.We were stumped when facing subtle words like “reverse” and “opposite” and the only way out was to come up with some kind of way to “pin down” those slippery words. We found that operational definitions were very useful.
A little over a hundred years ago Einstein was facing some similar situations. It seemed that the way light rays behaved was very odd. When there was motion involving the source of the light or the observer of the light, then the velocity of the light rays was a big problem.
It seemed that no matter what combinations of source motion or observer motion, the speed of light measured always the same.
***
When we think about a jet plane firing a bullet forward, we would expect (and rightly too) that the airplane's velocity gives more oomph to the bullet, and that the bullet would go faster than normal. We might think that the bullet would be moving at the airplane speed PLUS its normal muzzle velocity. In this case the source velocity (airplane speed) affected the bullet velocity.
But with light it's different. The velocity of a source of light was found to NOT affect the light speed at all. Not even a little.
Consider now a bullet fired from a gun pointed East on the ground at the normal muzzle velocity. A jet plane with a Highway Patrol Radar Gun, and moving West, headlong toward the bullet, would see that bullet coming at it with additional velocity, again higher than mere muzzle velocity. This is a case of the observer’s motion affecting the measured speed of the bullet.
But, again, observer motion had NO effect on light ray velocity. NONE at all! This was a HUGE puzzle in the late 1800’s. The velocity of light was absolutely always the same, in vacuum that is. Air or glass will always slow it down some, but that was avoided.
***
Two physicists named Lorentz and FitzGerald found a solution, but it was pretty quirky. They found that the math worked out better if space shrunk (whatever that means) when motion was involved. Then they noticed that they also should fiddle with time to get their equations to look neat.
So, the situation was one of “space” and “time” behaving in a very slippery fashion, and light was absolutely stuck in a rut, unaffected by any motion. It was a huge riddle, and THIS riddle had plenty of practical applications that made it worth solving. But no one could.
Then Einstein came along and proposed using operational definitions to pin down space and time.
See where I got my ideas from?
***
Light velocity, like all velocities, is found by measuring miles per hour. The miles traveled divided by the hours it took, or the meters divided by seconds it took, or whatever, all are measures of space divided by time. Einstein’s theory started out with a very new way of thinking about the peculiar behavior of light velocity measurments.
He simply accepted it.
Einstein thought that the strange un-affectability of light velocity should be his starting point, instead of at the end of some long winded explanation. It made things much more simple to think this way.
Then he came up with another incredible simplification. It was an
operational definition for how to think about time. Up until then time was something philosophers, poets, and songwriters thought of as fertile ground for the imagination. And it WAS! Time was a VERY slippery idea and very difficult to define.
Einstein’s definition for time was astoundingly simple:
Time is that which is measured by clocks.
End of story, end of song, end of essay.
He then came up with a very useful operational definition of a clock. It was a yardstick
with a mirror at each end.
Yes, that’s right
MIRRORS at either end! And then he asked
why did his mirror clock
reverse time but not his mortgage rate!
;D Sorry, I couldn’t resist.
Seriously, Einstein’s clock went tick-tock every time this trapped light ray bounced back and forth.
The amount of ticks was the measure of the amount of time.
***
He then operationally defined space, or length as that which is measured by the following simple procedure:
1 - Set the clock tic-tock count to zero and send out a second light beam from point A.
2 - Count how many tic-tocks it takes (there’s a tongue twister!) for the second beam to reach point B.
3 - The length between points A and B is calculated by
. L= c * t.,
.or
c multiplied by
t, where
c is the
......unchanging speed of light and
t is the time it took for the second beam to get there.
And, with his operational definition of a clock (yardstick with bouncing light), and with his operational definition of time (that which is measured by the clock), and with his operational definition of space (that 3 step procedure above),
Einstein "did the math" and was able, after a just few pages of Physics,
to come up with his most famous formula of E = mc squared!His operational definitions took the slippery stuff and nailed it down.
So in how many OTHER situations would we benefit by the use of operational definitions?
Something to think on...