reference to the question that I am most interested in. Thus this question: Why is the speed of light what it is (approx 300,000 km/s) and not (say) 10 x slower or 10x faster? I understand Hedgie's analogy of the three angles of a triangle always adding up to 180 degrees, and I understand the mass/time boundary of c dictated by e=mc2 However, I can't intellectually 'see' 300,000 km/s as being a boundary in the same way as I can 180 degrees. I would appreciate a high level (non mathematical) explanation of the current understanding of why the speed of light boundary is what it is and not another arbitary 'relative velocity' (either slower or faster). If this isn't known, that is fine - please explain the current thinking.
 Subject: Re: Speed of light - why? Answered By: hedgie-ga on 19 Mar 2006 04:51 PST Rated:
 eppy-ga rated this answer: and gave an additional tip of: \$5.00 Comprehensive and no less than 19 good references! What takes the cake is to get a personal "Hedgie's cosmological conjecture of the Alien's value of c" out of a \$10 question; outstanding value!

 Subject: Re: Speed of light - why? From: kottekoe-ga on 18 Mar 2006 07:08 PST
 Now that is a very interesting question. The short answer is: no one knows why the speed of light "c" has the particular value of 3x10^8 m/s. Your question can be generalized to "Why do any of the fundamental constants of nature, like the speed of light, the gravitational constant, and the charge of the electron have their particular values?" We need to get one thing sorted out first. The speed of light depends on the units we use to measure length and time. Our units like meters and seconds are completely arbitrary, chosen for odd historical reasons like the Babylonian's fascination with the number 60 and the rotation period of the Earth. In theoretical physics, one recognizes that c is just the conversion factor between our units for distance and time. To make the equations simpler and get to the heart of the matter, theorists commonly use a set of units in which c is equal to one, so E=mc^2 becomes E=m (Energy equals mass). This can be done with other units and constants as well. The goal of theoretical physics then becomes explaining and predicting all dimensionless ratios (that is, all pure numbers with no units on them). Your question about c is then replaced by questions like this: why is a particular combination of fundamental constants called the "fine structure constant" equal to approximately 1/137? This constant is just the square of the charge of the electron divided by the product of the speed of light and Planck's constant. It is a pure number in any system of units and thus does not depend on arbitrary choices like measuring distance in multiples of some King's foot size. Other questions you could ask include things like: 1) why is the ratio of the electron's mass to the proton's mass about 1/1800, 2) why is the gravitational force between two protons ~10^40 times smaller than the electromagnetic force, etc. Again, the answer is that we do not know and it is a major goal of physics to predict all these things. One possible answer is something I personally detest but many others like called the "Anthropic Principle". It notes that the existence of intelligent life depends in detail on the physical constants and on the fact that slight changes in any of these dimensionless ratios would render life as we know it impossible. Thus, among the infinite possibilities for a universe, it should be no surprise that we live in one in which intelligent life can exist and, "Voila" that explains the values of the fundamental constants. Your question is very timely, since this week John Barrow just won the Templeton Prize of \$1.4 M dollars for his work including the formulation of the Anthropic Principle. Who says mixing science and religion does not pay? http://www.templetonprize.org/bios.html
 Subject: Re: Speed of light - why? From: siliconsamurai-ga on 18 Mar 2006 07:58 PST
 An even better answer is that "why" isn't a question addressed by science, it is a question for religion or philosophy. Physics is about what IS.
 Subject: Re: Speed of light - why? From: siliconsamurai-ga on 18 Mar 2006 08:02 PST
 who says mixing science and religion doesn't pay? All the people over the centuries who were tortured by various religions for trying to promote science, anyone with a disease that could probably be cured by stem cell research, anyone who caught AIDS because a government thought it was "against god" to tell people about condoms, etc., etc., etc.
 Subject: Re: Speed of light - why? From: kottekoe-ga on 18 Mar 2006 09:16 PST
 Science often answers the question "Why?" Why is the sky blue? Why is the hydrogen atom stable? The answers are given in terms of something simpler and more fundamental. At the bottom, you are left with questions that may be beyond our ability to answer and in the realm of philosophy. It is certainly my hope that a more fundamental theory will explain the fine structure constant, the masses of the quarks (in dimensionless units), etc. This won't answer all the questions, like why do quantum field theories explain so much of our universe, but I hope they will provide the answer to Eppy's question without invoking voodoo like the Anthropic principle.
 Subject: Re: Speed of light - why? From: eppy-ga on 18 Mar 2006 09:20 PST
 Thanks very much Kottekoe, if you were a reasearcher I would have asked you to post as an answer. So, to paraphrase what you said, my question is not much different from asking why pi=3.1415926535... c is really a conversion factor and only has context in the world of realtivity when considered from a 4 dimensional space/time perspective. However, because the concept of velocity is embedded in our thinking so much in an (apparently) non-relativistic way, we intellectually tend to consider it one dimensionally, without boundary. A couple more quick comments. I note from a paper http://www.btinternet.com/~ugah174/ on the fine structure constant that you refer to that it also incorporates pi. Fascinating.. I remember about 20 years reading an article by Isaac Asimov on the development of our knowledge of the speed of light. He mentioned that that the number being within 1% of 300,000 km/s was no co-incidence, as the early metric definitions had the same variables, and should have equaled exactly 300,000 km/s but the speed of light was fined tuned after the metric units were agreed.
 Subject: Re: Speed of light - why? From: kottekoe-ga on 18 Mar 2006 10:20 PST
 Eppy, thanks for your kind words. I agree that alpha is in many ways to physics what pi is to mathematics, but there are major differences. We can use mathematics to calculate the value of pi in any number of consistent ways. In physics, we have no theory whatever to explain the value of alpha. I had never heard of James Gilson's work that is described at the URL you gave, but I am very skeptical. My immediate impression was that it sounds like the kind of numerology that Eddington used almost 100 years ago when he claimed that 1/alpha was an integer equal to 1^2+6^2+10^2. I just did a Google search for Gilson and found a nice article on the Fine Structure Constant on Wikipedia, which mentions Gilson's work, also relating it to Eddington's numerology. With regard to c being within 1% of 3x10^8 m/s, this is pure coincidence. If Asimov really wrote what you said, he was really off base. The meter was originally defined so that the distance from the pole to the equator was 10,000 km. The second was defined so that a solar day has 24x60x60 seconds. All these things are entirely arbitrary and have nothing whatever to do with the speed of light. Perhaps Asimov was talking about the modern definition of the second and meter, which are made in such a way that the speed of light is now defined exactly to be: 299 792 458 m/s The meter used to be the length of a platinum iridium bar carefully maintained in Paris. Now it's definition is more prosaic. According to the web site of the National Institute of Standards and Technology: 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. The appearance of that strange number with six digits is to make the new definition agree closely with the historical one. It is still just a coincidence that it is so close to 1/300 000 000.
 Subject: Re: Speed of light - why? From: richard-ga on 18 Mar 2006 14:42 PST
 Thank you kottekoe-ga for the thoughtful and enlightening (no pun) contributions you make to Google Answers.
 Subject: Re: Speed of light - why? From: kottekoe-ga on 18 Mar 2006 15:43 PST