Re: The Speed of Light


Gary Edstrom wrote:
Ok, I have a limited physics background. I have just enough knowledge
of relativity to be dangerous! A couple of questions from a simpleton
concerning the speed of light:

1. Why is the speed of light 300E6 m/s? Why isn't it a tenth that
speed? Why isn't it ten times that speed?

The speed of light is 1. We just have goofy units that make it seem
like it's an oddball number. I'll give you an analogy.
Suppose we wanted to measure the slope grade of roads and we chose to
say that a 45 degree angle corresponded to a slope of 1, because that
means 1 ft of vertical rise for every 1 ft of horizontal run. So the
slope is 1/1 = 1. But why is it 45 degrees? Why 45? Why not 1 degree?
Why not 62.3 degrees? Or, more appropriately, road grade is often
measured in ft per mile, so that a slope of 1 corresponds to a quoted
value of 5280 ft/mile. Why 5280? Why not 4200? Why not 6300?
And you might say, well that just comes from applying a conversion
factor. You have to convert ft to miles to get a slope of 1. The odd
number comes only from using a different unit for the numerator than
what you use for the denominator.
Aha! And that's exactly the same answer for the speed of light. You
have to apply a conversion factor to get from meters to seconds. The
odd number comes only from using a different unit for the numerator
than what you use for the denominator. And the conversion factor to get
from meters to seconds is precisely that: 300E6 m/s.


2. Since the speed of light is finite, what is there in a vacuum that
limits its speed? If a vacuum is truly empty as we classically think
of 'empty', shouldn't the speed of light in a vacuum be infinite? What
holds it back?

Well, contrary to what you might think, things don't go at infinite
speed unless there is something holding it back. A satellite on its way
to Mars doesn't just go at 17,500 mph because there is something
limiting its speed. There isn't.

PD

.

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